Science.gov

Sample records for acoustic impedance contrast

  1. Acoustic ground impedance meter

    NASA Technical Reports Server (NTRS)

    Zuckerwar, A. J.

    1981-01-01

    A compact, portable instrument was developed to measure the acoustic impedance of the ground, or other surfaces, by direct pressure-volume velocity measurement. A Helmholz resonator, constructed of heavy-walled stainless steel but open at the bottom, is positioned over the surface having the unknown impedance. The sound source, a cam-driven piston of known stroke and thus known volume velocity, is located in the neck of the resonator. The cam speed is a variable up to a maximum 3600 rpm. The sound pressure at the test surface is measured by means of a microphone flush-mounted in the wall of the chamber. An optical monitor of the piston displacement permits measurement of the phase angle between the volume velocity and the sound pressure, from which the real and imaginary parts of the impedance can be evaluated. Measurements using a 5-lobed cam can be made up to 300 Hz. Detailed design criteria and results on a soil sample are presented.

  2. Acoustic impedance microscopy for biological tissue characterization.

    PubMed

    Kobayashi, Kazuto; Yoshida, Sachiko; Saijo, Yoshifumi; Hozumi, Naohiro

    2014-09-01

    A new method for two-dimensional acoustic impedance imaging for biological tissue characterization with micro-scale resolution was proposed. A biological tissue was placed on a plastic substrate with a thickness of 0.5mm. A focused acoustic pulse with a wide frequency band was irradiated from the "rear side" of the substrate. In order to generate the acoustic wave, an electric pulse with two nanoseconds in width was applied to a PVDF-TrFE type transducer. The component of echo intensity at an appropriate frequency was extracted from the signal received at the same transducer, by performing a time-frequency domain analysis. The spectrum intensity was interpreted into local acoustic impedance of the target tissue. The acoustic impedance of the substrate was carefully assessed prior to the measurement, since it strongly affects the echo intensity. In addition, a calibration was performed using a reference material of which acoustic impedance was known. The reference material was attached on the same substrate at different position in the field of view. An acoustic impedance microscopy with 200×200 pixels, its typical field of view being 2×2 mm, was obtained by scanning the transducer. The development of parallel fiber in cerebella cultures was clearly observed as the contrast in acoustic impedance, without staining the specimen. The technique is believed to be a powerful tool for biological tissue characterization, as no staining nor slicing is required. PMID:24852259

  3. Effects of Liner Geometry on Acoustic Impedance

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Tracy, Maureen B.; Watson, Willie R.; Parrott, Tony L.

    2002-01-01

    Current aircraft engine nacelles typically contain acoustic liners consisting of perforated sheets bonded onto honeycomb cavities. Numerous models have been developed to predict the acoustic impedance of these liners in the presence of grazing flow, and to use that information with aeroacoustic propagation codes to assess nacelle liner noise suppression. Recent efforts have provided advances in impedance education methodologies that offer more accurate determinations of acoustic liner properties in the presence of grazing flow. The current report provides the results of a parametric study, in which a finite element method was used to assess the effects of variations of the following geometric parameters on liner impedance, with and without the presence of grazing flow: percent open area, sheet thickness, sheet thickness-to-hole diameter ratio and cavity depth. Normal incidence acoustic impedances were determined for eight acoustic liners, consisting of punched aluminum facesheets bonded to hexcell honeycomb cavities. Similar liners were tested in the NASA Langley Research Center grazing incidence tube to determine their response in the presence of grazing flow. The resultant data provide a quantitative assessment of the effects of these perforate, single-layer liner parameters on the acoustic impedance of the liner.

  4. Method of Adjusting Acoustic Impedances for Impedance-Tunable Acoustic Segments

    NASA Technical Reports Server (NTRS)

    Jones, Kennie H (Inventor); Nark, Douglas M. (Inventor); Jones, Michael G. (Inventor); Parrott, Tony L. (Inventor); Lodding, Kenneth N. (Inventor)

    2012-01-01

    A method is provided for making localized decisions and taking localized actions to achieve a global solution. In an embodiment of the present invention, acoustic impedances for impedance-tunable acoustic segments are adjusted. A first acoustic segment through an N-th acoustic segment are defined. To start the process, the first acoustic segment is designated as a leader and a noise-reducing impedance is determined therefor. This is accomplished using (i) one or more metrics associated with the acoustic wave at the leader, and (ii) the metric(s) associated with the acoustic wave at the N-th acoustic segment. The leader, the N-th acoustic segment, and each of the acoustic segments exclusive of the leader and the N-th acoustic segment, are tuned to the noise-reducing impedance. The current leader is then excluded from subsequent processing steps. The designation of leader is then given one of the remaining acoustic segments, and the process is repeated for each of the acoustic segments through an (N-1)-th one of the acoustic segments.

  5. Respiratory acoustic impedance in left ventricular failure.

    PubMed

    Depeursinge, F B; Feihl, F; Depeursinge, C; Perret, C H

    1989-12-01

    The measurement of respiratory acoustic impedance (Zrs) by forced pseudorandom noise provides a simple means of assessing respiratory mechanics in nonintubated intensive care patients. To characterize the lung mechanical alterations induced by acute vascular congestion of the lung, Zrs was measured in 14 spontaneously breathing patients hospitalized for acute left ventricular failure. The Zrs data in the cardiac patients were compared with those of 48 semirecumbent normal subjects and those of 23 sitting asthmatic patients during allergen-induced bronchospasm. In the patients with acute left ventricular failure, the Zrs abnormalities noted were an excessive frequency dependence of resistance from 10 to 20 Hz and an abnormally low reactance at all frequencies, abnormalities qualitatively similar to those observed in the asthmatic patients but of lesser magnitude. Acute lung vascular congestion modifies the acoustic impedance of the respiratory system. Reflex-induced bronchospasm might be the main mechanism altering respiratory acoustic impedance in acute left ventricular failure. PMID:2582846

  6. Nonlinear acoustic impedance of thermoacoustic stack

    NASA Astrophysics Data System (ADS)

    Ge, Huan; Fan, Li; Xiao, Shu-yu; Tao, Sha; Qiu, Mei-chen; Zhang, Shu-yi; Zhang, Hui

    2012-09-01

    In order to optimize the performances of the thermoacoustic refrigerator working with the high sound pressure level, the nonlinear acoustic characteristics of the thermoacoustic stack in the resonant pipe are studied. The acoustic fluid impedance of the stack made of copper mesh and set up in a resonant pipe is measured in the acoustic fields with different intensities. It is found that when the sound pressure level in the pipe increases to a critical value, the resistance of the stack increases nonlinearly with the sound pressure, while the reactance of the stack keeps constant. Based on the experimental results, a theory model is set up to describe the acoustic characteristics of the stack, according to the rigid frame theory and Forchheimmer equation. Furthermore, the influences of the sound pressure level, operating frequency, volume porosity, and length of the stack on the nonlinear impedance of the stack are evaluated.

  7. Acoustic grazing flow impedance using waveguide principles

    NASA Technical Reports Server (NTRS)

    Armstrong, D. L.

    1971-01-01

    A grazing flow apparatus was designed to measure the impedance of acoustic materials when installed in environments that subject the material to grazing airflow. The design of the apparatus and the data analysis technique is based on the solution of the convected wave equation in an infinite length waveguide.

  8. Acoustic input impedance measurements on brass instruments

    NASA Astrophysics Data System (ADS)

    Pyle, Robert W., Jr.

    2002-11-01

    Measurement of the acoustic input impedance of a brass instrument can reveal something about the instrument's intonation, its reasonable playing range, its tone color, and perhaps whether the mouthpiece used for the impedance measurement is appropriate for the instrument. Such measurements are made at sound-presssure levels much lower than those encountered under playing conditions. Thus, impedance measurements may offer the only feasible way to infer something about the playing characteristics of instruments, typically museum specimens, that are too rare or too fragile to be played. In this paper the effects of some of the available choices of sound source and stimulus signal on measurement accuracy will be explored. Driver-transducer nonlinearity, source impedance, signal-to-noise ratio, and any necessary signal processing will be discussed.

  9. Active acoustical impedance using distributed electrodynamical transducers.

    PubMed

    Collet, M; David, P; Berthillier, M

    2009-02-01

    New miniaturization and integration capabilities available from emerging microelectromechanical system (MEMS) technology will allow silicon-based artificial skins involving thousands of elementary actuators to be developed in the near future. SMART structures combining large arrays of elementary motion pixels coated with macroscopic components are thus being studied so that fundamental properties such as shape, stiffness, and even reflectivity of light and sound could be dynamically adjusted. This paper investigates the acoustic impedance capabilities of a set of distributed transducers connected with a suitable controlling strategy. Research in this domain aims at designing integrated active interfaces with a desired acoustical impedance for reaching an appropriate global acoustical behavior. This generic problem is intrinsically connected with the control of multiphysical systems based on partial differential equations (PDEs) and with the notion of multiscaled physics when a dense array of electromechanical systems (or MEMS) is considered. By using specific techniques based on PDE control theory, a simple boundary control equation capable of annihilating the wave reflections has been built. The obtained strategy is also discretized as a low order time-space operator for experimental implementation by using a dense network of interlaced microphones and loudspeakers. The resulting quasicollocated architecture guarantees robustness and stability margins. This paper aims at showing how a well controlled semidistributed active skin can substantially modify the sound transmissibility or reflectivity of the corresponding homogeneous passive interface. In Sec. IV, numerical and experimental results demonstrate the capabilities of such a method for controlling sound propagation in ducts. Finally, in Sec. V, an energy-based comparison with a classical open-loop strategy underlines the system's efficiency. PMID:19206865

  10. Acoustic characteristics of the medium with gradient change of impedance

    NASA Astrophysics Data System (ADS)

    Hu, Bo; Yang, Desen; Sun, Yu; Shi, Jie; Shi, Shengguo; Zhang, Haoyang

    2015-10-01

    The medium with gradient change of acoustic impedance is a new acoustic structure which developed from multiple layer structures. In this paper, the inclusion is introduced and a new set of equations is developed. It can obtain better acoustic properties based on the medium with gradient change of acoustic impedance. Theoretical formulation has been systematically addressed which demonstrates how the idea of utilizing this method. The sound reflection and absorption coefficients were obtained. At last, the validity and the correctness of this method are assessed by simulations. The results show that appropriate design of parameters of the medium can improve underwater acoustic properties.

  11. Modifying the acoustic impedance of polyurea-based composites

    NASA Astrophysics Data System (ADS)

    Nantasetphong, Wiroj; Amirkhizi, Alireza V.; Jia, Zhanzhan; Nemat-Nasser, Sia

    2013-04-01

    Acoustic impedance is a material property that depends on mass density and acoustic wave speed. An impedance mismatch between two media leads to the partial reflection of an acoustic wave sent from one medium to another. Active sonar is one example of a useful application of this phenomenon, where reflected and scattered acoustic waves enable the detection of objects. If the impedance of an object is matched to that of the surrounding medium, however, the object may be hidden from observation (at least directly) by sonar. In this study, polyurea composites are developed to facilitate such impedance matching. Polyurea is used due to its excellent blast-mitigating properties, easy casting, corrosion protection, abrasion resistance, and various uses in current military technology. Since pure polyurea has impedance higher than that of water (the current medium of interest), low mass density phenolic microballoon particles are added to create composite materials with reduced effective impedances. The volume fraction of particles is varied to study the effect of filler quantity on the acoustic impedance of the resulting composite. The composites are experimentally characterized via ultrasonic measurements. Computational models based on the method of dilute-randomly-distributed inclusions are developed and compared with the experimental results. These experiments and models will facilitate the design of new elastomeric composites with desirable acoustic impedances.

  12. Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

    PubMed Central

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-01-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

  13. Manipulating acoustic wavefront by inhomogeneous impedance and steerable extraordinary reflection.

    PubMed

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-01-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators. PMID:23985717

  14. Manipulating Acoustic Wavefront by Inhomogeneous Impedance and Steerable Extraordinary Reflection

    NASA Astrophysics Data System (ADS)

    Zhao, Jiajun; Li, Baowen; Chen, Zhining; Qiu, Cheng-Wei

    2013-08-01

    We unveil the connection between the acoustic impedance along a flat surface and the reflected acoustic wavefront, in order to empower a wide wariety of novel applications in acoustic community. Our designed flat surface can generate double reflections: the ordinary reflection and the extraordinary one whose wavefront is manipulated by the proposed impedance-governed generalized Snell's law of reflection (IGSL). IGSL is based on Green's function and integral equation, instead of Fermat's principle for optical wavefront manipulation. Remarkably, via the adjustment of the designed specific acoustic impedance, extraordinary reflection can be steered for unprecedented acoustic wavefront while that ordinary reflection can be surprisingly switched on or off. The realization of the complex discontinuity of the impedance surface has been proposed using Helmholtz resonators.

  15. Active acoustical impedance using distributed electrodynamic transducers

    NASA Astrophysics Data System (ADS)

    Collet, M.; Berthillier, M.; David, P.

    2006-03-01

    New miniaturization and integration capabilities available from the emerging MEMS technology will allow silicon-based artificial skins involving thousands of elementary actuators to be developed in the near future. SMART structures combining large arrays of elementary motion pixels coated with macroscopic components are thus being studied so that fundamental properties such as shape, stiffness, color, and even reflectivity of light and sound could be dynamically adjusted. This paper investigates acoustic impedance capabilities of a set of distributed transducers connected with suitable controlling laws. Basically, we search to design an integrated electro-mechanical system which presents a global behavior with appropriate acoustical characteristics. This problem is intrinsically connected with the control of multi physical system based on PDE and with the notion of multi-scaled physics when we dispose MEMS devices. By using specific techniques based on partial differential equation control theory, we have first build a simple boundary control equation able to annihilate wave reflection. The obtained control strategies can also be discretized to be implemented like a zero or first order spatial operator. Thus, we can use quasi-collocated transducers and their well-known poles-zeros interlacing property to guarantee robust stability. This paper aims at showing in a first part how a well controlled semi-distributed active skin can substantially modify transmissibility or reflectivity of the corresponding homogeneous wall. In a second part numerical and experimental results underline the capabilities of the method. Finally efficiency of such a device is compared theoretically with those obtained by classical x-filtered LMS strategy.

  16. Tests Of Shear-Flow Model For Acoustic Impedance

    NASA Technical Reports Server (NTRS)

    Parrot, Tony L.; Watson, Willie R.; Jones, Michael G.

    1992-01-01

    Tests described in report conducted to validate two-dimensional shear-flow analytical model for determination of acoustic impedance of acoustic liner in grazing-incidence, grazing-flow environment by use of infinite-waveguide method. Tests successful for both upstream and downstream propagations. Work has potential for utility in testing of engine ducts in commercial aircraft.

  17. Comparison of Two Acoustic Waveguide Methods for Determining Liner Impedance

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Watson, Willie R.; Tracy, Maureen B.; Parrott, Tony L.

    2001-01-01

    Acoustic measurements taken in a flow impedance tube are used to assess the relative accuracy of two waveguide methods for impedance eduction in the presence of grazing flow. The aeroacoustic environment is assumed to contain forward and backward-traveling acoustic waves, consisting of multiple modes, and uniform mean flow. Both methods require a measurement of the complex acoustic pressure profile over the length of the test liner. The Single Mode Method assumes that the sound pressure level and phase decay-rates of a single progressive mode can be extracted from this measured complex acoustic pressure profile. No a priori assumptions are made in the Finite Element. Method regarding the modal or reflection content in the measured acoustic pressure profile. The integrity of each method is initially demonstrated by how well their no-flow impedances match those acquired in a normal incidence impedance tube. These tests were conducted using ceramic tubular and conventional perforate liners. Ceramic tubular liners were included because of their impedance insensitivity to mean flow effects. Conversely, the conventional perforate liner was included because its impedance is known to be sensitive to mean flow velocity effects. Excellent comparisons between impedance values educed with the two waveguide methods in the absence of mean flow and the corresponding values educed with the normal incident impedance tube were observed. The two methods are then compared for mean flow Mach numbers up to 0.5, and are shown to give consistent results for both types of test liners. The quality of the results indicates that the Single Mode Method should be used when the measured acoustic pressure profile is clearly dominated by a single progressive mode, and the Finite Element Method should be used for all other cases.

  18. Estimating surface acoustic impedance with the inverse method.

    PubMed

    Piechowicz, Janusz

    2011-01-01

    Sound field parameters are predicted with numerical methods in sound control systems, in acoustic designs of building and in sound field simulations. Those methods define the acoustic properties of surfaces, such as sound absorption coefficients or acoustic impedance, to determine boundary conditions. Several in situ measurement techniques were developed; one of them uses 2 microphones to measure direct and reflected sound over a planar test surface. Another approach is used in the inverse boundary elements method, in which estimating acoustic impedance of a surface is expressed as an inverse boundary problem. The boundary values can be found from multipoint sound pressure measurements in the interior of a room. This method can be applied to arbitrarily-shaped surfaces. This investigation is part of a research programme on using inverse methods in industrial room acoustics. PMID:21939599

  19. Optimization and Control of Acoustic Liner Impedance with Bias Flow

    NASA Technical Reports Server (NTRS)

    Wood, Houston; Follet, Jesse

    2000-01-01

    Because communities are impacted by steady increases in aircraft traffic, aircraft noise continues to be a growing problem for the growth of commercial aviation. Research has focused on improving the design of specific high noise source areas of aircraft and on noise control measures to alleviate noise radiated from aircraft to the surrounding environment. Engine duct liners have long been a principal means of attenuating engine noise. The ability to control in-situ the acoustic impedance of a liner would provide a valuable tool to improve the performance of liners. The acoustic impedance of a liner is directly related to the sound absorption qualities of that liner. Increased attenuation rates, the ability to change liner acoustic impedance to match various operating conditions, or the ability to tune a liner to more precisely match design impedance represent some ways that in-situ impedance control could be useful. With this in mind, the research to be investigated will focus on improvements in the ability to control liner impedance using a mean flow through the liner which is referred to as bias flow.

  20. Validation of an Acoustic Impedance Prediction Model for Skewed Resonators

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Parrott, Tony L.

    2009-01-01

    An impedance prediction model was validated experimentally to determine the composite impedance of a series of high-aspect ratio slot resonators incorporating channel skew and sharp bends. Such structures are useful for packaging acoustic liners into constrained spaces for turbofan noise control applications. A formulation of the Zwikker-Kosten Transmission Line (ZKTL) model, incorporating the Richards correction for rectangular channels, is used to calculate the composite normalized impedance of a series of six multi-slot resonator arrays with constant channel length. Experimentally, acoustic data was acquired in the NASA Langley Normal Incidence Tube over the frequency range of 500 to 3500 Hz at 120 and 140 dB OASPL. Normalized impedance was reduced using the Two-Microphone Method for the various combinations of channel skew and sharp 90o and 180o bends. Results show that the presence of skew and/or sharp bends does not significantly alter the impedance of a slot resonator as compared to a straight resonator of the same total channel length. ZKTL predicts the impedance of such resonators very well over the frequency range of interest. The model can be used to design arrays of slot resonators that can be packaged into complex geometries heretofore unsuitable for effective acoustic treatment.

  1. Measuring the Acoustic Impedance of Pipes and Musical Instruments

    NASA Astrophysics Data System (ADS)

    Jaeger, Herbert

    2007-05-01

    Using a small electret microphone and a piezo-buzzer we have constructed a simple impedance transducer to measure the input impedance of air columns, such as cylindrical pipes, as well as musical instruments. The input impedance of an air column is given as the ratio of the pressure to the volume flow of air at the input of the air column. The microphone serves as the pressure transducer, while the piezo-buzzer is controlled to provide a constant velocity amplitude. Therefore the microphone signal is proportional to the acoustical impedance and, if required, can be calibrated using a simple air column for which the impedance can be calculated. This impedance transducer is currently in use as demonstration equipment for a physical acoustics class. It is simple to use and robust, so that it is well-suited for an undergraduate introductory laboratory environment. This talk will discuss the function of the impedance transducer and show examples of the type of measurements that can be performed. To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.OSS07.C1.1

  2. Effects of Flow Profile on Educed Acoustic Liner Impedance

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Watson, Willie r.; Nark, Douglas M.

    2010-01-01

    This paper presents results of an investigation of the effects of shear flow profile on impedance eduction processes employed at NASA Langley. Uniform and 1-D shear-flow propagation models are used to educe the acoustic impedance of three test liners based on aeroacoustic data acquired in the Langley Grazing Flow Impedance Tube, at source levels of 130, 140 and 150 dB, and at centerline Mach numbers of 0.0, 0.3 and 0.5. A ceramic tubular, calibration liner is used to evaluate the propagation models, as this liner is expected to be insensitive to SPL, grazing flow Mach number, and flow profile effects. The propagation models are then used to investigate the effects of shear flow profile on acoustic impedances educed for two conventional perforate-over-honeycomb liners. Results achieved with the uniform-flow models follow expected trends, but those educed with the 1-D shear-flow model do not, even for the calibration liner. However, when the flow profile used with the shear-flow model is varied to increase the Mach number gradient near the wall, results computed with the shear-flow model are well matched to those achieved with the uniform-flow model. This indicates the effects of flow profile on educed acoustic liner impedance are small, but more detailed investigations of the flow field throughout the duct are needed to better understand these effects.

  3. Modal decomposition method for acoustic impedance testing in square ducts.

    PubMed

    Schultz, Todd; Cattafesta, Louis N; Sheplak, Mark

    2006-12-01

    Accurate duct acoustic propagation models are required to predict and reduce aircraft engine noise. These models ultimately rely on measurements of the acoustic impedance to characterize candidate engine nacelle liners. This research effort increases the frequency range of normal-incidence acoustic impedance testing in square ducts by extending the standard two-microphone method (TMM), which is limited to plane wave propagation, to include higher-order modes. The modal decomposition method (MDM) presented includes four normal modes in the model of the sound field, thus increasing the bandwidth from 6.7 to 13.5 kHz for a 25.4 mm square waveguide. The MDM characterizes the test specimen for normal- and oblique-incident acoustic impedance and mode scattering coefficients. The MDM is first formulated and then applied to the measurement of the reflection coefficient matrix for a ceramic tubular specimen. The experimental results are consistent with results from the TMM for the same specimen to within the 95% confidence intervals for the TMM. The MDM results show a series of resonances for the ceramic tubular material exhibiting a monotonic decrease in the resonant peaks of the acoustic resistance with increasing frequency, resembling a rigidly-terminated viscous tube, and also evidence of mode scattering is visible at the higher frequencies. PMID:17225402

  4. Impedance matched joined drill pipe for improved acoustic transmission

    DOEpatents

    Moss, William C.

    2000-01-01

    An impedance matched jointed drill pipe for improved acoustic transmission. A passive means and method that maximizes the amplitude and minimize the temporal dispersion of acoustic signals that are sent through a drill string, for use in a measurement while drilling telemetry system. The improvement in signal transmission is accomplished by replacing the standard joints in a drill string with joints constructed of a material that is impedance matched acoustically to the end of the drill pipe to which it is connected. Provides improvement in the measurement while drilling technique which can be utilized for well logging, directional drilling, and drilling dynamics, as well as gamma-ray spectroscopy while drilling post shot boreholes, such as utilized in drilling post shot boreholes.

  5. Prediction of the acoustic impedance of duct liners

    NASA Technical Reports Server (NTRS)

    Zorumski, W. E.; Tester, B. J.

    1976-01-01

    Recent research which contributes to the prediction of the acoustic impedance of duct liners is reviewed. This review includes the linear and nonlinear properties of sheet and bulk type materials and methods for the measurement of these properties. It also includes the effect of grazing flow on the acoustic properties of materials. Methods for predicting the properties of single or multilayered, point reacting or extended reaction, and flat or curved liners are discussed. Based on this review, methods for predicting the properties of the duct liners which are typically used in aircraft engines are recommended. Some areas of needed research are discussed briefly.

  6. Tungsten Oxide Layers of High Acoustic Impedance for Fully Insulating Acoustic Reflectors.

    PubMed

    DeMiguel-Ramos, M; Diaz-Duran, Barbara; Munir, Junaid; Clement, Marta; Mirea, Teona; Olivares, Jimena; Iborra, Enrique

    2016-07-01

    Gravimetric sensors based on solidly mounted resonators require fully insulating acoustic reflectors to avoid parasitics when operating in liquid media. In this work, we propose a new high-acoustic impedance material, tungsten oxide ([Formula: see text]), for acoustic reflectors. We have optimized the sputtering conditions of [Formula: see text] to obtain nonconductive layers with mass density around [Formula: see text] and acoustic velocities for the shear and the longitudinal modes up to 2700 and 4500 m/s, respectively. Compared to other conventionally used high impedance layers, [Formula: see text] films display several manufacture advantages, such as high deposition rates, great reproducibility, and good adhesion to underlying substrates. We have demonstrated the applicability of [Formula: see text] in practical shear mode bulk acoustic wave resonators that display good performance in liquid environments. PMID:26571521

  7. Fluid mechanical model of the acoustic impedance of small orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Rogers, T.

    1975-01-01

    A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice impedance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values (in both water and air) of orifice impedance is excellent. The model shows that (1) the acoustic flow in the immediate neighborhood of the orifice can be modelled as a locally spherical flow, (2) within this near field, the flow is, to a first approximation, unsteady and incompressible, and (3) at very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundary-layer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the orifice neighborhood.-

  8. Tunable acoustic radiation pattern assisted by effective impedance boundary

    NASA Astrophysics Data System (ADS)

    Qian, Feng; Quan, Li; Wang, Li-Wei; Liu, Xiao-Zhou; Gong, Xiu-Fen

    2016-02-01

    The acoustic wave propagation from a two-dimensional subwavelength slit surrounded by metal plates decorated with Helmholtz resonators (HRs) is investigated both numerically and experimentally in this work. Owing to the presence of HRs, the effective impedance of metal surface boundary can be manipulated. By optimizing the distribution of HRs, the asymmetric effective impedance boundary will be obtained, which contributes to generating tunable acoustic radiation pattern such as directional acoustic beaming. These dipole-like radiation patterns have high radiation efficiency, no fingerprint of sidelobes, and a wide tunable range of the radiation pattern directivity angle which can be steered by the spatial displacements of HRs. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB921504 and 2011CB707902), the National Natural Science Foundation of China (Grant No.11474160), the Fundamental Research Funds for Central Universities, China (Grant No. 020414380001), the State Key Laboratory of Acoustics, Chinese Academy of Sciences (Grant No. SKLOA201401), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

  9. Fluid mechanical model of the acoustic impedance of small orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Rogers, T.

    1976-01-01

    A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice resistance and reactance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values is excellent. The model shows the following: (1) The acoustic flow in immediate neighborhood of the orifice can be modeled as a locally spherical flow. Within this near field, the flow is, to a first approximation, unsteady and incompressible. (2) At very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundary-layer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the neighborhood of the orifice. (3) For large values of the incident acoustic pressure, the impedance is dominated by nonlinear jet-like effects. (4) For low values of the pressure, the resistance and reactance are roughly equal.

  10. Numerical analysis of acoustic impedance microscope utilizing acoustic lens transducer to examine cultured cells.

    PubMed

    Gunawan, Agus Indra; Hozumi, Naohiro; Takahashi, Kenta; Yoshida, Sachiko; Saijo, Yoshifumi; Kobayashi, Kazuto; Yamamoto, Seiji

    2015-12-01

    A new technique is proposed for non-contact quantitative cell observation using focused ultrasonic waves. This technique interprets acoustic reflection intensity into the characteristic acoustic impedance of the biological cell. The cells are cultured on a plastic film substrate. A focused acoustic beam is transmitted through the substrate to its interface with the cell. A two-dimensional (2-D) reflection intensity profile is obtained by scanning the focal point along the interface. A reference substance is observed under the same conditions. These two reflections are compared and interpreted into the characteristic acoustic impedance of the cell based on a calibration curve that was created prior to the observation. To create the calibration curve, a numerical analysis of the sound field is performed using Fourier Transforms and is verified using several saline solutions. Because the cells are suspended by two plastic films, no contamination is introduced during the observation. In a practical observation, a sapphire lens transducer with a center frequency of 300 MHz was employed using ZnO thin film. The objects studied were co-cultured rat-derived glial (astrocyte) cells and glioma cells. The result was the clear observation of the internal structure of the cells. The acoustic impedance of the cells was spreading between 1.62 and 1.72 MNs/m(3). Cytoskeleton was indicated by high acoustic impedance. The introduction of cytochalasin-B led to a significant reduction in the acoustic impedance of the glioma cells; its effect on the glial cells was less significant. It is believed that this non-contact observation method will be useful for continuous cell inspections. PMID:26163739

  11. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    SciTech Connect

    Kaduchak, Gregory; Ward, Michael D

    2014-10-21

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  12. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D.

    2011-12-27

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  13. Apparatus for separating particles utilizing engineered acoustic contrast capture particles

    DOEpatents

    Kaduchak, Gregory; Ward, Michael D

    2016-05-17

    An apparatus for separating particles from a medium includes a capillary defining a flow path therein that is in fluid communication with a medium source. The medium source includes engineered acoustic contrast capture particle having a predetermined acoustic contrast. The apparatus includes a vibration generator that is operable to produce at least one acoustic field within the flow path. The acoustic field produces a force potential minima for positive acoustic contrast particles and a force potential minima for negative acoustic contrast particles in the flow path and drives the engineered acoustic contrast capture particles to either the force potential minima for positive acoustic contrast particles or the force potential minima for negative acoustic contrast particles.

  14. Acoustics of contrastive prosody in children

    NASA Astrophysics Data System (ADS)

    Patel, Rupal; Piel, Jordan; Grigos, Maria

    2005-04-01

    Empirical data on the acoustics of prosodic control in children is limited, particularly for linguistically contrastive tasks. Twelve children aged 4, 7, and 11 years were asked to produce two utterances ``Show Bob a bot'' (voiced consonants) and ``Show Pop a pot'' (voiceless consonants) 10 times each with emphasis placed on the second word (Bob/Pop) and 10 times with emphasis placed on the last word (bot/pot). A total of 40 utterances were analyzed per child. The following acoustic measures were obtained for each word within each utterance: average fundamental frequency (f0), peak f0, average intensity, peak intensity, and duration. Preliminary results suggest that 4 year olds are unable to modulate prosodic cues to signal the linguistic contrast. The 7 year olds, however, not only signaled the appropriate stress location, but did so with the most contrastive differences in f0, intensity, and duration, of all age groups. Prosodic differences between stressed and unstressed words were more pronounced for the utterance with voiced consonants. These findings suggest that the acoustics of linguistic prosody begin to differentiate between age 4 and 7 and may be highly influenced by changes in physiological control and flexibility that may also affect segmental features.

  15. A state feedback electro-acoustic transducer for active control of acoustic impedance

    NASA Astrophysics Data System (ADS)

    Samejima, Toshiya

    2003-03-01

    In this paper, a new control system in which the acoustic impedance of an electro-acoustic transducer diaphragm can be actively varied by modifying design parameters is presented and its effectiveness is theoretically investigated. The proposed control system is based on a state-space description of the control system derived from an electrical equivalent circuit of an electro-acoustic transducer to which a differentiating circuit is connected, and is designed using modern control theory. The optimal quadratic regulator is used in the control system design, with its quadratic performance index formulated for producing desired acoustic impedance. Computer simulations indicate that the acoustic impedance of the diaphragm can be significantly varied over a wide frequency range that includes the range below the resonance frequency of the electro-acoustic transducer. A computer model of the proposed control system is used to illustrate its application to semi-active noise control in a duct. It is demonstrated that the proposed control system provides substantial reductions in the noise radiating from the outlet of the duct, both in the stiffness control range and in the mass control range.

  16. An analysis of the acoustic input impedance of the ear.

    PubMed

    Withnell, Robert H; Gowdy, Lauren E

    2013-10-01

    Ear canal acoustics was examined using a one-dimensional lossy transmission line with a distributed load impedance to model the ear. The acoustic input impedance of the ear was derived from sound pressure measurements in the ear canal of healthy human ears. A nonlinear least squares fit of the model to data generated estimates for ear canal radius, ear canal length, and quantified the resistance that would produce transmission losses. Derivation of ear canal radius has application to quantifying the impedance mismatch at the eardrum between the ear canal and the middle ear. The length of the ear canal was found, in general, to be longer than the length derived from the one-quarter wavelength standing wave frequency, consistent with the middle ear being mass-controlled at the standing wave frequency. Viscothermal losses in the ear canal, in some cases, may exceed that attributable to a smooth rigid wall. Resistance in the middle ear was found to contribute significantly to the total resistance. In effect, this analysis "reverse engineers" physical parameters of the ear from sound pressure measurements in the ear canal. PMID:23917695

  17. Preliminary Results on Different Impedance Contrast Agents for Pulmonary Perfusion Imaging with Electrical Impedance Tomography

    NASA Astrophysics Data System (ADS)

    Nguyen, D. T.; Kosobrodov, R.; Barry, M. A.; Chik, W.; Pouliopoulos, J.; Oh, T. I.; Thiagalingam, A.; McEwan, A.

    2013-04-01

    Recent studies in animal models suggest that the use of small volume boluses of NaCl as an impedance contrast agent can significantly improve pulmonary perfusion imaging by Electrical Impedance Tomography (EIT). However, these studies used highly concentrated NaCl solution (20%) which may have adverse effects on the patients. In a pilot experiment, we address this problem by comparing a number of different Impedance Contrast Boluses (ICBs). Conductivity changes in the lungs of a sheep after the injection of four different ICBs were compared, including three NaCl-based ICBs and one glucose-based ICB. The following procedure was followed for each ICB. Firstly, ventilation was turned off to provide an apneic window of approximately 40s to image the conductivity changes due to the ICB. Each ICB was then injected through a pig-tail catheter directly into the right atrium. EIT images were acquired throughout the apnea to capture the conductivity change. For each ICB, the experiment was repeated three times. The three NaCl-based ICB exhibited similar behaviour in which following the injection of each of these ICBs, the conductivity of each lung predictably increased. The effect of the ICB of 5% glucose solution was inconclusive. A small decrease in conductivity in the left lung was observed in two out of three cases and none was discernible in the right lung.

  18. Soil amplification with a strong impedance contrast: Boston, Massachusetts

    USGS Publications Warehouse

    Baise, Laurie G.; Kaklamanos, James; Berry, Bradford M; Thompson, Eric

    2016-01-01

    In this study, we evaluate the effect of strong sediment/bedrock impedance contrasts on soil amplification in Boston, Massachusetts, for typical sites along the Charles and Mystic Rivers. These sites can be characterized by artificial fill overlying marine sediments overlying glacial till and bedrock, where the depth to bedrock ranges from 20 to 80 m. The marine sediments generally consist of organic silts, sand, and Boston Blue Clay. We chose these sites because they represent typical foundation conditions in the city of Boston, and the soil conditions are similar to other high impedance contrast environments. The sediment/bedrock interface in this region results in an impedance ratio on the order of ten, which in turn results in a significant amplification of the ground motion. Using stratigraphic information derived from numerous boreholes across the region paired with geologic and geomorphologic constraints, we develop a depth-to-bedrock model for the greater Boston region. Using shear-wave velocity profiles from 30 locations, we develop average velocity profiles for sites mapped as artificial fill, glaciofluvial deposits, and bedrock. By pairing the depth-to-bedrock model with the surficial geology and the average shear-wave velocity profiles, we can predict soil amplification in Boston. We compare linear and equivalent-linear site response predictions for a soil layer of varying thickness over bedrock, and assess the effects of varying the bedrock shear-wave velocity (VSb) and quality factor (Q). In a moderate seismicity region like Boston, many earthquakes will result in ground motions that can be modeled with linear site response methods. We also assess the effect of bedrock depth on soil amplification for a generic soil profile in artificial fill, using both linear and equivalent-linear site response models. Finally, we assess the accuracy of the model results by comparing the predicted (linear site response) and observed site response at the Northeastern

  19. Sensing the characteristic acoustic impedance of a fluid utilizing acoustic pressure waves

    PubMed Central

    Antlinger, Hannes; Clara, Stefan; Beigelbeck, Roman; Cerimovic, Samir; Keplinger, Franz; Jakoby, Bernhard

    2012-01-01

    Ultrasonic sensors can be used to determine physical fluid parameters like viscosity, density, and speed of sound. In this contribution, we present the concept for an integrated sensor utilizing pressure waves to sense the characteristic acoustic impedance of a fluid. We note that the basic setup generally allows to determine the longitudinal viscosity and the speed of sound if it is operated in a resonant mode as will be discussed elsewhere. In this contribution, we particularly focus on a modified setup where interferences are suppressed by introducing a wedge reflector. This enables sensing of the liquid's characteristic acoustic impedance, which can serve as parameter in condition monitoring applications. We present a device model, experimental results and their evaluation. PMID:23565036

  20. Optimization of Acoustic Pressure Measurements for Impedance Eduction

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Watson, W. R.; Nark, D. M.

    2007-01-01

    As noise constraints become increasingly stringent, there is continued emphasis on the development of improved acoustic liner concepts to reduce the amount of fan noise radiated to communities surrounding airports. As a result, multiple analytical prediction tools and experimental rigs have been developed by industry and academia to support liner evaluation. NASA Langley has also placed considerable effort in this area over the last three decades. More recently, a finite element code (Q3D) based on a quasi-3D implementation of the convected Helmholtz equation has been combined with measured data acquired in the Langley Grazing Incidence Tube (GIT) to reduce liner impedance in the presence of grazing flow. A new Curved Duct Test Rig (CDTR) has also been developed to allow evaluation of liners in the presence of grazing flow and controlled, higher-order modes, with straight and curved waveguides. Upgraded versions of each of these two test rigs are expected to begin operation by early 2008. The Grazing Flow Impedance Tube (GFIT) will replace the GIT, and additional capabilities will be incorporated into the CDTR. The current investigation uses the Q3D finite element code to evaluate some of the key capabilities of these two test rigs. First, the Q3D code is used to evaluate the microphone distribution designed for the GFIT. Liners ranging in length from 51 to 610 mm are investigated to determine whether acceptable impedance eduction can be achieved with microphones placed on the wall opposite the liner. This analysis indicates the best results are achieved for liner lengths of at least 203 mm. Next, the effects of moving this GFIT microphone array to the wall adjacent to the liner are evaluated, and acceptable results are achieved if the microphones are placed off the centerline. Finally, the code is used to investigate potential microphone placements in the CDTR rigid wall adjacent to the wall containing an acoustic liner, to determine if sufficient fidelity can be

  1. Simulating Reflex Induced Changes in the Acoustic Impedance of the Ear.

    ERIC Educational Resources Information Center

    Sirlin, Mindy W.; Levitt, Harry

    1991-01-01

    A simple procedure for measuring changes in the acoustic impedance of the ear is described. The technique has several applications, including simulation using a standard coupler of changes in real ear impedance produced by the acoustic reflex, and calibration of response time of an otoadmittance meter. (Author/DB)

  2. Otosclerosis in a black child: diagnostic acoustic impedance studies.

    PubMed

    Schweitzer, V G; Lilly, D J

    1984-10-01

    Otosclerosis classically describes an osteodystrophic change in the bony labyrinth and stapes footplate, of autosomal dominant inheritance, reported rare under the age of 5, extremely "rare" in the Oriental and Black race, "non-existent" in the American Indian, and with a clinical incidence of 5 per 1000 Caucasians. The differential diagnosis of a non-effusion conductive hearing loss in a child should include otosclerosis, congenital malleus or footplate fixation, tympanosclerotic fixation, congenital cholesteatoma, lysis of the incus long process, Paget's disease, osteogenesis imperfecta, and fibromuscular hyperplasia of the renal artery. Presented is a case report of a 14-year-old black male with bilateral clinical otosclerosis and a persistent stapedial artery. Preoperative multiple-frequency tympanometry and Zwislocki acoustic reactance and resistance analysis demonstrated absence of the "W" resonance pattern on high-frequency tympanometry and the classic friction and stiffness patterns of otosclerotic fixation. Repeat multiple-frequency tympanometry testing post-stapedectomy demonstrated prosthesis articulation. Prosthesis position can be monitored postoperatively by these acoustic impedance studies. PMID:6500827

  3. Gas hydrate saturation from acoustic impedance and resistivity logs in the shenhu area, south china sea

    USGS Publications Warehouse

    Wang, X.; Wu, S.; Lee, M.; Guo, Y.; Yang, S.; Liang, J.

    2011-01-01

    During the China's first gas hydrate drilling expedition -1 (GMGS-1), gas hydrate was discovered in layers ranging from 10 to 25 m above the base of gas hydrate stability zone in the Shenhu area, South China Sea. Water chemistry, electrical resistivity logs, and acoustic impedance were used to estimate gas hydrate saturations. Gas hydrate saturations estimated from the chloride concentrations range from 0 to 43% of the pore space. The higher gas hydrate saturations were present in the depth from 152 to 177 m at site SH7 and from 190 to 225 m at site SH2, respectively. Gas hydrate saturations estimated from the resistivity using Archie equation have similar trends to those from chloride concentrations. To examine the variability of gas hydrate saturations away from the wells, acoustic impedances calculated from the 3 D seismic data using constrained sparse inversion method were used. Well logs acquired at site SH7 were incorporated into the inversion by establishing a relation between the water-filled porosity, calculated using gas hydrate saturations estimated from the resistivity logs, and the acoustic impedance, calculated from density and velocity logs. Gas hydrate saturations estimated from acoustic impedance of seismic data are ???10-23% of the pore space and are comparable to those estimated from the well logs. The uncertainties in estimated gas hydrate saturations from seismic acoustic impedances were mainly from uncertainties associated with inverted acoustic impedance, the empirical relation between the water-filled porosities and acoustic impedances, and assumed background resistivity. ?? 2011 Elsevier Ltd.

  4. Covert contrast in velar fronting: An acoustic and ultrasound study.

    PubMed

    McAllister Byun, Tara; Buchwald, Adam; Mizoguchi, Ai

    2016-01-01

    There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralised. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralised the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed in this article. PMID:26325303

  5. Covert contrast in velar fronting: An acoustic and ultrasound study

    PubMed Central

    Byun, Tara McAllister; Buchwald, Adam; Mizoguchi, Ai

    2016-01-01

    There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralized. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralized the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed. PMID:26325303

  6. Development of an Acoustic Impedance Tube Testbed for Material Sample Testing

    NASA Technical Reports Server (NTRS)

    Doty, Benjamin J.; Kolaini, Ali R.

    2012-01-01

    Acoustic impedance tube method: uses Traveling wave amplitudes are measured on either side of a sample in a tube. Many acoustic properties of the sample can be calculated. It is Simple and inexpensive to set up, ideal for high volume optimization tests

  7. Surface impedance based microwave imaging method for breast cancer screening: contrast-enhanced scenario

    NASA Astrophysics Data System (ADS)

    Güren, Onan; Çayören, Mehmet; Tükenmez Ergene, Lale; Akduman, Ibrahim

    2014-10-01

    A new microwave imaging method that uses microwave contrast agents is presented for the detection and localization of breast tumours. The method is based on the reconstruction of breast surface impedance through a measured scattered field. The surface impedance modelling allows for representing the electrical properties of the breasts in terms of impedance boundary conditions, which enable us to map the inner structure of the breasts into surface impedance functions. Later a simple quantitative method is proposed to screen breasts against malignant tumours where the detection procedure is based on weighted cross correlations among impedance functions. Numerical results demonstrate that the method is capable of detecting small malignancies and provides reasonable localization.

  8. Duct wall impedance control as an advanced concept for acoustic impression

    NASA Technical Reports Server (NTRS)

    Dean, P. D.; Tester, B. J.

    1975-01-01

    Models and tests on an acoustic duct liner system which has the property of controlled-variable acoustic impedance are described. This is achieved by a novel concept which uses the effect of steady air flow through a multi-layer, locally reacting, resonant-cavity absorber. The scope of this work was limited to a 'proof of concept.' The test of the concept was implemented by means of a small-scale, square-section flow duct facility designed specifically for acoustic measurements, with one side of the duct acoustically lined. The test liners were designed with the aid of previously established duct acoustic theory and a semi-empirical impedance model of the liner system. Over the limited range tested, the liner behaved primarily as predicted, exhibiting significant changes in resistance and reactance, thus providing the necessary concept validation.

  9. Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus).

    PubMed

    Muyshondt, Pieter G G; Aerts, Peter; Dirckx, Joris J J

    2016-09-01

    In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10(12) Pa/m³, an inertial impedance of MIE = 0.652·10(6) Pa s(2)/m³, and a resistance of RIE = 1.57·10(9) Pa s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears. PMID:27473506

  10. Duct wall impedance control as an advanced concept for acoustic suppression enhancement. [engine noise reduction

    NASA Technical Reports Server (NTRS)

    Dean, P. D.

    1978-01-01

    A systems concept procedure is described for the optimization of acoustic duct liner design for both uniform and multisegment types. The concept was implemented by the use of a double reverberant chamber flow duct facility coupled with sophisticated computer control and acoustic analysis systems. The optimization procedure for liner insertion loss was based on the concept of variable liner impedance produced by bias air flow through a multilayer, resonant cavity liner. A multiple microphone technique for in situ wall impedance measurements was used and successfully adapted to produce automated measurements for all liner configurations tested. The complete validation of the systems concept was prevented by the inability to optimize the insertion loss using bias flow induced wall impedance changes. This inability appeared to be a direct function of the presence of a higher order energy carrying modes which were not influenced significantly by the wall impedance changes.

  11. Analysis of Diffraction of Dominant Mode in an Acoustic Impedance Loaded Trifurcated Duct

    NASA Astrophysics Data System (ADS)

    Ayub, Muhammad; Hussain Tiwana, Mazhar; Mann, Amer Bilad

    2010-11-01

    The paper presents the analytical description of diffraction phenomena of sound at the opening of a two dimensional semi-infinite acoustically soft duct. This soft duct is symmetrically located inside an infinite duct with normal impedance boundary conditions in the case where the surface acoustic impedances of the upper and lower infinite plates are different from each other. A matrix Wiener- Hopf equation associated with a new canonical scattering problem is solved explicitly. A new kernel function arose for the problem and has been factorized. The graphical results are also presented which show how effectively the unwanted noise can be reduced by proper selection of different parameters.

  12. Tracheo-bronchial soft tissue and cartilage resonances in the subglottal acoustic input impedance.

    PubMed

    Lulich, Steven M; Arsikere, Harish

    2015-06-01

    This paper offers a re-evaluation of the mechanical properties of the tracheo-bronchial soft tissues and cartilage and uses a model to examine their effects on the subglottal acoustic input impedance. It is shown that the values for soft tissue elastance and cartilage viscosity typically used in models of subglottal acoustics during phonation are not accurate, and corrected values are proposed. The calculated subglottal acoustic input impedance using these corrected values reveals clusters of weak resonances due to soft tissues (SgT) and cartilage (SgC) lining the walls of the trachea and large bronchi, which can be observed empirically in subglottal acoustic spectra. The model predicts that individuals may exhibit SgT and SgC resonances to variable degrees, depending on a number of factors including tissue mechanical properties and the dimensions of the trachea and large bronchi. Potential implications for voice production and large pulmonary airway tissue diseases are also discussed. PMID:26093432

  13. Underwater asymmetric acoustic transmission structure using the medium with gradient change of impedance

    NASA Astrophysics Data System (ADS)

    Bo, Hu; Jie, Shi; Sheng-Guo, Shi; Yu, Sun; Zhong-Rui, Zhu

    2016-02-01

    We propose an underwater asymmetric acoustic transmission structure comprised of two media each with a gradient change of acoustic impedance. By gradually increasing the acoustic impedances of the media, the propagating direction of the acoustic wave can be continuously bent, resulting in allowing the acoustic wave to pass through along the positive direction and blocking acoustic waves from the negative one. The main advantages of this structure are that the asymmetric transmission effect of this structure can be realized and enhanced more easily in water. We investigate both numerically and experimentally the asymmetric transmission effect. The experimental results show that a highly efficient asymmetric acoustic transmission can be yielded within a remarkable broadband frequency range, which agrees well with the numerical prediction. It is of potential practical significance for various underwater applications such as reducing vibration and noise. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204049 and 11204050), the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (Grant No. IRT1228), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant Nos. 20122304120023 and 20122304120011).

  14. Acoustic impedance rhinometry (AIR): a technique for monitoring dynamic changes in nasal congestion.

    PubMed

    Patuzzi, Robert; Cook, Alison

    2014-04-01

    We describe a simple and inexpensive method for monitoring nasal air flow resistance using measurement of the small-signal acoustic input impedance of the nasal passage, similar to the audiological measurement of ear drum compliance with acoustic tympanometry. The method requires generation of a fixed sinusoidal volume-velocity stimulus using ear-bud speakers, and an electret microphone to monitor the resultant pressure fluctuation in the nasal passage. Both are coupled to the nose via high impedance silastic tubing and a small plastic nose insert. The acoustic impedance is monitored in real-time using a laptop soundcard and custom-written software developed in LabView 7.0 (National Instruments). The compact, lightweight equipment and fast time resolution lends the technique to research into the small and rapid reflexive changes in nasal resistance caused by environmental and local neurological influences. The acoustic impedance rhinometry technique has the potential to be developed for use in a clinical setting, where the need exists for a simple and inexpensive objective nasal resistance measurement technique. PMID:24577261

  15. Variance of speed of sound and correlation with acoustic impedance in canine corneas.

    PubMed

    Tang, Junhua; Liu, Jun

    2011-10-01

    The clinical standard for measuring corneal thickness is ultrasound pachymetry that assumes a constant speed of sound. The purpose of this study was to examine the variance of speed of sound and its relationship with acoustic impedance in healthy eyes of canines with a large age span. Corneal speed of sound and acoustic impedance were measured in 34 canine eyes at room temperature (21 ± 1°C). The mean speed of sound was 1577 ± 10 m/s ranging from 1553 to 1594 m/s. There was a strong correlation between speed of sound and acoustic impedance (R = 0.84, p < 0.001). Corneal speed of sound had a small variance in healthy canines over 1-year-old, but was significantly lower in younger canines suggesting an age effect. The strong correlation between corneal speed of sound and acoustic impedance may offer a potential means to noninvasively detect abnormal speed of sound for more accurate corneal thickness estimation. PMID:21821348

  16. Mechanical impedance and acoustic mobility measurement techniques of specifying vibration environments

    NASA Technical Reports Server (NTRS)

    Kao, G. C.

    1973-01-01

    Method has been developed for predicting interaction between components and corresponding support structures subjected to acoustic excitations. Force environments determined in spectral form are called force spectra. Force-spectra equation is determined based on one-dimensional structural impedance model.

  17. Evaluation of Parallel-Element, Variable-Impedance, Broadband Acoustic Liner Concepts

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Howerton, Brian M.; Ayle, Earl

    2012-01-01

    Recent trends in aircraft engine design have highlighted the need for acoustic liners that provide broadband sound absorption with reduced liner thickness. Three such liner concepts are evaluated using the NASA normal incidence tube. Two concepts employ additive manufacturing techniques to fabricate liners with variable chamber depths. The first relies on scrubbing losses within narrow chambers to provide acoustic resistance necessary for sound absorption. The second employs wide chambers that provide minimal resistance, and relies on a perforated sheet to provide acoustic resistance. The variable-depth chambers used in both concepts result in reactance spectra near zero. The third liner concept employs mesh-caps (resistive sheets) embedded at variable depths within adjacent honeycomb chambers to achieve a desired impedance spectrum. Each of these liner concepts is suitable for use as a broadband sound absorber design, and a transmission line model is presented that provides good comparison with their respective acoustic impedance spectra. This model can therefore be used to design acoustic liners to accurately achieve selected impedance spectra. Finally, the effects of increasing the perforated facesheet thickness are demonstrated, and the validity of prediction models based on lumped element and wave propagation approaches is investigated. The lumped element model compares favorably with measured results for liners with thin facesheets, but the wave propagation model provides good comparisons for a wide range of facesheet thicknesses.

  18. Optimization of Microphone Locations for Acoustic Liner Impedance Eduction

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Watson, W. R.; June, J. C.

    2015-01-01

    Two impedance eduction methods are explored for use with data acquired in the NASA Langley Grazing Flow Impedance Tube. The first is an indirect method based on the convected Helmholtz equation, and the second is a direct method based on the Kumaresan and Tufts algorithm. Synthesized no-flow data, with random jitter to represent measurement error, are used to evaluate a number of possible microphone locations. Statistical approaches are used to evaluate the suitability of each set of microphone locations. Given the computational resources required, small sample statistics are employed for the indirect method. Since the direct method is much less computationally intensive, a Monte Carlo approach is employed to gather its statistics. A comparison of results achieved with full and reduced sets of microphone locations is used to determine which sets of microphone locations are acceptable. For the indirect method, each array that includes microphones in all three regions (upstream and downstream hard wall sections, and liner test section) provides acceptable results, even when as few as eight microphones are employed. The best arrays employ microphones well away from the leading and trailing edges of the liner. The direct method is constrained to use microphones opposite the liner. Although a number of arrays are acceptable, the optimum set employs 14 microphones positioned well away from the leading and trailing edges of the liner. The selected sets of microphone locations are also evaluated with data measured for ceramic tubular and perforate-over-honeycomb liners at three flow conditions (Mach 0.0, 0.3, and 0.5). They compare favorably with results attained using all 53 microphone locations. Although different optimum microphone locations are selected for the two impedance eduction methods, there is significant overlap. Thus, the union of these two microphone arrays is preferred, as it supports usage of both methods. This array contains 3 microphones in the upstream

  19. Air-ground interface: Surface waves, surface impedance and acoustic-to-seismic coupling coefficient

    NASA Technical Reports Server (NTRS)

    Daigle, Gilles; Embleton, Tony

    1990-01-01

    In atmospheric acoustics, the subject of surface waves has been an area of discussion for many years. The existence of an acoustic surface wave is now well established theoretically. The mathematical solution for spherical wave propagation above an impedance boundary includes the possibility of a contribution that possesses all the standard properties for a surface wave. Surface waves exist when the surface is sufficiently porous, relative to its acoustical resistance, that it can influence the airborne particle velocity near the surface and reduce the phase velocity of sound waves in air at the surface. This traps some of the sound energy in the air to remain near the surface as it propagates. Above porous grounds, the existence of surface waves has eluded direct experimental confirmation (pulse experiments have failed to show a separate arrival expected from the reduced phase speed) and indirect evidence for its existence has appeared contradictory. The experimental evidence for the existence of an acoustical surface wave above porous boundaries is reviewed. Recent measurements including pulse experiments are also described. A few years ago the acoustic impedance of a grass-covered surface was measured in the frequency range 30 to 300 Hz. Here, further measurements on the same site are discussed. These measurements include core samples, a shallow refractive survey to determine the seismic velocities, and measurements of the acoustic-to-seismic coupling coefficient.

  20. Measurement of cantilever vibration using impedance-loaded surface acoustic wave sensor

    NASA Astrophysics Data System (ADS)

    Oishi, Masaki; Hamashima, Hiromitsu; Kondoh, Jun

    2016-07-01

    In this study, an impedance-loaded surface acoustic wave (SAW) sensor was demonstrated to monitor the vibration frequency. Commercialized pressure sensors and a variable capacitor were chosen as external sensors, which were connected to a reflector on a SAW device. As the reflection coefficient of the reflector depended on the impedance, the echo amplitude was influenced by changes in the impedance of the external sensor. The vibration frequency of the cantilever was determined by monitoring the echo amplitude of the SAW device. Moreover, the attenuation constant of an envelope was estimated. The results of our feasibility study indicate that the impedance-loaded SAW sensor can be applied as a detector for structural health monitoring.

  1. On the Propagation of Plane Acoustic Waves in a Duct With Flexible and Impedance Walls

    NASA Technical Reports Server (NTRS)

    Frendi, Abdelkader; Vu, Bruce

    2003-01-01

    This Technical Memorandum (TM) discusses the harmonic and random plane acoustic waves propagating from inside a duct to its surroundings. Various duct surfaces are considered, such as rigid, flexible, and impedance. In addition, the effects of a mean flow are studied when the duct alone is considered. Results show a significant reduction in overall sound pressure levels downstream of the impedance wall for both mean flow and no mean flow cases and for a narrow duct. When a wider duct is used, the overall sound pressure level (OSPL) reduction downstream of the impedance wall is much smaller. In the far field, the directivity is such that the overall sound pressure level is reduced by about 5 decibels (dB) on the side of the impedance wall. When a flexible surface is used, the far field directivity becomes asymmetric with an increase in the OSPL on the side of the flexible surface of about 7 dB.

  2. Experimental validation of a two-dimensional shear-flow model for determining acoustic impedance

    NASA Technical Reports Server (NTRS)

    Parrott, Tony L.; Watson, Willie R.; Jones, Michael G.

    1987-01-01

    Tests were conducted to validate a two-dimensional shear-flow analytical model for determining the acoustic impedance of a liner test specimen in a grazing-incidence, grazing-flow environment. The tests were limited to a test specimen chosen to exhibit minimal effects of grazing flow so that the results obtained by using the shear-flow analytical model would be expected to match those obtained from normal-incidence impedance measurements. Impedances for both downstream and upstream sound propagation were generally consistent with those from normal-incidence measurements. However, sensitivity of the grazing-incidence impedance to small measurement or systematic errors in propagation constant varied dramatically over the range of test frequencies.

  3. Development of Microbubble Contrast Agents with Biochemical Recognition and Tunable Acoustic Response

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Matthew Allan Masao

    Microbubbles, consisting of gas-filled cores encapsulated within phospholipid or polymer shells, are the most widely used ultrasound contrast agents in the world. Because of their acoustic impedance mismatch with surrounding tissues and compressible gaseous interiors, they have high echogenicities that allow for efficient backscatter of ultrasound. They can also generate unique harmonic frequencies when insonated near their resonance frequency, depending on physical microbubble properties such as the stiffness and thickness of the encapsulating shell. Microbubbles are used to detect a number of cardiovascular diseases, but current methodologies lack the ability to detect and distinguish small, rapidly growing abnormalities that do not produce visible blockage or slowing of blood flow. This work describes the development, formulation, and validation of microbubbles with various polymer shell architectures designed to modulate their acoustic ability. We demonstrate that the addition of a thick disulfide crosslinked, poly(acrylic acid) encapsulating shell increases a bubble's resistance to cavitation and changes its resonance frequency. Modification of this shell architecture to use hybridized DNA strands to form crosslinks between the polymer chains allows for tuning of the bubble acoustic response. When the DNA crosslinks are in place, shell stiffness is increased so the bubbles do not oscillate and acoustic signal is muted. Subsequently, when these DNA strands are displaced, partial acoustic activity is restored. By using aptamer sequences with a specific affinity towards the biomolecule thrombin as the DNA crosslinking strand, this acoustic "ON/OFF" behavior can be specifically tailored towards the presence of a specific biomarker, and produces a change in acoustic signal at concentrations of thrombin consistent with acute deep venous thrombosis. Incorporation of the emulsifying agent poly(ethylene glycol) into the encapsulating shell improves microbubble yield

  4. A finite element propagation model for extracting normal incidence impedance in nonprogressive acoustic wave fields

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.; Tanner, Sharon E.; Parrott, Tony L.

    1995-01-01

    A propagation model method for extracting the normal incidence impedance of an acoustic material installed as a finite length segment in a wall of a duct carrying a nonprogressive wave field is presented. The method recasts the determination of the unknown impedance as the minimization of the normalized wall pressure error function. A finite element propagation model is combined with a coarse/fine grid impedance plane search technique to extract the impedance of the material. Results are presented for three different materials for which the impedance is known. For each material, the input data required for the prediction scheme was computed from modal theory and then contaminated by random error. The finite element method reproduces the known impedance of each material almost exactly for random errors typical of those found in many measurement environments. Thus, the method developed here provides a means for determining the impedance of materials in a nonprogressirve wave environment such as that usually encountered in a commercial aircraft engine and most laboratory settings.

  5. Acoustic Treatment Design Scaling Methods. Volume 2; Advanced Treatment Impedance Models for High Frequency Ranges

    NASA Technical Reports Server (NTRS)

    Kraft, R. E.; Yu, J.; Kwan, H. W.

    1999-01-01

    The primary purpose of this study is to develop improved models for the acoustic impedance of treatment panels at high frequencies, for application to subscale treatment designs. Effects that cause significant deviation of the impedance from simple geometric scaling are examined in detail, an improved high-frequency impedance model is developed, and the improved model is correlated with high-frequency impedance measurements. Only single-degree-of-freedom honeycomb sandwich resonator panels with either perforated sheet or "linear" wiremesh faceplates are considered. The objective is to understand those effects that cause the simple single-degree-of- freedom resonator panels to deviate at the higher-scaled frequency from the impedance that would be obtained at the corresponding full-scale frequency. This will allow the subscale panel to be designed to achieve a specified impedance spectrum over at least a limited range of frequencies. An advanced impedance prediction model has been developed that accounts for some of the known effects at high frequency that have previously been ignored as a small source of error for full-scale frequency ranges.

  6. Directional Reflective Surface Formed via Gradient-Impeding Acoustic Meta-Surfaces

    PubMed Central

    Song, Kyungjun; Kim, Jedo; Hur, Shin; Kwak, Jun-Hyuk; Lee, Seong-Hyun; Kim, Taesung

    2016-01-01

    Artificially designed acoustic meta-surfaces have the ability to manipulate sound energy to an extraordinary extent. Here, we report on a new type of directional reflective surface consisting of an array of sub-wavelength Helmholtz resonators with varying internal coiled path lengths, which induce a reflection phase gradient along a planar acoustic meta-surface. The acoustically reshaped reflective surface created by the gradient-impeding meta-surface yields a distinct focal line similar to a parabolic cylinder antenna, and is used for directive sound beamforming. Focused beam steering can be also obtained by repositioning the source (or receiver) off axis, i.e., displaced from the focal line. Besides flat reflective surfaces, complex surfaces such as convex or conformal shapes may be used for sound beamforming, thus facilitating easy application in sound reinforcement systems. Therefore, directional reflective surfaces have promising applications in fields such as acoustic imaging, sonic weaponry, and underwater communication. PMID:27562634

  7. Directional Reflective Surface Formed via Gradient-Impeding Acoustic Meta-Surfaces.

    PubMed

    Song, Kyungjun; Kim, Jedo; Hur, Shin; Kwak, Jun-Hyuk; Lee, Seong-Hyun; Kim, Taesung

    2016-01-01

    Artificially designed acoustic meta-surfaces have the ability to manipulate sound energy to an extraordinary extent. Here, we report on a new type of directional reflective surface consisting of an array of sub-wavelength Helmholtz resonators with varying internal coiled path lengths, which induce a reflection phase gradient along a planar acoustic meta-surface. The acoustically reshaped reflective surface created by the gradient-impeding meta-surface yields a distinct focal line similar to a parabolic cylinder antenna, and is used for directive sound beamforming. Focused beam steering can be also obtained by repositioning the source (or receiver) off axis, i.e., displaced from the focal line. Besides flat reflective surfaces, complex surfaces such as convex or conformal shapes may be used for sound beamforming, thus facilitating easy application in sound reinforcement systems. Therefore, directional reflective surfaces have promising applications in fields such as acoustic imaging, sonic weaponry, and underwater communication. PMID:27562634

  8. Evaluation of a multi-point method for determining acoustic impedance

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Parrott, Tony L.

    1988-01-01

    An investigation was conducted to explore potential improvements provided by a Multi-Point Method (MPM) over the Standing Wave Method (SWM) and Two-Microphone Method (TMM) for determining acoustic impedance. A wave propagation model was developed to model the standing wave pattern in an impedance tube. The acoustic impedance of a test specimen was calculated from a best fit of this standing wave pattern to pressure measurements obtained along the impedance tube centerline. Three measurement spacing distributions were examined: uniform, random, and selective. Calculated standing wave patterns match the point pressure measurement distributions with good agreement for a reflection factor magnitude range of 0.004 to 0.999. Comparisons of results using 2, 3, 6, and 18 measurement points showed that the most consistent results are obtained when using at least 6 evenly spaced pressure measurements per half-wavelength. Also, data were acquired with broadband noise added to the discrete frequency noise and impedances were calculated using the MPM and TMM algorithms. The results indicate that the MPM will be superior to the TMM in the presence of significant broadband noise levels associated with mean flow.

  9. Reflection of an acoustic line source by an impedance surface with uniform flow

    NASA Astrophysics Data System (ADS)

    Brambley, E. J.; Gabard, G.

    2014-10-01

    An exact analytic solution is derived for the 2D acoustic pressure field generated by a time-harmonic line mass source located above an impedance surface with uniform grazing flow. Closed-form asymptotic solutions in the far field are also provided. The analysis is valid for both locally-reacting and nonlocally-reacting impedances, as is demonstrated by analyzing a nonlocally reacting effective impedance representing the presence of a thin boundary layer over the surface. The analytic solution may be written in a form suggesting a generalization of the method of images to account for the impedance surface. The line source is found to excite surface waves on the impedance surface, some of which may be leaky waves which contradict the assumption of decay away from the surface predicted in previous analyses of surface waves with flow. The surface waves may be treated either (correctly) as unstable waves or (artificially) as stable waves, enabling comparison with previous numerical or mathematical studies which make either of these assumptions. The computer code for evaluating the analytic solution and far-field asymptotics is provided in the supplementary material. It is hoped this work will provide a useful benchmark solution for validating 2D numerical acoustic codes.

  10. Acoustic and Perceptual Cues to Contrastive Stress in Dysarthria

    ERIC Educational Resources Information Center

    Patel, Rupal; Campellone, Pamela

    2009-01-01

    Purpose: In this study, the authors sought to understand acoustic and perceptual cues to contrastive stress in speakers with dysarthria (DYS) and healthy controls (HC). Method: The production experiment examined the ability of 12 DYS (9 male, 3 female; M = 39 years of age) and 12 age- and gender-matched HC (9 male, 3 female; M = 37.5 years of age)…

  11. Mathematical justification of the acoustic method for measuring the impedance of the respiratory tract.

    PubMed

    Bogomolov, A V; Dragan, S P

    2015-01-01

    A new method for measuring a complex frequency-dependent acoustic impedance of the respiratory tract based on two-microphone method was developed. The measuring device consists of a waveguide connected through a mouthpiece to the patient's mouth. A sound field with a frequency range from 5 to 100 Hz is created in the waveguide. The impedance of the respiratory tract is determined at free respiration of the patient in the set frequency range; the duration of examination does not exceed 15 s. The criteria for the recognition of respiratory tract pathologies are proposed. PMID:26518558

  12. Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1981-01-01

    The cutoff mode instability problem associated with a transient finite difference solution to the wave equation is explained. The steady-state impedance boundary condition is found to produce acoustic reflections during the initial transient, which cause finite instabilities in the cutoff modes. The stability problem is resolved by extending the duct length to prevent transient reflections. Numerical calculations are presented at forcing frequencies above, below, and nearly at the cutoff frequency, and exit impedance models are presented for use in the practical design of turbofan inlets.

  13. Multi-stage pulse tube cryocooler with acoustic impedance constructed to reduce transient cool down time and thermal loss

    NASA Technical Reports Server (NTRS)

    Gedeon, David R. (Inventor); Wilson, Kyle B. (Inventor)

    2008-01-01

    The cool down time for a multi-stage, pulse tube cryocooler is reduced by configuring at least a portion of the acoustic impedance of a selected stage, higher than the first stage, so that it surrounds the cold head of the selected stage. The surrounding acoustic impedance of the selected stage is mounted in thermally conductive connection to the warm region of the selected stage for cooling the acoustic impedance and is fabricated of a high thermal diffusivity, low thermal radiation emissivity material, preferably aluminum.

  14. Influence of acoustic dominant mode propagation in a trifurcated lined duct with different impedances

    NASA Astrophysics Data System (ADS)

    Ayub, M.; Tiwana, M. H.; Mann, A. B.

    2010-03-01

    In this study, we analyzed the diffraction of the acoustic dominant mode in a parallel-plate trifurcated waveguide with normal impedance boundary conditions in the case where surface impedances of the upper and lower infinite plates are different from each other. The acoustic dominant mode is incident in a soft/hard semi-infinite duct located symmetrically in the infinite lined duct. The solution of the boundary value problem using Fourier transform leads to two simultaneous modified Wiener-Hopf equations that are uncoupled using the pole removal technique. Two infinite sets of unknown coefficients are involved in the solution, which satisfy two infinite systems of linear algebraic equations. These systems are solved numerically. The new kernel functions are factorized. Some graphical results showing the influence of sundry parameters of interest on the reflection coefficient are presented.

  15. Measurement of acoustic impedance and reflectance in the human ear canal.

    PubMed

    Voss, S E; Allen, J B

    1994-01-01

    The pressure reflectance R (omega) is the transfer function which may be defined for a linear one-port network by the ratio of the reflected complex pressure divided by the incident complex pressure. The reflectance is a function that is closely related to the impedance of the 1-port. The energy reflectance R (omega) is defined as magnitude of [R]2. It represents the ratio of reflected to incident energy. In the human ear canal the energy reflectance is important because it is a measure of the inefficiency of the middle ear and cochlea, and because of the insight provided by its simple frequency domain interpretation. One may characterize the ear canal impedance by use of the pressure reflectance and its magnitude, sidestepping the difficult problems of (a) the unknown canal length from the measurement point to the eardrum, (b) the complicated geometry of the drum, and (c) the cross-sectional area changes in the canal as a function of distance. Reported here are acoustic impedance measurements, looking into the ear canal, measured on ten young adults with normal hearing (ages 18-24). The measurement point in the canal was approximately 0.85 cm from the entrance of the canal. From these measurements, the pressure reflectance in the canal is computed and impedance and reflectance measurements from 0.1 to 15.0 kHz are compared among ears. The average reflectance and the standard deviation of the reflectance for the ten subjects have been determined. The impedance and reflectance of two common ear simulators, the Brüel & Kjaer 4157 and the Industrial Research Products DB-100 (Zwislocki) coupler are also measured and compared to the average human measurements. All measurements are made using controls that assure a uniform accuracy in the acoustic calibration across subjects. This is done by the use of two standard acoustic resistors whose impedances are known. From the experimental results, it is concluded that there is significant subject variability in the magnitude

  16. Acoustic contrast control in an arc-shaped area using a linear loudspeaker array.

    PubMed

    Zhao, Sipei; Qiu, Xiaojun; Burnett, Ian

    2015-02-01

    This paper proposes a method of creating acoustic contrast control in an arc-shaped area using a linear loudspeaker array. The boundary of the arc-shaped area is treated as the envelope of the tangent lines that can be formed by manipulating the phase profile of the loudspeakers in the array. When compared with the existing acoustic contrast control method, the proposed method is able to generate sound field inside an arc-shaped area and achieve a trade-off between acoustic uniformity and acoustic contrast. The acoustic contrast created by the proposed method increases while the acoustic uniformity decreases with frequency. PMID:25698035

  17. Acoustic impedance studies in Triassic reservoirs in the Netherlands - application to development and exploration

    SciTech Connect

    Griffiths, M.; Ford, J.

    1995-08-01

    Simple and cost effective seismic forward modelling techniques have been used in conjunction with petrophysical and geological data to provide an integrated approach to understanding the seismic response of Triassic gas reservoirs onshore and offshore Netherlands. Analysis shows that for the Volpriehausen Sandstone in the offshore sector a relationship exists between reservoir acoustic impedance and porosity such that an increase in porosity leads to a decrease in acoustic impedance. Data can be sub-divided on the basis of fluid fill and cementation with trends for both gas and water cases. Regression analysis has defined the optimum relationship for each fluid case and these relationships have been used to predict the acoustic impedance profiles for a variety of reservoir scenarios. Modelling shows that the highest seismic amplitudes and the greatest relative amplitude variation with fluid fill are related to high porosity reservoir. In the onshore sector, analysis for the Roet Sandstone has shown that even small scale variations in reservoir properties can be recorded within the detail of the seismic response. Results from seismic forward modelling compare with amplitude variations observed in real data and suggest that, within the limitations of the dataset and methodology, the technique can be used to predict reservoir attributes from the seismic response. So far, the technique has been sucessfully applied to both exploration and field development projects.

  18. Acoustic impedance of micro perforated membranes: Velocity continuity condition at the perforation boundary.

    PubMed

    Li, Chenxi; Cazzolato, Ben; Zander, Anthony

    2016-01-01

    The classic analytical model for the sound absorption of micro perforated materials is well developed and is based on a boundary condition where the velocity of the material is assumed to be zero, which is accurate when the material vibration is negligible. This paper develops an analytical model for finite-sized circular micro perforated membranes (MPMs) by applying a boundary condition such that the velocity of air particles on the hole wall boundary is equal to the membrane vibration velocity (a zero-slip condition). The acoustic impedance of the perforation, which varies with its position, is investigated. A prediction method for the overall impedance of the holes and the combined impedance of the MPM is also provided. The experimental results for four different MPM configurations are used to validate the model and good agreement between the experimental and predicted results is achieved. PMID:26827008

  19. Investigation of the thickness effect to impedance analysis results AlGaN acoustic sensor

    NASA Astrophysics Data System (ADS)

    Özen, Soner; Bilgiç, Eyüp; Gülmez, Gülay; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan; Mohammadigharehbagh, Reza

    2016-03-01

    In this study, AlGaN acoustic sensors were deposited on aluminum metal substrate by thermionic vacuum arc (TVA) method, for the first time. Impedance analyses of the fabricated acoustic sensors were investigated for the determining of effect of the nano layer thickness. Thickness values are very close to each others. Fabricated sensors have been fabricated from AlGaN deposited on aluminum substrates. Gallium materials are used in many applications for optoelectronic device and semiconductor technology. Thermionic vacuum arc is the deposition technology for the variously materials and applications field. TVA production parameters and some properties of the deposited layers were investigated. TVA is the fast deposition technology for the gallium compounds and doped gallium compounds. Obtained results that AlGaN layer are very promising material for an acoustic sensor but also TVA is proper fast technology for the production.

  20. Comparison of Acoustic Impedance Eduction Techniques for Locally-Reacting Liners

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Parrott, T. L.; Watson, W. R.

    2003-01-01

    Typical acoustic liners used in current aircraft inlets and aft-fan ducts consist of some type of perforated facesheet bonded to a honeycomb core. A number of techniques for determining the acoustic impedance of these locallyreacting liners have been developed over the last five decades. In addition, a number of models have been developed to predict the acoustic impedance of locallyreacting liners in the presence of grazing flow, and to use that information together with aeroacoustic propagation codes to assess the noise absorption provided by these liners. These prediction models have incorporated the results from databases acquired with specific impedance eduction techniques. Thus, while these prediction models are acceptable for liners that are similar to those tested in these databases, their application to new liner configurations must be viewed with caution. The primary purpose of this paper is to provide a comparison of impedance eduction techniques that have been implemented at various aerospace research laboratories in the United States (NASA Langley Research Center, General Electric Aircraft Engines, B. F. Goodrich and Boeing). A secondary purpose is to provide data for liner configurations that extend the porosity range beyond that which has been previously used in common aircraft engine nacelles. Two sets of liners were designed to study the effects of three parameters: perforate hole diameter, facesheet thickness and porosity. These two sets of liners were constructed for testing in each of the laboratories listed above. The first set of liners was designed to fit into the NASA Langley and Boeing test facilities. The second set was designed to fit into the General Electric Aircraft Engines and B. F. Goodrich test facilities. By using the same parent material, both sets of liners were identical to within the limits of material and fabrication variability. Baseline data were obtained in the normal incidence impedance tubes at NASA Langley and B. F

  1. Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1981-01-01

    The time-dependent governing acoustic-difference equations and boundary conditions are developed and solved for sound propagation in an axisymmetric (cylindrical) hard-wall duct without flow and with spinning acoustic modes. The analysis begins with a harmonic sound source radiating into a quiescent duct. This explicit iteration method then calculates stepwise in real time to obtain the steady solutions of the acoustic field. The transient method did not converge to the steady-state solution for cutoff acoustic duct modes. This has implications as to its use in a variable-area duct, where modes may become cutoff in the smal-area portion of the duct. For single cutoff mode propagation the steady-state impedance boundary condition produced acoustic reflections during the initial transient that caused finite instabilities in the numerical calculations. The stability problem is resolved by reformulating the exit boundary condition. Example calculations show good agreement with exact analytical and numerical results for forcing frequencies above, below, and nearly at the cutoff frequency.

  2. Measurements and computational fluid dynamics predictions of the acoustic impedance of orifices

    NASA Astrophysics Data System (ADS)

    Su, J.; Rupp, J.; Garmory, A.; Carrotte, J. F.

    2015-09-01

    The response of orifices to incident acoustic waves, which is important for many engineering applications, is investigated with an approach combining both experimental measurements and numerical simulations. This paper presents experimental data on acoustic impedance of orifices, which is subsequently used for validation of a numerical technique developed for the purpose of predicting the acoustic response of a range of geometries with moderate computational cost. Measurements are conducted for orifices with length to diameter ratios, L/D, of 0.5, 5 and 10. The experimental data is obtained for a range of frequencies using a configuration in which a mean (or bias) flow passes from a duct through the test orifices before issuing into a plenum. Acoustic waves are provided by a sound generator on the upstream side of the orifices. Computational fluid dynamics (CFD) calculations of the same configuration have also been performed. These have been undertaken using an unsteady Reynolds averaged Navier-Stokes (URANS) approach with a pressure based compressible formulation with appropriate characteristic based boundary conditions to simulate the correct acoustic behaviour at the boundaries. The CFD predictions are in very good agreement with the experimental data, predicting the correct trend with both frequency and orifice L/D in a way not seen with analytical models. The CFD was also able to successfully predict a negative resistance, and hence a reflection coefficient greater than unity for the L / D = 0.5 case.

  3. Information passage from acoustic impedance to seismogram: Perspectives from wavelet-based multiscale analysis

    NASA Astrophysics Data System (ADS)

    Li, Chun-Feng

    2004-07-01

    Traditional seismic interpretation of surface seismic data is focused primarily on seismic oscillation. Rich singularity information carried by, but deeply buried in, seismic data is often ignored. We show that wavelet-based singularity analysis reveals generic singularity information conducted from acoustic impedance to seismogram. The singularity exponents (known as Hölder exponent α) calculated from seismic data are independent of amplitude and robust to phase changes and noises. These unique properties of α offer potentially important application in many fields, especially in studying seismic data interpretation, processing, inversion, and wave attenuation.

  4. Acoustic properties of organic powders as ultrasonic contrast agents

    NASA Astrophysics Data System (ADS)

    Burov, V. A.; Loginov, S. V.; Dmitriev, K. V.

    2011-11-01

    The results of experiments on measuring attenuation and the effective acoustic nonlinear parameter of the second order are given for a suspension of cocoa-powder in water at different concentrations of the suspension. In the process of evaluating the value of the nonlinear parameter the attenuation in the suspension and generation of the second harmonic not only in the suspension but also in water are taken into account. The obtained results are evidence of the possibility of using a suspension of cocoa-powder in water as a technical substitute for ultrasonic contrast agents. The values of attenuation (up to 60 m-1 at the concentration of 1 g of the powder per 1 l of water) and the nonlinear parameter (up to 120 m-1 at the same concentration) mean that the suspension of cocoa-powder in water has smaller attenuation and the nonlinear parameter than ultrasonic contrast agents at the same concentration. However, these values for the suspension differ considerably from corresponding values for water or blood and, therefore, a suspension of cocoa-powder in water is a promising "substitute" for ultrasonic contrast agents in the case of technical testing of systems for nonlinear tomography of a blood flow, but cannot replace them in medical studies.

  5. Digital PIV Measurements of Acoustic Particle Displacements in a Normal Incidence Impedance Tube

    NASA Technical Reports Server (NTRS)

    Humphreys, William M., Jr.; Bartram, Scott M.; Parrott, Tony L.; Jones, Michael G.

    1998-01-01

    Acoustic particle displacements and velocities inside a normal incidence impedance tube have been successfully measured for a variety of pure tone sound fields using Digital Particle Image Velocimetry (DPIV). The DPIV system utilized two 600-mj Nd:YAG lasers to generate a double-pulsed light sheet synchronized with the sound field and used to illuminate a portion of the oscillatory flow inside the tube. A high resolution (1320 x 1035 pixel), 8-bit camera was used to capture double-exposed images of 2.7-micron hollow silicon dioxide tracer particles inside the tube. Classical spatial autocorrelation analysis techniques were used to ascertain the acoustic particle displacements and associated velocities for various sound field intensities and frequencies. The results show that particle displacements spanning a range of 1-60 microns can be measured for incident sound pressure levels of 100-130 dB and for frequencies spanning 500-1000 Hz. The ability to resolve 1 micron particle displacements at sound pressure levels in the 100 dB range allows the use of DPIV systems for measurement of sound fields at much lower sound pressure levels than had been previously possible. Representative impedance tube data as well as an uncertainty analysis for the measurements are presented.

  6. A Comparison Study of Normal-Incidence Acoustic Impedance Measurements of a Perforate Liner

    NASA Technical Reports Server (NTRS)

    Schultz, Todd; Liu, Fei; Cattafesta, Louis; Sheplak, Mark; Jones, Michael

    2009-01-01

    The eduction of the acoustic impedance for liner configurations is fundamental to the reduction of noise from modern jet engines. Ultimately, this property must be measured accurately for use in analytical and numerical propagation models of aircraft engine noise. Thus any standardized measurement techniques must be validated by providing reliable and consistent results for different facilities and sample sizes. This paper compares normal-incidence acoustic impedance measurements using the two-microphone method of ten nominally identical individual liner samples from two facilities, namely 50.8 mm and 25.4 mm square waveguides at NASA Langley Research Center and the University of Florida, respectively. The liner chosen for this investigation is a simple single-degree-of-freedom perforate liner with resonance and anti-resonance frequencies near 1.1 kHz and 2.2 kHz, respectively. The results show that the ten measurements have the most variation around the anti-resonance frequency, where statistically significant differences exist between the averaged results from the two facilities. However, the sample-to-sample variation is comparable in magnitude to the predicted cross-sectional area-dependent cavity dissipation differences between facilities, providing evidence that the size of the present samples does not significantly influence the results away from anti-resonance.

  7. Acoustic radiation pressure: A 'phase contrast' agent for x-ray phase contrast imaging

    SciTech Connect

    Bailat, Claude J.; Hamilton, Theron J.; Rose-Petruck, Christoph; Diebold, Gerald J.

    2004-11-08

    We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high-resolution x-ray imaging of tissue and soft materials. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. The potential of the method is demonstrated by imaging microscopic tumor phantoms embedded into tissue with a thickness typically presented in mammography. The detection limit of micrometer size masses exceeds the resolution of currently available mammography imaging systems. The directionality of the acoustic radiation force and its localization in space permits the imaging of ultrasound-selected tissue volumes. The results presented here suggest that the method may permit the detection of tumors in soft tissue in their early stage of development.

  8. How stable are acoustic metrics of contrastive speech rhythm?

    PubMed

    Wiget, Lukas; White, Laurence; Schuppler, Barbara; Grenon, Izabelle; Rauch, Olesya; Mattys, Sven L

    2010-03-01

    Acoustic metrics of contrastive speech rhythm, based on vocalic and intervocalic interval durations, are intended to capture stable typological differences between languages. They should consequently be robust to variation between speakers, sentence materials, and measurers. This paper assesses the impact of these sources of variation on the metrics %V (proportion of utterance comprised of vocalic intervals), VarcoV (rate-normalized standard deviation of vocalic interval duration), and nPVI-V (a measure of the durational variability between successive pairs of vocalic intervals). Five measurers analyzed the same corpus of speech: five sentences read by six speakers of Standard Southern British English. Differences between sentences were responsible for the greatest variation in rhythm scores. Inter-speaker differences were also a source of significant variability. However, there was relatively little variation due to segmentation differences between measurers following an agreed protocol. An automated phone alignment process was also used: Rhythm scores thus derived showed good agreement with the human measurers. A number of recommendations for researchers wishing to exploit contrastive rhythm metrics are offered in conclusion. PMID:20329856

  9. Random and systematic measurement errors in acoustic impedance as determined by the transmission line method

    NASA Technical Reports Server (NTRS)

    Parrott, T. L.; Smith, C. D.

    1977-01-01

    The effect of random and systematic errors associated with the measurement of normal incidence acoustic impedance in a zero-mean-flow environment was investigated by the transmission line method. The influence of random measurement errors in the reflection coefficients and pressure minima positions was investigated by computing fractional standard deviations of the normalized impedance. Both the standard techniques of random process theory and a simplified technique were used. Over a wavelength range of 68 to 10 cm random measurement errors in the reflection coefficients and pressure minima positions could be described adequately by normal probability distributions with standard deviations of 0.001 and 0.0098 cm, respectively. An error propagation technique based on the observed concentration of the probability density functions was found to give essentially the same results but with a computation time of about 1 percent of that required for the standard technique. The results suggest that careful experimental design reduces the effect of random measurement errors to insignificant levels for moderate ranges of test specimen impedance component magnitudes. Most of the observed random scatter can be attributed to lack of control by the mounting arrangement over mechanical boundary conditions of the test sample.

  10. Accuracy of acoustic ear canal impedances: finite element simulation of measurement methods using a coupling tube.

    PubMed

    Schmidt, Sebastian; Hudde, Herbert

    2009-06-01

    Acoustic impedances measured at the entrance of the ear canal provide information on both the ear canal geometry and the terminating impedance at the eardrum, in principle. However, practical experience reveals that measured results in the audio frequency range up to 20 kHz are frequently not very accurate. Measurement methods successfully tested in artificial tubes with varying area functions often fail when applied to real ear canals. The origin of these errors is investigated in this paper. To avoid mixing of systematical and other errors, no real measurements are performed. Instead finite element simulations focusing on the coupling between a connecting tube and the ear canal are regarded without simulating a particular measuring method in detail. It turns out that realistic coupling between the connecting tube and the ear canal causes characteristic shifts of the frequencies of measured pressure minima and maxima. The errors in minima mainly depend on the extent of the area discontinuity arising at the interface; the errors in maxima are determined by the alignment of the tube with respect to the ear canal. In summary, impedance measurements using coupling tubes appear questionable beyond 3 kHz. PMID:19507964

  11. Evaluation of a Variable-Impedance Ceramic Matrix Composite Acoustic Liner

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Watson, W. R.; Nark, D. M.; Howerton, B. M.

    2014-01-01

    As a result of significant progress in the reduction of fan and jet noise, there is growing concern regarding core noise. One method for achieving core noise reduction is via the use of acoustic liners. However, these liners must be constructed with materials suitable for high temperature environments and should be designed for optimum absorption of the broadband core noise spectrum. This paper presents results of tests conducted in the NASA Langley Liner Technology Facility to evaluate a variable-impedance ceramic matrix composite acoustic liner that offers the potential to achieve each of these goals. One concern is the porosity of the ceramic matrix composite material, and whether this might affect the predictability of liners constructed with this material. Comparisons between two variable-depth liners, one constructed with ceramic matrix composite material and the other constructed via stereolithography, are used to demonstrate this material porosity is not a concern. Also, some interesting observations are noted regarding the orientation of variable-depth liners. Finally, two propagation codes are validated via comparisons of predicted and measured acoustic pressure profiles for a variable-depth liner.

  12. Automatic and controlled processing of acoustic and phonetic contrasts.

    PubMed

    Sussman, Elyse; Kujala, Teija; Halmetoja, Jaana; Lyytinen, Heikki; Alku, Paavo; Näätänen, Risto

    2004-04-01

    Changes in the temporal properties of the speech signal provide important cues for phoneme identification. An impairment or inability to detect such changes may adversely affect one's ability to understand spoken speech. The difference in meaning between the Finnish words tuli (fire) and tuuli (wind), for example, lies in the difference between the duration of the vowel /u/. Detecting changes in the temporal properties of the speech signal, therefore, is critical for distinguishing between phonemes and identifying words. In the current study, we tested whether detection of changes in speech sounds, in native Finnish speakers, would vary as a function of the position within the word that the informational changes occurred (beginning, middle, or end) by evaluating how length contrasts in segments of three-syllable Finnish pseudo-words and their acoustic correlates were discriminated. We recorded a combination of cortical components of event-related brain potentials (MMN, N2b, P3b) along with behavioral measures of the perception of the same sounds. It was found that speech sounds were not processed differently than non-speech sounds in the early stages of auditory processing indexed by MMN. Differences occurred only in later stages associated with controlled processes. The effects of position and attention on speech and non-speech stimuli are discussed. PMID:15051135

  13. Perceptual development of phoneme contrasts: how sensitivity changes along acoustic dimensions that contrast phoneme categories.

    PubMed

    Heeren, W F L; Schouten, M E H

    2008-10-01

    Listeners discriminate acoustic differences between phoneme categories at a higher level than similarly sized differences within phoneme categories. The question this paper aims to answer is how this pattern in perceptual sensitivity develops along an acoustic dimension that contrasts two non-native speech sounds: through acquired distinctiveness, through acquired similarity, or through a combination of the two. A pretest-training-post-test experiment was designed to study perceptual development directly, i.e., by including (i) a discrimination task to measure perceptual sensitivity, (ii) a transfer test to ensure language learning instead of stimulus learning, and (iii) a control group to exclude task repetition as an explanation of improvement. It is shown that the typical peak in perceptual sensitivity near a phoneme boundary that native listeners show is not found in relatively inexperienced language learners, despite their ability to classify a continuum in a nativelike way after short laboratory training. Experiment II indicates that a discrimination peak may be achieved by language learners, but only after much more language experience than short-term laboratory training can offer. Furthermore, reasons are given why classification improvement in the laboratory should not be taken as evidence for (i) increased discrimination of the newly learned phonemes and (ii) learning of phoneme representations. PMID:19062867

  14. Contribution to classification of buried objects based on acoustic impedance matching.

    PubMed

    Stepanić, J; Wüstenberg, H; Krstelj, V; Mrasek, H

    2003-03-01

    Determination of material the buried objects are made of could contribute significantly to their recognition, or classification. This is important in detecting buried antipersonnel landmines within the context of humanitarian demining, as well as in a variety of other applications. In this article the concept has been formulated of the approach to buried object's material determination starting with ultrasonic impulse propagation analysis in a particular testing set configuration. The impulse propagates through a characterized transfer material in such a way that a part of it, a reflected wave, carries the information about the buried object's surface material acoustic impedance. The limit of resolution capability is theoretically analyzed and experimentally evaluated and the influencing factors described. Among these, the contact between clean surfaces of the transfer material and buried object is emphasized. PMID:12565075

  15. Minimization of sonic-boom parameters in real and isothermal atmospheres. [overpressure and acoustic impedance

    NASA Technical Reports Server (NTRS)

    Darden, C. M.

    1975-01-01

    The procedure for sonic-boom minimization introduced by Seebass and George for an isothermal atmosphere was converted for use in the real atmosphere by means of the appropriate equations for sonic-boom pressure signature advance, ray-tube area, and acoustic impedance. Results of calculations using both atmospheres indicate that except for low Mach numbers or high altitudes, the isothermal atmosphere with a scale height of 7620 m (25 000 ft) gives a reasonable estimate of the values of overpressure, impulse, and characteristic overpressure obtained by using the real atmosphere. The results also show that for aircraft design studies, propagation of a known F-function, or minimization studies at low supersonic Mach numbers, the isothermal approximation is not adequate.

  16. A model for the pressure excitation spectrum and acoustic impedance of sound absorbers in the presence of grazing flow

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1973-01-01

    The acoustic impedance of sound absorbers in the presence of grazing flow is essential information when analyzing sound propagation within ducts. A unification of the theory of the nonlinear acoustic resistance of Helmholtz resonators including grazing flow is presented. The nonlinear resistance due to grazing flow is considered to be caused by an exciting pressure spectrum produced by the interaction of the grazing flow and the jets flowing from the resonator orifices. With this exciting pressure spectrum the resonator can be treated in the same manner as a resonator without grazing flow but with an exciting acoustic spectrum.

  17. Comparison of acoustic and impedance methods with mask capnometry to assess respiration rate in obese patients recovering from general anaesthesia.

    PubMed

    Frasca, D; Geraud, L; Charriere, J M; Debaene, B; Mimoz, O

    2015-01-01

    Respiratory depression, a potentially serious complication after general anaesthesia, can be detected promptly by close monitoring of both oxygen saturation and respiratory rate. Obese patients have morphological changes that may impair the reliability of monitoring devices. In this study, respiration rate was simultaneously recorded every second for up to 60 min using a computer in 30 adult obese patients (body mass index ≥ 35 kg.m(-2)), by three methods: acoustic; thoracic impedance; and capnometry via a facemask (Capnomask, reference method). Of the 99,771 data triplets collected, only 85,520 (86%) were included; 12,021 (84%) were not studied due to failure of capnometry and 2240 (16%) due to failure of the acoustic method. Compared with capnometry, bias was similar using both the acoustic method and impedance (-0.3 bpm vs. -0.6 bpm, respectively, p = 0.09), but limits of agreement were narrower for the acoustic method (±3.5 bpm vs. ±5.3 bpm, respectively, p = 0.0008). The proportion of respiration rate values obtained with the acoustic method and impedance that differed by at least 10% or 20% for more than 15 s were 11% vs. 23% and 2% vs. 6%, respectively (p = 0.0009 for both comparisons). The acoustic sensor was well tolerated, while the facemask was pulled off on several occasions by four (13%) agitated patients. In obese patients requiring close monitoring of respiration rate, the acoustic method may be more precise than thoracic impedance and better tolerated than capnometry with a facemask. PMID:25040754

  18. Density, ultrasound velocity, acoustic impedance, reflection and absorption coefficient determination of liquids via multiple reflection method.

    PubMed

    Hoche, S; Hussein, M A; Becker, T

    2015-03-01

    The accuracy of density, reflection coefficient, and acoustic impedance determination via multiple reflection method was validated experimentally. The ternary system water-maltose-ethanol was used to execute a systematic, temperature dependent study over a wide range of densities and viscosities aiming an application as inline sensor in beverage industries. The validation results of the presented method and setup show root mean square errors of: 1.201E-3 g cm(-3) (±0.12%) density, 0.515E-3 (0.15%) reflection coefficient and 1.851E+3 kg s(-1) m(-2) (0.12%) specific acoustic impedance. The results of the diffraction corrected absorption showed an average standard deviation of only 0.12%. It was found that the absorption change shows a good correlation to concentration variations and may be useful for laboratory analysis of sufficiently pure liquids. The main part of the observed errors can be explained by the observed noise, temperature variation and the low signal resolution of 50 MHz. In particular, the poor signal-to-noise ratio of the second reflector echo was found to be a main accuracy limitation. Concerning the investigation of liquids the unstable properties of the reference material PMMA, due to hygroscopicity, were identified to be an additional, unpredictable source of uncertainty. While dimensional changes can be considered by adequate methodology, the impact of the time and temperature dependent water absorption on relevant reference properties like the buffer's sound velocity and density could not be considered and may explain part of the observed deviations. PMID:25465962

  19. Effects of grazing flow on the steady-state flow resistance and acoustic impedance of thin porous-faced liners

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.

    1978-01-01

    The effects of grazing flow on the steady state flow resistance and acoustic impedance of seven Feltmetal and three Rigimesh thin porous faced liners were studied. The steady-state flow resistance of the ten specimens was measured using standard fluid mechanical experimental techniques. The acoustic impedance was measured using the two microphone method. The principal findings of the study are that the effects of grazing flow were measured and found to be small; small differences were measured between steady-state and acoustic resistance, and a semi-empirical model was derived that correlated the steady-state resistance data of the seven Feltmetal liners and the face sheet reactance of both the Feltmetal and Rigimesh liners.

  20. Measured and calculated acoustic attenuation rates of tuned resonator arrays for two surface impedance distribution models with flow

    NASA Technical Reports Server (NTRS)

    Parrott, Tony L.; Abrahamson, A. Louis; Jones, Michael G.

    1988-01-01

    An experiment was performed to validate two analytical models for predicting low frequency attenuation of duct liner configurations built from an array of seven resonators that could be individually tuned via adjustable cavity depths. These analytical models had previously been developed for high frequency aero-engine inlet duct liner design. In the low frequency application, the liner surface impedance distribution is unavoidably spatially varying by virtue of available fabrication techniques. The characteristic length of this spatial variation may be a significant fraction of the acoustic wavelength. Comparison of measured and predicted attenuation rates and transmission losses for both modal decomposition and finite element propagation models were in good to excellent agreement for a test frequency range that included the first and second cavity resonance frequencies. This was true for either of two surface impedance distribution modeling procedures used to simplify the impedance boundary conditions. In the presence of mean flow, measurements revealed a fine scale structure of acoustic hot spots in the attenuation and phase profiles. These details were accurately predicted by the finite element model. Since no impedance changes due to mean flow were assumed, it is concluded that this fine scale structure was due to convective effects of the mean flow interacting with the surface impedance nonuniformities.

  1. Multiscale analysis of the acoustic scattering by many scatterers of impedance type

    NASA Astrophysics Data System (ADS)

    Challa, Durga Prasad; Sini, Mourad

    2016-06-01

    We are concerned with the acoustic scattering problem, at a frequency {κ}, by many small obstacles of arbitrary shapes with impedance boundary condition. These scatterers are assumed to be included in a bounded domain {Ω} in {{R}^3} which is embedded in an acoustic background characterized by an eventually locally varying index of refraction. The collection of the scatterers {D_m, m=1,ldots,M} is modeled by four parameters: their number M, their maximum radius a, their minimum distance d and the surface impedances {λ_m, m=1,ldots,M}. We consider the parameters M, d and {λ_m}'s having the following scaling properties: {M:=M(a)=O(a^{-s}), d:=d(a)≈ a^t} and {λ_m:=λ_m(a)=λ_{m,0}a^{-β}}, as {a→ 0}, with non negative constants s, t and {β} and complex numbers {λ_{m, 0}}'s with eventually negative imaginary parts. We derive the asymptotic expansion of the far-fields with explicit error estimate in terms of a, as {a→ 0}. The dominant term is the Foldy-Lax field corresponding to the scattering by the point-like scatterers located at the centers {z_m}'s of the scatterers {D_m}'s with {λ_m \\vert partial D_m\\vert} as the related scattering coefficients. This asymptotic expansion is justified under the following conditions a ≤ a_0, \\vert Re (λ_{m,0})\\vert ≥ λ_-,quad \\vertλ_{m,0}\\vert ≤ λ_+,quad β < 1,quad 0 ≤ s ≤2-β,quads/3 ≤ t and the error of the approximation is {C a^{3-2β-s}}, as {a → 0}, where the positive constants {a_0, λ_-,λ_+} and C depend only on the a priori uniform bounds of the Lipschitz characters of the obstacles {D_m}'s and the ones of {M(a)a^s} and {d(a)/a^t}. We do not assume the periodicity in distributing the small scatterers. In addition, the scatterers can be arbitrary close since t can be arbitrary large, i.e., we can handle the mesoscale regime. Finally, for spherical scatterers, we can also allow the limit case {β=1} with a slightly better error of the approximation.

  2. The point source method for reconstructing an inclusion from boundary measurements in electrical impedance tomography and acoustic scattering

    NASA Astrophysics Data System (ADS)

    Erhard, Klaus; Potthast, Roland

    2003-10-01

    We employ the point source method (PSM) for the reconstruction of some field u on parts of a domain Omega from the Cauchy data for the field on the boundary partialOmega of the domain. Then, the boundary condition for a perfectly conducting inclusion or a sound-soft object in Omega can be used to find the location and shape of the inhomogeneity. The results show that we can detect perfectly conducting inclusions in impedance tomography from the voltages for one injected current. For acoustic scattering a sound-soft object is found from the knowledge of one (total) field and its normal derivative on partialOmega. The work redesigns the PSM, which was first proposed in the framework of inverse scattering, to solve inverse boundary value problems. Numerical examples are provided for impedance tomography and the sound-soft acoustic boundary value problem.

  3. Locating interfaces in vertically-layered materials and determining concentrations in mixed materials utilizing acoustic impedance measurements

    DOEpatents

    Langlois, G.N.

    1983-09-13

    Measurement of the relative and actual value of acoustic characteristic impedances of an unknown substance, location of the interfaces of vertically-layered materials, and the determination of the concentration of a first material mixed in a second material are disclosed. A highly damped ultrasonic pulse is transmitted into one side of a reference plate, such as a tank wall, where the other side of the reference plate is in physical contact with the medium to be measured. The amplitude of a return signal, which is the reflection of the transmitted pulse from the interface between the other side of the reference plate and the medium, is measured. The amplitude value indicates the acoustic characteristic impedance of the substance relative to that of the reference plate or relative to that of other tested materials. Discontinuities in amplitude with repeated measurements for various heights indicate the location of interfaces in vertically-layered materials. Standardization techniques permit the relative acoustic characteristic impedance of a substance to be converted to an actual value. Calibration techniques for mixtures permit the amplitude to be converted to the concentration of a first material mixed in a second material. 6 figs.

  4. Locating interfaces in vertically-layered materials and determining concentrations in mixed materials utilizing acoustic impedance measurements

    DOEpatents

    Langlois, Gary N.

    1983-09-13

    Measurement of the relative and actual value of acoustic characteristic impedances of an unknown substance, location of the interfaces of vertically-layered materials, and the determination of the concentration of a first material mixed in a second material. A highly damped ultrasonic pulse is transmitted into one side of a reference plate, such as a tank wall, where the other side of the reference plate is in physical contact with the medium to be measured. The amplitude of a return signal, which is the reflection of the transmitted pulse from the interface between the other side of the reference plate and the medium, is measured. The amplitude value indicates the acoustic characteristic impedance of the substance relative to that of the reference plate or relative to that of other tested materials. Discontinuities in amplitude with repeated measurements for various heights indicate the location of interfaces in vertically-layered materials. Standardization techniques permit the relative acoustic characteristic impedance of a substance to be converted to an actual value. Calibration techniques for mixtures permit the amplitude to be converted to the concentration of a first material mixed in a second material.

  5. Locating interfaces in vertically-layered materials and determining concentrations in mixed materials utilizing acoustic-impedance measurements. [Patent application

    DOEpatents

    Not Available

    1981-06-10

    Measurement of the relative and actual value of acoustic characteristic impedances of an unknown substance, location of the interfaces of vertically-layered materials, and the determination of the concentration of a first material mixed in a second material are presented. A highly damped ultrasonic pulse is transmitted into one side of a reference plate, such as a tank wall, where the other side of the reference plate is in physical contact with the medium to be measured. The amplitude of a return signal, which is the reflection of the transmitted pulse from the interface between the other side of the reference plate and the medium, is measured. The amplitude value indicates the acoustic characteristic impedance of the substance relative to that of the reference plate or relative to that of other tested materials. Discontinuities in amplitude with repeated measurements for various heights indicate the location of interfaces in vertically-layered materials. Standardization techniques permit the relative acoustic characteristic impedance of a substance to be converted to an actual value. Calibration techniques for mixtures permit the amplitude to be converted to the concentration of a first material mixed in a second material.

  6. Impedance analysis of nano thickness layered AlGaN acoustic sensor deposited by thermionic vacuum arc

    NASA Astrophysics Data System (ADS)

    Özen, Soner; Bilgiç, Eyüp; Gülmez, Gülay; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan; Mohammadigharehbagh, Reza

    2016-03-01

    In this study, AlGaN acoustic sensor was deposited on aluminum metal substrate by thermionic vacuum arc (TVA) method for the first time. Gallium materials are used in many applications for optoelectronic device and semiconductor technology. Thermionic vacuum arc is the deposition technology for the variously materials and applications field. The thickness of the acoustic sensor is in deposited as nano layer. Impedance analyses were realized. Also, TVA production parameters and some properties of the deposited layers were investigated. TVA is a fast deposition technology for the gallium compounds and doped gallium compounds. Obtained results show that AlGaN materials are very promising materials. Moreover, these acoustic sensors have been produced by TVA technology.

  7. Electroless deposition of metallic silver from a choline chloride-based ionic liquid: a study using acoustic impedance spectroscopy, SEM and atomic force microscopy.

    PubMed

    Abbott, Andrew P; Nandhra, Satvinder; Postlethwaite, Stella; Smith, Emma L; Ryder, Karl S

    2007-07-28

    In this paper, we describe the first example of a sustained galvanic coating deposited on a surface from a non-aqueous liquid. We present the surface characterization of electroless silver deposits on copper substrates from a solution of Ag(+) ions in an ionic liquid based on a choline chloride (ChCl) eutectic. Through a study of these deposits and the mechanism of formation using acoustic impedance spectroscopy (QCM), probe microscopy (AFM) and electron microscopy (SEM/EDX), we demonstrate that sustained growth of the silver deposit is facilitated by the porous nature of the silver. This is in contrast to the dip-coating reaction of silver ions in aqueous media, where the reaction stops when surface coverage is reached. Electroless silver deposits of up to several microns have been obtained by dip coating in ionic liquids without the use of catalysts of strong inorganic acids. PMID:17622408

  8. Simultaneous backward data transmission and power harvesting in an ultrasonic transcutaneous energy transfer link employing acoustically dependent electric impedance modulation.

    PubMed

    Ozeri, Shaul; Shmilovitz, Doron

    2014-09-01

    The advancement and miniaturization of body implanted medical devices pose several challenges to Ultrasonic Transcutaneous Energy Transfer (UTET), such as the need to reduce the size of the piezoelectric resonator, and the need to maximize the UTET link power-transfer efficiency. Accordingly, the same piezoelectric resonator that is used for energy harvesting at the body implant, may also be used for ultrasonic backward data transfer, for instance, through impedance modulation. This paper presents physical considerations and design guidelines of the body implanted transducer of a UTET link with impedance modulation for a backward data transfer. The acoustic matching design procedure was based on the 2×2 transfer matrix chain analysis, in addition to the Krimholtz Leedom and Matthaei KLM transmission line model. The UTET power transfer was carried out at a frequency of 765 kHz, continuous wave (CW) mode. The backward data transfer was attained by inserting a 9% load resistance variation around its matched value (550 Ohm), resulting in a 12% increase in the acoustic reflection coefficient. A backward data transmission rate of 1200 bits/s was experimentally demonstrated using amplitude shift keying, simultaneously with an acoustic power transfer of 20 mW to the implant. PMID:24861424

  9. Acoustic Characteristics of the Question-Statement Contrast in Severe Dysarthria Due to Cerebral Palsy

    ERIC Educational Resources Information Center

    Patel, Rupal

    2003-01-01

    Studies of prosodic control in severe dysarthria (DYS) have focused on differences between impaired and nonimpaired speech in terms of the range and variation of fundamental frequency (F0), intensity, and duration. Whether individuals with severe DYS can adequately signal prosodic contrasts and "which" acoustic cues they use to do so has received…

  10. Saturation diving with heliox to 350 meters. Observation on hearing threshold, brainstem evoked response and acoustic impedance.

    PubMed

    Wang, L; Jiang, W; Gong, J H; Zheng, X Y

    1994-12-01

    Four divers were compressed to 350 m to observe changes in hearing threshold, brainstem evoked response and acoustic impedance. The divers experienced no tinnitus, impairment of hearing, earache during compression. Examination showed that the threshold of lower frequency range of hearing was elevated because of the masking effect of the noise in the hyperbaric chamber. Changes in waveform and latency of brainstem evoked response were due to changes in sound wave transmission affected by the chamber pressure and a poor ratio of signal to noise in the hyperbaric environment with heliox. All these changes were transient. After leaving the chamber, the hearing threshold and brainstem evoked response returned to normal. Besides, there were no changes in tympanogram, acoustic compliance and stapedius reflex before and after diving. This indicated the designed speed of compression and decompression in the experiment caused no damage to the divers' acoustic system, and the functions of their Eustachain tubes, middle and inner ears were normal during the diving test. PMID:7882734

  11. Flow Duct Data for Validation of Acoustic Liner Codes for Impedance Eduction

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Munro, Scott; Gaeta, R. J., Jr.

    2000-01-01

    The objective of the study reported here was to acquire acoustic and flow data with hard and lined duct wall duct sections for validation of a liner prediction code being developed at NASA LaRC. Both the mean flowfield and acoustic flowfields were determined in a cross-plane of the rectangular duct. A flow duct facility with acoustic drivers connected to a rectangular (4.7 x 2.0 inch) source section and a linear acoustic liner mounted downstream of the source section was used in this study. The liner section was designed to allow liner materials to be placed on all 4 walls of the duct. The test liner was of the locally-reacting type and was made from a ceramic material. The material, consisting of a tubular structure, was provided by NASA LaRC. The liner was approximately 8.89 cm (3.5 inches) thick. For the current study, only the two "short" sides of the duct were lined with liner material. The other two sides were hard walls. Two especially built instrumentation sections were attached on either sides of the liner section to allow acoustic and flow measurements to be made upstream and downstream of the liner. The two instrumentation duct sections were built to allow measurement of acoustic and flow properties at planes perpendicular to flow upstream and downstream of the liner section. The instrumentation section was also designed to provide a streamwise gradient in acoustic (complex) pressure from which the acoustic particle velocity, needed for the model validation, can be computed. Flow measurements included pressure, temperature, and velocity profiles upstream of the liner section. The in-flow sound pressure levels and phases were obtained with a microphone probe equipped with a nose cone in two cross planes upstream of the liner and two cross plane downstream of the liner. In addition to the acoustic measurements at the cross planes. axial centerline acoustic data was acquired using an axially traversing microphone probe which was traversed from a location

  12. Acoustic contrast, planarity and robustness of sound zone methods using a circular loudspeaker array.

    PubMed

    Coleman, Philip; Jackson, Philip J B; Olik, Marek; Møller, Martin; Olsen, Martin; Abildgaard Pedersen, Jan

    2014-04-01

    Since the mid 1990s, acoustics research has been undertaken relating to the sound zone problem-using loudspeakers to deliver a region of high sound pressure while simultaneously creating an area where the sound is suppressed-in order to facilitate independent listening within the same acoustic enclosure. The published solutions to the sound zone problem are derived from areas such as wave field synthesis and beamforming. However, the properties of such methods differ and performance tends to be compared against similar approaches. In this study, the suitability of energy focusing, energy cancelation, and synthesis approaches for sound zone reproduction is investigated. Anechoic simulations based on two zones surrounded by a circular array show each of the methods to have a characteristic performance, quantified in terms of acoustic contrast, array control effort and target sound field planarity. Regularization is shown to have a significant effect on the array effort and achieved acoustic contrast, particularly when mismatched conditions are considered between calculation of the source weights and their application to the system. PMID:25234991

  13. The development of acoustic cues to coda contrasts in young children learning American Englisha

    PubMed Central

    Song, Jae Yung; Demuth, Katherine; Shattuck-Hufnagel, Stefanie

    2012-01-01

    Research on children’s speech perception and production suggests that consonant voicing and place contrasts may be acquired early in life, at least in word-onset position. However, little is known about the development of the acoustic correlates of later-acquired, word-final coda contrasts. This is of particular interest in languages like English where many grammatical morphemes are realized as codas. This study therefore examined how various non-spectral acoustic cues vary as a function of stop coda voicing (voiced vs. voiceless) and place (alveolar vs. velar) in the spontaneous speech of 6 American-English-speaking mother-child dyads. The results indicate that children as young as 1;6 exhibited many adult-like acoustic cues to voicing and place contrasts, including longer vowels and more frequent use of voice bar with voiced codas, and a greater number of bursts and longer post-release noise for velar codas. However, 1;6-year-olds overall exhibited longer durations and more frequent occurrence of these cues compared to mothers, with decreasing values by 2;6. Thus, English-speaking 1;6-year-olds already exhibit adult-like use of some of the cues to coda voicing and place, though implementation is not yet fully adult-like. Physiological and contextual correlates of these findings are discussed. PMID:22501078

  14. Investigation on the reproduction performance versus acoustic contrast control in sound field synthesis.

    PubMed

    Bai, Mingsian R; Wen, Jheng-Ciang; Hsu, Hoshen; Hua, Yi-Hsin; Hsieh, Yu-Hao

    2014-10-01

    A sound reconstruction system is proposed for audio reproduction with extended sweet spot and reduced reflections. An equivalent source method (ESM)-based sound field synthesis (SFS) approach, with the aid of dark zone minimization is adopted in the study. Conventional SFS that is based on the free-field assumption suffers from synthesis error due to boundary reflections. To tackle the problem, the proposed system utilizes convex optimization in designing array filters with both reproduction performance and acoustic contrast taken into consideration. Control points are deployed in the dark zone to minimize the reflections from the walls. Two approaches are employed to constrain the pressure and velocity in the dark zone. Pressure matching error (PME) and acoustic contrast (AC) are used as performance measures in simulations and experiments for a rectangular loudspeaker array. Perceptual Evaluation of Audio Quality (PEAQ) is also used to assess the audio reproduction quality. The results show that the pressure-constrained (PC) method yields better acoustic contrast, but poorer reproduction performance than the pressure-velocity constrained (PVC) method. A subjective listening test also indicates that the PVC method is the preferred method in a live room. PMID:25324063

  15. Acoustic responses of monodisperse lipid-encapsulated microbubble contrast agents produced by flow focusing

    PubMed Central

    Kaya, Mehmet; Feingold, Steven; Hettiarachchi, Kanaka; Lee, Abraham P; Dayton, Paul A

    2010-01-01

    Lipid-encapsulated microbubbles are used as contrast agents in ultrasound imaging. Currently available commercially made contrast agents have a polydisperse size distribution. It has been hypothesised that improved imaging sensitivity could be achieved with a uniform microbubble radius. We have recently developed microfluidics technology to produce contrast agents with a nearly monodisperse distribution. In this manuscript, we analyze echo responses from individual microbubbles from monodisperse populations in order to establish the relationship between scattered echo, microbubble radius, and excitation frequency. Simulations of bubble response from a modified Rayleigh-Plesset type model corroborate experimental data. Results indicate that microbubble echo response can be greatly increased by optimal combinations of microbubble radius and acoustic excitation frequency. These results may have a significant impact in the formulation of contrast agents to improve ultrasonic sensitivity. PMID:21475641

  16. Tuning and switching the hypersonic phononic properties of elastic impedance contrast nanocomposites.

    PubMed

    Sato, Akihiro; Pennec, Yan; Shingne, Nitin; Thurn-Albrecht, Thomas; Knoll, Wolfgang; Steinhart, Martin; Djafari-Rouhani, Bahram; Fytas, George

    2010-06-22

    Anodic aluminum oxide (AAO) containing arrays of aligned cylindrical nanopores infiltrated with polymers is a well-defined model system for the study of hypersound propagation in polymer nanocomposites. Hypersonic phononic properties of AAO/polymer nanocomposites such as phonon localization and anisotropic sound propagation can be tailored by adjusting elastic contrast and density contrast between the components. Changes in density and elastic properties of the component located in the nanopores induced by phase transitions allow reversible modification of the phononic band structure and mode switching. As example in case, the crystallization and melting of poly(vinylidene difluoride) inside AAO was investigated. PMID:20509665

  17. Scatterer size and concentration estimation technique based on a 3D acoustic impedance map from histologic sections

    NASA Astrophysics Data System (ADS)

    Mamou, Jonathan; Oelze, Michael L.; O'Brien, William D.; Zachary, James F.

    2001-05-01

    Accurate estimates of scatterer parameters (size and acoustic concentration) are beneficial adjuncts to characterize disease from ultrasonic backscatterer measurements. An estimation technique was developed to obtain parameter estimates from the Fourier transform of the spatial autocorrelation function (SAF). A 3D impedance map (3DZM) is used to obtain the SAF of tissue. 3DZMs are obtained by aligning digitized light microscope images from histologic preparations of tissue. Estimates were obtained for simulated 3DZMs containing spherical scatterers randomly located: relative errors were less than 3%. Estimates were also obtained from a rat fibroadenoma and a 4T1 mouse mammary tumor (MMT). Tissues were fixed (10% neutral-buffered formalin), embedded in paraffin, serially sectioned and stained with H&E. 3DZM results were compared to estimates obtained independently against ultrasonic backscatter measurements. For the fibroadenoma and MMT, average scatterer diameters were 91 and 31.5 μm, respectively. Ultrasonic measurements yielded average scatterer diameters of 105 and 30 μm, respectively. The 3DZM estimation scheme showed results similar to those obtained by the independent ultrasonic measurements. The 3D impedance maps show promise as a powerful tool to characterize ultrasonic scattering sites of tissue. [Work supported by the University of Illinois Research Board.

  18. Effect of grazing flow on the acoustic impedance of Helmholtz resonators consisting of single and clustered orifices

    NASA Technical Reports Server (NTRS)

    Hersch, A. S.; Walker, B.

    1979-01-01

    A semiempirical fluid mechanical model is derived for the acoustic behavior of thin-walled single orifice Helmholtz resonators in a grazing flow environment. The incident and cavity sound fields are connected in terms of an orifice discharge coefficient whose values are determined experimentally using the two-microphone method. Measurements show that at high grazing flow speeds, acoustical resistance is almost linearly proportional to the grazing flow speed and almost independent of incident sound pressure. The corresponding values of reactance are much smaller and tend towards zero. For thicker-walled orifice plates, resistance and reactance were observed to be less sensitive to grazing flow as the ratio of plate thickness to orifice diameter increased. Loud tones were observed to radiate from a single orifice Helmholtz resonator due to interaction between the grazing flow shear layer and the resonator cavity. Measurements showed that the tones radiated at a Strouhal number equal to 0.26. The effects of grazing flow on the impedance of Helmholtz resonators consisting of clusters of orifices was also studied. In general, both resistance and reaction were found to be virtually independent of orifice relative spacing and number. These findings are valid with and without grazing flow.

  19. Effect of grazing flow on the acoustic impedance of interacting cavity-backed orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.

    1977-01-01

    The two-microphone method was used to investigate the impedance of interacting cavity-backed orifices in the presence of a grazing flow; the investigation has relevance for the control of turbomachinery noise generated within jet engines. The number (varied from one to 16), the diameter, and the spacing of the orifices were the chief parameters studied in the experimental program. It was found that interactions between adjacent orifices, while increasing reactance, do not significantly alter resistance. In addition, the grazing flow appears to reduce the rate of increase of the reactance.

  20. Sound reproduction in personal audio systems using the least-squares approach with acoustic contrast control constraint.

    PubMed

    Cai, Yefeng; Wu, Ming; Yang, Jun

    2014-02-01

    This paper describes a method for focusing the reproduced sound in the bright zone without disturbing other people in the dark zone in personal audio systems. The proposed method combines the least-squares and acoustic contrast criteria. A constrained parameter is introduced to tune the balance between two performance indices, namely, the acoustic contrast and the spatial average error. An efficient implementation of this method using convex optimization is presented. Offline simulations and real-time experiments using a linear loudspeaker array are conducted to evaluate the performance of the presented method. Results show that compared with the traditional acoustic contrast control method, the proposed method can improve the flatness of response in the bright zone by sacrificing the level of acoustic contrast. PMID:25234882

  1. Permeability, electrical impedance, and acoustic velocities on reservoir rocks from the Geysers geothermal field

    SciTech Connect

    Boitnott, G.N.; Boyd, P.J.

    1996-01-24

    Previous measurements of acoustic velocities on NEGU- 17 cores indicate that saturation effects are significant enough to cause Vp/Vs anomalies observed in the field. In this study we report on the results of new measurements on core recently recovered from SB-15-D along with some additional measurements on the NEGU-17 cores. The measurements indicate correlations between mechanical, transport, and water storage properties of the matrix which may prove useful for reservoir assessment and management. The SB-15-D material is found to be similar to the NEGU-17 material in terms of acoustic velocities, being characterized by a notably weak pressure dependence on the velocities and a modest Vp/Vs signature of saturation. The effect of saturation on Vp/Vs appears to result in part from a chemo-mechanical weakening of the shear modulus due to the presence of water. Electrical properties of SB-15-D material are qualitatively similar to those of the NEGU-17 cores, although resistivities of SB-15-D cores are notably lower and dielectric permittivities higher than in their NEGU- 17 counterparts. While some limited correlations of measured properties with depth are noted, no clear change in character is observed within SB-15-D cores which can be associated with the proposed cap-rock/reservoir boundary.

  2. Site-targeted acoustic contrast agent detects molecular expression of tissue factor after balloon angioplasty

    NASA Astrophysics Data System (ADS)

    Hall, Christopher S.; Abendschein, Dana R.; Scherrer, David E.; Scott, Michael J.; Marsh, Jon N.; Wickline, Samuel A.; Lanza, Gregory M.

    2000-04-01

    Complex molecular signaling heralds the early stages of pathologies such as angiogenesis, inflammation, and cellular responses to mechanically damaged coronary arteries after balloon angioplasty. In previous studies, we have demonstrated acoustic enhancement of blood clot morphology with the use of a nongaseous, ligand-targeted acoustic nanoparticle emulsion delivered to areas of thrombosis both in vitro and in vivo. In this paper, we characterize the early expression of tissue factor which contributes to subsequent arterial restenosis. Tissue factor is a 42kd glycoprotein responsible for blood coagulation but also plays a well-described role in cancer metastasis, angiogenesis, and vascular restenosis. This study was designed to determine whether the targeted contrast agent could localize tissue factor expressed within the wall of balloon-injured arteries. Both carotid arteries of five pigs (20 kg) were injured using an 8 X 20 mm angioplasty balloon. The carotids were treated in situ with a perfluorocarbon nanoparticle emulsion covalently complexed to either specific anti-tissue factor polyclonal F(ab) fragments (treatment) or non-specific IgG F(ab) fragments (control). Intravascular ultrasound (30 MHz) images of the arteries were obtained before and after exposure to the emulsions. Tissue- factor targeted ultrasonic contrast agent acoustically enhanced the subintima and media at the site of balloon- induced injury compared with control contrast arteries (p less than 0.05). Immunohistochemical staining confirmed the presence of increased tissue factor at the sites of acoustic enhancement. Binding of the targeted agents was demonstrated in vitro by scanning electron microscope images of cultured smooth muscle cells that constitutively express tissue factor. This study demonstrates the concept of molecular imaging and localization of carotid arteries' tissue factor in vivo using a new, nanoparticulate emulsion. Enhancement of the visualization of the molecular

  3. The effects of acoustic radiation force on contrast agents: Experimental and theoretial analysis

    NASA Astrophysics Data System (ADS)

    Dayton, Paul Alexander

    The goal of this research is to understand the response of ultrasound contrast agents to acoustic radiation force. Ultrasound contrast agents are encapsulated microbubbles similar in size and rheologic behavior to human erythrocytes. A core of either air or a high- molecular weight gas makes these microbubbles extremely compressible and highly echogenic. Clinically, the detection of blood is difficult without contrast agents because the echoes from blood cells are typically 30-40 dB less than tissue echoes. Ultrasound contrast agents have been shown to be extremely useful in assisting delineation of perfused tissue in echocardiography, and are being increasingly used for tumor detection in radiology. The high compressibility of gas-filled contrast agents makes these microbubbles susceptible to translation due to radiation force. Thus, it is important to understand the effects of this force in order to avoid erroneous measurements based on the location and flow velocity of microbubbles. In addition, the ability to displace and concentrate microbubbles may be an advantage in targeted imaging, targeted therapy, or industrial applications where it is desired to localize microbubbles in a region. In this study, experimental and theoretical tools are combined to investigate the interaction between microbubbles and an acoustic pulse. Several unique experimental systems allow visualization and analysis of the radius-time curves of individual microbubbles, the displacement of individual microbubbles in-vitro, and the displacement of microbubbles in-vivo. Theoretical analysis illustrates that the effect of radiation force on microbubbles is directly proportional to the product of the bubble volume and the acoustic pressure gradient. A model designed to simulate the radius-time behavior of individual microbubbles is verified from experimental data, and used to estimate the magnitude of radiation force. The resulting bubble translation is determined using a second model

  4. Feature-space assessment of electrical impedance tomography coregistered with computed tomography in detecting multiple contrast targets

    SciTech Connect

    Krishnan, Kalpagam; Liu, Jeff; Kohli, Kirpal

    2014-06-15

    Purpose: Fusion of electrical impedance tomography (EIT) with computed tomography (CT) can be useful as a clinical tool for providing additional physiological information about tissues, but requires suitable fusion algorithms and validation procedures. This work explores the feasibility of fusing EIT and CT images using an algorithm for coregistration. The imaging performance is validated through feature space assessment on phantom contrast targets. Methods: EIT data were acquired by scanning a phantom using a circuit, configured for injecting current through 16 electrodes, placed around the phantom. A conductivity image of the phantom was obtained from the data using electrical impedance and diffuse optical tomography reconstruction software (EIDORS). A CT image of the phantom was also acquired. The EIT and CT images were fused using a region of interest (ROI) coregistration fusion algorithm. Phantom imaging experiments were carried out on objects of different contrasts, sizes, and positions. The conductive medium of the phantoms was made of a tissue-mimicking bolus material that is routinely used in clinical radiation therapy settings. To validate the imaging performance in detecting different contrasts, the ROI of the phantom was filled with distilled water and normal saline. Spatially separated cylindrical objects of different sizes were used for validating the imaging performance in multiple target detection. Analyses of the CT, EIT and the EIT/CT phantom images were carried out based on the variations of contrast, correlation, energy, and homogeneity, using a gray level co-occurrence matrix (GLCM). A reference image of the phantom was simulated using EIDORS, and the performances of the CT and EIT imaging systems were evaluated and compared against the performance of the EIT/CT system using various feature metrics, detectability, and structural similarity index measures. Results: In detecting distilled and normal saline water in bolus medium, EIT as a stand

  5. Alternating current impedance imaging of high-resistance membrane pores using a scanning electrochemical microscope. Application of membrane electrical shunts to increase measurement sensitivity and image contrast.

    PubMed

    Ervin, Eric Nathan; White, Henry S; Baker, Lane A; Martin, Charles R

    2006-09-15

    Whether an individual pore in a porous membrane can be imaged using scanning electrochemical microscopy (SECM), operated in ac impedance mode, is determined by the magnitude of the change in the total impedance of the imaging system as the SECM tip is scanned over the pore. In instances when the SECM tip resistance is small relative to the internal pore resistance, the total impedance changes by a negligible amount, rendering the pore invisible during impedance imaging. A simple solution to this problem is to introduce a low-impedance electrical shunt (i.e., a salt bridge) across the membrane. This principle is demonstrated by imaging polycarbonate membranes (6-12-microm thickness) containing between 1 and 2000 conical-shaped pores (60-nm- and 2.5-microm-diameter openings) using an approximately 1-microm-radius Pt tip. Theory and experiments show that image contrast (the change in ac current measured as the probe is scanned over the pore) is inversely proportional to the total resistance of the membrane and can be increased by a factor of approximately 50x by introducing a low-resistance electrical shunt across the membrane. Remarkably, SECM images of membranes containing a single high-resistance (approximately 1 G Omega) pore can only be imaged by short-circuiting the membrane. Image contrast also becomes independent of membrane resistance when an electrical shunt is used, allowing for more quantitative comparisons of the features in ac impedance images of different membranes. PMID:16970331

  6. Acoustic characterization of ultrasound contrast microbubbles and echogenic liposomes: Applications to imaging and drug-delivery

    NASA Astrophysics Data System (ADS)

    Paul, Shirshendu

    Micron- to nanometer - sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes (ELIPs), are being actively developed for possible clinical implementations in diagnostic imaging and ultrasound mediated drug/gene delivery. The primary objective of this thesis is to characterize the acoustic behavior of and the ultrasound-mediated contents release from these contrast agents for developing multi-functional ultrasound contrast agents. Subharmonic imaging using contrast microbubbles can improve image quality by providing a higher signal to noise ratio. However, the design and development of contrast microbubbles with favorable subharmonic behavior requires accurate mathematical models capable of predicting their nonlinear dynamics. To this goal, 'strain-softening' viscoelastic interfacial models of the encapsulation were developed and subsequently utilized to simulate the dynamics of encapsulated microbubbles. A hierarchical two-pronged approach of modeling --- a model is applied to one set of experimental data to obtain the model parameters (material characterization), and then the model is validated against a second independent experiment --- is demonstrated in this thesis for two lipid coated (SonazoidRTM and DefinityRTM) and a few polymer (polylactide) encapsulated microbubbles. The proposed models were successful in predicting several experimentally observed behaviors e.g., low subharmonic thresholds and "compression-only" radial oscillations. Results indicate that neglecting the polydisperse size distribution of contrast agent suspensions, a common practice in the literature, can lead to inaccurate results. In vitro experimental investigation of the dependence of subharmonic response from these microbubbles on the ambient pressure is also in conformity with the recent numerical investigations, showing both increase or decrease under appropriate excitation conditions. Experimental characterization of the ELIPs and polymersomes was performed

  7. Acoustic characterization and pharmacokinetic analyses of new nanobubble ultrasound contrast agents.

    PubMed

    Wu, Hanping; Rognin, Nicolas G; Krupka, Tianyi M; Solorio, Luis; Yoshiara, Hiroki; Guenette, Gilles; Sanders, Christopher; Kamiyama, Naohisa; Exner, Agata A

    2013-11-01

    In contrast to the clinically used microbubble ultrasound contrast agents, nanoscale bubbles (or nanobubbles) may potentially extravasate into tumors that exhibit more permeable vasculature, facilitating targeted molecular imaging and drug delivery. Our group recently presented a simple strategy using the non-ionic surfactant Pluronic as a size control excipient to produce nanobubbles with a mean diameter of 200 nm that exhibited stability and echogenicity on par with microbubbles. The objective of this study was to carry out an in-depth characterization of nanobubble properties as compared with Definity microbubbles, both in vitro and in vivo. Through use of a tissue-mimicking phantom, in vitro experiments measured the echogenicity of the contrast agent solutions and the contrast agent dissolution rate over time. Nanobubbles were found to be more echogenic than Definity microbubbles at three different harmonic frequencies (8, 6.2 and 3.5 MHz). Definity microbubbles also dissolved 1.67 times faster than nanobubbles. Pharmacokinetic studies were then performed in vivo in a subcutaneous human colorectal adenocarcinoma (LS174T) in mice. The peak enhancement and decay rates of contrast agents after bolus injection in the liver, kidney and tumor were analyzed. No significant differences were observed in peak enhancement between the nanobubble and Definity groups in the three tested regions (tumor, liver and kidney). However, the decay rates of nanobubbles in tumor and kidney were significantly slower than those of Definity in the first 200-s fast initial phase. There were no significant differences in the decay rates in the liver in the initial phase or in three regions of interest in the terminal phase. Our results suggest that the stability and acoustic properties of the new nanobubble contrast agents are superior to those of the clinically used Definity microbubbles. The slower washout of nanobubbles in tumors suggests potential entrapment of the bubbles within

  8. ACOUSTIC CHARACTERIZATION AND PHARAMACOKINETIC ANALYSES OF NEW NANOBUBBLE ULTRASOUND CONTRAST AGENTS

    PubMed Central

    Wu, Hanping; Rognin, Nicolas G.; Krupka, Tianyi M.; Solorio, Luis; Yoshiara, Hiroki; Guenette, Gilles; Sanders, Christoher; Kamiyama, Naohisa; Exner, Agata A.

    2013-01-01

    In contrast to the clinically used microbubble ultrasound contrast agents, nanoscale bubbles (or nanobubbles) may potentially extravasate into tumors that exhibit more permeable vasculature, facilitating targeted molecular imaging and drug delivery. Our group recently presented a simple strategy using the non-ionic surfactant Pluronic as a size control excipient to produce nanobubbles with a mean diameter of 200 nm that exhibited stability and echogenicity on par with microbubbles. The objective of this study was to carry out an in-depth characterization of nanobubble properties as compared with Definity microbubbles, both in vitro and in vivo. Through use of a tissue-mimicking phantom, in vitro experiments measured the echogenicity of the contrast agent solutions and the contrast agent dissolution rate over time. Nanobubbles were found to be more echogenic than Definity microbubbles at three different harmonic frequencies (8, 6.2 and 3.5 MHz). Definity microbubbles also dissolved 1.67 times faster than nanobubbles. Pharmacokinetic studies were then performed in vivo in a subcutaneous human colorectal adenocarcinoma (LS174T) in mice. The peak enhancement and decay rates of contrast agents after bolus injection in the liver, kidney and tumor were analyzed. No significant differences were observed in peak enhancement between the nanobubble and Definity groups in the three tested regions (tumor, liver and kidney). However, the decay rates of nanobubbles in tumor and kidney were significantly slower than those of Definity in the first 200-s fast initial phase. There were no significant differences in the decay rate in the liver in the initial phase or in three regions of interest in the terminal phase. Our results suggest that the stability and acoustic properties of the new nanobubble contrast agents are superior to those of the clinically used Definity microbubbles. The slower washout of nanobubbles in tumors suggests potential entrapment of the bubbles within the

  9. Coherent heat transport in 2D phononic crystals with acoustic impedance mismatch

    NASA Astrophysics Data System (ADS)

    Arantes, A.; Anjos, V.

    2016-03-01

    In this work we have calculated the cumulative thermal conductivities of micro-phononic crystals formed by different combinations of inclusions and matrices at a sub-Kelvin temperature regime. The low-frequency phonon spectra (up to tens of GHz) were obtained by solving the generalized wave equation for inhomogeneous media with the plane wave expansion method. The thermal conductivity was calculated from Boltzmann transport theory highlighting the role of the low-frequency thermal phonons and neglecting phonon-phonon scattering. A purely coherent thermal transport regime was assumed throughout the structures. Our findings show that the cumulative thermal conductivity drops dramatically when compared with their bulk counterpart. Depending on the structural composition this reduction may be attributed to the phonon group velocity due to a flattening of the phonon dispersion relation, the extinction of phonon modes in the density of states or due to the presence of complete band gaps. According to the contrast between the inclusions and the matrices, three types of two dimensional phononic crystals were considered: carbon/epoxy, carbon/polyethylene and tungsten/silicon, which correspond respectively to a moderate, strong and very strong mismatch in the mechanical properties of these materials.

  10. Streaming flow from ultrasound contrast agents by acoustic waves in a blood vessel model.

    PubMed

    Cho, Eunjin; Chung, Sang Kug; Rhee, Kyehan

    2015-09-01

    To elucidate the effects of streaming flow on ultrasound contrast agent (UCA)-assisted drug delivery, streaming velocity fields from sonicated UCA microbubbles were measured using particle image velocimetry (PIV) in a blood vessel model. At the beginning of ultrasound sonication, the UCA bubbles formed clusters and translated in the direction of the ultrasound field. Bubble cluster formation and translation were faster with 2.25MHz sonication, a frequency close to the resonance frequency of the UCA. Translation of bubble clusters induced streaming jet flow that impinged on the vessel wall, forming symmetric vortices. The maximum streaming velocity was about 60mm/s at 2.25MHz and decreased to 15mm/s at 1.0MHz for the same acoustic pressure amplitude. The effect of the ultrasound frequency on wall shear stress was more noticeable. Maximum wall shear stress decreased from 0.84 to 0.1Pa as the ultrasound frequency decreased from 2.25 to 1.0MHz. The maximum spatial gradient of the wall shear stress also decreased from 1.0 to 0.1Pa/mm. This study showed that streaming flow was induced by bubble cluster formation and translation and was stronger upon sonication by an acoustic wave with a frequency near the UCA resonance frequency. Therefore, the secondary radiant force, which is much stronger at the resonance frequency, should play an important role in UCA-assisted drug delivery. PMID:26025507

  11. Quantitative measurement of ultrasound pressure field by optical phase contrast method and acoustic holography

    NASA Astrophysics Data System (ADS)

    Oyama, Seiji; Yasuda, Jun; Hanayama, Hiroki; Yoshizawa, Shin; Umemura, Shin-ichiro

    2016-07-01

    A fast and accurate measurement of an ultrasound field with various exposure sequences is necessary to ensure the efficacy and safety of various ultrasound applications in medicine. The most common method used to measure an ultrasound pressure field, that is, hydrophone scanning, requires a long scanning time and potentially disturbs the field. This may limit the efficiency of developing applications of ultrasound. In this study, an optical phase contrast method enabling fast and noninterfering measurements is proposed. In this method, the modulated phase of light caused by the focused ultrasound pressure field is measured. Then, a computed tomography (CT) algorithm used to quantitatively reconstruct a three-dimensional (3D) pressure field is applied. For a high-intensity focused ultrasound field, a new approach that combines the optical phase contrast method and acoustic holography was attempted. First, the optical measurement of focused ultrasound was rapidly performed over the field near a transducer. Second, the nonlinear propagation of the measured ultrasound was simulated. The result of the new approach agreed well with that of the measurement using a hydrophone and was improved from that of the phase contrast method alone with phase unwrapping.

  12. Design factors of intravascular dual frequency transducers for super-harmonic contrast imaging and acoustic angiography

    NASA Astrophysics Data System (ADS)

    Ma, Jianguo; Martin, K. Heath; Li, Yang; Dayton, Paul A.; Shung, K. Kirk; Zhou, Qifa; Jiang, Xiaoning

    2015-05-01

    Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Dual frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced intravascular ultrasound (CE-IVUS) platform with the capability of vasa vasorum imaging. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with low frequency transmitter performance. In this paper, transducer designs encompassing different transducer layouts, transmitting frequencies, and transducer materials are compared for optimization of imaging performance. In the layout selection, the stacked configuration showed superior super-harmonic imaging compared with the interleaved configuration. In the transmitter frequency selection, a decrease in frequency from 6.5 MHz to 5 MHz resulted in an increase of CTR from 15 dB to 22 dB when receiving frequency was kept constant at 30 MHz. In the material selection, the dual frequency transducer with the lead magnesium niobate-lead titanate (PMN-PT) 1-3 composite transmitter yielded higher axial resolution compared to single crystal transmitters (70 μm compared to 150 μm pulse length). These comparisons provide guidelines for the design of intravascular acoustic angiography transducers.

  13. Design factors of intravascular dual frequency transducers for super-harmonic contrast imaging and acoustic angiography.

    PubMed

    Ma, Jianguo; Martin, K Heath; Li, Yang; Dayton, Paul A; Shung, K Kirk; Zhou, Qifa; Jiang, Xiaoning

    2015-05-01

    Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Dual frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced intravascular ultrasound (CE-IVUS) platform with the capability of vasa vasorum imaging. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with low frequency transmitter performance. In this paper, transducer designs encompassing different transducer layouts, transmitting frequencies, and transducer materials are compared for optimization of imaging performance. In the layout selection, the stacked configuration showed superior super-harmonic imaging compared with the interleaved configuration. In the transmitter frequency selection, a decrease in frequency from 6.5 MHz to 5 MHz resulted in an increase of CTR from 15 dB to 22 dB when receiving frequency was kept constant at 30 MHz. In the material selection, the dual frequency transducer with the lead magnesium niobate-lead titanate (PMN-PT) 1-3 composite transmitter yielded higher axial resolution compared to single crystal transmitters (70 μm compared to 150 μm pulse length). These comparisons provide guidelines for the design of intravascular acoustic angiography transducers. PMID:25856384

  14. Design factors of intravascular dual frequency transducers for super-harmonic contrast imaging and acoustic angiography

    PubMed Central

    Ma, Jianguo; Martin, K. Heath; Li, Yang; Dayton, Paul A.; Shung, K. Kirk; Zhou, Qifa; Jiang, Xiaoning

    2015-01-01

    Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Dual frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced intravascular ultrasound (CE-IVUS) platform with the capability of vasa vasorum imaging. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with the low frequency transmitter performance. In this paper, transducer designs encompassing different transducer layouts, transmitting frequencies, and transducer materials are compared for optimization of imaging performance. In the layout selection, the stacked configuration showed superior super-harmonic imaging compared with the interleaved configuration. In the transmitter frequency selection, a decrease in frequency from 6.5 MHz to 5 MHz resulted in an increase of CTR from 15 dB to 22 dB when receiving frequency was kept constant at 30 MHz. In the material selection, the dual frequency transducer with the lead magnesium niobate-lead titanate (PMN-PT) 1-3 composite transmitter yielded higher axial resolution compared to single crystal transmitters (70 μm compared to 150 μm pulse length). These comparisons provide guidelines for design of intravascular acoustic angiography transducers. PMID:25856384

  15. Iso-acoustic focusing of cells for size-insensitive acousto-mechanical phenotyping

    PubMed Central

    Augustsson, Per; Karlsen, Jonas T.; Su, Hao-Wei; Bruus, Henrik; Voldman, Joel

    2016-01-01

    Mechanical phenotyping of single cells is an emerging tool for cell classification, enabling assessment of effective parameters relating to cells' interior molecular content and structure. Here, we present iso-acoustic focusing, an equilibrium method to analyze the effective acoustic impedance of single cells in continuous flow. While flowing through a microchannel, cells migrate sideways, influenced by an acoustic field, into streams of increasing acoustic impedance, until reaching their cell-type specific point of zero acoustic contrast. We establish an experimental procedure and provide theoretical justifications and models for iso-acoustic focusing. We describe a method for providing a suitable acoustic contrast gradient in a cell-friendly medium, and use acoustic forces to maintain that gradient in the presence of destabilizing forces. Applying this method we demonstrate iso-acoustic focusing of cell lines and leukocytes, showing that acoustic properties provide phenotypic information independent of size. PMID:27180912

  16. Iso-acoustic focusing of cells for size-insensitive acousto-mechanical phenotyping.

    PubMed

    Augustsson, Per; Karlsen, Jonas T; Su, Hao-Wei; Bruus, Henrik; Voldman, Joel

    2016-01-01

    Mechanical phenotyping of single cells is an emerging tool for cell classification, enabling assessment of effective parameters relating to cells' interior molecular content and structure. Here, we present iso-acoustic focusing, an equilibrium method to analyze the effective acoustic impedance of single cells in continuous flow. While flowing through a microchannel, cells migrate sideways, influenced by an acoustic field, into streams of increasing acoustic impedance, until reaching their cell-type specific point of zero acoustic contrast. We establish an experimental procedure and provide theoretical justifications and models for iso-acoustic focusing. We describe a method for providing a suitable acoustic contrast gradient in a cell-friendly medium, and use acoustic forces to maintain that gradient in the presence of destabilizing forces. Applying this method we demonstrate iso-acoustic focusing of cell lines and leukocytes, showing that acoustic properties provide phenotypic information independent of size. PMID:27180912

  17. Iso-acoustic focusing of cells for size-insensitive acousto-mechanical phenotyping

    NASA Astrophysics Data System (ADS)

    Augustsson, Per; Karlsen, Jonas T.; Su, Hao-Wei; Bruus, Henrik; Voldman, Joel

    2016-05-01

    Mechanical phenotyping of single cells is an emerging tool for cell classification, enabling assessment of effective parameters relating to cells' interior molecular content and structure. Here, we present iso-acoustic focusing, an equilibrium method to analyze the effective acoustic impedance of single cells in continuous flow. While flowing through a microchannel, cells migrate sideways, influenced by an acoustic field, into streams of increasing acoustic impedance, until reaching their cell-type specific point of zero acoustic contrast. We establish an experimental procedure and provide theoretical justifications and models for iso-acoustic focusing. We describe a method for providing a suitable acoustic contrast gradient in a cell-friendly medium, and use acoustic forces to maintain that gradient in the presence of destabilizing forces. Applying this method we demonstrate iso-acoustic focusing of cell lines and leukocytes, showing that acoustic properties provide phenotypic information independent of size.

  18. Contrasting movements and connectivity of reef-associated sharks using acoustic telemetry: implications for management.

    PubMed

    Espinoza, Mario; Lédée, Elodie J I; Simpfendorfer, Colin A; Tobin, Andrew J; Heupel, Michelle R

    2015-12-01

    Understanding the efficacy of marine protected areas (MPAs) for wide-ranging predators is essential to designing effective management and conservation approaches. The use of acoustic monitoring and network analysis can improve our understanding of the spatial ecology and functional connectivity of reef-associated species, providing a useful approach for reef-based conservation planning. This study compared and contrasted the movement and connectivity of sharks with different degrees of reef association. We examined the residency, dispersal, degree of reef connectivity, and MPA use of grey reef (Carcharhinus amblyrhynchos), silvertip (C. albimarginatus), and bull (C. leucas) sharks monitored in the central Great Barrier Reef (GBR). An array of 56 acoustic receivers was used to monitor shark movements on 17 semi-isolated reefs. Carcharhinus amblyrhynchos and C. albimarginatus were detected most days at or near their tagging reef. However, while C. amblyrhynchos spent 80% of monitoring days in the array, C. albimarginatus was only detected 50% of the time. Despite both species moving similar distances (< 50 km), a large portion of the population of C. albimarginatus (71%) was detected on multiple reefs and moved more frequently between reefs and management zones than C. amblyrhynchos. Carcharhinus leucas was detected less than 20% of the time within the tagging array, and 42% of the population undertook long-range migrations to other arrays in the GBR. Networks derived for C. leucas were larger and more complex than those for C. amblyrhynchos and C. albimarginatus. Our findings suggest that protecting specific reefs based on prior knowledge (e.g., healthier reefs with high fish biomass) and increasing the level of protection to include nearby, closely spaced reef habitats (< 20 km) may perform better for species like C. albimarginatus than having either a single or a network of isolated MPAs. This design would also provide protection for larger male C. amblyrhynchos

  19. Acoustic cue weighting in the singleton vs geminate contrast in Lebanese Arabic: The case of fricative consonants.

    PubMed

    Al-Tamimi, Jalal; Khattab, Ghada

    2015-07-01

    This paper is the first reported investigation of the role of non-temporal acoustic cues in the singleton-geminate contrast in Lebanese Arabic, alongside the more frequently reported temporal cues. The aim is to explore the extent to which singleton and geminate consonants show qualitative differences in a language where phonological length is prominent and where moraic structure governs segment timing and syllable weight. Twenty speakers (ten male, ten female) were recorded producing trochaic disyllables with medial singleton and geminate fricatives preceded by phonologically short and long vowels. The following acoustic measures were applied on the medial fricative and surrounding vowels: absolute duration; intensity; fundamental frequency; spectral peak and shape, dynamic amplitude, and voicing patterns of medial fricatives; and vowel quality and voice quality correlates of surrounding vowels. Discriminant analysis and receiver operating characteristics (ROC) curves were used to assess each acoustic cue's contribution to the singleton-geminate contrast. Classification rates of 89% and ROC curves with an area under the curve rate of 96% confirmed the major role played by temporal cues, with non-temporal cues contributing to the contrast but to a much lesser extent. These results confirm that the underlying contrast for gemination in Arabic is temporal, but highlight [+tense] (fortis) as a secondary feature. PMID:26233034

  20. Acoustic Treatment Design Scaling Methods. Volume 4; Numerical Simulation of the Nonlinear Acoustic Impedance of a Perforated Plate Single-Degree-of-Freedom Resonator Using a Time-Domain Finite Difference Method

    NASA Technical Reports Server (NTRS)

    Kraft, R. E.

    1999-01-01

    Single-degree-of-freedom resonators consisting of honeycomb cells covered by perforated facesheets are widely used as acoustic noise suppression liners in aircraft engine ducts. The acoustic resistance and mass reactance of such liners are known to vary with the intensity of the sound incident upon the panel. Since the pressure drop across a perforated liner facesheet increases quadratically with the flow velocity through the facesheet, this is known as the nonlinear resistance effect. In the past, two different empirical frequency domain models have been used to predict the Sound Pressure Level effect of the incident wave on the perforated liner impedance, one that uses the incident particle velocity in isolated narrowbands, and one that models the particle velocity as the overall velocity. In the absence of grazing flow, neither frequency domain model is entirely accurate in predicting the nonlinear effect that is measured for typical perforated sheets. The time domain model is developed in an attempt to understand and improve the model for the effect of spectral shape and amplitude of multi-frequency incident sound pressure on the liner impedance. A computer code for the time-domain finite difference model is developed and predictions using the models are compared to current frequency-domain models.

  1. Characterization of mechanical properties of hybrid contrast agents by combining atomic force microscopy with acoustic/optic assessments.

    PubMed

    Guo, Gepu; Tu, Juan; Guo, Xiasheng; Huang, Pintong; Wu, Junru; Zhang, Dong

    2016-02-01

    Multi-parameter fitting algorithms, which are currently used for the characterization of coated-bubbles, inevitably introduce uncertainty into the results. Therefore, a better technique that can accurately determine the microbubbles׳ mechanical properties is urgently needed. A comprehensive technology combining atomic force microscopy, optical, and acoustic measurements with simulations of coated-bubble dynamics was developed. Using this technique, the mechanical parameters (size distribution, shell thickness, elasticity, and viscosity) of hybrid (ultrasound/magnetic-resonance-imaging) contrast microbubbles and their structure-property relationship were determined. The measurements indicate that when more superparamagnetic iron oxide nanoparticles are embedded in the microbubbles׳ shells, their mean diameter and effective viscosity increase, and their elastic modulus decreases. This reduces the microbubbles׳ resonance frequency and thus enhances acoustic scattering and attenuation effects. PMID:26726783

  2. Perceptual integration of acoustic cues to laryngeal contrasts in Korean fricatives.

    PubMed

    Lee, Sarah; Katz, Jonah

    2016-02-01

    This paper provides evidence that multiple acoustic cues involving the presence of low-frequency energy integrate in the perception of Korean coronal fricatives. This finding helps explain a surprising asymmetry between the production and perception of these fricatives found in previous studies: lower F0 onset in the following vowel leads to a response bias for plain [s] over fortis [s*], despite the fact that there is no evidence for a corresponding acoustic asymmetry in the production of [s] and [s*]. A fixed classification task using the Garner paradigm provides evidence that low F0 in a following vowel and the presence of voicing during frication perceptually integrate. This suggests that Korean listeners in previous experiments were responding to an "intermediate perceptual property" of stimuli, despite the fact that the individual acoustic components of that property are not all present in typical Korean fricative productions. The finding also broadens empirical support for the general idea of perceptual integration to a language, a different manner of consonant, and a situation where covariance of the acoustic cues under investigation is not generally present in a listener's linguistic input. PMID:26936544

  3. Acoustics

    NASA Astrophysics Data System (ADS)

    The acoustics research activities of the DLR fluid-mechanics department (Forschungsbereich Stroemungsmechanik) during 1988 are surveyed and illustrated with extensive diagrams, drawings, graphs, and photographs. Particular attention is given to studies of helicopter rotor noise (high-speed impulsive noise, blade/vortex interaction noise, and main/tail-rotor interaction noise), propeller noise (temperature, angle-of-attack, and nonuniform-flow effects), noise certification, and industrial acoustics (road-vehicle flow noise and airport noise-control installations).

  4. Effect of grazing flow on the acoustic impedance of Helmholtz resonators consisting of single and clustered orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.; Bucka, M.

    1978-01-01

    A semiempirical fluid mechanical model is presented which predicts impedance of a Helmholtz resonator consisting of a single cavity-backed orifice as a function of grazing flow speed, boundary-layer thickness, incident sound amplitude and frequency, and resonator geometry. The incident and cavity sound fields are connected in terms of an orifice discharge coefficient. The effect of multiple orifices was studied experimentally. Interaction between orifices is important only for orifices aligned parallel to the grazing flow. Resistance was virtually independent of both orifice relative spacing and number. Reactance was found to be quite dependent upon orifice spacing but insensitive to the number of orifices.

  5. Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment

    PubMed Central

    Nightingale, Kathryn R.; Church, Charles C.; Harris, Gerald; Wear, Keith A.; Bailey, Michael R.; Carson, Paul L.; Jiang, Hui; Sandstrom, Kurt L.; Szabo, Thomas L.; Ziskin, Marvin C.

    2016-01-01

    The mechanical index (MI) has been used by the US Food and Drug Administration (FDA) since 1992 for regulatory decisions regarding the acoustic output of diagnostic ultrasound equipment. Its formula is based on predictions of acoustic cavitation under specific conditions. Since its implementation over 2 decades ago, new imaging modes have been developed that employ unique beam sequences exploiting higher-order acoustic phenomena, and, concurrently, studies of the bioeffects of ultrasound under a range of imaging scenarios have been conducted. In 2012, the American Institute of Ultrasound in Medicine Technical Standards Committee convened a working group of its Output Standards Subcommittee to examine and report on the potential risks and benefits of the use of conditionally increased acoustic pressures (CIP) under specific diagnostic imaging scenarios. The term “conditionally” is included to indicate that CIP would be considered on a per-patient basis for the duration required to obtain the necessary diagnostic information. This document is a result of that effort. In summary, a fundamental assumption in the MI calculation is the presence of a preexisting gas body. For tissues not known to contain preexisting gas bodies, based on theoretical predications and experimentally reported cavitation thresholds, we find this assumption to be invalid. We thus conclude that exceeding the recommended maximum MI level given in the FDA guidance could be warranted without concern for increased risk of cavitation in these tissues. However, there is limited literature assessing the potential clinical benefit of exceeding the MI guidelines in these tissues. The report proposes a 3-tiered approach for CIP that follows the model for employing elevated output in magnetic resonance imaging and concludes with summary recommendations to facilitate Institutional Review Board (IRB)-monitored clinical studies investigating CIP in specific tissues. PMID:26112617

  6. Articulatory and Acoustic Correlates of Contrastive Focus in Congenitally Blind Adults and Sighted Adults

    ERIC Educational Resources Information Center

    Ménard, Lucie; Leclerc, Annie; Tiede, Mark

    2014-01-01

    Purpose: The role of vision in speech representation was investigated in congenitally blind speakers and sighted speakers by studying the correlates of contrastive focus, a prosodic condition in which phonemic contrasts are enhanced. It has been reported that the lips (visible articulators) are less involved in implementing the rounding feature…

  7. Acoustics

    NASA Technical Reports Server (NTRS)

    Goodman, Jerry R.; Grosveld, Ferdinand

    2007-01-01

    The acoustics environment in space operations is important to maintain at manageable levels so that the crewperson can remain safe, functional, effective, and reasonably comfortable. High acoustic levels can produce temporary or permanent hearing loss, or cause other physiological symptoms such as auditory pain, headaches, discomfort, strain in the vocal cords, or fatigue. Noise is defined as undesirable sound. Excessive noise may result in psychological effects such as irritability, inability to concentrate, decrease in productivity, annoyance, errors in judgment, and distraction. A noisy environment can also result in the inability to sleep, or sleep well. Elevated noise levels can affect the ability to communicate, understand what is being said, hear what is going on in the environment, degrade crew performance and operations, and create habitability concerns. Superfluous noise emissions can also create the inability to hear alarms or other important auditory cues such as an equipment malfunctioning. Recent space flight experience, evaluations of the requirements in crew habitable areas, and lessons learned (Goodman 2003; Allen and Goodman 2003; Pilkinton 2003; Grosveld et al. 2003) show the importance of maintaining an acceptable acoustics environment. This is best accomplished by having a high-quality set of limits/requirements early in the program, the "designing in" of acoustics in the development of hardware and systems, and by monitoring, testing and verifying the levels to ensure that they are acceptable.

  8. A theoretical study of the acoustic impedance of orifices in the presence of a steady grazing flow

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1976-01-01

    An analysis of the oscillatory fluid flow in the vicinity of a circular orifice with a steady grazing flow is presented. The study is similar to that of Hersh and Rogers but with the addition of the grazing flow. Starting from the momentum and continuity equations, a considerably simplified system of partial differential equations is developed with the assumption that the flow can be described by an oscillatory motion superimposed upon the known steady flow. The equations are seen to be linear in the region where the grazing flow effects are dominant, and a solution and the resulting orifice impedance are presented for this region. The nonlinearity appears to be unimportant for the usual conditions found in aircraft noise suppressors. Some preliminary conclusions of the study are that orifice resistance is directly proportional to grazing flow velocity (known previously from experimental data) and that the orifice inductive (mass reactance) end correction is not a function of grazing flow. This latter conclusion is contrary to the widely held notion that grazing flow removes the effect of the orifice inductive end correction. This conclusion also implies that the experimentally observed total inductance reduction with grazing flow might be in the flow within the orifice rather than in the end correction.

  9. Near-infrared absorbing polymer nano-particle as a sensitive contrast agent for photo-acoustic imaging.

    PubMed

    Aoki, Hiroyuki; Nojiri, Mayumi; Mukai, Rieko; Ito, Shinzaburo

    2015-01-01

    Polymer nano-particles (PNPs) with a near-infrared (NIR) light absorption were prepared by the nano-emulsion method to develop contrast agents for photo-acoustic (PA) imaging. The PNP containing silicon naphthalocyanine showed a high absorption coefficient up to 10(10) M(-1) cm(-1). This is comparable to plasmonic gold nano-particles, which have been studied as PA contrast agents. For the PNP larger than 100 nm, the enhancement of the PA signal was observed compared to the gold nano-particle with a similar absorption coefficient and size. In the case of the PNP, the heat by the light absorption is confined in the particle due to the low thermal diffusivity of polymer materials. We showed that the strong thermal confinement effect of PNP results in the enhancement of the efficiency of the PA signal generation and that the PA intensity can be enhanced by the increase of the Grüneisen parameter of the matrix polymer of PNP. The PA signal from the PNP of poly(methyl methacrylate) was 9-fold larger than that of gold nano-particles with the same absorption coefficient. We demonstrated that in the in vivo PA imaging the detection limit of PNP was of the order of 10(-13) M. The NIR absorbing PNP will be a promising candidate of a sensitive contrast agent for PA imaging. PMID:25407911

  10. Single- and Multiple- Track Location Shear Wave and Acoustic Radiation Force Impulse Imaging: Matched Comparison of Contrast, CNR, and Resolution

    PubMed Central

    Hollender, Peter J.; Rosenzweig, Stephen J.; Nightingale, Kathryn R.; Trahey, Gregg E.

    2014-01-01

    Acoustic radiation force impulse (ARFI) imaging and shear wave elasticity imaging (SWEI) use the dynamic response of tissue to impulsive mechanical stimulus to characterize local elasticity. A variant of conventional, multiple track location SWEI (MTL-SWEI), denoted single track location SWEI (STL-SWEI) offers the promise of creating speckle-free shear wave images. This work compares the three imaging modalities using a high push and track beam density combined acquisition sequence to image inclusions of different sizes and contrasts. STL-SWEI is shown to have significantly higher CNR than MTL-SWEI, allowing for operation at higher resolution. ARFI and STL-SWEI perform similarly in the larger inclusions, with STL-SWEI providing better visualization of small targets ≤2.5 mm in diameter. The processing of each modality introduces different trade-offs between smoothness and resolution of edges and structures; these are discussed in detail. PMID:25701531

  11. An assessment of acoustic contrast between long and short vowels using convex hulls.

    PubMed

    Haynes, Erin F; Taylor, Michael

    2014-08-01

    An alternative to the spectral overlap assessment metric (SOAM), first introduced by Wassink [(2006). J. Acoust. Soc. Am. 119(4), 2334-2350], is introduced. The SOAM quantifies the intra- and inter-language differences between long-short vowel pairs through a comparison of spectral (F1, F2) and temporal properties modeled with best fit ellipses (F1 × F2 space) and ellipsoids (F1 × F2 × duration). However, the SOAM ellipses and ellipsoids rely on a Gaussian distribution of vowel data and a dense dataset, neither of which can be assumed in endangered languages or languages with limited available data. The method presented in this paper, called the Vowel Overlap Assessment with Convex Hulls (VOACH) method, improves upon the earlier metric through the use of best-fit convex shapes. The VOACH method reduces the incorporation of "empty" data into calculations of vowel space. Both methods are applied to Numu (Oregon Northern Paiute), an endangered language of the western United States. Calculations from the VOACH method suggest that Numu is a primary quantity language, a result that is well aligned with impressionistic analyses of spectral and durational data from the language and with observations by field researchers. PMID:25096122

  12. Light comfort zones of mesopelagic acoustic scattering layers in two contrasting optical environments

    NASA Astrophysics Data System (ADS)

    Røstad, Anders; Kaartvedt, Stein; Aksnes, Dag L.

    2016-07-01

    We make a comparison of the mesopelagic sound scattering layers (SLs) in two contrasting optical environments; the clear Red Sea and in murkier coastal waters of Norway (Masfjorden). The depth distributions of the SL in Masfjorden are shallower and narrower than those of the Red Sea. This difference in depth distribution is consistent with the hypothesis that the organisms of the SL distribute according to similar light comfort zones (LCZ) in the two environments. Our study suggest that surface and underwater light measurements ranging more than 10 orders of magnitude is required to assess the controlling effects of light on SL structure and dynamics.

  13. An In Vitro Study of the Correlation Between Bubble Distribution, Acoustic Emission, and Cell Damage by Contrast Ultrasound

    PubMed Central

    Fowlkes, J. Brian; Miller, Douglas L.

    2009-01-01

    The objective of this study was to investigate the influences of total exposure duration and pulse-to-pulse bubble distribution on contrast-mediated cell damage. Murine macrophage cells were grown as monolayers on thin polyester sheets. Contrast agent microbubbles were attached to these cells by incubation. Focused ultrasound exposures (Pr = 2 MPa) were implemented at a frequency of 2.25 MHz with 46 cycle pulses and pulse repetition frequencies (PRF) of 1 kHz, 500 Hz, 100 Hz, and 10 Hz in a degassed water bath at 10 or 100 pulses. A 1 MHz receive transducer measured the scattered signal. The frequency spectrum was normalized to a control spectrum from linear scatterers. Photomicrographs were captured before, during, and after exposure at a frame rate of 2000 fps and a pixel resolution of 960 × 720. Results clearly show that cell death is increased, up to 60%, by increasing total exposure duration from 0 ms to 100 ms. There was an increasing difference in cell damage between a 10-pulse exposure and a 100-pulse exposure with increasing PRF. The greatest change in damage occurred at 1000 Hz PRF with a 53% increase between 10-pulse and 100-pulse exposures. For each pulse from 0 to 10, an overlay of the 2 μm bubble count with corresponding emission shows consistent behavior in its pulse-to-pulse changes, indicating a correlation between acoustic emission, bubble distribution, and cell damage. PMID:19411217

  14. Aerogel as a Soft Acoustic Metamaterial for Airborne Sound

    NASA Astrophysics Data System (ADS)

    Guild, Matthew D.; García-Chocano, Victor M.; Sánchez-Dehesa, José; Martin, Theodore P.; Calvo, David C.; Orris, Gregory J.

    2016-03-01

    Soft acoustic metamaterials utilizing mesoporous structures have been proposed recently as a means for tuning the overall effective properties of the metamaterial and providing better coupling to the surrounding air. In this paper, the use of silica aerogel is examined theoretically and experimentally as part of a compact soft acoustic metamaterial structure, which enables a wide range of exotic effective macroscopic properties to be demonstrated, including negative density, density near zero, and nonresonant broadband slow-sound propagation. Experimental data are obtained on the effective density and sound speed using an air-filled acoustic impedance tube for flexural metamaterial elements, which have been investigated previously only indirectly due to the large contrast in acoustic impedance compared to that of air. Experimental results are presented for silica aerogel arranged in parallel with either one or two acoustic ports and are in very good agreement with the theoretical model.

  15. Intense acoustic burst ultrasound modulated optical tomography for elasticity mapping of soft biological tissue mimicking phantom: a laser speckle contrast analysis study

    NASA Astrophysics Data System (ADS)

    Singh, M. Suheshkumar; Rajan, K.; Vasu, R. M.

    2014-03-01

    This report addresses the assessment of variation in elastic property of soft biological tissues non-invasively using laser speckle contrast measurement. The experimental as well as the numerical (Monte-Carlo simulation) studies are carried out. In this an intense acoustic burst of ultrasound (an acoustic pulse with high power within standard safety limits), instead of continuous wave, is employed to induce large modulation of the tissue materials in the ultrasound insonified region of interest (ROI) and it results to enhance the strength of the ultrasound modulated optical signal in ultrasound modulated optical tomography (UMOT) system. The intensity fluctuation of speckle patterns formed by interference of light scattered (while traversing through tissue medium) is characterized by the motion of scattering sites. The displacement of scattering particles is inversely related to the elastic property of the tissue. We study the feasibility of laser speckle contrast analysis (LSCA) technique to reconstruct a map of the elastic property of a soft tissue-mimicking phantom. We employ source synchronized parallel speckle detection scheme to (experimentally) measure the speckle contrast from the light traversing through ultrasound (US) insonified tissue-mimicking phantom. The measured relative image contrast (the ratio of the difference of the maximum and the minimum values to the maximum value) for intense acoustic burst is 86.44 % in comparison to 67.28 % for continuous wave excitation of ultrasound. We also present 1-D and 2-D image of speckle contrast which is the representative of elastic property distribution.

  16. Impedance analysis of acupuncture points and pathways

    NASA Astrophysics Data System (ADS)

    Teplan, Michal; Kukučka, Marek; Ondrejkovičová, Alena

    2011-12-01

    Investigation of impedance characteristics of acupuncture points from acoustic to radio frequency range is addressed. Discernment and localization of acupuncture points in initial single subject study was unsuccessfully attempted by impedance map technique. Vector impedance analyses determined possible resonant zones in MHz region.

  17. Micro-Horn Arrays for Ultrasonic Impedance Matching

    NASA Technical Reports Server (NTRS)

    Rao, Shanti; Palmer, Dean

    2009-01-01

    Thin-layered structures containing arrays of micromachined horns, denoted solid micro-horn arrays (SMIHAs), have been conceived as improved means of matching acoustic impedances between ultrasonic transducers and the media with which the transducers are required to exchange acoustic energy. Typically, ultrasonic transducers (e.g., those used in medical imaging) are piezoelectric or similar devices, which produce small displacements at large stresses. However, larger displacements at smaller stresses are required in the target media (e.g., human tissues) with which acoustic energy is to be exchanged. Heretofore, efficiencies in transmission of acoustic energy between ultrasonic transducers and target media have been severely limited because substantial mismatches of acoustic impedances have remained, even when coupling material layers have been interposed between the transducers and the target media. In contrast, SMIHAs can, in principle, be designed to effect more nearly complete acoustic impedance matching, leading to power transmission efficiencies of 90 percent or even greater. The SMIHA concept is based on extension, into the higher-frequency/ lower-wavelength ultrasonic range, of the use of horns to match acoustic impedances in the audible and lower-frequency ultrasonic ranges. In matching acoustic impedance in transmission from a higher-impedance acoustic source (e.g., a piezoelectric transducer) and a lowerimpedance target medium (e.g., air or human tissue), a horn acts as a mechanical amplifier. The shape and size of the horn can be optimized for matching acoustic impedance in a specified frequency range. A typical SMIHA would consist of a base plate, a face plate, and an array of horns that would constitute pillars that connect the two plates (see figure). In use, the base plate would be connected to an ultrasonic transducer and the face plate would be placed in contact with the target medium. As at lower frequencies, the sizes and shapes of the pillars

  18. Influence of temperature, needle gauge and injection rate on the size distribution, concentration and acoustic responses of ultrasound contrast agents at high frequency.

    PubMed

    Sun, Chao; Panagakou, Ioanna; Sboros, Vassilis; Butler, Mairead B; Kenwright, David; Thomson, Adrian J W; Moran, Carmel M

    2016-08-01

    This paper investigated the influence of needle gauge (19G and 27G), injection rate (0.85ml·min(-1), 3ml·min(-1)) and temperature (room temperature (RT) and body temperature (BT)) on the mean diameter, concentration, acoustic attenuation, contrast to tissue ratio (CTR) and normalised subharmonic intensity (NSI) of three ultrasound contrast agents (UCAs): Definity, SonoVue and MicroMarker (untargeted). A broadband substitution technique was used to acquire the acoustic properties over the frequency range 17-31MHz with a preclinical ultrasound scanner Vevo770 (Visualsonics, Canada). Significant differences (P<0.001-P<0.05) between typical in vitro setting (19G needle, 3ml·min(-1) at RT) and typical in vivo setting (27G needle, 0.85ml·min(-1) at BT) were found for SonoVue and MicroMarker. Moreover we found that the mean volume-based diameter and concentration of both SonoVue and Definity reduced significantly when changing from typical in vitro to in vivo experimental set-ups, while those for MicroMarker did not significantly change. From our limited measurements of Definity, we found no significant change in attenuation, CTR and NSI with needle gauge. For SonoVue, all the measured acoustic properties (attenuation, CTR and NSI) reduced significantly when changing from typical in vitro to in vivo experimental conditions, while for MicroMarker, only the NSI reduced, with attenuation and CTR increasing significantly. These differences suggest that changes in physical compression and temperature are likely to alter the shell structure of the UCAs resulting in measureable and significant changes in the physical and high frequency acoustical properties of the contrast agents under typical in vitro and preclinical in vivo experimental conditions. PMID:27140502

  19. Electron Impedances

    SciTech Connect

    P Cameron

    2011-12-31

    It is only recently, and particularly with the quantum Hall effect and the development of nanoelectronics, that impedances on the scale of molecules, atoms and single electrons have gained attention. In what follows the possibility that characteristic impedances might be defined for the photon and the single free electron is explored is some detail, the premise being that the concepts of electrical and mechanical impedances are relevant to the elementary particle. The scale invariant quantum Hall impedance is pivotal in this exploration, as is the two body problem and Mach's principle.

  20. Acoustic calibration apparatus for calibrating plethysmographic acoustic pressure sensors

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J. (Inventor); Davis, David C. (Inventor)

    1995-01-01

    An apparatus for calibrating an acoustic sensor is described. The apparatus includes a transmission material having an acoustic impedance approximately matching the acoustic impedance of the actual acoustic medium existing when the acoustic sensor is applied in actual in-service conditions. An elastic container holds the transmission material. A first sensor is coupled to the container at a first location on the container and a second sensor coupled to the container at a second location on the container, the second location being different from the first location. A sound producing device is coupled to the container and transmits acoustic signals inside the container.

  1. Unique pumping-out fracturing mechanism of a polymer-shelled contrast agent: an acoustic characterization and optical visualization.

    PubMed

    Kothapalli, Satya V V N; Daeichin, Verya; Mastik, Frits; Brodin, Lars Åke; Janerot-Sjoberg, Birgitta; Paradossi, Gaio; de Jong, Nico; Grishenkov, Dmitry

    2015-03-01

    This work describes the fracturing mechanism of air-filled microbubbles (MBs) encapsulated by a cross-linked poly(vinyl alcohol) (PVA) shell. The radial oscillation and fracturing events following the ultrasound exposure were visualized with an ultrahigh-speed camera, and backscattered timedomain signals were acquired with the acoustic setup specific for harmonic detection. No evidence of gas emerging from defects in the shell with the arrival of the first insonation burst was found. In optical recordings, more than one shell defect was noted, and the gas core was drained without any sign of air extrusion when several consecutive bursts of 1 MPa amplitude were applied. In acoustic tests, the backscattered peak-to-peak voltage gradually reached its maximum and exponentially decreased when the PVA-based MB suspension was exposed to approximately 20 consecutive bursts arriving at pulse repetition frequencies of 100 and 500 Hz. Taking into account that the PVA shell is porous and possibly contains large air pockets between the cross-linked PVA chains, the aforementioned acoustic behavior might be attributed to pumping gas from these pockets in combination with gas release from the core through shell defects. We refer to this fracturing mechanism as pumping-out behavior, and this behavior could have potential use for the local delivery of therapeutic gases, such as nitric oxide. PMID:25768814

  2. Measurement of pulmonary arterial impedance and reflection from single-slice phase-contrast and steady-state free precession MRI

    NASA Astrophysics Data System (ADS)

    Leimbigler, Peter John

    Pulmonary arterial hypertension (PAH) alters vessel wall mechanics and vasomotor tone, driving up pulmonary hemodynamic variables such as pulse wave velocity, input and characteristic impedance, and pulse wave reflection magnitude. Heterogeneous treatment response necessitates frequent hemodynamic evaluation, for which right-heart catheterization (RHC) remains the gold standard; however, several disadvantages limit its frequency of use. In this work, a non-invasive magnetic resonance (MR) imaging protocol is developed to address the shortcomings of invasive hemodynamic monitoring and may support existing diagnostic procedures. First, accuracy and precision of the proposed method is characterized through linear uncertainty propagation and numerical simulation of the data-processing pipeline. Second, the MR protocol is tested in seven healthy adult volunteers. Third, a rapid version of the MR protocol is tested in a healthy volunteer, yielding good agreement with mean values obtained in the seven-volunteer study.

  3. The 2.5D MST for sound propagation through an array of acoustically rigid cylinders perpendicular to an impedance surface

    NASA Astrophysics Data System (ADS)

    van der Aa, Bart; Forssén, Jens

    2015-07-01

    In this work a study of sound propagation through arrays of semi-infinitely long cylinders placed perpendicular to an impedance surface has been carried out. The cross sections of the structures are assumed to be invariant along the main axis of the cylinders, and the cylinders are considered rigid. It is further assumed that the structures are insonified by a monopole source placed above the impedance surface. To study such configurations, we introduce the two-and-a-half-dimensional multiple scattering theory (2.5D MST), which essentially solves the pressure in a three-dimensional domain by post-processing a set of precomputed solutions obtained in a two-dimensional domain. The total pressure can then be obtained by complex addition of four contributions: source-to-receiver, source-to-array-to-receiver, image source-to-receiver, and image source-to-array-to-receiver. The proposed method is validated using both analytical and numerical tools, showing very good agreement for all studied cases. Among other things, we show that a cylinder array placed on top of flat rigid ground can deteriorate the ground interference dips that exist without the array. In addition, we show that the characteristic response of the cylinder array, i.e. in terms of pass and stop bands, may be shifted up in frequency due to a projection phenomenon, which happens when the source or receiver is elevated along the main axis of the cylinders.

  4. Optimization of contrast-to-tissue ratio through pulse windowing in dual-frequency “acoustic angiography” imaging

    PubMed Central

    Lindsey, Brooks D.; Shelton, Sarah E.; Dayton, Paul A.

    2016-01-01

    Early-stage tumors in many cancers are characterized by vascular remodeling, indicative of transformations in cell function. We have previously presented a high-resolution ultrasound imaging approach for detecting these changes which is based on microbubble contrast agents. In this technique, images are formed from only the higher harmonics of microbubble contrast agents, producing images of vasculature alone with 100–200 μm resolution. In this article, shaped transmit pulses are applied to imaging the higher broadband harmonic echoes of microbubble contrast agents, and the effects of varying pulse window and phasing on microbubble and tissue harmonic echoes are evaluated using a dual-frequency transducer in vitro and in vivo. An increase in contrast-to-tissue ratio of 6.8 ± 2.3 dB was observed in vitro by using an inverted pulse with a cosine window relative to a non-inverted pulse with a rectangular window. The increase in mean image intensity due to contrast enhancement in vivo in five rodents was 13.9 ± 3.0 dB greater for an inverted cosine-windowed pulse and 17.8 ± 3.6 dB greater for a non-inverted Gaussian-windowed relative to a non-inverted pulse with a rectangular window. Implications for pre-clinical and diagnostic imaging are also discussed. PMID:25819467

  5. A Preliminary Engineering Design of Intravascular Dual-Frequency Transducers for Contrast-Enhanced Acoustic Angiography and Molecular Imaging

    PubMed Central

    Ma, Jianguo; Martin, K. Heath; Dayton, Paul A.; Jiang, Xiaoning

    2014-01-01

    Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, −6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-μm-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging. PMID:24801226

  6. Acoustic source for generating an acoustic beam

    DOEpatents

    Vu, Cung Khac; Sinha, Dipen N.; Pantea, Cristian

    2016-05-31

    An acoustic source for generating an acoustic beam includes a housing; a plurality of spaced apart piezo-electric layers disposed within the housing; and a non-linear medium filling between the plurality of layers. Each of the plurality of piezoelectric layers is configured to generate an acoustic wave. The non-linear medium and the plurality of piezo-electric material layers have a matching impedance so as to enhance a transmission of the acoustic wave generated by each of plurality of layers through the remaining plurality of layers.

  7. Petrologic composition model of the upper crust in Bohai Bay basin, China, based on Lamé impedances

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Tsang, Louisa L. H.; Wang, Yanghua; Zhao, Bing

    2009-12-01

    Seismic attributes, such as P- and S-wave velocity, Poisson’s ratio, and acoustic impedances, all generally can be used for distinguishing different rock types. The non-uniqueness can be largely reduced using Lamé impedances instead of acoustic impedances as additional constraints. We have followed this method to constitute a petrologic composition model of the upper crust in the Bohai Bay basin, China. We briefly review the seismic parameters used for discrimination of rock types and focus our attention on the sensitivity of different combinations of parameters to determine the composition of materials. Corrections for pressure and temperature are performed in order to compare elastic wave velocities and densities measured at room temperature and surface pressure in laboratory with those for representative rock parameters. In a second step, we find the rock classes in the tested area by contrasting known data to laboratory measurements on a variety of rock samples extracted in the area. The basic field data are P-wave velocity values collected along a seismic profile conducted in the Bozhong Depression. The different rock types belonging to a particular rock class are finally constrained by the seismic velocities, Poisson’s ratio, density, acoustic impedance, and Lamé impedance related to the topmost 10 km of the Bohai Bay crust.

  8. Acoustic data transmission through a drill string

    DOEpatents

    Drumheller, D.S.

    1988-04-21

    Acoustical signals are transmitted through a drill string by canceling upward moving acoustical noise and by preconditioning the data in recognition of the comb filter impedance characteristics of the drill string. 5 figs.

  9. Perception of acoustic cues to Tokyo Japanese pitch-accent contrasts in native Japanese and naive English listeners.

    PubMed

    Shport, Irina A

    2015-07-01

    This study examines how native language shapes the perception of a prosodic contrast. In Tokyo Japanese, a high-low pitch accent is a lexical property of a word, and the F0 fall after the peak associated with the accented syllable is the fundamental cue to accent perception. In English, pitch accents do not create lexically contrastive F0 patterns. A hypothesis that English listeners naive to Japanese use the F0 fall cue less than Japanese listeners was tested in two experiments. The alignment of F0 peak, the presence and magnitude of F0 fall were manipulated in a trisyllabic nonword to resynthesize Japanese 1st-syllable accented, 2nd-syllable accented, and unaccented patterns. In an AX-discrimination experiment, both listener groups showed sensitivity to the presence of F0 fall at every peak location. In a categorization experiment, the English group did not use the F0 fall cue in decisions about whether the 1st or the 2nd syllable sounded more prominent. The Japanese group relied on the F0 fall information, some listeners much heavily than others. These findings suggest that one's native language constrains how much attention the prosodic dimension of F0 change receives and that individual listeners may have qualitatively different perceptual strategies. PMID:26233031

  10. Validation of a Numerical Method for Determining Liner Impedance

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.; Tanner, Sharon E.; Parrott, Tony L.

    1996-01-01

    This paper reports the initial results of a test series to evaluate a method for determining the normal incidence impedance of a locally reacting acoustically absorbing liner, located on the lower wall of a duct in a grazing incidence, multi-modal, non-progressive acoustic wave environment without flow. This initial evaluation is accomplished by testing the methods' ability to converge to the known normal incidence impedance of a solid steel plate, and to the normal incidence impedance of an absorbing test specimen whose impedance was measured in a conventional normal incidence tube. The method is shown to converge to the normal incident impedance values and thus to be an adequate tool for determining the impedance of specimens in a grazing incidence, multi-modal, nonprogressive acoustic wave environment for a broad range of source frequencies.

  11. Transition section for acoustic waveguides

    DOEpatents

    Karplus, H.H.B.

    1975-10-28

    A means of facilitating the transmission of acoustic waves with minimal reflection between two regions having different specific acoustic impedances is described comprising a region exhibiting a constant product of cross-sectional area and specific acoustic impedance at each cross-sectional plane along the axis of the transition region. A variety of structures that exhibit this feature is disclosed, the preferred embodiment comprising a nested structure of doubly reentrant cones. This structure is useful for monitoring the operation of nuclear reactors in which random acoustic signals are generated in the course of operation.

  12. Impedance magnetocardiogram.

    PubMed

    Kandori, A; Miyashita, T; Suzuki, D; Yokosawa, K; Tsukada, K

    2001-02-01

    We have developed an impedance magnetocardiogram (IMCG) system to detect the change of magnetic field corresponding to changes in blood volume in the heart. A low magnetic field from the electrical activity of the human heart--the so-called magnetocardiogram (MCG)--can be simultaneously detected by using this system. Because the mechanical and electrical functions in the heart can be monitored by non-invasive and non-contact measurements, it is easy to observe the cardiovascular functions from an accurate sensor position. This system uses a technique to demodulate induced current in a subject. A flux-locked circuit of a superconducting quantum interference device has a wide frequency range (above 1 MHz) because a constant current (40 kHz) is fed through the subject. It is shown for the first time that the system could measure IMCG signals at the same time as MCG signals. PMID:11229740

  13. Nonlinear acoustic detection of weathered, low compliance landmines

    NASA Astrophysics Data System (ADS)

    Sabatier, James M.; Alberts, W. C. Kirkpatrick; Korman, Murray S.

    2005-09-01

    Two potential impediments to acoustic landmine detection are soil weathering processes and low compliance landmines. To bury landmines, the soil within a mine diameter is removed and replaced such that bulk density, compression, and shear strength all decrease, leaving an acoustic scar detectable with the linear acoustic measurement technique. After a few soil wetting and drying cycles, this contrast is reduced. Linear acoustic mine detection measurements were made on a low impedance contrast landmine before the first rainfall on several occasions over the subsequent 5 years. During this period of time, both the spatial and frequency resolution had to be increased to maintain an on/off target velocity ratio that allowed detection. In some cases, the landmine remains undetectable. To address this, two-tone nonlinear acoustic measurements have been made on these landmines. When the landmine is detectable with linear acoustics, two tones are broadcast at the frequency where the on/off target velocity ratio is the largest. For the cases when the landmine is undetectable, a two-tone sweep is performed and the operator observes the real-time velocity FFT, noting nonlinear sidebands. Next, two-tone tests are conducted at these sidebands to determine nonlinear velocity profiles. [Work supported by U.S. Army RDECOM, NVESD.

  14. Graphical Acoustic Liner Design and Analysis Tool

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M. (Inventor); Jones, Michael G. (Inventor)

    2016-01-01

    An interactive liner design and impedance modeling tool comprises software utilized to design acoustic liners for use in constrained spaces, both regularly and irregularly shaped. A graphical user interface allows the acoustic channel geometry to be drawn in a liner volume while the surface impedance calculations are updated and displayed in real-time. A one-dimensional transmission line model may be used as the basis for the impedance calculations.

  15. Contour mode resonators with acoustic reflectors

    DOEpatents

    Olsson, Roy H.; Fleming, James G.; Tuck, Melanie R.

    2008-06-10

    A microelectromechanical (MEM) resonator is disclosed which has a linear or ring-shaped acoustic resonator suspended above a substrate by an acoustic reflector. The acoustic resonator can be formed with a piezoelectric material (e.g. aluminum nitride, zinc oxide or PZT), or using an electrostatically-actuated material. The acoustic reflector (also termed an acoustic mirror) uses alternating sections of a relatively low acoustic impedance Z.sub.L material and a relatively high acoustic impedance Z.sub.H material to isolate the acoustic resonator from the substrate. The MEM resonator, which can be formed on a silicon substrate with conventional CMOS circuitry, has applications for forming oscillators, rf filters, and acoustic sensors.

  16. ADVANCES IN IMPEDANCE THEORY

    SciTech Connect

    Stupakov, G.; /SLAC

    2009-06-05

    We review recent progress in the following areas of the impedance theory: calculation of impedance of tapers and small angle collimators; optical approximation and parabolic equation for the high-frequency impedance; impedance due to resistive inserts in a perfectly conducting pipe.

  17. X-ray elastography: Modification of x-ray phase contrast images using ultrasonic radiation pressure

    SciTech Connect

    Hamilton, Theron J.; Bailat, Claude; Rose-Petruck, Christoph; Diebold, Gerald J.; Gehring, Stephan; Laperle, Christopher M.; Wands, Jack

    2009-05-15

    The high resolution characteristic of in-line x-ray phase contrast imaging can be used in conjunction with directed ultrasound to detect small displacements in soft tissue generated by differential acoustic radiation pressure. The imaging method is based on subtraction of two x-ray images, the first image taken with, and the second taken without the presence of ultrasound. The subtraction enhances phase contrast features and, to a large extent, removes absorption contrast so that differential movement of tissues with different acoustic impedances or relative ultrasonic absorption is highlighted in the image. Interfacial features of objects with differing densities are delineated in the image as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. Experiments with ex vivo murine tumors and human tumor phantoms point out a diagnostic capability of the method for identifying tumors.

  18. Noncontact scanning electrical impedance imaging.

    PubMed

    Liu, Hongze; Hawkins, Aaron; Schultz, Stephen; Oliphant, Travis E

    2004-01-01

    We are interested in applying electrical impedance imaging to a single cell because it has potential to reveal both cell anatomy and cell function. Unfortunately, classic impedance imaging techniques are not applicable to this small scale measurement due to their low resolution. In this paper, a different method of impedance imaging is developed based on a noncontact scanning system. In this system, the imaging sample is immersed in an aqueous solution allowing for the use of various probe designs. Among those designs, we discuss a novel shield-probe design that has the advantage of better signal-to-noise ratio with higher resolution compared to other probes. Images showing the magnitude of current for each scanned point were obtained using this configuration. A low-frequency linear physical model helps to relate the current to the conductivity at each point. Line-scan data of high impedance contrast structures can be shown to be a good fit to this model. The first two-dimensional impedance image of biological tissues generated by this technique is shown with resolution on the order of 100 mum. The image reveals details not present in the optical image. PMID:17271930

  19. Topics in the interpretation of seismic data: I. Earthquake seismogram interpretation for the classroom. II. Gas saturation prediction and effect of low frequencies on acoustic impedance images at Foinaven Field. III. Physical reasonability and accuracy of spheroidal porosity models for seismic velocity prediction

    NASA Astrophysics Data System (ADS)

    Wagner, Sean R.

    2005-11-01

    Low frequencies are necessary in seismic data for proper acoustic impedance imaging and for petrophysical interpretation. Without lower frequencies, images can be distorted leading to incorrect reservoir interpretation and petrophysical predictions. As part of the Foinaven Active Reservoir Management (FARM) project, a Towed Streamer and Ocean Bottom Hydrophone (OBH) survey were shot in both 1995 and 1998. The OBH surveys contain lower frequencies than the streamer surveys, providing a unique opportunity to study the effects low frequencies have on both the acoustic impedance image along with petrophysical time-lapse predictions. Artifacts that could easily have been interpreted as high-resolution features in the streamer data impedance volumes can be distinguished by comparison with the impedance volumes created from the OBH surveys containing lower frequencies. In order to obtain results from the impedance volumes, impedance must be related to saturation. The mixing of exsolved gas, oil, and water phases involves using the Reuss (uniform) or Voigt (patchy approximation) mixing laws. The Voigt average is easily misused by assuming that the end points correspond to 0% and 100% gas saturation. This implies that the patches are either 0% gas saturation or 100% gas saturation, which is never the case. Here the distribution of gas as it comes out of solution is assumed to be uniform until the gas saturation reaches a sufficiently high value (critical gas saturation) to allow gas to flow. Therefore, at low gas saturations the distribution is uniform, but at saturations above critical, it is patchy, with patches that range from critical gas saturation to the highest gas saturation possible (1 minus residual oil and irreducible water saturation). The Xu and White method predicts a shear (S-) sonic log in a sand-clay mixture using a theoretical (Kuster-Toksoz) model to embed pores with aspect ratios that provide a best-fit to a known compressional (P-) sonic log. In the Xu

  20. Time-Domain Impedance Boundary Conditions for Computational Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Auriault, Laurent

    1996-01-01

    It is an accepted practice in aeroacoustics to characterize the properties of an acoustically treated surface by a quantity known as impedance. Impedance is a complex quantity. As such, it is designed primarily for frequency-domain analysis. Time-domain boundary conditions that are the equivalent of the frequency-domain impedance boundary condition are proposed. Both single frequency and model broadband time-domain impedance boundary conditions are provided. It is shown that the proposed boundary conditions, together with the linearized Euler equations, form well-posed initial boundary value problems. Unlike ill-posed problems, they are free from spurious instabilities that would render time-marching computational solutions impossible.

  1. Acoustic neuroma

    MedlinePlus

    Vestibular schwannoma; Tumor - acoustic; Cerebellopontine angle tumor; Angle tumor ... Acoustic neuromas have been linked with the genetic disorder neurofibromatosis type 2 (NF2). Acoustic neuromas are uncommon.

  2. Numerical study of acoustophoretic motion of particles in a PDMS microchannel driven by surface acoustic waves

    PubMed Central

    Nama, Nitesh; Barnkob, Rune; Mao, Zhangming; Kähler, Christian J.

    2015-01-01

    We present a numerical study of the acoustophoretic motion of particles suspended in a liquid-filled PDMS microchannel on a lithium niobate substrate acoustically driven by surface acoustic waves. We employ a perturbation approach where the flow variables are divided into first- and second-order fields. We use impedance boundary conditions to model the PDMS microchannel walls and we model the acoustic actuation by a displacement function from the literature based on a numerical study of piezoelectric actuation. Consistent with the type of actuation, the obtained first-order field is a horizontal standing wave that travels vertically from the actuated wall towards the upper PDMS wall. This is in contrast to what is observed in bulk acoustic wave devices. The first-order fields drive the acoustic streaming, as well as the time-averaged acoustic radiation force acting on suspended particles. We analyze the motion of suspended particles driven by the acoustic streaming drag and the radiation force. We examine a range of particle diameters to demonstrate the transition from streaming-drag-dominated acoustophoresis to radiation-force-dominated acoustophoresis. Finally, as an application of our numerical model, we demonstrate the capability to tune the position of the vertical pressure node along the channel width by tuning the phase difference between two incoming surface acoustic waves. PMID:26001199

  3. Numerical study of acoustophoretic motion of particles in a PDMS microchannel driven by surface acoustic waves.

    PubMed

    Nama, Nitesh; Barnkob, Rune; Mao, Zhangming; Kähler, Christian J; Costanzo, Francesco; Huang, Tony Jun

    2015-06-21

    We present a numerical study of the acoustophoretic motion of particles suspended in a liquid-filled PDMS microchannel on a lithium niobate substrate acoustically driven by surface acoustic waves. We employ a perturbation approach where the flow variables are divided into first- and second-order fields. We use impedance boundary conditions to model the PDMS microchannel walls and we model the acoustic actuation by a displacement function from the literature based on a numerical study of piezoelectric actuation. Consistent with the type of actuation, the obtained first-order field is a horizontal standing wave that travels vertically from the actuated wall towards the upper PDMS wall. This is in contrast to what is observed in bulk acoustic wave devices. The first-order fields drive the acoustic streaming, as well as the time-averaged acoustic radiation force acting on suspended particles. We analyze the motion of suspended particles driven by the acoustic streaming drag and the radiation force. We examine a range of particle diameters to demonstrate the transition from streaming-drag-dominated acoustophoresis to radiation-force-dominated acoustophoresis. Finally, as an application of our numerical model, we demonstrate the capability to tune the position of the vertical pressure node along the channel width by tuning the phase difference between two incoming surface acoustic waves. PMID:26001199

  4. Acoustic metasurface with hybrid resonances.

    PubMed

    Ma, Guancong; Yang, Min; Xiao, Songwen; Yang, Zhiyu; Sheng, Ping

    2014-09-01

    An impedance-matched surface has the property that an incident wave generates no reflection. Here we demonstrate that by using a simple construction, an acoustically reflecting surface can acquire hybrid resonances and becomes impedance-matched to airborne sound at tunable frequencies, such that no reflection is generated. Each resonant cell of the metasurface is deep-subwavelength in all its spatial dimensions, with its thickness less than the peak absorption wavelength by two orders of magnitude. As there can be no transmission, the impedance-matched acoustic wave is hence either completely absorbed at one or multiple frequencies, or converted into other form(s) of energy, such as an electrical current. A high acoustic-electrical energy conversion efficiency of 23% is achieved. PMID:24880731

  5. Active Control of Liner Impedance by Varying Perforate Orifice Geometry

    NASA Technical Reports Server (NTRS)

    Ahuji, K. K.; Gaeta, R. J., Jr.

    2000-01-01

    The present work explored the feasibility of controlling the acoustic impedance of a resonant type acoustic liner. This was accomplished by translating one perforate over another of the same porosity creating a totally new perforate that had an intermediate porosity. This type of adjustable perforate created a variable orifice perforate whose orifices were non-circular. The key objective of the present study was to quantify, the degree of attenuation control that can be achieved by applying such a concept to the buried septum in a two-degree-of-freedom (2DOF) acoustic liner. An additional objective was to examine the adequacy of the existing impedance models to explain the behavior of the unique orifice shapes that result from the proposed silding perforate concept. Different orifice shapes with equivalent area were also examined to determine if highly non-circular orifices had a significant impact on the impedance.

  6. Acoustic cooling engine

    DOEpatents

    Hofler, Thomas J.; Wheatley, John C.; Swift, Gregory W.; Migliori, Albert

    1988-01-01

    An acoustic cooling engine with improved thermal performance and reduced internal losses comprises a compressible fluid contained in a resonant pressure vessel. The fluid has a substantial thermal expansion coefficient and is capable of supporting an acoustic standing wave. A thermodynamic element has first and second ends and is located in the resonant pressure vessel in thermal communication with the fluid. The thermal response of the thermodynamic element to the acoustic standing wave pumps heat from the second end to the first end. The thermodynamic element permits substantial flow of the fluid through the thermodynamic element. An acoustic driver cyclically drives the fluid with an acoustic standing wave. The driver is at a location of maximum acoustic impedance in the resonant pressure vessel and proximate the first end of the thermodynamic element. A hot heat exchanger is adjacent to and in thermal communication with the first end of the thermodynamic element. The hot heat exchanger conducts heat from the first end to portions of the resonant pressure vessel proximate the hot heat exchanger. The hot heat exchanger permits substantial flow of the fluid through the hot heat exchanger. The resonant pressure vessel can include a housing less than one quarter wavelength in length coupled to a reservoir. The housing can include a reduced diameter portion communicating with the reservoir. The frequency of the acoustic driver can be continuously controlled so as to maintain resonance.

  7. Robust impedance shaping telemanipulation

    SciTech Connect

    Colgate, J.E.

    1993-08-01

    When a human operator performs a task via a bilateral manipulator, the feel of the task is embodied in the mechanical impedance of the manipulator. Traditionally, a bilateral manipulator is designed for transparency; i.e., so that the impedance reflected through the manipulator closely approximates that of the task. Impedance shaping bilateral control, introduced here, differs in that it treats the bilateral manipulator as a means of constructively altering the impedance of a task. This concept is particularly valuable if the characteristic dimensions (e.g., force, length, time) of the task impedance are very different from those of the human limb. It is shown that a general form of impedance shaping control consists of a conventional power-scaling bilateral controller augmented with a real-time interactive task simulation (i.e., a virtual environment). An approach to impedance shaping based on kinematic similarity between tasks of different scale is introduced and illustrated with an example. It is shown that an important consideration in impedance shaping controller design is robustness; i.e., guaranteeing the stability of the operator/manipulator/task system. A general condition for the robustness of a bilateral manipulator is derived. This condition is based on the structured singular value ({mu}). An example of robust impedance shaping bilateral control is presented and discussed.

  8. Acoustic attenuation analysis program for ducts with mean flow

    NASA Technical Reports Server (NTRS)

    Kunze, R. K., Jr.

    1972-01-01

    A computerized acoustic attenuation prediction procedure has been developed to evaluate acoustically lined ducts for various geometric and environmental parameters. The analysis procedure is based on solutions to the acoustic wave equation, assuming uniform airflow on a duct cross section, combined with appropriate mathematical lining impedance models. The impedance models included in the analysis procedure are representative of either perforated sheet or porous polyimide impregnated fiberglass facing sheet coupled with a cellular backing space. Advantages and limitations of the analysis procedure are reviewed.

  9. Stability of acoustic individuality in the alarm calls of wild yellow ground squirrels Spermophilus fulvus and contrasting calls from trapped and free-ranging callers.

    PubMed

    Matrosova, Vera A; Volodin, Ilya A; Volodina, Elena V; Vasilieva, Nina A

    2010-08-01

    The questions of individuality and stability of cues to identity in vocal signals are of considerable importance from theoretical and conservation perspectives. While individuality in alarm calls has been reported for many sciurids, it is not well-documented that the vocal identity encoded in the alarm calls is stable between different encounters with predators. Previous studies of two obligate hibernating rodents, speckled ground squirrels Spermophilus suslicus, and yellow ground squirrels Spermophilus fulvus demonstrated that, after hibernation, most individuals could not be identified reliably by their alarm calls. Moreover, in most speckled ground squirrels, individual patterns of alarm calls changed progressively over as little as 2 weeks. However, these previous data have been obtained using the collection of alarm calls from trapped animals. Here, we examined ten free-ranging dye-marked yellow ground squirrels to determine whether their alarm calls retain the cues to individuality between two encounters of surrogate predators (humans), separated on average by 3 days. Discriminant function analysis showed that the alarm calls of individual yellow ground squirrels were very similar within a recording session, providing very high individual distinctiveness. However, in six of the ten animals, the alarm calls were unstable between recording sessions. Also, we examined ten dye-marked individuals for consistency of acoustic characteristics of their alarm calls between the encounters of humans, differing in techniques of call collection, from free-ranging vs trapped animals. We found differences only in two variables, both related to sound degradation in the environment. Data are discussed in relation to hypotheses explaining the adaptive utility of acoustic individuality in alarm calls. PMID:20559613

  10. Impedance of a nanoantenna

    SciTech Connect

    Greffet, Jean-Jacques; Laroche, Marine; Marquier, Francois

    2009-10-07

    We introduce a generalized definition of the impedance of a nanoantenna that can be applied to any system. We also introduce a definition of the impedance of a two level system. Using this framework, we establish a link between the electrical engineering and the quantum optics picture of light emission.

  11. Acoustical problems in high energy pulsed E-beams lasers

    NASA Technical Reports Server (NTRS)

    Horton, T. E.; Wylie, K. F.

    1976-01-01

    During the pulsing of high energy, CO2, electron beam lasers, a significant fraction of input energy ultimately appears as acoustical disturbances. The magnitudes of these disturbances were quantified by computer analysis. Acoustical and shock impedance data are presented on materials (Rayleigh type) which show promise in controlling acoustical disturbance in E-beam systems.

  12. Formant frequencies and bandwidths of the vocal tract transfer function are affected by the mechanical impedance of the vocal tract wall.

    PubMed

    Fleischer, Mario; Pinkert, Silke; Mattheus, Willy; Mainka, Alexander; Mürbe, Dirk

    2015-08-01

    The acoustical properties of the vocal tract, the air-filled cavity between the vocal folds and the mouth opening, are determined by its individual geometry, the physical properties of the air and of its boundaries. In this article, we address the necessity of complex impedance boundary conditions at the mouth opening and at the border of the acoustical domain inside the human vocal tract. Using finite element models based on MRI data for spoken and sung vowels /a/, /i/ and /Ω(-1)/ and comparison of the transfer characteristics by analysis of acoustical data using an inverse filtering method, the global wall impedance showed a frequency-dependent behaviour and depends on the produced vowel and therefore on the individual vocal tract geometry. The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz. In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3). These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies. It implies that the timbre characteristics of vowel sounds are likely to be tuned by specific control of relaxation and strain of the surrounding structures of the vocal tract. PMID:25416844

  13. Acoustic trauma caused by lightning.

    PubMed

    Mora-Magaña, I; Collado-Corona, M A; Toral-Martiñòn, R; Cano, A

    1996-03-01

    Lesions produced by exposure to noise are frequent in everyday life. Injuries may be found in all systems of the human body, from the digestive to the endocrine, from the cardiovascular to the nervous system. Many organs may be damaged, the ear being one of them. It is known that noise produced by factories, airports, musical instruments and even toys can cause auditory loss. Noises in nature can also cause acoustic trauma. This report is the case history of acoustic trauma caused by lightning. The patient was studied with CAT scan, electroencephalogram, and brain mapping, impedance audiometry with tympanogram and acoustic reflex, audiometry and evoked otoacoustics emissions: distortion products and transients. PMID:8882110

  14. Enhanced plane wave expansion analysis for the band structure of bulk modes in two-dimensional high-contrast solid-solid phononic crystals

    NASA Astrophysics Data System (ADS)

    Baboly, Mohammadhosein Ghasemi; Soliman, Yasser; Su, Mehmet F.; Reinke, Charles M.; Leseman, Zayd C.; El-Kady, Ihab

    2014-11-01

    Plane wave expansion analyses that use the inverse rule to obtain the Fourier coefficients of the elastic tensor instead of the more conventional Laurent's rule, exhibit faster convergence rates for solid-solid phononic crystals. In this work, the band structure convergence of calculations using the inverse rule is investigated and applied to the case of high acoustic impedance contrast solid-solid phononic crystals, previously known for convergence difficulties. Results are contrasted to those obtained with the conventional plane wave expansion method. The inverse rule is found to converge at a much rate for all ranges of impedance contrast, and the ratio between the computational times needed to obtain a convergent band structure for a high-contrast solid-solid phononic crystal with the conventional plane wave expansion method using 1369 reciprocal lattice vectors is as large as 6800:1. This ratio decreases for material sets with lower impedance contrast; however, the inverse rule is still faster for a given error threshold for even the lowest impedance contrast phononic crystals reported in the literature. This convergence enhancement is a major factor in reconsidering the plane wave expansion method as an important tool in obtaining propagating elastic modes in phononic crystals.

  15. Validation of an Impedance Education Method in Flow

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.; Parrott, Tony L.

    2004-01-01

    This paper reports results of a research effort to validate a method for educing the normal incidence impedance of a locally reacting liner, located in a grazing incidence, nonprogressive acoustic wave environment with flow. The results presented in this paper test the ability of the method to reproduce the measured normal incidence impedance of a solid steel plate and two soft test liners in a uniform flow. The test liners are known to be locally react- ing and exhibit no measurable amplitude-dependent impedance nonlinearities or flow effects. Baseline impedance spectra for these liners were therefore established from measurements in a conventional normal incidence impedance tube. A key feature of the method is the expansion of the unknown impedance function as a piecewise continuous polynomial with undetermined coefficients. Stewart's adaptation of the Davidon-Fletcher-Powell optimization algorithm is used to educe the normal incidence impedance at each Mach number by optimizing an objective function. The method is shown to reproduce the measured normal incidence impedance spectrum for each of the test liners, thus validating its usefulness for determining the normal incidence impedance of test liners for a broad range of source frequencies and flow Mach numbers. Nomenclature

  16. Overview Of Impedance Sensors

    NASA Astrophysics Data System (ADS)

    Abele, John E.

    1989-08-01

    Electrical impedance has been one of the many "tools of great promise" that physicians have employed in their quest to measure and/or monitor body function or physiologic events. So far, the expectations for its success have always exceeded its performance. In simplistic terms, physiologic impedance is a measure of the resistance in the volume between electrodes which changes as a function of changes in that volume, the relative impedance of that volume, or a combination of these two. The history and principles of electrical impedance are very nicely reviewed by Geddes and Baker in their textbook "Principles of Applied Biomedical Instrumentation". It is humbling, however, to note that Cremer recorded variations in electrical impedance in frog hearts as early as 1907. The list of potential applications includes the measurement of thyroid function, estrogen activity, galvanic skin reflex, respiration, blood flow by conductivity dilution, nervous activity and eye movement. Commercial devices employing impedance have been and are being used to measure respiration (pneumographs and apneamonitors), pulse volume (impedance phlebographs) and even noninvasive cardiac output.

  17. An investigation of the diffraction of an acoustic plane wave by a curved surface of finite impedance. Ph.D. Thesis Final Technical Report, 1 Feb. 1985 - 1 Sep. 1989

    NASA Technical Reports Server (NTRS)

    Kearns, James A.

    1989-01-01

    Phenomena associated with long range propagation of sound over irregular topography motivated this work, which was to analyze the diffraction effects which would occur near the tops of hills and ridges. The diffraction of a high frequency plane wave due to its grazing of a two-dimensional curved surface of finite impedance was also studied. Laboratory scale models were constructed and measurements were made of the field on, above, and behind either of two curved surfaces possessing distinctly different impedances; that is, one was soft while the other was hard. The experimental technique consisted of simultaneously measuring the pressure at a reference point and at a field point due to a transient pulse generated by an electric spark. The pressure waveforms were digitized and processed. The ratio of the discrete Fourier transforms of the two waveforms provided an estimate of the insertion loss between them. The results of the measurements were compared with the predictions of a theory which was derived by Pierce using the method of Matched Asymptotic Expansions (MAE). The predictions relied upon the experimental evaluation of the impedance of each surface at grazing angles of incidence. This evaluation was achieved by a fairly standard technique involving empirical models of various generic types of surfaces. An example was shown of the important role that the structural intricacies of a surface play in the determination of an appropriate model. The comparison between the measurements and predictions indicated that the theory gives an excellent description of the field anywhere near a curved surface. Further, with a simple modification, the theory was also shown to give nearly as good of a description of the field surrounding a curved surface even at distances far behind the surface yet near the line of sight.

  18. Acoustic Absorption in Porous Materials

    NASA Technical Reports Server (NTRS)

    Kuczmarski, Maria A.; Johnston, James C.

    2011-01-01

    An understanding of both the areas of materials science and acoustics is necessary to successfully develop materials for acoustic absorption applications. This paper presents the basic knowledge and approaches for determining the acoustic performance of porous materials in a manner that will help materials researchers new to this area gain the understanding and skills necessary to make meaningful contributions to this field of study. Beginning with the basics and making as few assumptions as possible, this paper reviews relevant topics in the acoustic performance of porous materials, which are often used to make acoustic bulk absorbers, moving from the physics of sound wave interactions with porous materials to measurement techniques for flow resistivity, characteristic impedance, and wavenumber.

  19. Microfabricated AC impedance sensor

    DOEpatents

    Krulevitch, Peter; Ackler, Harold D.; Becker, Frederick; Boser, Bernhard E.; Eldredge, Adam B.; Fuller, Christopher K.; Gascoyne, Peter R. C.; Hamilton, Julie K.; Swierkowski, Stefan P.; Wang, Xiao-Bo

    2002-01-01

    A microfabricated instrument for detecting and identifying cells and other particles based on alternating current (AC) impedance measurements. The microfabricated AC impedance sensor includes two critical elements: 1) a microfluidic chip, preferably of glass substrates, having at least one microchannel therein and with electrodes patterned on both substrates, and 2) electrical circuits that connect to the electrodes on the microfluidic chip and detect signals associated with particles traveling down the microchannels. These circuits enable multiple AC impedance measurements of individual particles at high throughput rates with sufficient resolution to identify different particle and cell types as appropriate for environmental detection and clinical diagnostic applications.

  20. Detection and quantification of bacterial biofilms combining high-frequency acoustic microscopy and targeted lipid microparticles

    PubMed Central

    2014-01-01

    Background Immuno-compromised patients such as those undergoing cancer chemotherapy are susceptible to bacterial infections leading to biofilm matrix formation. This surrounding biofilm matrix acts as a diffusion barrier that binds up antibiotics and antibodies, promoting resistance to treatment. Developing non-invasive imaging methods that detect biofilm matrix in the clinic are needed. The use of ultrasound in conjunction with targeted ultrasound contrast agents (UCAs) may provide detection of early stage biofilm matrix formation and facilitate optimal treatment. Results Ligand-targeted UCAs were investigated as a novel method for pre-clinical non-invasive molecular imaging of early and late stage biofilms. These agents were used to target, image and detect Staphylococcus aureus biofilm matrix in vitro. Binding efficacy was assessed on biofilm matrices with respect to their increasing biomass ranging from 3.126 × 103 ± 427 UCAs per mm2 of biofilm surface area within 12 h to 21.985 × 103 ± 855 per mm2 of biofilm matrix surface area at 96 h. High-frequency acoustic microscopy was used to ultrasonically detect targeted UCAs bound to a biofilm matrix and to assess biofilm matrix mechanoelastic physical properties. Acoustic impedance data demonstrated that biofilm matrices exhibit impedance values (1.9 MRayl) close to human tissue (1.35 - 1.85 MRayl for soft tissues). Moreover, the acoustic signature of mature biofilm matrices were evaluated in terms of integrated backscatter (0.0278 - 0.0848 mm-1 × sr-1) and acoustic attenuation (3.9 Np/mm for bound UCAs; 6.58 Np/mm for biofilm alone). Conclusions Early diagnosis of biofilm matrix formation is a challenge in treating cancer patients with infection-associated biofilms. We report for the first time a combined optical and acoustic evaluation of infectious biofilm matrices. We demonstrate that acoustic impedance of biofilms is similar to the impedance of human tissues, making in vivo imaging and detection of biofilm

  1. Improving photoacoustic imaging contrast of brachytherapy seeds

    NASA Astrophysics Data System (ADS)

    Pan, Leo; Baghani, Ali; Rohling, Robert; Abolmaesumi, Purang; Salcudean, Septimiu; Tang, Shuo

    2013-03-01

    Prostate brachytherapy is a form of radiotherapy for treating prostate cancer where the radiation sources are seeds inserted into the prostate. Accurate localization of seeds during prostate brachytherapy is essential to the success of intraoperative treatment planning. The current standard modality used in intraoperative seeds localization is transrectal ultrasound. Transrectal ultrasound, however, suffers in image quality due to several factors such speckle, shadowing, and off-axis seed orientation. Photoacoustic imaging, based on the photoacoustic phenomenon, is an emerging imaging modality. The contrast generating mechanism in photoacoustic imaging is optical absorption that is fundamentally different from conventional B-mode ultrasound which depicts changes in acoustic impedance. A photoacoustic imaging system is developed using a commercial ultrasound system. To improve imaging contrast and depth penetration, absorption enhancing coating is applied to the seeds. In comparison to bare seeds, approximately 18.5 dB increase in signal-to-noise ratio as well as a doubling of imaging depth are achieved. Our results demonstrate that the coating of the seeds can further improve the discernibility of the seeds.

  2. Impedance of accelerator components

    SciTech Connect

    Corlett, J.N.

    1996-05-01

    As demands for high luminosity and low emittance particle beams increase, an understanding of the electromagnetic interaction of these beams with their vacuum chamber environment becomes more important in order to maintain the quality of the beam. This interaction is described in terms of the wake field in time domain, and the beam impedance in frequency domain. These concepts are introduced, and related quantities such as the loss factor are presented. The broadband Q = 1 resonator impedance model is discussed. Perturbation and coaxial wire methods of measurement of real components are reviewed.

  3. Superconducting active impedance converter

    DOEpatents

    Ginley, D.S.; Hietala, V.M.; Martens, J.S.

    1993-11-16

    A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductors allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology. 12 figures.

  4. Superconducting active impedance converter

    DOEpatents

    Ginley, David S.; Hietala, Vincent M.; Martens, Jon S.

    1993-01-01

    A transimpedance amplifier for use with high temperature superconducting, other superconducting, and conventional semiconductor allows for appropriate signal amplification and impedance matching to processing electronics. The amplifier incorporates the superconducting flux flow transistor into a differential amplifier configuration which allows for operation over a wide temperature range, and is characterized by high gain, relatively low noise, and response times less than 200 picoseconds over at least a 10-80 K. temperature range. The invention is particularly useful when a signal derived from either far-IR focal plane detectors or from Josephson junctions is to be processed by higher signal/higher impedance electronics, such as conventional semiconductor technology.

  5. Point source moving above a finite impedance reflecting plane - Experiment and theory

    NASA Technical Reports Server (NTRS)

    Norum, T. D.; Liu, C. H.

    1978-01-01

    A widely used experimental version of the acoustic monopole consists of an acoustic driver of restricted opening forced by a discrete frequency oscillator. To investigate the effects of forward motion on this source, it was mounted above an automobile and driven over an asphalt surface at constant speed past a microphone array. The shapes of the received signal were compared to results computed from an analysis of a fluctuating-mass-type point source moving above a finite impedance reflecting plane. Good agreement was found between experiment and theory when a complex normal impedance representative of a fairly hard acoustic surface was used in the analysis.

  6. Non-contact scanning electrical impedance imaging.

    PubMed

    Liu, Hongze; Hawkins, Aaron; Schultz, Stephen; Oliphant, Travis

    2004-01-01

    We are interested in applying electrical impedance imaging to a single cell because it has potential to reveal both cell anatomy and cell function. Unfortunately, classic impedance imaging techniques are not applicable to this small scale measurement due to their low resolution. In this paper, a different method of impedance imaging is developed based on a non-contact scanning system. In this system, the imaging sample is immersed in an aqueous solution allowing for the use of various probe designs. Among those designs, we discuss a novel shield-probe design that has the advantage of better signal-to-noise ratio with higher resolution compared to other probes. Images showing the magnitude of current for each scanned point were obtained using this configuration. A low-frequency linear physical model helps to relate the current to the conductivity at each point. Line-scan data of high impedance contrast structures can be shown to be a good fit to this model. The first two-dimensional impedance image of biological tissues generated by this technique is shown with resolution on the order of 100 mum. The image reveals details not present in the optical image. PMID:17271931

  7. Acoustic Neuroma

    MedlinePlus

    An acoustic neuroma is a benign tumor that develops on the nerve that connects the ear to the brain. ... can press against the brain, becoming life-threatening. Acoustic neuroma can be difficult to diagnose, because the ...

  8. Impedance cardiography: recent advancements.

    PubMed

    Cybulski, Gerard; Strasz, Anna; Niewiadomski, Wiktor; Gąsiorowska, Anna

    2012-01-01

    The aim of this paper is the presentation of recent advancements in impedance cardiography regarding methodical approach, applied equipment and clinical or research implementations. The review is limited to the papers which were published over last 17 months (dated 2011 and 2012) in well recognised scientific journals. PMID:23042327

  9. Impedances of Tevatron separators

    SciTech Connect

    K. Y. Ng

    2003-05-28

    The impedances of the Tevatron separators are revisited and are found to be negligibly small in the few hundred MHz region, except for resonances at 22.5 MHz. The later are contributions from the power cables which may drive head-tail instabilities if the bunch is long enough.

  10. Longitudinal impedance of RHIC

    SciTech Connect

    Blaskiewicz, M.; Brennan, J. M.; Mernick, K.

    2015-05-03

    The longitudinal impedance of the two RHIC rings has been measured using the effect of potential well distortion on longitudinal Schottky measurements. For the blue RHIC ring Im(Z/n) = 1.5±0.2Ω. For the yellow ring Im(Z/n) = 5.4±1Ω.

  11. A new approach to the study of impedance characteristics of tympanic membrane.

    PubMed

    Bogomolov, A V; Dragan, S P

    2015-01-01

    A new approach to studying the tympanic membrane impedance characteristics, based on the analysis of polyharmonic acoustic signals reflected by the tympanic membrane, is described. For this purpose, the acoustic pressure and the phase difference between the acoustic vibrations in two sections of a waveguide sealingly connecting the external auditory meatus and a generator of polyharmonic audio signals is measured. By processing the results of measurements, the estimates of the frequency-dependent reflection coefficients, absorption coefficients, and components of the acoustic impedance of the tympanic membrane are calculated. The features that principally distinguish the developed approach from other approaches are the absence of the necessity to create a positive pressure in the external auditory meatus, the absence of ultrasonic radiation into the external auditory meatus and a high-intensity sound, and the possibility of direct measurement of the tympanic membrane impedance in the audio frequency range with any step. PMID:26518544

  12. Acoustic radiation from lined, unflanged ducts: Acoustic source distribution program

    NASA Technical Reports Server (NTRS)

    Beckemeyer, R. J.; Sawdy, D. T.

    1971-01-01

    An acoustic radiation analysis was developed to predict the far-field characteristics of fan noise radiated from an acoustically lined unflanged duct. This analysis is comprised of three modular digital computer programs which together provide a capability of accounting for the impedance mismatch at the duct exit plane. Admissible duct configurations include circular or annular, with or without an extended centerbody. This variation in duct configurations provides a capability of modeling inlet and fan duct noise radiation. The computer programs are described in detail.

  13. On the Use of Experimental Methods to Improve Confidence in Educed Impedance

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Watson, Willie R.

    2011-01-01

    Results from impedance eduction methods developed by NASA Langley Research Center are used throughout the acoustic liner community. In spite of recent enhancements, occasional anomalies persist with these methods, generally at frequencies where the liner produces minimal attenuation. This investigation demonstrates an experimental approach to educe impedance with increased confidence over a desired frequency range, by combining results from successive tests with different cavity depths. A series of tests is conducted with three wire-mesh facesheets, for which the results should be weakly dependent on source sound pressure level and mean grazing flow speed. First, a raylometer is used to measure the DC flow resistance of each facesheet. These facesheets are then mounted onto a frame and a normal incidence tube is used to determine their respective acoustic impedance spectra. A comparison of the acoustic resistance component with the DC flow resistance for each facesheet is used to validate the measurement process. Next, each facesheet is successively mounted onto three frames with different cavity depths, and a grazing flow impedance tube is used to educe their respective acoustic impedance spectra with and without mean flow. The no-flow results are compared with those measured in the normal incidence tube to validate the impedance eduction method. Since the anti-resonance frequency varies with cavity depth, each sample provides robust results over a different frequency range. Hence, a combination of results can be used to determine the facesheet acoustic resistance. When combined with the acoustic reactance, observed to be weakly dependent on the source sound pressure level and grazing flow Mach number, the acoustic impedance can be educed with increased confidence. Representative results of these tests are discussed, and the complete database is available in electronic format upon request.

  14. Recycler short kicker beam impedance

    SciTech Connect

    Crisp, Jim; Fellenz, Brian; /Fermilab

    2009-07-01

    Measured longitudinal and calculated transverse beam impedance is presented for the short kicker magnets being installed in the Fermilab Recycler. Fermi drawing number ME-457159. The longitudinal impedance was measured with a stretched wire and the Panofsky equation was used to estimate the transverse impedance. The impedance of 3319 meters (the Recycler circumference) of stainless vacuum pipe is provided for comparison. Although measurements where done to 3GHz, impedance was negligible above 30MHz. The beam power lost to the kicker impedance is shown for a range of bunch lengths. The measurements are for one kicker assuming a rotation frequency of 90KHz. Seven of these kickers are being installed.

  15. Acoustic Seal

    NASA Technical Reports Server (NTRS)

    Steinetz, Bruce M. (Inventor)

    2006-01-01

    The invention relates to a sealing device having an acoustic resonator. The acoustic resonator is adapted to create acoustic waveforms to generate a sealing pressure barrier blocking fluid flow from a high pressure area to a lower pressure area. The sealing device permits noncontacting sealing operation. The sealing device may include a resonant-macrosonic-synthesis (RMS) resonator.

  16. Acoustic seal

    NASA Technical Reports Server (NTRS)

    Steinetz, Bruce M. (Inventor)

    2006-01-01

    The invention relates to a sealing device having an acoustic resonator. The acoustic resonator is adapted to create acoustic waveforms to generate a sealing pressure barrier blocking fluid flow from a high pressure area to a lower pressure area. The sealing device permits noncontacting sealing operation. The sealing device may include a resonant-macrosonic-synthesis (RMS) resonator.

  17. ONERA-NASA Cooperative Effort on Liner Impedance Eduction

    NASA Technical Reports Server (NTRS)

    Primus, Julien; Piot, Estelle; Simon, Frank; Jones, Michael G.; Watson, Willie R

    2013-01-01

    As part of a cooperation between ONERA and NASA, the liner impedance eduction methods developed by the two research centers are compared. The NASA technique relies on an objective function built on acoustic pressure measurements located on the wall opposite the test liner, and the propagation code solves the convected Helmholtz equation in uniform ow using a finite element method that implements a continuous Galerkin discretization. The ONERA method uses an objective function based either on wall acoustic pressure or on acoustic velocity acquired above the liner by Laser Doppler Anemometry, and the propagation code solves the linearized Euler equations by a discontinuous Galerkin discretization. Two acoustic liners are tested in both ONERA and NASA ow ducts and the measured data are treated with the corresponding impedance eduction method. The first liner is a wire mesh facesheet mounted onto a honeycomb core, designed to be linear with respect to incident sound pressure level and to grazing ow velocity. The second one is a conventional, nonlinear, perforate-over-honeycomb single layer liner. Configurations without and with ow are considered. For the nonlinear liner, the comparison of liner impedance educed by NASA and ONERA shows a sensitivity to the experimental conditions, namely to the nature of the source and to the sample width.

  18. Acoustic resonant spectroscopy for characterization of thin polymer films

    NASA Astrophysics Data System (ADS)

    Tohmyoh, Hironori; Imaizumi, Takuya; Saka, Masumi

    2006-10-01

    An acoustic resonant spectroscopy technique for measuring the acoustic impedance, ultrasonic velocity, and density of micron-scale polymer films is developed. The method, which is based on spectral analysis, observes the acoustic resonance between water, the film, and a tungsten plate with high acoustic impedance in the frequency range of 20-70MHz. The interface between the film being examined and the plate is vacuum sealed, enabling us to characterize the low-density polyethylene film with acoustic impedances as low as about 1.9MNm-3s and the poly(vinyl chloride) film as thin as about 8μm. The error in the film density measurements is found to be less than 1%, and the validity of the technique is verified.

  19. In Vivo Impedance of the Gerbil Cochlear Partition at Auditory Frequencies

    PubMed Central

    Dong, Wei; Olson, Elizabeth S.

    2009-01-01

    Abstract The specific acoustic impedance of the cochlear partition was measured from 4 to 20 kHz in the basal turn of the gerbil cochlea, where the best frequency is ∼40 kHz. The acoustic impedance was found as the ratio of driving pressure to velocity response. It is the physical attribute that governs cochlear mechanics and has never before been directly measured, to our knowledge. The basilar membrane velocity was measured through the transparent round window membrane. Simultaneously, the intracochlear pressure was measured close to the stapes and quite close to the cochlear partition. The impedance phase was close to −90° and the magnitude decreased with frequency, consistent with stiffness-dominated impedance. The resistive component of the impedance was relatively small. Usually the resistance was negative at frequencies below 8 kHz; this unexpected finding might be due to other vibration modes within the cochlear partition. PMID:19720011

  20. Impedance measurement using a two-microphone, random-excitation method

    NASA Technical Reports Server (NTRS)

    Seybert, A. F.; Parrott, T. L.

    1978-01-01

    The feasibility of using a two-microphone, random-excitation technique for the measurement of acoustic impedance was studied. Equations were developed, including the effect of mean flow, which show that acoustic impedance is related to the pressure ratio and phase difference between two points in a duct carrying plane waves only. The impedances of a honeycomb ceramic specimen and a Helmholtz resonator were measured and compared with impedances obtained using the conventional standing-wave method. Agreement between the two methods was generally good. A sensitivity analysis was performed to pinpoint possible error sources and recommendations were made for future study. The two-microphone approach evaluated in this study appears to have some advantages over other impedance measuring techniques.

  1. Anomalous acoustic reflection on a sliding interface or a shear band.

    PubMed

    Caroli, C; Velický, B

    2003-06-01

    We study the reflection of an acoustic plane wave from a steadily sliding planar interface with velocity-strengthening friction or a shear band in a confined granular medium. The corresponding acoustic impedance is utterly different from that of the static interface. In particular, the system being open, the energy of an in-plane polarized wave is no longer conserved, the work of the external pulling force being partitioned between frictional dissipation and gain (of either sign) of coherent acoustic energy. Large values of the friction coefficient favor energy gain, while velocity strengthening tends to suppress it. An interface with infinite elastic contrast (one rigid medium) and v-independent (Coulomb) friction exhibits spontaneous acoustic emission, as already shown by Nosonovsky and Adams [Int. J. Eng. Sci. 39, 1257 (2001)]. But this pathology is cured by a moderately large V strengthening of friction, or, for systems with not too large friction coefficients, by any finite elastic contrast. We show that (i) positive gain should be observable for rough-on-flat multicontact interfaces and (ii) a sliding shear band in a granular medium should give rise to sizable reflection, which opens a promising possibility for the detection of shear localization. PMID:16241215

  2. Uncertainty Analysis of the Grazing Flow Impedance Tube

    NASA Technical Reports Server (NTRS)

    Brown, Martha C.; Jones, Michael G.; Watson, Willie R.

    2012-01-01

    This paper outlines a methodology to identify the measurement uncertainty of NASA Langley s Grazing Flow Impedance Tube (GFIT) over its operating range, and to identify the parameters that most significantly contribute to the acoustic impedance prediction. Two acoustic liners are used for this study. The first is a single-layer, perforate-over-honeycomb liner that is nonlinear with respect to sound pressure level. The second consists of a wire-mesh facesheet and a honeycomb core, and is linear with respect to sound pressure level. These liners allow for evaluation of the effects of measurement uncertainty on impedances educed with linear and nonlinear liners. In general, the measurement uncertainty is observed to be larger for the nonlinear liners, with the largest uncertainty occurring near anti-resonance. A sensitivity analysis of the aerodynamic parameters (Mach number, static temperature, and static pressure) used in the impedance eduction process is also conducted using a Monte-Carlo approach. This sensitivity analysis demonstrates that the impedance eduction process is virtually insensitive to each of these parameters.

  3. Turbofan Acoustic Propagation and Radiation

    NASA Technical Reports Server (NTRS)

    Eversman, Walter

    2000-01-01

    This document describes progress in the development of finite element codes for the prediction of near and far field acoustic radiation from the inlet and aft fan ducts of turbofan engines. The report consists of nine papers which have appeared in archival journals and conference proceedings, or are presently in review for publication. Topics included are: 1. Aft Fan Duct Acoustic Radiation; 2. Mapped Infinite Wave Envelope Elements for Acoustic Radiation in a Uniformly Moving Medium; 3. A Reflection Free Boundary Condition for Propagation in Uniform Flow Using Mapped Infinite Wave Envelope Elements; 4. A Numerical Comparison Between Multiple-Scales and FEM Solution for Sound Propagation in Lined Flow Ducts; 5. Acoustic Propagation at High Frequencies in Ducts; 6. The Boundary Condition at an Impedance Wall in a Nonuniform Duct with Potential Flow; 7. A Reverse Flow Theorem and Acoustic Reciprocity in Compressible Potential Flows; 8. Reciprocity and Acoustics Power in One Dimensional Compressible Potential Flows; and 9. Numerical Experiments on Acoustic Reciprocity in Compressible Potential Flows.

  4. Contrast studies.

    PubMed

    Anderson, Susan M

    2006-01-01

    Contrast media plays an important role in imaging soft tissues and organs. Though contrast imaging is considered safe, radiologic technologists can improve the safety of contrast examinations by reviewing institutional safety procedures, safe practices for different methods of contrast administration and possible complications. The need for efficient communication and attention to detail during contrast procedures is essential for patient safety. PMID:16998193

  5. Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies

    NASA Astrophysics Data System (ADS)

    Gelda, Dhruv; Sadhu, Jyothi; Ghossoub, Marc G.; Ertekin, Elif; Sinha, Sanjiv

    2016-04-01

    High-frequency surface acoustic waves (SAWs) in the gigahertz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanisms in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic Bragg reflectors in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than five times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can enable future measurements of intrinsic damping in SAWs at ˜100 GHz.

  6. Impedance calculation for ferrite inserts

    SciTech Connect

    Breitzmann, S.C.; Lee, S.Y.; Ng, K.Y.; /Fermilab

    2005-01-01

    Passive ferrite inserts were used to compensate the space charge impedance in high intensity space charge dominated accelerators. They study the narrowband longitudinal impedance of these ferrite inserts. they find that the shunt impedance and the quality factor for ferrite inserts are inversely proportional to the imaginary part of the permeability of ferrite materials. They also provide a recipe for attaining a truly passive space charge impedance compensation and avoiding narrowband microwave instabilities.

  7. Improved Calibration Of Acoustic Plethysmographic Sensors

    NASA Technical Reports Server (NTRS)

    Zuckerwar, Allan J.; Davis, David C.

    1993-01-01

    Improved method of calibration of acoustic plethysmographic sensors involves acoustic-impedance test conditions like those encountered in use. Clamped aluminum tube holds source of sound (hydrophone) inside balloon. Test and reference sensors attached to outside of balloon. Sensors used to measure blood flow, blood pressure, heart rate, breathing sounds, and other vital signs from surfaces of human bodies. Attached to torsos or limbs by straps or adhesives.

  8. A theoretical study of the feasibility of acoustical tweezers: Ray acoustics approach

    NASA Astrophysics Data System (ADS)

    Lee, Jungwoo; Ha, Kanglyeol; Shung, K. Kirk

    2005-05-01

    The optical tweezer has been found to have many biomedical applications in trapping macromolecules and cells. For the trapping mechanism, there has to be a sharp spatial change in axial optical intensity and the particle size must be much greater than the wavelength. Similar phenomenon may exist in acoustics. This work was undertaken to demonstrate theoretically that it is possible to acoustically trap particles near the focal point where most of the acoustic energy is concentrated if certain conditions are met. Acoustic force exerted on a fluid particle in ultrasonic fields is analyzed in a ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In order to apply the acoustical tweezer to manipulating macromolecules and cells whose size is in the order of a few microns or less, a prerequisite is that the ultrasound wavelength has to be much smaller than a few microns. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. For the realization of acoustic trapping, negative axial radiation force has to be generated to pull a particle towards a focus. The fat particle considered for acoustic trapping in this paper has an acoustic impedance of 1.4 MRayls. The magnitude of the acoustic axial radiation force that has been calculated as the size of the fat particle is varied from 8λ to 14λ. In addition, both Fresnel coefficients at various positions are also calculated to assess the interaction of reflection and refraction and their relative contribution to the effect of the acoustical tweezer. The simulation results show that the feasibility of the acoustical tweezer depends on both the degree of acoustic impedance mismatch and the degree of focusing relative to the particle size. .

  9. Impedance Measurement Box

    ScienceCinema

    Christophersen, Jon

    2013-05-28

    Energy storage devices, primarily batteries, are now more important to consumers, industries and the military. With increasing technical complexity and higher user expectations, there is also a demand for highly accurate state-of-health battery assessment techniques. IMB incorporates patented, proprietary, and tested capabilities using control software and hardware that can be part of an embedded monitoring system. IMB directly measures the wideband impedance spectrum in seconds during battery operation with no significant impact on service life. It also can be applied to batteries prior to installation, confirming health before entering active service, as well as during regular maintenance. For more information about this project, visit http://www.inl.gov/rd100/2011/impedance-measurement-box/

  10. Impedance Measurement Box

    2014-11-20

    The IMB 50V software provides functionality for design of impedance measurement tests or sequences of tests, execution of these tests or sequences, processing measured responses and displaying and saving of the results. The software consists of a Graphical User Interface that allows configuration of measurement parameters and test sequencing, a core engine that controls test sequencing, execution of measurements, processing and storage of results and a hardware/software data acquisition interface with the IMB hardware system.

  11. Gynecologic electrical impedance tomograph

    NASA Astrophysics Data System (ADS)

    Korjenevsky, A.; Cherepenin, V.; Trokhanova, O.; Tuykin, T.

    2010-04-01

    Electrical impedance tomography extends to the new and new areas of the medical diagnostics: lungs, breast, prostate, etc. The feedback from the doctors who use our breast EIT diagnostic system has induced us to develop the 3D electrical impedance imaging device for diagnostics of the cervix of the uterus - gynecologic impedance tomograph (GIT). The device uses the same measuring approach as the breast imaging system: 2D flat array of the electrodes arranged on the probe with handle is placed against the body. Each of the 32 electrodes of the array is connected in turn to the current source while the rest electrodes acquire the potentials on the surface. The current flows through the electrode of the array and returns through the remote electrode placed on the patient's limb. The voltages are measured relative to another remote electrode. The 3D backprojection along equipotential surfaces is used to reconstruct conductivity distribution up to approximately 1 cm in depth. Small number of electrodes enables us to implement real time imaging with a few frames per sec. rate. The device is under initial testing and evaluation of the imaging capabilities and suitability of usage.

  12. High input impedance amplifier

    NASA Technical Reports Server (NTRS)

    Kleinberg, Leonard L.

    1995-01-01

    High input impedance amplifiers are provided which reduce the input impedance solely to a capacitive reactance, or, in a somewhat more complex design, provide an extremely high essentially infinite, capacitive reactance. In one embodiment, where the input impedance is reduced in essence, to solely a capacitive reactance, an operational amplifier in a follower configuration is driven at its non-inverting input and a resistor with a predetermined magnitude is connected between the inverting and non-inverting inputs. A second embodiment eliminates the capacitance from the input by adding a second stage to the first embodiment. The second stage is a second operational amplifier in a non-inverting gain-stage configuration where the output of the first follower stage drives the non-inverting input of the second stage and the output of the second stage is fed back to the non-inverting input of the first stage through a capacitor of a predetermined magnitude. These amplifiers, while generally useful, are very useful as sensor buffer amplifiers that may eliminate significant sources of error.

  13. ACOUSTIC LINERS FOR TURBOFAN ENGINES

    NASA Technical Reports Server (NTRS)

    Minner, G. L.

    1994-01-01

    This program was developed to design acoustic liners for turbofan engines. This program combines results from theoretical models of wave alternation in acoustically treated passages with experimental data from full-scale fan noise suppressors. By including experimentally obtained information, the program accounts for real effects such as wall boundary layers, duct terminations, and sound modal structure. The program has its greatest use in generating a number of design specifications to be used for evaluation of trade-offs. The program combines theoretical and empirical data in designing annular acoustic liners. First an estimate of the noise output of the fan is made based on basic fan aerodynamic design variables. Then, using a target noise spectrum after alternation and the estimated fan noise spectrum, a design spectrum is calculated as their difference. Next, the design spectrum is combined with knowledge of acoustic liner performance and the liner design variables to specify the acoustic design. Details of the liner design are calculated by combining the required acoustic impedance with a mathematical model relating acoustic impedance to the physical structure of the liner. Input to the noise prediction part of the program consists of basic fan operating parameters, distance that the target spectrum is to be measured and the target spectrum. The liner design portion of the program requires the required alternation spectrum, desired values of length to height and several option selection parameters. Output from the noise prediction portion is a noise spectrum consisting of discrete tones and broadband noise. This may be used as input to the liner design portion of the program. The liner design portion of the program produces backing depths, open area ratios, and face plate thicknesses. This program is written in FORTRAN V and has been implemented in batch mode on a UNIVAC 1100 series computer with a central memory requirement of 12K (decimal) of 36 bit words.

  14. Investigation of ground reflection and impedance from flyover noise measurements

    NASA Technical Reports Server (NTRS)

    Chapkis, R. L.; Marsh, A. H.

    1978-01-01

    An extensive series of flyover noise tests was conducted for the primary purpose of studying meteorological effects on propagation of aircraft noise. The test airplane, a DC 9-10, flew several level-flight passes at various heights over a taxiway. Two microphone stations were located under the flight path. A total of 37 runs was selected for analysis and processed to obtain a consistant set of 1/3 octave band sound pressure levels at half-second intervals. The goal of the present study was to use the flyover noise data to deduce acoustical reflection coefficients and hence, acoustical impedances.

  15. Acoustics of the piezo-electric pressure probe

    NASA Technical Reports Server (NTRS)

    Dutt, G. S.

    1974-01-01

    Acoustical properties of a piezoelectric device are reported for measuring the pressure in the plasma flow from an MPD arc. A description and analysis of the acoustical behavior in a piezoelectric probe is presented for impedance matching and damping. The experimental results are presented in a set of oscillographic records.

  16. Development and Validation of an Interactive Liner Design and Impedance Modeling Tool

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Jones, Michael G.; Buckley, James L.

    2012-01-01

    The Interactive Liner Impedance Analysis and Design (ILIAD) tool is a LabVIEW-based software package used to design the composite surface impedance of a series of small-diameter quarter-wavelength resonators incorporating variable depth and sharp bends. Such structures are useful for packaging broadband acoustic liners into constrained spaces for turbofan engine noise control applications. ILIAD s graphical user interface allows the acoustic channel geometry to be drawn in the liner volume while the surface impedance and absorption coefficient calculations are updated in real-time. A one-dimensional transmission line model serves as the basis for the impedance calculation and can be applied to many liner configurations. Experimentally, tonal and broadband acoustic data were acquired in the NASA Langley Normal Incidence Tube over the frequency range of 500 to 3000 Hz at 120 and 140 dB SPL. Normalized impedance spectra were measured using the Two-Microphone Method for the various combinations of channel configurations. Comparisons between the computed and measured impedances show excellent agreement for broadband liners comprised of multiple, variable-depth channels. The software can be used to design arrays of resonators that can be packaged into complex geometries heretofore unsuitable for effective acoustic treatment.

  17. Method and apparatus of spectro-acoustically enhanced ultrasonic detection for diagnostics

    DOEpatents

    Vo-Dinh, Tuan; Norton, Stephen J.

    2001-01-01

    An apparatus for detecting a discontinuity in a material includes a source of electromagnetic radiation has a wavelength and an intensity sufficient to induce an enhancement in contrast between a manifestation of an acoustic property in the material and of the acoustic property in the discontinuity, as compared to when the material is not irradiated by the electromagnetic radiation. An acoustic emitter directs acoustic waves to the discontinuity in the material. The acoustic waves have a sensitivity to the acoustic property. An acoustic receiver receives the acoustic waves generated by the acoustic emitter after the acoustic waves have interacted with the material and the discontinuity. The acoustic receiver also generates a signal representative of the acoustic waves received by the acoustic receiver. A processor, in communication with the acoustic receiver and responsive to the signal generated by the acoustic receiver, is programmed to generate informational output about the discontinuity based on the signal generated by the acoustic receiver.

  18. Acoustic microscopy of living cells.

    PubMed Central

    Hildebrand, J A; Rugar, D; Johnston, R N; Quate, C F

    1981-01-01

    This paper reports preliminary results of the observation by acoustic microscopy of living cells in vitro. The scanning acoustic microscope uses high-frequency sound waves to produce images with submicrometer resolution. The contrast observed in acoustic micrographs of living cells depends on the acoustic properties (i.e., density, stiffness, and attenuation) and on the topographic contour of the cell. Variation in distance separating the acoustic lens and the viewed cell also has a profound effect on the image. When the substratum is located at the focal plane, thick regions of the cell show a darkening that can be related to cellular acoustic attenuation (a function of cytoplasmic viscosity). When the top of the cell is placed near the focal plane, concentric bright and dark rings appear in the image. The location of the rings can be related to cell topography, and the ring contrast can be correlated to the stiffness and density of the cell. In addition, the character of the images of single cells varies dramatically when the substratum upon which they are grown is changed to a different material. By careful selection of the substratum, the information content of the acoustic images can be increased. Our analysis of acoustic images of actively motile cells indicates that leading lamella are less dense or stiff than the quiescent trailing processes of the cells. Images PMID:6940179

  19. Experimental Impedance of Single Liner Elements with Bias Flow

    NASA Technical Reports Server (NTRS)

    Follet, J. I.; Betts, J. F.; Kelly, Jeffrey J.; Thomas, Russell H.

    2000-01-01

    An experimental investigation was conducted to generate a high quality database, from which the effects of a mean bias flow on the acoustic impedance of lumped-element single-degree-of-freedom liners was determined. Acoustic impedance measurements were made using the standard two-microphone method in the NASA Langley Normal Incidence Tube. Each liner consisted of a perforated sheet with a constant-area cavity. Liner resistance was shown to increase and to become less frequency and sound pressure level dependent as the bias flow was increased. The resistance was also consistently lower for a negative bias flow (suction) than for a positive bias flow (blowing) of equal magnitude. The slope of the liner reactance decreased with increased flow.

  20. Topological Acoustics

    NASA Astrophysics Data System (ADS)

    Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile

    2015-03-01

    The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers.

  1. Topological acoustics.

    PubMed

    Yang, Zhaoju; Gao, Fei; Shi, Xihang; Lin, Xiao; Gao, Zhen; Chong, Yidong; Zhang, Baile

    2015-03-20

    The manipulation of acoustic wave propagation in fluids has numerous applications, including some in everyday life. Acoustic technologies frequently develop in tandem with optics, using shared concepts such as waveguiding and metamedia. It is thus noteworthy that an entirely novel class of electromagnetic waves, known as "topological edge states," has recently been demonstrated. These are inspired by the electronic edge states occurring in topological insulators, and possess a striking and technologically promising property: the ability to travel in a single direction along a surface without backscattering, regardless of the existence of defects or disorder. Here, we develop an analogous theory of topological fluid acoustics, and propose a scheme for realizing topological edge states in an acoustic structure containing circulating fluids. The phenomenon of disorder-free one-way sound propagation, which does not occur in ordinary acoustic devices, may have novel applications for acoustic isolators, modulators, and transducers. PMID:25839273

  2. Effects of Liner Length and Attenuation on NASA Langley Impedance Eduction

    NASA Technical Reports Server (NTRS)

    Jones, M. G.; Watson, W. R.

    2016-01-01

    This study explores the effects of liner length and attenuation on the CHE (convected Helmholtz equation) impedance eduction method, in which the surface impedance of an acoustic liner is inferred through an iterative process based on repeated solutions to the convected Helmholtz equation. Wire mesh-over-honeycomb and perforate-over-honeycomb acoustic liners are tested in the NASA Langley Grazing Flow Impedance Tube, and the resultant data are processed using two impedance eduction methods. The first is the CHE method, and the second is a direct method (labeled the KT method) that uses the Kumaresan and Tufts algorithm to compute the impedance directly. The CHE method has been extensively used for acoustic liner evaluation, but experiences anomalous behavior under some test conditions. It is postulated that the anomalies are related to the liner length and/or attenuation. Since the KT method only employs data measured over the length of the liner, it is expected to be unaffected by liner length. A comparison of results achieved with the two impedance eduction methods is used to explore the interactive effects of liner length and attenuation on the CHE impedance eduction method.

  3. Acoustic neuroma

    MedlinePlus

    Vestibular schwannoma; Tumor - acoustic; Cerebellopontine angle tumor; Angle tumor ... 177. Battista RA. Gamma knife radiosurgery for vestibular schwannoma. Otolaryngol Clin North Am . 2009;42:635-654. ...

  4. Acoustic focusing by an array of heat sources in air

    NASA Astrophysics Data System (ADS)

    Ge, Yong; Sun, Hong-xiang; Liu, Chen; Qian, Jiao; Yuan, Shou-qi; Xia, Jian-ping; Guan, Yi-jun; Zhang, Shu-yi

    2016-06-01

    We report on a broadband acoustic focusing lens comprising 20 heat sources of different temperatures, 10 on each side of the array, in air. This focusing phenomenon is attributed to temperature gradients inducing the desired refractive index in one medium (air) and to the continuously changing acoustic impedance, which avoids any acoustic impedance difference that would occur between a lens and air. The results indicate that this focusing lens has a broader bandwidth (>3.5 kHz), higher intensity amplification (about 5.0 times), and a simpler structure. This focusing lens has great potential for applications in ultrasonic devices.

  5. Broadband metamaterial for nonresonant matching of acoustic waves

    NASA Astrophysics Data System (ADS)

    D'Aguanno, G.; Le, K. Q.; Trimm, R.; Alù, A.; Mattiucci, N.; Mathias, A. D.; Aközbek, N.; Bloemer, M. J.

    2012-03-01

    Unity transmittance at an interface between bulk media is quite common for polarized electromagnetic waves incident at the Brewster angle, but it is rarely observed for sound waves at any angle of incidence. In the following, we theoretically and experimentally demonstrate an acoustic metamaterial possessing a Brewster-like angle that is completely transparent to sound waves over an ultra-broadband frequency range with >100% bandwidth. The metamaterial, consisting of a hard metal with subwavelength apertures, provides a surface impedance matching mechanism that can be arbitrarily tailored to specific media. The nonresonant nature of the impedance matching effectively decouples the front and back surfaces of the metamaterial allowing one to independently tailor the acoustic impedance at each interface. On the contrary, traditional methods for acoustic impedance matching, for example in medical imaging, rely on resonant tunneling through a thin antireflection layer, which is inherently narrowband and angle specific.

  6. Limitations of the acoustic approximation for seismic crosshole tomography

    NASA Astrophysics Data System (ADS)

    Marelli, Stefano; Maurer, Hansruedi

    2010-05-01

    Modelling and inversion of seismic crosshole data is a challenging task in terms of computational resources. Even with the significant increase in power of modern supercomputers, full three-dimensional elastic modelling of high-frequency waveforms generated from hundreds of source positions in several boreholes is still an intractable task. However, it has been recognised that full waveform inversion offers substantially more information compared with traditional travel time tomography. A common strategy to reduce the computational burden for tomographic inversion is to approximate the true elastic wave propagation by acoustic modelling. This approximation assumes that the solid rock units can be treated like fluids (with no shear wave propagation) and is generally considered to be satisfactory so long as only the earliest portions of the recorded seismograms are considered. The main assumption is that most of the energy in the early parts of the recorded seismograms is carried by the faster compressional (P-) waves. Although a limited number of studies exist on the effects of this approximation for surface/marine synthetic reflection seismic data, and show it to be generally acceptable for models with low to moderate impedance contrasts, to our knowledge no comparable studies have been published on the effects for cross-borehole transmission data. An obvious question is whether transmission tomography should be less affected by elastic effects than surface reflection data when only short time windows are applied to primarily capture the first arriving wavetrains. To answer this question we have performed 2D and 3D investigations on the validity of the acoustic approximation for an elastic medium and using crosshole source-receiver configurations. In order to generate consistent acoustic and elastic data sets, we ran the synthetic tests using the same finite-differences time-domain elastic modelling code for both types of simulations. The acoustic approximation was

  7. Musical Acoustics

    NASA Astrophysics Data System (ADS)

    Gough, Colin

    This chapter provides an introduction to the physical and psycho-acoustic principles underlying the production and perception of the sounds of musical instruments. The first section introduces generic aspects of musical acoustics and the perception of musical sounds, followed by separate sections on string, wind and percussion instruments.

  8. Two- and three-electrode impedance studies on 18650 Li-ion cells

    NASA Astrophysics Data System (ADS)

    Nagasubramanian, G.

    Two- and three-electrode impedance measurements were made on 18650 Li-ion cells at different temperatures ranging from 35°C to -40°C. The ohmic resistance of the cell is nearly constant in the temperature range studied although the total cell impedance increases by an order of magnitude in the same temperature range. In contrast to what is commonly believed, we show from our three-electrode impedance results that, the increase in cell impedance comes mostly from the cathode and not from the anode. Further, the anode and cathode contribute to both the impedance loops (in the NyQuist plot).

  9. Two and Three-Electrode Impedance Studies on 18650 Li-Ion Cells

    SciTech Connect

    Nagasubramanian, Ganesan

    1999-08-11

    Two and three electrode impedance measurements were made on 18650 Li-ion cells at different QB temperatures ranging from 35 C to {minus}40 C. The ohmic resistance of the cell is nearly constant the temperature range studied although the total cell impedance increases by an order of magnitude in the same temperature range. In contrast to what is commonly believed, we show from our three-electrode impedance results that, the increase in cell impedance comes mostly from the cathode and not from the anode. Further, the anode and cathode contribute to both the impedance loops (in the NyQuist plot).

  10. Piezoelectric materials used in underwater acoustic transducers

    SciTech Connect

    Li, Huidong; Deng, Zhiqun; Carlson, Thomas J.

    2012-07-07

    Piezoelectric materials have been used in underwater acoustic transducers for nearly a century. In this paper, we reviewed four different types of piezoelectric materials: piezoelectric ceramics, single crystals, composites, and polymers, which are widely used in underwater acoustic transducers nowadays. Piezoelectric ceramics are the most dominant material type and are used as a single-phase material or one of the end members in composites. Piezoelectric single crystals offer outstanding electromechanical response but are limited by their manufacturing cost. Piezoelectric polymers provide excellent acoustic impedance matching and transducer fabrication flexibility although their piezoelectric properties are not as good as ceramics and single crystals. Composites combined the merits of ceramics and polymers and are receiving increased attention. The typical structure and electromechanical properties of each type of materials are introduced and discussed with respect to underwater acoustic transducer applications. Their advantages and disadvantages are summarized. Some of the critical design considerations when developing underwater acoustic transducers with these materials are also touched upon.

  11. Comparative Study of Impedance Eduction Methods, Part 2: NASA Tests and Methodology

    NASA Technical Reports Server (NTRS)

    Jones, Michael G.; Watson, Willie R.; Howerton, Brian M.; Busse-Gerstengarbe, Stefan

    2013-01-01

    A number of methods have been developed at NASA Langley Research Center for eduction of the acoustic impedance of sound-absorbing liners mounted in the wall of a flow duct. This investigation uses methods based on the Pridmore-Brown and convected Helmholtz equations to study the acoustic behavior of a single-layer, conventional liner fabricated by the German Aerospace Center and tested in the NASA Langley Grazing Flow Impedance Tube. Two key assumptions are explored in this portion of the investigation. First, a comparison of results achieved with uniform-flow and shear-flow impedance eduction methods is considered. Also, an approach based on the Prony method is used to extend these methods from single-mode to multi-mode implementations. Finally, a detailed investigation into the effects of harmonic distortion on the educed impedance is performed, and the results are used to develop guidelines regarding acceptable levels of harmonic distortion

  12. Wave guide impedance matching method and apparatus

    DOEpatents

    Kronberg, James W.

    1990-01-01

    A technique for modifying the end portion of a wave guide, whether hollow or solid, carrying electromagnetic, acoustic or optical energy, to produce a gradual impedance change over the length of the end portion, comprising the cutting of longitudinal, V-shaped grooves that increase in width and depth from beginning of the end portion of the wave guide to the end of the guide so that, at the end of the guide, no guide material remains and no surfaces of the guide as modified are perpendicular to the direction of energy flow. For hollow guides, the grooves are cut beginning on the interior surface; for solid guides, the grooves are cut beginning on the exterior surface. One or more resistive, partially conductive or nonconductive sleeves can be placed over the exterior of the guide and through which the grooves are cut to smooth the transition to free space.

  13. Acoustical properties of highly porous fibrous materials

    NASA Technical Reports Server (NTRS)

    Lambert, R. F.

    1979-01-01

    Highly porous, fibrous bulk sound absorbing materials are studied with a view toward understanding their acoustical properties and performance in a wide variety of applications including liners of flow ducts. The basis and criteria for decoupling of acoustic waves in the pores of the frame and compressional waves in the frame structure are established. The equations of motion are recast in a form that elucidates the coupling mechanisms. The normal incidence surface impedance and absorption coefficient of two types of Kevlar 29 and an open celled foam material are studied. Experimental values and theoretical results are brought into agreement when the structure factor is selected to provide a fit to the experimental data. A parametric procedure for achieving that fit is established. Both a bulk material quality factor and a high frequency impedance level are required to characterize the real and imaginary part of the surface impedance and absorption coefficient. A derivation of the concepts of equivalent density and dynamic resistance is presented.

  14. Ionospheric effects to antenna impedance

    NASA Technical Reports Server (NTRS)

    Bethke, K. H.

    1986-01-01

    The reciprocity between high power satellite antennas and the surrounding plasma are examined. The relevant plasma states for antenna impedance calculations are presented and plasma models, and hydrodynamic and kinetic theory, are discussed. A theory from which a variation in antenna impedance with regard to the radiated power can be calculated for a frequency range well above the plasma resonance frequency is give. The theory can include photo and secondary emission effects in antenna impedance calculations.

  15. Reflection and Scattering of Acoustical Waves from a Discontinuity in Absorption

    NASA Astrophysics Data System (ADS)

    Jones, J. P.; Leeman, S.; Nolan, E.; Lee, D.

    The reflection and transmission of a plane acoustical wave from a planar boundary at the interface between two homogeneous media of different acoustical properties is a classical problem in acoustics that has served as a basis for many developments in acoustics for over 100 years. This problem, detailed in virtually every textbook on acoustics, provides us with the acoustical analogue to Snell's Law in optics and gives us correspondingly simple results. Classical acoustics predicts that a reflection from a boundary occurs only if the characteristic acoustical impedances of the two media are different. Here we show that a reflection also occurs if the media have the same impedances but different absorption coefficients. Our analysis yields some surprising results. For example, a reflection will occur at a discontinuity in absorption even if the impedance is uniform and continuous across the interface. In addition, a discontinuity in impedance at an interface between two media that have constant and equal, but non-zero absorption, results in a reflection coefficient that is dependent on absorption as well as impedance. In general, reflection coefficients now become frequency dependent. To experimentally test our results, we measured the reflection at the interface between water and castor oil, two liquids with similar impedances but very different absorption coefficients. Measurement of the reflection coefficient between 1 and 50 MHz demonstrated a frequency dependence that was in good agreement with our analysis.

  16. Optically stimulated differential impedance spectroscopy

    DOEpatents

    Maxey, Lonnie C; Parks, II, James E; Lewis, Sr., Samuel A; Partridge, Jr., William P

    2014-02-18

    Methods and apparatuses for evaluating a material are described. Embodiments typically involve use of an impedance measurement sensor to measure the impedance of a sample of the material under at least two different states of illumination. The states of illumination may include (a) substantially no optical stimulation, (b) substantial optical stimulation, (c) optical stimulation at a first wavelength of light, (d) optical stimulation at a second wavelength of light, (e) a first level of light intensity, and (f) a second level of light intensity. Typically a difference in impedance between the impedance of the sample at the two states of illumination is measured to determine a characteristic of the material.

  17. IMPEDANCE OF FINITE LENGTH RESISTOR

    SciTech Connect

    KRINSKY, S.; PODOBEDOV, B.; GLUCKSTERN, R.L.

    2005-05-15

    We determine the impedance of a cylindrical metal tube (resistor) of radius a, length g, and conductivity {sigma}, attached at each end to perfect conductors of semi-infinite length. Our main interest is in the asymptotic behavior of the impedance at high frequency, k >> 1/a. In the equilibrium regime, , the impedance per unit length is accurately described by the well-known result for an infinite length tube with conductivity {sigma}. In the transient regime, ka{sup 2} >> g, we derive analytic expressions for the impedance and wakefield.

  18. Bound states in one-dimensional acoustic parity-time-symmetric lattices for perfect sensing

    NASA Astrophysics Data System (ADS)

    Zhao, Degang; Shen, Yaxi; Zhang, Yu; Zhu, Xuefeng; Yi, Lin

    2016-08-01

    In this letter, we study the propagation of acoustic waves through a one-dimensional multilayer structure composed of a thin defect layer sandwiched by two phononic crystals. Two kinds of defect states will generate in band gaps and both of them cause unitary transmission. However, they have very unlike field distributions due to the different contrasted acoustic impedances between the defect layer and its neighboring layers. Spectral positions of transmission peaks can be exactly determined by the resonant phase condition. In a non-dissipative system, these resonant states correspond to single crossing point of two eigenvalues of scattering matrix. When gain and loss are introduced to judiciously construct an acoustic parity-time-symmetric lattice, the crossing point will split into a pair of exceptional points (EPs). Interestingly, the EPs correspond to unidirectional zero reflection that is very sensitive to the thickness of defect layer. Taking advantage of this virtue, a very sensitive acoustic sensor can be designed, which has potentially applications in ultrasonic inspection, noise detection, ultrasonic medicine, etc.

  19. Monolithically compatible impedance measurement

    DOEpatents

    Ericson, Milton Nance; Holcomb, David Eugene

    2002-01-01

    A monolithic sensor includes a reference channel and at least one sensing channel. Each sensing channel has an oscillator and a counter driven by the oscillator. The reference channel and the at least one sensing channel being formed integrally with a substrate and intimately nested with one another on the substrate. Thus, the oscillator and the counter have matched component values and temperature coefficients. A frequency determining component of the sensing oscillator is formed integrally with the substrate and has an impedance parameter which varies with an environmental parameter to be measured by the sensor. A gating control is responsive to an output signal generated by the reference channel, for terminating counting in the at least one sensing channel at an output count, whereby the output count is indicative of the environmental parameter, and successive ones of the output counts are indicative of changes in the environmental parameter.

  20. Bioelectrical impedance analysis revisited.

    PubMed

    Mikes, D M; Cha, B A; Dym, C L; Baumgaertner, J; Hartzog, A G; Tacey, A D; Calabria, M R

    1999-12-01

    Although total limb volume measurements are used to track the progress of lymphedema and its treatment, these measurements can be confounded by changes other than fluid excess namely muscle or fat gain. Bioelectrical impedance analysis (BIA) is a technique that specifically quantifies both total body fluid and extracellular fluid in extremities. Whereas BIA has potential as a quick, inexpensive, and quantitative technique to measure directly fluid gain or loss from lymphedema, it also has certain shortcomings that must be addressed before it can be validated. this paper examines the back-ground that explains why measuring total limb volume is insufficient to quantify the extent of peripheral lymphedema and explores the advantages and drawbacks of using BIA for this purpose. PMID:10652699

  1. Acousto-electrical speckle pattern in Lorentz force electrical impedance tomography

    NASA Astrophysics Data System (ADS)

    Grasland-Mongrain, Pol; Destrempes, François; Mari, Jean-Martial; Souchon, Rémi; Catheline, Stefan; Chapelon, Jean-Yves; Lafon, Cyril; Cloutier, Guy

    2015-05-01

    Ultrasound speckle is a granular texture pattern appearing in ultrasound imaging. It can be used to distinguish tissues and identify pathologies. Lorentz force electrical impedance tomography is an ultrasound-based medical imaging technique of the tissue electrical conductivity. It is based on the application of an ultrasound wave in a medium placed in a magnetic field and on the measurement of the induced electric current due to Lorentz force. Similarly to ultrasound imaging, we hypothesized that a speckle could be observed with Lorentz force electrical impedance tomography imaging. In this study, we first assessed the theoretical similarity between the measured signals in Lorentz force electrical impedance tomography and in ultrasound imaging modalities. We then compared experimentally the signal measured in both methods using an acoustic and electrical impedance interface. Finally, a bovine muscle sample was imaged using the two methods. Similar speckle patterns were observed. This indicates the existence of an ‘acousto-electrical speckle’ in the Lorentz force electrical impedance tomography with spatial characteristics driven by the acoustic parameters but due to electrical impedance inhomogeneities instead of acoustic ones as is the case of ultrasound imaging.

  2. Evaluation of human middle ear function via an acoustic power assessment.

    PubMed

    Allen, Jont B; Jeng, Patricia S; Levitt, Harry

    2005-01-01

    Measurements of middle ear (ME) acoustic power flow (power reflectance, power absorption, and transmittance) and normalized impedance (acoustic resistance, acoustic reactance, and impedance magnitude) were compared for their utility in clinical applications. Transmittance, a measure of the acoustic power absorbed by the ME, was found to have several important advantages over other measures of acoustic power flow. In addition to its simple and audiologically relevant physical interpretation (absorbed power), the normal transmittance curve has a simple shape that is visually similar to the ME transfer function. The acoustic impedance measures (resistance and reactance) provided important additional information about ME status and supplemented transmittance measurements. Together these measurements can help identify unusual conditions such as eardrum perforations. While this article is largely a review of the development of a commercial power reflectance measurement system, previously unpublished experimental results are presented. PMID:16470465

  3. Analysis of left ventricular impedance in comparison with ultrasound images.

    PubMed

    Choi, Seong Wook; Park, Sung Min

    2012-05-01

    Cardiac monitoring of ventricular assist devices (VADs) is important for detecting heart failure risks, such as critical arrhythmia and ventricular fibrillation, and for supplying data that are useful for hemodynamic control. Specifically, impedance cardiograms (ICGs) are especially beneficial because they have no effect on the tissue or organs and can monitor various parameters simultaneously, including the heart rate and heart contractions. In this article, we measured impedance changes in porcine left ventricles using electrodes placed around the inlet and outlet cannulae of the VAD. The measured left ventricular impedance (LVI) waveform changes are caused by heart movements, such as cardiac muscle contraction and changes in blood volume as a result of heart filling and emptying. In contrast to other impedance measurements, LVI is less affected by the movement of other organs. Using a porcine model, LVIs were measured and compared with blood flow data measured with an ultrasound blood flowmeter. The ICG showed the same frequency as the animal's heart rate, and their amplitudes were closely related to cardiac output (CO). However, the waveform differed from other vital signs, such as CO, electrocardiogram, and blood pressure. Ultrasound images were used to explain the impedance waveform. In the ultrasound images, we obtained the shape and size of the animal's heart and calculated the predicted impedance data. We then compared these to the actual measured data. These results show that the impedance signal contains detailed information on heart rate and CO; these results were unaffected by the cannulae or VAD perfusion. PMID:22188560

  4. Acoustic Properties of Lens Materials for Ultrasonic Probes

    NASA Astrophysics Data System (ADS)

    Fujii, Hideji; Nakaya, Chitose; Takeuchi, Hiroshi; Kondo, Toshio; Ishikawa, Yasuo

    1995-01-01

    The acoustic velocities and densities of 20 types of commercial rubber have been measured at a frequency of 2 MHz at room temperature, and they are evaluated in terms of their application to an acoustic lens or an acoustic window of probes of an ultrasonic diagnostic instrument. Fluorosilicone rubber and phoshazene rubber have lower acoustic velocities than the human body, and they have excellent impedance matching with the human body. Both the acoustic velocities and densities of butadiene rubber, polybutadiene rubber, acrylic rubber and polyurethane match those of the human body. It is also described that rubber having good impedance matching with the human body can be fabricated by adjusting the volume fraction of the added filler.

  5. The development of algorithms in electrical impedance computerized tomography.

    PubMed

    Shie, J R; Li, C J; Lin, J T

    2000-01-01

    Electrical Impedance Computerized Tomography (EICT) is an imaging method to reconstruct the impedance distribution inside of domain through the boundary injected current and display the impedance contrast ratio as an image. This paper concentrates on developing two algorithms to enhance the quality of the conductivity image. The two algorithms are "Fine-Mesh Conversion Method" and "Sub-Domain EICT Method". "Fine-Mesh Conversion Method" is a numerical calibration process to find a coarse mesh impedance network that behaves like a fine mesh network in terms of giving similar voltages under the same current excitations. "Sub-Domain EICT" solves a higher resolution EICT with the cost of a lower resolution EICT by combining "Fine-Mesh Conversion Method", and a Fuzzy Logic Inference Systems (FLIS) classifier. PMID:10834231

  6. Impedance in School Screening Programs.

    ERIC Educational Resources Information Center

    Robarts, John T.

    1985-01-01

    This paper examines the controversy over use of impedance screening in public schools to identify students with hearing problems, including otitis media, a common ear condition in infants and young children. It cites research that questions the value of pure tone screening as a single test and raises critics' objections to the use of impedance,…

  7. Ultra-wideband impedance sensor

    DOEpatents

    McEwan, Thomas E.

    1999-01-01

    The ultra-wideband impedance sensor (UWBZ sensor, or Z-sensor) is implemented in differential and single-ended configurations. The differential UWBZ sensor employs a sub-nanosecond impulse to determine the balance of an impedance bridge. The bridge is configured as a differential sample-and-hold circuit that has a reference impedance side and an unknown impedance side. The unknown impedance side includes a short transmission line whose impedance is a function of the near proximity of objects. The single-ended UWBZ sensor eliminates the reference side of the bridge and is formed of a sample and hold circuit having a transmission line whose impedance is a function of the near proximity of objects. The sensing range of the transmission line is bounded by the two-way travel time of the impulse, thereby eliminating spurious Doppler modes from large distant objects that would occur in a microwave CW impedance bridge. Thus, the UWBZ sensor is a range-gated proximity sensor. The Z-sensor senses the near proximity of various materials such as metal, plastic, wood, petroleum products, and living tissue. It is much like a capacitance sensor, yet it is impervious to moisture. One broad application area is the general replacement of magnetic sensors, particularly where nonferrous materials need to be sensed. Another broad application area is sensing full/empty levels in tanks, vats and silos, e.g., a full/empty switch in water or petroleum tanks.

  8. Ultra-wideband impedance sensor

    DOEpatents

    McEwan, T.E.

    1999-03-16

    The ultra-wideband impedance sensor (UWBZ sensor, or Z-sensor) is implemented in differential and single-ended configurations. The differential UWBZ sensor employs a sub-nanosecond impulse to determine the balance of an impedance bridge. The bridge is configured as a differential sample-and-hold circuit that has a reference impedance side and an unknown impedance side. The unknown impedance side includes a short transmission line whose impedance is a function of the near proximity of objects. The single-ended UWBZ sensor eliminates the reference side of the bridge and is formed of a sample and hold circuit having a transmission line whose impedance is a function of the near proximity of objects. The sensing range of the transmission line is bounded by the two-way travel time of the impulse, thereby eliminating spurious Doppler modes from large distant objects that would occur in a microwave CW impedance bridge. Thus, the UWBZ sensor is a range-gated proximity sensor. The Z-sensor senses the near proximity of various materials such as metal, plastic, wood, petroleum products, and living tissue. It is much like a capacitance sensor, yet it is impervious to moisture. One broad application area is the general replacement of magnetic sensors, particularly where nonferrous materials need to be sensed. Another broad application area is sensing full/empty levels in tanks, vats and silos, e.g., a full/empty switch in water or petroleum tanks. 2 figs.

  9. Room Acoustics

    NASA Astrophysics Data System (ADS)

    Kuttruff, Heinrich; Mommertz, Eckard

    The traditional task of room acoustics is to create or formulate conditions which ensure the best possible propagation of sound in a room from a sound source to a listener. Thus, objects of room acoustics are in particular assembly halls of all kinds, such as auditoria and lecture halls, conference rooms, theaters, concert halls or churches. Already at this point, it has to be pointed out that these conditions essentially depend on the question if speech or music should be transmitted; in the first case, the criterion for transmission quality is good speech intelligibility, in the other case, however, the success of room-acoustical efforts depends on other factors that cannot be quantified that easily, not least it also depends on the hearing habits of the listeners. In any case, absolutely "good acoustics" of a room do not exist.

  10. Acoustic Neuroma

    MedlinePlus

    ... slow growing tumor which arise primarily from the vestibular portion of the VIII cranial nerve and lie ... you have a "brain tumor" called acoustic neuroma (vestibular schwannoma). You think you are the only one ...

  11. Underwater Acoustics

    NASA Astrophysics Data System (ADS)

    Kuperman, William A.; Roux, Philippe

    It is well underwater established that sound waves, compared to electromagnetic waves, propagate long distances in the ocean. Hence, in the ocean as opposed to air or a vacuum, one uses sound navigation and ranging (SONAR) instead navigation and ranging (SONAR) of radar, acoustic communication instead of radio, and acoustic imaging and tomography instead of microwave or optical imaging or X-ray tomography. Underwater acoustics is the science of sound in water (most commonly in the ocean) and encompasses not only the study of sound propagation, but also the masking of sound signals by interfering phenomenon and signal processing for extracting these signals from interference. This chapter we will present the basics physics of ocean acoustics and then discuss applications.

  12. Electromagnetic scattering by impedance structures

    NASA Technical Reports Server (NTRS)

    Balanis, Constantine A.; Griesser, Timothy

    1987-01-01

    The scattering of electromagnetic waves from impedance structures is investigated, and current work on antenna pattern calculation is presented. A general algorithm for determining radiation patterns from antennas mounted near or on polygonal plates is presented. These plates are assumed to be of a material which satisfies the Leontovich (or surface impedance) boundary condition. Calculated patterns including reflection and diffraction terms are presented for numerious geometries, and refinements are included for antennas mounted directly on impedance surfaces. For the case of a monopole mounted on a surface impedance ground plane, computed patterns are compared with experimental measurements. This work in antenna pattern prediction forms the basis of understanding of the complex scattering mechanisms from impedance surfaces. It provides the foundation for the analysis of backscattering patterns which, in general, are more problematic than calculation of antenna patterns. Further proposed study of related topics, including surface waves, corner diffractions, and multiple diffractions, is outlined.

  13. Electrochemical Impedance Spectroscopy

    NASA Astrophysics Data System (ADS)

    Retter, Utz; Lohse, Heinz

    Non-steady-state measuring techniques are known to be extremely suitable for the investigation of the electrode kinetics of more complex electrochemical systems. Perturbation of the electrochemical system leads to a shift of the steady state. The rate at which it proceeds to a new steady state depends on characteristic parameters (reaction rate constants, diffusion coefficients, charge transfer resistance, double-layer capacity). Due to non-linearities caused by the electron transfer, low-amplitude perturbation signals are necessary. The small perturbation of the electrode state has the advantage that the solutions of relevant mathematical equations used are transformed in limiting forms that are normally linear. Impedance spectroscopy represents a powerful method for investigation of electrical properties of materials and interfaces of conducting electrodes. Relevant fields of application are the kinetics of charges in bulk or interfacial regions, the charge transfer of ionic or mixed ionic-ionic conductors, semiconducting electrodes, the corrosion inhibition of electrode processes, investigation of coatings on metals, characterisation of materials and solid electrolyte as well as solid-state devices.

  14. Acoustic asymmetric transmission based on time-dependent dynamical scattering

    PubMed Central

    Wang, Qing; Yang, Yang; Ni, Xu; Xu, Ye-Long; Sun, Xiao-Chen; Chen, Ze-Guo; Feng, Liang; Liu, Xiao-ping; Lu, Ming-Hui; Chen, Yan-Feng

    2015-01-01

    An acoustic asymmetric transmission device exhibiting unidirectional transmission property for acoustic waves is extremely desirable in many practical scenarios. Such a unique property may be realized in various configurations utilizing acoustic Zeeman effects in moving media as well as frequency-conversion in passive nonlinear acoustic systems and in active acoustic systems. Here we demonstrate a new acoustic frequency conversion process in a time-varying system, consisting of a rotating blade and the surrounding air. The scattered acoustic waves from this time-varying system experience frequency shifts, which are linearly dependent on the blade’s rotating frequency. Such scattering mechanism can be well described theoretically by an acoustic linear time-varying perturbation theory. Combining such time-varying scattering effects with highly efficient acoustic filtering, we successfully develop a tunable acoustic unidirectional device with 20 dB power transmission contrast ratio between two counter propagation directions at audible frequencies. PMID:26038886

  15. Contrastive Lexicology.

    ERIC Educational Resources Information Center

    Hartmann, R. R. K.

    This paper deals with the relation between etymologically related words in different languages. A survey is made of seven stages in the development of contrastive lexicology. These are: prelinguistic word studies, semantics, lexicography, translation, foreign language learning, bilingualism, and finally contrastive analysis. Concerning contrastive…

  16. Impedance Eduction in Sound Fields With Peripherally Varying Liners and Flow

    NASA Technical Reports Server (NTRS)

    Watson, W. R.; Jones, M. G.

    2015-01-01

    A two-dimensional impedance eduction theory is extended to three-dimensional sound fields and peripherally varying duct liners. The approach is to first measure the acoustic pressure field at a series of flush-mounted wall microphones located around the periphery of the flow duct. The numerical solution for the acoustic pressure field at these microphones is also obtained by solving the three-dimensional convected Helmholtz equation using the finite element method. A quadratic objective function based on the difference between the measured and finite element solution is constructed and the unknown impedance function is obtained by minimizing this objective function. Impedance spectra educed for two uniform-structure liners (a wire-mesh and a conventional liner) and a hard-soft-hard peripherally varying liner (for which the soft segment is that of the conventional liner) are presented. Results are presented at three mean flow Mach numbers and fourteen sound source frequencies. The impedance spectra of the uniform-structure liners are also computed using a two-dimensional impedance eduction theory. The primary conclusions of the study are: 1) when measured data is used with the uniform-structure liners, the three-dimensional theory reproduces the same impedance spectra as the two-dimensional theory except for frequencies corresponding to very low or very high liner attenuation; and 2) good agreement between the educed impedance spectra of the uniform structure conventional liner and the soft segment of the peripherally varying liner is obtained.

  17. Broadband manipulation of acoustic wavefronts by pentamode metasurface

    SciTech Connect

    Tian, Ye; Wei, Qi Cheng, Ying; Xu, Zheng; Liu, Xiaojun

    2015-11-30

    An acoustic metasurface with a sub-wavelength thickness can manipulate acoustic wavefronts freely by the introduction of abrupt phase variation. However, the existence of a narrow bandwidth and a low transmittance limits further applications. Here, we present a broadband and highly transparent acoustic metasurface based on a frequency-independent generalized acoustic Snell's law and pentamode metamaterials. The proposal employs a gradient velocity to redirect refracted waves and pentamode metamaterials to improve impedance matching between the metasurface and the background medium. Excellent wavefront manipulation based on the metasurface is further demonstrated by anomalous refraction, generation of non-diffracting Bessel beam, and sub-wavelength flat focusing.

  18. Broadband manipulation of acoustic wavefronts by pentamode metasurface

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Wei, Qi; Cheng, Ying; Xu, Zheng; Liu, Xiaojun

    2015-11-01

    An acoustic metasurface with a sub-wavelength thickness can manipulate acoustic wavefronts freely by the introduction of abrupt phase variation. However, the existence of a narrow bandwidth and a low transmittance limits further applications. Here, we present a broadband and highly transparent acoustic metasurface based on a frequency-independent generalized acoustic Snell's law and pentamode metamaterials. The proposal employs a gradient velocity to redirect refracted waves and pentamode metamaterials to improve impedance matching between the metasurface and the background medium. Excellent wavefront manipulation based on the metasurface is further demonstrated by anomalous refraction, generation of non-diffracting Bessel beam, and sub-wavelength flat focusing.

  19. I/O impedance controller

    DOEpatents

    Ruesch, Rodney; Jenkins, Philip N.; Ma, Nan

    2004-03-09

    There is disclosed apparatus and apparatus for impedance control to provide for controlling the impedance of a communication circuit using an all-digital impedance control circuit wherein one or more control bits are used to tune the output impedance. In one example embodiment, the impedance control circuit is fabricated using circuit components found in a standard macro library of a computer aided design system. According to another example embodiment, there is provided a control for an output driver on an integrated circuit ("IC") device to provide for forming a resistor divider network with the output driver and a resistor off the IC device so that the divider network produces an output voltage, comparing the output voltage of the divider network with a reference voltage, and adjusting the output impedance of the output driver to attempt to match the output voltage of the divider network and the reference voltage. Also disclosed is over-sampling the divider network voltage, storing the results of the over sampling, repeating the over-sampling and storing, averaging the results of multiple over sampling operations, controlling the impedance with a plurality of bits forming a word, and updating the value of the word by only one least significant bit at a time.

  20. Impedance-estimation methods, modeling methods, articles of manufacture, impedance-modeling devices, and estimated-impedance monitoring systems

    DOEpatents

    Richardson, John G.

    2009-11-17

    An impedance estimation method includes measuring three or more impedances of an object having a periphery using three or more probes coupled to the periphery. The three or more impedance measurements are made at a first frequency. Three or more additional impedance measurements of the object are made using the three or more probes. The three or more additional impedance measurements are made at a second frequency different from the first frequency. An impedance of the object at a point within the periphery is estimated based on the impedance measurements and the additional impedance measurements.

  1. Investigation and optimization of a finite element simulation of transducer array systems for 3D ultrasound computer tomography with respect to electrical impedance characteristics

    NASA Astrophysics Data System (ADS)

    Kohout, B.; Pirinen, J.; Ruiter, N. V.

    2012-03-01

    The established standard screening method to detect breast cancer is X-ray mammography. However X-ray mammography often has low contrast for tumors located within glandular tissue. A new approach is 3D Ultrasound Computer Tomography (USCT), which is expected to detect small tumors at an early stage. This paper describes the development, improvement and the results of Finite Element Method (FEM) simulations of the Transducer Array System (TAS) used in our 3D USCT. The focus of this work is on researching the influence of meshing and material parameters on the electrical impedance curves. Thereafter, these findings are used to optimize the simulation model. The quality of the simulation was evaluated by comparing simulated impedance characteristics with measured data of the real TAS. The resulting FEM simulation model is a powerful tool to analyze and optimize transducer array systems applied for USCT. With this simulation model, the behavior of TAS for different geometry modifications was researched. It provides a means to understand the acoustical performances inside of any ultrasound transducer represented by its electrical impedance characteristic.

  2. Acoustic panels using magnetostrictive Metglas

    NASA Astrophysics Data System (ADS)

    Gerver, Michael J.; Goldie, James H.; Makseyn, Scott; Oleksy, John; Doherty, John J.; Remington, Paul

    1999-06-01

    Passive barriers to transmission of sound waves at frequencies below 500 Hz require large masses. Active noise cancellation systems, on the other hand, are complicated and expensive. We are developing a method for noise control, using an array of panels of magnetostrictive Metglas, which combines the low mass and flexibility of active noise control with the relatively low cost and simplicity of passive noise control. The method is based on the well known fact that an acoustic panel with a reaction mass, resonant at the frequency of the sound wave, will completely reflect that wave, simulating an infinite mass. By wrapping a coil around each Metglas panel, and terminating the coil in an impedance, the stiffness of the Metglas, and hence the resonant frequency of the panel, can be controlled by varying the terminal impedance. By choosing a terminal impedance which is itself frequency dependent, the panel can be made to resonate, and hence to have effective infinite mass, at all frequencies (over some fairly large range) simultaneously. This generally requires negative impedance, which can be produced by a simple circuit with an amplifier and feedback loop. In effect, the Metglas acts like both microphone and speaker in an active noise control system. Preliminary experimental results will be presented.

  3. Acoustic biosensors

    PubMed Central

    Fogel, Ronen; Seshia, Ashwin A.

    2016-01-01

    Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g. analyte adsorption) as a modulation in the physical properties of the acoustic wave (e.g. resonant frequency, acoustic velocity, dissipation) that can then be correlated with the amount of adsorbed analyte. These devices can also be miniaturized with advantages in terms of cost, size and scalability, as well as potential additional features including integration with microfluidics and electronics, scaled sensitivities associated with smaller dimensions and higher operational frequencies, the ability to multiplex detection across arrays of hundreds of devices embedded in a single chip, increased throughput and the ability to interrogate a wider range of modes including within the same device. Additionally, device fabrication is often compatible with semiconductor volume batch manufacturing techniques enabling cost scalability and a high degree of precision and reproducibility in the manufacturing process. Integration with microfluidics handling also enables suitable sample pre-processing/separation/purification/amplification steps that could improve selectivity and the overall signal-to-noise ratio. Three device types are reviewed here: (i) bulk acoustic wave sensors, (ii) surface acoustic wave sensors, and (iii) micro/nano-electromechanical system (MEMS/NEMS) sensors. PMID:27365040

  4. Acoustic biosensors.

    PubMed

    Fogel, Ronen; Limson, Janice; Seshia, Ashwin A

    2016-06-30

    Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g. analyte adsorption) as a modulation in the physical properties of the acoustic wave (e.g. resonant frequency, acoustic velocity, dissipation) that can then be correlated with the amount of adsorbed analyte. These devices can also be miniaturized with advantages in terms of cost, size and scalability, as well as potential additional features including integration with microfluidics and electronics, scaled sensitivities associated with smaller dimensions and higher operational frequencies, the ability to multiplex detection across arrays of hundreds of devices embedded in a single chip, increased throughput and the ability to interrogate a wider range of modes including within the same device. Additionally, device fabrication is often compatible with semiconductor volume batch manufacturing techniques enabling cost scalability and a high degree of precision and reproducibility in the manufacturing process. Integration with microfluidics handling also enables suitable sample pre-processing/separation/purification/amplification steps that could improve selectivity and the overall signal-to-noise ratio. Three device types are reviewed here: (i) bulk acoustic wave sensors, (ii) surface acoustic wave sensors, and (iii) micro/nano-electromechanical system (MEMS/NEMS) sensors. PMID:27365040

  5. Narrowband impedance matching layer for high efficiency thickness mode ultrasonic transducers.

    PubMed

    Toda, Minoru

    2002-03-01

    A new matching layer design concept has been proposed for narrowband continuous wave (CW) devices. Analysis has shown that the mechanical impedance of a resonant-type transducer in thickness mode CW operation does not equal its acoustic impedance rhoVs but roughly equals rhoVs/Q, where p is density, Vs is acoustic velocity, and Q is the mechanical quality factor. The value of rhoVs/Q is much lower than the acoustic impedance of water for any transducer material, including lead zirconium titanate (PZT), single crystals, or polyvinylidene fluoride (PVDF). With this new approach, the impedance of the matching layer must also be between water and pVs/Q, but there are few such practical low impedance materials. To realize equivalent low impedance structure, a novel double layer design is presented: a relatively low impedance material (such as polyethylene or polyurethane) on the inside and a relatively high impedance material (such as polyester or metal) on the outside. A high power CW transducer structure was designed and fabricated with PVDF-TrFE (polyvinylidene fluoride trifluoroethylene) to operate at 1.4 MHz. The basic quarter wavelength resonator structure is 0.7-mm alumina/0.2-mm piezo-polymer/0.25-mm polyester, and the matching section is 0.2-mm polyurethane and 0.25-mm polyester. A maximum power output of 6 to 9 W/cm2 with conversion efficiency of 30 to 35% was observed. For the transducer without matching section, the observed power was 3 to 4 W/cm2. Mason's model analyses (1) predict that the traditional matching layer is for broadband purposes and reduces output power both for PZT and PVDF-TrFE (2); this new matching scheme can be applied to PZT high power transducer. This high efficiency technique has application in various CW systems, such as Doppler sensors, interferometry, phase-sensitive imaging, or high energy focused beam systems. PMID:12322878

  6. Contrast Materials

    MedlinePlus

    ... or other reactions to contrast materials are rare, radiology departments are well-equipped to deal with them. ... is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology ...

  7. A short history of bad acoustics.

    PubMed

    Wright, M C M

    2006-10-01

    Every branch of science attracts its share of cranks and pseudoscientists, and acoustics has been no exception. A brief survey of those who touched on acoustics is given with quotations from the more interesting or egregious examples. A contrast is drawn between the nineteenth century contrarian's quarrel with particular theories and the modern new age wholesale rejection of theory. This world-view is traced back to the later scientific writings of Goethe. Examples of pseudoscience applied to biomedical acoustics, architectural acoustics, and audio reproduction are given. PMID:17069279

  8. The acoustic monopole in motion

    NASA Technical Reports Server (NTRS)

    Norum, T. D.; Liu, C. H.

    1976-01-01

    The results of an experiment are presented in which a small monochromatic source which behaves like an acoustic monopole when stationary is moved at a constant speed over an asphalt surface past stationary microphones. An analysis of the monopole moving above a finite impedance reflecting plane is given. The theoretical and experimental results are compared for different ground to observer heights, source frequencies, and source velocities. A computation of the effects of source acceleration on the noise radiated by the monopole is also presented.

  9. Acoustic sensor array extracts physiology during movement

    NASA Astrophysics Data System (ADS)

    Scanlon, Michael V.

    2001-08-01

    An acoustic sensor attached to a person's neck can extract heart and breath sounds, as well as voice and other physiology related to their health and performance. Soldiers, firefighters, law enforcement, and rescue personnel, as well as people at home or in health care facilities, can benefit form being remotely monitored. ARLs acoustic sensor, when worn around a person's neck, picks up the carotid artery and breath sounds very well by matching the sensor's acoustic impedance to that of the body via a gel pad, while airborne noise is minimized by an impedance mismatch. Although the physiological sounds have high SNR, the acoustic sensor also responds to motion-induced artifacts that obscure the meaningful physiology. To exacerbate signal extraction, these interfering signals are usually covariant with the heart sounds, in that as a person walks faster the heart tends to beat faster, and motion noises tend to contain low frequency component similar to the heart sounds. A noise-canceling configuration developed by ARL uses two acoustic sensor on the front sides of the neck as physiology sensors, and two additional acoustic sensor on the back sides of the neck as noise references. Breath and heart sounds, which occur with near symmetry and simultaneously at the two front sensor, will correlate well. The motion noise present on all four sensor will be used to cancel the noise on the two physiology sensors. This report will compare heart rate variability derived from both the acoustic array and from ECG data taken simultaneously on a treadmill test. Acoustically derived breath rate and volume approximations will be introduced as well. A miniature 3- axis accelerometer on the same neckband provides additional noise references to validate footfall and motion activity.

  10. LDV measurement of bird ear vibrations to determine inner ear impedance and middle ear power flow

    NASA Astrophysics Data System (ADS)

    Muyshondt, Pieter G. G.; Pires, Felipe; Dirckx, Joris J. J.

    2016-06-01

    The mechanical behavior of the middle ear structures in birds and mammals is affected by the fluids in the inner ear (IE) that are present behind the oval window. In this study, the aim was to gather knowledge of the acoustic impedance of the IE in the ostrich, to be able to determine the effect on vibrations and power flow in the single-ossicle bird middle ear for future studies. To determine the IE impedance, vibrations of the ossicle were measured for both the quasi-static and acoustic stimulus frequencies. In the acoustic regime, vibrations were measured with a laser Doppler vibrometer and electromagnetic stimulation of the ossicle. The impedance of the inner ear could be determined by means of a simple RLC model in series, which resulted in a stiffness reactance of KIE = 0.20.1012 Pa/m3, an inertial impedance of MIE = 0.652.106 Pa s2/m3, and a resistance of RIE = 1.57.109 Pa s/m. The measured impedance is found to be considerably smaller than what is found for the human IE.

  11. Impedance Eduction in Ducts with Higher-Order Modes and Flow

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.

    2009-01-01

    An impedance eduction technique, previously validated for ducts with plane waves at the source and duct termination planes, has been extended to support higher-order modes at these locations. Inputs for this method are the acoustic pressures along the source and duct termination planes, and along a microphone array located in a wall either adjacent or opposite to the test liner. A second impedance eduction technique is then presented that eliminates the need for the microphone array. The integrity of both methods is tested using three sound sources, six Mach numbers, and six selected frequencies. Results are presented for both a hardwall and a test liner (with known impedance) consisting of a perforated plate bonded to a honeycomb core. The primary conclusion of the study is that the second method performs well in the presence of higher-order modes and flow. However, the first method performs poorly when most of the microphones are located near acoustic pressure nulls. The negative effects of the acoustic pressure nulls can be mitigated by a judicious choice of the mode structure in the sound source. The paper closes by using the first impedance eduction method to design a rectangular array of 32 microphones for accurate impedance eduction in the NASA LaRC Curved Duct Test Rig in the presence of expected measurement uncertainties, higher order modes, and mean flow.

  12. Coupling impedance for modern accelerators

    SciTech Connect

    Heifets, S.A.; Kheifets, S.A. )

    1992-03-10

    A systematic review of theoretical results for the longitudinal and transverse impedances obtained by different methods is presented. The paper comprises definitions, general theorems, modal analysis, a diffraction model, and analytical results. Several new results are included. In particular, necessary and sufficient conditions are given for the independence of the impedance from the beam longitudinal direction. The impedances of two basic simple structures---that of a {ital cavity} and that of a {ital step}---are studied in detail. The transition from the regime of a cavity to the regime of a step is explained, an approximate formula describing this transition is given, and the criterion for determining the applicability of each regime is established. The asymptotic behavior of the impedance for a finite number {ital M} of periodically arranged cavities as a function of {ital M} is studied. The different behaviors of the impedance for a single cavity and that for an infinite number of cavities are explained as resulting from the interference of the diffracted waves. A criterion for determining the transition in the impedance behavior from small {ital M} to large {ital M} is presented.

  13. Comparative Study of Impedance Eduction Methods. Part 1; DLR Tests and Methodology

    NASA Technical Reports Server (NTRS)

    Busse-Gerstengarbe, Stefan; Bake, Friedrich; Enghardt, Lars; Jones, Michael G.

    2013-01-01

    The absorption efficiency of acoustic liners used in aircraft engines is characterized by the acoustic impedance. World wide, many grazing ow test rigs and eduction methods are available that provide values for that impedance. However, a direct comparison and assessment of the data of the di erent rigs and methods is often not possible because test objects and test conditions are quite di erent. Only a few papers provide a direct comparison. Therefore, this paper together with a companion paper, present data measured with a reference test object under similar conditions in the DLR and NASA grazing ow test rigs. Additionally, by applying the in-house methods Liner Impedance Non-Uniform ow Solving algorithm (LINUS, DLR) and Convected Helmhholtz Equation approach (CHE, NASA) on the data sets, similarities and differences due to underlying theory are identi ed and discussed.

  14. Polyimide Aerogels and Porous Membranes for Ultrasonic Impedance Matching to Air

    NASA Technical Reports Server (NTRS)

    Swank, Aaron J.; Sands, Obed S.; Meador, Mary Ann B.

    2014-01-01

    This work investigates acoustic impedance matching materials for coupling 200 kHz ultrasonic signals from air to materials with similar acoustic properties to that of water, flesh, rubber and plastics. Porous filter membranes as well as a new class of cross-linked polyimide aerogels are evaluated. The results indicate that a single impedance matching layer consisting of these new aerogel materials will recover nearly half of the loss in the incident-to-transmitted ultrasound intensity associated with an air/water, air/flesh or air/gelatin boundary. Furthermore, the experimental results are obtained where other uncertainties of the "real world" are present such that the observed impedance matching gains are representative of real-world applications. Performance of the matching layer devices is assessed using the idealized 3-layer model of infinite half spaces, yet the experiments conducted use a finite gelatin block as the destination medium.

  15. Acoustic modeling of the speech organ

    NASA Astrophysics Data System (ADS)

    Kacprowski, J.

    The state of research on acoustic modeling of phonational and articulatory speech producing elements is reviewed. Consistent with the physical interpretation of the speech production process, the acoustic theory of speech production is expressed as the product of three factors: laryngeal involvement, sound transmission, and emanations from the mouth and/or nose. Each of these factors is presented in the form of a simplified mathematical description which provides the theoretical basis for the formation of physical models of the appropriate functional members of this complex bicybernetic system. Vocal tract wall impedance, vocal tract synthesizers, laryngeal dysfunction, vowel nasalization, resonance circuits, and sound wave propagation are discussed.

  16. Contrast lipocryolysis

    PubMed Central

    Pinto, Hernán; Melamed, Graciela

    2014-01-01

    Alternative crystal structures are possible for all lipids and each different crystal structure is called a polymorphic form. Inter-conversion between polymorphisms would imply the possibility of leaning crystal formation toward the most effective polymorphism for adipocyte destruction. Food industry has been tempering lipids for decades. Tempering technology applied to lipocryolysis gave birth to “contrast lipocryolysis”, which involves pre- and post-lipocryolysis fat layer heating as part of a specific tempering protocol. In this study, we evaluated the skinfold thickness of 10 subjects after a single contrast lipocryolysis session and witnessed important and fast reductions. PMID:25068088

  17. Impedance of pistons on a two-layer medium in a planar infinite rigid baffle.

    PubMed

    Hassan, Scott E

    2007-07-01

    An integral transform technique is used to develop a general solution for the impedance of rigid pistons acting on a two-layer medium. The medium consists of a semi-infinite acoustic fluid on a viscoelastic thick plate in a rigid infinite baffle. The stresses acting on the planar baffle, as a result of piston motion, are determined using theory of linear elasticity and are therefore unrestricted in terms of applicable frequency range. The special case of a circular piston is considered and expressions for the self-and mutual impedances are developed and evaluated numerically. Numerical results are compared with classical piston impedance functions and finite-element model results. At low frequencies (k(0)a<1), the self-impedances vary significantly from the classical piston impedance functions due to the shear properties of the viscoelastic medium. In the midfrequency range (1impedances vary from the classical piston impedance functions for moderate viscoelastic layer thicknesses (0.5impedances associated with pistons on a two-layer medium generally exhibit an increased decay, as a function of separation distance, over the classical results. PMID:17614483

  18. A Numerical Theory for Impedance Education in Three-Dimensional Normal Incidence Tubes

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.

    2016-01-01

    A method for educing the locally-reacting acoustic impedance of a test sample mounted in a 3-D normal incidence impedance tube is presented and validated. The unique feature of the method is that the excitation frequency (or duct geometry) may be such that high-order duct modes may exist. The method educes the impedance, iteratively, by minimizing an objective function consisting of the difference between the measured and numerically computed acoustic pressure at preselected measurement points in the duct. The method is validated on planar and high-order mode sources with data synthesized from exact mode theory. These data are then subjected to random jitter to simulate the effects of measurement uncertainties on the educed impedance spectrum. The primary conclusions of the study are 1) Without random jitter the method is in excellent agreement with that for known impedance samples, and 2) Random jitter that is compatible to that found in a typical experiment has minimal impact on the accuracy of the educed impedance.

  19. [Monitoring cervical dilatation by impedance].

    PubMed

    Salvat, J; Lassen, M; Sauze, C; Baud, S; Salvat, F

    1992-01-01

    Several different physics procedures have been tried to mechanize the recording of partograms. Can a measure of impedance of tissue Z using potential difference V, according to Ohm's law V = Z1, and 1 is a constant, be correlated with a measure of cervical dilatation using vaginal examination? This was our hypothesis. The tissue impedance meter was made to our design and applied according to a bipolar procedure. Our work was carried out on 28 patients. 10 patients were registered before labour started in order to test the apparatus and to record the impedance variations without labour taking place, and 18 patients were registered in labour to see whether there was any correlation. The level of impedance in the cervix without labour was 302.7 Ohms with a deviation of 8.2. Using student's t tests it was found that there was a significant correlation (p less than 0.001) in four measurements between the impedance measure and measures obtained by extrapolating the degrees of dilatation calculated from vaginal examination. This is a preliminary study in which we have defined the conditions that are necessary to confirm these first results and to further develop the method. PMID:1401774

  20. Acoustic transducer for acoustic microscopy

    DOEpatents

    Khuri-Yakub, Butrus T.; Chou, Ching H.

    1990-01-01

    A shear acoustic transducer-lens system in which a shear polarized piezoelectric material excites shear polarized waves at one end of a buffer rod having a lens at the other end which excites longitudinal waves in a coupling medium by mode conversion at selected locations on the lens.

  1. Acoustic transducer for acoustic microscopy

    DOEpatents

    Khuri-Yakub, B.T.; Chou, C.H.

    1990-03-20

    A shear acoustic transducer-lens system is described in which a shear polarized piezoelectric material excites shear polarized waves at one end of a buffer rod having a lens at the other end which excites longitudinal waves in a coupling medium by mode conversion at selected locations on the lens. 9 figs.

  2. Broadband enhanced transmission of acoustic waves through serrated metal gratings

    NASA Astrophysics Data System (ADS)

    Qi, Dong-Xiang; Fan, Ren-Hao; Deng, Yu-Qiang; Peng, Ru-Wen; Wang, Mu; Jiangnan University Collaboration

    In this talk, we present our studies on broadband properties of acoustic waves through metal gratings. We have demonstrated that serrated metal gratings, which introduce gradient coatings, can give rise to broadband transmission enhancement of acoustic waves. Here, we have experimentally and theoretically studied the acoustic transmission properties of metal gratings with or without serrated boundaries. The average transmission is obviously enhanced for serrated metal gratings within a wide frequency range, while the Fabry-Perot resonance is significantly suppressed. An effective medium hypothesis with varying acoustic impedance is proposed to analyze the mechanism, which was verified through comparison with finite-element simulation. The serrated boundary supplies gradient mass distribution and gradient normal acoustic impedance, which could efficiently reduce the boundary reflection. Further, by increasing the region of the serrated boundary, we present a broadband high-transmission grating for wide range of incident angle. Our results may have potential applications to broadband acoustic imaging, acoustic sensing and new acoustic devices. References: [1] Dong-Xiang Qi, Yu-Qiang Deng, Di-Hu Xu, Ren-Hao Fan, Ru-Wen Peng, Ze-Guo Chen, Ming-Hui Lu, X. R. Huang and Mu Wang, Appl. Phys. Lett. 106, 011906 (2015); [2] Dong-Xiang Qi, Ren-Hao Fan, Ru-Wen Peng, Xian-Rong Huang, Ming-Hui Lu, Xu Ni, Qing Hu, and Mu Wang, Applied Physics Letters 101, 061912 (2012).

  3. Ensemble averaged surface normal impedance of material using an in-situ technique: preliminary study using boundary element method.

    PubMed

    Otsuru, Toru; Tomiku, Reiji; Din, Nazli Bin Che; Okamoto, Noriko; Murakami, Masahiko

    2009-06-01

    An in-situ measurement technique of a material surface normal impedance is proposed. It includes a concept of "ensemble averaged" surface normal impedance that extends the usage of obtained values to various applications such as architectural acoustics and computational simulations, especially those based on the wave theory. The measurement technique itself is a refinement of a method using a two-microphone technique and environmental anonymous noise, or diffused ambient noise, as proposed by Takahashi et al. [Appl. Acoust. 66, 845-865 (2005)]. Measured impedance can be regarded as time-space averaged normal impedance at the material surface. As a preliminary study using numerical simulations based on the boundary element method, normal incidence and random incidence measurements are compared numerically: results clarify that ensemble averaging is an effective mode of measuring sound absorption characteristics of materials with practical sizes in the lower frequency range of 100-1000 Hz, as confirmed by practical measurements. PMID:19507960

  4. Impedances of Laminated Vacuum Chambers

    SciTech Connect

    Burov, A.; Lebedev, V.; /Fermilab

    2011-06-22

    First publications on impedance of laminated vacuum chambers are related to early 70s: those are of S. C. Snowdon [1] and of A. G. Ruggiero [2]; fifteen years later, a revision paper of R. Gluckstern appeared [3]. All the publications were presented as Fermilab preprints, and there is no surprise in that: the Fermilab Booster has its laminated magnets open to the beam. Being in a reasonable mutual agreement, these publications were all devoted to the longitudinal impedance of round vacuum chambers. The transverse impedance and the flat geometry case were addressed in more recent paper of K. Y. Ng [4]. The latest calculations of A. Macridin et al. [5] revealed some disagreement with Ref. [4]; this fact stimulated us to get our own results on that matter. Longitudinal and transverse impendances are derived for round and flat laminated vacuum chambers. Results of this paper agree with Ref. [5].

  5. Microfabricated Thin Film Impedance Sensor & AC Impedance Measurements

    PubMed Central

    Yu, Jinsong; Liu, Chung-Chiun

    2010-01-01

    Thin film microfabrication technique was employed to fabricate a platinum based parallel-electrode structured impedance sensor. Electrochemical impedance spectroscopy (EIS) and equivalent circuit analysis of the small amplitude (±5 mV) AC impedance measurements (frequency range: 1 MHz to 0.1 Hz) at ambient temperature were carried out. Testing media include 0.001 M, 0.01 M, 0.1 M NaCl and KCl solutions, and alumina (∼3 μm) and sand (∼300 μm) particulate layers saturated with NaCl solutions with the thicknesses ranging from 0.6 mm to 8 mm in a testing cell, and the results were used to assess the effect of the thickness of the particulate layer on the conductivity of the testing solution. The calculated resistances were approximately around 20 MΩ, 4 MΩ, and 0.5 MΩ for 0.001 M, 0.01 M, and 0.1 M NaCl solutions, respectively. The presence of the sand particulates increased the impedance dramatically (6 times and 3 times for 0.001 M and 0.1 M NaCl solutions, respectively). A cell constant methodology was also developed to assess the measurement of the bulk conductivity of the electrolyte solution. The cell constant ranged from 1.2 to 0.8 and it decreased with the increase of the solution thickness. PMID:22219690

  6. Medical Acoustics

    NASA Astrophysics Data System (ADS)

    Beach, Kirk; Dunmire, Barbrina

    Medical acoustics can be subdivided into diagnostics and therapy. Diagnostics are further separated into auditory and ultrasonic methods, and both employ low amplitudes. Therapy (excluding medical advice) uses ultrasound for heating, cooking, permeablizing, activating and fracturing tissues and structures within the body, usually at much higher amplitudes than in diagnostics. Because ultrasound is a wave, linear wave physics are generally applicable, but recently nonlinear effects have become more important, even in low-intensity diagnostic applications.

  7. Acoustic chaos

    SciTech Connect

    Lauterborn, W.; Parlitz, U.; Holzfuss, J.; Billo, A.; Akhatov, I.

    1996-06-01

    Acoustic cavitation, a complex, spatio-temporal dynamical system, is investigated with respect to its chaotic properties. The sound output, the {open_quote}{open_quote}noise{close_quote}{close_quote}, is subjected to time series analysis. The spatial dynamics of the bubble filaments is captured by high speed holographic cinematography and subsequent digital picture processing from the holograms. Theoretical models are put forward for describing the pattern formation. {copyright} {ital 1996 American Institute of Physics.}

  8. Acoustic Microfluidics for Bioanalytical Application

    NASA Astrophysics Data System (ADS)

    Lopez, Gabriel

    2013-03-01

    This talk will present new methods the use of ultrasonic standing waves in microfluidic systems to manipulate microparticles for the purpose of bioassays and bioseparations. We have recently developed multi-node acoustic focusing flow cells that can position particles into many parallel flow streams and have demonstrated the potential of such flow cells in the development of high throughput, parallel flow cytometers. These experiments show the potential for the creation of high throughput flow cytometers in applications requiring high flow rates and rapid detection of rare cells. This talk will also present the development of elastomeric capture microparticles and their use in acoustophoretic separations. We have developed simple methods to form elastomeric particles that are surface functionalized with biomolecular recognition reagents. These compressible particles exhibit negative acoustic contrast in ultrasound when suspended in aqueous media, blood serum or diluted blood. These particles can be continuously separated from cells by flowing them through a microfluidic device that uses an ultrasonic standing wave to align the blood cells, which exhibit positive acoustic contrast, at a node in the acoustic pressure distribution while aligning the negative acoustic contrast elastomeric particles at the antinodes. Laminar flow of the separated particles to downstream collection ports allows for collection of the separated negative contrast particles and cells. Separated elastomeric particles were analyzed via flow cytometry to demonstrate nanomolar detection for prostate specific antigen in aqueous buffer and picomolar detection for IgG in plasma and diluted blood samples. This approach has potential applications in the development of rapid assays that detect the presence of low concentrations of biomarkers (including biomolecules and cells) in a number of biological sample types. We acknowledge support through the NSF Research Triangle MRSEC.

  9. Single Mode Theory for Impedance Eduction in Large-Scale Ducts with Grazing Flow

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Gerhold, Carl H.; Jones, Michael G.; June, Jason C.

    2014-01-01

    An impedance eduction theory for a rigid wall duct containing an acoustic liner with an unknown impedance and uniform grazing flow is presented. The unique features of the theory are: 1) non-planar waves propagate in the hard wall sections of the duct, 2) input data consist solely of complex acoustic pressures acquired on a wall adjacent to the liner, and 3) multiple higher-order modes may exist in the direction perpendicular to the liner and the opposite rigid wall. The approach is to first measure the axial propagation constant of a dominant higher-order mode in the liner sample section. This axial propagation constant is then used in conjunction with a closed-form solution to a reduced form of the convected Helmholtz equation and the wall impedance boundary condition to educe the liner impedance. The theory is validated on a conventional liner whose impedance spectrum is educed in two flow ducts with different cross sections. For the frequencies and Mach numbers of interest, no higher-order modes propagate in the hard wall sections of the smaller duct. A benchmark method is used to educe the impedance spectrum in this duct. A dominant higher-order vertical mode propagates in the larger duct for similar test conditions, and the current theory is applied to educe the impedance spectrum. Results show that when the theory is applied to data acquired in the larger duct with a dominant higher-order vertical mode, the same impedance spectra is educed as that obtained in the small duct where only the plane wave mode is present and the benchmark method is used. This result holds for each higher-order vertical mode that is considered.

  10. Acoustical properties of materials and muffler configurations for the 80 by 120 foot wind tunnel

    NASA Technical Reports Server (NTRS)

    Scharton, T. D.; Sneddon, M. D.

    1977-01-01

    Techniques for measuring the impedance of the muffler configurations and of porous plates with grazing flow were investigated and changes in the configuration parameters to enhance acoustic performance are explored. The feasibility of a pulse reflection technique for measuring the impedance of built-up structures in situ was demonstrated. A second technique involving the use of an open-end impedance tube with grazing flow was used to obtain detailed design data for the perforated plate configuration. Acoustic benefits associated with configuration changes such as curving the baffles, spacing and staggering baffle partitions, and techniques for alleviating baffle self-generated noise are described.

  11. Detachable acoustic electric feedthrough

    NASA Astrophysics Data System (ADS)

    Moss, Scott; Skippen, Jeremy; Konak, Michael; Powlesland, Ian; Galea, Steve

    2010-04-01

    This paper outlines the development and characterisation of a detachable acoustic electric feedthrough (DAEF) to transfer power and data across a metal (or composite) plate. The DAEF approach is being explored as a potential means of wirelessly powering in-situ structural health monitoring systems embedded within aircraft and other high value engineering assets. The DAEF technique operates via two axially aligned piezoelectric-magnet structures mounted on opposite sides of a plate. Magnetic force is used to align the two piezoelectric-magnet structures, to create an acoustic path across a plate. The piezoelectric-magnet structures consisted of Pz26 piezoelectric disk elements bonded to NdFeB magnets, with a standard ultrasonic couplant (High-Z) used between the magnet and plate to facilitate the passage of ultrasound. Measured impedance curves are matched to modeled curves using the Comsol multi-physics software coupled with a particle-swarm approach, allowing optimised Pz26 material parameters to be found (i.e. stiffness, coupling and permittivity matrices). The optimised Pz26 parameters are then used in an axi-symmetric Comsol model to make predictions about the DAEF power transfer, which is then experimentally confirmed. With an apparent input power of 1 VA and 4.2 MHz drive frequency, the measured power transfer efficiency across a 1.6 mm Al plate is ~34%. The effect of various system parameters on power transfer is explored, including bondline thickness and plate thickness. DAEF data communication is modelled using LTspice with three-port one-dimensional piezoelectric models, indicating that data rates of 115 kBit/s are feasible.

  12. Characteristic impedance of microstrip lines

    NASA Technical Reports Server (NTRS)

    Bailey, M. C.; Deshpande, M. D.

    1989-01-01

    The dyadic Green's function for a current embedded in a grounded dielectric slab is used to analyze microstrip lines at millimeter wave frequencies. The dyadic Green's function accounts accurately for fringing fields and dielectric cover over the microstrip line. Using Rumsey's reaction concept, an expression for the characteristic impedance is obtained. The numerical results are compared with other reported results.

  13. The Aberdeen Impedance Imaging System.

    PubMed

    Kulkarni, V; Hutchison, J M; Mallard, J R

    1989-01-01

    The Aberdeen Impedance Imaging System is designed to reconstruct 2 dimensional images of the average distribution of the amplitude and phase of the complex impedance within a 3 dimensional region. The system uses the four electrode technique in a 16 electrode split-array. The system hardware consists of task-orientated electronic modules for: driving a constant current, multiplexing the current drive, demultiplexing peripheral voltages, differential amplification, phase sensitive detection and low-pass filtration, digitisation with a 14 bit analog to digital converter (ADC), and -control logic for the ADC and multiplexors. A BBC microprocessor (Master series), initiates a controlled sequence for the collection of a number of data sets which are averaged and stored on disk. Image reconstruction is by a process of convolution-backprojection similar to the fan-beam reconstruction of computerised tomography and is also known as Equipotential Backprojection. In imaging impedance changes associated with fracture healing the changes may be large enough to allow retrieval of both the amplitude and phase of the complex impedance. Sequential imaging of these changes would necessitate monitoring electronic and electrode drift by imaging an equivalent region of the contralateral limb. Differential images could be retrieved when the image of the normal limb is the image template. Better characterisation of tissues would necessitate a cleaner retrieval of the quadrature signal. PMID:2742979

  14. Calibration of electrical impedance tomography

    SciTech Connect

    Daily, W; Ramirez, A

    2000-05-01

    Over the past 10 years we have developed methods for imaging the electrical resistivity of soil and rock formations. These technologies have been called electrical resistance tomography of ERT (e.g. Daily and Owen, 1991). Recently we have been striving to extend this capability to include images of electric impedance--with a new nomenclature of electrical impedance tomography or EIT (Ramirez et al., 1999). Electrical impedance is simply a generalization of resistance. Whereas resistance is the zero frequency ratio of voltage and current, impedance includes both the magnitude and phase relationship between voltage and current at frequency. This phase and its frequency behavior is closely related to what in geophysics is called induced polarization or (Sumner, 1976). Why is this phase or IP important? IP is known to be related to many physical phenomena of importance so that image of IP will be maps of such things as mineralization and cation exchange IP (Marshall and Madden, 1959). Also, it is likely that IP, used in conjunction with resistivity, will yield information about the subsurface that can not be obtained by either piece of information separately. In order to define the accuracy of our technologies to image impedance we have constructed a physical model of known impedance that can be used as a calibration standard. It consists of 616 resistors, along with some capacitors to provide the reactive response, arranged in a three dimensional structure as in figure 1. Figure 2 shows the construction of the network and defines the coordinate system used to describe it. This network of components is a bounded and discrete version of the unbounded and continuous medium with which we normally work (the subsurface). The network has several desirable qualities: (1) The impedance values are known (to the accuracy of the component values). (2) The component values and their 3D distribution is easily controlled. (3) Error associated with electrode noise is eliminated. (4

  15. Acoustic Immittance, Absorbance, and Reflectance in the Human Ear Canal

    PubMed Central

    Rosowski, John J.; Wilber, Laura Ann

    2015-01-01

    Ear canal measurements of acoustic immittance (a term that groups impedance and its inverse, admittance) and the related quantities of acoustic reflectance and power absorbance have been used to assess auditory function and aid in the differential diagnosis of conductive hearing loss for over 50 years. The change in such quantities after stimulation of the acoustic reflex also has been used in diagnosis. In this article, we define these quantities, describe how they are commonly measured, and discuss appropriate calibration procedures and standards necessary for accurate immittance/reflectance measurements.

  16. Surface area measurement utilizing an acoustic bridge

    PubMed

    Torigoe; Ishii

    2000-05-01

    A new method is proposed for measuring the surface area of an object. The acoustic conductance of a cavity is proportional to the surface area of the cavity inner wall. The surface area of an object thus can be known from the measurement of the acoustic impedance of a chamber in which the object is placed. In order to measure the acoustic impedance accurately; the proposed method employs the acoustic bridge technique. The experimental device is composed of the following elements so arranged that their electric equivalents form a bridge circuit: a measuring chamber in which an object under test is placed and whose volume can be adjusted; a reference chamber whose inner surface area can be varied; a loudspeaker (the signal source) mounted between the two chambers; and a bypass channel at the midpoint of which a microphone (the null detector) is installed. This bridge balances when the volume and the inner surface area of each chamber become equal. The surface area of the object can then be known from the inner surface area of the reference chamber. Several experiments were performed with this device and the success of the proposed method was verified. PMID:10830378

  17. Acoustic lens for capacitive micromachined ultrasonic transducers

    NASA Astrophysics Data System (ADS)

    Chang, Chienliu; Firouzi, Kamyar; Park, Kwan Kyu; Sarioglu, Ali Fatih; Nikoozadeh, Amin; Yoon, Hyo-Seon; Vaithilingam, Srikant; Carver, Thomas; Khuri-Yakub, Butrus T.

    2014-08-01

    Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with traditional piezoelectric transducers in therapeutic ultrasound applications. In this paper we have designed, fabricated and developed an acoustic lens formed on the CMUT to mechanically focus ultrasound. The acoustic lens was designed based on the paraxial theory and made of silicone rubber for acoustic impedance matching and encapsulation. The CMUT was fabricated based on the local oxidation of silicon (LOCOS) and fusion-bonding. The fabricated CMUT was verified to behave like an electromechanical resonator in air and exhibited wideband response with a center frequency of 2.2 MHz in immersion. The fabrication for the acoustic lens contained two consecutive mold castings and directly formed on the surface of the CMUT. Applied with ac burst input voltages at the center frequency, the CMUT with the acoustic lens generated an output pressure of 1.89 MPa (peak-to-peak) at the focal point with an effective focal gain of 3.43 in immersion. Compared to the same CMUT without a lens, the CMUT with the acoustic lens demonstrated the ability to successfully focus ultrasound and provided a viable solution to the miniaturization of the multi-modality forward-looking endoscopes without electrical focusing.

  18. Acoustic properties of alumina colloidal/polymer nano-composite film on silicon.

    PubMed

    Zhang, Rui; Cao, Wenwu; Zhou, Qifa; Cha, Jung Hyui; Shung, K Kirk; Huang, Yuhong

    2007-03-01

    Alumina colloidal/polymer composite films on silicon substrates have been successfully fabricated using the sol-gel method, in which the crystallite sizes of alumina are between 20 and 50 nm. The density and ultrasonic phase velocities in these films with different alumina ratios from 14% to 32% were measured at the desired operating frequency. We have proved that the density, acoustic phase velocities, and hence the acoustic impedance of the nano-composite films increase with the alumina content, which gives us another option of tailoring the acoustic impedance of the nano-composite film for making the matching layer of high-frequency medical ultrasonic transducers. PMID:17375816

  19. A Comparative Study of Four Impedance Eduction Methodologies Using Several Test Liners

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.

    2013-01-01

    A comparative study of four commonly used impedance eduction methods is presented for a range of liner structures and test conditions. Two of the methods are restricted to uniform flow while the other two accommodate both uniform and boundary layer flows. Measurements on five liner structures (a rigid-wall insert, a ceramic tubular liner, a wire mesh liner, a low porosity conventional liner, and a high porosity conventional liner) are obtained using the NASA Langley Grazing Flow Impedance Tube. The educed impedance of each liner is presented for forty-two test conditions (three Mach numbers and fourteen frequencies). In addition, the effects of moving the acoustic source from upstream to downstream and the refractive effects of the mean boundary layer on the wire mesh liner are investigated. The primary conclusions of the study are that: (1) more accurate results are obtained for the upstream source, (2) the uniform flow methods produce nearly identical impedance spectra at and below Mach 0.3 but significant scatter in the educed impedance occurs at the higher Mach number, (3) there is better agreement in educed impedance among the methods for the conventional liners than for the rigid-wall insert, ceramic, or wire mesh liner, and (4) the refractive effects of the mean boundary layer on the educed impedance of the wire mesh liner are generally small except at Mach 0.5.

  20. Acoustic Tooth Cleaner

    NASA Technical Reports Server (NTRS)

    Heyman, J. S.

    1984-01-01

    Acoustically-energized water jet aids in plaque breakdown. Acoustic Wand includes acoustic transducer 1/4 wave plate, and tapered cone. Together elements energize solution of water containing mild abrasive injected into mouth to help prevent calculous buildup.

  1. Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials

    PubMed Central

    Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

    2014-01-01

    Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential. PMID:25354997

  2. Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials

    NASA Astrophysics Data System (ADS)

    Li, Yong; Yu, Gaokun; Liang, Bin; Zou, Xinye; Li, Guangyun; Cheng, Su; Cheng, Jianchun

    2014-10-01

    Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential.

  3. False Paradoxes of Superposition in Electric and Acoustic Waves.

    ERIC Educational Resources Information Center

    Levine, Richard C.

    1980-01-01

    Corrected are several misconceptions concerning the apparently "missing" energy that results when acoustic or electromagnetic waves cancel by destructive interference and the wave impedance reflected to the sources of the wave energy changes so that the input power is reduced. (Author/CS)

  4. A theoretical study of the feasibility of acoustical tweezer: Ray acoustics approach

    NASA Astrophysics Data System (ADS)

    Lee, Jungwoo; Shung, Kirk

    2005-04-01

    Optical tweezer has been found to have many biomedical applications in trapping macromolecules and cells. For the trapping mechanism, there has to be a sharp spatial change in axial optical intensity and the particle size must be much greater than the wavelength. Similar phenomenon may exist in acoustics. This work was undertaken to demonstrate theoretically that it is possible to acoustically trap particles near the focal point if certain conditions are met. Acoustic force exerted on fat tissue in ultrasonic fields is analyzed in ray acoustics regime where the wavelength of acoustic beam is much smaller than the size of the particle. In this paper, the analysis is therefore based on the field pattern produced by a strongly focused 100 MHz ultrasonic transducer with Gaussian intensity distribution. The magnitude of force and Fresnel coefficients at various positions are calculated. According to the simulation results, acoustical tweezer works particularly when the beam width at focus is one wavelength and the tolerance of acoustic impedance mismatch between two media lies within 6.7%. [Work supported by NIH Grant P41-EB2182.

  5. A Reconstruction Algorithm of Magnetoacoustic Tomography with Magnetic Induction for Acoustically Inhomogeneous Tissue

    PubMed Central

    Zhou, Lian; Zhu, Shanan

    2014-01-01

    Magnetoacoustic tomography with Magnetic Induction (MAT-MI) is a noninvasive electrical conductivity imaging approach that measures ultrasound wave induced by magnetic stimulation, for reconstructing the distribution of electrical impedance in biological tissue. Existing reconstruction algorithms for MAT-MI are based on the assumption that the acoustic properties in the tissue are homogeneous. However, the tissue in most parts of human body, has heterogeneous acoustic properties, which leads to potential distortion and blurring of small buried objects in the impedance images. In the present study, we proposed a new algorithm for MAT-MI to image the impedance distribution in tissues with inhomogeneous acoustic speed distributions. With a computer head model constructed from MR images of a human subject, a series of numerical simulation experiments were conducted. The present results indicate that the inhomogeneous acoustic properties of tissues in terms of speed variation can be incorporated in MAT-MI imaging. PMID:24845284

  6. A reconstruction algorithm of magnetoacoustic tomography with magnetic induction for an acoustically inhomogeneous tissue.

    PubMed

    Zhou, Lian; Zhu, Shanan; He, Bin

    2014-06-01

    Magnetoacoustic tomography with magnetic induction (MAT-MI) is a noninvasive electrical conductivity imaging approach that measures ultrasound wave induced by magnetic stimulation, for reconstructing the distribution of electrical impedance in a biological tissue. Existing reconstruction algorithms for MAT-MI are based on the assumption that the acoustic properties in the tissue are homogeneous. However, the tissue in most parts of human body has heterogeneous acoustic properties, which leads to potential distortion and blurring of small buried objects in the impedance images. In this study, we proposed a new algorithm for MAT-MI to image the impedance distribution in tissues with inhomogeneous acoustic speed distributions. With a computer head model constructed from MR images of a human subject, a series of numerical simulation experiments were conducted. The present results indicate that the inhomogeneous acoustic properties of tissues in terms of speed variation can be incorporated in MAT-MI imaging. PMID:24845284

  7. Acoustic transmission enhancement through a soft interlayer with a reactance boundary.

    PubMed

    Quan, Li; Qian, Feng; Liu, Xiaozhou; Gong, Xiufen

    2015-08-01

    Research has shown that acoustic transmission enhancement (ATE) can occur in stiff materials with high acoustic impedance that include a soft interlayer with low acoustic impedance inserted between them without any opening (i.e., without any links between the two stiff materials). Previously, ATE was induced either by coupling acoustic surface waves or Love waves with the Fabry-Perot resonant modes inside the apertures or by the locally resonant modes of the structure. However, in this article ATE is achieved using wave-vector redistribution induced by a reactance boundary. An optimal boundary was designed to adjust the wave vector in the propagation direction, decreasing reflection caused by impedance differences. The role of boundary conditions on ATE was also clarified. PMID:26328694

  8. Optimal impedance on transmission of Lorentz force EMATs

    NASA Astrophysics Data System (ADS)

    Isla, Julio; Seher, Matthias; Challis, Richard; Cegla, Frederic

    2016-02-01

    Electromagnetic-acoustic transducers (EMATs) are attractive for non-destructive inspections because direct contact with the specimen under test is not required. This advantage comes at a high cost in sensitivity and therefore it is important to optimise every aspect of an EMAT. The signal strength produced by EMATs is in part determined by the coil impedance regardless of the transduction mechanism (e.g. Lorentz force, magnetostriction, etc.). There is very little literature on how to select the coil impedance that maximises the wave intensity; this paper addresses that gap. A transformer circuit is used to model the interaction between the EMAT coil and the eddy currents that are generated beneath the coil in the conducting specimen. Expressions for the coil impedances that satisfy the maximum efficiency and maximum power transfer conditions on transmission are presented. To support this analysis, a tunable coil that consists of stacked identical thin layers independently accessed is used so that the coil inductance can be modified while leaving the radiation pattern of the EMAT unaffected.

  9. Laser-induced acoustic imaging of underground objects

    NASA Astrophysics Data System (ADS)

    Li, Wen; DiMarzio, Charles A.; McKnight, Stephen W.; Sauermann, Gerhard O.; Miller, Eric L.

    1999-02-01

    This paper introduces a new demining technique based on the photo-acoustic interaction, together with results from photo- acoustic experiments. We have buried different types of targets (metal, rubber and plastic) in different media (sand, soil and water) and imaged them by measuring reflection of acoustic waves generated by irradiation with a CO2 laser. Research has been focused on the signal acquisition and signal processing. A deconvolution method using Wiener filters is utilized in data processing. Using a uniform spatial distribution of laser pulses at the ground's surface, we obtained 3D images of buried objects. The images give us a clear representation of the shapes of the underground objects. The quality of the images depends on the mismatch of acoustic impedance of the buried objects, the bandwidth and center frequency of the acoustic sensors and the selection of filter functions.

  10. Dynamic response and acoustic fatigue of stiffened composite structure

    NASA Technical Reports Server (NTRS)

    Soovere, J.

    1984-01-01

    The results of acoustic fatigue and dynamic response tests performed on L-1011 graphite-epoxy (GrE) aileron and panel components are reported. The aileron featured glass microballoons between the GrE skins. Tests yielded random fatigue data from double and single cantilever coupons and modal data from impedance hammer and loudspeaker impulses. Numerical and sample test data were obtained on combined acoustic and shear loads, acoustic and thermal loads, random fatigue and damping of the integrally stiffened and secondary bonded panels. The fatigue data indicate a fatigue life beyond 10 million cycles. The acoustic data suggested that noise transmission could be enhanced in the integrally stiffened panels, which were more acoustic-fatigue resistant than were the secondary bonded panels.

  11. Acoustic transducer

    DOEpatents

    Drumheller, D.S.

    1997-12-30

    An acoustic transducer is described comprising a one-piece hollow mandrel into the outer surface of which is formed a recess with sides perpendicular to the central axis of the mandrel and separated by a first distance and with a bottom parallel to the central axis and within which recess are a plurality of washer-shaped discs of a piezoelectric material and at least one disc of a temperature-compensating material with the discs being captured between the sides of the recess in a pre-stressed interference fit, typically at 2,000 psi of compressive stress. The transducer also includes a power supply and means to connect to a measurement device. The transducer is intended to be used for telemetry between a measurement device located downhole in an oil or gas well and the surface. The transducer is of an construction that is stronger with fewer joints that could leak fluids into the recess holding the piezoelectric elements than is found in previous acoustic transducers. 4 figs.

  12. Acoustic transducer

    DOEpatents

    Drumheller, Douglas S.

    1997-01-01

    An acoustic transducer comprising a one-piece hollow mandrel into the outer surface of which is formed a recess with sides perpendicular to the central axis of the mandrel and separated by a first distance and with a bottom parallel to the central axis and within which recess are a plurality of washer-shaped discs of a piezoelectric material and at least one disc of a temperature-compensating material with the discs being captured between the sides of the recess in a pre-stressed interference fit, typically at 2000 psi of compressive stress. The transducer also includes a power supply and means to connect to a measurement device. The transducer is intended to be used for telemetry between a measurement device located downhole in an oil or gas well and the surface. The transducer is of an construction that is stronger with fewer joints that could leak fluids into the recess holding the piezoelectric elements than is found in previous acoustic transducers.

  13. Flow aeroacoustic damping using coupled mechanical-electrical impedance in lined pipeline

    NASA Astrophysics Data System (ADS)

    Chen, Yong; Huang, Yi-Yong; Chen, Xiao-Qian; Bai, Yu-Zhu; Tan, Xiao-Dong

    2015-05-01

    We report a new noise-damping concept which utilizes a coupled mechanical-electrical acoustic impedance to attenuate an aeroacoustic wave propagating in a moving gas confined by a cylindrical pipeline. An electrical damper is incorporated to the mechanical impedance, either through the piezoelectric, electrostatic, or electro-magnetic principles. Our numerical study shows the advantage of the proposed methodology on wave attenuation. With the development of the micro-electro-mechanical system and material engineering, the proposed configuration may be promising for noise reduction. Project supported by the National Natural Science Foundation of China (Grant Nos. 11404405, 91216201, 51205403, and 11302253).

  14. Acousto-electric impedance of ferroelectric phononic superlattice

    NASA Astrophysics Data System (ADS)

    Nusierat, Ola Hassan

    The acousto-electric impedance Z(ƒ) of a ferroelectric phononic superlattice (FPS) is investigated. The analytical derivation of Z(ƒ) and its phase reveal that both are functions of physical parameters such as the electromechanical coupling coefficient, the mechanical quality factor, the domain length and the phase velocity of the plate acoustic waves (PAW). Mathematica code is produced that allows for modeling Z(ƒ) in a two dimensional FPS. It is observed that Z(ƒ) depends on the number of domains in the FPS structure. Fewer domains in the structure might minimize Z(ƒ) or make it approach zero at certain conditions. A series of experiments is performed to investigate the impedance and its phase shift for a ZX-cut periodically poled lithium niobate in the frequency range 3-4 MHz. The experimental results of studying Z(ƒ) and its phase shift are in a good agreement with the developed theory. Experiments reveal the stopband, when an acoustic wavelength is close to a double-length of ferroelectric domain within the inversely poled structure, in which Z(ƒ) has minima close to it. Furthermore, these experiments show that the displacement components of the acoustic mode are decoupled in the transition zone, a small frequency range that extends a few kilohertz from the boundary of the stopband, and the amplitude of those decoupled components goes to zero in that zone. The equations obtained, the computation codes developed, and the experimental investigations can be applied to the ultrasonic transducers and the field of energy harvesting.

  15. Acoustic Treatment Design Scaling Methods. Phase 2

    NASA Technical Reports Server (NTRS)

    Clark, L. (Technical Monitor); Parrott, T. (Technical Monitor); Jones, M. (Technical Monitor); Kraft, R. E.; Yu, J.; Kwan, H. W.; Beer, B.; Seybert, A. F.; Tathavadekar, P.

    2003-01-01

    The ability to design, build and test miniaturized acoustic treatment panels on scale model fan rigs representative of full scale engines provides not only cost-savings, but also an opportunity to optimize the treatment by allowing multiple tests. To use scale model treatment as a design tool, the impedance of the sub-scale liner must be known with confidence. This study was aimed at developing impedance measurement methods for high frequencies. A normal incidence impedance tube method that extends the upper frequency range to 25,000 Hz. without grazing flow effects was evaluated. The free field method was investigated as a potential high frequency technique. The potential of the two-microphone in-situ impedance measurement method was evaluated in the presence of grazing flow. Difficulties in achieving the high frequency goals were encountered in all methods. Results of developing a time-domain finite difference resonator impedance model indicated that a re-interpretation of the empirical fluid mechanical models used in the frequency domain model for nonlinear resistance and mass reactance may be required. A scale model treatment design that could be tested on the Universal Propulsion Simulator vehicle was proposed.

  16. The quantum Hall impedance standard

    NASA Astrophysics Data System (ADS)

    Schurr, J.; Kučera, J.; Pierz, K.; Kibble, B. P.

    2011-02-01

    Alternating current measurements of double-shielded quantum Hall devices have revealed a fascinating property of which only a quantum effect is capable: it can detect its own frequency dependence and convert it to a current dependence which can be used to eliminate both of them. According to an experimentally verified model, the residual frequency dependence is smaller than the measuring uncertainty of 1.3 × 10-9 kHz-1. In this way, a highly precise quantum standard of impedance can be established, without having to correct for any calculated frequency dependence and without the need for any artefact with a calculated frequency dependence. Nothing else like that is known to us and we hope that our results encourage other national metrology institutes to also apply it to impedance metrology and further explore its beautiful properties.

  17. FXR accelerator cavity impedance experiments

    SciTech Connect

    Avalle, C.A.

    1998-01-05

    One of the goals of the present Flash X-Ray (FXR) accelerator upgrade effort [1][2] at Lawrence Livermore National Laboratory (LLNL) is to reduce the cavity transverse impedance, since it has been shown that beam stability is significantly affected by this parameter [3]. Recently, we have evaluated various techniques and cell modifications to accomplish that, both through lab measurements and computer models. A spare cell, identical in every way to cells in the accelerator, was specially modified for the experiments. The impedance measurements were done without the beam, by applying twin-wire techniques. This report describes the results of these experiments and suggests possible cell modifications to improve their performance. The techniques and modifications which are suggested might also be applicable to AHF and DARHT-2 long-pulse accelerator development.

  18. Impedance based automatic electrode positioning.

    PubMed

    Miklody, Daniel; Hohne, Johannes

    2015-08-01

    The position of electrodes in electrical imaging and stimulation of the human brain is an important variable with vast influences on the precision in modeling approaches. Nevertheless, the exact position is obscured by many factors. 3-D Digitization devices can measure the distribution over the scalp surface but remain uncomfortable in application and often imprecise. We demonstrate a new approach that uses solely the impedance information between the electrodes to determine the geometric position. The algorithm involves multidimensional scaling to create a 3 dimensional space based on these impedances. The success is demonstrated in a simulation study. An average electrode position error of 1.67cm over all 6 subjects could be achieved. PMID:26736345

  19. 21 CFR 870.2770 - Impedance plethysmograph.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Impedance plethysmograph. 870.2770 Section 870...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2770 Impedance plethysmograph. (a) Identification. An impedance plethysmograph is a device used to estimate peripheral...

  20. 21 CFR 870.2750 - Impedance phlebograph.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Impedance phlebograph. 870.2750 Section 870.2750...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2750 Impedance phlebograph. (a) Identification. An impedance phlebograph is a device used to provide a visual display of...

  1. 21 CFR 870.2770 - Impedance plethysmograph.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Impedance plethysmograph. 870.2770 Section 870...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2770 Impedance plethysmograph. (a) Identification. An impedance plethysmograph is a device used to estimate peripheral...

  2. 21 CFR 870.2750 - Impedance phlebograph.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Impedance phlebograph. 870.2750 Section 870.2750...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2750 Impedance phlebograph. (a) Identification. An impedance phlebograph is a device used to provide a visual display of...

  3. 21 CFR 870.2750 - Impedance phlebograph.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Impedance phlebograph. 870.2750 Section 870.2750...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2750 Impedance phlebograph. (a) Identification. An impedance phlebograph is a device used to provide a visual display of...

  4. 21 CFR 870.2750 - Impedance phlebograph.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Impedance phlebograph. 870.2750 Section 870.2750...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2750 Impedance phlebograph. (a) Identification. An impedance phlebograph is a device used to provide a visual display of...

  5. 21 CFR 870.2750 - Impedance phlebograph.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Impedance phlebograph. 870.2750 Section 870.2750...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2750 Impedance phlebograph. (a) Identification. An impedance phlebograph is a device used to provide a visual display of...

  6. 21 CFR 870.2770 - Impedance plethysmograph.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Impedance plethysmograph. 870.2770 Section 870...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2770 Impedance plethysmograph. (a) Identification. An impedance plethysmograph is a device used to estimate peripheral...

  7. 21 CFR 870.2770 - Impedance plethysmograph.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Impedance plethysmograph. 870.2770 Section 870...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2770 Impedance plethysmograph. (a) Identification. An impedance plethysmograph is a device used to estimate peripheral...

  8. 21 CFR 870.2770 - Impedance plethysmograph.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Impedance plethysmograph. 870.2770 Section 870...) MEDICAL DEVICES CARDIOVASCULAR DEVICES Cardiovascular Monitoring Devices § 870.2770 Impedance plethysmograph. (a) Identification. An impedance plethysmograph is a device used to estimate peripheral...

  9. Three-Dimensional Acoustic Tissue Model: A Computational Tissue Phantom for Image Analyses

    NASA Astrophysics Data System (ADS)

    Mamou, J.; Oelze, M. L.; O'Brien, W. D.; Zachary, J. F.

    A novel methodology to obtain three-dimensional (3D) acoustic tissue models (3DATMs) is introduced. 3DATMs can be used as computational tools for ultrasonic imaging algorithm development and analysis. In particular, 3D models of biological structures can provide great benefit to better understand fundamentally how ultrasonic waves interact with biological materials. As an example, such models were used to generate ultrasonic images that characterize tumor tissue microstructures. 3DATMs can be used to evaluate a variety of tissue types. Typically, excised tissue is fixed, embedded, serially sectioned, and stained. The stained sections are digitally imaged (24-bit bitmap) with light microscopy. Contrast of each stained section is equalized and an automated registration algorithm aligns consecutive sections. The normalized mutual information is used as a similarity measure, and simplex optimization is conducted to find the best alignment. Both rigid and non-rigid registrations are performed. During tissue preparation, some sections are generally lost; thus, interpolation prior to 3D reconstruction is performed. Interpolation is conducted after registration using cubic Hermite polynoms. The registered (with interpolated) sections yield a 3D histologic volume (3DHV). Acoustic properties are then assigned to each tissue constituent of the 3DHV to obtain the 3DATMs. As an example, a 3D acoustic impedance tissue model (3DZM) was obtained for a solid breast tumor (EHS mouse sarcoma) and used to estimate ultrasonic scatterer size. The 3DZM results yielded an effective scatterer size of 32.9 (±6.1) μm. Ultrasonic backscatter measurements conducted on the same tumor tissue in vivo yielded an effective scatterer size of 33 (±8) μm. This good agreement shows that 3DATMs may be a powerful modeling tool for acoustic imaging applications

  10. Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Jones, Michael G.

    2016-01-01

    Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance.

  11. Miniature Sapphire Acoustic Resonator - MSAR

    NASA Technical Reports Server (NTRS)

    Wang, Rabi T.; Tjoelker, Robert L.

    2011-01-01

    A room temperature sapphire acoustics resonator incorporated into an oscillator represents a possible opportunity to improve on quartz ultrastable oscillator (USO) performance, which has been a staple for NASA missions since the inception of spaceflight. Where quartz technology is very mature and shows a performance improvement of perhaps 1 dB/decade, these sapphire acoustic resonators when integrated with matured quartz electronics could achieve a frequency stability improvement of 10 dB or more. As quartz oscillators are an essential element of nearly all types of frequency standards and reference systems, the success of MSAR would advance the development of frequency standards and systems for both groundbased and flight-based projects. Current quartz oscillator technology is limited by quartz mechanical Q. With a possible improvement of more than x 10 Q with sapphire acoustic modes, the stability limit of current quartz oscillators may be improved tenfold, to 10(exp -14) at 1 second. The electromagnetic modes of sapphire that were previously developed at JPL require cryogenic temperatures to achieve the high Q levels needed to achieve this stability level. However sapphire fs acoustic modes, which have not been used before in a high-stability oscillator, indicate the required Q values (as high as Q = 10(exp 8)) may be achieved at room temperature in the kHz range. Even though sapphire is not piezoelectric, such a high Q should allow electrostatic excitation of the acoustic modes with a combination of DC and AC voltages across a small sapphire disk (approximately equal to l mm thick). The first evaluations under this task will test predictions of an estimated input impedance of 10 kilohms at Q = 10(exp 8), and explore the Q values that can be realized in a smaller resonator, which has not been previously tested for acoustic modes. This initial Q measurement and excitation demonstration can be viewed similar to a transducer converting electrical energy to

  12. Acoustic cryocooler

    DOEpatents

    Swift, Gregory W.; Martin, Richard A.; Radenbaugh, Ray

    1990-01-01

    An acoustic cryocooler with no moving parts is formed from a thermoacoustic driver (TAD) driving a pulse tube refrigerator (PTR) through a standing wave tube. Thermoacoustic elements in the TAD are spaced apart a distance effective to accommodate the increased thermal penetration length arising from the relatively low TAD operating frequency in the range of 15-60 Hz. At these low operating frequencies, a long tube is required to support the standing wave. The tube may be coiled to reduce the overall length of the cryocooler. One or two PTR's are located on the standing wave tube adjacent antinodes in the standing wave to be driven by the standing wave pressure oscillations. It is predicted that a heat input of 1000 W at 1000 K will maintian a cooling load of 5 W at 80 K.

  13. Acoustic transducer

    DOEpatents

    Drumheller, Douglas S.

    2000-01-01

    An active acoustic transducer tool for use down-hole applications. The tool includes a single cylindrical mandrel including a shoulder defining the boundary of a narrowed portion over which is placed a sandwich-style piezoelectric tranducer assembly. The piezoelectric transducer assembly is prestressed by being placed in a thermal interference fit between the shoulder of the mandrel and the base of an anvil which is likewise positioned over the narrower portion of the mandrel. In the preferred embodiment, assembly of the tool is accomplished using a hydraulic jack to stretch the mandrel prior to emplacement of the cylindrical sandwich-style piezoelectric transducer assembly and anvil. After those elements are positioned and secured, the stretched mandrel is allowed to return substantially to its original (pre-stretch) dimensions with the result that the piezoelectric transducer elements are compressed between the anvil and the shoulder of the mandrel.

  14. Acoustic hemostasis

    NASA Astrophysics Data System (ADS)

    Crum, L.; Andrew, M.; Bailey, M.; Beach, K.; Brayman, A.; Curra, F.; Kaczkowski, P.; Kargl, S.; Martin, R.; Vaezy, S.

    2003-04-01

    Over the past several years, the Center for Industrial and Medical Ultrasound (CIMU) at the Applied Physics Laboratory in the University of Washington has undertaken a broad research program in the general area of High Intensity Focused Ultrasound (HIFU). Our principal emphasis has been on the use of HIFU to induce hemostasis; in particular, CIMU has sought to develop a small, lightweight, portable device that would use ultrasound for both imaging and therapy. Such a technology is needed because nearly 50% of combat casualty mortality results from exsanguinations, or uncontrolled bleeding. A similar percentage occurs for civilian death due to trauma. In this general review, a presentation of the general problem will be given, as well as our recent approaches to the development of an image-guided, transcutaneous, acoustic hemostasis device. [Work supported in part by the USAMRMC, ONR and the NIH.

  15. Properties of cells through life and death – an acoustic microscopy investigation

    PubMed Central

    Pasternak, Maurice M; Strohm, Eric M; Berndl, Elizabeth SL; Kolios, Michael C

    2015-01-01

    Current methods to evaluate the status of a cell are largely focused on fluorescent identification of molecular biomarkers. The invasive nature of these methods – requiring either fixation, chemical dyes, genetic alteration, or a combination of these – prevents subsequent analysis of samples. In light of this limitation, studies have considered the use of physical markers to differentiate cell stages. Acoustic microscopy is an ultrahigh frequency (>100 MHz) ultrasound technology that can be used to calculate the mechanical and physical properties of biological cells in real-time, thereby evaluating cell stage in live cells without invasive biomarker evaluation. Using acoustic microscopy, MCF-7 human breast adenocarcinoma cells within the G1, G2, and metaphase phases of the proliferative cell cycle, in addition to early and late programmed cell death, were examined. Physical properties calculated include the cell height, sound speed, acoustic impedance, cell density, adiabatic bulk modulus, and the ultrasonic attenuation. A total of 290 cells were measured, 58 from each cell phase, assessed using fluorescent and phase contrast microscopy. Cells actively progressing from G1 to metaphase were marked by a 28% decrease in attenuation, in contrast to the induction of apoptosis from G1, which was marked by a significant 81% increase in attenuation. Furthermore late apoptotic cells separated into 2 distinct groups based on ultrasound attenuation, suggesting that presently-unidentified sub-stages may exist within late apoptosis. A methodology has been implemented for the identification of cell stages without the use of chemical dyes, fixation, or genetic manipulation. PMID:26178635

  16. Acoustic telemetry.

    SciTech Connect

    Drumheller, Douglas Schaeffer; Kuszmaul, Scott S.

    2003-08-01

    Broadcasting messages through the earth is a daunting task. Indeed, broadcasting a normal telephone conversion through the earth by wireless means is impossible with todays technology. Most of us don't care, but some do. Industries that drill into the earth need wireless communication to broadcast navigation parameters. This allows them to steer their drill bits. They also need information about the natural formation that they are drilling. Measurements of parameters such as pressure, temperature, and gamma radiation levels can tell them if they have found a valuable resource such as a geothermal reservoir or a stratum bearing natural gas. Wireless communication methods are available to the drilling industry. Information is broadcast via either pressure waves in the drilling fluid or electromagnetic waves in the earth and well tubing. Data transmission can only travel one way at rates around a few baud. Given that normal Internet telephone modems operate near 20,000 baud, these data rates are truly very slow. Moreover, communication is often interrupted or permanently blocked by drilling conditions or natural formation properties. Here we describe a tool that communicates with stress waves traveling through the steel drill pipe and production tubing in the well. It's based on an old idea called Acoustic Telemetry. But what we present here is more than an idea. This tool exists, it's drilled several wells, and it works. Currently, it's the first and only acoustic telemetry tool that can withstand the drilling environment. It broadcasts one way over a limited range at much faster rates than existing methods, but we also know how build a system that can communicate both up and down wells of indefinite length.

  17. Constant current loop impedance measuring system that is immune to the effects of parasitic impedances

    NASA Technical Reports Server (NTRS)

    Anderson, Karl F. (Inventor)

    1994-01-01

    A constant current loop measuring system is provided for measuring a characteristic of an environment. The system comprises a first impedance positionable in the environment, a second impedance coupled in series with said first impedance and a parasitic impedance electrically coupled to the first and second impedances. A current generating device, electrically coupled in series with the first and second impedances, provides a constant current through the first and second impedances to produce first and second voltages across the first and second impedances, respectively, and a parasitic voltage across the parasitic impedance. A high impedance voltage measuring device measures a voltage difference between the first and second voltages independent of the parasitic voltage to produce a characteristic voltage representative of the characteristic of the environment.

  18. A membrane-type acoustic metamaterial with adjustable acoustic properties

    NASA Astrophysics Data System (ADS)

    Langfeldt, F.; Riecken, J.; Gleine, W.; von Estorff, O.

    2016-07-01

    A new realization of a membrane-type acoustic metamaterial (MAM) with adjustable sound transmission properties is presented. The proposed design distinguishes itself from other realizations by a stacked arrangement of two MAMs which is inflated using pressurized air. The static pressurization leads to large nonlinear deformations and, consequently, geometrical stiffening of the MAMs which is exploited to adjust the eigenmodes and sound transmission loss of the structure. A theoretical analysis of the proposed inflatable MAM design using numerical and analytical models is performed in order to identify two important mechanisms, namely the shifting of the eigenfrequencies and modal residuals due to the pressurization, responsible for the transmission loss adjustment. Analytical formulas are provided for predicting the eigenmode shifting and normal incidence sound transmission loss of inflated single and double MAMs using the concept of effective mass. The investigations are concluded with results from a test sample measurement inside an impedance tube, which confirm the theoretical predictions.

  19. Contrast and covert contrast: The phonetic development of voiceless sibilant fricatives in English and Japanese toddlers

    PubMed Central

    Li, Fangfang; Edwards, Jan; Beckman, Mary E.

    2009-01-01

    This paper examines the acoustic characteristics of voiceless sibilant fricatives in English-and Japanese-speaking adults and the acquisition of contrasts involving these sounds in 2- and 3-year-old children. Both English and Japanese have a two-way contrast between an alveolar fricative (/s/), and a postalveolar fricative (/∫/ in English and /ɕ/ in Japanese). Acoustic analysis of the adult productions revealed cross-linguistic differences in what acoustic parameters were used to differentiate the two fricatives in the two languages and in how well the two fricatives were differentiated by the acoustic parameters that were investigated. For the children’s data, the transcription results showed that English-speaking children generally produced the alveolar fricative more accurately than the postalveolar one, whereas the opposite was true for Japanese-speaking children. In addition, acoustic analysis revealed the presence of covert contrast in the productions of some English-speaking and some Japanese-speaking children. The different development patterns are discussed in terms of the differences in the fine phonetic detail of the contrast in the two languages. PMID:19672472

  20. Combined electromechanical impedance and fiber optic diagnosis of aerospace structures

    NASA Astrophysics Data System (ADS)

    Schlavin, Jon; Zagrai, Andrei; Clemens, Rebecca; Black, Richard J.; Costa, Joey; Moslehi, Behzad; Patel, Ronak; Sotoudeh, Vahid; Faridian, Fereydoun

    2014-03-01

    Electromechanical impedance is a popular diagnostic method for assessing structural conditions at high frequencies. It has been utilized, and shown utility, in aeronautic, space, naval, civil, mechanical, and other types of structures. By contrast, fiber optic sensing initially found its niche in static strain measurement and low frequency structural dynamic testing. Any low frequency limitations of the fiber optic sensing, however, are mainly governed by its hardware elements. As hardware improves, so does the bandwidth (frequency range * number of sensors) provided by the appropriate enabling fiber optic sensor interrogation system. In this contribution we demonstrate simultaneous high frequency measurements using fiber optic and electromechanical impedance structural health monitoring technologies. A laboratory specimen imitating an aircraft wing structure, incorporating surfaces with adjustable boundary conditions, was instrumented with piezoelectric and fiber optic sensors. Experiments were conducted at different structural boundary conditions associated with deterioration of structural health. High frequency dynamic responses were collected at multiple locations on a laboratory wing specimen and conclusions were drawn about correspondence between structural damage and dynamic signatures as well as correlation between electromechanical impedance and fiber optic sensors spectra. Theoretical investigation of the effect of boundary conditions on electromechanical impedance spectra is presented and connection to low frequency structural dynamics is suggested. It is envisioned that acquisition of high frequency structural dynamic responses with multiple fiber optic sensors may open new diagnostic capabilities for fiber optic sensing technologies.

  1. Joint Impedance Decreases during Movement Initiation

    PubMed Central

    Ludvig, Daniel; Antos, Stephen A.; Perreault, Eric J.

    2013-01-01

    The mechanical properties of the joint influence how we interact with our environment and hence are important in the control of both posture and movement. Many studies have investigated how the mechanical properties—specifically the impedance—of different joints vary with different postural tasks. However, studies on how joint impedance varies with movement remain limited. The few studies that have investigated how impedance varies with movement have found that impedance is lower during movement than during posture. In this study we investigated how impedance changed as people transitioned from a postural task to a movement task. We found that subjects’ joint impedances decreased at the initiation of movement, prior to increasing at the cessation of movement. This decrease in impedance occurred even though the subjects’ torque and EMG levels increased. These findings suggest that during movement the central nervous system may control joint impedance independently of muscle activation. PMID:23366632

  2. Impedance-based control and piezoelectric shell actuators for suppressing interior noise

    NASA Astrophysics Data System (ADS)

    Jayachandran, Vijay

    The damaging effects of high level acoustic noise are visible in many aspects of engineering as well as in our everyday life. The active control of interior noise in fixed-wing aircraft, helicopters, automobiles and HVAC equipment have received considerable attention in the recent past. Various techniques have been investigated, of which Active Noise Cancellation (ANC) and Active Structural-Acoustic Control (ASAC) are quite popular. Some researchers have investigated the possibility of using acoustic impedance as the controlled variable at the secondary sources in active interior noise control systems. However, there are no detailed studies of impedance conditions in actively controlled three- dimensional systems, and many control approaches are based on results from one-dimensional studies. The first part of this thesis investigates the steady-state impedance conditions in an actively controlled three- dimensional rectangular enclosure, with a tonal disturbance field. This is followed by an investigation into the adaptive-passive impedance control of tonal duct noise using mass-spring type of absorptive elements. The studies provide a better understanding of active and passive impedance control strategies and serve as a foundation for building impedance-based controllers. The second part of the thesis investigates new actuation schemes for ANC in aircraft. The severe weight and space limitations encountered in the design of commercial aircraft have created a need for low-profiled and lightweight acoustic sources that can be used as control elements. To this end, a detailed analytical and experimental investigation into the possible use of the commercially available RAINBOW and THUNDER actuators as controllable acoustic sources is performed. The RAINBOW actuator is modeled analytically as a piezoceramic spherical shallow shell and the effects of curvature, support stiffness, loading mass and other parameters on the natural frequencies, linear stroke and volume

  3. Passive acoustic monitoring of human physiology during activity indicates health and performance of soldiers and firefighters

    NASA Astrophysics Data System (ADS)

    Scanlon, Michael V.

    2003-04-01

    The Army Research Laboratory has developed a unique gel-coupled acoustic physiological monitoring sensor that has acoustic impedance properties similar to the skin. This facilitates the transmission of body sounds into the sensor pad, yet significantly repels ambient airborne noises due to an impedance mismatch. The sensor's sensitivity and bandwidth produce excellent signatures for detection and spectral analysis of diverse physiological events. Acoustic signal processing detects heartbeats, breaths, wheezes, coughs, blood pressure, activity, motion, and voice for communication and automatic speech recognition. The health and performance of soldiers, firefighters, and other first responders in strenuous and hazardous environments can be continuously and remotely monitored with body-worn acoustic sensors. Comfortable acoustic sensors can be in a helmet or in a strap around the neck, chest, and wrist. Noise-canceling sensor arrays help remove out-of-phase motion noise and enhance covariant physiology by using two acoustic sensors on the front sides of the neck and two additional acoustic sensors on each wrist. Pulse wave transit time between neck and wrist acoustic sensors will indicate systolic blood pressure. Larger torso-sized arrays can be used to acoustically inspect the lungs and heart, or built into beds for sleep monitoring. Acoustics is an excellent input for sensor fusion.

  4. A new acoustic lens material for large area detectors in photoacoustic breast tomography☆

    PubMed Central

    Xia, Wenfeng; Piras, Daniele; van Hespen, Johan C.G.; Steenbergen, Wiendelt; Manohar, Srirang

    2013-01-01

    Objectives We introduce a new acoustic lens material for photoacoustic tomography (PAT) to improve lateral resolution while possessing excellent acoustic acoustic impedance matching with tissue to minimize lens induced image artifacts. Background A large surface area detector due to its high sensitivity is preferable to detect weak signals in photoacoustic mammography. The lateral resolution is then limited by the narrow acceptance angle of such detectors. Acoustic lenses made of acrylic plastic (PMMA) have been used to enlarge the acceptance angle of such detectors and improve lateral resolution. However, such PMMA lenses introduce image artifacts due to internal reflections of ultrasound within the lenses, the result of acoustic impedance mismatch with the coupling medium or tissue. Methods A new lens is proposed based on the 2-component resin Stycast 1090SI. We characterized the acoustic properties of the proposed lens material in comparison with commonly used PMMA, inspecting the speed of sound, acoustic attenuation and density. We fabricated acoustic lenses based on the new material and PMMA, and studied the effect of the acoustic lenses on detector performance comparing finite element (FEM) simulations and measurements of directional sensitivity, pulse-echo response and frequency response. We further investigated the effect of using the acoustic lenses on the image quality of a photoacoustic breast tomography system using k-Wave simulations and experiments. Results Our acoustic characterization shows that Stycast 1090SI has tissue-like acoustic impedance, high speed of sound and low acoustic attenuation. These acoustic properties ensure an excellent acoustic lens material to minimize the acoustic insertion loss. Both acoustic lenses show significant enlargement of detector acceptance angle and lateral resolution improvement from modeling and experiments. However, the image artifacts induced by the presence of an acoustic lens are reduced using the proposed

  5. Acoustic force mapping in a hybrid acoustic-optical micromanipulation device supporting high resolution optical imaging.

    PubMed

    Thalhammer, Gregor; McDougall, Craig; MacDonald, Michael Peter; Ritsch-Marte, Monika

    2016-04-12

    Many applications in the life-sciences demand non-contact manipulation tools for forceful but nevertheless delicate handling of various types of sample. Moreover, the system should support high-resolution optical imaging. Here we present a hybrid acoustic/optical manipulation system which utilizes a transparent transducer, making it compatible with high-NA imaging in a microfluidic environment. The powerful acoustic trapping within a layered resonator, which is suitable for highly parallel particle handling, is complemented by the flexibility and selectivity of holographic optical tweezers, with the specimens being under high quality optical monitoring at all times. The dual acoustic/optical nature of the system lends itself to optically measure the exact acoustic force map, by means of direct force measurements on an optically trapped particle. For applications with (ultra-)high demand on the precision of the force measurements, the position of the objective used for the high-NA imaging may have significant influence on the acoustic force map in the probe chamber. We have characterized this influence experimentally and the findings were confirmed by model simulations. We show that it is possible to design the chamber and to choose the operating point in such a way as to avoid perturbations due to the objective lens. Moreover, we found that measuring the electrical impedance of the transducer provides an easy indicator for the acoustic resonances. PMID:27025398

  6. Compressible turbulent channel flow with impedance boundary conditions

    NASA Astrophysics Data System (ADS)

    Scalo, Carlo; Bodart, Julien; Lele, Sanjiva K.

    2015-03-01

    We have performed large-eddy simulations of isothermal-wall compressible turbulent channel flow with linear acoustic impedance boundary conditions (IBCs) for the wall-normal velocity component and no-slip conditions for the tangential velocity components. Three bulk Mach numbers, Mb = 0.05, 0.2, 0.5, with a fixed bulk Reynolds number, Reb = 6900, have been investigated. For each Mb, nine different combinations of IBC settings were tested, in addition to a reference case with impermeable walls, resulting in a total of 30 simulations. The adopted numerical coupling strategy allows for a spatially and temporally consistent imposition of physically realizable IBCs in a fully explicit compressible Navier-Stokes solver. The IBCs are formulated in the time domain according to Fung and Ju ["Time-domain impedance boundary conditions for computational acoustics and aeroacoustics," Int. J. Comput. Fluid Dyn. 18(6), 503-511 (2004)]. The impedance adopted is a three-parameter damped Helmholtz oscillator with resonant angular frequency, ωr, tuned to the characteristic time scale of the large energy-containing eddies. The tuning condition, which reads ωr = 2πMb (normalized with the speed of sound and channel half-width), reduces the IBCs' free parameters to two: the damping ratio, ζ, and the resistance, R, which have been varied independently with values, ζ = 0.5, 0.7, 0.9, and R = 0.01, 0.10, 1.00, for each Mb. The application of the tuned IBCs results in a drag increase up to 300% for Mb = 0.5 and R = 0.01. It is shown that for tuned IBCs, the resistance, R, acts as the inverse of the wall-permeability and that varying the damping ratio, ζ, has a secondary effect on the flow response. Typical buffer-layer turbulent structures are completely suppressed by the application of tuned IBCs. A new resonance buffer layer is established characterized by large spanwise-coherent Kelvin-Helmholtz rollers, with a well-defined streamwise wavelength λx, traveling downstream with

  7. Implementation of In-Situ Impedance Techniques on a Full Scale Aero-Engine System

    NASA Technical Reports Server (NTRS)

    Gaeta, R. J.; Mendoza, J. M.; Jones, M. G.

    2007-01-01

    Determination of acoustic liner impedance for jet engine applications remains a challenge for the designer. Although suitable models have been developed that take account of source amplitude and the local flow environment experienced by the liner, experimental validation of these models has been difficult. This is primarily due to the inability of researchers to faithfully mimic the environment in jet engine nacelles in the laboratory. An in-situ measurement technique, one that can be implemented in an actual engine, is desirable so an accurate impedance can be determined for future modeling and quality control. This paper documents the implementation of such a local acoustic impedance measurement technique that is used under controlled laboratory conditions as well as on full scale turbine engine liner test article. The objective for these series of in-situ measurements is to substantiate treatment design, provide understanding of flow effects on installed liner performance, and provide modeling input for fan noise propagation computations. A series of acoustic liner evaluation tests are performed that includes normal incidence tube, grazing incidence tube, and finally testing on a full scale engine on a static test stand. Lab tests were intended to provide insight and guidance for accurately measuring the impedance of the liner housed in the inlet of a Honeywell Tech7000 turbofan. Results have shown that one can acquire very reasonable liner impedance data for a full scale engine under realistic test conditions. Furthermore, higher fidelity results can be obtained by using a three-microphone coherence technique that can enhance signal-to-noise ratio at high engine power settings. This research has also confirmed the limitations of this particular type of in-situ measurement. This is most evident in the installation of instrumentation and its effect on what is being measured.

  8. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba

    2002-08-30

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or nonmetallic objects in the proximity of the HDD head. The system will use a thin film sensor conformal with the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is capacitively coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD

  9. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba; Christopher J. Ziolkowski

    2004-10-29

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or non-metallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment. Imaging

  10. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba

    2004-05-03

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or nonmetallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment. Imaging

  11. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba

    2004-02-01

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or nonmetallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment. Imaging

  12. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba; Christopher J. Ziolkowski

    2005-01-17

    This project aimed at developing a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GTI. GTI proposed to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or non-metallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment

  13. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba

    2003-10-01

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or nonmetallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment. Imaging

  14. Bilateral Impedance Control For Telemanipulators

    NASA Technical Reports Server (NTRS)

    Moore, Christopher L.

    1993-01-01

    Telemanipulator system includes master robot manipulated by human operator, and slave robot performing tasks at remote location. Two robots electronically coupled so slave robot moves in response to commands from master robot. Teleoperation greatly enhanced if forces acting on slave robot fed back to operator, giving operator feeling he or she manipulates remote environment directly. Main advantage of bilateral impedance control: enables arbitrary specification of desired performance characteristics for telemanipulator system. Relationship between force and position modulated at both ends of system to suit requirements of task.

  15. DIFFERENTIAL SOIL IMPEDANCE OBSTACLE DETECTION

    SciTech Connect

    Maximillian J. Kieba; Christopher J. Ziolkowski

    2004-06-30

    This project develops a new and unique obstacle detection sensor for horizontal directional drilling (HDD) equipment. The development of this new technology will greatly improve the reliability and safety of natural gas HDD construction practices. This sensor utilizes a differential soil impedance measurement technique that will be sensitive to the presence of plastic and ceramic, as well as metallic obstacles. The use of HDD equipment has risen significantly in the gas industry because HDD provides a much more cost-effective and less disruptive method for gas pipe installation than older, trenching methods. However, there have been isolated strikes of underground utilities by HDD equipment, which may have been avoided if methods were available to detect other underground obstacles when using HDD systems. GTI advisors from the gas industry have ranked the value of solving the obstacle detection problem as the most important research and development project for GTI to pursue using Federal Energy Regulatory Commission (FERC) funds available through its industry partner, GRI. GTI proposes to develop a prototype down-hole sensor system that is simple and compact. The sensor utilizes an impedance measurement technique that is sensitive to the presence of metallic or nonmetallic objects in the proximity of the HDD head. The system will use a simple sensor incorporated into the drill head. The impedance of the soil will be measured with a low frequency signal injected through the drill head itself. A pair of bridge type impedance sensors, mounted orthogonal to one another, is coupled to the soil. Inclusions in the soil will cause changes to the sensor balance distinguishable from homogeneous soil. The sensor will provide range and direction data for obstacles near the HDD head. The goal is to provide a simple, robust system that provides the information required to avoid obstacles. This must be done within the size and ruggedness constraints of the HDD equipment. Imaging

  16. Impedance spectroscopy of food mycotoxins

    NASA Astrophysics Data System (ADS)

    Bilyy, Oleksandr I.; Yaremyk, Roman Ya.; Kotsyumbas, Ihor Ya.; Kotsyumbas, Halyna I.

    2012-01-01

    A new analytical method of high-selective detection of mycotoxins in food and feed are considered. A method is based on optical registration the changes of conduct of the electric polarized bacterial agents in solution at the action of the external gradient electric fields. Measuring are conducted in integrated electrode-optical cuvette of the special construction, which provides the photometric analysis of forward motion of the objects registration in liquid solution under act of the enclosed electric field and simultaneous registration of kinetics of change of electrical impedance parameters solution and electrode system.

  17. Hierarchical Assembly of Tungsten Spheres and Epoxy Composites in Three-Dimensional Graphene Foam and Its Enhanced Acoustic Performance as a Backing Material.

    PubMed

    Qiu, Yunfeng; Liu, Jingjing; Lu, Yue; Zhang, Rui; Cao, Wenwu; Hu, PingAn

    2016-07-20

    Backing materials play important role in enhancing the acoustic performance of an ultrasonic transducer. Most backing materials prepared by conventional methods failed to show both high acoustic impedance and attenuation, which however determine the bandwidth and axial resolution of acoustic transducer, respectively. In the present work, taking advantage of the structural feature of 3D graphene foam as a confined space for dense packing of tungsten spheres with the assistance of centrifugal force, the desired structural requirement for high impedance is obtained. Meanwhile, superior thermal conductivity of graphene contributes to the acoustic attenuation via the conversion of acoustic waves to thermal energy. The tight contact between tungstate spheres, epoxy matrix, or graphene makes the acoustic wave depleted easily for the absence of air barrier. The as-prepared 3DG/W80 wt %/epoxy film in 1 mm, prepared using ∼41 μm W spheres in diameter, not only displays acoustic impedance of 13.05 ± 0.11 MRayl but also illustrates acoustic attenuation of 110.15 ± 1.23 dB/cm MHz. Additionally, the composite film exhibits a high acoustic absorption coefficient, which is 94.4% at 1 MHz and 100% at 3 MHz, respectively. Present composite film outperforms most of the reported backing materials consisting of metal fillers/polymer blending in terms of the acoustic impedance and attenuation. PMID:27352024

  18. Multiple Exhaust Nozzle Effects on J-2X Gas Generator Outlet Impedance

    NASA Technical Reports Server (NTRS)

    Kenny, R. Jeremy; Muss, Jeffrey; Hulka, James R.; Casiano, Matthew

    2010-01-01

    The current test setup of the J-2X gas generator system uses a multiple nozzle configuration to exhaust hot gases to drive the propellant supply turbines. Combustion stability assessment of this gas generator design requires knowledge of the impedance effects the multiple nozzle configuration creates on the combustion chamber acoustic modes. Parallel work between NASA and Sierra Engineering is presented, showing two methods used to calculate the effective end impedance resulting from multiple nozzle configurations. The NASA method is a simple estimate of the effective impedance using the long wavelength approximation. Sierra Engineering has developed a more robust numerical integration method implemented in ROCCID to accommodate for multiple nozzles. Analysis using both methods are compared to J-2X gas generator test data collected over the past year.

  19. Spin Start Line Effects on the J2X Gas Generator Chamber Acoustics

    NASA Technical Reports Server (NTRS)

    Kenny, R. Jeremy

    2011-01-01

    The J2X Gas Generator engine design has a spin start line connected near to the turbine inlet vanes. This line provides helium during engine startup to begin turbomachinery operation. The spin start line also acts as an acoustic side branch which alters the chamber's acoustic modes. The side branch effectively creates 'split modes' in the chamber longitudinal modes, in particular below the first longitudinal mode and within the frequency range associated with the injection-coupled response of the Gas Generator. Interaction between the spin start-modified chamber acoustics and the injection-driven response can create a higher system response than without the spin start attached to the chamber. This work reviews the acoustic effects of the spin start line as seen throughout the workhorse gas generator test program. A simple impedance model of the spin start line is reviewed. Tests were run with no initial spin start gas existing in the line, as well as being initially filled with nitrogen gas. Tests were also run with varying spin start line lengths from 0" to 40". Acoustic impedance changes due to different spin start gas constituents and line lengths are shown. Collected thermocouple and static pressure data in the spin start line was used to help estimate the fluid properties along the line length. The side branch impedance model was coupled to a chamber impedance model to show the effects on the overall chamber response. Predictions of the spin start acoustic behavior for helium operation are shown and compared against available data.

  20. Acoustic hemostasis

    NASA Astrophysics Data System (ADS)

    Crum, Lawrence; Beach, Kirk; Carter, Stephen; Chandler, Wayne; Curra, Francesco; Kaczkowski, Peter; Keilman, George; Khokhlova, Vera; Martin, Roy; Mourad, Pierre; Vaezy, Shahram

    2000-07-01

    In cases of severe injury, physicians speak of a "golden hour"—a brief grace period in which quickly applied, proper therapy can save the life of the patient. Much of this mortality results from exsanguination, i.e., bleeding to death—often from internal hemorrhage. The inability of a paramedic to treat breaches in the vascular system deep within the body or to stem the loss of blood from internal organs is a major reason for the high level of mortality associated with blunt trauma. We have undertaken an extensive research program to treat the problem of internal bleeding. Our approach is as follows: (a) We use scanning ultrasound to identify internal bleeding and hemorrhage, (b) we use ultrasound imaging to locate specific breaches in the vascular system, both from damaged vessels and gross damage to the capillary bed, and (c) we use High Intensity Focused Ultrasound (HIFU) to treat the damaged region and to induce hemostasis. We present a general review of this research with some emphasis on the role of nonlinear acoustics.

  1. Acoustic Inversion in Optoacoustic Tomography: A Review

    PubMed Central

    Rosenthal, Amir; Ntziachristos, Vasilis; Razansky, Daniel

    2013-01-01

    Optoacoustic tomography enables volumetric imaging with optical contrast in biological tissue at depths beyond the optical mean free path by the use of optical excitation and acoustic detection. The hybrid nature of optoacoustic tomography gives rise to two distinct inverse problems: The optical inverse problem, related to the propagation of the excitation light in tissue, and the acoustic inverse problem, which deals with the propagation and detection of the generated acoustic waves. Since the two inverse problems have different physical underpinnings and are governed by different types of equations, they are often treated independently as unrelated problems. From an imaging standpoint, the acoustic inverse problem relates to forming an image from the measured acoustic data, whereas the optical inverse problem relates to quantifying the formed image. This review focuses on the acoustic aspects of optoacoustic tomography, specifically acoustic reconstruction algorithms and imaging-system practicalities. As these two aspects are intimately linked, and no silver bullet exists in the path towards high-performance imaging, we adopt a holistic approach in our review and discuss the many links between the two aspects. Four classes of reconstruction algorithms are reviewed: time-domain (so called back-projection) formulae, frequency-domain formulae, time-reversal algorithms, and model-based algorithms. These algorithms are discussed in the context of the various acoustic detectors and detection surfaces which are commonly used in experimental studies. We further discuss the effects of non-ideal imaging scenarios on the quality of reconstruction and review methods that can mitigate these effects. Namely, we consider the cases of finite detector aperture, limited-view tomography, spatial under-sampling of the acoustic signals, and acoustic heterogeneities and losses. PMID:24772060

  2. Spheromak Impedance and Current Amplification

    SciTech Connect

    Fowler, T K; Hua, D D; Stallard, B W

    2002-01-31

    It is shown that high current amplification can be achieved only by injecting helicity on the timescale for reconnection, {tau}{sub REC}, which determines the effective impedance of the spheromak. An approximate equation for current amplification is: dI{sub TOR}{sup 2}/dt {approx} I{sup 2}/{tau}{sub REC} - I{sub TOR}{sup 2}/{tau}{sub closed} where I is the gun current, I{sub TOR} is the spheromak toroidal current and {tau}{sub CLOSED} is the ohmic decay time of the spheromak. Achieving high current amplification, I{sub TOR} >> I, requires {tau}{sub REC} <<{tau}{sub CLOSED}. For resistive reconnection, this requires reconnection in a cold zone feeding helicity into a hot zone. Here we propose an impedance model based on these ideas in a form that can be implemented in the Corsica-based helicity transport code. The most important feature of the model is the possibility that {tau}{sub REC} actually increases as the spheromak temperature increases, perhaps accounting for the ''voltage sag'' observed in some experiments, and a tendency toward a constant ratio of field to current, B {proportional_to} I, or I{sub TOR} {approx} I. Program implications are discussed.

  3. Effective impedance spectra for predicting rough sea effects on atmospheric impulsive sounds.

    PubMed

    Boulanger, Patrice; Attenborough, Keith

    2005-02-01

    Two methods of calculating the effective impedance spectra of acoustically hard, randomly rough, two-dimensional surfaces valid for acoustic wavelengths large compared with the roughness scales have been explored. The first method uses the complex excess attenuation spectrum due to a point source above a rough boundary predicted by a boundary element method (BEM) and solves for effective impedance roots identified by a winding number integral method. The second method is based on an analytical theory in which the contributions from random distributions of surface scatterers are summed to obtain the total scattered field. Effective impedance spectra deduced from measurements of the complex excess attenuation above 2D randomly rough surfaces formed by semicylinders and wedges have been compared to predictions from the two approaches. Although the analytical theory gives relatively poor predictions, BEM-deduced effective impedance spectra agree tolerably well with measured data. Simple polynomials have been found to fit BEM-deduced spectra for surfaces formed by intersecting parabolas corresponding to average roughness heights between 0.25 and 7.5 m and for five incidence angles for each average height. Predicted effects of sea-surface roughness on sonic boom profiles and rise time are comparable to those due to turbulence and molecular relaxation effects. PMID:15759695

  4. An impedance-based integrated biosensor for suspended DNA characterization

    PubMed Central

    Ma, Hanbin; Wallbank, Richard W. R.; Chaji, Reza; Li, Jiahao; Suzuki, Yuji; Jiggins, Chris; Nathan, Arokia

    2013-01-01

    Herein, we describe a novel integrated biosensor for performing dielectric spectroscopy to analyze biological samples. We analyzed biomolecule samples with different concentrations and demonstrated that the solution's impedance is highly correlated with the concentration, indicating that it may be possible to use this sensor as a concentration sensor. In contrast with standard spectrophotometers, this sensor offers a low-cost and purely electrical solution for the quantitative analysis of biomolecule solutions. In addition to determining concentrations, we found that the sample solution impedance is highly correlated with the length of the DNA fragments, indicating that the sizes of PCR products could be validated with an integrated chip-based, sample-friendly system within a few minutes. The system could be the basis of a rapid, low-cost platform for DNA characterization with broad applications in cancer and genetic disease research. PMID:24060937

  5. Impedance studies on Li-ion cathodes

    SciTech Connect

    NAGASUBRAMANIAN, GANESAN

    2000-04-17

    This paper describes the author's 2- and 3-electrode impedance results of metal oxide cathodes. These results were extracted from impedance data on 18650 Li-ion cells. The impedance results indicate that the ohmic resistance of the cell is very nearly constant with state-of-charge (SOC) and temperature. For example, the ohmic resistance of 18650 Li-ion cells is around 60 m{Omega} for different SOCS (4.1V to 3.0V) and temperatures from 35 C to {minus}20 C. However, the interfacial impedance shows a modest increase with SOC and a huge increase of between 10 and 100 times with decreasing temperature. For example, in the temperature regime (35 C down to {minus}20 C) the overall cell impedance has increased from nearly 200 m{Omega} to 8,000 m{Omega}. Most of the increase in cell impedance comes from the metal oxide cathode/electrolyte interface.

  6. Acoustic Holography

    NASA Astrophysics Data System (ADS)

    Kim, Yang-Hann

    One of the subtle problems that make noise control difficult for engineers is the invisibility of noise or sound. A visual image of noise often helps to determine an appropriate means for noise control. There have been many attempts to fulfill this rather challenging objective. Theoretical (or numerical) means for visualizing the sound field have been attempted, and as a result, a great deal of progress has been made. However, most of these numerical methods are not quite ready for practical applications to noise control problems. In the meantime, rapid progress with instrumentation has made it possible to use multiple microphones and fast signal-processing systems. Although these systems are not perfect, they are useful. A state-of-the-art system has recently become available, but it still has many problematic issues; for example, how can one implement the visualized noise field. The constructed noise or sound picture always consists of bias and random errors, and consequently, it is often difficult to determine the origin of the noise and the spatial distribution of the noise field. Section 26.2 of this chapter introduces a brief history, which is associated with sound visualization, acoustic source identification methods and what has been accomplished with a line or surface array. Section 26.2.3 introduces difficulties and recent studies, including de-Dopplerization and de-re verberation methods, both essential for visualizing a moving noise source, such as occurs for cars or trains. This section also addresses what produces ambiguity in realizing real sound sources in a room or closed space. Another major issue associated with sound/noise visualization is whether or not we can distinguish between mutual dependencies of noise in space (Sect. 26.2.4); for example, we are asked to answer the question, Can we see two birds singing or one bird with two beaks?

  7. Acoustic Holography

    NASA Astrophysics Data System (ADS)

    Kim, Yang-Hann

    One of the subtle problems that make noise control difficult for engineers is the invisibility of noise or sound. A visual image of noise often helps to determine an appropriate means for noise control. There have been many attempts to fulfill this rather challenging objective. Theoretical (or numerical) means for visualizing the sound field have been attempted, and as a result, a great deal of progress has been made. However, most of these numerical methods are not quite ready for practical applications to noise control problems. In the meantime, rapid progress with instrumentation has made it possible to use multiple microphones and fast signal-processing systems. Although these systems are not perfect, they are useful. A state-of-the-art system has recently become available, but it still has many problematic issues; for example, how can one implement the visualized noise field. The constructed noise or sound picture always consists of bias and random errors, and consequently, it is often difficult to determine the origin of the noise and the spatial distribution of the noise field. Section 26.2 of this chapter introduces a brief history, which is associated with "sound visualization," acoustic source identification methods and what has been accomplished with a line or surface array. Section 26.2.3 introduces difficulties and recent studies, including de-Dopplerization and de-reverberation methods, both essentialfor visualizing a moving noise source, such as occurs for cars or trains. This section also addresses what produces ambiguity in realizing real sound sources in a room or closed space. Another major issue associated with sound/noise visualization is whether or not we can distinguish between mutual dependencies of noise in space (Sect. 26.2.4); for example, we are asked to answer the question, "Can we see two birds singing or one bird with two beaks?"

  8. Advanced Nacelle Acoustic Lining Concepts Development

    NASA Technical Reports Server (NTRS)

    Bielak, G.; Gallman, J.; Kunze, R.; Murray, P.; Premo, J.; Kosanchick, M.; Hersh, A.; Celano, J.; Walker, B.; Yu, J.; Parrott, Tony L. (Technical Monitor)

    2002-01-01

    The work reported in this document consisted of six distinct liner technology development subtasks: 1) Analysis of Model Scale ADP Fan Duct Lining Data (Boeing): An evaluation of an AST Milestone experiment to demonstrate 1995 liner technology superiority relative to that of 1992 was performed on 1:5.9 scale model fan rig (Advanced Ducted Propeller) test data acquired in the NASA Glenn 9 x 15 foot wind tunnel. The goal of 50% improvement was deemed satisfied. 2) Bias Flow Liner Investigation (Boeing, VCES): The ability to control liner impedance by low velocity bias flow through liner was demonstrated. An impedance prediction model to include bias flow was developed. 3) Grazing Flow Impedance Testing (Boeing): Grazing flow impedance tests were conducted for comparison with results achieved at four different laboratories. 4) Micro-Perforate Acoustic Liner Technology (BFG, HAE, NG): Proof of concept testing of a "linear liner." 5) Extended Reaction Liners (Boeing, NG): Bandwidth improvements for non-locally reacting liner were investigated with porous honeycomb core test liners. 6) Development of a Hybrid Active/Passive Lining Concept (HAE): Synergism between active and passive attenuation of noise radiated by a model inlet was demonstrated.

  9. TRANSVERSE IMPEDANCE MEASUREMENT AT THE RHIC.

    SciTech Connect

    ZHANG,S.Y.; HUANG,H.; CAMERON,P.; DREES,A.; FLILLER,R.; SATOGATA,T.

    2002-06-02

    The RHIC transverse impedance was measured during the last operation run. Measurement of the imaginary part of the broadband impedance was the main goal. No large difference between the two rings was found nor in either plane. The measured tune shift is larger than the expected by a factor of 2.5 to 3. Several other issues such as the real part impedance measurement are also presented.

  10. Modified sparse regularization for electrical impedance tomography.

    PubMed

    Fan, Wenru; Wang, Huaxiang; Xue, Qian; Cui, Ziqiang; Sun, Benyuan; Wang, Qi

    2016-03-01

    Electrical impedance tomography (EIT) aims to estimate the electrical properties at the interior of an object from current-voltage measurements on its boundary. It has been widely investigated due to its advantages of low cost, non-radiation, non-invasiveness, and high speed. Image reconstruction of EIT is a nonlinear and ill-posed inverse problem. Therefore, regularization techniques like Tikhonov regularization are used to solve the inverse problem. A sparse regularization based on L1 norm exhibits superiority in preserving boundary information at sharp changes or discontinuous areas in the image. However, the limitation of sparse regularization lies in the time consumption for solving the problem. In order to further improve the calculation speed of sparse regularization, a modified method based on separable approximation algorithm is proposed by using adaptive step-size and preconditioning technique. Both simulation and experimental results show the effectiveness of the proposed method in improving the image quality and real-time performance in the presence of different noise intensities and conductivity contrasts. PMID:27036798

  11. What Is an Acoustic Neuroma

    MedlinePlus

    ... Acoustic Neuroma An acoustic neuroma, also called a vestibular schwannoma, is a rare benign tumor of the ... Acoustic Neuroma? An acoustic neuroma, known as a vestibular schwannoma, is a benign (non-cancerous) growth that ...

  12. Canonical Acoustics and Its Application to Surface Acoustic Wave on Acoustic Metamaterials

    NASA Astrophysics Data System (ADS)

    Shen, Jian Qi

    2016-08-01

    In a conventional formalism of acoustics, acoustic pressure p and velocity field u are used for characterizing acoustic waves propagating inside elastic/acoustic materials. We shall treat some fundamental problems relevant to acoustic wave propagation alternatively by using canonical acoustics (a more concise and compact formalism of acoustic dynamics), in which an acoustic scalar potential and an acoustic vector potential (Φ ,V), instead of the conventional acoustic field quantities such as acoustic pressure and velocity field (p,u) for characterizing acoustic waves, have been defined as the fundamental variables. The canonical formalism of the acoustic energy-momentum tensor is derived in terms of the acoustic potentials. Both the acoustic Hamiltonian density and the acoustic Lagrangian density have been defined, and based on this formulation, the acoustic wave quantization in a fluid is also developed. Such a formalism of acoustic potentials is employed to the problem of negative-mass-density assisted surface acoustic wave that is a highly localized surface bound state (an eigenstate of the acoustic wave equations). Since such a surface acoustic wave can be strongly confined to an interface between an acoustic metamaterial (e.g., fluid-solid composite structures with a negative dynamical mass density) and an ordinary material (with a positive mass density), it will give rise to an effect of acoustic field enhancement on the acoustic interface, and would have potential applications in acoustic device design for acoustic wave control.

  13. Acoustic metasurface-based perfect absorber with deep subwavelength thickness

    NASA Astrophysics Data System (ADS)

    Li, Yong; Assouar, Badreddine M.

    2016-02-01

    Conventional acoustic absorbers are used to have a structure with a thickness comparable to the working wavelength, resulting in major obstacles in real applications in low frequency range. We present a metasurface-based perfect absorber capable of achieving the total absorption of acoustic wave in an extremely low frequency region. The metasurface possessing a deep subwavelength thickness down to a feature size of ˜ λ / 223 is composed of a perforated plate and a coiled coplanar air chamber. Simulations based on fully coupled acoustic with thermodynamic equations and theoretical impedance analysis are utilized to reveal the underlying physics and the acoustic performances, showing an excellent agreement. Our realization should have an high impact on amount of applications due to the extremely thin thickness, easy fabrication, and high efficiency of the proposed structure.

  14. Coupled resonator filter with single-layer acoustic coupler.

    PubMed

    Jamneala, Tiberiu; Small, Martha; Ruby, Rich; Larson, John D

    2008-10-01

    We discuss the operation of novel coupled-resonator filters with single-layer acoustic couplers. Our analysis employs the physical Mason model for acoustic resonators. Their simpler fabrication process is counterbalanced by the high acoustic attenuation of suitable coupler materials. At high levels of attenuation, both the phase and the acoustic impedance must be treated as complex quantities to accurately predict the filter insertion loss. We demonstrate that the typically poor near-band rejection of coupled resonator filters can be improved at the die level by connecting a small capacitance between the input and output of the filter to produce a pair of tunable transmission minima. We make use of these theoretical findings to fabricate coupled resonators filters operating at 2.45 GHz. PMID:18986880

  15. Adaptive Impedance Control Of Redundant Manipulators

    NASA Technical Reports Server (NTRS)

    Seraji, Homayoun; Colbaugh, Richard D.; Glass, Kristin L.

    1994-01-01

    Improved method of controlling mechanical impedance of end effector of redundant robotic manipulator based on adaptive-control theory. Consists of two subsystems: adaptive impedance controller generating force-control inputs in Cartesian space of end effector to provide desired end-effector-impedance characteristics, and subsystem implementing algorithm that maps force-control inputs into torques applied to joints of manipulator. Accurate control of end effector and effective utilization of redundancy achieved simultaneously by use of method. Potential use to improve performance of such typical impedance-control tasks as deburring edges and accommodating transitions between unconstrained and constrained motions of end effectors.

  16. A finite element surface impedance representation for steady-state problems

    NASA Technical Reports Server (NTRS)

    Kalinowski, A. J.

    1986-01-01

    A procedure for determining the scattered pressure field resulting from a monochromatic harmonic wave that is incident upon a layer energy absorbing structure is treated. The situation where the structure is modeled with finite elements and the surrounding acoustic medium (water or air) is represented with either acoustic finite elements, or some type of boundary integral formulation, is considered. Finite element modeling problems arise when the construction of the structure, at the fluid structure interface, are nonhomogeneous and in particular, when the inhomogeneities are small relative to the acoustic wave length. An approximate procedure is presented for replacing the detailed microscopic representation of the layered surface configuration with an equivalent simple surface impedance finite element, which is especially designed to work only at limited frequencies. An example problem is presented using NASTRAN. However, the procedure is general enough to adapt to practically any finite element code having a steady state option.

  17. An overview of acoustic telemetry

    SciTech Connect

    Drumheller, D.S.

    1992-01-01

    Acoustic telemetry has been a dream of the drilling industry for the past 50 years. It offers the promise of data rates which are one-hundred times greater than existing technology. Such a system would open the door to true logging-while-drilling technology and bring enormous profits to its developers. The basic idea is to produce an encoded sound wave at the bottom of the well, let it propagate up the steel drillpipe, and extract the data from the signal at the surface. Unfortunately, substantial difficulties arise. The first difficult problem is to produce the sound wave. Since the most promising transmission wavelengths are about 20 feet, normal transducer efficiencies are quire low. Compounding this problem is the structural complexity of the bottomhole assembly and drillstring. For example, the acoustic impedance of the drillstring changes every 30 feet and produces an unusual scattering pattern in the acoustic transmission. This scattering pattern causes distortion of the signal and is often confused with signal attenuation. These problems are not intractable. Recent work has demonstrated that broad frequency bands exist which are capable of transmitting data at rates up to 100 bits per second. Our work has also identified the mechanism which is responsible for the observed anomalies in the patterns of signal attenuation. Furthermore in the past few years a body of experience has been developed in designing more efficient transducers for application to metal waveguides. The direction of future work is clear. New transducer designs which are more efficient and compatible with existing downhole power supplies need to be built and tested; existing field test data need to be analyzed for transmission bandwidth and attenuation; and the new and less expensive methods of collecting data on transmission path quality need to be incorporated into this effort. 11 refs.

  18. Development of an analytical solution of modified Biot's equations for the optimization of lightweight acoustic protection.

    PubMed

    Kanfoud, Jamil; Ali Hamdi, Mohamed; Becot, François-Xavier; Jaouen, Luc

    2009-02-01

    During lift-off, space launchers are submitted to high-level of acoustic loads, which may damage sensitive equipments. A special acoustic absorber has been previously integrated inside the fairing of space launchers to protect the payload. A new research project has been launched to develop a low cost fairing acoustic protection system using optimized layers of porous materials covered by a thin layer of fabric. An analytical model is used for the analysis of acoustic wave propagation within the multilayer porous media. Results have been validated by impedance tube measurements. A parametric study has been conducted to determine optimal mechanical and acoustical properties of the acoustic protection under dimensional thickness constraints. The effect of the mounting conditions has been studied. Results reveal the importance of the lateral constraints on the absorption coefficient particularly in the low frequency range. A transmission study has been carried out, where the fairing structure has been simulated by a limp mass layer. The transmission loss and noise reduction factors have been computed using Biot's theory and the local acoustic impedance approximation to represent the porous layer effect. Comparisons between the two models show the frequency domains for which the local impedance model is valid. PMID:19206863

  19. Molecular Engineering of Acoustic Protein Nanostructures.

    PubMed

    Lakshmanan, Anupama; Farhadi, Arash; Nety, Suchita P; Lee-Gosselin, Audrey; Bourdeau, Raymond W; Maresca, David; Shapiro, Mikhail G

    2016-08-23

    Ultrasound is among the most widely used biomedical imaging modalities, but has limited ability to image specific molecular targets due to the lack of suitable nanoscale contrast agents. Gas vesicles-genetically encoded protein nanostructures isolated from buoyant photosynthetic microbes-have recently been identified as nanoscale reporters for ultrasound. Their unique physical properties give gas vesicles significant advantages over conventional microbubble contrast agents, including nanoscale dimensions and inherent physical stability. Furthermore, as a genetically encoded material, gas vesicles present the possibility that the nanoscale mechanical, acoustic, and targeting properties of an imaging agent can be engineered at the level of its constituent proteins. Here, we demonstrate that genetic engineering of gas vesicles results in nanostructures with new mechanical, acoustic, surface, and functional properties to enable harmonic, multiplexed, and multimodal ultrasound imaging as well as cell-specific molecular targeting. These results establish a biomolecular platform for the engineering of acoustic nanomaterials. PMID:27351374

  20. Electrical Impedance Tomography of Electrolysis

    PubMed Central

    Meir, Arie; Rubinsky, Boris

    2015-01-01

    The primary goal of this study is to explore the hypothesis that changes in pH during electrolysis can be detected with Electrical Impedance Tomography (EIT). The study has relevance to real time control of minimally invasive surgery with electrolytic ablation. To investigate the hypothesis, we compare EIT reconstructed images to optical images acquired using pH-sensitive dyes embedded in a physiological saline agar gel phantom treated with electrolysis. We further demonstrate the biological relevance of our work using a bacterial E.Coli model, grown on the phantom. The results demonstrate the ability of EIT to image pH changes in a physiological saline phantom and show that these changes correlate with cell death in the E.coli model. The results are promising, and invite further experimental explorations. PMID:26039686

  1. Impedance Spectroscopy of Human Blood

    NASA Astrophysics Data System (ADS)

    Mesa, Francisco; Bernal, José J.; Sosa, Modesto A.; Villagómez, Julio C.; Palomares, Pascual

    2004-09-01

    The blood is one of the corporal fluids more used with analytical purposes. When the blood is extracted, immediately it is affected by agents that act on it, producing transformations in its elements. Among the effects of these transformations the hemolysis phenomenon stands out, which consists of the membrane rupture and possible death of the red blood cells. The main purpose of this investigation was the quantification of this phenomenon. A Solartron SI-1260 Impedance Spectrometer was used, which covers a frequency range of work from 1 μHz to 10 MHz, and its accuracy has been tested in the accomplishment of several applications. Measurements were performed on 3 mL human blood samples, from healthy donors. Reactive strips for sugar test of 2 μL, from Bayer, were used as electrodes, which allow gathering a portion of the sample, to be analyzed by the spectrometer. Preliminary results of these measurements are presented.

  2. Refractive acoustic devices for airborne sound.

    PubMed

    Cervera, F; Sanchis, L; Sánchez-Pérez, J V; Martínez-Sala, R; Rubio, C; Meseguer, F; López, C; Caballero, D; Sánchez-Dehesa, J

    2002-01-14

    We show that a sonic crystal made of periodic distributions of rigid cylinders in air acts as a new material which allows the construction of refractive acoustic devices for airborne sound. It is demonstrated that, in the long-wave regime, the crystal has low impedance and the sound is transmitted at subsonic velocities. Here, the fabrication and characterization of a convergent lens are presented. Also, an example of a Fabry-Perot interferometer based on this crystal is analyzed. It is concluded that refractive devices based on sonic crystals behave in a manner similar to that of optical systems. PMID:11801014

  3. Symptoms of Acoustic Neuroma

    MedlinePlus

    ... Watch and Wait Radiation Microsurgery Acoustic Neuroma Decision Tree Questions for Your Physician Questions to Ask Yourself ... Watch and Wait Radiation Microsurgery Acoustic Neuroma Decision Tree Questions for Your Physician Questions to Ask Yourself ...

  4. The acoustics of the echo cornet

    NASA Astrophysics Data System (ADS)

    Pyle, Robert W., Jr.; Klaus, Sabine K.

    2002-11-01

    The echo cornet was an instrument produced by a number of makers in several countries from about the middle of the nineteenth to the early twentieth centuries. It consists of an ordinary three-valve cornet to which a fourth valve has been added, downstream of the three normal valves. The extra valve diverts the airstream from the normal bell to an ''echo'' bell that gives a muted tone quality. Although the air column through the echo bell is typically 15 cm longer than the path through the normal bell, there is no appreciable change of playing pitch when the echo bell is in use. Acoustic input impedance and impulse response measurements and consideration of the standing-wave pattern within the echo bell show how this can be so. Acoustically, the echo bell is more closely related to hand-stopping on the French horn than to the mutes commonly used on the trumpet and cornet.

  5. Compressible turbulent channel flow with impedance boundary conditions

    NASA Astrophysics Data System (ADS)

    Scalo, Carlo; Bodart, Julien; Lele, Sanjiva

    2014-11-01

    We have performed large-eddy simulations of compressible turbulent channel flow at one bulk Reynolds number, Reb = 6900, for bulk Mach numbers Mb = 0.05, 0.2, 0.5, with linear acoustic impedance boundary conditions (IBCs). The IBCs are formulated in the time domain following Fung and Ju (2004) and coupled with a Navier-Stokes solver. The impedance model adopted is a three-parameter Helmholtz oscillator with resonant frequency tuned to the outer layer eddies. The IBC's resistance, R, has been varied in the range, R = 0.01, 0.10, 1.00. Tuned IBCs result in a noticeable drag increase for sufficiently high Mb and/or low R, exceeding 300% for Mb = 0.5 and R = 0.01, and thus represents a promising passive control technique for delaying boundary layer separation and/or enhancing wall heat transfer. Alterations to the turbulent flow structure are confined to the first 15% of the boundary layer thickness where the classical buffer-layer coherent vortical structures are replaced by an array of Kelvin-Helmholtz-like rollers. The non-zero asymptotic value of the Reynolds shear stress gradient at the wall results in the disappearance of the viscous sublayer and very early departure of the mean velocity profiles from the law of the wall.

  6. A MEMS-based valveless impedance pump utilizing electromagnetic actuation

    NASA Astrophysics Data System (ADS)

    Lee, Chia-Yen; Chang, Hsien-Tsung; Wen, Chih-Yung

    2008-03-01

    This study presents a planar valveless impedance-based micro pump for biomedical applications. The micro pump comprises four major components, namely a lower glass substrate containing a copper micro coil, a microchannel, an upper glass cover plate and a PDMS diaphragm with a magnet mounted on its upper surface. When a current is passed through the micro coil, an electromagnetic force is established between the coil and the magnet. The resulting deflection of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. The performance of the micro pump is characterized both experimentally and numerically using Ansoft/Maxwell3D FEA software. The results show that the mechanical integrity of the micro pump is assured provided that the diaphragm deflection does not exceed 110 µm. This deflection is obtained by supplying the micro coil with an input current of 0.6 A, and results in a flow rate of 7.2 ml min-1 when the PDMS membrane is driven by an actuating frequency of 200 Hz.

  7. Acoustic emission frequency discrimination

    NASA Technical Reports Server (NTRS)

    Sugg, Frank E. (Inventor); Graham, Lloyd J. (Inventor)

    1988-01-01

    In acoustic emission nondestructive testing, broadband frequency noise is distinguished from narrow banded acoustic emission signals, since the latter are valid events indicative of structural flaws in the material being examined. This is accomplished by separating out those signals which contain frequency components both within and beyond (either above or below) the range of valid acoustic emission events. Application to acoustic emission monitoring during nondestructive bond verification and proof loading of undensified tiles on the Space Shuttle Orbiter is considered.

  8. RF discharge impedance measurements using a new method to determine the stray impedances

    SciTech Connect

    Bakker, L.P.; Kroesen, G.M.W.; Hoog, F.J. de )

    1999-06-01

    The impedance of a capacitively coupled radio frequency discharge in a tubular fluorescent lamp filled with neon and mercury is measured. The stray impedances in the electrical network are determined using a new method that requires no extra instruments. The reflection of power is used to determine the stray impedances. Making use of a simple discharge impedance model, the electron density in the lamp is estimated.

  9. Tutorial on architectural acoustics

    NASA Astrophysics Data System (ADS)

    Shaw, Neil; Talaske, Rick; Bistafa, Sylvio

    2002-11-01

    This tutorial is intended to provide an overview of current knowledge and practice in architectural acoustics. Topics covered will include basic concepts and history, acoustics of small rooms (small rooms for speech such as classrooms and meeting rooms, music studios, small critical listening spaces such as home theatres) and the acoustics of large rooms (larger assembly halls, auditoria, and performance halls).

  10. Acoustic imaging systems (for robotic object acquisition)

    NASA Astrophysics Data System (ADS)

    Richardson, J. M.; Martin, J. F.; Marsh, K. A.; Schoenwald, J. S.

    1985-03-01

    The long-term objective of the effort is to establish successful approaches for 3D acoustic imaging of dense solid objects in air to provide the information required for acquisition and manipulation of these objects by a robotic system. The objective of this first year's work was to achieve and demonstrate the determination of the external geometry (shape) of such objects with a fixed sparse array of sensors, without the aid of geometrical models or extensive training procedures. Conventional approaches for acoustic imaging fall into two basic categories. The first category is used exclusively for dense solid objects. It involves echo-ranging from a large number of sensor positions, achieved either through the use of a larger array of transducers or through extensive physical scanning of a small array. This approach determines the distance to specular reflection points from each sensor position; with suitable processing an image can be inferred. The second category uses the full acoustic waveforms to provide an image, but is strictly applicable only to weak inhomogeneities. The most familiar example is medical imaging of the soft tissue portions of the body where the range of acoustic impedance is relatively small.

  11. Numerics of surface acoustic wave (SAW) driven acoustic streaming and radiation force

    NASA Astrophysics Data System (ADS)

    Nama, Nitesh; Barnkob, Rune; Kahler, Christian; Costanzo, Francesco; Jun Huang, Tony

    2015-11-01

    Recently, surface acoustic wave (SAW) based systems have shown great potential for various lab-on-a-chip applications. However, the physical understanding of the precise acoustic fields and associated acoustophoresis is rather limited. In this work, we present a numerical study of the acoustophoretic particle motion inside a SAW-actuated, liquid-filled polydimethylsiloxane (PDMS) microchannel. We utilize a perturbation approach to divide the flow variables into first- and second-order components. The first-order fields result in a time-averaged acoustic radiation force on suspended particles, as well as the time-averaged body force terms that drive the second-order fields. We model the SAW actuation by a displacement function while we utilize impedance boundary conditions to model the PDMS walls. We identify the precise acoustic fields generated inside the microchannel and investigate a range of particle sizes to characterize the transition from streaming-dominated acoustophoresis to radiation-force-dominated acoustophoresis. Lastly, we demonstrate the ability of SAW devices to tune the position of vertical pressure node inside the microchannel by tuning the phase difference between the two incoming surface acoustic waves.

  12. Numerical solutions to ill-posed and well-posed impedance boundary condition integral equations

    NASA Astrophysics Data System (ADS)

    Rogers, J. R.

    1983-11-01

    Exterior scattering from a three-dimensional impedance body can be formulated in terms of various integral equations derived from the Leontovich impedance boundary condition (IBC). The electric and magnetic field integral equations are ill-posed because they theoretically admit spurious solutions at the frequencies of interior perfect conductor cavity resonances. A combined field formulation is well-posed because it does not allow the spurious solutions. This report outlines the derivation of IBC integral equations and describes a procedure for constructing moment-method solutions for bodies of revolution. Numerical results for scattering from impedance spheres are presented which contrast the stability and accuracy of solutions to the ill-posed equations with those of the well-posed equation. The results show that numerical solutions for exterior scattering to the electric and magnetic field integral equations can be severely contaminated by spurious resonant solutions regardless of whether the surface impedance of the body is lossy or lossless.

  13. Bio-impedance detector for Staphylococcus aureus exposed to magnetic fields

    NASA Astrophysics Data System (ADS)

    Younis Yacoob Aldosky, Haval; Barwari, Waleed Jameel Omar; Salih Al-mlaly, Janan M.

    2012-12-01

    Rapid detection of viability and growth of pathogenic microorganisms is very important in many applications such as food and drug production, health care, and national defense. Measurements on the electrical characteristics of cells have been used successfully in the past to detect many different physiological events. The effect of electromagnetic fields on the growth of bacteria (Staphylococcus aureus) was studied with the bio-impedance technique. The growth situations of bacteria in the absence and presence of different intensities of static and alternative magnetic fields were examined and analyzed. The results show that the impedance of bacteria fell in the presence of DC magnetic fields. In contrast the impedance increased when the bacteria were exposed to AC magnetic fields. Based on these results the bacterial growth indicated by the change in the impedance is inhibited under DC magnetic fields and enhanced under AC fields.

  14. Mathematical model of acoustic speech production with mobile walls of the vocal tract

    NASA Astrophysics Data System (ADS)

    Lyubimov, N. A.; Zakharov, E. V.

    2016-03-01

    A mathematical speech production model is considered that describes acoustic oscillation propagation in a vocal tract with mobile walls. The wave field function satisfies the Helmholtz equation with boundary conditions of the third kind (impedance type). The impedance mode corresponds to a threeparameter pendulum oscillation model. The experimental research demonstrates the nonlinear character of how the mobility of the vocal tract walls influence the spectral envelope of a speech signal.

  15. Far-infrared embedding impedance measurements

    NASA Technical Reports Server (NTRS)

    Neikirk, D. P.; Rutledge, D. B.

    1984-01-01

    A technique which allows the measurement of detector embedding impedance has been developed. By using a bismuth microbolometer as a variable resistance load the impedance of one element in a bow-tie antenna array operating at 94 GHz was inferred. The technique is frequency insensitive, and could be used throughout the far-infrared.

  16. How good is the impedance boundary condition?

    NASA Technical Reports Server (NTRS)

    Lee, Shung-Wu; Gee, W.

    1987-01-01

    The impedance boundary condition (IBC) is often used in scattering problems involving material-coated conducting bodies. It is shown that for some commonly encountered coating configurations, the value of the impedance varies significantly as functions of the incident angle and polarization. Hence, the use of IBC in a rigorously formulated problem may affect the accuracy of the final solution.

  17. FDTD modeling of thin impedance sheets

    NASA Technical Reports Server (NTRS)

    Luebbers, Raymond J.; Kunz, Karl S.

    1991-01-01

    Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. In this paper it is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods.

  18. Esophageal Impedance Monitoring: Clinical Pearls and Pitfalls.

    PubMed

    Ravi, Karthik; Katzka, David A

    2016-09-01

    The development of intraluminal esophageal impedance monitoring has improved our ability to detect and measure gastroesophageal reflux without dependence on acid content. This ability to detect previously unrecognized weak or nonacid reflux episodes has had important clinical implications in the diagnosis and management of gastroesophageal reflux disease (GERD). In addition, with the ability to assess bolus transit within the esophageal lumen, impedance monitoring has enhanced the recognition and characterization of esophageal motility disorders in patients with nonobstructive dysphagia. The assessment of the intraluminal movement of gas and liquid has also been proven to be of diagnostic value in conditions such as rumination syndrome and excessive belching. Further, alternative applications of impedance monitoring, such as the measurement of mucosal impedance, have provided novel insights into assessing esophageal mucosal integrity changes as a consequence of inflammatory change. Future applications for esophageal impedance monitoring also hold promise in esophageal conditions other than GERD. However, despite all of the clinical benefits afforded by esophageal impedance monitoring, important clinical and technical shortcomings limit its diagnostic value and must be considered when interpreting study results. Overinterpretation of studies or application of impedance monitoring in patients can have deleterious clinical implications. This review will highlight the clinical benefits and limitations of esophageal impedance monitoring and provide clinical pearls and pitfalls associated with this technology. PMID:27325223

  19. Possibilities of electrical impedance tomography in gynecology

    NASA Astrophysics Data System (ADS)

    V, Trokhanova O.; A, Chijova Y.; B, Okhapkin M.; V, Korjenevsky A.; S, Tuykin T.

    2013-04-01

    The paper describes results of comprehensive EIT diagnostics of mammary glands and cervix. The data were obtained from examinations of 170 patients by EIT system MEM (multi-frequency electrical impedance mammograph) and EIT system GIT (gynecological impedance tomograph). Mutual dependence is discussed.

  20. Active impedance matching of complex structural systems

    NASA Technical Reports Server (NTRS)

    Macmartin, Douglas G.; Miller, David W.; Hall, Steven R.

    1991-01-01

    Viewgraphs on active impedance matching of complex structural systems are presented. Topics covered include: traveling wave model; dereverberated mobility model; computation of dereverberated mobility; control problem: optimal impedance matching; H2 optimal solution; statistical energy analysis (SEA) solution; experimental transfer functions; interferometer actuator and sensor locations; active strut configurations; power dual variables; dereverberation of complex structure; dereverberated transfer function; compensators; and relative power flow.

  1. Acoustic cloaking in two dimensions: a feasible approach

    NASA Astrophysics Data System (ADS)

    Torrent, Daniel; Sánchez-Dehesa, José

    2008-06-01

    This work proposes an acoustic structure feasible to engineer that accomplishes the requirements of acoustic cloaking design recently introduced by Cummer and Schurig (2007 New J. Phys. 9 45). The structure, which consists of a multilayered composite made of two types of isotropic acoustic metamaterials, exactly matches the conditions for the acoustic cloaking. It is also shown that the isotropic metamaterials needed can be made of sonic crystals containing two types of material cylinders, whose elastic parameters should be properly chosen in order to satisfy (in the homogenization limit) the acoustic properties under request. In contrast to electromagnetic cloaking, the structure here proposed verifies the acoustic cloaking in a wide range of wavelengths; its performance is guaranteed for any wavelength above a certain cutoff defined by the homogenization limit of the sonic crystal employed in its fabrication.

  2. Distinct effects of moisture and air contents on acoustic properties of sandy soil.

    PubMed

    Oshima, Takuya; Hiraguri, Yasuhiro; Okuzono, Takeshi

    2015-09-01

    Knowledge of distinct effects of moisture content and air volume on acoustic properties of soil is sought to predict the influence of human activities such as cultivation on acoustic propagation outdoors. This work used an impedance tube with the two-thickness method to investigate such effects. For a constant moisture weight percentage, the magnitude of the characteristic impedance became smaller and the absorption coefficient became higher with increase of the air space ratio. For a constant air space ratio, the absorption coefficient became larger and the magnitude of the propagation constant became smaller with increasing moisture weight percentage. PMID:26428823

  3. Impedance of finite length resistive cylinder

    NASA Astrophysics Data System (ADS)

    Krinsky, S.; Podobedov, B.; Gluckstern, R. L.

    2004-11-01

    We determine the impedance of a cylindrical metal tube (resistor) of radius a, length g, and conductivity σ attached at each end to perfect conductors of semi-infinite length. Our main interest is in the asymptotic behavior of the impedance at high frequency (k≫1/a). In the equilibrium regime, ka2≪g, the impedance per unit length is accurately described by the well-known result for an infinite length tube with conductivity σ. In the transient regime, ka2≫g, where the contribution of transition radiation arising from the discontinuity in conductivity is important, we derive an analytic expression for the impedance and compute the short-range wakefield. The analytic results are shown to agree with numerical evaluation of the impedance.

  4. Lightweight acoustic treatments for aerospace applications

    NASA Astrophysics Data System (ADS)

    Naify, Christina Jeanne

    2011-12-01

    Increase in the use of composites for aerospace applications has the benefit of decreased structural weight, but at the cost of decreased acoustic performance. Stiff, lightweight structures (such as composites) are traditionally not ideal for acoustic insulation applications because of high transmission loss at low frequencies. A need has thus arisen for effective sound insulation materials for aerospace and automotive applications with low weight addition. Current approaches, such as the addition of mass law dominated materials (foams) also perform poorly when scaled to small thickness and low density. In this dissertation, methods which reduce sound transmission without adding significant weight are investigated. The methods presented are intended to be integrated into currently used lightweight structures such as honeycomb sandwich panels and to cover a wide range of frequencies. Layering gasses of differing acoustic impedances on a panel substantially reduced the amount of sound energy transmitted through the panel with respect to the panel alone or an equivalent-thickness single species gas layer. The additional transmission loss derives from successive impedance mismatches at the interfaces between gas layers and the resulting inefficient energy transfer. Attachment of additional gas layers increased the transmission loss (TL) by as much as 17 dB at high (>1 kHz) frequencies. The location and ordering of the gasses with respect to the panel were important factors in determining the magnitude of the total TL. Theoretical analysis using a transfer matrix method was used to calculate the frequency dependence of sound transmission for the different configurations tested. The method accurately predicted the relative increases in TL observed with the addition of different gas layer configurations. To address low-frequency sound insulation, membrane-type locally resonant acoustic materials (LRAM) were fabricated, characterized, and analyzed to understand their

  5. Comparison of a Convected Helmholtz and Euler Model for Impedance Eduction in Flow

    NASA Technical Reports Server (NTRS)

    Watson, Willie R.; Jones, Michael G.

    2006-01-01

    Impedances educed from a well-tested convected Helmholtz model are compared to that of a recently developed linearized Euler model using two ceramic test liners under the assumed conditions or uniform flow and a plane wave source. The convected Helmholtz model is restricted to uniform mean flow whereas the linearized Euler model can account for the effect or the shear layer. Test data to educe the impedance is acquired from measurements obtained in the NASA Langley Research Center Grazing Incidence Tube for mean flow Mach numbers ranging from 0.0 to 0.5 and source frequencies ranging from 0.5 kHz to 3.0 kHz. The unknown impedance of the liner b educed by judiciously chooingth e impedance via an optimization method to match the measured acoustic pressure on the wall opposite the test liner. Results are presented on four spatial grids using three different optimization methods (contour deformation, Davidon-Fletcher Powell, and the Genetic Algorithm). All three optimization methods converge to the same impedance when used with the same model and to nearly identical impedances when used on different models. h anomaly was observed only at 0.5 kHz for high mean flow speeds. The anomaly is likely due to the use of measured data in a flow regime where shear layer effects are important but are neglected in the math models. Consistency between the impedances educed using the two models provides confidence that the linearized Euler model is ready For application to more realistic flows, such as those containing shear layers.

  6. Study of acoustic field modulation in the regenerator by double loudspeakers method.

    PubMed

    Zhou, Lihua; Xie, Xiujuan; Li, Qing

    2011-11-01

    A model to modulate acoustic field in a regenerator of a thermoacoustic system by the double loudspeakers method is presented in this paper. The equations are derived for acoustic field modulation. They represent the relations among acoustic field (complex pressure p(0), complex velocity u(0), and acoustic impedance Z(0)), driving parameters of loudspeakers (voltage amplitude and its phase difference), and operating parameters involved in a matrix H (frequency, temperature of regenerator). The range of acoustic field is adjustable and limited by the maximal driving voltages of loudspeakers according to driving parameters. The range is simulated and analyzed in the amplitude-phase and complex coordinate planes for a given or variable H. The simulated results indicate that the range has its intrinsic characteristics. The expected acoustic field in a regenerator can be obtained feasibly by the modulation. PMID:22087899

  7. Geo-Acoustic Doppler Spectroscopy: A Novel Acoustic Technique For Surveying The Seabed

    NASA Astrophysics Data System (ADS)

    Buckingham, Michael J.

    2010-09-01

    An acoustic inversion technique, known as Geo-Acoustic Doppler Spectroscopy, has recently been developed for estimating the geo-acoustic parameters of the seabed in shallow water. The technique is unusual in that it utilizes a low-flying, propeller-driven light aircraft as an acoustic source. Both the engine and propeller produce sound and, since they are rotating sources, the acoustic signature of each takes the form of a sequence of narrow-band harmonics. Although the coupling of the harmonics across the air-sea interface is inefficient, due to the large impedance mismatch between air and water, sufficient energy penetrates the sea surface to provide a useable underwater signal at sensors either in the water column or buried in the sediment. The received signals, which are significantly Doppler shifted due to the motion of the aircraft, will have experienced a number of reflections from the seabed and thus they contain information about the sediment. A geo-acoustic inversion of the Doppler-shifted modes associated with each harmonic yields an estimate of the sound speed in the sediment; and, once the sound speed has been determined, the known correlations between it and the remaining geo-acoustic parameters allow all of the latter to be computed. This inversion technique has been applied to aircraft data collected in the shallow water north of Scripps pier, returning values of the sound speed, shear speed, porosity, density and grain size that are consistent with the known properties of the sandy sediment in the channel.

  8. Finite-difference, time-domain analysis of a folded acoustic transmission line.

    PubMed

    Jackson, Charles M

    2005-03-01

    Recently designed, modern versions of renais sance woodwind instruments such as the recorder and serpent use square cross sections and a folded acoustic transmission line. Conventional microwave techniques would expect that this bend would cause unwanted reflections and impedance discontinuities. This paper analyses the folded acoustic transmission line using finite-difference, time-domain techniques and shows that the discontinuity can be compensated with by the use of a manufacturable method. PMID:15857045

  9. Evaluation of the applicability of Helmholtz resonators for low frequency acoustic liners

    NASA Astrophysics Data System (ADS)

    Vanderwal, J. M. M.

    1988-09-01

    A literature study was performed on the acoustic behavior of those Helmholtz resonator type liners which are most promising for low frequency sound absorption in aero-engine applications. The equations for the acoustic impedance of various types of Helmholtz resonators were analyzed as well as the conditions for the validity of these equations. An experimental program is defined for a further analysis of various types of resonators.

  10. Unique gel-coupled acoustic sensor array monitors human voice and physiology

    NASA Astrophysics Data System (ADS)

    Scanlon, Michael

    2002-11-01

    The health and performance of soldiers, firefighters, and other first responders in strenuous and hazardous environments can be continuously and remotely monitored with body-worn acoustic sensors. The Army Research Laboratory's gel-coupled acoustic physiological monitoring sensor has acoustic impedance properties similar to the skin that facilitate the transmission of body sounds into the sensor pad, yet significantly repel ambient airborne noises due to an impedance mismatch. Acoustic signal processing detects physiological events such as heartbeats, breaths, wheezes, coughs, blood pressure, activity, motion, and voice for communication and automatic speech recognition. Acoustic sensors can be in a helmet or in a strap around the neck, chest, and wrist. Although the physiological sounds have high SNR, the acoustic sensor also responds to motion-induced artifacts that sometimes obscure meaningful physiology. A noise-canceling sensor array configuration helps remove motion noise by using two acoustic sensors on the front sides of the neck and 2 additional acoustic sensors on each wrist. The motion noise detected on all 4 sensors will be dissimilar and out of phase, yet the physiology on all 4 sensors is covariant. Pulse wave transit time between neck and wrist will indicate systolic blood pressure. Data from a firefighter experiment will be presented.

  11. Rotor damage detection by using piezoelectric impedance

    NASA Astrophysics Data System (ADS)

    Qin, Y.; Tao, Y.; Mao, Y. F.

    2016-04-01

    Rotor is a core component of rotary machinery. Once the rotor has the damage, it may lead to a major accident. Thus the quantitative rotor damage detection method based on piezoelectric impedance is studied in this paper. With the governing equation of piezoelectric transducer (PZT) in a cylindrical coordinate, the displacement along the radius direction is derived. The charge of PZT is calculated by the electric displacement. Then, by the use of the obtained displacement and charge, an analytic piezoelectric impedance model of the rotor is built. Given the circular boundary condition of a rotor, annular elements are used as the analyzed objects and spectral element method is used to set up the damage detection model. The Electro-Mechanical (E/M) coupled impedance expression of an undamaged rotor is deduced with the application of a low-cost impedance test circuit. A Taylor expansion method is used to obtain the approximate E/M coupled impedance expression for the damaged rotor. After obtaining the difference between the undamaged and damaged rotor impedance, a rotor damage detection method is proposed. This method can directly calculate the change of bending stiffness of the structural elements, it follows that the rotor damage can be effectively detected. Finally, a preset damage configuration is used for the numerical simulation. The result shows that the quantitative damage detection algorithm based on spectral element method and piezoelectric impedance proposed in this paper can identify the location and the severity of the damaged rotor accurately.

  12. Tracking of electrochemical impedance of batteries

    NASA Astrophysics Data System (ADS)

    Piret, H.; Granjon, P.; Guillet, N.; Cattin, V.

    2016-04-01

    This paper presents an evolutionary battery impedance estimation method, which can be easily embedded in vehicles or nomad devices. The proposed method not only allows an accurate frequency impedance estimation, but also a tracking of its temporal evolution contrary to classical electrochemical impedance spectroscopy methods. Taking into account constraints of cost and complexity, we propose to use the existing electronics of current control to perform a frequency evolutionary estimation of the electrochemical impedance. The developed method uses a simple wideband input signal, and relies on a recursive local average of Fourier transforms. The averaging is controlled by a single parameter, managing a trade-off between tracking and estimation performance. This normalized parameter allows to correctly adapt the behavior of the proposed estimator to the variations of the impedance. The advantage of the proposed method is twofold: the method is easy to embed into a simple electronic circuit, and the battery impedance estimator is evolutionary. The ability of the method to monitor the impedance over time is demonstrated on a simulator, and on a real Lithium ion battery, on which a repeatability study is carried out. The experiments reveal good tracking results, and estimation performance as accurate as the usual laboratory approaches.

  13. Estimates of Acausal Joint Impedance Models

    PubMed Central

    Perreault, Eric J.

    2013-01-01

    Estimates of joint or limb impedance are commonly used in the study of how the nervous system controls posture and movement, and how that control is altered by injury to the neural or musculoskeletal systems. Impedance characterizes the dynamic relationship between an imposed perturbation of joint position and the torques generated in response. While there are many practical reasons for estimating impedance rather than its inverse, admittance, it is an acausal representation of the limb mechanics that can lead to difficulties in interpretation or use. The purpose of this study was to explore the acausal nature of nonparametric estimates of joint impedance representations to determine how they are influenced by common experimental and computational choices. This was accomplished by deriving discrete-time realizations of first-and second-order derivatives to illustrate two key difficulties in the physical interpretation of impedance impulse response functions. These illustrations were provided using both simulated and experimental data. It was found that the shape of the impedance impulse response depends critically on the selected sampling rate, and on the bandwidth and noise characteristics of the position perturbation used during the estimation process. These results provide important guidelines for designing experiments in which nonparametric estimates of impedance will be obtained, especially when those estimates are to be used in a multistep identification process. PMID:22907963

  14. Estimates of acausal joint impedance models.

    PubMed

    Westwick, David T; Perreault, Eric J

    2012-10-01

    Estimates of joint or limb impedance are commonly used in the study of how the nervous system controls posture and movement, and how that control is altered by injury to the neural or musculoskeletal systems. Impedance characterizes the dynamic relationship between an imposed perturbation of joint position and the torques generated in response. While there are many practical reasons for estimating impedance rather than its inverse, admittance, it is an acausal representation of the limb mechanics that can lead to difficulties in interpretation or use. The purpose of this study was to explore the acausal nature of nonparametric estimates of joint impedance representations to determine how they are influenced by common experimental and computational choices. This was accomplished by deriving discrete-time realizations of first- and second-order derivatives to illustrate two key difficulties in the physical interpretation of impedance impulse response functions. These illustrations were provided using both simulated and experimental data. It was found that the shape of the impedance impulse response depends critically on the selected sampling rate, and on the bandwidth and noise characteristics of the position perturbation used during the estimation process. These results provide important guidelines for designing experiments in which nonparametric estimates of impedance will be obtained, especially when those estimates are to be used in a multistep identification process. PMID:22907963

  15. Measurements of electrical impedance of biomedical objects.

    PubMed

    Frączek, Marcin; Kręcicki, Tomasz; Moron, Zbigniew; Krzywaźnia, Adam; Ociepka, Janusz; Rucki, Zbigniew; Szczepanik, Zdzisław

    2016-01-01

    Some basic problems related to measurements of electrical impedance of biological objects (bioimpedance) have been presented in this paper. Particularly problems arising from impedance occurring at the sensor-tissue interface (interfacial impedances) in contact measuring methods have been discussed. The influence of finite values of impedances of the current source and voltage measuring device has also been taken into consideration. A model of the impedance sensor for the four-electrode measurement method containing the interfacial, source and measuring device impedances has been given and its frequency characteristics obtained by the computer simulation have been presented. The influence of these impedances on the shape of frequency characteristic of the sensor model has been discussed. Measurements of bioimpedance of healthy and anomalous soft tissues have been described. Some experimental results, particularly the frequency characteristics of bioimpedance, have been shown. The presented results of measurement show that bioimpedance can be a valuable source of information about the tissues, so measurement of bioimpedance can be a useful supplement to other medical diagnostic methods. PMID:27151250

  16. Analyzing Acoustic Propagation In A Pump Diffuser And Volute

    NASA Technical Reports Server (NTRS)

    Chon, Juliet T.; Szabo, Roland J.

    1994-01-01

    Theory and computer codes developed for use in analyzing propagation of sinusoidal components of fluctuations of pressure (acoustic waves) through fluid in diffuser and in volute or discharge duct of centrifugal pump. Reflections from impedance mismatches taken into account. Such analysis of propagation and resultant fluctuations of pressure important part of analysis of fluid-borne contributions to stresses on volute housing, volute liner, and/or discharge duct.

  17. AST Launch Vehicle Acoustics

    NASA Technical Reports Server (NTRS)

    Houston, Janice; Counter, D.; Giacomoni, D.

    2015-01-01

    The liftoff phase induces acoustic loading over a broad frequency range for a launch vehicle. These external acoustic environments are then used in the prediction of internal vibration responses of the vehicle and components which result in the qualification levels. Thus, predicting these liftoff acoustic (LOA) environments is critical to the design requirements of any launch vehicle. If there is a significant amount of uncertainty in the predictions or if acoustic mitigation options must be implemented, a subscale acoustic test is a feasible pre-launch test option to verify the LOA environments. The NASA Space Launch System (SLS) program initiated the Scale Model Acoustic Test (SMAT) to verify the predicted SLS LOA environments and to determine the acoustic reduction with an above deck water sound suppression system. The SMAT was conducted at Marshall Space Flight Center and the test article included a 5% scale SLS vehicle model, tower and Mobile Launcher. Acoustic and pressure data were measured by approximately 250 instruments. The SMAT liftoff acoustic results are presented, findings are discussed and a comparison is shown to the Ares I Scale Model Acoustic Test (ASMAT) results.

  18. Acoustic Characteristics of Various Treatment Panel Designs for HSCT Ejector Liner Acoustic Technology Development Program

    NASA Technical Reports Server (NTRS)

    Salikuddin, M.; Kraft, R. E.; Syed, A. a.; Vu, D. D.; Mungur, P.; Langenbrunner, L. E.; Majjigi, R. K.

    2006-01-01

    The objectives of the initial effort (Phase I) of HSR Liner Technology Program, the selection of promising liner concepts, design and fabrication of these concepts for laboratory tests, testing these liners in the laboratory by using impedance tube and flow ducts, and developing empirical impedance/suppression correlation, are successfully completed. Acoustic and aerodynamic criteria for the liner design are established. Based on these criteria several liners are designed. The liner concepts designed and fabricated include Single-Degree-of-Freedom (SDOF), Two-Degree-of-Freedom (2DOF), and Bulk Absorber. Two types of SDOF treatment are fabricated, one with a perforated type face plate and the other with a wiremesh (woven) type faceplate. In addition, special configurations of these concepts are also included in the design. Several treatment panels are designed for parametric study. In these panels the facesheets of different porosity, hole diameter, and sheet thickness are utilized. Several deep panels (i.e., 1 in. deep) are designed and instrumented to measure DC flow resistance and insitu impedance in the presence of grazing flow. Basic components of these panels (i.e., facesheets, bulk materials, etc.) are also procured and tested. The results include DC flow resistance, normal impedance, and insertion loss.

  19. Summary of the impedance working group

    SciTech Connect

    Chao, A.W.

    1995-05-01

    The impedance working group concentrated on the LHC design during the workshop. They look at the impedance contributions of liner, beam position monitors, shielded bellows, experimental chambers, superconducting cavities, recombination chambers, space charge, kickers, and the resistive wall. The group concluded that the impedance budgeting and the conceptual designs of the vacuum chamber components looked basically sound. It also noted, not surprisingly, that a large amount of studies are to be carried out further, and it ventured to give a partial list of these studies.

  20. FDTD modeling of thin impedance sheets

    NASA Technical Reports Server (NTRS)

    Luebbers, Raymond; Kunz, Karl

    1991-01-01

    Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. It is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods. These sheets are characterized by a discontinuity in the tangential magnetic field on either side of the sheet but no discontinuity in tangential electric field. This continuity, or single valued behavior of the electric field, allows the sheet current to be expressed in terms of an impedance multiplying this electric field.

  1. Koch fractal boundary patch over reactive impedance

    NASA Astrophysics Data System (ADS)

    Reddy V, Venkateshwar; Sarma, N. V. S. N.

    2013-04-01

    This paper describes the enhancement of bandwidth and miniaturization for patch antennas. Introduction of fractal structure (Square Koch) over reactive impedance surface (RIS) is used to enhance impedance bandwidth while minimizing the patch size. Comparison has been made with those of a single-layer (sub1) antenna and the corresponding dual-layer (RIS) antenna. Approximately double the impedance bandwidth is achieved with the proposed RIS Square Koch antenna 1 when compared with Square Koch antenna 1without RIS. There is a 55 % reduction in the patch size. The simulated results indicate that the presented antennas provide gain of about 2.5dBi over the entire band of frequencies.

  2. RHIC ABORT KICKER WITH REDUCED COUPLING IMPEDANCE.

    SciTech Connect

    HAHN,H.; DAVINO,D.

    2002-06-02

    Kicker magnets typically represent the most important contributors to the transverse impedance budget of accelerators and storage rings. Methods of reducing the impedance value of the SNS extraction kicker presently under construction and, in view of a future performance upgrade, that of the RHIC abort kicker have been thoroughly studied at this laboratory. In this paper, the investigation of a potential improvement from using ferrite different from the BNL standard CMD5005 is reported. Permeability measurements of several ferrite types have been performed. Measurements on two kicker magnets using CMD5005 and C2050 suggest that the impedance of a magnet without external resistive damping, such as the RHIC abort kicker, would benefit.

  3. Enhancing phonon flow through one-dimensional interfaces by impedance matching

    SciTech Connect

    Polanco, Carlos A. Ghosh, Avik W.

    2014-08-28

    We extend concepts from microwave engineering to thermal interfaces and explore the principles of impedance matching in 1D. The extension is based on the generalization of acoustic impedance to nonlinear dispersions using the contact broadening matrix Γ(ω), extracted from the phonon self energy. For a single junction, we find that for coherent and incoherent phonons, the optimal thermal conductance occurs when the matching Γ(ω) equals the Geometric Mean of the contact broadenings. This criterion favors the transmission of both low and high frequency phonons by requiring that (1) the low frequency acoustic impedance of the junction matches that of the two contacts by minimizing the sum of interfacial resistances and (2) the cut-off frequency is near the minimum of the two contacts, thereby reducing the spillage of the states into the tunneling regime. For an ultimately scaled single atom/spring junction, the matching criterion transforms to the arithmetic mean for mass and the harmonic mean for spring constant. The matching can be further improved using a composite graded junction with an exponential varying broadening that functions like a broadband antireflection coating. There is, however, a trade off as the increased length of the interface brings in additional intrinsic sources of scattering.

  4. Acoustic Translation of an Acoustically Levitated Sample

    NASA Technical Reports Server (NTRS)

    Barmatz, M. B.; Allen, J. L.

    1986-01-01

    Acoustic-levitation apparatus uses only one acoustic mode to move sample from one region of chamber to another. Sample heated and cooled quickly by translation between hot and cold regions of levitation chamber. Levitated sample is raised into furnace region by raising plunger. Frequency of sound produced by transducers adjusted by feedback system to maintain (102) resonant mode, which levitates sample midway between transducers and plunger regardless of plunger position.

  5. The acoustic properties of panels with rectangular apertures.

    PubMed

    Vigran, T E

    2014-05-01

    A model for the acoustic properties of a plate perforated with slots of rectangular shape is proposed. The model is based on known expressions for the complex density and compressibility of a pore of rectangular shape together with the radiation impedance of a rectangular shaped piston in a baffle. For the so-called end correction of a rectangular aperture in a plate, an approximate solution is shown to fit an exact solution for the imaginary part of the radiation impedance, the latter solution based on the work of Lindemann [J. Acoust. Soc. Am, 55, 708-717 (1974)]. Two different procedures are tested to calculate the mutual influence of the apertures on the end correction, the one calculating the mutual impedance of neighboring pistons in the plate, the other by calculating the end correction of a piston placed in the end of an infinitely long tube. The model is used calculating the input impedance and absorption coefficient of a Helmholtz resonator with such a plate, comparing with measurement results. The fit between predicted and measured results, using plates with narrow slits, is good, but it is believed that the model also cover a wider range of dimensions for such a slotted plate. PMID:24815260

  6. Nonlinear Acoustics in Fluids

    NASA Astrophysics Data System (ADS)

    Lauterborn, Werner; Kurz, Thomas; Akhatov, Iskander

    At high sound intensities or long propagation distances at in fluids sufficiently low damping acoustic phenomena become nonlinear. This chapter focuses on nonlinear acoustic wave properties in gases and liquids. The origin of nonlinearity, equations of state, simple nonlinear waves, nonlinear acoustic wave equations, shock-wave formation, and interaction of waves are presented and discussed. Tables are given for the nonlinearity parameter B/A for water and a range of organic liquids, liquid metals and gases. Acoustic cavitation with its nonlinear bubble oscillations, pattern formation and sonoluminescence (light from sound) are modern examples of nonlinear acoustics. The language of nonlinear dynamics needed for understanding chaotic dynamics and acoustic chaotic systems is introduced.

  7. Mutual impedance computation between printed dipoles

    NASA Astrophysics Data System (ADS)

    Alexopoulos, N. G.; Rana, I. E.

    1981-01-01

    The mutual impedance between microstrip dipoles printed on a grounded substrate is computed. Results for the microstrip dipoles in broadside, collinear, and echelon arrangements are presented. The significance of surface wave to mutual coupling is discussed.

  8. Antenna pattern control using impedance surfaces

    NASA Technical Reports Server (NTRS)

    Balanis, Constantine A.; Liu, Kefeng; Tirkas, Panayiotis A.

    1993-01-01

    During the period of this research project, a comprehensive study of pyramidal horn antennas was conducted. Full-wave analytical and numerical techniques were developed to analyze horn antennas with or without impedance surfaces. Based on these full-wave analytic techniques, research was conducted on the use of impedance surfaces on the walls of the horn antennas to control the antenna radiation patterns without a substantial loss of antenna gain. It was found that the use of impedance surfaces could modify the antenna radiation patterns. In addition to the analytical and numerical models, experimental models were also constructed and they were used to validate the predictions. Excellent agreement between theoretical predictions and the measured data was obtained for pyramidal horns with perfectly conducting surfaces. Very good comparisons between numerical and experimental models were also obtained for horns with impedance surfaces.

  9. Impedance feedback control for scanning electrochemical microscopy.

    PubMed

    Alpuche-Aviles, M A; Wipf, D O

    2001-10-15

    A new constant-distance imaging method based on the relationship between tip impedance and tip-substrate separation has been developed for the scanning electrochemical microscope. The tip impedance is monitored by application of a high-frequency ac voltage bias between the tip and auxiliary electrode. The high-frequency ac current is easily separated from the dc-level faradaic electrochemistry with a simple RC filter, which allows impedance measurements during feedback or generation/collection experiments. By employing a piezo-based feedback controller, we are able to maintain the impedance at a constant value and, thus, maintain a constant tip-substrate separation. Application of the method to feedback and generation/collection experiments with tip electrodes as small as 2 microm is presented. PMID:11681463

  10. Inversion of elastic impedance for unconsolidated sediments

    USGS Publications Warehouse

    Lee, Myung W.

    2006-01-01

    Elastic properties of gas-hydrate-bearing sediments are important for quantifying gas hydrate amounts as well as discriminating the gas hydrate effect on velocity from free gas or pore pressure. This paper presents an elastic inversion method for estimating elastic properties of gas-hydrate-bearing sediments from angle stacks using sequential inversion of P-wave impedance from the zero-offset stack and S-wave impedance from the far-offset stack without assuming velocity ratio.

  11. CSR Impedance for Non-Ultrarelativistic Beams

    SciTech Connect

    Li, Rui; Tsai, Cheng Y.

    2015-09-01

    For the analysis of the coherent synchrotron radiation (CSR)-induced microbunching gain in the low energy regime, such as when a high-brightness electron beam is transported through a low-energy merger in an energy-recovery linac (ERL) design, it is necessary to extend the CSR impedance expression in the ultrarelativistic limit to the non-ultrarelativistic regime. This paper presents our analysis of CSR impedance for general beam energies.

  12. Wave impedance of an atomically thin crystal.

    PubMed

    Merano, Michele

    2015-11-30

    I propose an expression for the electromagnetic wave impedance of a two-dimensional atomic crystal, and I deduce the Fresnel coefficients in terms of this quantity. It is widely known that a two-dimensional crystal can absorb light, if its conductivity is different from zero. It is less emphasized that they can also store a certain amount of electromagnetic energy. The concept of impedance is useful to quantify this point. PMID:26698783

  13. Localized acoustic surface modes

    NASA Astrophysics Data System (ADS)

    Farhat, Mohamed; Chen, Pai-Yen; Bağcı, Hakan

    2016-04-01

    We introduce the concept of localized acoustic surface modes. We demonstrate that they are induced on a two-dimensional cylindrical rigid surface with subwavelength corrugations under excitation by an incident acoustic plane wave. Our results show that the corrugated rigid surface is acoustically equivalent to a cylindrical scatterer with uniform mass density that can be represented using a Drude-like model. This, indeed, suggests that plasmonic-like acoustic materials can be engineered with potential applications in various areas including sensing, imaging, and cloaking.

  14. Low frequency acoustic microscope

    DOEpatents

    Khuri-Yakub, Butrus T.

    1986-11-04

    A scanning acoustic microscope is disclosed for the detection and location of near surface flaws, inclusions or voids in a solid sample material. A focused beam of acoustic energy is directed at the sample with its focal plane at the subsurface flaw, inclusion or void location. The sample is scanned with the beam. Detected acoustic energy specularly reflected and mode converted at the surface of the sample and acoustic energy reflected by subsurface flaws, inclusions or voids at the focal plane are used for generating an interference signal which is processed and forms a signal indicative of the subsurface flaws, inclusions or voids.

  15. Acoustic dispersive prism.

    PubMed

    Esfahlani, Hussein; Karkar, Sami; Lissek, Herve; Mosig, Juan R

    2016-01-01

    The optical dispersive prism is a well-studied element, which allows separating white light into its constituent spectral colors, and stands in nature as water droplets. In analogy to this definition, the acoustic dispersive prism should be an acoustic device with capability of splitting a broadband acoustic wave into its constituent Fourier components. However, due to the acoustical nature of materials as well as the design and fabrication difficulties, there is neither any natural acoustic counterpart of the optical prism, nor any artificial design reported so far exhibiting an equivalent acoustic behaviour. Here, based on exotic properties of the acoustic transmission-line metamaterials and exploiting unique physical behaviour of acoustic leaky-wave radiation, we report the first acoustic dispersive prism, effective within the audible frequency range 800 Hz-1300 Hz. The dispersive nature, and consequently the frequency-dependent refractive index of the metamaterial are exploited to split the sound waves towards different and frequency-dependent directions. Meanwhile, the leaky-wave nature of the structure facilitates the sound wave radiation into the ambient medium. PMID:26739504

  16. Acoustic dispersive prism

    PubMed Central

    Esfahlani, Hussein; Karkar, Sami; Lissek, Herve; Mosig, Juan R.

    2016-01-01

    The optical dispersive prism is a well-studied element, which allows separating white light into its constituent spectral colors, and stands in nature as water droplets. In analogy to this definition, the acoustic dispersive prism should be an acoustic device with capability of splitting a broadband acoustic wave into its constituent Fourier components. However, due to the acoustical nature of materials as well as the design and fabrication difficulties, there is neither any natural acoustic counterpart of the optical prism, nor any artificial design reported so far exhibiting an equivalent acoustic behaviour. Here, based on exotic properties of the acoustic transmission-line metamaterials and exploiting unique physical behaviour of acoustic leaky-wave radiation, we report the first acoustic dispersive prism, effective within the audible frequency range 800 Hz–1300 Hz. The dispersive nature, and consequently the frequency-dependent refractive index of the metamaterial are exploited to split the sound waves towards different and frequency-dependent directions. Meanwhile, the leaky-wave nature of the structure facilitates the sound wave radiation into the ambient medium. PMID:26739504

  17. Acoustic dispersive prism

    NASA Astrophysics Data System (ADS)

    Esfahlani, Hussein; Karkar, Sami; Lissek, Herve; Mosig, Juan R.

    2016-01-01

    The optical dispersive prism is a well-studied element, which allows separating white light into its constituent spectral colors, and stands in nature as water droplets. In analogy to this definition, the acoustic dispersive prism should be an acoustic device with capability of splitting a broadband acoustic wave into its constituent Fourier components. However, due to the acoustical nature of materials as well as the design and fabrication difficulties, there is neither any natural acoustic counterpart of the optical prism, nor any artificial design reported so far exhibiting an equivalent acoustic behaviour. Here, based on exotic properties of the acoustic transmission-line metamaterials and exploiting unique physical behaviour of acoustic leaky-wave radiation, we report the first acoustic dispersive prism, effective within the audible frequency range 800 Hz-1300 Hz. The dispersive nature, and consequently the frequency-dependent refractive index of the metamaterial are exploited to split the sound waves towards different and frequency-dependent directions. Meanwhile, the leaky-wave nature of the structure facilitates the sound wave radiation into the ambient medium.

  18. Modeling magnetically insulated devices using flow impedance

    SciTech Connect

    Mendel, C.W. Jr.; Rosenthal, S.E. )

    1995-04-01

    In modern pulsed power systems the electric field stresses at metal surfaces in vacuum transmission lines are so high that negative surfaces are space-charge-limited electron emitters. These electrons do not cause unacceptable losses because magnetic fields due to system currents result in net motion parallel to the electrodes. It has been known for several years that a parameter known as flow impedance is useful for describing these flows. Flow impedance is a measure of the separation between the anode and the mean position of the electron cloud, and it will be shown in this paper that in many situations flow impedance depends upon the geometry of the transmission line upstream of the point of interest. It can be remarkably independent of other considerations such as line currents and voltage. For this reason flow impedance is a valuable design parameter. Models of impedance transitions and voltage adders using flow impedance will be developed. Results of these models will be compared to two-dimensional, time-dependent, particle-in-cell simulations.

  19. History of structural acoustics and vibrations in the Acoustical Society of America

    NASA Astrophysics Data System (ADS)

    Feit, David; Strasberg, Murray; Ungar, Eric E.

    2002-05-01

    Structural acoustics refers to the interaction of sound and structures-the response of structures to sound, the radiation of sound from vibrating structures, and the effect of the acoustic medium on the structural vibrations. Interest in these subjects increased greatly during the 1930s and 40s because of practical applications in the design of microphones and loud speakers used in telephones, radios, and electronic phonographs. The combination of electrical and mechanical systems lead to the use of electrical engineering concepts such as impedance, circuits, and electrical analogies, in the analysis of mechanical systems. In later years, much of the work dealt with various aspects of underwater structures, prompted by U.S. Navy interests. The field, which began with classical analytical mechanics applications, has progressed to new approaches, including statistical energy analysis, near-field acoustical holography, fuzzy structures, active control of vibrations, and smart materials. In recognition of these new developments, the name of the technical committee was changed in 1987 from ``Shock and Vibration'' to ``Structural Acoustics and Vibration.''

  20. Experimental study of coupling impedance: Part I longitudinal impedance measurement techniques

    SciTech Connect

    Song, J.J.

    1991-10-22

    Beam coupling impedances for the 7-GeV APS storage ring have been numerically estimated. In order to confirm these calculations, measurements of the coupling impedance of various vacuum components around the main storage ring were done with a coaxial wire method. In this paper, the procedure of the longitudinal impedance measurement techniques will be described. As an example, sections of the Cu beam chamber, the Cu beam + antechambers, and the Al beam + antechambers were used as a device under test (DUT) to obtain the results. The transverse impedance measurements will be described in a separate paper.

  1. Ultrasonic waveguide sensor for acoustic monitoring of nuclear power plants

    SciTech Connect

    Mel'nikov, V.I.; Khokhlov, V.N.; Duntsev, A.V.

    1988-02-01

    Waveguide sensors are being increasingly used for acoustic emission monitoring of equipment in nuclear power plants and in systems for acoustic diagnostics of the coolant. In this paper we examine the construction of a waveguide sensor for acoustic monitoring for the example of an impedance sensor for the steam content of water coolant, intended for use in the active emission-reception mode. The dynamic properties of the sensor are determined by the construction and the dimensions of the transducer, and are usually represented by its amplitude-frequency characteristic, which, as a rule, is of the resonance type. The longitudinal-wave waveguide, made from steel wire 0.8-1.2 mm in diameter, can transmit signals in the band 50-1000 kHz. To increase the reliability and the ease of maintenance of the monitoring system the transducer and the waveguide are connected in a detachable manner.

  2. Acoustic Liner Drag: A Parametric Study of Conventional Configurations

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Jones, Michael G.

    2015-01-01

    Interest in the characterization of the aerodynamic drag performance of acoustic liners has increased in the past several years. This paper details experiments in NASA Langley's Grazing Flow Impedance Tube to quantify the relative drag of several conventional perforate-over-honeycomb liner configurations. For a fixed porosity, facesheet hole diameter and cavity depth are varied to study the effect of each. These configurations are selected to span the range of conventional liner geometries used in commercial aircraft engines. Detailed static pressure and acoustic measurements are made for grazing flows up to M=0.5 at 140 dB SPL for tones between 400 and 2800 Hz. These measurements are used to calculate a resistance factor (?) for each configuration. Analysis shows a correlation between perforate hole size and the resistance factor but cavity depth seems to have little influence. Acoustic effects on liner drag are observed to be limited to the lower Mach numbers included in this investigation.

  3. Acoustic carpet cloak based on an ultrathin metasurface

    NASA Astrophysics Data System (ADS)

    Esfahlani, Hussein; Karkar, Sami; Lissek, Herve; Mosig, Juan R.

    2016-07-01

    An acoustic metasurface carpet cloak based on membrane-capped cavities is proposed and investigated numerically. This design has been chosen for allowing ultrathin geometries, although adapted to airborne sound frequencies in the range of 1 kHz (λ ≈30 cm), surpassing the designs reported in the literature in terms of thinness. A formulation of generalized Snell's laws is first proposed, mapping the directions of the incident and reflected waves to the metasurface phase function. This relation is then applied to achieve a prescribed wavefront reflection direction, for a given incident direction, by controlling the acoustic impedance grading along the metasurface. The carpet cloak performance of the proposed acoustic metasurface is then assessed on a triangular bump obstacle, generally considered as a baseline configuration in the literature.

  4. Enhancement of acoustical performance of hollow tube sound absorber

    NASA Astrophysics Data System (ADS)

    Putra, Azma; Khair, Fazlin Abd; Nor, Mohd Jailani Mohd

    2016-03-01

    This paper presents acoustical performance of hollow structures utilizing the recycled lollipop sticks as acoustic absorbers. The hollow cross section of the structures is arranged facing the sound incidence. The effects of different length of the sticks and air gap on the acoustical performance are studied. The absorption coefficient was measured using impedance tube method. Here it is found that improvement on the sound absorption performance is achieved by introducing natural kapok fiber inserted into the void between the hollow structures. Results reveal that by inserting the kapok fibers, both the absorption bandwidth and the absorption coefficient increase. For test sample backed by a rigid surface, best performance of sound absorption is obtained for fibers inserted at the front and back sides of the absorber. And for the case of test sample with air gap, this is achieved for fibers introduced only at the back side of the absorber.

  5. A cluster of many small holes with negative imaginary surface impedances may generate a negative refraction index

    NASA Astrophysics Data System (ADS)

    Alsaedi, Ahmed; Ahmad, Bashir; Challa, Durga Prasad; Kirane, Mokhtar; Sini, Mourad

    2016-09-01

    We deal with the scattering of an acoustic medium modeled by an index of refraction $n$ varying in a bounded region $\\Omega$ of $\\mathbb{R}^3$ and equal to unity outside $\\Omega$. This region is perforated with an extremely large number of small holes $D_m$'s of maximum radius $a$, $a<<1$, modeled by surface impedance functions. Precisely, we are in the regime described by the number of holes of the order $M:=O(a^{\\beta-2})$, the minimum distance between the holes is $d\\sim a^t$ and the surface impedance functions of the form $\\lambda_m \\sim \\lambda_{m,0} a^{-\\beta}$ with $\\beta >0$ and $\\lambda_{m,0}$ being constants and eventually complex numbers. Under some natural conditions on the parameters $\\beta, t$ and $\\lambda_{m,0}$, we characterize the equivalent medium generating, approximately, the same scattered waves as the original perforated acoustic medium. We give an explicit error estimate between the scattered waves generated by the perforated medium and the equivalent one respectively, as $a \\rightarrow 0$. As applications of these results, we discuss the following findings: 1. If we choose negative valued imaginary surface impedance functions, attached to each surface of the holes, then the equivalent medium behaves as a passive acoustic medium only if it is an acoustic metamaterial with index of refraction $\\tilde{n}(x)=-n(x),\\; x \\in \\Omega$ and $\\tilde{n}(x)=1,\\; x \\in \\mathbb{R}^3\\setminus{\\overline{\\Omega}}$. This means that, with this process, we can switch the sign of the index of the refraction from positive to negative values. 2. We can choose the surface impedance functions attached to each surface of the holes so that the equivalent index of refraction $\\tilde{n}$ is $\\tilde{n}(x)=1,\\; x \\in \\mathbb{R}^3$. This means that the region $\\Omega$ modeled by the original index of refraction $n$ is approximately cloaked.

  6. Radiation impedance study of a capacitive micromachined ultrasonic transducer by finite element analysis.

    PubMed

    Bayram, Baris

    2015-08-01

    In this study, radiation impedance of a capacitive micromachined ultrasonic transducer composed of square-shaped membranes arranged in m × m configuration (m = 1 - 5) is investigated using finite element analysis (FEA) of a commercially available software package(ANSYS). Radiation impedance is calculated for immersed membranes operating in conventional and collapse modes. Individual membrane response within the multi-membrane configuration is analyzed, and excited modes and their effects on radiation impedance and the pressure spectra are reported. This FEA provides an accurate behavior of the acoustic coupling of a thin membrane in a multi-membrane configuration, and extends above the anti-resonance frequency. The first resonance frequency of the membrane is excited for m × m (m ≥ 3) configuration in conventional mode and for m × m (m ≥ 2) configuration in collapse mode. Therefore, this frequency is determined to be responsible for the adverse effects observed in radiation impedance and pressure spectrum. A membrane configuration, which is missing the central membrane from the full m × m configuration is proposed, and is investigated with the FEA. This study is beneficial for the design of precise transducers suited for biomedical applications. PMID:26328680

  7. Modelling acoustic scattering by suspended flocculating sediments

    NASA Astrophysics Data System (ADS)

    Thorne, Peter D.; MacDonald, Iain T.; Vincent, Christopher E.

    2014-10-01

    The development of a theoretical description of how sound interacts with flocculating sediments has been lacking and this deficiency has impeded sound being used to extract quantitative suspended sediment parameters in suspensions containing flocs. As a step towards theoretically examining this problem a relatively simple heuristic approach has been adopted to provide a description of the interaction of sound with suspensions that undergo flocculation. A model is presented for the interpretation of acoustic scattering from suspensions of fine sediments as they transition from primary particles, through an intermediate regime, to the case where low density flocs dominate the acoustic scattering. The approach is based on modified spherical elastic solid and elastic fluid scatterers and a combination of both. To evaluate the model the variation of density and compressional velocity within the flocs as they form and grow in size is required. The density can be estimated from previous studies; however, the velocity is unknown and is formulated here using a fluid mixture approach. Uncertainties in these parameters can have a significant effect on the predicted scattering characteristics and are therefore investigated in the present study. Furthermore, to assess the proposed model, outputs are compared with recently published laboratory observations of acoustic scattering by flocculating cohesive suspensions.

  8. Acoustic properties of low growing plants.

    PubMed

    Horoshenkov, Kirill V; Khan, Amir; Benkreira, Hadj

    2013-05-01

    The plane wave normal incidence acoustic absorption coefficient of five types of low growing plants is measured in the presence and absence of soil. These plants are generally used in green living walls and flower beds. Two types of soil are considered in this work: a light-density, man-made soil and a heavy-density natural clay base soil. The absorption coefficient data are obtained in the frequency range of 50-1600 Hz using a standard impedance tube of diameter 100 mm. The equivalent fluid model for sound propagation in rigid frame porous media proposed by Miki [J. Acoust. Soc. Jpn. (E) 11, 25-28 (1990)] is used to predict the experimentally observed behavior of the absorption coefficient spectra of soils, plants, and their combinations. Optimization analysis is employed to deduce the effective flow resistivity and tortuosity of plants which are assumed to behave acoustically as an equivalent fluid in a rigid frame porous medium. It is shown that the leaf area density and dominant angle of leaf orientation are two key morphological characteristics which can be used to predict accurately the effective flow resistivity and tortuosity of plants. PMID:23654364

  9. Preliminary Experiments on Noise Reduction in Cavities Using Active Impedance Changes

    NASA Astrophysics Data System (ADS)

    LACOUR, O.; GALLAND, M. A.; THENAIL, D.

    2000-02-01

    This paper reports experiments on the active control of enclosed sound fields via wall impedance changes. Two methods previously developed allow one to implement practically active acoustic impedances: the first is referred to as “direct” control and permits precise realizations for harmonic excitations, while the second is a hybrid passive/active feedback control well suited for random noise treatments. The two techniques have been already presented [1]; the contribution of this work relies on testing the efficiency of both systems in silencing two enclosures through experimental analyses, subsequently compared with classical analytical description. The first test cavity is one-dimensional; a global sound reduction is achieved by the hybrid system for a broadband primary excitation. The second system is a reactangular three-dimensional cavity closed by a simply supported elastic plate. The noise source is an external load applied at one point of the plate. Different impedance values are successively assigned, their effect being estimated through a global sound level indicator. Attention is also given to plate vibration changes, which may occur. Three typical behaviours of the plate-cavity system are investigated. A first experiment involves an excitation at an acoustic resonance and induces a weak plate-cavity coupling. The second, also at an acoustic resonance of the cavity, yields a strong coupling while the third corresponds to an off-resonance excitation. The hybrid feedback control system provides useful attenuation for all cases, and shows also a promising behaviour when dealing with broadband excitations. It confirms the interest of the method when classical feedforward active control fails, i.e., when reliable prior information of the undesired disturbance is not available.

  10. Full-Field Imaging of GHz Film Bulk Acoustic Resonator Motion

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert; Cottle, David Lynn; Larson III, J. D.

    2003-10-01

    A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by using dynamic holography with photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed that is capable of operation at gigahertz frequency and micron length scales. Both acoustic amplitude and phase are recorded, allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies of 800-900 MHz, illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric-to-acoustic coupling of these devices and their performance. Images of 256 /spl times/ 240 pixels are recorded at 18 fps rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level at each pixel calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.

  11. Large area planar fiber optic accelerometers for measurement of acoustic velocity

    SciTech Connect

    Bucaro, J.A.; Lagakos, N.; Houston, B.H.; Kraus, L.

    1996-04-01

    Large area, flexible planar fiber optic accelerometers have been developed for use as acoustic velocity sensors in underwater applications. The devices use a specially designed optical fiber with specific jackets which suppress the fiber sensor{close_quote}s response to acoustic pressure. The sensor has been subjected to a variety of tests including direct acceleration response, direct pressure response, and response to flexural wave excitation when mounted to a {open_quote}{open_quote}hull simulator{close_quote}{close_quote} backing structure. A thorough analysis has been carried out to understand the dynamic responses and limitations of these sensor types. This work is motivated by the desire to measure spatially averaged acoustic velocity while suppressing higher wavenumber mechanical excitations. In conjunction with existing large area pressure sensors (or with suitable structural models), these devices would provide a powerful capability for the measurement and detection of acoustic fields near structures having general impedance properties. This would allow, for example, the decomposition of the acoustic field into backward and forward propagating waves near such a boundary, the determination of acoustic intensity, the detection of the acoustic field with high signal-to-noise ratios even near a soft, pressure release boundary, and determination of the impedance of the structure itself. {copyright} {ital 1996 American Institute of Physics.}

  12. An Overview of Acoustic Telemetry

    SciTech Connect

    Drumheller, D.S.

    1992-03-24

    Acoustic telemetry has been a dream of the drilling industry for the past 50 years. It offers the promise of data rates which are one-hundred times greater than existing technology. Such a system would open the door to true logging-while-drilling technology and bring enormous profits to its developers. The oil and gas industry has led in most of the attempts to develop this type of telemetry system; however, very substantial efforts have also been made through government sponsored work in the geothermal industry. None of these previous attempts have lead to a commercial telemetry system. Conceptually, the problem looks easy. The basic idea is to produce an encoded sound wave at the bottom of the well, let it propagate up the steel drillpipe, and extract the data from the signal at the surface. Unfortunately, substantial difficulties arise. The first difficult problem is to produce the sound wave. Since the most promising transmission wavelengths are about 20 feet, normal transducer efficiencies are quite low. Compounding this problem is the structural complexity of the bottomhole assembly and drillstring. For example, the acoustic impedance of the drillstring changes every 30 feet and produces an unusual scattering pattern in the acoustic transmission. This scattering pattern causes distortion of the signal and is often confused with signal attenuation. These problems are not intractable. Recent work has demonstrated that broad frequency bands exist which are capable of transmitting data at rates up to 100 bits per second. Our work has also identified the mechanism which is responsible for the observed anomalies in the patterns of signal attenuation. Furthermore in the past few years a body of experience has been developed in designing more efficient transducers for application to metal Waveguides. The direction of future work is clear. New transducer designs which are more efficient and compatible with existing downhole power supplies need to be built and tested

  13. On the acoustic properties of vaporized submicron perfluorocarbon droplets.

    PubMed

    Reznik, Nikita; Lajoinie, Guillaume; Shpak, Oleksandr; Gelderblom, Erik C; Williams, Ross; de Jong, Nico; Versluis, Michel; Burns, Peter N

    2014-06-01

    The acoustic characteristics of microbubbles created from vaporized submicron perfluorocarbon droplets with fluorosurfactant coating are examined. Utilizing ultra-high-speed optical imaging, the acoustic response of individual microbubbles to low-intensity diagnostic ultrasound was observed on clinically relevant time scales of hundreds of milliseconds after vaporization. It was found that the vaporized droplets oscillate non-linearly and exhibit a resonant bubble size shift and increased damping relative to uncoated gas bubbles due to the presence of coating material. Unlike the commercially available lipid-coated ultrasound contrast agents, which may exhibit compression-only behavior, vaporized droplets may exhibit expansion-dominated oscillations. It was further observed that the non-linearity of the acoustic response of the bubbles was comparable to that of SonoVue microbubbles. These results suggest that vaporized submicron perfluorocarbon droplets possess the acoustic characteristics necessary for their potential use as ultrasound contrast agents in clinical practice. PMID:24462162

  14. Acoustic Gaits: Gait Analysis With Footstep Sounds.

    PubMed

    Altaf, M Umair Bin; Butko, Taras; Juang, Biing-Hwang Fred

    2015-08-01

    We describe the acoustic gaits-the natural human gait quantitative characteristics derived from the sound of footsteps as the person walks normally. We introduce the acoustic gait profile, which is obtained from temporal signal analysis of sound of footsteps collected by microphones and illustrate some of the spatio-temporal gait parameters that can be extracted from the acoustic gait profile by using three temporal signal analysis methods-the squared energy estimate, Hilbert transform and Teager-Kaiser energy operator. Based on the statistical analysis of the parameter estimates, we show that the spatio-temporal parameters and gait characteristics obtained using the acoustic gait profile can consistently and reliably estimate a subset of clinical and biometric gait parameters currently in use for standardized gait assessments. We conclude that the Teager-Kaiser energy operator provides the most consistent gait parameter estimates showing the least variation across different sessions and zones. Acoustic gaits use an inexpensive set of microphones with a computing device as an accurate and unintrusive gait analysis system. This is in contrast to the expensive and intrusive systems currently used in laboratory gait analysis such as the force plates, pressure mats and wearable sensors, some of which may change the gait parameters that are being measured. PMID:25769144

  15. Virtual Acoustics: Evaluation of Psychoacoustic Parameters

    NASA Technical Reports Server (NTRS)

    Begault, Durand R.; Null, Cynthia H. (Technical Monitor)

    1997-01-01

    Current virtual acoustic displays for teleconferencing and virtual reality are usually limited to very simple or non-existent renderings of reverberation, a fundamental part of the acoustic environmental context that is encountered in day-to-day hearing. Several research efforts have produced results that suggest that environmental cues dramatically improve perceptual performance within virtual acoustic displays, and that is possible to manipulate signal processing parameters to effectively reproduce important aspects of virtual acoustic perception in real-time. However, the computational resources for rendering reverberation remain formidable. Our efforts at NASA Ames have been focused using a several perceptual threshold metrics, to determine how various "trade-offs" might be made in real-time acoustic rendering. This includes both original work and confirmation of existing data that was obtained in real rather than virtual environments. The talk will consider the importance of using individualized versus generalized pinnae cues (the "Head-Related Transfer Function"); the use of head movement cues; threshold data for early reflections and late reverberation; and consideration of the necessary accuracy for measuring and rendering octave-band absorption characteristics of various wall surfaces. In addition, a consideration of the analysis-synthesis of the reverberation within "everyday spaces" (offices, conference rooms) will be contrasted to the commonly used paradigm of concert hall spaces.

  16. Acoustics Critical Readiness Review

    NASA Technical Reports Server (NTRS)

    Ballard, Kenny

    2010-01-01

    This presentation reviews the status of the acoustic equipment from the medical operations perspective. Included is information about the acoustic dosimeters, sound level meter, and headphones that are planned for use while on orbit. Finally there is information about on-orbit hearing assessments.

  17. The challenge of acoustics

    NASA Astrophysics Data System (ADS)

    Lord, P.

    1981-01-01

    The various applications of acoustics, including sonar, ultrasonic examination of unborn foetuses and architectural applications, are briefly reviewed. Problems in traffic and industrial noise, auditorium design and explosive noise are considered in more detail. The educational aspects of acoustical science and technology are briefly considered.

  18. Acoustic pollution in hospital environments

    NASA Astrophysics Data System (ADS)

    Olivera, J. M.; Rocha, L. A.; Rotger, V. I.; Herrera, M. C.

    2011-12-01

    There are many different services within a hospital. This means different types of noise which can be considered as acoustic pollution. Knowing that preterm infants exposed to high amounts of noise in the NICU are at a much higher risk because of their neurologic immaturity and physiologic instability, that excessive levels of noise also affect the persons and it can also impede some studies on patients, it was proposed to evaluate the Sound Pressure Level in some services of the Instituto de Maternidad, Tucumán, Argentina. There were evaluated the Level III NICU, the laundry service, a physical space destined for a service of evoked potential and a neonatal incubator under working conditions. The measurements were performed with a type II sonometer (CENTER 322) and it was also used an incubator analyzer (FLUKE INCU) for the incubator. The average values obtained were of 63.6 dBA for the NICU, 82.5dBA for the laundry room, 52.7 dBA for the evoked potential room and 62.8 dBA in the inside of the incubator under 64 dBA in the outside. The reports were documented in compliance with the appropriate standards.

  19. Mointoring Thickness Deviations in Planar Multi-Layered Elastic Structures Using Impedance Signatures

    SciTech Connect

    Fisher, K A

    2007-01-26

    In this letter, a low frequency ultrasonic resonance technique that operates in the (20 - 80 kHz) regime is presented that demonstrates detection of thickness changes on the order of +/- 10{micro}m. This measurement capability is a result of the direct correlation between the electrical impedance of an electro-acoustic transducer and the mechanical loading it experiences when placed in contact with a layered elastic structure. The relative frequency shifts of the resonances peaks can be estimated through a simple one-dimensional transmission model. Separate experimental measurements confirm this technique to be sensitive to subtle changes in the underlying layered elastic structure.

  20. Correlation of the effects of grazing flow on the impedance of Helmholtz resonators

    NASA Technical Reports Server (NTRS)

    Walker, B. E.; Charwat, A. F.

    1982-01-01

    Measurements of the acoustic impedance of a two-dimensional Helmholtz resonator, i.e., a cavity coupled to the environment through a high-aspect ratio slot are presented as a function of the velocity of a steady flow above the orifice of the resonator. The structure of the unsteady flow above the orifice is outlined from hot-wire measurements. A simplified model of it is proposed and analyzed, leading to a successful correlation of both the resistance and the reactance of the resonator.

  1. Adaptive contrast imaging: transmit frequency optimization

    NASA Astrophysics Data System (ADS)

    Ménigot, Sébastien; Novell, Anthony; Voicu, Iulian; Bouakaz, Ayache; Girault, Jean-Marc

    2010-01-01

    Introduction: Since the introduction of ultrasound (US) contrast imaging, the imaging systems use a fixed emitting frequency. However it is known that the insonified medium is time-varying and therefore an adapted time-varying excitation is expected. We suggest an adaptive imaging technique which selects the optimal transmit frequency that maximizes the acoustic contrast. Two algorithms have been proposed to find an US excitation for which the frequency was optimal with microbubbles. Methods and Materials: Simulations were carried out for encapsulated microbubbles of 2 microns by considering the modified Rayleigh-Plesset equation for 2 MHz transmit frequency and for various pressure levels (20 kPa up to 420kPa). In vitro experiments were carried out using a transducer operating at 2 MHz and using a programmable waveform generator. Contrast agent was then injected into a small container filled with water. Results and discussions: We show through simulations and in vitro experiments that our adaptive imaging technique gives: 1) in case of simulations, a gain of acoustic contrast which can reach 9 dB compared to the traditional technique without optimization and 2) for in vitro experiments, a gain which can reach 18 dB. There is a non negligible discrepancy between simulations and experiments. These differences are certainly due to the fact that our simulations do not take into account the diffraction and nonlinear propagation effects. Further optimizations are underway.

  2. Highly directional acoustic receivers.

    PubMed

    Cray, Benjamin A; Evora, Victor M; Nuttall, Albert H

    2003-03-01

    The theoretical directivity of a single combined acoustic receiver, a device that can measure many quantities of an acoustic field at a collocated point, is presented here. The formulation is developed using a Taylor series expansion of acoustic pressure about the origin of a Cartesian coordinate system. For example, the quantities measured by a second-order combined receiver, denoted a dyadic sensor, are acoustic pressure, the three orthogonal components of acoustic particle velocity, and the nine spatial gradients of the velocity vector. The power series expansion, which can be of any order, is cast into an expression that defines the directivity of a single receiving element. It is shown that a single highly directional dyadic sensor can have a directivity index of up to 9.5 dB. However, there is a price to pay with highly directive sensors; these sensors can be significantly more sensitive to nonacoustic noise sources. PMID:12656387

  3. Ocean acoustic hurricane classification.

    PubMed

    Wilson, Joshua D; Makris, Nicholas C

    2006-01-01

    Theoretical and empirical evidence are combined to show that underwater acoustic sensing techniques may be valuable for measuring the wind speed and determining the destructive power of a hurricane. This is done by first developing a model for the acoustic intensity and mutual intensity in an ocean waveguide due to a hurricane and then determining the relationship between local wind speed and underwater acoustic intensity. From this it is shown that it should be feasible to accurately measure the local wind speed and classify the destructive power of a hurricane if its eye wall passes directly over a single underwater acoustic sensor. The potential advantages and disadvantages of the proposed acoustic method are weighed against those of currently employed techniques. PMID:16454274

  4. Acoustic Remote Sensing

    NASA Astrophysics Data System (ADS)

    Dowling, David R.; Sabra, Karim G.

    2015-01-01

    Acoustic waves carry information about their source and collect information about their environment as they propagate. This article reviews how these information-carrying and -collecting features of acoustic waves that travel through fluids can be exploited for remote sensing. In nearly all cases, modern acoustic remote sensing involves array-recorded sounds and array signal processing to recover multidimensional results. The application realm for acoustic remote sensing spans an impressive range of signal frequencies (10-2 to 107 Hz) and distances (10-2 to 107 m) and involves biomedical ultrasound imaging, nondestructive evaluation, oil and gas exploration, military systems, and Nuclear Test Ban Treaty monitoring. In the past two decades, approaches have been developed to robustly localize remote sources; remove noise and multipath distortion from recorded signals; and determine the acoustic characteristics of the environment through which the sound waves have traveled, even when the recorded sounds originate from uncooperative sources or are merely ambient noise.

  5. Acoustic integrated extinction

    PubMed Central

    Norris, Andrew N.

    2015-01-01

    The integrated extinction (IE) is defined as the integral of the scattering cross section as a function of wavelength. Sohl et al. (2007 J. Acoust. Soc. Am. 122, 3206–3210. (doi:10.1121/1.2801546)) derived an IE expression for acoustic scattering that is causal, i.e. the scattered wavefront in the forward direction arrives later than the incident plane wave in the background medium. The IE formula was based on electromagnetic results, for which scattering is causal by default. Here, we derive a formula for the acoustic IE that is valid for causal and non-causal scattering. The general result is expressed as an integral of the time-dependent forward scattering function. The IE reduces to a finite integral for scatterers with zero long-wavelength monopole and dipole amplitudes. Implications for acoustic cloaking are discussed and a new metric is proposed for broadband acoustic transparency. PMID:27547100

  6. Virtual acoustics displays

    NASA Technical Reports Server (NTRS)

    Wenzel, Elizabeth M.; Fisher, Scott S.; Stone, Philip K.; Foster, Scott H.

    1991-01-01

    The real time acoustic display capabilities are described which were developed for the Virtual Environment Workstation (VIEW) Project at NASA-Ames. The acoustic display is capable of generating localized acoustic cues in real time over headphones. An auditory symbology, a related collection of representational auditory 'objects' or 'icons', can be designed using ACE (Auditory Cue Editor), which links both discrete and continuously varying acoustic parameters with information or events in the display. During a given display scenario, the symbology can be dynamically coordinated in real time with 3-D visual objects, speech, and gestural displays. The types of displays feasible with the system range from simple warnings and alarms to the acoustic representation of multidimensional data or events.

  7. Cochlear bionic acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Ma, Fuyin; Wu, Jiu Hui; Huang, Meng; Fu, Gang; Bai, Changan

    2014-11-01

    A design of bionic acoustic metamaterial and acoustic functional devices was proposed by employing the mammalian cochlear as a prototype. First, combined with the experimental data in previous literatures, it is pointed out that the cochlear hair cells and stereocilia cluster are a kind of natural biological acoustic metamaterials with the negative stiffness characteristics. Then, to design the acoustic functional devices conveniently in engineering application, a simplified parametric helical structure was proposed to replace actual irregular cochlea for bionic design, and based on the computational results of such a bionic parametric helical structure, it is suggested that the overall cochlear is a local resonant system with the negative dynamic effective mass characteristics. There are many potential applications in the bandboard energy recovery device, cochlear implant, and acoustic black hole.

  8. Electron-acoustic solitary waves in a nonextensive plasma

    SciTech Connect

    Tribeche, Mouloud; Djebarni, Lyes

    2010-12-15

    The problem of arbitrary amplitude electron-acoustic solitary waves (EASWs) in a plasma having cold fluid electrons, hot nonextensive electrons, and stationary ions is addressed. It is found that the 'Maxwellianization' process of the hot nonextensive component does not favor the propagation of the EASWs. In contrast to superthermality, nonextensivity makes the electron-acoustic solitary structure less spiky. Our theoretical analysis brings a possibility to develop more refined theories of nonlinear solitary structures in astrophysical plasmas.

  9. Vascular impedance analysis in human pulmonary circulation.

    PubMed

    Zhou, Qinlian; Gao, Jian; Huang, Wei; Yen, Michael

    2006-01-01

    Vascular impedance is determined by morphometry and mechanical properties of the vascular system, as well as the rheology of the blood. The interactions between all these factors are complicated and difficult to investigate solely by experiments. A mathematical model representing the entire system of human pulmonary circulation was constructed based on experimentally measured morphometric and elasticity data of the vessels. The model consisted of 16 orders of arteries and 15 orders of veins. The pulmonary arteries and veins were considered as elastic tubes and their impedance was calculated based on Womersley's theory. The flow in capillaries was described by the "sheet-flow" theory. The model yielded an impedance modulus spectrum that fell steeply from a high value at 0 Hz to a minimum around 1.5 Hz. At about 4 Hz, it reached a second high and then oscillated around a relatively small value at higher frequencies. Characteristic impedance was 27.9 dyn-sec/cm5. Influence of variations in vessel geometry and elasticity on impedance spectra was analyzed. Simulation results showed good agreement with experimental measurements. PMID:16817653

  10. Next Generation Plasma Impedance Probe Instrumentation Technique

    NASA Astrophysics Data System (ADS)

    Carlson, C. G.; Swenson, C. M.; Fish, C.

    2003-12-01

    Four Utah State University Plasma Impedance Probes (PIP) were part of NASA's Sequential Rocket Study of Descending Layers in the E-Region (E-Winds). The payloads were launched at 11:19 pm, 1:41 am, 2:50 am and 3:07 am on June 30 and July 1, 2003 from Wallops Island, Virginia into the nighttime D and E-regions. The PIP is a suite of instruments for observing relative and absolute electron densities, magnetic field strength, and electron-neutral collision frequency. The suite consists of a Plasma Frequency Probe, a Swept Impedance Probe, a Q probe, an experimental Ion Impedance probe, and a DC Langmuir probe. The first four instrument diagnostics are based on the impedance characteristics of an antenna immersed in plasma. Resonance effects at low frequencies (1-100 kHz) where ion dynamics become important were observed by the Ion Impedance Probe. This data set may lead to the first mid-latitude measurements of ion-neutral collision frequency and full conductivity measurements of the ionosphere. Preliminary analysis of flight data shows a considerable amount of sensitivity in all of the instruments that should allow for absolute electron density measurement in the 1 to 10 per cc range and comparable accuracy in electron neutral collision frequency. This paper presents the instrumentation techniques, calibrations and initial results for this flight.

  11. Antenna pattern control using impedence surfaces

    NASA Technical Reports Server (NTRS)

    Balanis, Constantine A.; Liu, Kefeng

    1991-01-01

    During this research period, September 16, 1990 to March 15, 1991, a design method for selecting a low-loss impedance material coating for a horn antenna pattern control has been developed. This method and the stepped waveguide technique can be employed to accurately compute the electromagnetic wave phenomenon inside the transition region of the horn antenna, with or without the impedance surfaces, from the feed to the radiating aperture. For moment method solutions of the electric and magnetic current distributions on the radiating aperture and the outer surface of the horn antenna, triangular surface-patch modes are introduced to replace the sinusoidal surface-patch modes as expansion and testing functions to provide a more physical expansion of the current distributions. In the synthesis problem, a numerical optimization process is formulated to minimize the error function between the desired waveguide modes and the modes provided by the horn transition with impedance surfaces. Since the modes generated by the horn transition with impedance surface are computed by analytical techniques, the computational error involved in the synthesis of the antenna pattern is minimum. Therefore, the instability problem can be avoided. A preliminary implementation of the techniques has demonstrated that the developed theory of the horn antenna pattern control using the impedance surfaces is realizable.

  12. Combined Photoacoustic-Acoustic Technique for Crack Imaging

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Chigarev, N.; Tournat, V.; Gusev, V.

    2010-01-01

    Nonlinear imaging of a crack by combination of a common photoacoustic imaging technique with additional acoustic loading has been performed. Acoustic signals at two different fundamental frequencies were launched in the sample, one photoacoustically through heating of the sample surface by the intensity-modulated scanning laser beam and another by a piezoelectrical transducer. The acoustic signal at mixed frequencies, generated due to system nonlinearity, has been detected by an accelerometer. Different physical mechanisms of the nonlinearity contributing to the contrast in linear and nonlinear photoacoustic imaging of the crack are discussed.

  13. Particle manipulation by a non-resonant acoustic levitator

    SciTech Connect

    Andrade, Marco A. B.; Pérez, Nicolás; Adamowski, Julio C.

    2015-01-05

    We present the analysis of a non-resonant acoustic levitator, formed by an ultrasonic transducer and a concave reflector. In contrast to traditional levitators, the geometry presented herein does not require the separation distance between the transducer and the reflector to be a multiple of half wavelength. The levitator behavior is numerically predicted by applying a numerical model to calculate the acoustic pressure distribution and the Gor'kov theory to obtain the potential of the acoustic radiation force that acts on a levitated particle. We also demonstrate that levitating particles can be manipulated by controlling the reflector position while maintaining the transducer in a fixed position.

  14. Particle manipulation by a non-resonant acoustic levitator

    NASA Astrophysics Data System (ADS)

    Andrade, Marco A. B.; Pérez, Nicolás; Adamowski, Julio C.

    2015-01-01

    We present the analysis of a non-resonant acoustic levitator, formed by an ultrasonic transducer and a concave reflector. In contrast to traditional levitators, the geometry presented herein does not require the separation distance between the transducer and the reflector to be a multiple of half wavelength. The levitator behavior is numerically predicted by applying a numerical model to calculate the acoustic pressure distribution and the Gor'kov theory to obtain the potential of the acoustic radiation force that acts on a levitated particle. We also demonstrate that levitating particles can be manipulated by controlling the reflector position while maintaining the transducer in a fixed position.

  15. Tunable microwave impedance matching to a high impedance source using a Josephson metamaterial

    SciTech Connect

    Altimiras, Carles Parlavecchio, Olivier; Joyez, Philippe; Vion, Denis; Roche, Patrice; Esteve, Daniel; Portier, Fabien

    2013-11-18

    We report the efficient coupling of a 50  Ω microwave circuit to a high impedance conductor. We use an impedance transformer consisting of a λ/4 co-planar resonator whose inner conductor contains an array of superconducting quantum interference devices (SQUIDs), providing it with a tunable lineic inductance L∼80 μ{sub 0}, resulting in a characteristic impedance Z{sub C}∼1 kΩ. The impedance matching efficiency is characterized by measuring the shot noise power emitted by a dc biased tunnel junction connected to the resonator. We demonstrate matching to impedances in the 15 to 35 kΩ range with bandwidths above 100 MHz around a resonant frequency tunable between 4 and 6 GHz.

  16. Tunable microwave impedance matching to a high impedance source using a Josephson metamaterial

    NASA Astrophysics Data System (ADS)

    Altimiras, Carles; Parlavecchio, Olivier; Joyez, Philippe; Vion, Denis; Roche, Patrice; Esteve, Daniel; Portier, Fabien

    2013-11-01

    We report the efficient coupling of a 50 Ω microwave circuit to a high impedance conductor. We use an impedance transformer consisting of a λ/4 co-planar resonator whose inner conductor contains an array of superconducting quantum interference devices (SQUIDs), providing it with a tunable lineic inductance L ˜80 μ0, resulting in a characteristic impedance ZC˜1 k Ω. The impedance matching efficiency is characterized by measuring the shot noise power emitted by a dc biased tunnel junction connected to the resonator. We demonstrate matching to impedances in the 15 to 35 kΩ range with bandwidths above 100 MHz around a resonant frequency tunable between 4 and 6 GHz.

  17. Ocean seismo-acoustics. Low-frequency underwater acoustics

    SciTech Connect

    Akal, T.; berkson, J.M.

    1986-01-01

    This book presents information on seismo-acoustic propagation in seawater and sea beds that includes theoretical developments, modelling and experiments, and fluctuations. Boundary scatteiring, seismo-acoustic waves and seismo-acoustic noise are discussed. Technology and new approaches in seismo-acoustic measurements are presented.

  18. Assessment of noninvasive acoustic respiration rate monitoring in patients admitted to an Emergency Department for drug or alcoholic poisoning.

    PubMed

    Guechi, Youcef; Pichot, Amélie; Frasca, Denis; Rayeh-Pelardy, Fatima; Lardeur, Jean-Yves; Mimoz, Olivier

    2015-12-01

    To compare respiration rate measurement by an acoustic method and thoracic impedance to capnometry as the reference method, in patients at the Emergency Department after drug or alcoholic poisoning. In this observational study, 30 patients aged 18 or older, hospitalized at the Emergency Department for drug or alcoholic poisoning, without any contraindication to a face mask and/or a cervical acoustic sensor, were included in the study. They benefited from a simultaneous recording of their respiration rate by the acoustic method (RRa(®), Masimo Corp., Irvine, CA, USA), by thoracic impedance (Philips Intellivue(®) MP2, Suresnes, France) and by capnometry (Capnostream(®) 20, Oridion, Jerusalem, Israël) through a face mask (Capnomask(®), Mediplus Ltd, Raleigh, NC, USA) for 40-60 min. Of the 86,578 triplets collected, 77,155 (89.1%) were exploitable. Median (range) respiration rate measured by capnometry was 18 (7-29) bpm. Compared to capnometry, bias and limits of agreement were 0.1 ± 3.8 bpm for the acoustic method and 0.3 ± 5.5 bpm for thoracic impedance. The proportions of RR values collected by acoustic method or by thoracic impedance which differed over 10 or 20% during more than 15 s, compared to capnometry, were 8.3 versus 14.3, and 1.5 versus 3.8%, respectively (p < 0.0001). The acoustic sensor had to be repositioned on three patients. For 11 patients, the Capnomask(®) was removed several times. In patients with drug or alcoholic poisoning, the acoustic method seems more accurate than thoracic impedance and better tolerated than face mask capnometry. PMID:25614223

  19. Propellant injection strategy for suppressing acoustic combustion instability

    NASA Astrophysics Data System (ADS)

    Diao, Qina

    Shear-coaxial injector elements are often used in liquid-propellant-rocket thrust chambers, where combustion instabilities remain a significant problem. A conventional solution to the combustion instability problem relies on passive control techniques that use empirically-developed hardware such as acoustic baffles and tuned cavities. In addition to adding weight and decreasing engine performance, these devices are designed using trial-and-error methods, which do not provide the capability to predict the overall system stability characteristics in advance. In this thesis, two novel control strategies that are based on propellant fluid dynamics were investigated for mitigating acoustic instability involving shear-coaxial injector elements. The new control strategies would use a set of controlled injectors allowing local adjustment of propellant flow patterns for each operating condition, particularly when instability could become a problem. One strategy relies on reducing the oxidizer-fuel density gradient by blending heavier methane with the main fuel, hydrogen. Another strategy utilizes modifying the equivalence ratio to affect the acoustic impedance through mixing and reaction rate changes. The potential effectiveness of these strategies was assessed by conducting unit-physics experiments. Two different model combustors, one simulating a single-element injector test and the other a double-element injector test, were designed and tested for flame-acoustic interaction. For these experiments, the Reynolds number of the central oxygen jet was kept between 4700 and 5500 making the injector flames sufficiently turbulent. A compression driver, mounted on one side of the combustor wall, provided controlled acoustic excitation to the injector flames, simulating the initial phase of flame-acoustic interaction. Acoustic excitation was applied either as band-limited white noise forcing between 100 Hz and 5000 Hz or as single-frequency, fixed-amplitude forcing at 1150 Hz

  20. Experimental study of the thermal-acoustic efficiency in a long turbulent diffusion-flame burner

    NASA Technical Reports Server (NTRS)

    Mahan, J. R.

    1983-01-01

    An acoustic source/propagation model is used to interpret measured noise spectra from a long turbulent burner. The acoustic model is based on the perturbation solution of the equations describing the unsteady one-dimensional flow of an inviscid ideal gas with a distributed heat source. The model assumes that the measured noise spectra are due uniquely to the unsteady component of combustion heat release. The model was applied to a long cylindrical hydrogen burner operating over a range of power levels between 4.5 kW and 22.3 kW. Acoustic impedances at the inlet to the burner and at the exit of the tube downstream of the burner were measured and are used as boundary conditions for the model. These measured impedances are also presented.