The acoustic field scattered from some approximate pressure release materials
NASA Astrophysics Data System (ADS)
Caille, Gary W.
1988-03-01
The objective was to determine if a pressure release boundary condition can be achieved by coating an elastic shell with a visco-elastic material. One necessary condition is that the coating must acoustically decouple the shell from the scattering problem. Two closed cell rubbers and two cork-rubber composites (nitrile and neoprene based) were investigated. The dynamic viscoelastic constants of the materials were determined by wave propagation techniques. The far field scattering form functions for an infinite cylindrical shell coated with the viscoelastic material were calculated using the complete elastic equations of motion. The form functions were experimentally measured for the different materials at different thicknesses as verification of the theory. A thick finite right cylindrical shell was coated with .25 inches of closed cell neoprene and the normalized scattered pressure measured. The pressure release normalized scattered pressure was determined for the end on incident plane wave case using the acoustic radiation Simplified Helmholtz Integral Program (SHIP).
Sound field reproduction as an equivalent acoustical scattering problem.
Fazi, Filippo Maria; Nelson, Philip A
2013-11-01
Given a continuous distribution of acoustic sources, the determination of the source strength that ensures the synthesis of a desired sound field is shown to be identical to the solution of an equivalent acoustic scattering problem. The paper begins with the presentation of the general theory that underpins sound field reproduction with secondary sources continuously arranged on the boundary of the reproduction region. The process of reproduction by a continuous source distribution is modeled by means of an integral operator (the single layer potential). It is then shown how the solution of the sound reproduction problem corresponds to that of an equivalent scattering problem. Analytical solutions are computed for two specific instances of this problem, involving, respectively, the use of a secondary source distribution in spherical and planar geometries. The results are shown to be the same as those obtained with analyses based on High Order Ambisonics and Wave Field Synthesis, respectively, thus bringing to light a fundamental analogy between these two methods of sound reproduction. Finally, it is shown how the physical optics (Kirchhoff) approximation enables the derivation of a high-frequency simplification for the problem under consideration, this in turn being related to the secondary source selection criterion reported in the literature on Wave Field Synthesis.
Fischell, Erin M; Schmidt, Henrik
2015-12-01
One of the long term goals of autonomous underwater vehicle (AUV) minehunting is to have multiple inexpensive AUVs in a harbor autonomously classify hazards. Existing acoustic methods for target classification using AUV-based sensing, such as sidescan and synthetic aperture sonar, require an expensive payload on each outfitted vehicle and post-processing and/or image interpretation. A vehicle payload and machine learning classification methodology using bistatic angle dependence of target scattering amplitudes between a fixed acoustic source and target has been developed for onboard, fully autonomous classification with lower cost-per-vehicle. To achieve the high-quality, densely sampled three-dimensional (3D) bistatic scattering data required by this research, vehicle sampling behaviors and an acoustic payload for precision timed data acquisition with a 16 element nose array were demonstrated. 3D bistatic scattered field data were collected by an AUV around spherical and cylindrical targets insonified by a 7-9 kHz fixed source. The collected data were compared to simulated scattering models. Classification and confidence estimation were shown for the sphere versus cylinder case on the resulting real and simulated bistatic amplitude data. The final models were used for classification of simulated targets in real time in the LAMSS MOOS-IvP simulation package [M. Benjamin, H. Schmidt, P. Newman, and J. Leonard, J. Field Rob. 27, 834-875 (2010)].
NASA Astrophysics Data System (ADS)
Caille, Gary William
1988-12-01
The objective was to determine if a pressure release boundary condition can be achieved by coating an elastic shell with a viscoelastic material. One necessary condition is that the coating must acoustically decouple the shell from the scattering problem. Two closed cell rubbers and two cork-rubber composites (nitrile and neoprene based) were investigated. The dynamic viscoelastic constants of the materials were determined by wave propagation techniques. The far field scattering form functions for an infinite cylindrical shell coated with the viscoelastic material were calculated using the complete elastic equations of motion. The form functions were experimentally measured for the different materials at different thicknesses as verification of the theory. A thick finite right cylindrical shell was coated with.25 inches of closed cell neoprene and the normalized scattered pressure measured. The pressure release normalized scattered pressure was determined for the end on incident plane wave case using the acoustic radiation Simplified Helmholtz Integral Program (SHIP). The pressure release normalized scattered pressure was determined for the side incident case using a modified Combined Helmholtz Integral Equation Formulation (CHIEF) radiation program. The material property measurements showed the closed cell rubbers have longitudinal wave propagation speeds of approximately 150 m/sec and attenuations of 30 dB/cm. The cork-rubber composites have longitudinal wave speeds of approximately 300 m/sec and attenuations of 7 dB/cm. The scattering measurements demonstrated that a thin shell (inner radius to outer radius ratio of.97) could be made to scatter in a pressure release manner with a.25 inches of nitrile. The rubber-cork composites could not produce the pressure release effect for nondimensionalized wave number (product of the wave number and the radius of the cylinder) values less than 4 with reasonable thicknesses. The coated finite thick shell, with side
NASA Astrophysics Data System (ADS)
Oguri, Takuma; Tamura, Kazuki; Yoshida, Kenji; Mamou, Jonathan; Hasegawa, Hideyuki; Maruyama, Hitoshi; Hachiya, Hiroyuki; Yamaguchi, Tadashi
2015-07-01
Although there have been several quantitative ultrasound studies on the methods of estimation of scatterer size and acoustic concentration based on the analysis of RF signals for tissue characterization, some problems, e.g., narrow frequency bandwidths and complex sound fields, have limited the clinical applications of such methods. In this report, two types of ultrasound transducer are investigated for the estimation of the scatterer size and acoustic concentration in two glass bead phantoms of different weight concentrations of 0.25 and 2.50% and those in an excised pig liver. The diameters of the glass beads ranged from 5 to 63 µm with an average of 50 µm. The first transducer is a single element and the other is a linear phased array. A comparison of the estimations obtained using both transducers gives an insight into how these methods could be applied clinically. Results obtained using the two transducers were significantly different. One of the possible explanations is that beamforming could significantly affect the backscatter coefficient estimation, which was not taken into account.
NASA Astrophysics Data System (ADS)
Xu, Qiang; Gao, Weiqing; Li, Xue; Ni, Chenquan; Chen, Xiangcai; Chen, Li; Zhang, Wei; Hu, Jigang; Chen, Xiangdong; Yuan, Zijun
2016-10-01
The optical and acoustic fields of stimulated Brillouin scattering (SBS) effect in the As2S3 chalcogenide suspended-core microstructured optical fibers (MOFs) are investigated by the finite-element method (FEM). The optical and acoustic fundamental modes at 1550 nm are analyzed with the core diameters of the MOFs varying from 1.0 to 6.0 μm. For each case, the holes of the MOFs are filled with different materials such as trichlormethane (CHCL3), alcohol and water. When the core diameter is 6.0 μm, the maximum peak intensity of the optical fundamental mode is in the case with air holes, while the minimum value is in the case filled with CHCL3. The ratio of difference is 0.66%. The minimum peak intensity of the acoustic fundamental mode is in the case with air holes, while the maximum value is in the case filled with water. The ratio of difference is 0.13%. The same rule occurs in the fiber cores of 4.5, 3.0 and 2.0 μm, where the decreases of 0.97%, 1.48%, 1.94% for optical field and the increases of 0.24%, 0.34%, 0.74% for acoustic field are obtained, respectively. When the core diameter is 1.0 μm, ratios of difference for optical and acoustic fields are much higher than those in the cases of 2.0-6.0 μm, which are 3.55% and 29.13%, respectively. The overlap factors between optical and acoustic fields are calculated, which are changed with the core diameter and the filled material in holes. Our results will be helpful to strengthen or suppress the SBS effect in practical applications.
Acoustic far-field of shroud-lip-scattered instability modes of supersonic co-flowing jets
NASA Astrophysics Data System (ADS)
Samanta, Arnab; Freund, Jonathan B.
2013-11-01
We consider the acoustic radiation of instability modes in dual-stream jets, with the inner nozzle buried within the outer shroud, particularly the upstream scattering into acoustic modes that occurs at the shroud lip. For supersonic core jets, several families of instability waves are possible, beyond the regular Kelvin-Helmholtz (K-H) mode, with very different modal shapes and propagation characteristics, which are candidates for changing the sound character of very high-speed jets. The co-axial shear layers are modeled as vortex sheets, with the Wiener-Hopf method used to compute these modes coupled with an asymptotic solution for the far-field radiation. A broadband mode spectra as well as single propagating modes are considered as incident and scattered waves. The resulting far-field directivity patterns are quantified, to show the efficiency of some of these radiation mechanisms, particularly in the upstream direction, which is not directly affected by the Mach-wave-like sound that is radiated from these modes irrespective of any scattering surface. A full Kutta condition, which provides the usual boundary condition at the shroud lip, is altered to examine how vortex shedding, perhaps controllable at the lip, affects the radiated sound.
Acoustic Coherent Backscatter Enhancement from Aggregations of Point Scatterers
2014-09-30
acoustic multiple scattering from two- and now three-dimensional aggregations of omni-directional point scatterers to determine the parametric realms in...given by the sum in (1), N is the number of scatterers , gn is the scattering coefficient of the nth scatterer , ψn(rn) is the field incident on the nth...SUBTITLE Acoustic Coherent Backscatter Enhancement from Aggregations of Point Scatterers 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT
Modelling of the acoustic field of a multi-element HIFU array scattered by human ribs.
Gélat, Pierre; Ter Haar, Gail; Saffari, Nader
2011-09-07
The efficacy of high-intensity focused ultrasound (HIFU) for the treatment of a range of different cancers, including those of the liver, prostate and breast, has been demonstrated. As a non-invasive focused therapy, HIFU offers considerable advantages over techniques such as chemotherapy and surgical resection in terms of reduced risk of harmful side effects. Despite this, there are a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the rib cage to induce tissue necrosis in the required volume whilst minimizing the formation of side lobes. Multi-element random-phased arrays are currently showing great promise in overcoming the limitations of single-element transducers. Nevertheless, successful treatment of a patient with liver tumours requires a thorough understanding of the way in which the ultrasonic pressure field from a HIFU array is scattered by the rib cage. In order to address this, a boundary element approach based on a generalized minimal residual (GMRES) implementation of the Burton-Miller formulation was used in conjunction with phase conjugation techniques to focus the field of a 256-element random HIFU array behind human ribs at locations requiring intercostal and transcostal treatment. Simulations were carried out on a 3D mesh of quadratic pressure patches generated using CT scan anatomical data for adult ribs 9-12 on the right side. The methodology was validated on spherical and cylindrical scatterers. Field calculations were also carried out for idealized ribs, consisting of arrays of strip-like scatterers, demonstrating effects of splitting at the focus. This method has the advantage of fully accounting for the effect of scattering and diffraction in 3D under continuous wave excitation.
Acoustic Scattering from Compact Bubble Clouds.
NASA Astrophysics Data System (ADS)
Schindall, Jeffrey Alan
In this study, a simple model describing the low -frequency scattering properties of high void fraction bubble clouds in both the free field and near the ocean surface is developed. This model, which is based on an effective medium approximation and acoustically compact scatters, successfully predicts the results of the bubble cloud scattering experiment carried out at Lake Seneca in New York state for frequencies consistent with the model assumptions (Roy et al., 1992). The introduction of the surface is facilitated by the method of images and is subject to the same constraint of low-acoustic frequency imposed by the compact scatterer assumption. This model is not intended to serve as an exact replicate of oceanic bubble cloud scattering. The model herein was kept simple by design, for only then can the complex physical behavior be expressed in a simple analytical form. Simple, analytic theories facilitate the exploration of parameter space, and more importantly serve to illuminate the underlying physics.
Scattering of Acoustic Waves from Ocean Boundaries
2014-09-30
derived reflection coefficients as a function of range along the reverberation track (right). RESULTS Analysis of Acoustic Scattering for Layered and... acoustic interaction with the ocean floor, including penetration through and reflection from smooth and rough water/sediment interfaces, scattering ...can account for the all of the physical processes and variability of acoustic propagation and scattering in ocean environments with special emphasis
An invariance theorem in acoustic scattering theory
NASA Astrophysics Data System (ADS)
Ha-Duong, T.
1996-10-01
Karp's theorem states that if the far-field pattern corresponding to the scattering of a time-harmonic acoustic plane wave by a sound-soft obstacle is invariant under the group of orthogonal transformations in 0266-5611/12/5/007/img1 (rotations in 0266-5611/12/5/007/img2), then the scatterer is a sphere (circle). The theorem is generalized to the case where the invariant group of the far field pattern is only a subgroup of the orthogonal group, and for a class of mixed boundary conditions.
1988-03-01
Center Frequency) 101 Figure 3-29 Normalized Scattered Pressure Versus ka for Thick Finite Shell (b/a =.9) with Axial Incidence (Solid Line is Shell...Incidence (45 kiz Center Frequency) 104 Figure 3-31 Normalized Scattered Pressure Versus ka for Thick Finite Shell (b/a =.9) with Axial Incidence and...with 0.25 inches of Neoprene for Normal Incidence (20 kHz Center Frequency) 112 X; Figure 3-36 Normalized Scattered Pressure Versus ka for Thick Finite
Novel Acoustic Scattering Processes for Target Discrimination
2007-09-30
acoustic signal using algorithms originally developed for high-frequency acoustical holography [11]. Data is only acquired by scanning a hydrophone ...by the application of a back-propagation algorithm based on the methods of acoustic holography . Selected results relevant to the interpretation of...Novel Acoustic Scattering Processes for Target Discrimination Philip L. Marston Physics and Astronomy Dept., Washington State University, Pullman
Acoustic Coherent Backscatter Enhancement from Aggregations of Point Scatterers
2015-09-30
an aggregation of omnidirectional point scatterers [1]. If ψ(r) is the harmonic acoustic pressure field at frequency ω at the point r and ψ0(r) is...the harmonic field incident on the aggregation of scatterers located at rn, then , (1) where ψ(r) is the
Acoustic Scattering Models of Zooplankton and Microstructures
1998-09-30
Acoustic Scattering Models of Zooplankton and Microstructure Timothy K. Stanton Department of Applied Ocean Physics and Engineering Woods Hole...understand the acoustic reverberation properties of zooplankton and microstructure. The results will lead to improved capability in 1) predicting sonar...performance and 2) use of sonars in the mapping of the zooplankton and microstructure. OBJECTIVES To understand the physics of the scattering by
Acoustic Scattering Models of Zooplankton and Microstructure
1998-09-30
Acoustic Scattering Models of Zooplankton and Microstructure Timothy K. Stanton Department of Applied Ocean Physics and Engineering Woods Hole...understand the acoustic reverberation properties of zooplankton and microstructure. The results will lead to improved capability in 1) predicting sonar...performance and 2) use of sonars in the mapping of the zooplankton and microstructure. OBJECTIVES To understand the physics of the scattering by
Liu, Gang; Jayathilake, Pahala Gedara; Khoo, Boo Cheong
2014-02-01
Two nonlinear models are proposed to investigate the focused acoustic waves that the nonlinear effects will be important inside the liquid around the scatterer. Firstly, the one dimensional solutions for the widely used Westervelt equation with different coordinates are obtained based on the perturbation method with the second order nonlinear terms. Then, by introducing the small parameter (Mach number), a dimensionless formulation and asymptotic perturbation expansion via the compressible potential flow theory is applied. This model permits the decoupling between the velocity potential and enthalpy to second order, with the first potential solutions satisfying the linear wave equation (Helmholtz equation), whereas the second order solutions are associated with the linear non-homogeneous equation. Based on the model, the local nonlinear effects of focused acoustic waves on certain volume are studied in which the findings may have important implications for bubble cavitation/initiation via focused ultrasound called HIFU (High Intensity Focused Ultrasound). The calculated results show that for the domain encompassing less than ten times the radius away from the center of the scatterer, the non-linear effect exerts a significant influence on the focused high intensity acoustic wave. Moreover, at the comparatively higher frequencies, for the model of spherical wave, a lower Mach number may result in stronger nonlinear effects.
NASA Astrophysics Data System (ADS)
Bellis, Cédric; Bonnet, Marc; Cakoni, Fioralba
2013-07-01
Originally formulated in the context of topology optimization, the concept of topological derivative has also proved effective as a qualitative inversion tool for a wave-based identification of finite-sized objects. This approach remains, however, largely based on a heuristic interpretation of the topological derivative, whereas most other qualitative approaches to inverse scattering are backed by a mathematical justification. As an effort toward bridging this gap, this study focuses on a topological derivative approach applied to the L2-norm of the misfit between far-field measurements. Either an inhomogeneous medium or a finite number of point-like scatterers are considered, using either the Born approximation or a full-scattering model. Topological derivative-based imaging functionals are analyzed using a suitable factorization of the far-field operator, for each of the considered cases, in order to characterize their behavior and assess their ability to reconstruct the unknown scatterer(s). Results include the justification of the usual sign heuristic underpinning the method for (i) the Born approximation and (ii) full-scattering models limited to moderately strong scatterers. Semi-analytical and numerical examples are presented. Within the chosen framework, the topological derivative approach is finally discussed and compared to other well-known qualitative methods.
NASA Astrophysics Data System (ADS)
Ouyang, Wei; Mao, Weijian; Li, Xuelei; Li, Wuqun
2014-08-01
Sound velocity inversion problem based on scattering theory is formulated in terms of a nonlinear integral equation associated with scattered field. Because of its nonlinearity, in practice, linearization algorisms (Born/single scattering approximation) are widely used to obtain an approximate inversion solution. However, the linearized strategy is not congruent with seismic wave propagation mechanics in strong perturbation (heterogeneous) medium. In order to partially dispense with the weak perturbation assumption of the Born approximation, we present a new approach from the following two steps: firstly, to handle the forward scattering by taking into account the second-order Born approximation, which is related to generalized Radon transform (GRT) about quadratic scattering potential; then to derive a nonlinear quadratic inversion formula by resorting to inverse GRT. In our formulation, there is a significant quadratic term regarding scattering potential, and it can provide an amplitude correction for inversion results beyond standard linear inversion. The numerical experiments demonstrate that the linear single scattering inversion is only good in amplitude for relative velocity perturbation () of background media up to 10 %, and its inversion errors are unacceptable for the perturbation beyond 10 %. In contrast, the quadratic inversion can give more accurate amplitude-preserved recovery for the perturbation up to 40 %. Our inversion scheme is able to manage double scattering effects by estimating a transmission factor from an integral over a small area, and therefore, only a small portion of computational time is added to the original linear migration/inversion process.
Acoustic scattering by a modified Werner method
Ravel; Trad
2000-02-01
A modified integral Werner method is used to calculate pressure scattered by an axisymmetric body immersed in a perfect and compressible fluid subject to a harmonic acoustic field. This integral representation is built as the sum of a potential of a simple layer and a potential of volume. It is equivalent to the exterior Helmholtz problem with Neumann boundary condition for all real wave numbers of the incident acoustic field. For elastic structure scattering problems, the modified Werner method is coupled with an elastodynamic integral formulation in order to account for the elastic contribution of the displacement field at the fluid/structure interface. The resulting system of integral equations is solved by the collocation method with a quadratic interpolation. The introduction of a weighting factor in the modified Werner method decreases the number of volume elements necessary for a good convergence of results. This approach becomes very competitive when it is compared with other integral methods that are valid for all wave numbers. A numerical comparison with an experiment on a tungsten carbide end-capped cylinder allows a glimpse of the interesting possibilities for using the coupling of the modified Werner method and the integral elastodynamic equation used in this research.
Nonlinear ion acoustic waves scattered by vortexes
NASA Astrophysics Data System (ADS)
Ohno, Yuji; Yoshida, Zensho
2016-09-01
The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.
NASA Technical Reports Server (NTRS)
Larkin, Paul; Goldstein, Bob
2008-01-01
This paper presents an update to the methods and procedures used in Direct Field Acoustic Testing (DFAT). The paper will discuss some of the recent techniques and developments that are currently being used and the future publication of a reference standard. Acoustic testing using commercial sound system components is becoming a popular and cost effective way of generating a required acoustic test environment both in and out of a reverberant chamber. This paper will present the DFAT test method, the usual setup and procedure and the development and use of a closed-loop, narrow-band control system. Narrow-band control of the acoustic PSD allows all standard techniques and procedures currently used in random control to be applied to acoustics and some examples are given. The paper will conclude with a summary of the development of a standard practice guideline that is hoped to be available in the first quarter of next year.
2005-09-30
approximation in many practical situations. The equation for the average acoustic field in the statistically homogeneous in horizontal plane stratified...using diagrammatic technique similar to the one used in the theory of wave propagation in the homogeneous medium. The mass operator was calculated...perturbations on various eigenrays due to the horizontal refraction induced by internal waves with the Garrett-Munk spectrum: rigorous internal wave model
Shape recognition of acoustic scatterers using the singularity expansion method
NASA Astrophysics Data System (ADS)
Cao, Pei; Wu, Jiu Hui
2017-03-01
Acoustic target recognition for two-dimensional (2D) acoustic scatterers is investigated using the singularity expansion method (SEM). Based on the Watson transformation series of the scattering field, the SEM poles can be calculated and their physical interpretation given, along with the exact normal mode for any acoustic scattering problem. Typical oscillatory phenomena appear as a series of damped sinusoidal signals in the time domain and as a standing-wave distribution in the space. These external oscillation modes are associated with the SEM poles. We note that the positions of these poles in the complex frequency plane are uniquely determined by the shape and flexible characteristics of the target regardless of the waveforms and positions of the incident signals. We then infer that SEM poles can be used as the characteristic parameters for target shape recognition. The relationship between the positions of SEM poles and the geometrical characters of 2D scatterers has been established not only for cylinders but also for other general 2D scatterers. The new method and the related calculation results provide an effective way to perform shape recognition using an acoustic scattering field, with potential applications in non-destructive testing and acoustic imaging.
2006-09-30
situations. The equation for the average acoustic field in the statistically homogeneous in horizontal plane stratified waveguide satisfies an...is the vertical coordinate, and integration is along an perturbed eigenray between a source at (xS, 0, zS) and the mid-point (xR, 0, zR RR ) between...angle on the eigenray , ( ) ( )( ) ( ) ( )( ) ( ) 00 0 , ; ,, tan ; , , ; , , , cos S x R R R R R R R R R R Rx c x z x x z dxp x b z x x z x q x
Cancellation of acoustic scattering from an elastic sphere.
Guild, Matthew D; Alù, Andrea; Haberman, Michael R
2011-03-01
Recent research has suggested the possibility of creating acoustic cloaks using metamaterial layers to eliminate the acoustic field scattered from an elastic object. This paper explores the possibility of applying the scattering cancellation cloaking technique to acoustic waves and the use of this method to investigate its effectiveness in cloaking elastic and fluid spheres using only a single isotropic elastic layer. Parametric studies showing the influence of cloak stiffness and geometry on the frequency dependent scattering cross-section of spheres have been developed to explore the design space of the cloaking layer. This analysis shows that an appropriately designed single isotropic elastic cloaking layer can provide up to 30 dB of scattering reduction for ka values up to 1.6. This work also illustrates the importance of accounting for the elasticity of the object and the relevant limitations of simplistic quasi-static analyses proposed in recent papers.
Acoustic scattering reduction using layers of elastic materials
NASA Astrophysics Data System (ADS)
Dutrion, Cécile; Simon, Frank
2017-02-01
Making an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles. These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This paper examines the possibility of designing an acoustic cloak using a bi-layer elastic cylindrical shell to eliminate the acoustic field scattered from a rigid cylinder hit by plane waves. This field depends on the dimensional and mechanical characteristics of the elastic layers. It is computed by a semi-analytical code modelling the vibrations of the coating under plane wave excitation. Optimization by genetic algorithm is performed to determine the characteristics of a bi-layer material minimizing the scattering. Considering an external fluid consisting of air, realistic configurations of elastic coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or over a larger frequency band.
Acoustic Scattering Models of Zooplankton and Microstructure
1999-09-30
Acoustic Scattering Models of Zooplankton and Microstructure Timothy K. Stanton Department of Applied Ocean Physics and Engineering Woods Hole...LONG-TERM GOALS To understand the acoustic reverberation properties of zooplankton and microstructure. The results will lead to improved capability...in 1) predicting sonar performance and 2) use of sonars in the mapping of the zooplankton and microstructure. OBJECTIVES To understand the physics of
High frequency acoustic wave scattering from turbulent premixed flames
NASA Astrophysics Data System (ADS)
Narra, Venkateswarlu
This thesis describes an experimental investigation of high frequency acoustic wave scattering from turbulent premixed flames. The objective of this work was to characterize the scattered incoherent acoustic field and determine its parametric dependence on frequency, flame brush thickness, incident and measurement angles, mean velocity and flame speed. The experimental facility consists of a slot burner with a flat flame sheet that is approximately 15 cm wide and 12 cm tall. The baseline cold flow characteristics and flame sheet statistics were extensively characterized. Studies were performed over a wide range of frequencies (1-24 kHz) in order to characterize the role of the incident acoustic wave length. The spectrum of the scattered acoustic field showed distinct incoherent spectral sidebands on either side of the driving frequency. The scattered incoherent field was characterized in terms of the incoherent field strength and spectral bandwidth and related to the theoretical predictions. The role of the flame front wrinkling scale, i.e., flame brush thickness, was also studied. Flame brush thickness was varied independent of the mean velocity and flame speed by using a variable turbulence generator. Results are reported for five flame brush thickness cases, ranging from 1.2 mm to 5.2 mm. Some dependence of scattered field characteristics on flame brush thickness was observed, but the magnitude of the effect was much smaller than expected from theoretical considerations. The spatial dependence of the scattered field was investigated by measuring the scattered field at four measurement angles and exciting the flame at four incident angles. Theory predicts that these variations influence the spatial scale of the acoustic wave normal to the flame, a result confirmed by the measurements. Measurements were performed for multiple combinations of mean velocities and flame speeds. The scattered field was observed to depend strongly on the flame speed. Further analysis
Acoustic field modulation in regenerators
NASA Astrophysics Data System (ADS)
Hu, J. Y.; Wang, W.; Luo, E. C.; Chen, Y. Y.
2016-12-01
The regenerator is a key component that transfers energy between heat and work. The conversion efficiency is significantly influenced by the acoustic field in the regenerator. Much effort has been spent to quantitatively determine this influence, but few comprehensive experimental verifications have been performed because of difficulties in modulating and measuring the acoustic field. In this paper, a method requiring two compressors is introduced and theoretically investigated that achieves acoustic field modulation in the regenerator. One compressor outputs the acoustic power for the regenerator; the other acts as a phase shifter. A RC load dissipates the acoustic power out of both the regenerator and the latter compressor. The acoustic field can be modulated by adjusting the current in the two compressors and opening the RC load. The acoustic field is measured with pressure sensors instead of flow-field imaging equipment, thereby greatly simplifying the experiment.
Acoustic scattering on spheroidal shapes near boundaries
NASA Astrophysics Data System (ADS)
Miloh, Touvia
2016-11-01
A new expression for the Lamé product of prolate spheroidal wave functions is presented in terms of a distribution of multipoles along the axis of the spheroid between its foci (generalizing a corresponding theorem for spheroidal harmonics). Such an "ultimate" singularity system can be effectively used for solving various linear boundary-value problems governed by the Helmholtz equation involving prolate spheroidal bodies near planar or other boundaries. The general methodology is formally demonstrated for the axisymmetric acoustic scattering problem of a rigid (hard) spheroid placed near a hard/soft wall or inside a cylindrical duct under an axial incidence of a plane acoustic wave.
Inverse Scattering Problems for Acoustic Waves in AN Inhomogeneous Medium.
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
1990-01-01
This dissertation considers the inverse scattering problem of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far-field patterns of the scattered fields corresponding to many incident time -harmonic plane waves. First, we consider the inverse problem in the case when the scattering object is an inhomogeneous medium with complex refraction index having compact support. Our approach to this problem is the orthogonal projection method of Colton-Monk (cf. The inverse scattering problem for time acoustic waves in an inhomogeneous medium, Quart. J. Mech. Appl. Math. 41 (1988), 97-125). After that, we prove the analogue of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. We then generalize some of these results to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. We solve the inverse impedance problem of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (cf. R. Kress, Linear Integral Equations, Springer-Verlag, New York, 1989).
Acoustic multiple scattering using recursive algorithms
NASA Astrophysics Data System (ADS)
Amirkulova, Feruza A.; Norris, Andrew N.
2015-10-01
Acoustic multiple scattering by a cluster of cylinders in an acoustic medium is considered. A fast recursive technique is described which takes advantage of the multilevel Block Toeplitz structure of the linear system. A parallelization technique is described that enables efficient application of the proposed recursive algorithm for solving multilevel Block Toeplitz systems on high performance computer clusters. Numerical comparisons of CPU time and total elapsed time taken to solve the linear system using the direct LAPACK and TOEPLITZ libraries on Intel FORTRAN, show the advantage of the TOEPLITZ solver. Computations are optimized by multi-threading which displays improved efficiency of the TOEPLITZ solver with the increase of the number of scatterers and frequency.
Acoustic asymmetric transmission based on time-dependent dynamical scattering
NASA Astrophysics Data System (ADS)
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
2015-06-01
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.
Acoustic asymmetric transmission based on time-dependent dynamical scattering
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
Experimental Demonstration of Underwater Acoustic Scattering Cancellation
Rohde, Charles A.; Martin, Theodore P.; Guild, Matthew D.; Layman, Christopher N.; Naify, Christina J.; Nicholas, Michael; Thangawng, Abel L.; Calvo, David C.; Orris, Gregory J.
2015-01-01
We explore an acoustic scattering cancellation shell for buoyant hollow cylinders submersed in a water background. A thin, low-shear, elastic coating is used to cancel the monopole scattering from an air-filled, neutrally buoyant steel shell for all frequencies where the wavelength is larger than the object diameter. By design, the uncoated shell also has an effective density close to the aqueous background, independently canceling its dipole scattering. Due to the significantly reduced monopole and dipole scattering, the compliant coating results in a hollow cylindrical inclusion that is simultaneously impedance and sound speed matched to the water background. We demonstrate the proposed cancellation method with a specific case, using an array of hollow steel cylinders coated with thin silicone rubber shells. These experimental results are matched to finite element modeling predictions, confirming the scattering reduction. Additional calculations explore the optimization of the silicone coating properties. Using this approach, it is found that scattering cross-sections can be reduced by 20 dB for all wavelengths up to k0a = 0.85. PMID:26282067
Experimental Demonstration of Underwater Acoustic Scattering Cancellation
NASA Astrophysics Data System (ADS)
Rohde, Charles A.; Martin, Theodore P.; Guild, Matthew D.; Layman, Christopher N.; Naify, Christina J.; Nicholas, Michael; Thangawng, Abel L.; Calvo, David C.; Orris, Gregory J.
2015-08-01
We explore an acoustic scattering cancellation shell for buoyant hollow cylinders submersed in a water background. A thin, low-shear, elastic coating is used to cancel the monopole scattering from an air-filled, neutrally buoyant steel shell for all frequencies where the wavelength is larger than the object diameter. By design, the uncoated shell also has an effective density close to the aqueous background, independently canceling its dipole scattering. Due to the significantly reduced monopole and dipole scattering, the compliant coating results in a hollow cylindrical inclusion that is simultaneously impedance and sound speed matched to the water background. We demonstrate the proposed cancellation method with a specific case, using an array of hollow steel cylinders coated with thin silicone rubber shells. These experimental results are matched to finite element modeling predictions, confirming the scattering reduction. Additional calculations explore the optimization of the silicone coating properties. Using this approach, it is found that scattering cross-sections can be reduced by 20 dB for all wavelengths up to k0a = 0.85.
Numerical solution of acoustic scattering by finite perforated elastic plates
NASA Astrophysics Data System (ADS)
Cavalieri, A. V. G.; Wolf, W. R.; Jaworski, J. W.
2016-04-01
We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k0 based on the plate length. However, at low k0, finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k0. The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k0 for perforated elastic plates.
Transformational Acoustics Applied to Scattering from a Thin Elastic Shell
2011-06-01
invariant form.” New Journal of Physics, 8 (248), 2006. [6] H. Chen and C. T. Chan. “ Acoustic cloaking in three dimensions using acoustic metamaterials ...NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS TRANSFORMATIONAL ACOUSTICS APPLIED TO SCATTERING FROM A THIN ELASTIC SHELL by Ana Margarida R...Prescribed by ANSI Std. Z39.18 22–6–2011 Master’s Thesis 2102-06-01—2104-10-31 Transformational Acoustics Applied to Scattering From a Thin Elastic
Low frequency acoustic and electromagnetic scattering
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Maccamy, R. C.
1983-01-01
This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k(2) log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.
Low frequency acoustic and electromagnetic scattering
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Maccamy, R. C.
1986-01-01
This paper deals with two classes of problems arising from acoustics and electromagnetics scattering in the low frequency stations. The first class of problem is solving Helmholtz equation with Dirichlet boundary conditions on an arbitrary two dimensional body while the second one is an interior-exterior interface problem with Helmholtz equation in the exterior. Low frequency analysis show that there are two intermediate problems which solve the above problems accurate to 0(k/2/ log k) where k is the frequency. These solutions greatly differ from the zero frequency approximations. For the Dirichlet problem numerical examples are shown to verify the theoretical estimates.
Inverse scattering problems for acoustic waves in an inhomogeneous medium
NASA Astrophysics Data System (ADS)
Kedzierawski, Andrzej Wladyslaw
The inverse scattering problem is considered of determining either the absorption of sound in an inhomogeneous medium or the surface impedance of an obstacle from a knowledge of the far field patterns of the scattered field corresponding to many incident time-harmonic plane waves. First, the inverse problem is studied in the case when the scattering object is an inhomogeneous medium with complex refractive index having compact support. The approach to this problem is the orthogonal projection method of Colton-Monk (1988). After that, the analogue is proven of Karp's Theorem for the scattering of acoustic waves through an inhomogeneous medium with compact support. Some of these results are then generalized to the case when the inhomogeneous medium is no longer of compact support. If the acoustic wave penetrates the inhomogeneous medium by only a small amount then the inverse medium problem leads to the inverse obstacle problem with an impedance boundary condition. The inverse impedance problem is solved of determining the surface impedance of an obstacle of known shape by using both the methods of Kirsch-Kress and Colton-Monk (1989).
2007-09-30
less pronounced for steeper and shallower rays (Figs. 2 - 4). Results obtained with eigenrays and unconstrained rays are similar as long as the...intervals of the launch angle (yellow), and averages over the internal wave field realizations for eigenrays with additional averaging over 0.5º...realizations for eigenrays with additional averaging over 0.5º (magenta dots) and 2º (magenta line) intervals of the launch angle. Propagation range r
Microparticle column geometry in acoustic stationary fields.
Hancock, Andrew; Insana, Michael F; Allen, John S
2003-01-01
Particles suspended in a fluid will experience forces from stationary acoustic fields. The magnitude of the force depends on the time-averaged energy density of the field and the material properties of the particles and fluid. Forces acting on known particles smaller than 20 microm were studied. Within a 500 kHz acoustic beam generated by a plane-piston circular source, observations were made of the geometry of the particle column that is formed. Varying the acoustic energy altered the column width in a manner predicted by equations for the primary acoustic radiation force from scattering of particles in the long-wavelength limit. The minimum pressures required to trap gas, solid, and liquid particles in a water medium at room temperature were also estimated to within 12%. These results highlight the ability of stationary acoustic fields from a plane-piston radiator to impose nano-Newton-scale forces onto fluid particles with properties similar to biological cells, and suggest that it is possible to accurately quantify these forces.
Axisymmetric acoustic scattering from submerged prolate spheroidal shells
NASA Astrophysics Data System (ADS)
Boisvert, Jeffrey E.; Hayek, Sabih I.
2005-09-01
The equations of motion for nonaxisymmetric vibration of prolate spheroidal shells of constant thickness were derived using Hamilton's principle [S. I. Hayek and J. E. Boisvert, J. Acoust. Soc. Am. 114, 2799-2811 (2003)]. The shell theory used in this derivation includes shear deformations and rotatory inertias. The shell displacements and rotations were expanded in infinite series of comparison functions. These include associated Legendre functions in terms of the prolate spheroidal angular coordinate and circular functions in the azimuthal angle coordinate. The shell is insonified by a plane wave incident along the major axis. The external (heavy) fluid loading impedance was computed using an eigenfunction expansion of prolate spheroidal wavefunctions. Far-field scattered acoustic pressure spectra are presented for several shell thickness-to-half-length ratios ranging from 0.005 to 0.1, and for various shape parameters, a, ranging from an elongated spheroidal shell (a=1.01) to a spherical shell (a~100). The far-field directivity of acoustic scattering is presented at selected frequencies. [Work supported by the ONR/ASEE Summer Faculty Research Program.
NASA Astrophysics Data System (ADS)
Wei, Qi; Cheng, Ying; Liu, Xiao-jun
2012-07-01
We present a three-dimensional acoustic concentrator capable of significantly enhancing the sound intensity in the compressive region with scattering cancellation, imaging, and mirage effects. The concentrator shell is built by isotropic gradient negative-index materials, which together with an exterior host medium slab constructs a pair of complementary media. The enhancement factor, which can approach infinity by tuning the geometric parameters, is always much higher than that of a traditional concentrator made by positive-index materials with the same size. The acoustic scattering theory is applied to derive the pressure field distribution of the concentrator, which is consistent with the numerical full-wave simulations. The inherent acoustic impedance match at the interfaces of the shell as well as the inverse processes of “negative refraction—progressive curvature—negative refraction” for arbitrary sound rays can exactly cancel the scattering of the concentrator. In addition, the concentrator shell can also function as an acoustic spherical magnifying superlens, which produces a perfect image with the same shape, with bigger geometric and acoustic parameters located at a shifted position. Then some acoustic mirages are observed whereby the waves radiated from (scattered by) an object located in the center region may seem to be radiated from (scattered by) its image. Based on the mirage effect, we further propose an intriguing acoustic transformer which can transform the sound scattering pattern of one object into another object at will with arbitrary geometric, acoustic, and location parameters.
Flow velocity measurement with the nonlinear acoustic wave scattering
Didenkulov, Igor; Pronchatov-Rubtsov, Nikolay
2015-10-28
A problem of noninvasive measurement of liquid flow velocity arises in many practical applications. To this end the most often approach is the use of the linear Doppler technique. The Doppler frequency shift of signal scattered from the inhomogeneities distributed in a liquid relatively to the emitted frequency is proportional to the sound frequency and velocities of inhomogeneities. In the case of very slow flow one needs to use very high frequency sound. This approach fails in media with strong sound attenuation because acoustic wave attenuation increases with frequency and there is limit in increasing sound intensity, i.e. the cavitation threshold. Another approach which is considered in this paper is based on the method using the difference frequency Doppler Effect for flows with bubbles. This method is based on simultaneous action of two high-frequency primary acoustic waves with closed frequencies on bubbles and registration of the scattered by bubbles acoustic field at the difference frequency. The use of this method is interesting since the scattered difference frequency wave has much lower attenuation in a liquid. The theoretical consideration of the method is given in the paper. The experimental examples confirming the theoretical equations, as well as the ability of the method to be applied in medical diagnostics and in technical applications on measurement of flow velocities in liquids with strong sound attenuation is described. It is shown that the Doppler spectrum form depends on bubble concentration velocity distribution in the primary acoustic beams crossing zone that allows one to measure the flow velocity distribution.
Acoustic scattering from ellipses by the modal element method
NASA Technical Reports Server (NTRS)
Kreider, Kevin L.; Baumeister, Kenneth J.
1995-01-01
The modal element method is used to study acoustic scattering from ellipses, which may be acoustically soft (absorbing) or hard (reflecting). Because exact solutions are available, the results provide a benchmark for algorithm performance for scattering from airfoils and similar shapes. Numerical results for scattering from rigid ellipses are presented for a wide variety of eccentricities at moderate frequencies. These results indicate that the method is practical.
Modulation of Radio Frequency Signals by Nonlinearly Generated Acoustic Fields
NASA Astrophysics Data System (ADS)
Johnson, Spencer Joseph
Acousto-electromagnetic scattering is a process in which an acoustic excitation is utilized to induce modulation on an electromagnetic (EM) wave. This phenomenon can be exploited in remote sensing and detection schemes whereby target objects are mechanically excited by high powered acoustic waves resulting in unique object characterizations when interrogated with EM signals. Implementation of acousto-EM sensing schemes, however, are limited by a lack of fundamental understanding of the nonlinear interaction between acoustic and EM waves and inefficient simulation methods in the determination of the radiation patterns of higher order scattered acoustic fields. To address the insufficient simulation issue, a computationally efficient mathematical model describing higher order scattered sound fields, particularly of third-order in which a 40x increase in computation speed is achieved, is derived using a multi-Gaussian beam (MGB) expansion that expresses the sound field of any arbitrary axially symmetric beam as a series of Gaussian base functions. The third-order intermodulation (IM3) frequency components are produced by considering the cascaded nonlinear second-order effects when analyzing the interaction between the first- and second-order frequency components during the nonlinear scattering of sound by sound from two noncollinear ultrasonic baffled piston sources. The theory is extended to the modeling of the sound beams generated by parametric transducer arrays, showing that the MGB model can be efficiently used to calculate both the second- and third-order sound fields of the array. Additionally, a near-to-far-field (NTFF) transformation method is developed to model the far-field characteristics of scattered sound fields, extending Kirchhoff's theorem, typically applied to EM waves, determining the far-field patterns of an acoustic source from amplitude and phase measurements made in the near-field by including the higher order sound fields generated by the
On the scattering of an acoustic plane wave by a soft prolate spheroid
NASA Astrophysics Data System (ADS)
Borromeo, Joseph Michael
This thesis solves the scattering problem in which an acoustic plane wave of propagation number K1 is scattered by a soft prolate spheroid. The interior field of the scatterer is characterized by a propagation number K2, while the field radiated by the scatterer is characterized by the propagation number K3. The three fields and their normal derivatives satisfy boundary conditions at the surface of the scatterer. These boundary conditions involve six complex parameters depending on the propagation numbers. The scattered wave also satisfies the Sommerfeld radiation condition at infinity. Through analytical methods, series representations are constructed for the interior field and scattered field for an arbitrary sphere and a prolate spheroid. In addition, results for the reciprocity relations and Energy theorem are derived. Application to detection of whales and submarines are discussed, as well as classification of fish, squid and zoo plankton. In general Ref[ ] is used for reference and the work is done in three dimensions.
Novel Acoustic Scattering Processes for Target Discrimination
2006-09-30
based on acoustic holography algorithms): It has been possible to form images from data acquired as noted in item (2) by the application of a back...propagation algorithm based on the methods of acoustic holography . Selected results relevant to the interpretation of Bistatic SAS images are noted...to back-propagate the sampled acoustic signal using algorithms originally developed for high-frequency acoustical holography [10]. Data is only
Nonlinear Scattering of Acoustic Waves by Vibrating Obstacles.
1983-06-01
AD-A129 282 NONLINEAR SCATTERING OF ACOUSTIC WAVES BY VIBRATING OBSTACLES (U) NAVAL RESEARCH LAR WASHINOTON DC d C PIQUETTE 01 JUN 83 NRL-MR-5077...MICROCOPY RESOLUTION TEST CHART NAIOAL IBtJ[IAU Of S1ANDARD~If A3 NRL Memorandum Report 5077 Nonlinear Scattering of Acoustic Waves by Vibrating Obstacles ... Obstacles continuing problem. S. PERFORMING ORG. REPORT NUMMER 7. AUTHOR(s) 6. CONTRACT OR GRANT NUMIISER( ) Jean C. Piquette* S. PERFORMING
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.
Acoustical scattering cross section of gas bubbles under dual-frequency acoustic excitation.
Zhang, Yuning; Li, Shengcai
2015-09-01
The acoustical scattering cross section is a paramount parameter determining the scattering ability of cavitation bubbles when they are excited by the incident acoustic waves. This parameter is strongly related with many important applications of acoustic cavitation including facilitating the reaction of chemical process, boosting bubble sonoluminescence, and performing non-invasive therapy and drug delivery. In present paper, both the analytical and numerical solutions of acoustical scattering cross section of gas bubbles under dual-frequency excitation are obtained. The validity of the analytical solution is shown with demonstrating examples. The nonlinear characteristics (e.g., harmonics, subharmonics and ultraharmonics) of the scattering cross section curve under dual-frequency approach are investigated. Compared with single-frequency approach, the dual-frequency approach displays more resonances termed as "combination resonances" and could promote the acoustical scattering cross section significantly within a much broader range of bubble sizes due to the generation of more resonances. The influence of several paramount parameters (e.g., acoustic pressure amplitude, power allocations between two acoustic components, and the ratio of the frequencies) in the dual-frequency system on the predictions of scattering cross section has been discussed.
Acoustic scattering by a spliced turbofan inlet duct liner at supersonic fan speeds
NASA Astrophysics Data System (ADS)
McAlpine, A.; Wright, M. C. M.
2006-05-01
Fan noise is one of the principal noise sources generated by a turbofan aero-engine. At supersonic fan speeds, fan tones are generated by the "rotor-alone" pressure field. In general, these tones can be well absorbed by an inlet duct acoustic liner, apart from at high supersonic fan speeds. However, in practice inlet duct liners contain acoustically hard longitudinal splices which cause scattering. This leads to acoustic energy being scattered into a range of different azimuthal mode orders, similar to the modal content resulting from rotor-stator interactions. The effectiveness of an inlet duct lining is reduced because acoustic energy is scattered into modes that are poorly absorbed by the liner. In this article, the effect of this acoustic scattering is examined by three-dimensional finite-element simulations of sound transmission in a turbofan inlet duct. Results include predictions of the sound power transmission loss with different splice widths, and at different supersonic fan speeds. These results demonstrate how acoustic scattering by liner splices can adversely affect fan tone noise levels at low supersonic fan speeds, but have little adverse affect on noise levels at high supersonic fan speeds. The potential noise benefit that could be achieved by manufacturing thinner splices is also examined.
Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields
NASA Astrophysics Data System (ADS)
Karlsen, Jonas T.; Augustsson, Per; Bruus, Henrik
2016-09-01
We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip.
3-D Acoustic Scattering from 2-D Rough Surfaces Using A Parabolic Equation Model
2013-12-01
acoustic propagation signals, especially at mid- frequencies and higher (e.g., acoustic communications systems). For many years, the effects of rough...of the effect of surface scattering on 3-D propagation , which is critical in evaluating the variability in underwater acoustic propagation . Results...14. SUBJECT TERMS Acoustic Propagation , Acoustic Scattering, Sea Surface Perturbations, Split- Step Fourier Algorithm, Finite Difference Algorithm
Arbitrary scattering of an acoustical Bessel beam by a rigid spheroid with large aspect-ratio
NASA Astrophysics Data System (ADS)
Gong, Zhixiong; Li, Wei; Mitri, Farid G.; Chai, Yingbin; Zhao, Yao
2016-11-01
In this paper, the T-matrix (null-field) method is applied to investigate the acoustic scattering by a large-aspect-ratio rigid spheroid immersed in a non-viscous fluid under the illumination of an unbounded zeroth-order Bessel beam with arbitrary orientation. Based on the proposed method, a MATLAB software package is constructed accordingly, and then verified and validated to compute the acoustic scattering by a rigid oblate or prolate spheroid in the Bessel beam. Several numerical examples are carried out to investigate the novel phenomenon of acoustic scattering by spheroids in Bessel beams with arbitrary incidence, with particular emphasis on the aspect ratio (i.e. the ratio of the polar radius over the equatorial radius of the spheroid), the half-cone angle of Bessel beam, the dimensionless frequency, as well as the angle of incidence. The quasi-periodic oscillations are observed in the plots of the far-field backscattering form function modulus versus the dimensionless frequency, owing to the interference between the specular reflection and the Franz wave circumnavigating the spheroid in the surrounding fluid. Furthermore, the 3D far-field scattering directivity patterns at end-on incidence and 2D polar plots at arbitrary angles of incidence are exhibited, which could provide new insights into the physical mechanisms of Bessel beam scattering by flat or elongated spheroid. This research work may provide an impetus for the application of acoustic Bessel beam in engineering practices.
The integrated extinction for broadband scattering of acoustic waves.
Sohl, Christian; Gustafsson, Mats; Kristensson, Gerhard
2007-12-01
In this paper, physical bounds on scattering of acoustic waves over a frequency interval are discussed based on the holomorphic properties of the scattering amplitude in the forward direction. The result is given by a dispersion relation for the extinction cross section which yields an upper bound on the product of the extinction cross section and the associated bandwidth of any frequency interval. The upper bound is shown to depend only on the geometry and the material properties of the scatterer in the static or low-frequency limit. The results are exemplified by permeable and impermeable scatterers with homogeneous and isotropic material properties.
Scattering matrix theory for stochastic scalar fields.
Korotkova, Olga; Wolf, Emil
2007-05-01
We consider scattering of stochastic scalar fields on deterministic as well as on random media, occupying a finite domain. The scattering is characterized by a generalized scattering matrix which transforms the angular correlation function of the incident field into the angular correlation function of the scattered field. Within the accuracy of the first Born approximation this matrix can be expressed in a simple manner in terms of the scattering potential of the scatterer. Apart from determining the angular distribution of the spectral intensity of the scattered field, the scattering matrix makes it possible also to determine the changes in the state of coherence of the field produced on scattering.
Kinetic Enhancement of Raman Backscatter, and Electron Acoustic Thomson Scatter
Strozzi, D J; Williams, E A; Langdon, A B; Bers, A
2006-09-01
1-D Eulerian Vlasov-Maxwell simulations are presented which show kinetic enhancement of stimulated Raman backscatter (SRBS) due to electron trapping in regimes of heavy linear Landau damping. The conventional Raman Langmuir wave is transformed into a set of beam acoustic modes [L. Yin et al., Phys. Rev. E 73, 025401 (2006)]. For the first time, a low phase velocity electron acoustic wave (EAW) is seen developing from the self-consistent Raman physics. Backscatter of the pump laser off the EAW fluctuations is reported and referred to as electron acoustic Thomson scatter. This light is similar in wavelength to, although much lower in amplitude than, the reflected light between the pump and SRBS wavelengths observed in single hot spot experiments, and previously interpreted as stimulated electron acoustic scatter [D. S. Montgomery et al., Phys. Rev. Lett. 87, 155001 (2001)]. The EAW observed in our simulations is strongest well below the phase-matched frequency for electron acoustic scatter, and therefore the EAW is not produced by it. The beating of different beam acoustic modes is proposed as the EAW excitation mechanism, and is called beam acoustic decay. Supporting evidence for this process, including bispectral analysis, is presented. The linear electrostatic modes, found by projecting the numerical distribution function onto a Gauss-Hermite basis, include beam acoustic modes (some of which are unstable even without parametric coupling to light waves) and a strongly-damped EAW similar to the observed one. This linear EAW results from non-Maxwellian features in the electron distribution, rather than nonlinearity due to electron trapping.
FDTD scattered field formulation for scatterers in stratified dispersive media.
Olkkonen, Juuso
2010-03-01
We introduce a simple scattered field (SF) technique that enables finite difference time domain (FDTD) modeling of light scattering from dispersive objects residing in stratified dispersive media. The introduced SF technique is verified against the total field scattered field (TFSF) technique. As an application example, we study surface plasmon polariton enhanced light transmission through a 100 nm wide slit in a silver film.
Scattering of Acoustic Waves from Ocean Boundaries
2015-09-30
of buried mines and improve SONAR performance in shallow water. OBJECTIVES 1) Determination of the correct physical model of acoustic propagation...Measurements for Range Dependent Geoacoustic Parameters: Bottom loss data from 5 – 30 kHz were collected as part of the Target and Reverberation Experiment...2013 (TREX13). These data were analyzed and range dependent geoacoustic parameters were derived for the TREX reverberation site including bottom loss
Frustrated total internal reflection acoustic field sensor
Kallman, Jeffrey S.
2000-01-01
A frustrated total internal reflection acoustic field sensor which allows the acquisition of the acoustic field over an entire plane, all at once. The sensor finds use in acoustic holography and acoustic diffraction tomography. For example, the sensor may be produced by a transparent plate with transparent support members tall enough to support one or more flexible membranes at an appropriate height for frustrated total internal reflection to occur. An acoustic wave causes the membrane to deflect away from its quiescent position and thus changes the amount of light that tunnels through the gap formed by the support members and into the membrane, and so changes the amount of light reflected by the membrane. The sensor(s) is illuminated by a uniform tight field, and the reflection from the sensor yields acoustic wave amplitude and phase information which can be picked up electronically or otherwise.
Scattering of acoustic duct modes by axial liner splices
NASA Astrophysics Data System (ADS)
Tam, Christopher K. W.; Ju, Hongbin; Chien, Eugene W.
2008-03-01
Recent engine test data and results of computational analysis show that the engine inlet acoustic liner splices have a significant impact on aircraft flight noise certification and cabin noise levels. The phenomenon of scattering of acoustic duct modes by axial liner splices is investigated. Previous studies, invariably, follow the frequency-domain approach. The present study, however, uses the time-domain approach. It is demonstrated that time-domain computation yields results that are in close agreement with frequency-domain results. The scattering phenomenon under consideration is very complex. This study concentrates on the effects of four parameters. They are the width of the splices, the frequency of the incident duct mode, the number of splices and the length of splices. Based on the computed results, the conditions under which scattered wave modes would significantly increase the intensity of transmitted waves are identified. It is also found that surface scattering by liner splices has the tendency to distribute energy equally to all the cut-on scattered azimuthal modes. On the other hand, for each scattered azimuthal mode, the high-order cut-on radial mode, generally, has the highest intensity. Moreover, scattering by liner splices is a local phenomenon. It is confined primarily to an area of the duct adjacent to the junction between the hard wall near the fan face and the spliced liner.
Acoustic scattering by an axially-segmented turbofan inlet duct liner at supersonic fan speeds
NASA Astrophysics Data System (ADS)
McAlpine, A.; Astley, R. J.; Hii, V. J. T.; Baker, N. J.; Kempton, A. J.
2006-07-01
Fan noise is one of the principal noise sources in turbofan aero-engines. At supersonic fan speeds, fan tones are generated by the "rotor-alone" pressure field. In general, these tones can be well absorbed by an inlet duct acoustic liner, except at high supersonic fan speeds when the rotor-alone pressure field is well cut-on. In this article an axially segmented liner is proposed, which is predicted to improve the attenuation of tones at high supersonic fan speeds. The analysis is based on locally reacting cavity liners. The axially segmented liner is axisymmetric and consists of two circular sections of different linings joined together. The optimum design consists of two linings with the same face-sheet resistance, but with different cavity depths. The depth of the liner adjacent to the fan is very thin. This means that where the two liners are joined there is a wall impedance discontinuity that can cause acoustic scattering. Fan tones can be modelled in terms of spinning modes in a uniform circular-section duct. The liner is axisymmetric, so modal scattering will be only between different radial modes. The optimum design minimizes the acoustic energy scattered into the first radial mode. This improves the attenuation of fan tones at high supersonic fan speeds, because acoustic energy is scattered into high radial mode orders, which are better absorbed by the lining.
Near-field acoustic streaming jet
NASA Astrophysics Data System (ADS)
Moudjed, B.; Botton, V.; Henry, D.; Millet, S.; Garandet, J. P.; Ben Hadid, H.
2015-03-01
A numerical and experimental investigation of the acoustic streaming flow in the near field of a circular plane ultrasonic transducer in water is performed. The experimental domain is a parallelepipedic cavity delimited by absorbing walls to avoid acoustic reflection, with a top free surface. The flow velocities are measured by particle image velocimetry, leading to well-resolved velocity profiles. The theoretical model is based on a linear acoustic propagation model, which correctly reproduces the acoustic field mapped experimentally using a hydrophone, and an acoustic force term introduced in the Navier-Stokes equations under the plane-wave assumption. Despite the complexity of the acoustic field in the near field, in particular in the vicinity of the acoustic source, a good agreement between the experimental measurements and the numerical results for the velocity field is obtained, validating our numerical approach and justifying the planar wave assumption in conditions where it is a priori far from obvious. The flow structure is found to be correlated with the acoustic field shape. Indeed, the longitudinal profiles of the velocity present a wavering linked to the variations in acoustic intensity along the beam axis and transverse profiles exhibit a complex shape strongly influenced by the transverse variations of the acoustic intensity in the beam. Finally, the velocity in the jet is found to increase as the square root of the acoustic force times the distance from the origin of the jet over a major part of the cavity, after a strong short initial increase, where the velocity scales with the square of the distance from the upstream wall.
Quantum corral resonance widths: lossy scattering as acoustics.
Barr, Matthew C; Zaletel, Michael P; Heller, Eric J
2010-09-08
We present an approach to predicting extrinsic electron resonance widths within quantum corral nanostructures based on analogies with acoustics. Established quantum mechanical methods for calculating resonance widths, such as multiple scattering theory, build up the scattering atom by atom, ignoring the structure formed by the atoms, such as walls or enclosures. Conversely, particle-in-a-box models, assuming continuous walls, have long been successful in predicting quantum corral energy levels, but not resonance widths. In acoustics, partial reflection from walls and various enclosures has long been incorporated for determining reverberation times. Pursuing an exact analogy between the local density of states of a quantum corral and the acoustic impedance of a concert hall, we show electron lifetimes in nanoscopic structures of arbitrary convex shape are well accounted for by the Sabine formula for acoustic reverberation times. This provides a particularly compact and intuitive prescription for extrinsic finite lifetimes in a particle-in-a-box with leaky walls, including quantum corral atomic walls, given single particle scattering properties.
Scattering of Acoustic Waves from Ocean Boundaries
2012-09-30
environments with special emphasis on propagation in shallow water waveguides and scattering from ocean sediments. 3 ) Development of the new experimental...it does not display a currently valid OMB control number. 1. REPORT DATE 2012 2. REPORT TYPE N/A 3 . DATES COVERED - 4. TITLE AND SUBTITLE...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 3 ) Incorporation of the Texas Advanced Computing Center for finite element analysis
NASA Astrophysics Data System (ADS)
Nikolaeva, Anastasiia V.; Kryzhanovsky, Maxim A.; Tsysar, Sergey A.; Kreider, Wayne; Sapozhnikov, Oleg A.
2015-10-01
Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of an obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter.
Nikolaeva, Anastasiia V.; Kryzhanovsky, Maxim A.; Tsysar, Sergey A.; Kreider, Wayne; Sapozhnikov, Oleg A.
2016-01-01
Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of an obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter. PMID:27147775
Nikolaeva, Anastasiia V. Kryzhanovsky, Maxim A.; Tsysar, Sergey A.; Kreider, Wayne; Sapozhnikov, Oleg A.
2015-10-28
Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of an obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter.
Finite Element Prediction of Acoustic Scattering and Radiation from Submerged Elastic Structures
NASA Technical Reports Server (NTRS)
Everstine, G. C.; Henderson, F. M.; Lipman, R. R.
1984-01-01
A finite element formulation is derived for the scattering and radiation of acoustic waves from submerged elastic structures. The formulation uses as fundamental unknowns the displacement in the structure and a velocity potential in the field. Symmetric coefficient matrices result. The outer boundary of the fluid region is terminated with an approximate local wave-absorbing boundary condition which assumes that outgoing waves are locally planar. The finite element model is capable of predicting only the near-field acoustic pressures. Far-field sound pressure levels may be determined by integrating the surface pressures and velocities over the wet boundary of the structure using the Helmholtz integral. Comparison of finite element results with analytic results show excellent agreement. The coupled fluid-structure problem may be solved with general purpose finite element codes by using an analogy between the equations of elasticity and the wave equation of linear acoustics.
Acoustic scattering from mud volcanoes and carbonate mounds.
Holland, Charles W; Weber, Thomas C; Etiope, Giuseppe
2006-12-01
Submarine mud volcanoes occur in many parts of the world's oceans and form an aperture for gas and fluidized mud emission from within the earth's crust. Their characteristics are of considerable interest to the geology, geophysics, geochemistry, and underwater acoustics communities. For the latter, mud volcanoes are of interest in part because they pose a potential source of clutter for active sonar. Close-range (single-interaction) scattering measurements from a mud volcano in the Straits of Sicily show scattering 10-15 dB above the background. Three hypotheses were examined concerning the scattering mechanism: (1) gas entrained in sediment at/near mud volcano, (2) gas bubbles and/or particulates (emitted) in the water column, (3) the carbonate bio-construction covering the mud volcano edifice. The experimental evidence, including visual, acoustic, and nonacoustic sensors, rules out the second hypothesis (at least during the observation time) and suggests that, for this particular mud volcano the dominant mechanism is associated with carbonate chimneys on the mud volcano. In terms of scattering levels, target strengths of 4-14 dB were observed from 800 to 3600 Hz for a monostatic geometry with grazing angles of 3-5 degrees. Similar target strengths were measured for vertically bistatic paths with incident and scattered grazing angles of 3-5 degrees and 33-50 degrees, respectively.
Acoustic Scattering in Flexible Waveguide Involving Step Discontinuity
Afzal, Muhammad; Nawaz, Rab; Ayub, Muhammad; Wahab, Abdul
2014-01-01
In this paper, the propagation and scattering of acoustic waves in a flexible wave-guide involving step discontinuity at an interface is considered. The emerging boundary value problem is non-Sturm-Liouville and is solved by employing a hybrid mode-matching technique. The physical scattering process and attenuation of duct modes versus frequency regime and change of height is studied. Moreover, the mode-matching solution is validated through a series of numerical experiments by testifying the power conservation identity and matching interface conditions. PMID:25084019
On the Inverse Scattering Problem in the Acoustic Environment
2008-03-03
16 21 ( 1 − cos(3t)) + 5 28 ( 1 − cos(4t)) ) . (264) The scatterer is a c50 -function in R with support in the interval [− 1 , 1 ]. The performance of the...On the inverse scattering problem in the acoustic environment Ran Duan and Vladimir Rokhlin Technical Report YALEU/DCS/TR-1395 March 3, 2008 1 Report...Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per
Acoustic Coherent Backscatter Enhancement from Aggregations of Point Scatterers
2013-09-30
Figure 2 for a cubical aggregation with a five- wavelength edge, 256 to 1024 Monte - Carlo trials, = 3.5, and four different average scatterer spacings...ensemble average over Monte - Carlo trials. The central peak at ϕ = 0 for k0s = 3.2 and 2.5 is produced by coherent backscattering enhancement...were placed in a cubical aggregation with 5 wavelength edges. The ensemble average was computed from 256 to 1024 Monte - Carlo trials. The acoustic
Application of the Discontinuous Galerkin Method to Acoustic Scatter Problems
NASA Technical Reports Server (NTRS)
Atkins, H. L.
1997-01-01
The application of the quadrature-free form of the discontinuous Galerkin method to two problems from Category 1 of the Second Computational Aeroacoustics Workshop on Benchmark problems is presented. The method and boundary conditions relevant to this work are described followed by two test problems, both of which involve the scattering of an acoustic wave off a cylinder. The numerical test performed to evaluate mesh-resolution requirements and boundary-condition effectiveness are also described.
Roles of a scatter on boundary-layer instability and acoustic radiation
NASA Astrophysics Data System (ADS)
Dong, Ming; Wu, Xuesong
2015-11-01
When a boundary-layer instability mode propagates through a region of rapid distortion, the ensuing scattering causes two consequences of physical interest. First, the amplitude of the instability mode may be suppressed or energized. Second, substantial sound wave can be radiated by the boundary-layer instability mode. This paper focuses on this issue by proposing a framework which is called Local Scattering Theory. In this framework, a transmission coefficient, defined as the ratio of the T-S wave amplitude downstream of the scatter to that upstream, is introduced to characterize the effect of a local scatter on boundary-layer instability and transition. The mathematical formulation is based on triple-deck formulism, but in order to accommodate the acoustic far field, the unsteady terms in the upper deck are retained. By computation, the impacts of a steady local suction on flow instability and acoustic radiation are studied. It is found that, (1) a suction slot would suppress the oncoming T-S wave; (2) the acoustic waves radiated by the scattering effect have similar directivities; (3) the intensity of the sound increases with the mass flux when the latter is not too large, and it also increases with the frequency monotonously.
Acoustic Scattering Kernels from Arctic Sea Ice.
1986-10-01
84-C-0180 S. PErfORMING ORGANIZATION NAME AND AOMRSSS 10. PROGRAM ELEMENT. PROJECT . TASK Science Applications International Corp. AREA & WORK UNIT...al. (1986) described an implementation of SISM/ICE for the ASTRAL and PE models. The concepts are also relevant to other models, including FACT, FFP...Even if the ice field contains keels of only a single size, the projected keel width intercepted by any particular track will take on a range of
Detection of nonlinear picosecond acoustic pulses by time-resolved Brillouin scattering
Gusev, Vitalyi E.
2014-08-14
In time-resolved Brillouin scattering (also called picosecond ultrasonic interferometry), the time evolution of the spatial Fourier component of an optically excited acoustic strain distribution is monitored. The wave number is determined by the momentum conservation in photon-phonon interaction. For linear acoustic waves propagating in a homogeneous medium, the detected time-domain signal of the optical probe transient reflectivity shows a sinusoidal oscillation at a constant frequency known as the Brillouin frequency. This oscillation is a result of heterodyning the constant reflection from the sample surface with the Brillouin-scattered field. Here, we present an analytical theory for the nonlinear reshaping of a propagating, finite amplitude picosecond acoustic pulse, which results in a time-dependence of the observed frequency. In particular, we examine the conditions under which this information can be used to study the time-evolution of the weak-shock front speed. Depending on the initial strain pulse parameters and the time interval of its nonlinear transformation, our theory predicts the detected frequency to either be monotonically decreasing or oscillating in time. We support these theoretical predictions by comparison with available experimental data. In general, we find that picosecond ultrasonic interferometry of nonlinear acoustic pulses provides access to the nonlinear acoustic properties of a medium spanning most of the GHz frequency range.
Haynes, Mark; Verweij, Sacha A. M.; Moghaddam, Mahta; Carson, Paul L.
2014-01-01
A self-contained source characterization method for commercial ultrasound probes in transmission acoustic inverse scattering is derived and experimentally tested. The method is based on modified scattered field volume integral equations that are linked to the source-scattering transducer model. The source-scattering parameters are estimated via pair-wise transducer measurements and the nonlinear inversion of an acoustic propagation model that is derived. This combination creates a formal link between the transducer characterization and the inverse scattering algorithm. The method is tested with two commercial ultrasound probes in a transmission geometry including provisions for estimating the probe locations and aligning a robotic rotator. The transducer characterization results show that the nonlinear inversion fit the measured data well. The transducer calibration and inverse scattering algorithm are tested on simple targets. Initial images show that the recovered contrasts are physically consistent with expected values. PMID:24569251
Light scattering from acoustic vibrational modes in confined structures
NASA Astrophysics Data System (ADS)
Bandhu, Rudra Shyam
The acoustic vibrational modes and their light scattering intensities in confined structures such as supported films, double layer free-standing membrane and sub-micron sized wires on a free-standing membrane have been studied using Brillouin Light Scattering (BLS). Standing wave type acoustic phonons were recently observed in supported thin films of silicon oxy-nitride. We build upon this finding to study the acoustic modes in thin zinc selenide (ZnSe) films on gallium arsenide (GaAs). The surprising behaviour of the Brillouin intensities of the standing wave modes in ZnSe are explained in terms of interference of the elasto-optic scattering amplitudes from the film and substrate. Numerical calculations of the scattering cross-section, which takes into account ripple and elasto-optic scattering mechanism, agrees well with the experimental data. Light scattering studies of standing wave type modes in free-standing polymethyl methacrylate (PMMA) layer on Si3N4 were carried out. In these bilayer structures PMMA is much softer than Si3N 4, a property that leads to confinement of low frequency modes associated with the PMMA layer to within its boundaries. In addition, the flexural and the dilatational modes from the Si3N4 layer are observed and are found to hybridize with the standing wave modes from the PMMA layer. Our study of phonon modes in PMMA wires supported on a free-standing Si3N4 membrane extends our work on free-standing double layer membranes. In recent years there is much interest in the study of phonon modes in nano-scale structures such as wires or dots. Although much theoretical work has been carried out in this direction, no experiments exist that explore the dispersion of the phonon modes in such structures. Brillouin Light scattering is ideally suited for studying phonons in such reduced dimensions and our work represents the first effort in this direction. The spectra reveal modes which are quantized both along the width, as well along the thickness
Relation between near field and far field acoustic measurements
NASA Technical Reports Server (NTRS)
Bies, D. A.; Scharton, T. D.
1974-01-01
Several approaches to the problem of determining the far field directivity of an acoustic source located in a reverberant environment, such as a wind tunnel, are investigated analytically and experimentally. The decrease of sound pressure level with distance is illustrated; and the spatial extent of the hydrodynamic and geometric near fields, the far field, and the reverberant field are described. A previously-prosposed analytical technique for predicting the far field directivity of the acoustic source on the basis of near field data is investigated. Experiments are conducted with small acoustic sources and an analysis is performed to determine the variation with distance from the source of the directionality of the sound field. A novel experiment is conducted in which the sound pressure measured at various distances from an acoustic driver located in the NASA Ames 40 x 80 ft wind tunnel is crosscorrelated with the driver excitation voltage.
Mitri, Farid G
2009-05-01
The exact analytical solution for the acoustic scattering of a high-order (commonly known as generalized) Bessel beam (HOBB) by an elastic sphere immersed in an ideal fluid and centered along the beam axis is revisited. The far-field acoustic scattering field is expressed as a partial wave series involving the scattering angle relative to the beam axis, the order, and the half-conical angle of the wave number components of the generalized Bessel beam. Using an appropriate grouping of terms, the expressions for the incident and scattered pressures, as well as the scattering (complex) form function provided in a recent work are transformed into expressions involving the partial wave series starting from the order m of the generalized Bessel beam. In this new formulation, the scattering coefficients for a HOBB are found to equal those obtained from the study of sound scattering of plane progressive waves by an elastic sphere. This suggests that the (complex) form function presented here may be used to advantage toward studying the acoustic scattering of a HOBB by spherical shells, coated spheres, and coated spherical shells using their corresponding scattering partial wave coefficients available in standard and recent literature texts.
Inelastic ultraviolet scattering from high frequency acoustic modes in glasses.
Masciovecchio, C; Gessini, A; Di Fonzo, S; Comez, L; Santucci, S C; Fioretto, D
2004-06-18
The dynamic structure factor of vitreous silica and glycerol has been measured as a function of temperature and of the momentum transfer up to Q=0.105 nm(-1) using a novel experimental technique, the inelastic ultraviolet scattering. As in the case of Brillouin light scattering and ultrasonic measurements, the temperature dependence of the acoustic attenuation shows a plateau below the glass transition whose amplitude scales as Q2. Moreover, a slight temperature dependence of attenuation has been found in vitreous silica at about 130 K, which seems to be reminiscent of the peak measured at lower Qs. These two findings strongly support the idea that anharmonicity is responsible for sound attenuation at ultrasonic and hypersonic frequencies. Finally, we demonstrate that the attenuation mechanism should show a change of regime between 0.105 and 1 nm(-1).
NASA Astrophysics Data System (ADS)
Gan, W. S.
2008-12-01
This paper is to be dedicated to Prof C N Yang's 85th birthday celebration because the idea here was inspired by Prof Yang's public lecture in Singapore in 2006. There are many similarities between electromagnetic waves and acoustic waves. Maxwell's equations for em waves is the oldest gauge theory. We discover symmetries in the pair of wave equations in the acoustic stress field and the velocity field. We also derive a new equation in terms of the stress field for sound propagation in solids. This is different from the Christoffel's equation which is in term of the velocity field. We feel that stress field can better characterize the elastic properties of the sound waves. We also derive the acoustic gauge field condition and gauge invariance and symmetries for the acoustic fields. We also apply symmetries to study negative refraction. Note from Publisher: This article contains the abstract only.
Implementing and testing a panel-based method for modeling acoustic scattering from CFD input
NASA Astrophysics Data System (ADS)
Swift, S. Hales
Exposure of sailors to high levels of noise in the aircraft carrier deck environment is a problem that has serious human and economic consequences. A variety of approaches to quieting exhausting jets from high-performance aircraft are undergoing development. However, testing of noise abatement solutions at full-scale may be prohibitively costly when many possible nozzle treatments are under consideration. A relatively efficient and accurate means of predicting the noise levels resulting from engine-quieting technologies at personnel locations is needed. This is complicated by the need to model both the direct and the scattered sound field in order to determine the resultant spectrum and levels. While the direct sound field may be obtained using CFD plus surface integral methods such as the Ffowcs-Williams Hawkings method, the scattered sound field is complicated by its dependence on the geometry of the scattering surface--the aircraft carrier deck, aircraft control surfaces and other nearby structures. In this work, a time-domain boundary element method, or TD-BEM, (sometimes referred to in terms of source panels) is proposed and developed that takes advantage of and offers beneficial effects for the substantial planar components of the aircraft carrier deck environment and uses pressure gradients as its input. This method is applied to and compared with analytical results for planar surfaces, corners and spherical surfaces using an analytic point source as input. The method can also accept input from CFD data on an acoustic data surface by using the G1A pressure gradient formulation to obtain pressure gradients on the surface from the flow variables contained on the acoustic data surface. The method is also applied to a planar scattering surface characteristic of an aircraft carrier flight deck with an acoustic data surface from a supersonic jet large eddy simulation, or LES, as input to the scattering model. In this way, the process for modeling the complete
Inverse acoustic scattering by small-obstacle expansion of a misfit function
NASA Astrophysics Data System (ADS)
Bonnet, Marc
2008-06-01
This paper concerns an extension of the topological derivative concept for 3D inverse acoustic scattering problems, whereby the featured cost function J is expanded in powers of the characteristic size ɛ of a sound-hard scatterer about ɛ = 0. The O(ɛ6) approximation of J is established for a small scatterer of arbitrary shape of given location embedded in an arbitrary acoustic domain, and generalized to several such scatterers. Simpler and more explicit versions of this result are obtained for a centrally-symmetric scatterer and a spherical scatterer. An approximate and computationally fast global search procedure is proposed, where the location and size of the unknown scatterer is estimated by minimizing the O(ɛ6) approximation of J over a search grid. Its usefulness is demonstrated on numerical experiments, where the identification of a spherical, ellipsoidal or banana-shaped scatterer embedded in a acoustic half-space from known acoustic pressure on the surface is considered.
Scattering in a magnetic field
David C. Carey
2002-08-19
The fixed target program at Fermilab has come to an end. New projects are in the planning stage. Among them is a muon storage ring. Up to the present, all storage rings in high-energy physics have carried stable particles, namely the electron and proton and their antiparticles. The muon is unstable and decays with a mean lifetime of 2.0 x 10{sup -6} sec. Two types of cooling have been used in the past. One is stochastic cooling where an electrode is used to detect the positions of the particles and send a signal to another position across the ring. Through successive applications of this technique, the phase space is ultimately greatly reduced and beams can be made to collide with a useful event rate. The second type of cooling is electron cooling. Here protons and electrons are made to travel together for a short distance. Equipartition causes transfer of transverse energy of the protons to that of the electrons. Neither of these methods is fast enough to allow acceleration of a sufficient number of muons up to maximum energy before they decay. A new method known as ionization cooling has been proposed.[1] The muons are cooled by passing them through a container of liquid hydrogen. The energy loss reduces both transverse and longitudinal momentum. The longitudinal momentum is restored with RF cavities. The net result is to maintain the longitudinal momentum while cooling the transverse momentum. To minimize the total travel distance of the muons the liquid hydrogen is placed inside the focusing solenoids. The question arises as to whether the presence of the solenoids influences the phase space occupied by the muons. After the muon scatters it has transverse momentum. In a constant longitudinal magnetic field the trajectory wraps around the field lines and coincides in momentum and position with a particle which scatters one cycle later. Here we calculate the change in emittance for both a drift space and a solenoid. We find that the presence of the solenoid does
Scatter integration with right triangular fields.
Siddon, R L; Dewyngaert, J K; Bjärngard, B E
1985-01-01
The concept of the equivalent field is used extensively in radiotherapy dose calculation algorithms. The rationale for using equivalent fields is to allow dose calculations for a wide variety of field shapes, while maintaining dose calculational data for only a few, very regularly shaped fields. A common example is the table of equivalent squares of rectangular fields presented by Day in the British Journal of Radiology. Recently, in searching for fast dose calculation algorithms for irregular fields, we introduced the concept of the equivalent square of a right triangular field. It is shown that an arbitrary irregular field of N vertices may be decomposed into 2N right triangular fields, each with a precalculated equivalent square. The scatter at the point of calculation due to the irregular field is then obtained as a sum of the scatter contributions from the equivalent squares. The scatter integration with right triangles is compared with scatter integration using program IRREG.
Scatter factor corrections for elongated fields
Higgins, P.D.; Sohn, W.H.; Sibata, C.H.; McCarthy, W.A. )
1989-09-01
Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.
Scatter factor corrections for elongated fields.
Higgins, P D; Sohn, W H; Sibata, C H; McCarthy, W A
1989-01-01
Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.
Characteristic analysis of underwater acoustic scattering echoes in the wavelet transform domain
NASA Astrophysics Data System (ADS)
Yang, Mei; Li, Xiukun; Yang, Yang; Meng, Xiangxia
2017-01-01
Underwater acoustic scattering echoes have time-space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.
Characteristic analysis of underwater acoustic scattering echoes in the wavelet transform domain
NASA Astrophysics Data System (ADS)
Yang, Mei; Li, Xiukun; Yang, Yang; Meng, Xiangxia
2017-03-01
Underwater acoustic scattering echoes have time-space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.
Ion acoustic turbulence and transport in a plasma in a strong electric field
NASA Astrophysics Data System (ADS)
Bychenkov, V. Iu.; Gradov, O. M.; Silin, V. P.
1984-01-01
A theory is derived for the nonlinear state which is established in a plasma when the ion acoustic instability is suppressed by nonlinear induced wave scattering by ions, and there is a quasi-linear relaxation of electrons among turbulent fluctuations. The behavior of the ion acoustic noise spectrum and of transport processes in strong fields, where the anomalous plasma resistance is a square-root function of the field intensity, is found. In this region of electric fields there is a universal distribution of the ion acoustic fluctuations in the magnitude of the wave vector and in angle for the turbulence spectrum.
NASA Astrophysics Data System (ADS)
Cai, Chen; Yuan, Yin; Kan, Wei-Wei; Yang, Jing; Zou, Xin-Ye
2016-12-01
In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274168, 11374157, 11174138, 11174139, 11222442, and 81127901) and the National Basic Research Program of China (Grant Nos. 2010CB327803 and 2012CB921504).
Analysis of acoustic scattering from fluid bodies using a multipoint source model.
Boag, A; Leviatan, Y
1989-01-01
A moment-method solution is presented for the problem of acoustic scattering from homogeneous fluid bodies. It uses fictitious isotropic point sources to simulate both the field scattered by the body and the field inside the body and, in turn, point-matches the continuity conditions for the normal component of the velocity and for the pressure across the surface of the body. The procedure is simple to execute and is general in that bodies of arbitrary smooth shape can be handled effectively. Perfectly rigid bodies are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.
NASA Technical Reports Server (NTRS)
Turc, Catalin; Anand, Akash; Bruno, Oscar; Chaubell, Julian
2011-01-01
We present a computational methodology (a novel Nystrom approach based on use of a non-overlapping patch technique and Chebyshev discretizations) for efficient solution of problems of acoustic and electromagnetic scattering by open surfaces. Our integral equation formulations (1) Incorporate, as ansatz, the singular nature of open-surface integral-equation solutions, and (2) For the Electric Field Integral Equation (EFIE), use analytical regularizes that effectively reduce the number of iterations required by iterative linear-algebra solution based on Krylov-subspace iterative solvers.
Ostrovsky, Lev A; Sutin, Alexander M; Soustova, Irina A; Matveyev, Alexander L; Potapov, Andrey I; Kluzek, Zigmund
2003-02-01
The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31-37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.
Numerical method to compute acoustic scattering effect of a moving source.
Song, Hao; Yi, Mingxu; Huang, Jun; Pan, Yalin; Liu, Dawei
2016-01-01
In this paper, the aerodynamic characteristic of a ducted tail rotor in hover has been numerically studied using CFD method. An analytical time domain formulation based on Ffowcs Williams-Hawkings (FW-H) equation is derived for the prediction of the acoustic velocity field and used as Neumann boundary condition on a rigid scattering surface. In order to predict the aerodynamic noise, a hybrid method combing computational aeroacoustics with an acoustic thin-body boundary element method has been proposed. The aerodynamic results and the calculated sound pressure levels (SPLs) are compared with the known method for validation. Simulation results show that the duct can change the value of SPLs and the sound directivity. Compared with the isolate tail rotor, the SPLs of the ducted tail rotor are smaller at certain azimuth.
NASA Technical Reports Server (NTRS)
Meyer, Harold D.
1999-01-01
This second volume of Acoustic Scattering by Three-Dimensional Stators and Rotors Using the SOURCE3D Code provides the scattering plots referenced by Volume 1. There are 648 plots. Half are for the 8750 rpm "high speed" operating condition and the other half are for the 7031 rpm "mid speed" operating condition.
Acoustic backscatter by suspended cohesive sediments: Field observations, Seine Estuary, France
NASA Astrophysics Data System (ADS)
Sahin, Cihan; Verney, Romaric; Sheremet, Alexandru; Voulgaris, George
2017-02-01
Observations of suspended sediment size and concentration, flow and acoustic backscatter intensity collected on the Seine Estuary (France) are used to study the acoustic response in cohesive-sediment dominated environments. Estimates of suspended sediment concentration based on optical backscatter sensors and water samples are used to calibrate the acoustic backscatter intensity. The vertical structure of suspended sediment concentration is then estimated from acoustic backscatter information. To our knowledge, this is the first field application of the recently proposed model of acoustic scattering by flocculating suspensions based on the variation of particle density (floc-scattering model). The estimates of sediment concentration reproduce well the observations under different tidal (neap/spring) conditions, confirming the applicability of the new model in the field when detailed particle size measurements are available. When particle size measurements are not available, using estimated floc sizes based on the turbulence intensities may provide reasonable SSC profiles. During spring tide events (associated with strong currents, small flocs and large concentrations), the performances of the new floc-scattering model and the previous models given for solid particle-scattering are comparable. The floc-scattering model increases the quality of the SSC estimates especially during low-energy conditions characterized with larger flocs.
Fourth-order acoustic torque in intense sound fields
NASA Technical Reports Server (NTRS)
Wang, T. G.; Kanber, H.; Olli, E. E.
1978-01-01
The observation of a fourth-order acoustic torque in intense sound fields is reported. The torque was determined by measuring the acoustically induced angular deflection of a polished cylinder suspended by a torsion fiber. This torque was measured in a sound field of amplitude greater than that in which first-order acoustic torque has been observed.
NASA Astrophysics Data System (ADS)
Tchahame, Joël. Cabrel; Sylvestre, Thibaut; Phan Huy, Kien; Kudlinski, Alexandre; Laude, Vincent; Beugnot, Jean-Charles
2016-04-01
Light propagation in small-core photonic crystal fibers enables tight optical confinement over long propagation lengths to enhance light-matter interactions. Not only can photonic crystal fibers compress light spatially, they also provide a tunable means to control light-hypersound interactions. By exploring Brillouin light scattering in a small-core and high air-filling fraction microstructured fiber, we report the observation of Brillouin scattering from surface acoustic waves at lower frequencies than standard Brillouin scattering from bulk acoustic waves. This effect could find potential applications for optical sensing technologies that exploit surface acoustic waves.
Monte Carlo applications to acoustical field solutions
NASA Technical Reports Server (NTRS)
Haviland, J. K.; Thanedar, B. D.
1973-01-01
The Monte Carlo technique is proposed for the determination of the acoustical pressure-time history at chosen points in a partial enclosure, the central idea of this technique being the tracing of acoustical rays. A statistical model is formulated and an algorithm for pressure is developed, the conformity of which is examined by two approaches and is shown to give the known results. The concepts that are developed are applied to the determination of the transient field due to a sound source in a homogeneous medium in a rectangular enclosure with perfect reflecting walls, and the results are compared with those presented by Mintzer based on the Laplace transform approach, as well as with a normal mode solution.
NASA Technical Reports Server (NTRS)
Kolaini, Ali R.; Doty, Benjamin; Chang, Zensheu
2012-01-01
The aerospace industry has been using two methods of acoustic testing to qualify flight hardware: (1) Reverberant Acoustic Test (RAT), (2) Direct Field Acoustic Test (DFAT). The acoustic field obtained by RAT is generally understood and assumed to be diffuse, expect below Schroeder cut-of frequencies. DFAT method of testing has some distinct advantages over RAT, however the acoustic field characteristics can be strongly affected by test setup such as the speaker layouts, number and location of control microphones and control schemes. In this paper the following are discussed based on DEMO tests performed at APL and JPL: (1) Acoustic wave interference patterns and acoustic standing waves, (2) The structural responses in RAT and DFAT.
2015-09-30
1996 (Ref. 1), based upon the harmonic solution of sets of coupled differential equations, each describing scattering from one fish. The Love swim...side of the empty core, thus reducing the acoustic interactions between them. REFERENCES (1) C. Feuillade, R. W. Nero and R. H. Love , "A low...frequency acoustic scattering model for small schools offish," J. Acoust. Soc. Am., 99, 196-208 (1996). (2) R. H. Love , "Resonant acoustic scattering by
Numerical Studies on the Statistics of Acoustic Scattering from Rock Outcrops
2013-06-17
Results, Kos, Greece, eds. John S. Papadakis and Leif Bjorno. Olson, D.R. and A.P. Lyons, 2013, Numerical simulation of acoustic scattering from very rough...glacially- plucked surfaces using the boundary element method, in Proceedings of 5th Underwater Acoustic Measurements Conference: Technologies and Results, Corfu, Greece, eds. John S. Papadakis and Leif Bjorno.
Droplet Vaporization In A Levitating Acoustic Field
NASA Technical Reports Server (NTRS)
Ruff, G. A.; Liu, S.; Ciobanescu, I.
2003-01-01
Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. To eliminate the effect of the fiber, several researchers have conducted microgravity experiments using unsupported droplets. Jackson and Avedisian investigated single, unsupported drops while Nomura et al. studied droplet clouds formed by a condensation technique. The overall objective of this research is to extend the study of unsupported drops by investigating the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would provide unique experimental data for the verification and improvement of spray combustion models. In this work, the formation of drop clusters is precisely controlled using an acoustic levitation system so that dilute, as well as dense clusters can be created and stabilized before combustion in microgravity is begun. While the low-gravity test facility is being completed, tests have been conducted in 1-g to characterize the effect of the acoustic field on the vaporization of single and multiple droplets. This is important because in the combustion experiment, the droplets will be formed and
Acoustic Wood anomaly in transmitted diffraction field
NASA Astrophysics Data System (ADS)
Liu, Jingfei; Declercq, Nico F.
2017-03-01
In acoustics, the term Wood anomaly, in analogy to the Wood anomaly in optics, has so far referred to the anomalies observed in the specular reflection spectra of acoustic waves perpendicularly incident on periodic surfaces. Inspired by the pioneering work of Jungman et al. on the study of the transmission field of a solid-fluid periodic interface, this work attempts to provide a complete experimental investigation of the transmission fields of a broadband sound pulse transmitted through a periodic liquid-solid interface as well as a periodic solid-liquid interface. At different frequencies, two types of anomalies are observed: a spectral tip and a spectral dip, which correspond, respectively, to the brighter band and the darker band in optical Wood anomalies. The search for their physical origin suggests that the type and location of the observed spectral anomalies are strongly related to the generation and the diffraction of pseudosurface waves on the interface having superimposed periodic corrugations and time-domain windowing in spectral analysis. To compare with the surface waves on a plane surface, the properties of the pseudosurface waves are also investigated through examining their phase and by comparing their amplitudes.
Acoustic vibrations contribute to the diffuse scatter produced by ribosome crystals
Polikanov, Yury S.; Moore, Peter B.
2015-01-01
The diffuse scattering pattern produced by frozen crystals of the 70S ribosome from Thermus thermophilus is as highly structured as it would be if it resulted entirely from domain-scale motions within these particles. However, the qualitative properties of the scattering pattern suggest that acoustic displacements of the crystal lattice make a major contribution to it. PMID:26457426
Investigating acoustic-induced deformations in a foam using multiple light scattering.
Erpelding, M; Guillermic, R M; Dollet, B; Saint-Jalmes, A; Crassous, J
2010-08-01
We have studied the effect of an external acoustic wave on bubble displacements inside an aqueous foam. The signature of the acoustic-induced bubble displacements is found using a multiple light scattering technique, and occurs as a modulation on the photon correlation curve. Measurements for various sound frequencies and amplitudes are compared to analytical predictions and numerical simulations. These comparisons finally allow us to elucidate the nontrivial acoustic displacement profile inside the foam; in particular, we find that the acoustic wave creates a localized shear in the vicinity of the solid walls holding the foam, as a consequence of inertial contributions. This study of how bubbles "dance" inside a foam as a response to sound turns out to provide new insights on foam acoustics and sound transmission into a foam, foam deformation at high frequencies, and analysis of light scattering data in samples undergoing nonhomogeneous deformations.
Imaging of acoustic fields using optical feedback interferometry.
Bertling, Karl; Perchoux, Julien; Taimre, Thomas; Malkin, Robert; Robert, Daniel; Rakić, Aleksandar D; Bosch, Thierry
2014-12-01
This study introduces optical feedback interferometry as a simple and effective technique for the two-dimensional visualisation of acoustic fields. We present imaging results for several pressure distributions including those for progressive waves, standing waves, as well as the diffraction and interference patterns of the acoustic waves. The proposed solution has the distinct advantage of extreme optical simplicity and robustness thus opening the way to a low cost acoustic field imaging system based on mass produced laser diodes.
Bugay, A. N.; Sazonov, S. V.
2008-08-15
A new mechanism is proposed for continuous frequency down-conversion of acoustic waves propagating in a paramagnetic crystal at a low temperature in an applied magnetic field. A transverse hypersonic pulse generating a carrier-free longitudinal strain pulse via nonlinear effects is scattered by the generated pulse. This leads to a Stokes shift in the transverse hypersonic wave proportional to its intensity, and both pulses continue to propagate in the form of a mode-locked soliton. As the transverse-pulse frequency is Stokes shifted, its spectrum becomes narrower. This process can be effectively implemented only if the linear group velocity of the transverse hypersonic pulse equals the phase velocity of the longitudinal strain wave. These velocities are renormalized by spin-phonon coupling and can be made equal by adjusting the magnitude of the applied magnetic field. The transverse structure of the soliton depends on the sign of the group velocity dispersion of the transverse component. When the dispersion is positive, planar solitons can develop whose transverse component has a topological defect of dark vortex type and longitudinal component has a hole. In the opposite case, the formation of two-component acoustic 'bullets' or vortices localized in all directions is possible.
Inverse acoustic scattering problem in half-space with anisotropic random impedance
NASA Astrophysics Data System (ADS)
Helin, Tapio; Lassas, Matti; Päivärinta, Lassi
2017-02-01
We study an inverse acoustic scattering problem in half-space with a probabilistic impedance boundary value condition. The Robin coefficient (surface impedance) is assumed to be a Gaussian random function with a pseudodifferential operator describing the covariance. We measure the amplitude of the backscattered field averaged over the frequency band and assume that the data is generated by a single realization of λ. Our main result is to show that under certain conditions the principal symbol of the covariance operator of λ is uniquely determined. Most importantly, no approximations are needed and we can solve the full non-linear inverse problem. We concentrate on anisotropic models for the principal symbol, which leads to the analysis of a novel anisotropic spherical Radon transform and its invertibility.
Acoustic Tweezing and Patterning of Concentration Fields in Microfluidics
NASA Astrophysics Data System (ADS)
Karlsen, Jonas T.; Bruus, Henrik
2017-03-01
We demonstrate theoretically that acoustic forces acting on inhomogeneous fluids can be used to pattern and manipulate solute concentration fields into spatiotemporally controllable configurations stabilized against gravity. A theoretical framework describing the dynamics of concentration fields that weakly perturb the fluid density and speed of sound is presented and applied to study manipulation of concentration fields in rectangular-channel acoustic eigenmodes and in Bessel-function acoustic vortices. In the first example, methods to obtain horizontal and vertical multilayer stratification of the concentration field at the end of a flow-through channel are presented. In the second example, we demonstrate acoustic tweezing and spatiotemporal manipulation of a local high-concentration region in a lower-concentration medium, thereby extending the realm of acoustic tweezing to include concentration fields.
Acoustic resonance scattering from a multilayered cylindrical shell with imperfect bonding.
Rajabi, M; Hasheminejad, Seyyed M
2009-12-01
The method of wave function expansion is adopted to study the three dimensional scattering of a time-harmonic plane progressive sound field obliquely incident upon a multi-layered hollow cylinder with interlaminar bonding imperfection. For the generality of solution, each layer is assumed to be cylindrically orthotropic. An approximate laminate model in the context of the modal state equations with variable coefficients along with the classical T-matrix solution technique is set up for each layer to solve for the unknown modal scattering and transmission coefficients. A linear spring model is used to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. Following the classic acoustic resonance scattering theory (RST), the scattered field and response to surface waves are determined by constructing the partial waves and obtaining the non-resonance (backgrounds) and resonance components. The solution is first used to investigate the effect of interlayer imperfection of an air-filled and water submerged bilaminate aluminium cylindrical shell on the resonances associated with various modes of wave propagation (i.e., symmetric/asymmetric Lamb waves, fluid-borne A-type waves, Rayleigh and Whispering Gallery waves) appearing in the backscattered spectrum, according to their polarization and state of stress. An illustrative numerical example is also given for a multi-layered (five-layered) cylindrical shell for which the stiffness of the adhesive interlayers is artificially varied. The sensitivity of resonance frequencies associated with higher mode numbers to the stiffness coefficients is demonstrated to be a good measure of the bonding strength. Limiting cases are considered and fair agreements with solutions available in the literature are established.
MEASUREMENTS OF THE WAVEFUNCTIONS OF SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS
Zhao Hui; Chou, Dean-Yi; Yang, Ming-Hsu
2011-10-20
Solar acoustic waves are scattered by sunspots because of the interaction between the acoustic waves and sunspots. We use a deconvolution scheme to obtain the wavefunction of the acoustic wave on the solar surface at various times from cross-correlation functions computed between an incident wave and the signals at other points on the surface. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We study the wavefunctions of scattered waves with the incident waves of radial order n = 0-5 for two sunspots, NOAAs 11084 and 11092. The scattered wave is predominant in the forward direction of the incident wave, but its wavefronts are curved. The shape of the wavefronts depends on the ratio of sunspot dimension to wavelength of the incident wave. The smaller the ratio is, the closer to circular the scattered wave is. The scattering strength, i.e. the magnitude of the scattered wave relative to that of the incident wave, decreases with the radial order n. This suggests that the region generating the scattered wave is shallower than the depth of the f-modes.
Acoustic field effects on a negative corona discharge
NASA Astrophysics Data System (ADS)
Bálek, R.; Červenka, M.; Pekárek, S.
2014-06-01
For a negative corona discharge under atmospheric pressure in different regimes, we investigated the effects of an acoustic field both on its electrical parameters and on the change in its visual appearance. We found that the application of an acoustic field on the true corona discharge, for particular currents, decreases the discharge voltage. The application of an acoustic field on the discharge in the filamentary streamer regime substantially extends the range of currents for which the discharge voltage remains more or less constant, i.e. it allows a substantial increase in the power delivered to the discharge. The application of an acoustic field on the discharge causes the discharge to spread within the discharge chamber and consequently, a highly reactive non-equilibrium plasma is created throughout the inter-electrode space. Finally, our experimental apparatus radiates almost no acoustic energy from the discharge chamber.
Solution of an inverse scattering problem for the acoustic wave equation in three-dimensional media
NASA Astrophysics Data System (ADS)
Baev, A. V.
2016-12-01
A three-dimensional inverse scattering problem for the acoustic wave equation is studied. The task is to determine the density and acoustic impedance of a medium. A necessary and sufficient condition for the unique solvability of this problem is established in the form of an energy conservation law. The interpretation of the solution to the inverse problem and the construction of medium images are discussed.
Nonlinear Bubble Interactions in Acoustic Pressure Fields
NASA Technical Reports Server (NTRS)
Barbat, Tiberiu; Ashgriz, Nasser; Liu, Ching-Shi
1996-01-01
The systems consisting of a two-phase mixture, as clouds of bubbles or drops, have shown many common features in their responses to different external force fields. One of particular interest is the effect of an unsteady pressure field applied to these systems, case in which the coupling of the vibrations induced in two neighboring components (two drops or two bubbles) may result in an interaction force between them. This behavior was explained by Bjerknes by postulating that every body that is moving in an accelerating fluid is subjected to a 'kinetic buoyancy' equal with the product of the acceleration of the fluid multiplied by the mass of the fluid displaced by the body. The external sound wave applied to a system of drops/bubbles triggers secondary sound waves from each component of the system. These secondary pressure fields integrated over the surface of the neighboring drop/bubble may result in a force additional to the effect of the primary sound wave on each component of the system. In certain conditions, the magnitude of these secondary forces may result in significant changes in the dynamics of each component, thus in the behavior of the entire system. In a system containing bubbles, the sound wave radiated by one bubble at the location of a neighboring one is dominated by the volume oscillation mode and its effects can be important for a large range of frequencies. The interaction forces in a system consisting of drops are much smaller than those consisting of bubbles. Therefore, as a first step towards the understanding of the drop-drop interaction subject to external pressure fluctuations, it is more convenient to study the bubble interactions. This paper presents experimental results and theoretical predictions concerning the interaction and the motion of two levitated air bubbles in water in the presence of an acoustic field at high frequencies (22-23 KHz).
NASA Technical Reports Server (NTRS)
Kolaini, Ali R.; Doty, Benjamin; Chang, Zensheu
2012-01-01
Loudspeakers have been used for acoustic qualification of spacecraft, reflectors, solar panels, and other acoustically responsive structures for more than a decade. Limited measurements from some of the recent speaker tests used to qualify flight hardware have indicated significant spatial variation of the acoustic field within the test volume. Also structural responses have been reported to differ when similar tests were performed using reverberant chambers. To address the impact of non-uniform acoustic field on structural responses, a series of acoustic tests were performed using a flat panel and a 3-ft cylinder exposed to the field controlled by speakers and repeated in a reverberant chamber. The speaker testing was performed using multi-input-single-output (MISO) and multi-input-multi-output (MIMO) control schemes with and without the test articles. In this paper the spatial variation of the acoustic field due to acoustic standing waves and their impacts on the structural responses in RAT and DFAT (both using MISO and MIMO controls for DFAT) are discussed in some detail.
Diversity of acoustic streaming in a rectangular acoustofluidic field.
Tang, Qiang; Hu, Junhui
2015-04-01
Diversity of acoustic streaming field in a 2D rectangular chamber with a traveling wave and using water as the acoustic medium is numerically investigated by the finite element method. It is found that the working frequency, the vibration excitation source length, and the distance and phase difference between two separated symmetric vibration excitation sources can cause the diversity in the acoustic streaming pattern. It is also found that a small object in the acoustic field results in an additional eddy, and affects the eddy size in the acoustic streaming field. In addition, the computation results show that with an increase of the acoustic medium's temperature, the speed of the main acoustic streaming decreases first and then increases, and the angular velocity of the corner eddies increases monotonously, which can be clearly explained by the change of the acoustic dissipation factor and shearing viscosity of the acoustic medium with temperature. Commercialized FEM software COMSOL Multiphysics is used to implement the computation tasks, which makes our method very easy to use. And the computation method is partially verified by an established analytical solution.
Light scattering by surface acoustic waves on corrugated metal surfaces
Robertson, W.M.; Grimsditch, M. ); Moretti, A.L.; Kaufman, R.G.; Hulse, G.R. ); Fullerton, E.; Schuller, I.K. )
1990-03-15
We report the results of a Brillouin-scattering study of corrugated Ag surfaces. The corrugation plays a dramatic role in the wave-vector--selection rules governing coupling to surface phonons, and this effect is substantially different when the effective wave vector of the surface corrugation is collinear or perpendicular to the scattering plane. In processes that involve the grating wave vector, we show that the coupling mechanism between light and phonons is governed by surface plasmons which introduce a new scattering interaction with unusual polarization features in the Brillouin-scattering process.
Temperature Dependence of Brillouin Light Scattering Spectra of Acoustic Phonons in Silicon
NASA Astrophysics Data System (ADS)
Somerville, Kevin; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin
2015-03-01
Thermal management represents an outstanding challenge in many areas of technology. Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. Interest in non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report temperature dependent BLS spectra of silicon, with Raman spectra taken simultaneously for comparison. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. We determine that the integrated BLS intensity can be used measure the temperature of specific acoustic phonon modes. This work is supported by National Science Foundation (NSF) Thermal Transport Processes Program under Grant CBET-1336968.
Simulation of Acoustic Scattering from a Trailing Edge
NASA Technical Reports Server (NTRS)
Singer, Bart A.; Brentner, Kenneth S.; Lockhard, David P.; Lilley, Geoffrey M.
1999-01-01
Three model problems were examined to assess the difficulties involved in using a hybrid scheme coupling flow computation with the the Ffowcs Williams and Hawkings equation to predict noise generated by vortices passing over a sharp edge. The results indicate that the Ffowcs Williams and Hawkings equation correctly propagates the acoustic signals when provided with accurate flow information on the integration surface. The most difficult of the model problems investigated inviscid flow over a two-dimensional thin NACA airfoil with a blunt-body vortex generator positioned at 98 percent chord. Vortices rolled up downstream of the blunt body. The shed vortices possessed similarities to large coherent eddies in boundary layers. They interacted and occasionally paired as they convected past the sharp trailing edge of the airfoil. The calculations showed acoustic waves emanating from the airfoil trailing edge. Acoustic directivity and Mach number scaling are shown.
Thomson scattering in a magnetic field. II - Arbitrary field orientation
NASA Technical Reports Server (NTRS)
Whitney, Barbara A.
1991-01-01
This paper presents solutions to the equation of transfer for Thomson scattering in a constant magnetic field of arbitrary orientation. Results from several atmospheres are combined to give the flux from a dipole star. The results are compared to the polarization data of the magnetic white dwarf Grw + 70 deg 8247. The fit is good, though it implies a very large polarization in the ultraviolet. Thomson scattering is not thought to be an important opacity source in white dwarfs, so the good fit is either fortuitous or is perhaps explained by assuming the magnetic field affects the polarization processes in all opacities similarly.
MODE CONVERSION BETWEEN DIFFERENT RADIAL ORDERS FOR SOLAR ACOUSTIC WAVES SCATTERED BY SUNSPOTS
Zhao, Hui; Chou, Dean-Yi
2013-11-20
We study the mode conversion between different radial orders for solar acoustic waves interacting with sunspots. Solar acoustic waves are modified in the presence of sunspots. The modification in the wave can be viewed as that the sunspot, excited by the incident wave, generates the scattered wave, and the scattered wave is added to the incident wave to form the total wave inside and around the sunspot. The wavefunction of the acoustic wave on the solar surface is computed from the cross-correlation function. The wavefunction of the scattered wave is obtained by subtracting the wavefunction of the incident wave from that of the total wave. We use the incident waves of radial order n = 0-5 to measure the scattered wavefunctions from n to another radial order n' for NOAAs 11084 and 11092. The strength of scattered waves decreases rapidly with |Δn|, where Δn ≡ n' – n. The scattered waves of Δn = ±1 are visible for n ≤ 1, and significant for n ≥ 2. For the scattered wave of Δn = ±2, only few cases are visible. None of the scattered waves of Δn = ±3 are visible. The properties of scattered waves for Δn = 0 and Δn ≠ 0 are different. The scattered wave amplitude relative to the incident wave amplitude decreases with n for Δn = 0, while it increases with n for Δn ≠ 0. The scattered wave amplitudes of Δn = 0 are greater for the larger sunspot, while those of Δn ≠ 0 are insensitive to the sunspot size.
Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao
2016-03-01
As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.
Effects of multi-scattering on the performance of a single-beam acoustic manipulation device.
Azarpeyvand, Mahdi; Alibakhshi, Mohammad Amin; Self, Rod
2012-08-01
The effects of multiple scattering on acoustic manipulation of spherical particles using helicoidal Bessel-beams are discussed. A closed-form analytical solution is developed to calculate the acoustic radiation force resulting from a Bessel-beam on an acoustically reflective sphere, in the presence of an adjacent spherical particle, immersed in an unbounded fluid medium. The solution is based on the standard Fourier decomposition method and the effect of multi-scattering is taken into account using the addition theorem for spherical coordinates. Of particular interest here is the investigation of the effects of multiple scattering on the emergence of negative axial forces. To investigate the effects, the radiation force applied on the target particle resulting from a helicoidal Bessel-beam of different azimuthal indexes (m = 1 to 4), at different conical angles, is computed. Results are presented for soft and rigid spheres of various sizes, separated by a finite distance. Results have shown that the emergence of negative force regions is very sensitive to the level of cross-scattering between the particles. It has also been shown that in multiple scattering media, the negative axial force may occur at much smaller conical angles than previously reported for single particles, and that acoustic manipulation of soft spheres in such media may also become possible.
Nondestructive acoustic electric field probe apparatus and method
Migliori, Albert
1982-01-01
The disclosure relates to a nondestructive acoustic electric field probe and its method of use. A source of acoustic pulses of arbitrary but selected shape is placed in an oil bath along with material to be tested across which a voltage is disposed and means for receiving acoustic pulses after they have passed through the material. The received pulses are compared with voltage changes across the material occurring while acoustic pulses pass through it and analysis is made thereof to determine preselected characteristics of the material.
Modulation of Radio Frequency Signals by Nonlinearly Generated Acoustic Fields
2014-01-01
Kirchhoff’s theorem, typically applied to EM waves, determining the far-field patterns of an acoustic source from amplitude and phase measurements made in...two noncollinear ultrasonic baffled piston sources. The theory is extended to the modeling of the sound beams generated by parametric transducer arrays ...typically applied to EM waves, determining the far-field patterns of an acoustic source from amplitude and phase measurements made in the near-field by
Thomson scattering in a magnetic field. I - Field along z
NASA Technical Reports Server (NTRS)
Whitney, Barbara A.
1991-01-01
The Monte Carlo method is used here to solve the radiative transfer equation for Thomson scattering in a constant magnetic field perpendicular to the atmosphere. Emergent radiation and polarization are presented for various atmospheric thicknesses. The circular polarization peaks at frequencies near the cyclotron, omega(c), and for propagation direction along the field. At low field strengths, the circular polarization is roughly proportional to omega(c)/omega; the linear polarization is proportional to the square of omega(c)/omega and the amount of circular polarization present at each scatter and is therefore much smaller than the circular polarization. The linear polarization is large for propagation direction perpendicular to the magnetic field and at frequencies near the cyclotron and in the strong-field limit. The position angle of the linear polarization undergoes a rotation of 90 deg at a value of omega(c)/omega near the square root of three.
Field emission and scattering from conducting nanofibers
NASA Astrophysics Data System (ADS)
Marinov, Toma M.
Field emission from conducting nanofibers has a significant importance due to its possible application in electronics like flat panel displays, x-ray machines, sensors, etc. The standard theoretical model describing field emission is the Fowler-Nordheim model, which is valid for bulk material, constant applied electric field and O°K. A more general theoretical model is required in the realistic cases of arbitrary electromagnetic fields and arbitrary but finite temperature. This work presents an asymptotic procedure for calculating field emission from nanofibers of finite length for static and dynamic fields at arbitrary finite temperature. It investigates the behavior of a nanofiber in the presence of electrostatic and EM fields. The resultant field potentials outside the system are obtained by employing the slender-body approximation ([1], [2], [3]). The total external potential is used in conjunction with the the Wentzel-Krammers-Brillouin approximation [4] to estimate the tunneling probability of the electrons in the fiber due the total external field. Unlike the standard Fowler-Nordheim method [5], the current density of the field emission is obtained by using quantum wire density of states. In addition, this work investigates radiative and scattering properties of conducting nanofibers for the purpose of nanoantenna applications. The results for the distributions of the induced currents are compared to the results from the solution of Hallen's integral equation [6] and the corresponding radiation patterns are compared. The results are extended for the case of a broadside uniform array of N aligned fibers.
Basin Acoustic Seamount Scattering Experiment (BASSEX) Data Analysis and Modeling
2016-06-07
Kauai source at various ranges and bearings . OBJECTIVES The primary objective of this work is to measure aspects of acoustic propagation that...horizontal plane, arriving at the array from a different bearing . Further analysis will include processing all of the BASSEX KNPAL receptions and
NASA Astrophysics Data System (ADS)
Follett, R. K.; Delettrez, J. A.; Edgell, D. H.; Henchen, R. J.; Katz, J.; Myatt, J. F.; Froula, D. H.
2016-11-01
Collective Thomson scattering is a technique for measuring the plasma conditions in laser-plasma experiments. Simultaneous measurements of ion-acoustic and electron plasma-wave spectra were obtained using a 263.25-nm Thomson-scattering probe beam. A fully reflective collection system was used to record light scattered from electron plasma waves at electron densities greater than 1021 cm-3, which produced scattering peaks near 200 nm. An accurate analysis of the experimental Thomson-scattering spectra required accounting for plasma gradients, instrument sensitivity, optical effects, and background radiation. Practical techniques for including these effects when fitting Thomson-scattering spectra are presented and applied to the measured spectra to show the improvements in plasma characterization.
Field Measurement of the Acoustic Nonlinearity Parameter in Turbine Blades
NASA Technical Reports Server (NTRS)
Hinton, Yolanda L.; Na, Jeong K.; Yost, William T.; Kessel, Gregory L.
2000-01-01
Nonlinear acoustics techniques were used to measure fatigue in turbine blades in a power generation plant. The measurements were made in the field using a reference based measurement technique, and a reference sample previously measured in the laboratory. The acoustic nonlinearity parameter showed significant increase with fatigue in the blades, as indicated by service age and areas of increased stress. The technique shows promise for effectively measuring fatigue in field applications and predicting subsequent failures.
Initial Integration of Noise Prediction Tools for Acoustic Scattering Effects
NASA Technical Reports Server (NTRS)
Nark, Douglas M.; Burley, Casey L.; Tinetti, Ana; Rawls, John W.
2008-01-01
This effort provides an initial glimpse at NASA capabilities available in predicting the scattering of fan noise from a non-conventional aircraft configuration. The Aircraft NOise Prediction Program, Fast Scattering Code, and the Rotorcraft Noise Model were coupled to provide increased fidelity models of scattering effects on engine fan noise sources. The integration of these codes led to the identification of several keys issues entailed in applying such multi-fidelity approaches. In particular, for prediction at noise certification points, the inclusion of distributed sources leads to complications with the source semi-sphere approach. Computational resource requirements limit the use of the higher fidelity scattering code to predict radiated sound pressure levels for full scale configurations at relevant frequencies. And, the ability to more accurately represent complex shielding surfaces in current lower fidelity models is necessary for general application to scattering predictions. This initial step in determining the potential benefits/costs of these new methods over the existing capabilities illustrates a number of the issues that must be addressed in the development of next generation aircraft system noise prediction tools.
Baik, Kyungmin
2013-01-01
Love's model for the acoustic scattering by a spherical viscous fluid shell filled with gas and surrounded by inviscid liquid [J. Acoust. Soc. Am. 64, 571-580 (1978)] is reviewed. For certain material parameters, discrepancies are observed in Love's scattering cross section when compared with the exact solution near resonance. Those errors are corrected in this study. It is shown that there is excellent agreement between the corrected formulation and the exact solution in the resonance region where ka=1 and ε = b/a ≥ 2.5, where k is the acoustic wavenumber, and a and b are the inner and outer radii of the shell, respectively. Errors between Love's equation and the exact solution are not significant for the case of swimbladder-bearing fish where the bubble radius is typically greater than about 0.05 m, but could be large for bubbles and gas-bearing zooplankton where the radius is less than about 0.05 m.
Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon
Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li E-mail: elaineli@physics.utexas.edu; Li, Xiaoqin E-mail: elaineli@physics.utexas.edu
2015-02-02
Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.
Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon
NASA Astrophysics Data System (ADS)
Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin
2015-02-01
Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.
Modeling the near acoustic field of a rocket during launch
NASA Technical Reports Server (NTRS)
Mauritzen, David W.
1989-01-01
The design of launch pad structures is critically dependent upon the stresses imposed by the acoustical pressure field generated by the rocket engines during launch. The purpose of this effort is to better describe the acoustical field in the immediate launch area. Since the problem is not analytically tractable, empirical modeling will be employed so that useful results may be obtained for structural design purposes. The plume of the rocket is considered to be a volumetric acoustic source, and is broken down into incremental contributing volumes. A computer program has been written to sum all the contributions to find the total sound pressure level at an arbitrary point. A constant density source is initially assumed and the acoustic field evaluated for several cases to verify the correct operation of the program.
Particle Cloud Flames in Acoustic Fields
NASA Technical Reports Server (NTRS)
Berlad, A. L.; Tangirala, V.; Ross, H.; Facca, L.
1990-01-01
Results are presented on a study of flames supported by clouds of particles suspended in air, at pressures about 100 times lower than normal. In the experiment, an acoustic driver (4-in speaker) placed at one end of a closed tube, 0.75-m long and 0.05 m in diameter, disperses a cloud of lycopodium particles during a 0.5-sec powerful acoustic burst. Properties of the particle cloud and the flame were recorded by high-speed motion pictures and optical transmission detectors. Novel flame structures were observed, which owe their features to partial confinement, which encourages flame-acoustic interactions, segregation of particle clouds into laminae, and penetration of the flame's radiative flux density into the unburned particle-cloud regimes. Results of these experiments imply that, for particles in confined spaces, uncontrolled fire and explosion may be a threat even if the Phi(0) values are below some apparent lean limit.
Numerical Simulation of Acoustic Scatter from Subsurface Bubble Clouds
1989-10-18
Ellinthorpe, 1989. [6] Serge Baldy. Bubbles in the close vicinity of breaking waves: Statistical character- istics of the generation and dispersion...and J. Vlieger. Light scattering by a sphere on a substrate. Physica. 137(A):209-242, 1986. [13] R. H. Lang . Electromagnetic backscattering from a
Acoustic Inverse Scattering for Breast Cancer Microcalcification Detection. Addendum
2011-12-01
elliptical Radon transform have been developed. We conclude that inverse scattering algorithms for detecting microcalfications in heterogeneous tissue may be...bistatic ultrasound imaging geometry is the elliptical Radon transform (ERT). Small transducers can be modelled as having no directional sensitivity...elliptical Radon transform - a model for bistatic ultrasound array imaging in the breast One possible definition for the elliptical Radon transform would
Scattering Matrix for the Interaction between Solar Acoustic Waves and Sunspots. I. Measurements
NASA Astrophysics Data System (ADS)
Yang, Ming-Hsu; Chou, Dean-Yi; Zhao, Hui
2017-01-01
Assessing the interaction between solar acoustic waves and sunspots is a scattering problem. The scattering matrix elements are the most commonly used measured quantities to describe scattering problems. We use the wavefunctions of scattered waves of NOAAs 11084 and 11092 measured in the previous study to compute the scattering matrix elements, with plane waves as the basis. The measured scattered wavefunction is from the incident wave of radial order n to the wave of another radial order n‧, for n=0{--}5. For a time-independent sunspot, there is no mode mixing between different frequencies. An incident mode is scattered into various modes with different wavenumbers but the same frequency. Working in the frequency domain, we have the individual incident plane-wave mode, which is scattered into various plane-wave modes with the same frequency. This allows us to compute the scattering matrix element between two plane-wave modes for each frequency. Each scattering matrix element is a complex number, representing the transition from the incident mode to another mode. The amplitudes of diagonal elements are larger than those of the off-diagonal elements. The amplitude and phase of the off-diagonal elements are detectable only for n-1≤slant n\\prime ≤slant n+1 and -3{{Δ }}k≤slant δ {k}x≤slant 3{{Δ }}k, where δ {k}x is the change in the transverse component of the wavenumber and Δk = 0.035 rad Mm‑1.
Characterization of Biological Cells by Inverse Acoustic Scattering and Electrozone Sensing.
NASA Astrophysics Data System (ADS)
Chen, Xucai
A technique is presented which characterizes biological cells by their mechanical descriptors: size, compressibility and density. The experimental apparatus consists of two acoustic transducers and an electrozone sensor submerged in a bath of conducting host fluid. Diluted biological cells are convected through the apparatus by a coaxial jet. An individual cell passes through the electrozone where its volume is measured by the Coulter principle, and then through the confocal region of the two acoustic transducers. One acoustic transducer sends out tone bursts at a center frequency of 30 MHz and detects a back-scattered signal from the cell while the other transducer detects the scattered signal at 90^circ. Thus the volume, the 90^circ scattering function, and the 180^circ scattering function are recorded for each cell. The acoustic scattering functions are then inverted to provide the compressibility and density of that cell. Statistics of the mechanical properties for human red and white blood cells are generated and displayed. The size, compressibility and density of both normal and abnormal red blood cells are reported. By modeling a cell as an immiscible mixture of protein and saline solution, perfect mixture laws for compressibility and density are derived and confirmed by experimental results. With the mixture laws established, the mean corpuscular hemoglobin concentration (MCHC) is inferred from the compressibility and density data for red blood cells. Using only the data from the 180^circ back-scattered signal, different white cell subgroups are successfully distinguished by their locations in the two dimensional histograms of their mechanical descriptors.
Near-specular acoustic scattering from a buried submarine mud volcano.
Gerig, Anthony L; Holland, Charles W
2007-12-01
Submarine mud volcanoes are objects that form on the seafloor due to the emission of gas and fluidized sediment from the Earth's interior. They vary widely in size, can be exposed or buried, and are of interest to the underwater acoustics community as potential sources of active sonar clutter. Coincident seismic reflection data and low frequency bistatic scattering data were gathered from one such buried mud volcano located in the Straits of Sicily. The bistatic data were generated using a pulsed piston source and a 64-element horizontal array, both towed over the top of the volcano. The purpose of this work was to appropriately model low frequency scattering from the volcano using the bistatic returns, seismic bathymetry, and knowledge of the general geoacoustic properties of the area's seabed to guide understanding and model development. Ray theory, with some approximations, was used to model acoustic propagation through overlying layers. Due to the volcano's size, scattering was modeled using geometric acoustics and a simple representation of volcano shape. Modeled bistatic data compared relatively well with experimental data, although some features remain unexplained. Results of an inversion for the volcano's reflection coefficient indicate that it may be acoustically softer than expected.
Acoustic scattering for 3D multi-directional periodic structures using the boundary element method.
Karimi, Mahmoud; Croaker, Paul; Kessissoglou, Nicole
2017-01-01
An efficient boundary element formulation is proposed to solve three-dimensional exterior acoustic scattering problems with multi-directional periodicity. The multi-directional periodic acoustic problem is represented as a multilevel block Toeplitz matrix. By exploiting the Toeplitz structure, the computational time and storage requirements to construct and to solve the linear system of equations arising from the boundary element formulation are significantly reduced. The generalized minimal residual method is implemented to solve the linear system of equations. To efficiently calculate the matrix-vector product in the iterative algorithm, the original matrix is embedded into a multilevel block circulant matrix. A multi-dimensional discrete Fourier transform is then employed to accelerate the matrix-vector product. The proposed approach is applicable to a periodic acoustic problem for any arbitrary shape of the structure in both full space and half space. Two case studies involving sonic crystal barriers are presented. In the first case study, a sonic crystal barrier comprising rigid cylindrical scatterers is modeled. To demonstrate the effectiveness of the proposed technique, periodicity in one, two, or three directions is examined. In the second case study, the acoustic performance of a sonic crystal barrier with locally resonant C-shaped scatterers is studied.
Yin, Jie; Tao, Chao Cai, Peng; Liu, Xiaojun
2015-06-08
Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.
NASA Astrophysics Data System (ADS)
Yin, Jie; Tao, Chao; Cai, Peng; Liu, Xiaojun
2015-06-01
Acoustically inhomogeneous mediums with multiple scattering are often the nightmare of photoacoustic tomography. In order to break this limitation, a photoacoustic tomography scheme combining ultrasound interferometry and time reversal is proposed to achieve images in acoustically scattering medium. An ultrasound interferometry is developed to determine the unknown Green's function of strong scattering tissue. Using the determined Greens' function, a time-reversal process is carried out to restore images behind an acoustically inhomogeneous layer from the scattering photoacoustic signals. This method effectively decreases the false contrast, noise, and position deviation of images induced by the multiple scattering. Phantom experiment is carried out to validate the method. Therefore, the proposed method could have potential value in extending the biomedical applications of photoacoustic tomography in acoustically inhomogeneous tissue.
Reconstruction of the Acoustic Field Using a Conformal Array
NASA Technical Reports Server (NTRS)
Valdivia, Nichlas P.; Williams, Earl G.; Klos, Jacob
2006-01-01
Near-field acoustical holography (NAH) requires the measurement of the near-field pressure field over a conformal and closed surface in order to recover the acoustic field on a nearby surface. We are interested in the reconstruction of the acoustic field over the fuselage of a Boeing 757 airplane when pressure data is available over an array of microphones that are conformal to the fuselage surface. In this case the strict NAH theory does not hold, but still there are techniques used to overcome this difficulty. The best known is patch NAH, which has been used for planar surfaces. In this work we will discuss two new techniques used for surfaces with an arbitrarily shape: patch inverse boundary element methods (IBEM) and patch equivalent sources method (ESM). We will discuss the theoretical justification of the method and show reconstructions for in-flight data taken inside a Boeing 757 airplane.
Mitri, F. G.
2015-11-14
Using the partial-wave series expansion method in cylindrical coordinates, a formal analytical solution for the acoustical scattering of a 2D cylindrical quasi-Gaussian beam with an arbitrary angle of incidence θ{sub i}, focused on a rigid elliptical cylinder in a non-viscous fluid, is developed. The cylindrical focused beam expression is an exact solution of the Helmholtz equation. The scattering coefficients for the elliptical cylinder are determined by forcing the expression of the total (incident + scattered) field to satisfy the Neumann boundary condition for a rigid immovable surface, and performing the product of matrices involving an inversion procedure. Computations for the matrices elements require a single numerical integration procedure for each partial-wave mode. Numerical results are performed with particular emphasis on the focusing properties of the incident beam and its angle of incidence with respect to the major axis a of the ellipse as well as the aspect ratio a/b where b is the minor axis (assuming a > b). The method is validated and verified against previous results obtained via the T-matrix for plane waves. The present analysis is the first to consider an acoustical beam on an elliptic cylinder of variable cross-section as opposed to plane waves of infinite extent. Other 2D non-spherical and Chebyshev surfaces are mentioned that may be examined throughout this analytical formalism assuming a small deformation parameter ε.
Guided acoustic and optical waves in silicon-on-insulator for Brillouin scattering and optomechanics
NASA Astrophysics Data System (ADS)
Sarabalis, Christopher J.; Hill, Jeff T.; Safavi-Naeini, Amir H.
2016-10-01
We numerically study silicon waveguides on silica showing that it is possible to simultaneously guide optical and acoustic waves in the technologically important silicon on insulator (SOI) material system. Thin waveguides, or fins, exhibit geometrically softened mechanical modes at gigahertz frequencies with phase velocities below the Rayleigh velocity in glass, eliminating acoustic radiation losses. We propose slot waveguides on glass with telecom optical frequencies and strong radiation pressure forces resulting in Brillouin gains on the order of 500 and 50 000 W-1m-1 for backward and forward Brillouin scattering, respectively.
Observation of stimulated electron acoustic wave scattering: the case for nonlinear kinetic effects
NASA Astrophysics Data System (ADS)
Montgomery, D. S.; Cobble, J. A.; Fernandez, J. C.; Rose, H. A.; Focia, R. J.; Russell, D. A.
2001-10-01
Electrostatic waves with a frequency and phase velocity between an ion acoustic wave (IAW) and an electron plasma wave (EPW) have been observed with Thomson scattering in inhomogeneous plasmas, and in the backscattered spectrum for homogeneous single hot spot laser plasmas. We show that these waves are consistent with an electron-acoustic wave (EAW) that is a BGK-like mode due to electron trapping. The nonlinear dispersion relation for BGK-like EPW and EAW is discussed, and previous inhomogeneous Trident and Nova data are re-examined in this context. The possible implications of these results for backscattered SRS on the NIF are discussed.
Acoustic field distribution of sawtooth wave with nonlinear SBE model
Liu, Xiaozhou Zhang, Lue; Wang, Xiangda; Gong, Xiufen
2015-10-28
For precise prediction of the acoustic field distribution of extracorporeal shock wave lithotripsy with an ellipsoid transducer, the nonlinear spheroidal beam equations (SBE) are employed to model acoustic wave propagation in medium. To solve the SBE model with frequency domain algorithm, boundary conditions are obtained for monochromatic and sawtooth waves based on the phase compensation. In numerical analysis, the influence of sinusoidal wave and sawtooth wave on axial pressure distributions are investigated.
Gong, Zheng; Chen, Tianrun; Ratilal, Purnima; Makris, Nicholas C
2013-11-01
An analytical model derived from normal mode theory for the accumulated effects of range-dependent multiple forward scattering is applied to estimate the temporal coherence of the acoustic field forward propagated through a continental-shelf waveguide containing random three-dimensional internal waves. The modeled coherence time scale of narrow band low-frequency acoustic field fluctuations after propagating through a continental-shelf waveguide is shown to decay with a power-law of range to the -1/2 beyond roughly 1 km, decrease with increasing internal wave energy, to be consistent with measured acoustic coherence time scales. The model should provide a useful prediction of the acoustic coherence time scale as a function of internal wave energy in continental-shelf environments. The acoustic coherence time scale is an important parameter in remote sensing applications because it determines (i) the time window within which standard coherent processing such as matched filtering may be conducted, and (ii) the number of statistically independent fluctuations in a given measurement period that determines the variance reduction possible by stationary averaging.
NASA Astrophysics Data System (ADS)
Lei, Bo; Yang, Yi-Xin; Ma, Yuan-Liang; Chen, Dong-Xu
2016-12-01
Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type. Project supported by the National Natural Science Foundation of China (Grant No. 61571366), the Natural Science Basic Research in Shaanxi Province of China (Grant No. 2015JQ5199), and the Fund of Science and Technology from the Underwater Test and Control Laboratory (Grant No. 9140c260201130c26096).
2013-01-30
key results in the literature (#1) and advancing the field (#2 and #3): aoV^oWHI 1. Key results of Ehrenberg (1972) involving the echo statistics of... Ehrenberg (1972) "A method for extracting the fish target strength distribution from acoustic echoes," in Proc. Conf. Eng. Ocean Environ., Vol. 1
2014-09-30
Mathematical modeling of space-time variations in acoustic transmission and scattering from schools of swim bladder fish (FY14 Annual Report...domain theory of acoustic scattering from, and propagation through, schools of swim bladder fish at and near the swim bladder resonance frequency...coupled differential equations. It incorporates a verified swim bladder scattering kernel for the individual fish, includes multiple scattering
Fan, Li; Ge, Huan; Zhang, Shu-yi; Gao, Hai-fei; Liu, Yong-hui; Zhang, Hui
2013-06-01
Nonlinear acoustic fields in transmission-line acoustic metamaterials based on a cylindrical pipe with periodically arranged side holes are studied, in which the dispersions and characteristic parameters of the nonlinear acoustic waves are obtained with the Bloch theory, and meanwhile the distributions of the fundamental wave (FW) and second harmonic wave (SHW) in the metamaterial are simulated. Three characteristic frequency bands are defined according to the relations between the frequencies of the FW, SHW, and the low-frequency forbidden band (LFB) in the metamaterial. Especially, when the FW is in the LFB while the SHW is outside the LFB, the SHW can transmit through the metamaterial although the FW is blocked, which exhibits the possibility to extract the information from the SHW instead of the FW. In addition, experiments are carried out to measure the distributions of the acoustic pressures for the FW and SHW along the metamaterial and the experimental results are in agreement with the theory.
Madelin, Guillaume; Grucker, Daniel; Franconi, Jean-Michel; Thiaudiere, Eric
2006-07-01
In this study, magnetic resonance imaging (MRI) is used to visualize acoustic streaming in liquids. A single-shot spin echo sequence (HASTE) with a saturation band perpendicular to the acoustic beam permits the acquisition of an instantaneous image of the flow due to the application of ultrasound. An average acoustic streaming velocity can be estimated from the MR images, from which the ultrasonic absorption coefficient and the bulk viscosity of different glycerol-water mixtures can be deduced. In the same way, this MRI method could be used to assess the acoustic field and time-average power of ultrasonic transducers in water (or other liquids with known physical properties), after calibration of a geometrical parameter that is dependent on the experimental setup.
Propagation and scattering of acoustic-vorticity waves in annular swirling flows
NASA Astrophysics Data System (ADS)
Golubev, Vladimir Viktorovich
1997-08-01
The dissertation presents a fundamental extension of unsteady aerodynamic theory developed to predict fluctuating forces on aircraft structural components. These excitations may result from a variety of upstream flow non-uniformities such as atmospheric turbulence, airframe tip vortices and wakes, engine inlet distortions and secondary flows. In the frame of reference of a downstream aircraft component, an upstream flow non- uniformity appears as a propagating vorticity wave (a gust). Classical treatment of gust interaction problems developed for uniform, potential upstream mean flows is based on the fact that it is possible to consider separately incident or scattered acoustic, entropic and vortical modes of unsteady flow motion. A purely vortical gust remains 'frozen' as it convects with the flow. The coupling between different unsteady components may occur only at the surface of a solid structure, or in the close vicinity of a lifting body. The classical approach, however, is not justified for an aircraft engine system where the internal turbomachinery flow is non-uniform and non-potential as it exhibits a strong swirling motion. In such a flow, acting centrifugal and Coriolis forces couple the various unsteady modes which thus can no longer be determined independently of each other. The new developed theory follows the decomposition of unsteady velocity field into vortical and potential components. In spite of the modal coupling, this decomposition elucidates the physical phenomena associated with unsteady swirling motion by indicating the degree of interaction between the various modes. It paves the way for generalizing the classical definition of a gust for vortical swirling flows. The concept of a generalized gust is developed based on the eigenmode pseudospectral analysis of the coupled equations of unsteady swirling motion. This analysis reveals two distinct regions of eigenvalues corresponding to pressure-dominated nearly-sonic and vorticity- dominated
Depolarized guided acoustic wave Brillouin scattering in hollow-core photonic crystal fibers.
Zhong, Wenjia Elser née; Stiller, Birgit; Elser, Dominique; Heim, Bettina; Marquardt, Christoph; Leuchs, Gerd
2015-10-19
By performing quantum-noise-limited optical heterodyne detection, we observe polarization noise in light after propagation through a hollow-core photonic crystal fiber (PCF). We compare the noise spectrum to the one of a standard fiber and find an increase of noise even though the light is mainly transmitted in air in a hollow-core PCF. Combined with our simulation of the acoustic vibrational modes in the hollow-core PCF, we are offering an explanation for the polarization noise with a variation of guided acoustic wave Brillouin scattering (GAWBS). Here, instead of modulating the strain in the fiber core as in a solid core fiber, the acoustic vibrations in hollow-core PCF influence the effective refractive index by modulating the geometry of the photonic crystal structure. This induces polarization noise in the light guided by the photonic crystal structure.
NASA Astrophysics Data System (ADS)
Ariza, A.; Landeira, J. M.; Escánez, A.; Wienerroither, R.; Aguilar de Soto, N.; Røstad, A.; Kaartvedt, S.; Hernández-León, S.
2016-05-01
Diel vertical migration (DVM) facilitates biogeochemical exchanges between shallow waters and the deep ocean. An effective way of monitoring the migrant biota is by acoustic observations although the interpretation of the scattering layers poses challenges. Here we combine results from acoustic observations at 18 and 38 kHz with limited net sampling in order to unveil the origin of acoustic phenomena around the Canary Islands, subtropical northeast Atlantic Ocean. Trawling data revealed a high diversity of fishes, decapods and cephalopods (152 species), although few dominant species likely were responsible for most of the sound scattering in the region. We identified four different acoustic scattering layers in the mesopelagic realm: (1) at 400-500 m depth, a swimbladder resonance phenomenon at 18 kHz produced by gas-bearing migrant fish such as Vinciguerria spp. and Lobianchia dofleini, (2) at 500-600 m depth, a dense 38 kHz layer resulting primarily from the gas-bearing and non-migrant fish Cyclothone braueri, and to a lesser extent, from fluid-like migrant fauna also inhabiting these depths, (3) between 600 and 800 m depth, a weak signal at both 18 and 38 kHz ascribed either to migrant fish or decapods, and (4) below 800 m depth, a weak non-migrant layer at 18 kHz which was not sampled. All the dielly migrating layers reached the epipelagic zone at night, with the shorter-range migrations moving at 4.6 ± 2.6 cm s - 1 and the long-range ones at 11.5 ± 3.8 cm s - 1. This work reduces uncertainties interpreting standard frequencies in mesopelagic studies, while enhances the potential of acoustics for future research and monitoring of the deep pelagic fauna in the Canary Islands.
Methods for the treatment of acoustic and absorptive/dispersive wave field measurements
NASA Astrophysics Data System (ADS)
Innanen, Kristopher Albert Holm
Many recent methods of seismic wave field processing and inversion concern themselves with the fine detail of the amplitude and phase characteristics of measured events. Processes of absorption and dispersion have a strong impact on both; the impact is particularly deleterious to the effective resolution of images created from the data. There is a need to understand the dissipation of seismic wave energy as it affects such methods. I identify: algorithms based on the inverse scattering series, algorithms based on multiresolution analysis, and algorithms based on the estimation of the order of the singularities of seismic data, as requiring this kind of study. As it turns out, these approaches may be cast such that they deal directly with issues of attenuation, to the point where they can be seen as tools for viscoacoustic forward modelling, Q estimation; viscoacoustic inversion, and/or Q compensation. In this thesis I demonstrate these ideas in turn. The forward scattering series is formulated such that a viscoacoustic wave field is represented as an expansion about an acoustic reference; analysis of the convergence properties and scattering diagrams are carried out, and it is shown that (i) the attenuated wave field may be generated by the nonlinear interplay of acoustic reference fields, and (ii) the cumulative effect of certain scattering types is responsible for macroscopic wave field properties: also, the basic form of the absorptive/dispersive inversion problem is predicted. Following this, the impact of Q on measurements of the local regularity of a seismic trace, via Lipschitz exponents, is discussed, with the aim of using these exponents as a means to estimate local Q values. The problem of inverse scattering based imaging and inversion is treated next: I present a simple, computable form for the simultaneous imaging and wavespeed inversion of 1D acoustic wave field data. This method is applied to 1D, normal incidence synthetic data: its sensitivity with
NASA Astrophysics Data System (ADS)
Soenarko, B.; Setiadikarunia, D.
2016-11-01
A half space problem in acoustics is described by introducing an infinite plane boundary that reflects the wave coming into the plane. A numerical solution using Boundary Element Method (BEM) has been known which is formulated using a modified Green's function in the Helmholtz Integral Formulation, which eliminates the discretization over the infinite plane. Hence, the discretization are confined to the body or obstacle in question only. This feature constitutes the main advantage of the BEM formulation for half space problems. However, no general analytical solution is available to verify the BEM results for half space problems. This paper is aimed to propose an analytical solution for the BEM to compare with, hence to verify the BEM calculation. This analytical approach is currently developed for a half space problem involving radiation and scattering of acoustic waves from a rigid sphere. The image of sphere as well as the image of the field point are defined with respect to the infinite plane. Then, an ad hoc solution is assumed involving a constant and the distance from the center of the sphere to the field point and the distance from the center of the image of the sphere to the field point. The constant is determined by imposing the boundary conditions. Test cases were run with several configuration involving the location of field points and the sphere. Comparison of the analytical solution with BEM calculations shows a good agreement between the two results..
On noninvasive assessment of acoustic fields acting on the fetus
NASA Astrophysics Data System (ADS)
Antonets, V. A.; Kazakov, V. V.
2014-05-01
The aim of this study is to verify a noninvasive technique for assessing the characteristics of acoustic fields in the audible range arising in the uterus under the action of maternal voice, external sounds, and vibrations. This problem is very important in view of actively developed methods for delivery of external sounds to the uterus: music, maternal voice recordings, sounds from outside the mother's body, etc., that supposedly support development of the fetus at the prenatal stage psychologically and cognitively. However, the parameters of acoustic signals have been neither measured nor normalized, which may be dangerous for the fetus and hinder actual assessment of their impact on fetal development. The authors show that at frequencies below 1 kHz, acoustic pressure in the uterus may be measured noninvasively using a hydrophone placed in a soft capsule filled with liquid. It was found that the acoustic field at frequencies up to 1 kHz arising in the uterus under the action of an external sound field has amplitude-frequency parameters close to those of the external field; i.e., the external field penetrates the uterus with hardly any difficulty.
NASA Astrophysics Data System (ADS)
Buscombe, D.; Grams, P. E.; Kaplinski, M. A.
2013-12-01
Bed sediment classification using backscatter intensities from multibeam echosounder (MBES) systems in rivers is attractive due to its high coverage and resolution, limited costs compared to conventional sampling, and the potential combination of bathymetric and bottom sediment mapping in one instrument. Sediment classification by means of hydro-acoustic remote sensing is becoming an established discipline in oceanography. A number of techniques have been proposed, none of which has become the preferred method. In rivers, however, the field is relatively new and faces challenges not typically encountered in deep ocean settings. For example, river beds tend to have larger mean and maximum slopes than typical seabeds. Shallow water depths not only make MBES deployments more difficult, but also make the size of the beam footprint on the bed small which can lead to relatively noisy backscatter data. In particular, sediments can more heterogeneous in terms of: 1) range of particle sizes (both in a given area and over an entire mapped reach); 2) range of grain size over proximal bedform fields; 3) superimposed bedforms; and 4) abrupt sedimentological transitions over small scales. This sediment heterogeneity means grain-size usually changes along swath, which has a number of implications for existing sediment classification methods which use the distribution of backscatter intensities over all acoustic beams. We discuss these implications with reference to MBES data collected from the Colorado River in Grand Canyon, Arizona. We analyze the scale-dependence of probability density functions (PDF) of measured elevations in different sedimentological settings, which reveals the appropriate spatial scale at which to apply acoustic scattering theories. We also discuss the joint PDF of elevation and backscatter over different scales as a means by which to create an adaptive gridding scheme in which each grid is scaled appropriately, in situations with rapidly changing
One dimensional acoustic direct nonlinear inversion using the Volterra inverse scattering series
NASA Astrophysics Data System (ADS)
Yao, Jie; Lesage, Anne-Cécile; Bodmann, Bernhard G.; Hussain, Fazle; Kouri, Donald J.
2014-06-01
Direct inversion of acoustic scattering problems is nonlinear. One way to treat the inverse scattering problem is based on the reversion of the Born-Neumann series solution of the Lippmann-Schwinger equation. An important issue for this approach is the radius of convergence of the Born-Neumann series for the forward problem. However, this issue can be tackled by employing a renormalization technique to transform the Lippmann-Schwinger equation from a Fredholm to a Volterra integral form. The Born series of a Volterra integral equation converges absolutely and uniformly in the entire complex plane. We present a further study of this new mathematical framework. A Volterra inverse scattering series (VISS) using both reflection and transmission data is derived and tested for several acoustic velocity models. For large velocity contrast, series summation techniques (e.g., Cesàro summation, Euler transform, etc) are employed to improve the rate of convergence of VISS. It is shown that the VISS method with summation techniques can provide a relatively good estimation of the velocity profile. The method is fully data-driven in the respect that no prior information of the model is required. Besides, no internal multiple removal is needed. This one dimensional VISS approach is useful for inverse scattering and serves as an important step for studying more complicated and realistic inversions.
Weak scattering of scalar and electromagnetic random fields
NASA Astrophysics Data System (ADS)
Tong, Zhisong
This dissertation encompasses several studies relating to the theory of weak potential scattering of scalar and electromagnetic random, wide-sense statistically stationary fields from various types of deterministic or random linear media. The proposed theory is largely based on the first Born approximation for potential scattering and on the angular spectrum representation of fields. The main focus of the scalar counterpart of the theory is made on calculation of the second-order statistics of scattered light fields in cases when the scattering medium consists of several types of discrete particles with deterministic or random potentials. It is shown that the knowledge of the correlation properties for the particles of the same and different types, described with the newly introduced pair-scattering matrix, is crucial for determining the spectral and coherence states of the scattered radiation. The approach based on the pair-scattering matrix is then used for solving an inverse problem of determining the location of an "alien" particle within the scattering collection of "normal" particles, from several measurements of the spectral density of scattered light. Weak scalar scattering of light from a particulate medium in the presence of optical turbulence existing between the scattering centers is then approached using the combination of the Born's theory for treating the light interaction with discrete particles and the Rytov's theory for light propagation in extended turbulent medium. It is demonstrated how the statistics of scattered radiation depend on scattering potentials of particles and the power spectra of the refractive index fluctuations of turbulence. This theory is of utmost importance for applications involving atmospheric and oceanic light transmission. The second part of the dissertation includes the theoretical procedure developed for predicting the second-order statistics of the electromagnetic random fields, such as polarization and linear momentum
Characterizing riverbed sediment using high-frequency acoustics 1: spectral properties of scattering
Buscombe, Daniel D.; Grams, Paul E.; Kaplinski, Matt A.
2014-01-01
Bed-sediment classification using high-frequency hydro-acoustic instruments is challenging when sediments are spatially heterogeneous, which is often the case in rivers. The use of acoustic backscatter to classify sediments is an attractive alternative to analysis of topography because it is potentially sensitive to grain-scale roughness. Here, a new method is presented which uses high-frequency acoustic backscatter from multibeam sonar to classify heterogeneous riverbed sediments by type (sand, gravel,rock) continuously in space and at small spatial resolution. In this, the first of a pair of papers that examine the scattering signatures from a heterogeneous riverbed, methods are presented to construct spatially explicit maps of spectral properties from geo-referenced point clouds of geometrically and radiometrically corrected echoes. Backscatter power spectra are computed to produce scale and amplitude metrics that collectively characterize the length scales of stochastic measures of riverbed scattering, termed ‘stochastic geometries’. Backscatter aggregated over small spatial scales have spectra that obey a power-law. This apparently self-affine behavior could instead arise from morphological- and grain-scale roughnesses over multiple overlapping scales, or riverbed scattering being transitional between Rayleigh and geometric regimes. Relationships exist between stochastic geometries of backscatter and areas of rough and smooth sediments. However, no one parameter can uniquely characterize a particular substrate, nor definitively separate the relative contributions of roughness and acoustic impedance (hardness). Combinations of spectral quantities do, however, have the potential to delineate riverbed sediment patchiness, in a data-driven approach comparing backscatter with bed-sediment observations (which is the subject of part two of this manuscript).
Contactless Acoustic Manipulation and Sorting of Particles by Dynamic Acoustic Fields.
Andrade, Marco Aurelio; Skotis, George D; Ritchie, Scott; Cumming, David R S; Riehle, Mathis O; Bernassau, Anne L
2016-09-12
This paper presents a contactless, acoustic technique to manipulate and sort particles of varying size in both liquid and air media. An acoustic standing wave is generated by the superposition of counter-propagating waves emitted by two opposing emitters. The acoustic radiation force traps the smallest particles at the pressure nodes of the acoustic standing wave. The position of the particles can be manipulated by dynamically changing the phase difference between the two emitters. By applying a dynamic acoustic field (DAF), it is demonstrated that particles can be manipulated spatially and sorted according to size. The discrimination (sorting dynamic range) capability is initially demonstrated in liquid media by separating three different sets of polystyrene particles, ranging in size from 5 to 45 μm in diameter. The separation between particles was performed up to a ratio of 5/6 in diameter (20 % diameter difference). Finally, the scalability of the DAF method is demonstrated by sorting expanded polystyrene particles of 2 and 5 mm diameter in air.
Observation of induced longitudinal and shear acoustic phonons by Brillouin scattering.
Yoshida, Taisuke; Matsukawa, Mami; Yanagitani, Takahiko
2011-06-01
To improve the accuracy of velocity measurements in the Brillouin scattering technique using weak thermal phonons, we have used induced coherent phonons, which intensify the scattering. To induce phonons in the gigahertz range, we used a c-axis tilted ZnO film transducer that was developed in our laboratory. This allowed us to induce longitudinal and shear acoustic phonons effectively at hypersonic frequencies. As a result, we obtained scattered light in the silica glass sample that was much more intense than that obtained from the thermal phonons. Because the Brillouin scattering from induced phonons was measured, the shift frequency was that of the electric signal applied to the ZnO transducer. Strong peaks lead to a reduction of the measurement time. This is useful for two-dimensional mapping of thin film elasticity using Brillouin scattering. Additionally, Brillouin scattering enables the simultaneous measurement of longitudinal and shear phonon velocities in the sample plane. This opens up a potential new technique for non-destructive elasticity measurements of various materials.
1984-08-20
6]. 2.1 The New Wave -Surface Model: Surface Elevation We postulate the following potential mechanism for the small-scale scattering component of a...or hydraulic jumps, which ride upon the rough gravity-capillary wave surface, we develop the following ele- mentary second-moment model. * .~.’.. A...the covariance function, Ks here. ., 101 Accordingly, let us consider the following forms and definitions (for two-dimensional wave numbers k = (k ,ky
Modeling Steady Acoustic Fields Bounded in Cavities with Geometrical Imperfections
NASA Astrophysics Data System (ADS)
Albo, P. A. Giuliano; Gavioso, R. M.; Benedetto, G.
2010-07-01
A mathematical method is derived within the framework of classical Lagrangian field theory, which is suitable for the determination of the eigenstates of acoustic resonators of nearly spherical shape. The method is based on the expansion of the Helmholtz differential operator and the boundary condition in a power series of a small geometrical perturbation parameter {ɛ} . The method extends to orders higher than {ɛ^2} the calculation of the perturbed acoustic eigenvalues, which was previously limited by the use of variational formalism and the methods of Morse and Ingard. A specific example is worked out for radial modes of a prolate spheroid, with the frequency perturbation calculated to order {ɛ^3} . A possible strategy to tackle the problem of calculating the acoustic eigenvalues for cavities presenting non-smooth geometrical imperfections is also described.
Acoustic spectroscopy: A powerful analytical method for the pharmaceutical field?
Bonacucina, Giulia; Perinelli, Diego R; Cespi, Marco; Casettari, Luca; Cossi, Riccardo; Blasi, Paolo; Palmieri, Giovanni F
2016-04-30
Acoustics is one of the emerging technologies developed to minimize processing, maximize quality and ensure the safety of pharmaceutical, food and chemical products. The operating principle of acoustic spectroscopy is the measurement of the ultrasound pulse intensity and phase after its propagation through a sample. The main goal of this technique is to characterise concentrated colloidal dispersions without dilution, in such a way as to be able to analyse non-transparent and even highly structured systems. This review presents the state of the art of ultrasound-based techniques in pharmaceutical pre-formulation and formulation steps, showing their potential, applicability and limits. It reports in a simplified version the theory behind acoustic spectroscopy, describes the most common equipment on the market, and finally overviews different studies performed on systems and materials used in the pharmaceutical or related fields.
Sound field simulation and acoustic animation in urban squares
NASA Astrophysics Data System (ADS)
Kang, Jian; Meng, Yan
2005-04-01
Urban squares are important components of cities, and the acoustic environment is important for their usability. While models and formulae for predicting the sound field in urban squares are important for their soundscape design and improvement, acoustic animation tools would be of great importance for designers as well as for public participation process, given that below a certain sound level, the soundscape evaluation depends mainly on the type of sounds rather than the loudness. This paper first briefly introduces acoustic simulation models developed for urban squares, as well as empirical formulae derived from a series of simulation. It then presents an acoustic animation tool currently being developed. In urban squares there are multiple dynamic sound sources, so that the computation time becomes a main concern. Nevertheless, the requirements for acoustic animation in urban squares are relatively low compared to auditoria. As a result, it is important to simplify the simulation process and algorithms. Based on a series of subjective tests in a virtual reality environment with various simulation parameters, a fast simulation method with acceptable accuracy has been explored. [Work supported by the European Commission.
Acoustic phonon propagation in ultra-thin Si membranes under biaxial stress field
NASA Astrophysics Data System (ADS)
Graczykowski, B.; Gomis-Bresco, J.; Alzina, F.; Reparaz, J. S.; Shchepetov, A.; Prunnila, M.; Ahopelto, J.; Sotomayor Torres, C. M.
2014-07-01
We report on stress induced changes in the dispersion relations of acoustic phonons propagating in 27 nm thick single crystalline Si membranes. The static tensile stress (up to 0.3 GPa) acting on the Si membranes was achieved using an additional strain compensating silicon nitride frame. Dispersion relations of thermally activated hypersonic phonons were measured by means of Brillouin light scattering spectroscopy. The theory of Lamb wave propagation is developed for anisotropic materials subjected to an external static stress field. The dispersion relations were calculated using the elastic continuum approximation and taking into account the acousto-elastic effect. We find an excellent agreement between the theoretical and the experimental dispersion relations.
Stable Determination of a Scattered Wave from its Far-Field Pattern: The High Frequency Asymptotics
NASA Astrophysics Data System (ADS)
Rondi, Luca; Sini, Mourad
2015-10-01
We deal with the stability issue for the determination of outgoing time-harmonic acoustic waves from their far-field patterns. We are especially interested in keeping as explicit as possible the dependence of our stability estimates on the wavenumber of the corresponding Helmholtz equation and in understanding the high wavenumber, that is frequency, asymptotics. Applications include stability results for the determination from far-field data of solutions of direct scattering problems with sound-soft obstacles and an instability analysis for the corresponding inverse obstacle problem. The key tool consists of establishing precise estimates on the behavior of Hankel functions with large argument or order.
Doc, Jean-Baptiste; Conoir, Jean-Marc; Marchiano, Régis; Fuster, Daniel
2016-04-01
The weakly nonlinear propagation of acoustic waves in monodisperse bubbly liquids is investigated numerically. A hydrodynamic model based on the averaged two-phase fluid equations is coupled with the Rayleigh-Plesset equation to model the dynamics of bubbles at the local scale. The present model is validated in the linear regime by comparing with the Foldy approximation. The analysis of the pressure signals in the linear regime highlights two resonance frequencies: the Minnaert frequency and a multiple scattering resonance that strongly depends on the bubble concentration. For weakly nonlinear regimes, the generation of higher harmonics is observed only for the Minnaert frequency. Linear combinations between the Minnaert harmonics and the multiple scattering resonance are also observed. However, the most significant effect observed is the appearance of softening-hardening effects that share some similarities with those observed for sandstones or cracked materials. These effects are related to the multiple scattering resonance. Downward or upward resonance frequency shifts can be observed depending on the characteristic of the incident wave when increasing the excitation amplitude. It is shown that the frequency shift can be explained assuming that the acoustic wave velocity depends on a law different from those usually encountered for sandstones or cracked materials.
NASA Astrophysics Data System (ADS)
Ouyang, Wei; Mao, Weijian; Li, Wuqun; Zhang, Pan
2016-11-01
An approach for approximate direct quadratic nonlinear inversion in two-parameter (density and bulk modulus) heterogeneous acoustic media is being presented and discussed in this paper. The approach consists of two parts: the first is a linear generalized Radon transform (GRT) migration procedure based on the weighted true-amplitude summation of pre-stack seismic scattered data that is adapted to a virtually arbitrary observing system, and the second is a non-iterative quadratic inversion operation, produced from the explicit expression of amplitude radiation pattern that is acting on the migrated data. This ensures the asymptotic inversion can continue to simultaneously locate the discontinuities and reconstruct the size of the discontinuities in the perturbation parameters describing the acoustic media. We identify that the amplitude radiation pattern is the binary quadratic combination of the parameters in the process of formulating nonlinear inverse scattering problems based on second-order Born approximation. The coefficients of the quadratic terms are computed by appropriately handling the double scattering effects. These added quadratic terms provide a better amplitude correction for the parameters inversion. Through numerical tests, we show that for strong perturbations, the errors of the linear inversion are significant and unacceptable. In contrast, the quadratic nonlinear inversion can give fairly accurate inversion results and keep almost the same computational complexity as conventional GRT liner inversion.
NASA Astrophysics Data System (ADS)
Ouyang, Wei; Mao, Weijian; Li, Wuqun; Zhang, Pan
2017-02-01
An approach for approximate direct quadratic non-linear inversion in two-parameter (density and bulk modulus) heterogeneous acoustic media is being presented and discussed in this paper. The approach consists of two parts: the first is a linear generalized Radon transform (GRT) migration procedure based on the weighted true-amplitude summation of pre-stack seismic scattered data that is adapted to a virtually arbitrary observing system, and the second is a non-iterative quadratic inversion operation, produced from the explicit expression of amplitude radiation pattern that is acting on the migrated data. This ensures the asymptotic inversion can continue to simultaneously locate the discontinuities and reconstruct the size of the discontinuities in the perturbation parameters describing the acoustic media. We identify that the amplitude radiation pattern is the binary quadratic combination of the parameters in the process of formulating non-linear inverse scattering problems based on second-order Born approximation. The coefficients of the quadratic terms are computed by appropriately handling the double scattering effects. These added quadratic terms provide a better amplitude correction for the parameters inversion. Through numerical tests, we show that for strong perturbations, the errors of the linear inversion are significant and unacceptable. In contrast, the quadratic non-linear inversion can give fairly accurate inversion results and keep almost the same computational complexity as conventional GRT liner inversion.
Weber, Thomas C; Lutcavage, Molly E; Schroth-Miller, Madeline L
2013-06-01
Schools of Atlantic bluefin tuna (Thunnus thynnus) can exhibit highly organized spatial structure within the school. This structure was quantified for dome shaped schools using both aerial imagery collected from a commercial spotter plane and 400 kHz multibeam echo sounder data collected on a fishing vessel in 2009 in Cape Cod Bay, MA. Observations from one school, containing an estimated 263 fish within an approximately ellipsoidal volume of 1900 m(3), were used to seed an acoustic model that estimated the school target strength at frequencies between 10 and 2000 Hz. The fish's swimbladder resonance was estimated to occur at approximately 50 Hz. The acoustic model examined single and multiple scattering solutions and also a completely incoherent summation of scattering responses from the fish. Three levels of structure within the school were examined, starting with fish locations that were constrained by the school boundaries but placed according to a Poisson process, then incorporating a constraint on the distance to the nearest neighbor, and finally adding a constraint on the bearing to the nearest neighbor. Results suggest that both multiple scattering and spatial organization within the school should be considered when estimating the target strength of schools similar to the ones considered here.
NASA Astrophysics Data System (ADS)
Barr, H. C.; Boyd, T. J. M.; Lukyanov, A. V.
2000-03-01
In this report a complex Raman scattering event against a background of nonthermal ion coustic waves in an inhomogenous plasma is considered. The complex Raman process is a five-wave interaction in which three-wave stimulated Raman scattering (SRS) is accompanied by the decay of the Raman Langmuir wave into either a second Langmuir wave (LD) or a second scattered light wave (ED) and an ion acoustic wave. An extension of Stokes’ theory is used to obtain expressions for the gain in the Raman Langmuir and scattered waves. It is shown that only very modest levels of ion waves are needed to produce duce a significant effect on the net Raman convective gain which proves to be sensitive to the source levels of the amplifying waves. For LD the gain from the Raman Langmuir wave source is suppressed while that from the secondary Langmuir wave is enhanced such that the net gain is increased or decreased depending on which of the two sources is greater. When the source levels of both Langmuir waves are at thermal levels, opposing effects mean no net change in the gain factor irrespective of the ion acoustic wave amplitude. For ED the gain is invariably suppressed for any source distributions. Two possible regimes of an enhanced effect have been identified: exact sidescattering for ED and the supersonic point vicinity for LD(ED). The theory thus provides a possible explanation for a variety of the observed effects in the interplay between SRS and stimulated Brillouin scattering, both of concern in laser fusion schemes.
NASA Technical Reports Server (NTRS)
Hanson, Donald B.
1999-01-01
A reduced order modeling scheme has been developed for the unsteady acoustic and vortical coupling between blade rows of a turbomachine. The essential behavior of the system is governed by modal scattering coefficients (i.e., reflection and transmission coefficients) of the rotor, stator, inlet and nozzle, which are calculated as if they were connected to non-reflecting ducts. The objective of this report is to identify fundamental behavior of these scattering coefficients for a better understanding of the role of blade row reflection and transmission in noise generation. A 2D flat plate unsteady cascade model is used for the analysis with the expectation that the general behavior presented herein will carry over to models that include more realistic flow and geometry. It is shown that stators scatter input waves into many modes at the same frequency whereas rotors scatter on frequency, or harmonic order. Important cases are shown here the rotor reflection coefficient is greater than unity; a mode at blade passing frequency (BPF) traveling from the stator with unit sound power is reflected by the rotor with more than unit power at 2xBPF and 3xBPE Analysis is presented to explain this unexpected phenomenon. Scattering curves are presented in a format chosen for design use and for physical interpretation. To aid in interpretation of the curves, formulas are derived for special condition where waveforms are parallel to perpendicular to the rotor.
Long-range acoustic scattering from a shallow-water mud-volcano cluster.
Holland, Charles W; Preston, John R; Abraham, Douglas A
2007-10-01
Analysis of reverberation measurements in the Straits of Sicily shows high intensity, discrete, scattered returns 10-20 dB above background reverberation. These returns are due to scattering from mud volcanoes. The reverberation from the mud volcanoes at ranges of 15-22 km is reasonably consistent over these spatial scales (i.e., kilometers) and temporal scales of several hours; measurements separated by 4 years are also similar. Statistical characterization indicates that the reverberation associated with a mud-volcano cluster is strongly non-Rayleigh and that the reverberation can be characterized by a single (shape) parameter, roughly independent of frequency. The non-Rayleigh statistics, with a concomitant increase in the probability of false alarm, indicate that mud volcanoes are a likely source of clutter. Mean target strengths were estimated at 1-11 dB over 160-1400 Hz and are consistent with target strengths measured during a different year at short (direct-path) ranges. Accumulated evidence points to small (order 10 m diameter and several meters high) carbonate chimneys on the mud-volcano edifice as the scattering mechanism as opposed to the edifice itself or scattering from gas bubbles in the water column. Thus, the results represent acoustic scattering from mud volcanoes in a quiescent state.
Pinfield, Valerie J
2007-07-01
Measurements of ultrasound speed and attenuation can be related to the properties of dispersed systems by applying a scattering model. Rayleigh's method for scattering of sound by a spherical object, and its subsequent developments to include viscous, thermal, and other effects (known as the ECAH model) has been widely adopted. The ECAH method has difficulties, including numerical ill-conditioning, calculation of Bessel functions at large arguments, and inclusion of thermal effects in all cases. The present work develops techniques for improving the ECAH calculations to allow its use in instrumentation. It is shown that thermal terms can be neglected in some boundary equations up to approximately 100 GHz in water, and several simplified solutions result. An analytical solution for the zero-order coefficient is presented, with separate nonthermal and thermal parts, allowing estimation of the thermal contribution. Higher orders have been simplified by estimating the small shear contribution as the inertial limit is approached. The condition of the matrix solutions have been greatly improved by these techniques and by including appropriate scaling factors. A method is presented for calculating the required Bessel functions when the argument is large (high frequency or large particle size). The required number of partial wave orders is also considered.
Brillouin-scattering measurements of the acoustic absorption coefficient in liquid CS2
NASA Technical Reports Server (NTRS)
Coakley, R. W.; Detenbeck, R. W.
1975-01-01
High-resolution Brillouin spectra were recorded for light scattered at small angles from liquid CS2. The use of a single-mode He-Ne laser, locked in frequency to a Fabry-Perot interferometer, permitted measurements of line widths of the order of 10 MHz for frequencies in the range 300-1000 MHz. These measurements extend previous Brillouin line-width measurements at higher frequencies into the region where relaxation effects are dominant and connect the optical measurements with lower-frequency acoustical data.
Statistical Properties of the Acoustic Field in Inhomogeneous Oceanic Environments
2003-09-30
homogeneous , the expression for potential function can be written explicitly as a ratio of polynomials of the third and fifth order. The scattering...of the received field (“time reversal”). This procedure was accomplished both in the ideal situation of a homogeneous Pekeris waveguide, and with...rough surfaces in homogeneous media. Scattering in inhomogeneous media needs to be studied separately. A novel perturbation theory has been
Collins, David J; Ma, Zhichao; Ai, Ye
2016-05-17
Concentration and separation of particles and biological specimens are fundamental functions of micro/nanofluidic systems. Acoustic streaming is an effective and biocompatible way to create rapid microscale fluid motion and induce particle capture, though the >100 MHz frequencies required to directly generate acoustic body forces on the microscale have traditionally been difficult to generate and localize in a way that is amenable to efficient generation of streaming. Moreover, acoustic, hydrodynamic, and electrical forces as typically applied have difficulty manipulating specimens in the submicrometer regime. In this work, we introduce highly focused traveling surface acoustic waves (SAW) at high frequencies between 193 and 636 MHz for efficient and highly localized production of acoustic streaming vortices on microfluidic length scales. Concentration occurs via a novel mechanism, whereby the combined acoustic radiation and streaming field results in size-selective aggregation in fluid streamlines in the vicinity of a high-amplitude acoustic beam, as opposed to previous acoustic radiation induced particle concentration where objects typically migrate toward minimum pressure locations. Though the acoustic streaming is induced by a traveling wave, we are able to manipulate particles an order of magnitude smaller than possible using the traveling wave force alone. We experimentally and theoretically examine the range of particle sizes that can be captured in fluid streamlines using this technique, with rapid particle concentration demonstrated down to 300 nm diameters. We also demonstrate that locations of trapping and concentration are size-dependent, which is attributed to the combined effects of the acoustic streaming and acoustic forces.
Excised acoustic black holes: The scattering problem in the time domain
Cherubini, C.; Federici, F.; Tosi, M.P.; Succi, S.
2005-10-15
The scattering process of a dynamic perturbation impinging on a draining-tub model of an acoustic black hole is numerically solved in the time domain. Analogies with real black holes of general relativity are explored by using recently developed mathematical tools involving finite elements methods, excision techniques, and constrained evolution schemes for strongly hyperbolic systems. In particular it is shown that superradiant scattering of a quasimonochromatic wave packet can produce strong amplification of the signal, offering the possibility of a significant extraction of rotational energy at suitable values of the angular frequency of the vortex and of the central frequency of the wave packet. The results show that theoretical tools recently developed for gravitational waves can be brought to fruition in the study of other problems in which strong anisotropies are present.
2010-05-27
microstructure measurements were collected by Jim Mourn with a profiling microstructure instrument, Chameleon . The contribution to scattering from...measurements were performed by Jim Mourn using the turbulence profiler Chameleon (Mourn et al., 1995). The broadband acoustic system was fully operational...community animals with implications for spinner dolphin foraging," The Journal of the Acoustical Society of America 123: 2884-2894. Au, W.W.L
Plate Scattering Visualization: Images, Near Fields, Currents, and Far Field Patterns
NASA Technical Reports Server (NTRS)
Shaeffer, John; Hom, Kam
2004-01-01
This paper presents a case study of a simple yet robust target for demonstration of the EM visualization process. A five lambda square plate exhibits many scattering mechanisms depending on excitation angle and polarization: specular scattering, leading and trailing edge diffraction, traveling wave, and edge wave scattering. Bistatic k space radiation images, currents maps, and near scattered / total fields are examined for each of these scattering mechanisms.
Enhancement of gas phase heat transfer by acoustic field application.
Komarov, Sergey; Hirasawa, Masahiro
2003-06-01
This study discusses a possibility for enhancement of heat transfer between solids and ambient gas by application of powerful acoustic fields. Experiments are carried out by using preheated Pt wires (length 0.1-0.15 m, diameter 50 and 100 micro m) positioned at the velocity antinode of a standing wave (frequency range 216-1031 Hz) or in the path of a travelling wave (frequency range 6.9-17.2 kHz). A number of experiments were conducted under conditions of gas flowing across the wire surface. Effects of sound frequency, sound strength, gas flow velocity and wire preheating temperature on the Nusselt number are examined with and without sound application. The gas phase heat transfer rate is enhanced with acoustic field strength. Higher temperatures result in a vigorous radiation from the wire surface and attenuate the effect of sound. The larger the gas flow velocity, the smaller is the effect of sound wave on heat transfer enhancement.
Scanning Michelson interferometer for imaging surface acoustic wave fields.
Knuuttila, J V; Tikka, P T; Salomaa, M M
2000-05-01
A scanning homodyne Michelson interferometer is constructed for two-dimensional imaging of high-frequency surface acoustic wave (SAW) fields in SAW devices. The interferometer possesses a sensitivity of ~10(-5)nm/ radicalHz , and it is capable of directly measuring SAW's with frequencies ranging from 0.5 MHz up to 1 GHz. The fast scheme used for locating the optimum operation point of the interferometer facilitates high measuring speeds, up to 50,000 points/h. The measured field image has a lateral resolution of better than 1 mu;m . The fully optical noninvasive scanning system can be applied to SAW device development and research, providing information on acoustic wave distribution that cannot be obtained by merely electrical measurements.
Asymptotic Analysis of Ocean Bottom Reflected Acoustic Fields.
1984-05-01
dependence(e-i’t), the reflected spatial part of the acoustic pressure field P in a homogeneous medium due to a point source placed in that medium...reasonable to assume that the water colunm is homogeneous , especially for experiments which involve small source and receiver heights. In many abyssal plain...configuration, a homogeneous layer between two homo- eneous halfspaces. Using a modified uniform asymptotic method, Stickler and Ahluwalia[12] obtained
Electric field autocorrelation functions for beginning multiple rayleigh scattering.
Lock, J A
2001-08-20
The polarization-resolved electric field autocorrelation function for p-order scattering was derived from the order-of-scattering solution of the exact equations for electromagnetic multiple Rayleigh scattering and was calculated for 2 scattering-angle dependence of the p-order autocorrelation function approximately decoupled from the delay-time dependence for p ? 3. The polarization-channel and the scattering-angle dependence were analytically calculated, and the delay-time dependence was analytically approximated. The resulting analytical model for the polarization-resolved autocorrelation function for beginning multiple Rayleigh scattering was then tested against experimental autocorrelation data. The data were found to be well fitted by the model.
Electric Field Autocorrelation Functions for Beginning Multiple Rayleigh Scattering
NASA Astrophysics Data System (ADS)
Lock, James A.
2001-08-01
The polarization-resolved electric field autocorrelation function for p -order scattering was derived from the order-of-scattering solution of the exact equations for electromagnetic multiple Rayleigh scattering and was calculated for 2 p 6 for particles undergoing diffusive motion in an idealized sample cell. It was found that the polarization-channel and the scattering-angle dependence of the p -order autocorrelation function approximately decoupled from the delay-time dependence for p ~ 3 . The polarization-channel and the scattering-angle dependence were analytically calculated, and the delay-time dependence was analytically approximated. The resulting analytical model for the polarization-resolved autocorrelation function for beginning multiple Rayleigh scattering was then tested against experimental autocorrelation data. The data were found to be well fitted by the model.
a Numerical Method for Scattering from Acoustically Soft and Hard Thin Bodies in Two Dimensions
NASA Astrophysics Data System (ADS)
YANG, S. A.
2002-03-01
This paper presents a numerical method for predicting the acoustic scattering from two-dimensional (2-D) thin bodies. Both the Dirichlet and Neumann problems are considered. Applying the thin-body formulation leads to the boundary integral equations involving weakly singular and hypersingular kernels. Completely regularizing these kinds of singular kernels is thus the main concern of this paper. The basic subtraction-addition technique is adopted. The purpose of incorporating a parametric representation of the boundary surface with the integral equations is two-fold. The first is to facilitate the numerical implementation for arbitrarily shaped bodies. The second one is to facilitate the expansion of the unknown function into a series of Chebyshev polynomials. Some of the resultant integrals are evaluated by using the Gauss-Chebyshev integration rules after moving the series coefficients to the outside of the integral sign; others are evaluated exactly, including the modified hypersingular integral. The numerical implementation basically includes only two parts, one for evaluating the ordinary integrals and the other for solving a system of algebraic equations. Thus, the current method is highly efficient and accurate because these two solution procedures are easy and straightforward. Numerical calculations consist of the acoustic scattering by flat and curved plates. Comparisons with analytical solutions for flat plates are made.
Analysis of High-Frequency Broadband Acoustic Scattering from Non-Linear Internal Waves During SW06
2009-09-30
profiling microstructure instrument, Chameleon . The contribution to scattering from biological organisms was quantified using a multiple-opening and...performed by Jim Moum using the turbulence profiler Chameleon (Moum et al., 1995). The broadband acoustic system was fully operational throughout...boundary community animals with implications for spinner dolphin foraging,” The Journal of the Acoustical Society of America 123: 2884-2894. Au, W.W.L
Filtered Rayleigh Scattering Measurements in a Buoyant Flow Field
2008-03-01
John William Strutt , the third Baron of Rayleigh , or more commonly known as Lord Rayleigh , was the first to offer a correct explanation of the...FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD THESIS Steven Michael Meents, Captain, USAF...AFIT/GAE/ENY/08-M22 FILTERED RAYLEIGH SCATTERING MEASUREMENTS IN A BUOYANT FLOW FIELD THESIS Presented to the Faculty Department of Aeronautics
ADE-FDTD Scattered-Field Formulation for Dispersive Materials.
Kong, Soon-Cheol; Simpson, Jamesina J; Backman, Vadim
2008-01-01
This Letter presents a scattered-field formulation for modeling dispersive media using the finite-difference time-domain (FDTD) method. Specifically, the auxiliary differential equation method is applied to Drude and Lorentz media for a scattered field FDTD model. The present technique can also be applied in a straightforward manner to Debye media. Excellent agreement is achieved between the FDTD-calculated and exact theoretical results for the reflection coefficient in half-space problems.
Hesford, Andrew J.; Tillett, Jason C.; Astheimer, Jeffrey P.; Waag, Robert C.
2014-01-01
Accurate and efficient modeling of ultrasound propagation through realistic tissue models is important to many aspects of clinical ultrasound imaging. Simplified problems with known solutions are often used to study and validate numerical methods. Greater confidence in a time-domain k-space method and a frequency-domain fast multipole method is established in this paper by analyzing results for realistic models of the human breast. Models of breast tissue were produced by segmenting magnetic resonance images of ex vivo specimens into seven distinct tissue types. After confirming with histologic analysis by pathologists that the model structures mimicked in vivo breast, the tissue types were mapped to variations in sound speed and acoustic absorption. Calculations of acoustic scattering by the resulting model were performed on massively parallel supercomputer clusters using parallel implementations of the k-space method and the fast multipole method. The efficient use of these resources was confirmed by parallel efficiency and scalability studies using large-scale, realistic tissue models. Comparisons between the temporal and spectral results were performed in representative planes by Fourier transforming the temporal results. An RMS field error less than 3% throughout the model volume confirms the accuracy of the methods for modeling ultrasound propagation through human breast. PMID:25096103
NASA Astrophysics Data System (ADS)
Ressler, Patrick H.
2002-11-01
A 153 kHz narrowband acoustic Doppler current profiler (ADCP) was used to measure volume backscattering strength ( Sv) during a deepwater oceanographic survey of cetacean and seabird habitat in the northeastern Gulf of Mexico. Sv was positively related to zooplankton and micronekton biomass (wet displacement volume) in 'sea-truth' net hauls made with a 1 m 2 Multiple Opening-Closing Net Environmental Sensing System (MOCNESS). A subset of these MOCNESS tows was used to explore the relationship between the numerical densities of various taxonomic categories of zooplankton and the ADCP backscatter signal. Crustaceans, small fish, and fragments of non-gas-bearing siphonophores in the net samples all showed significant, positive correlations with the acoustic signal, while other types of gelatinous zooplankton, pteropod and atlantid molluscs, and gas-filled siphonophore floats showed no significant correlation with Sv. Previously published acoustic scattering models for zooplankton were used to calculate expected scattering for several general zooplankton types and sizes for comparison with the field data. Even though gelatinous material often made up a large fraction of the total biomass, crustaceans, small fish, and pteropods were most likely the important scatterers. Since only crustacean and small fish densities were significantly correlated with Sv, it is suggested that Sv at 153 kHz can be used as a relative proxy for the abundance of these organisms in the Gulf of Mexico.
Field tests of acoustic telemetry for a portable coastal observatory
Martini, M.; Butman, B.; Ware, J.; Frye, D.
2006-01-01
Long-term field tests of a low-cost acoustic telemetry system were carried out at two sites in Massachusetts Bay. At each site, an acoustic Doppler current profiler mounted on a bottom tripod was fitted with an acoustic modem to transmit data to a surface buoy; electronics mounted on the buoy relayed these data to shore via radio modem. The mooring at one site (24 m water depth) was custom-designed for the telemetry application, with a custom designed small buoy, a flexible electro-mechanical buoy to mooring joint using a molded chain connection to the buoy, quick-release electro-mechanical couplings, and dual hydrophones suspended 7 m above the bottom. The surface buoy at the second site (33 m water depth) was a U.S. Coast Guard (USCG) channel buoy fitted with telemetry electronics and clamps to hold the hydrophones. The telemetry was tested in several configurations for a period of about four years. The custom-designed buoy and mooring provided nearly error-free data transmission through the acoustic link under a variety of oceanographic conditions for 261 days at the 24 m site. The electro mechanical joint, cables and couplings required minimal servicing and were very reliable, lasting 862 days deployed before needing repairs. The acoustic communication results from the USCG buoy were poor, apparently due to the hard cobble bottom, noise from the all-steel buoy, and failure of the hydrophone assembly. Access to the USCG buoy at sea required ideal weather. ??2006 IEEE.
Direct Field and Reverberant Chamber Acoustic Test Comparisons
NASA Technical Reports Server (NTRS)
OConnell, Michael
2007-01-01
Reverberant and direct acoustic test comparisons were analyzed in this viewgraph presentation. The acoustic test data set includes: 1) CloudSat antenna subjected to PF reverberant chamber acoustic test; 2) CloudSat subjected to a PF direct speaker acoustic test; and 3) DAWN flight spacecraft subjected to PF direct speaker and a workmanship reverberant chamber acoustic test.
Acoustic source localization in mixed field using spherical microphone arrays
NASA Astrophysics Data System (ADS)
Huang, Qinghua; Wang, Tong
2014-12-01
Spherical microphone arrays have been used for source localization in three-dimensional space recently. In this paper, a two-stage algorithm is developed to localize mixed far-field and near-field acoustic sources in free-field environment. In the first stage, an array signal model is constructed in the spherical harmonics domain. The recurrent relation of spherical harmonics is independent of far-field and near-field mode strengths. Therefore, it is used to develop spherical estimating signal parameter via rotational invariance technique (ESPRIT)-like approach to estimate directions of arrival (DOAs) for both far-field and near-field sources. In the second stage, based on the estimated DOAs, simple one-dimensional MUSIC spectrum is exploited to distinguish far-field and near-field sources and estimate the ranges of near-field sources. The proposed algorithm can avoid multidimensional search and parameter pairing. Simulation results demonstrate the good performance for localizing far-field sources, or near-field ones, or mixed field sources.
Light fields in complex media: Mesoscopic scattering meets wave control
NASA Astrophysics Data System (ADS)
Rotter, Stefan; Gigan, Sylvain
2017-01-01
The newly emerging field of wave front shaping in complex media has recently seen enormous progress. The driving force behind these advances has been the experimental accessibility of the information stored in the scattering matrix of a disordered medium, which can nowadays routinely be exploited to focus light as well as to image or to transmit information even across highly turbid scattering samples. An overview of these new techniques, their experimental implementations, and the underlying theoretical concepts following from mesoscopic scattering theory is provided. In particular, the intimate connections between quantum transport phenomena and the scattering of light fields in disordered media, which can both be described by the same theoretical concepts, are highlighted. Particular emphasis is put on how these topics relate to application-oriented research fields such as optical imaging, sensing, and communication.
Potential scattering of electrons in a quantized radiation field
NASA Astrophysics Data System (ADS)
Bergou, J.; Ehlotzky, F.
1986-05-01
Potential scattering of electrons in a strong laser field is reconsidered. The laser beam is described by a quantized single-mode plane-wave field with a finite number of quanta in the mode. The scattering amplitude is expanded in powers of the potential, and the first two Born terms are considered. It is shown that in the limit of an infinite number of field quanta, the Kroll-Watson approximation is recovered. Additional insight is gained into the validity of this low-frequency theorem. The approach rests on the introduction of electron-dressed quantized-field states. Relations to earlier work are indicated.
The near-field acoustic levitation of high-mass rotors.
Hong, Z Y; Lü, P; Geng, D L; Zhai, W; Yan, N; Wei, B
2014-10-01
Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.
The near-field acoustic levitation of high-mass rotors
Hong, Z. Y.; Lü, P.; Geng, D. L.; Zhai, W.; Yan, N.; Wei, B.
2014-10-15
Here we demonstrate that spherical rotors with 40 mm diameter and 0-1 kg mass can be suspended more than tens of micrometers away from an ultrasonically vibrating concave surface by near-field acoustic radiation force. Their rotating speeds exceed 3000 rpm. An acoustic model has been developed to evaluate the near-field acoustic radiation force and the resonant frequencies of levitation system. This technique has potential application in developing acoustic gyroscope.
Array Receivers and Sound Sources for Three Dimensional Shallow Water Acoustic Field Experiments
2016-12-06
Water Acoustic Field Experiments NOOO 14-15-1-2893 Sc. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Sd. PROJECT NUMBER Ying Tsong-Lin 132893SP Se. TASK...testing. 1S. SUBJECT TERMS acoustics, shallow water , Arctic Ocean , 3-D acoustic propagation, shelfbreak 16. SECURITY CLASSIFICATION OF: R b...Approved f or public release; distribution is unlimited. Array Receivers and Sound Sources for Three-Dimensional Shallow- Water Acoustic Field
Nano concentration by acoustically generated complex spiral vortex field
NASA Astrophysics Data System (ADS)
Tang, Qiang; Wang, Xiaofei; Hu, Junhui
2017-03-01
A strategy to concentrate nanoscale materials on the boundary between a nano suspension droplet and non-vibration substrate is demonstrated and analyzed. It employs the spiral vortex of acoustic streaming, generated by an ultrasonically vibrating needle parallel to and above the non-vibration substrate. The vortex drags nanoscale materials to the center of itself, forming a concentration spot. For 250 nm-diameter SiO2 nano particle suspension with an initial concentration of 0.09 mg/ml, the diameter of the concentration spot can be up to several hundred microns. The dependency of the spiral vortex field on the vibration distribution of the acoustic needle in the droplet is also clarified by experiments and computation, and the concentration conditions are obtained by analyzing the nano particle dynamics in the spiral vortex.
Acoustic field of a ballistic shock wave therapy device.
Cleveland, Robin O; Chitnis, Parag V; McClure, Scott R
2007-08-01
Shock wave therapy (SWT) refers to the use of focused shock waves for treatment of musculoskeletal indications including plantar fascitis and dystrophic mineralization of tendons and joint capsules. Measurements were made of a SWT device that uses a ballistic source. The ballistic source consists of a handpiece within which compressed air (1-4 bar) is used to fire a projectile that strikes a metal applicator placed on the skin. The projectile generates stress waves in the applicator that transmit as pressure waves into tissue. The acoustic fields from two applicators were measured: one applicator was 15 mm in diameter and the surface slightly convex and the second was 12 mm in diameter the surface was concave. Measurements were made in a water tank and both applicators generated a similar pressure pulse consisting of a rectangular positive phase (4 micros duration and up to 8 MPa peak pressure) followed by a predominantly negative tail (duration of 20 micros and peak negative pressure of -6 MPa), with many oscillations. The rise times of the waveforms were around 1 micros and were shown to be too long for the pulses to be considered shock waves. Measurements of the field indicated that region of high pressure was restricted to the near-field (20-40 mm) of the source and was consistent with the Rayleigh distance. The measured acoustic field did not display focusing supported by calculations, which demonstrated that the radius of curvature of the concave surface was too large to effect a focusing gain. Other SWT devices use electrohydraulic, electromagnetic and piezoelectric sources that do result in focused shock waves. This difference in the acoustic fields means there is potentially a significant mechanistic difference between a ballistic source and other SWT devices.
Electromagnetic Scattered Field Evaluation and Data Compression Using Imaging Techniques
NASA Technical Reports Server (NTRS)
Gupta, I. J.; Burnside, W. D.
1996-01-01
This is the final report on Project #727625 between The Ohio State University and NASA, Lewis Research Center, Cleveland, Ohio. Under this project, a data compression technique for scattered field data of electrically large targets is developed. The technique was applied to the scattered fields of two targets of interest. The backscattered fields of the scale models of these targets were measured in a ra compact range. For one of the targets, the backscattered fields were also calculated using XPATCH computer code. Using the technique all scattered field data sets were compressed successfully. A compression ratio of the order 40 was achieved. In this report, the technique is described briefly and some sample results are included.
Wyczalkowski, Matthew; Szeri, Andrew J
2003-06-01
The second harmonic radiation of acoustically driven bubbles is a useful discriminant for their presence in clinical ultrasound applications. It is useful because the scatter from a bubble at a frequency different from the driving can have a contrast-to-tissue ratio better than at the drive frequency. In this work a technique is developed to optimize the scattering from a microbubble at a frequency different from the driving. This is accomplished by adjusting the relative phase and amplitudes of the components of a dual-frequency incident ultrasound wave form. The investigation is focused primarily on the example of dual-mode driving at frequencies of 1 MHz and 3 MHz, with the scattering optimized at 2 MHz. Bubble radii of primary interest are 0.5 to 2 microm and driving amplitudes to 0.5 atm. Bubbles in this size range are sensitive to modulation of driving. It is shown that an optimal forcing scheme can increase the target response eightfold or more. This suggests new applications in imaging and in bubble detection.
Acoustic and Cavitation Fields of Shock Wave Therapy Devices
NASA Astrophysics Data System (ADS)
Chitnis, Parag V.; Cleveland, Robin O.
2006-05-01
Extracorporeal shock wave therapy (ESWT) is considered a viable treatment modality for orthopedic ailments. Despite increasing clinical use, the mechanisms by which ESWT devices generate a therapeutic effect are not yet understood. The mechanistic differences in various devices and their efficacies might be dependent on their acoustic and cavitation outputs. We report acoustic and cavitation measurements of a number of different shock wave therapy devices. Two devices were electrohydraulic: one had a large reflector (HMT Ossatron) and the other was a hand-held source (HMT Evotron); the other device was a pneumatically driven device (EMS Swiss DolorClast Vet). Acoustic measurements were made using a fiber-optic probe hydrophone and a PVDF hydrophone. A dual passive cavitation detection system was used to monitor cavitation activity. Qualitative differences between these devices were also highlighted using a high-speed camera. We found that the Ossatron generated focused shock waves with a peak positive pressure around 40 MPa. The Evotron produced peak positive pressure around 20 MPa, however, its acoustic output appeared to be independent of the power setting of the device. The peak positive pressure from the DolorClast was about 5 MPa without a clear shock front. The DolorClast did not generate a focused acoustic field. Shadowgraph images show that the wave propagating from the DolorClast is planar and not focused in the vicinity of the hand-piece. All three devices produced measurable cavitation with a characteristic time (cavitation inception to bubble collapse) that varied between 95 and 209 μs for the Ossatron, between 59 and 283 μs for the Evotron, and between 195 and 431 μs for the DolorClast. The high-speed camera images show that the cavitation activity for the DolorClast is primarily restricted to the contact surface of the hand-piece. These data indicate that the devices studied here vary in acoustic and cavitation output, which may imply that the
Plasmonic and photonic scattering and near fields of nanoparticles
2014-01-01
We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell’s equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results. PMID:24475923
Plasmonic and photonic scattering and near fields of nanoparticles
NASA Astrophysics Data System (ADS)
Schmid, Martina; Andrae, Patrick; Manley, Phillip
2014-01-01
We theoretically compare the scattering and near field of nanoparticles from different types of materials, each characterized by specific optical properties that determine the interaction with light: metals with their free charge carriers giving rise to plasmon resonances, dielectrics showing zero absorption in wide wavelength ranges, and semiconductors combining the two beforehand mentioned properties plus a band gap. Our simulations are based on Mie theory and on full 3D calculations of Maxwell's equations with the finite element method. Scattering and absorption cross sections, their division into the different order electric and magnetic modes, electromagnetic near field distributions around the nanoparticles at various wavelengths as well as angular distributions of the scattered light were investigated. The combined information from these calculations will give guidelines for choosing adequate nanoparticles when aiming at certain scattering properties. With a special focus on the integration into thin film solar cells, we will evaluate our results.
Kaina, Nadège; Lemoult, Fabrice; Fink, Mathias; Lerosey, Geoffroy
2015-09-03
Metamaterials, man-made composite media structured on a scale much smaller than a wavelength, offer surprising possibilities for engineering the propagation of waves. One of the most interesting of these is the ability to achieve superlensing--that is, to focus or image beyond the diffraction limit. This originates from the left-handed behavior--the property of refracting waves negatively--that is typical of negative index metamaterials. Yet reaching this goal requires the design of 'double negative' metamaterials, which act simultaneously on the permittivity and permeability in electromagnetics, or on the density and compressibility in acoustics; this generally implies the use of two different kinds of building blocks or specific particles presenting multiple overlapping resonances. Such a requirement limits the applicability of double negative metamaterials, and has, for example, hampered any demonstration of subwavelength focusing using left-handed acoustic metamaterials. Here we show that these strict conditions can be largely relaxed by relying on media that consist of only one type of single resonant unit cell. Specifically, we show with a simple yet general semi-analytical model that judiciously breaking the symmetry of a single negative metamaterial is sufficient to turn it into a double negative one. We then demonstrate that this occurs solely because of multiple scattering of waves off the metamaterial resonant elements, a phenomenon often disregarded in these media owing to their subwavelength patterning. We apply our approach to acoustics and verify through numerical simulations that it allows the realization of negative index acoustic metamaterials based on Helmholtz resonators only. Finally, we demonstrate the operation of a negative index acoustic superlens, achieving subwavelength focusing and imaging with spot width and resolution 7 and 3.5 times better than the diffraction limit, respectively. Our findings have profound implications for the
Acoustic phonons in chrysotile asbestos probed by high-resolution inelastic x-ray scattering
Mamontov, Eugene; Vakhrushev, S. B.; Kumzerov, Yu. A,; Alatas, A.
2009-01-01
Acoustic phonons in an individual, oriented fiber of chrysotile asbestos (chemical formula Mg{sub 3}Si{sub 2}O{sub 5}(OH){sub 4}) were observed at room temperature in the inelastic x-ray measurement with a very high (meV) resolution. The x-ray scattering vector was aligned along [1 0 0] direction of the reciprocal lattice, nearly parallel to the long axis of the fiber. The latter coincides with [1 0 0] direction of the direct lattice and the axes of the nano-channels. The data were analyzed using a damped harmonic oscillator model. Analysis of the phonon dispersion in the first Brillouin zone yielded the longitudinal sound velocity of (9200 {+-} 600) m/s.
NASA Technical Reports Server (NTRS)
Golubev, Vladimir; Mankbadi, Reda R.; Dahl, Milo D.; Kiraly, L. James (Technical Monitor)
2002-01-01
This paper provides preliminary results of the study of the acoustic radiation from the source model representing spatially-growing instability waves in a round jet at high speeds. The source model is briefly discussed first followed by the analysis of the produced acoustic directivity pattern. Two integral surface techniques are discussed and compared for prediction of the jet acoustic radiation field.
Near-field acoustical holography of military jet aircraft noise
NASA Astrophysics Data System (ADS)
Wall, Alan T.; Gee, Kent L.; Neilsen, Tracianne; Krueger, David W.; Sommerfeldt, Scott D.; James, Michael M.
2010-10-01
Noise radiated from high-performance military jet aircraft poses a hearing-loss risk to personnel. Accurate characterization of jet noise can assist in noise prediction and noise reduction techniques. In this work, sound pressure measurements were made in the near field of an F-22 Raptor. With more than 6000 measurement points, this is the most extensive near-field measurement of a high-performance jet to date. A technique called near-field acoustical holography has been used to propagate the complex pressure from a two- dimensional plane to a three-dimensional region in the jet vicinity. Results will be shown and what they reveal about jet noise characteristics will be discussed.
Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer
NASA Astrophysics Data System (ADS)
Liu, W.; Zagzebski, J. A.; Hall, T. J.; Madsen, E. L.; Varghese, T.; Kliewer, M. A.; Panda, S.; Lowery, C.; Barnes, S.
2008-08-01
Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated
Acoustic backscatter and effective scatterer size estimates using a 2D CMUT transducer
Liu, W; Zagzebski, J A; Hall, T J; Madsen, E L; Varghese, T; Kliewer, M A; Panda, S; Lowery, C; Barnes, S
2009-01-01
Compared to conventional piezoelectric transducers, new capacitive microfabricated ultrasonic transducer (CMUT) technology is expected to offer a broader bandwidth, higher resolution and advanced 3D/4D imaging inherent in a 2D array. For ultrasound scatterer size imaging, a broader frequency range provides more information on frequency-dependent backscatter, and therefore, generally more accurate size estimates. Elevational compounding, which can significantly reduce the large statistical fluctuations associated with parametric imaging, becomes readily available with a 2D array. In this work, we show phantom and in vivo breast tumor scatterer size image results using a prototype 2D CMUT transducer (9 MHz center frequency) attached to a clinical scanner. A uniform phantom with two 1 cm diameter spherical inclusions of slightly smaller scatterer size was submerged in oil and scanned by both the 2D CMUT and a conventional piezoelectric linear array transducer. The attenuation and scatterer sizes of the sample were estimated using a reference phantom method. RF correlation analysis was performed using the data acquired by both transducers. The 2D CMUT results indicate that at a 2 cm depth (near the transmit focus for both transducers) the correlation coefficient reduced to less than 1/e for 0.2 mm lateral or 0.25 mm elevational separation between acoustic scanlines. For the conventional array this level of decorrelation requires a 0.3 mm lateral or 0.75 mm elevational translation. Angular and/or elevational compounding is used to reduce the variance of scatterer size estimates. The 2D array transducer acquired RF signals from 140 planes over a 2.8 cm elevational direction. If no elevational compounding is used, the fractional standard deviation of the size estimates is about 12% of the mean size estimate for both the spherical inclusion and the background. Elevational compounding of 11 adjacent planes reduces it to 7% for both media. Using an experimentally estimated
Mott scattering in an elliptically polarized laser field
Attaourti, Y.; Manaut, B.; Taj, S.
2004-08-01
We study Mott scattering in the presence of a strong elliptically polarized field. Using the first Born approximation and the Dirac-Volkov states for the electron, we obtain an analytic formula for the unpolarized differential cross section. This generalizes the results found for the linearly polarized field by Li et al. [ 67, 063409 (2003)] and for the circularly polarized field by Attaourti and Manaut [ 68, 067401 (2003)].
Mott scattering of polarized electrons in a strong laser field
Manaut, B.; Taj, S.; Attaourti, Y.
2005-04-01
We present analytical and numerical results of the relativistic calculation of the transition matrix element S{sub fi} and differential cross sections for Mott scattering of initially polarized Dirac particles (electrons) in the presence of a strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.
NASA Astrophysics Data System (ADS)
Marston, Philip L.; Zhang, Likun
2016-11-01
When evaluating radiation forces on spheres in soundfields (with or without orbital-angular momentum) the interpretation of analytical results is greatly simplified by retaining the use of s-function notation for partial-wave coefficients imported into acoustics from quantum scattering theory in the 1970s. This facilitates easy interpretation of various efficiency factors. For situations in which dissipation is negligible, each partial-wave s-function becomes characterized by a single parameter: a phase shift allowing for all possible situations. These phase shifts are associated with scattering by plane traveling waves and the incident wavefield of interest is separately parameterized. (When considering outcomes, the method of fabricating symmetric objects having a desirable set of phase shifts becomes a separate issue.) The existence of negative radiation force "islands" for beams reported in 2006 by Marston is manifested. This approach and consideration of conservation theorems illustrate the unphysical nature of various claims made by other researchers. This approach is also directly relevant to objects in standing waves. Supported by ONR.
Acoustic scattering by circular cylinders of various aspect ratios. [pressure gradient microphones
NASA Technical Reports Server (NTRS)
Maciulaitis, A.
1979-01-01
The effects of acoustic scattering on the useful frequency range of pressure gradient microphones were investigated experimentally between ka values of 0.407 and 4.232 using two circular cylindrical models (L/D = 0.5 and 0.25) having a 25 cm outside diameter. Small condenser microphones, attached to preamplifiers by flexible connectors, were installed from inside the cylindrical bodies, and flush mounted on the exterior surface of the cylinders. A 38 cm diameter woofer in a large speaker enclosure was used as the sound source. Surface pressure augmentation and phase differences were computed from measured data for various sound wave incidence angles. Results are graphically compared with theoretical predictions supplied by NASA for ka = 0.407, 2.288, and 4.232. All other results are tabulated in the appendices. With minor exceptions, the experimentally determined pressure augmentations agreed within 0.75 dB with theoretical predictions. The agreement for relative phase angles was within 5 percent without any exceptions. Scattering parameter variations with ka and L/D ratio, as computed from experimental data, are also presented.
Magnetic field contribution to the last electron-photon scattering
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2010-11-01
When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron-photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.
Study of acoustic field modulation in the regenerator by double loudspeakers method.
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.
Near-field beamforming analysis for acoustic emission source localization.
He, Tian; Pan, Qiang; Liu, Yaoguang; Liu, Xiandong; Hu, Dayong
2012-07-01
This paper attempts to introduce a near-field acoustic emission (AE) beamforming method to estimate the AE source locations by using a small array of sensors closely placed in a local region. The propagation characteristics of AE signals are investigated based on guided wave theory to discuss the feasibility of using beamforming techniques in AE signal processing. To validate the effectiveness of the AE beamforming method, a series of pencil lead break tests at various regions of a thin steel plate are conducted. The potential of this method for engineering applications are explored through rotor-stator rubbing tests. The experimental results demonstrate that the proposed method can effectively determine the region where rubbing occurs. It is expected that the work of this paper may provide a helpful analysis tool for near-field AE source localization.
Nonlinear electron acoustic waves in presence of shear magnetic field
Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Chakrabarti, Nikhil
2013-12-15
Nonlinear electron acoustic waves are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic wave. Whereas, nonlinear wave dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear wave characteristics are well depicted by KdV equation. The wave dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere.
Fatigue crack localization with near-field acoustic emission signals
NASA Astrophysics Data System (ADS)
Zhou, Changjiang; Zhang, Yunfeng
2013-04-01
This paper presents an AE source localization technique using near-field acoustic emission (AE) signals induced by crack growth and propagation. The proposed AE source localization technique is based on the phase difference in the AE signals measured by two identical AE sensing elements spaced apart at a pre-specified distance. This phase difference results in canceling-out of certain frequency contents of signals, which can be related to AE source direction. Experimental data from simulated AE source such as pencil breaks was used along with analytical results from moment tensor analysis. It is observed that the theoretical predictions, numerical simulations and the experimental test results are in good agreement. Real data from field monitoring of an existing fatigue crack on a bridge was also used to test this system. Results show that the proposed method is fairly effective in determining the AE source direction in thick plates commonly encountered in civil engineering structures.
Transient scattering from dielectric cylinders - E-field, H-field, and combined field solutions
NASA Technical Reports Server (NTRS)
Vechinski, Douglas A.; Rao, Sadasiva M.
1992-01-01
In this work, the problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the equivalence principle. Three different formulations, namely, the electric field integral equation formulation, the magnetic field integral equation formulation, and the combined field integral equation formulation are considered. Numerical results are presented for two cross sections, namely, a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.
Iodine-starch clathrate complexes in low-field acoustic fields
NASA Astrophysics Data System (ADS)
Fadeev, G. N.; Boldyrev, V. S.; Ermolaeva, V. I.; Eliseeva, N. M.
2013-01-01
Experimental data on the kinetics of formation and decomposition of iodine-starch clathrate complexes (amyloiodine and amylopectoiodine) in low-frequency (5-45 Hz) acoustic fields are reported. The biological activity of these compounds suggests their use as a model of biocatalysts, in which iodine represents the coenzyme active group and starch homopolysaccharides (amylopectin and amylose) represents the apoenzyme.
Field Assessment of Acoustic-Doppler Based Discharge Measurements
Mueller, D.S.; ,
2002-01-01
The use of equipment based on the Doppler principle for measuring water velocity and computing discharge is common within the U.S. Geological Survey (USGS). The instruments and software have changed appreciably during the last 5 years; therefore, the USGS has begun a field validation of the instruments currently (2002) available for making discharge measurements from a moving boat in streams of various sizes. Instruments manufactured by SonTek/YSI2 and RD Instruments, Inc. were used to collect discharge data at five different sites. One or more traditional discharge measurements were made by the use of a Price AA current meter and standard USGS procedures with the acoustic instruments at each site during data collection. The discharges measured with the acoustic instruments were compared with the discharges measured with Price AA meters and the current USGS stage-discharge rating for each site. The mean discharges measured by each acoustic instrument were within 5 percent of the Price AA-based measurement and (or) discharge from the stage-discharge rating. Additional analysis of the data collected indicates that the coefficient of variation of the discharge measurements consistently was less for the RD Instruments, Inc. Rio Grandes than it was for the SonTek/YSI RiverSurveyors. The bottom-tracking referenced measurement had a lower coefficient of variation than the differentially corrected global positioning system referenced measurements. It was observed that the higher frequency RiverSurveyors measured a moving bed more often than the lower frequency Rio Grandes. The detection of a moving bed caused RiverSurveyors to be consistently biased low when referenced to bottom tracking. Differentially corrected global positioning system data may be used to remove the bias observed in the bottom-tracking referenced measurements.
Fundamental Studies of Electric-Field-Induced Coherent Raman Scattering
2011-06-07
mechanisms of nanosecond- pulsed dielectric barrier discharges generated in open air. Our experimental observations have revealed that, in the pre...dynamics in nanosecond- pulsed discharges . a) Electric-field-induced coherent Raman scattering (E-CRS) In this section, I describe the...the electric field in hydrogen. With E-CRS method, our group has revealed very fast discharge dynamics in repetitively pulsed nanosecond discharges [4
2006-06-01
sech2 wave form is used because the amplitude and horizontal displacement are solutions of the Korteweg de Vries ( KdV ) non linear wave equation which...a solution to the KDV wave equation . After making the frozen field approximation, the soliton can be represented by the following mathematical...scattering. 3. The Gaussian Soliton As discussed, the sech2 form of a soliton is chosen because it is an exact solution to the KDV wave equation . For
Risk of a second cancer from scattered radiation in acoustic neuroma treatment
NASA Astrophysics Data System (ADS)
Yoon, Myonggeun; Lee, Hyunho; Sung, Jiwon; Shin, Dongoh; Park, Sungho; Chung, Weon Kuu; Jahng, Geon-Ho; Kim, Dong Wook
2014-06-01
The present study aimed to compare the risk of a secondary cancer from scattered and leakage doses in patients receiving intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS). Four acoustic neuroma patients were treated with IMRT, VMAT, or SRS. Their excess relative risk (ERR), excess absolute risk (EAR), and lifetime attributable risk (LAR) of a secondary cancer were estimated using the corresponding secondary doses measured at various organs by using radio-photoluminescence glass dosimeters (RPLGD) placed inside a humanoid phantom. When a prescription dose was delivered in the planning target volume of the 4 patients, the average organ equivalent doses (OED) at the thyroid, lung, liver, bowel, bladder, prostate (or ovary), and rectum were 14.6, 1.7, 0.9, 0.8, 0.6, 0.6, and 0.6 cGy, respectively, for IMRT whereas they were 19.1, 1.8, 2.0, 0.6, 0.4, 0.4, and 0.4 cGy, respectively, for VMAT, and 22.8, 4.6, 1.4, 0.7, 0.5, 0.5, and 0.5 cGy, respectively, for SRS. The OED decreased as the distance from the primary beam increased. The thyroid received the highest OED compared to other organs. A lifetime attributable risk evaluation estimated that more than 0.03% of acoustic neuroma (AN) patients would get radiation-induced cancer within 20 years of receiving radiation therapy. The organ with the highest radiation-induced cancer risk after radiation treatment for AN was the thyroid. We found that the LAR could be increased by the transmitted dose from the primary beam. No modality-specific difference in radiation-induced cancer risk was observed in our study.
Subharmonic scattering of phospholipid-shell microbubbles at low acoustic pressure amplitudes.
Frinking, Peter J A; Brochot, Jean; Arditi, Marcel
2010-08-01
Subharmonic scattering of phospholipid-shell microbubbles excited at relatively low acoustic pressure amplitudes (<30 kPa) has been associated with echo responses from compression-only bubbles having initial surface tension values close to zero. In this work, the relation between sbharmonics and compression-only behavior of phospholipid-shell microbubbles was investigated, experimentally and by simulation, as a function of the initial surface tension by applying ambient overpressures of 0 and 180 mmHg. The microbubbles were excited using a 64-cycle transmit burst with a center frequency of 4 MHz and peak-negative pressure amplitudes ranging from 20 of 150 kPa. In these conditions, an increase in subharmonic response of 28.9 dB (P < 0.05) was measured at 50 kPa after applying an overpressure of 180 mmHg. Simulations using the Marmottant model, taking into account the effect of ambient overpressure on bubble size and initial surface tension, confirmed the relation between subharmonics observed in the pressure-time curves and compression-only behavior observed in the radius-time curves. The trend of an increase in subharmonic response as a function of ambient overpressure, i.e., as a function of the initial surface tension, was predicted by the model. Subharmonics present in the echo responses of phospholipid-shell microbubbles excited at low acoustic pressure amplitudes are indeed related to the echo responses from compression-only bubbles. The increase in subharmonics as a function of ambient overpressure may be exploited for improving methods for noninvasive pressure measurement in heart cavities or big vessels in the human body.
NASA Astrophysics Data System (ADS)
Antonov, S. N.; Vainer, A. V.; Proklov, V. V.; Rezvov, Yu. G.
2010-03-01
Bragg’s acoustooptic diffraction in an acoustically anisotropic medium is considered taking into account the two-dimensional spatial diffraction structure of the acoustic beam. The conditions are determined under which reverse transfer of optical power from the diffracted to the transmitted beam in the regime of 100% efficiency of diffraction is considerably suppressed. It is shown that this effect is due to diffraction bending of wave fronts of the acoustic beam in the acoustooptic diffraction plane. The problem of optimization of the piezoelectric transducer size and the spatial position of the input light beam is solved using the criterion of the minimal required power of the acoustic field. The results of simulation in a wide range of the acoustooptic interaction parameters for a Gaussian light beam are reported. The correctness of the model is confirmed experimentally. Recommendations for designers of acoustooptic devices are formulated.
Investigation of crossed SAW fields by scanning acoustic force microscopy.
Behme, G; Hesjedal, T
2001-07-01
We used multimode scanning acoustic force microscopy (SAFM) for studying noncollinearly propagating Rayleigh and Love wave fields. By analyzing torsion and bending movement of SAFM cantilever, normal and in-plane wave oscillation components are accessible. The SAFM principle is the down-conversion of surface oscillations into cantilever vibrations caused by the nonlinearity of the tip-sample interaction. Through mixing of complementary oscillation components, phase velocities of crossed Rayleigh waves on GaAs and crossed Rayleigh and Love waves on the layered system SiO2/ST-cut quartz were obtained simultaneously. Now, it is possible to investigate elastic properties of submicron areas through multimode SAFM measurements. Finally, we present mixing experiments of four SAWs on GaAs and discuss the various influences on the measured SAFM amplitude and phase contrast.
Convergent acoustic field of view in echolocating bats.
Jakobsen, Lasse; Ratcliffe, John M; Surlykke, Annemarie
2013-01-03
Most echolocating bats exhibit a strong correlation between body size and the frequency of maximum energy in their echolocation calls (peak frequency), with smaller species using signals of higher frequency than larger ones. Size-signal allometry or acoustic detection constraints imposed on wavelength by preferred prey size have been used to explain this relationship. Here we propose the hypothesis that smaller bats emit higher frequencies to achieve directional sonar beams, and that variable beam width is critical for bats. Shorter wavelengths relative to the size of the emitter translate into more directional sound beams. Therefore, bats that emit their calls through their mouths should show a relationship between mouth size and wavelength, driving smaller bats to signals of higher frequency. We found that in a flight room mimicking a closed habitat, six aerial hawking vespertilionid species (ranging in size from 4 to 21 g, ref. 5) produced sonar beams of extraordinarily similar shape and volume. Each species had a directivity index of 11 ± 1 dB (a half-amplitude angle of approximately 37°) and an on-axis sound level of 108 ± 4 dB sound pressure level referenced to 20 μPa root mean square at 10 cm. Thus all bats adapted their calls to achieve similar acoustic fields of view. We propose that the necessity for high directionality has been a key constraint on the evolution of echolocation, which explains the relationship between bat size and echolocation call frequency. Our results suggest that echolocation is a dynamic system that allows different species, regardless of their body size, to converge on optimal fields of view in response to habitat and task.
Demi, L; van Dongen, K W A; Verweij, M D
2011-03-01
Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation.
Malhotra, M.
1996-12-31
Finite-element discretizations of time-harmonic acoustic wave problems in exterior domains result in large sparse systems of linear equations with complex symmetric coefficient matrices. In many situations, these matrix problems need to be solved repeatedly for different right-hand sides, but with the same coefficient matrix. For instance, multiple right-hand sides arise in radiation problems due to multiple load cases, and also in scattering problems when multiple angles of incidence of an incoming plane wave need to be considered. In this talk, we discuss the iterative solution of multiple linear systems arising in radiation and scattering problems in structural acoustics by means of a complex symmetric variant of the BL-QMR method. First, we summarize the governing partial differential equations for time-harmonic structural acoustics, the finite-element discretization of these equations, and the resulting complex symmetric matrix problem. Next, we sketch the special version of BL-QMR method that exploits complex symmetry, and we describe the preconditioners we have used in conjunction with BL-QMR. Finally, we report some typical results of our extensive numerical tests to illustrate the typical convergence behavior of BL-QMR method for multiple radiation and scattering problems in structural acoustics, to identify appropriate preconditioners for these problems, and to demonstrate the importance of deflation in block Krylov-subspace methods. Our numerical results show that the multiple systems arising in structural acoustics can be solved very efficiently with the preconditioned BL-QMR method. In fact, for multiple systems with up to 40 and more different right-hand sides we get consistent and significant speed-ups over solving the systems individually.
Thomson scattering in magnetic fields. [of white dwarf stars
NASA Technical Reports Server (NTRS)
Whitney, Barbara
1989-01-01
The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.
NASA Technical Reports Server (NTRS)
Hu, Fang Q.; Pizzo, Michelle E.; Nark, Douglas M.
2016-01-01
Based on the time domain boundary integral equation formulation of the linear convective wave equation, a computational tool dubbed Time Domain Fast Acoustic Scattering Toolkit (TD-FAST) has recently been under development. The time domain approach has a distinct advantage that the solutions at all frequencies are obtained in a single computation. In this paper, the formulation of the integral equation, as well as its stabilization by the Burton-Miller type reformulation, is extended to cases of a constant mean flow in an arbitrary direction. In addition, a "Source Surface" is also introduced in the formulation that can be employed to encapsulate regions of noise sources and to facilitate coupling with CFD simulations. This is particularly useful for applications where the noise sources are not easily described by analytical source terms. Numerical examples are presented to assess the accuracy of the formulation, including a computation of noise shielding by a thin barrier motivated by recent Historical Baseline F31A31 open rotor noise shielding experiments. Furthermore, spatial resolution requirements of the time domain boundary element method are also assessed using point per wavelength metrics. It is found that, using only constant basis functions and high-order quadrature for surface integration, relative errors of less than 2% may be obtained when the surface spatial resolution is 5 points-per-wavelength (PPW) or 25 points-per-wavelength squared (PPW2).
Acoustic scattering by elastic cylinders of elliptical cross-section and splitting up of resonances
Ancey, S. Bazzali, E. Gabrielli, P. Mercier, M.
2014-05-21
The scattering of a plane acoustic wave by an infinite elastic cylinder of elliptical cross section is studied from a modal formalism by emphasizing the role of the symmetries. More precisely, as the symmetry is broken in the transition from the infinite circular cylinder to the elliptical one, the splitting up of resonances is observed both theoretically and experimentally. This phenomenon can be interpreted using group theory. The main difficulty stands in the application of this theory within the framework of the vectorial formalism in elastodynamics. This method significantly simplifies the numerical treatment of the problem, provides a full classification of the resonances, and gives a physical interpretation of the splitting up in terms of symmetry breaking. An experimental part based on ultrasonic spectroscopy complements the theoretical study. A series of tank experiments is carried out in the case of aluminium elliptical cylinders immersed in water, in the frequency range 0 ≤ kr ≤ 50, where kr is the reduced wave number in the fluid. The symmetry is broken by selecting various cylinders of increasing eccentricity. More precisely, the greater the eccentricity, the higher the splitting up of resonances is accentuated. The experimental results provide a very good agreement with the theoretical ones, the splitting up is observed on experimental form functions, and the split resonant modes are identified on angular diagrams.
NASA Astrophysics Data System (ADS)
Na, Seong-Won; Kallivokas, Loukas F.
2008-03-01
In this article we discuss a formal framework for casting the inverse problem of detecting the location and shape of an insonified scatterer embedded within a two-dimensional homogeneous acoustic host, in terms of a partial-differential-equation-constrained optimization approach. We seek to satisfy the ensuing Karush-Kuhn-Tucker first-order optimality conditions using boundary integral equations. The treatment of evolving boundary shapes, which arise naturally during the search for the true shape, resides on the use of total derivatives, borrowing from recent work by Bonnet and Guzina [1-4] in elastodynamics. We consider incomplete information collected at stations sparsely spaced at the assumed obstacle’s backscattered region. To improve on the ability of the optimizer to arrive at the global optimum we: (a) favor an amplitude-based misfit functional; and (b) iterate over both the frequency- and wave-direction spaces through a sequence of problems. We report numerical results for sound-hard objects with shapes ranging from circles, to penny- and kite-shaped, including obstacles with arbitrarily shaped non-convex boundaries.
Fully automatic hp-adaptivity for acoustic and electromagnetic scattering in three dimensions
NASA Astrophysics Data System (ADS)
Kurtz, Jason Patrick
We present an algorithm for fully automatic hp-adaptivity for finite element approximations of elliptic and Maxwell boundary value problems in three dimensions. The algorithm automatically generates a sequence of coarse grids, and a corresponding sequence of fine grids, such that the energy norm of the error decreases exponentially with respect to the number of degrees of freedom in either sequence. At each step, we employ a discrete optimization algorithm to determine the refinements for the current coarse grid such that the projection-based interpolation error for the current fine grid solution decreases with an optimal rate with respect to the number of degrees of freedom added by the refinement. The refinements are restricted only by the requirement that the resulting mesh is at most 1-irregular, but they may be anisotropic in both element size h and order of approximation p. While we cannot prove that our method converges at all, we present numerical evidence of exponential convergence for a diverse suite of model problems from acoustic and electromagnetic scattering. In particular we show that our method is well suited to the automatic resolution of exterior problems truncated by the introduction of a perfectly matched layer. To enable and accelerate the solution of these problems on commodity hardware, we include a detailed account of three critical aspects of our implementation, namely an efficient implementation of sum factorization, several efficient interfaces to the direct multi-frontal solver MUMPS, and some fast direct solvers for the computation of a sequence of nested projections.
Burton-Miller-type singular boundary method for acoustic radiation and scattering
NASA Astrophysics Data System (ADS)
Fu, Zhuo-Jia; Chen, Wen; Gu, Yan
2014-08-01
This paper proposes the singular boundary method (SBM) in conjunction with Burton and Miller's formulation for acoustic radiation and scattering. The SBM is a strong-form collocation boundary discretization technique using the singular fundamental solutions, which is mathematically simple, easy-to-program, meshless and introduces the concept of source intensity factors (SIFs) to eliminate the singularities of the fundamental solutions. Therefore, it avoids singular numerical integrals in the boundary element method (BEM) and circumvents the troublesome placement of the fictitious boundary in the method of fundamental solutions (MFS). In the present method, we derive the SIFs of exterior Helmholtz equation by means of the SIFs of exterior Laplace equation owing to the same order of singularities between the Laplace and Helmholtz fundamental solutions. In conjunction with the Burton-Miller formulation, the SBM enhances the quality of the solution, particularly in the vicinity of the corresponding interior eigenfrequencies. Numerical illustrations demonstrate efficiency and accuracy of the present scheme on some benchmark examples under 2D and 3D unbounded domains in comparison with the analytical solutions, the boundary element solutions and Dirichlet-to-Neumann finite element solutions.
Baik, Kyungmin; Dudley, Christopher; Marston, Philip L
2011-12-01
When synthetic aperture sonar (SAS) is used to image elastic targets in water, subtle features can be present in the images associated with the dynamical response of the target being viewed. In an effort to improve the understanding of such responses, as well as to explore alternative image processing methods, a laboratory-based system was developed in which targets were illuminated by a transient acoustic source, and bistatic responses were recorded by scanning a hydrophone along a rail system. Images were constructed using a relatively conventional bistatic SAS algorithm and were compared with images based on supersonic holography. The holographic method is a simplification of one previously used to view the time evolution of a target's response [Hefner and Marston, ARLO 2, 55-60 (2001)]. In the holographic method, the space-time evolution of the scattering was used to construct a two-dimensional image with cross range and time as coordinates. Various features for vertically hung cylindrical targets were interpreted using high frequency ray theory. This includes contributions from guided surface elastic waves, as well as transmitted-wave features and specular reflection.
Collective Thomson scattering measurements of the Ion Acoustic Decay Instability. Final report
Mizuno, K.; DeGroot, J.S.; Drake, R.P.; Seka, W.
1993-12-31
We have developed an uv collective Thomson scattering system for plasma produced by a short wavelength laser. The Ion Acoustic Decay Instabilities are studied in a large ({approximately}mm) scale, hot ({approximately}keV) plasma, which is relevant to a direct-driven laser fusion plasma. The IADI primary decay process is measured by the CTS. We used a random phase plate to minimize the non uniform irradiation of the interaction laser. Nevertheless, the threshold of the most unstable mode driven by the IADI is quite low. The measured threshold value agrees favorably with the theoretical value of the large scale plasma. We have also shown that the CTS from the IADI can be a good tool for measuring a local electron temperature. The measured results agree reasonably with the SAGE computer calculations. We used the real part of the wave (frequency) to estimate T{sub e}. The real part is, in general, reliable compared to the imaginary part such as the damping, and the growth rates. We have shown that the IADI can be easily excited in a large scale, hot plasma. The IADI has potentially important applications to direct drive laser fusion, and also critical surface diagnostic.
Yu, Q Z; Zhang, J; Li, Y T; Lu, X; Hawreliak, J; Wark, J; Chambers, D M; Wang, Z B; Yu, C X; Jiang, X H; Li, W H; Liu, S Y; Zheng, Z J
2005-04-01
Thomson scattering (TS) measurements are performed at different locations in a laser-produced aluminum plasma. Variations of the separation, wavelength shift, and asymmetric distribution of the two ion-acoustic waves are investigated from their spectral-time-resolved TS images. Detailed information on the space-time evolution of the plasma parameters is obtained. Electron distribution and variation of the heat flux in the plasma are also obtained for a steep temperature gradient.
NASA Astrophysics Data System (ADS)
Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang
2016-09-01
A numerical method to concurrently characterize both aeroacoustic scattering and noise sources at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband acoustic excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both acoustic propagation and noise generation. The present work studies the aero-acoustic characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for acoustic scattering matrices and power spectral densities of broad-band noise are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.
NASA Astrophysics Data System (ADS)
Powell, Jesse R.; Ohman, Mark D.
2015-05-01
We report cross-frontal changes in the characteristics of plankton proxy variables measured by autonomous Spray ocean gliders operating within the Southern California Current System (SCCS). A comparison of conditions across the 154 positive frontal gradients (i.e., where density of the surface layer decreased in the offshore direction) identified from six years of continuous measurements showed that waters on the denser side of the fronts typically showed higher Chl-a fluorescence, shallower euphotic zones, and higher acoustic backscatter than waters on the less dense side. Transitions between these regions were relatively abrupt. For positive fronts the amplitude of Diel Vertical Migration (DVM), inferred from a 3-beam 750 kHz acoustic Doppler profiler, increased offshore of fronts and covaried with optical transparency of the water column. Average interbeam variability in acoustic backscatter also changed across many positive fronts within 3 depth strata (0-150 m, 150-400 m, and 400-500 m), revealing a front-related change in the acoustic scattering characteristics of the assemblages. The extent of vertical stratification of distinct scattering assemblages was also more pronounced offshore of positive fronts. Depth-stratified zooplankton samples collected by Mocness nets corroborated the autonomous measurements, showing copepod-dominated assemblages and decreased zooplankton body sizes offshore and euphausiid-dominated assemblages with larger median body sizes inshore of major frontal features.
Scatter dose summation for irregular fields: speed and accuracy study.
DeWyngaert, J K; Siddon, R L; Bjarngard, B E
1986-05-01
Using program IRREG as a standard, we have compared speed and accuracy of several algorithms that calculate the scatter dose in an irregular field. All the algorithms, in some manner, decompose the irregular field into component triangles and obtain the scatter dose as the sum of the contributions from those triangles. Two of the algorithms replace each such component triangle with a sector of a certain "effective radius": in one case the average radius of the triangle, in the other the radius of the sector having the same area as the component triangle. A third algorithm decomposes each triangle further into two right triangles and utilizes the precalculated "equivalent radius" of each, to find the scatter contribution. For points near the center of a square field, all the methods compare favorably in accuracy to program IRREG, with less than a 1% error in total dose and with approximately a factor of 3-5 savings in computation time. Even for extreme rectangular fields (2 cm X 30 cm), the methods using the average radius and the equivalent right triangles agree to within 2% in total dose and approximately a factor of 3-4 savings in computation time.
An effective field theory for forward scattering and factorization violation
NASA Astrophysics Data System (ADS)
Rothstein, Ira Z.; Stewart, Iain W.
2016-08-01
Starting with QCD, we derive an effective field theory description for forward scattering and factorization violation as part of the soft-collinear effective field theory (SCET) for high energy scattering. These phenomena are mediated by long distance Glauber gluon exchanges, which are static in time, localized in the longitudinal distance, and act as a kernel for forward scattering where | t| ≪ s. In hard scattering, Glauber gluons can induce corrections which invalidate factorization. With SCET, Glauber exchange graphs can be calculated explicitly, and are distinct from graphs involving soft, collinear, or ultrasoft gluons. We derive a complete basis of operators which describe the leading power effects of Glauber exchange. Key ingredients include regulating light-cone rapidity singularities and subtractions which prevent double counting. Our results include a novel all orders gauge invariant pure glue soft operator which appears between two collinear rapidity sectors. The 1-gluon Feynman rule for the soft operator coincides with the Lipatov vertex, but it also contributes to emissions with ≥ 2 soft gluons. Our Glauber operator basis is derived using tree level and one-loop matching calculations from full QCD to both SCETII and SCETI. The one-loop amplitude's rapidity renormalization involves mixing of color octet operators and yields gluon Reggeization at the amplitude level. The rapidity renormalization group equation for the leading soft and collinear functions in the forward scattering cross section are each given by the BFKL equation. Various properties of Glauber gluon exchange in the context of both forward scattering and hard scattering factorization are described. For example, we derive an explicit rule for when eikonalization is valid, and provide a direct connection to the picture of multiple Wilson lines crossing a shockwave. In hard scattering operators Glauber subtractions for soft and collinear loop diagrams ensure that we are not sensitive to
Far-field superresolution by imaging of resonance scattering
NASA Astrophysics Data System (ADS)
Schuster, Gerard T.; Huang, Yunsong
2014-12-01
We show that superresolution imaging in the far-field region of the sources and receivers is theoretically and practically possible if migration of resonant multiples is employed. A resonant multiple is one that bounces back and forth between two scattering points; it can also be the multiple between two smoothly varying interfaces as long as the reflection wave paths partially overlap and reflect from the same Fresnel zone. For a source with frequency f, compared to a one-way trip, N round trips in propagating between two scatterers increase the effective frequency by 2N × f and decrease the effective wavelength by λ/(2N). Thus, multiples can, in principle, be used as high-frequency probes to estimate detailed properties of layers. Tests with both synthetic and field data validate this claim. Improved resolution by multiple imaging is not only feasible for crustal reflections, but might be applicable to mantle and core reverberations recorded by earthquake seismologists.
Back Compton Scattering in Strong Uniform Magnetic Field
Xu, W.; Huang Wei; Yan Mulin
2006-11-02
In this paper, we show that there is a Non-Commutative Plane (NCP) in the perpendicular magnetic fields in the accelerator, and the QED with NCP (QED-NCP) has been formulated. Being similar to the theory of quantum Hall effects, an effective filling factor f(B) is introduced, which characters the possibility occupied the LLL state by the electrons living on NCP. The back Compton scattering amplitudes of QED-NCP are derived, and the differential cross sections for the process with fixed initial polarizing electrons and photons are calculated. We propose to precisely measure the polarization dependent differential cross sections of the back Compton scattering in the perpendicular magnetic fields experimentally, which may lead to reveal the effects of QED with NCP. This should be interesting and remarkable. The existing Spring-8's data have been analyzed primitively, and some hints for QED-NCP effects are seen.
On the radiation force fields of fractional-order acoustic vortices
NASA Astrophysics Data System (ADS)
Hong, Z. Y.; Zhang, J.; Drinkwater, B. W.
2015-04-01
Here we report the creation and observation of acoustic vortices of fractional order. Whilst integer orders are known to produce axisymmetric acoustic fields, fractional orders are shown to break this symmetry and produce a vast array of unexplored field patterns, typically exhibiting multiple closely spaced phase singularities. Here, fractional acoustic vortices are created by emitting ultrasonic waves from an annular array of sources using multiple ramps of phase delay around its circumference. Acoustic radiation force patterns, including multiple concentration points, short straight lines, triangles, squares and discontinuous circles are simulated and experimentally observed. The fractional acoustic vortex leading to two closely spaced phase singularities is used to trap, and by controlling the order, reversibly manipulate two microparticles to a proximity of 0.3 acoustic wavelengths.
Far-field image magnification for acoustic waves using anisotropic acoustic metamaterials.
Ao, Xianyu; Chan, C T
2008-02-01
A kind of two-dimensional acoustic metamaterial is designed so that it exhibits strong anisotropy along two orthogonal directions. Based on the rectangular equal frequency contour of this metamaterial, magnifying lenses for acoustic waves, analogous to electromagnetic hyperlenses demonstrated recently in the optical regime, can be realized. Such metamaterial may offer applications in imaging for systems that obey scalar wave equations.
Broadband Field Directionally Mapping using Maneuverable Acoustic Sensor Arrays
2015-09-30
Maneuverable Acoustic Sensor Arrays David Smith Dept. of Electrical and Computer Engineering Duke University, Box 90291 Durham, NC 27708 phone: (919) 660... acoustic arrays to resolve targets from interferers, and 2) improve the target detection, localization, and tracking performance of long arrays during tow...splines) EM algorithm. Both algorithms were run using a simulated 30 element acoustic vector sensor array with 900 snapshots. Attention has also
Longwave scattering effects on fluxes in broken cloud fields
Takara, E.E.; Ellingson, R.G.
1996-04-01
The optical properties of clouds in the radiative energy balance are important. Most works on the effects of scattering have been in the shortwave; but longwave effects can be significant. In this work, the fluxes above and below a single cloud layer are presented, along with the errors in assuming flat black plate clouds or black clouds. The predicted fluxes are the averaged results of analysis of several fields with the same cloud amount.
NASA Astrophysics Data System (ADS)
Guoyan, Liu; Kun, Gao; Xuefeng, Liu; Guoqiang, Ni
2016-10-01
We report the simulation and measurement results of near field spatial scattering spectra around nanoparticles. Our measurement and simulations results have indicated that Parametric Indirect Microscopic Imaging can image the near field spatial scattering to a much larger distance from the scattering source of the particle under measurement whereas this part of spatial scattering was lost in the conventional microscopy. Both FDTD modeling and measurement provided evidence that parameters of indirect optical wave vector have higher sensitivity to near field scattering.
Light scattering in colloidal solution of magnetite in electric and magnetic fields.
Yerin, Constantine V
2007-04-15
Light scattering by magnetite particles in kerosene under the simultaneous action of crossed electric and magnetic fields was studied. Decreasing of variation of light scattering intensity at some values of electric and magnetic fields have been found. Values of fields at which a minimum of light scattering intensity occur depend on the angle between laser beam and the plane of crossed fields.
Nonlinear Compton scattering in a strong rotating electric field
NASA Astrophysics Data System (ADS)
Raicher, Erez; Eliezer, Shalom; Zigler, Arie
2016-12-01
The nonlinear Compton scattering rate in a rotating electric field is explicitly calculated. For this purpose, an approximate solution to the Klein-Gordon equation in the presence of a rotating electric field is applied. An analytical expression for the emission rate is obtained, as well as a simplified approximation adequate for implementation in kinetic codes. The spectrum is numerically calculated for present-day optical and x-ray laser parameters. The results are compared to the standard Volkov-Ritus rate for a particle in a plane wave, which is commonly assumed to be valid for a rotating electric field under certain conditions. Substantial deviations between the two models, in both the radiated power and the spectral shape, are demonstrated. First, the typical number of photons participating in the scattering process is much smaller compared to the Volkov-Ritus rate, resulting in up to an order of magnitude lower emitted power. Furthermore, our model predicts a discrete harmonic spectrum for electrons with low asymptotic momentum compared to the field amplitude. This discrete structure is a clear imprint of the electric field frequency, as opposed to the Volkov-Ritus rate, which reduces to the constant crossed field rate for the physical conditions under consideration. Our model predictions can be tested with present-day laser facilities.
The Dynamics of Vapor Bubbles in Acoustic Pressure Fields
NASA Technical Reports Server (NTRS)
Hao, Y.; Prosperetti, A.
1999-01-01
In spite of a superficial similarity with gas bubbles, the intimate coupling between dynamical and thermal processes confers to oscillating vapor bubbles some unique characteristics. This paper examines numerically the validity of some asymptotic-theory predictions such as the existence of two resonant radii and a limit size for a given sound amplitude and frequency. It is found that a small vapor bubble in a sound field of sufficient amplitude grows quickly through resonance and continues to grow thereafter at a very slow rate, seemingly indefinitely. Resonance phenomena therefore play a role for a few cycles at most, and reaching a limit size-if one exists at all-is found to require far more than several tens of thousands of cycles. It is also found that some small bubbles may grow or collapse depending on the phase of the sound field. The model accounts in detail for the thermo-fluid-mechanic processes in the vapor. In the second part of the paper, an approximate formulation valid for bubbles small with respect to the thermal penetration length in the vapor is derived and its accuracy examined, The present findings have implications for acoustically enhanced boiling heat transfer and other special applications such as boiling in microgravity.
Tomographic reconstruction of transient acoustic fields recorded by pulsed TV holography.
Gren, P; Schedin, S; Li, X
1998-02-10
Pulsed TV holography combined with computerized tomography (CT) are used to evaluate the three-dimensional distribution of transient acoustic fields in air. Experiments are performed with an electrical discharge between two electrodes as the sound source. Holograms from several directions of the acoustic field are recorded directly onto a CCD detector by use of a double-pulsed ruby laser as the light source. Phase maps, representing projections of the acoustic field, are evaluated quantitatively from the recorded holograms. The projections are used for the CT reconstruction to evaluate the pressure-field distribution in any cross section of the measured volume of air.
APL - North Pacific Acoustic Laboratory
2015-03-04
Acoustic Lab” Encl: (1) Final Technical Report for Subject Grant (2) SF298 for Enclosure Enclosure (1) is the Final Technical Report for the subject...Laboratory (hard copy with SF 298) Defense Technical Information Center (electronic files with SF298) APL - North Pacific Acoustic ...speed perturbations and the characteristics of the ambient acoustic noise field. Scattering and diffraction resulting from internal waves and other
Full acoustic and thermal characterization of HIFU field in the presence of a ribcage model
NASA Astrophysics Data System (ADS)
Cao, Rui; Le, Nhan; Nabi, Ghulam; Huang, Zhihong
2017-03-01
In the treatment of abdominal organs using high intensity focused ultrasound (HIFU), the patient's ribs are in the pathway of the HIFU beams which could result in acoustic distortion, occasional skin burns and insufficient energy delivered to the target organs. To provide full characterization of HIFU field with the influence of ribcage, the ribcage phantom reconstructed from a patient's CT images was created by tissue mimicking materials and its effect on acoustic field was characterized. The effect of the ribcage on acoustic field has been provided in acoustic pressure distribution, acoustic power and focal temperature. Measurement result shows focus splitting with one main focus and two secondary intensity maxima. With the presence of ribcage phantom, the acoustic pressure was reduced by 48.3% and another two peak values were observed near the main focus, reduced by 65.0% and 71.7% respectively. The acoustic power was decreased by 47.5% to 52.5%. With these characterization results, the form of the focus, the acoustic power, acoustic pressure and temperature rise are provided before the transcostal HIFU treatment, which are significant to determine the energy delivery dose. In conclusion, this ribcage model and characterization technique will be useful for the further study in the abdominal HIFU treatment.
Benoit-Bird, Kelly J; Gilly, William F; Au, Whitlow W L; Mate, Bruce
2008-03-01
This study presents the first target strength measurements of Dosidicus gigas, a large squid that is a key predator, a significant prey, and the target of an important fishery. Target strength of live, tethered squid was related to mantle length with values standardized to the length squared of -62.0, -67.4, -67.9, and -67.6 dB at 38, 70, 120, and 200 kHz, respectively. There were relatively small differences in target strength between dorsal and anterior aspects and none between live and freshly dead squid. Potential scattering mechanisms in squid have been long debated. Here, the reproductive organs had little effect on squid target strength. These data support the hypothesis that the pen may be an important source of squid acoustic scattering. The beak, eyes, and arms, probably via the sucker rings, also play a role in acoustic scattering though their effects were small and frequency specific. An unexpected source of scattering was the cranium of the squid which provided a target strength nearly as high as that of the entire squid though the mechanism remains unclear. Our in situ measurements of the target strength of free-swimming squid support the use of the values presented here in D. gigas assessment studies.
Carvalho, Bruno R; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H; Malard, Leandro M; Pimenta, Marcos A
2017-03-09
Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2.
Carvalho, Bruno R.; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H.; Malard, Leandro M.; Pimenta, Marcos A.
2017-01-01
Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2. PMID:28276472
NASA Astrophysics Data System (ADS)
Carvalho, Bruno R.; Wang, Yuanxi; Mignuzzi, Sandro; Roy, Debdulal; Terrones, Mauricio; Fantini, Cristiano; Crespi, Vincent H.; Malard, Leandro M.; Pimenta, Marcos A.
2017-03-01
Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2.
NASA Astrophysics Data System (ADS)
Shiiba, Michihisa; Okada, Nagaya; Kurosawa, Minoru; Takeuchi, Shinichi
2016-07-01
Novel anticavitation hydrophones were fabricated by depositing a hydrothermally synthesized lead zirconate titanate polycrystalline film at the back of a titanium front plate. These anticavitation hydrophones were not damaged by the measurement of the acoustic field formed by a high-intensity focused ultrasound (HIFU) device. Their sensitivity was improved by approximately 20 dB over that of the conventional anticavitation hydrophone by modifying their basic structure and materials. The durability of the anticavitation hydrophone that we fabricated was compared by exposing it to a high-intensity acoustic field at the focal point of the HIFU field and in the water tank of an ultrasound cleaner. Therefore, the effect of the surface of the titanium front plate on acoustic cavitation was investigated by exposing such a surface to the high-intensity acoustic field. We found that the fabricated anticavitation hydrophone was robust and was not damaged easily, even in the focused acoustic field where acoustic cavitation occurs.
Li, Faqi; Zeng, Deping; He, Min; Wang, Zhibiao E-mail: wangzhibiao@haifu.com.cn; Song, Dan; Lei, Guangrong; Lin, Zhou; Zhang, Dong E-mail: wangzhibiao@haifu.com.cn; Wu, Junru
2015-12-15
Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.
Modified ion-acoustic solitary waves in plasmas with field-aligned shear flows
Saleem, H.; Haque, Q.
2015-08-15
The nonlinear dynamics of ion-acoustic waves is investigated in a plasma having field-aligned shear flow. A Korteweg-deVries-type nonlinear equation for a modified ion-acoustic wave is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.
Improving Classroom Acoustics (ICA): A Three-Year FM Sound Field Classroom Amplification Study.
ERIC Educational Resources Information Center
Rosenberg, Gail Gegg; Blake-Rahter, Patricia; Heavner, Judy; Allen, Linda; Redmond, Beatrice Myers; Phillips, Janet; Stigers, Kathy
1999-01-01
The Improving Classroom Acoustics (ICA) special project was designed to determine if students' listening and learning behaviors improved as a result of an acoustical environment enhanced through the use of FM sound field classroom amplification. The 3-year project involved 2,054 students in 94 general education kindergarten, first-, and…
NASA Technical Reports Server (NTRS)
Meyer, Harold D.
1999-01-01
This report provides a study of rotor and stator scattering using the SOURCE3D Rotor Wake/Stator Interaction Code. SOURCE3D is a quasi-three-dimensional computer program that uses three-dimensional acoustics and two-dimensional cascade load response theory to calculate rotor and stator modal reflection and transmission (scattering) coefficients. SOURCE3D is at the core of the TFaNS (Theoretical Fan Noise Design/Prediction System), developed for NASA, which provides complete fully coupled (inlet, rotor, stator, exit) noise solutions for turbofan engines. The reason for studying scattering is that we must first understand the behavior of the individual scattering coefficients provided by SOURCE3D, before eventually understanding the more complicated predictions from TFaNS. To study scattering, we have derived a large number of scattering curves for vane and blade rows. The curves are plots of output wave power divided by input wave power (in dB units) versus vane/blade ratio. Some of these plots are shown in this report. All of the plots are provided in a separate volume. To assist in understanding the plots, formulas have been derived for special vane/blade ratios for which wavefronts are either parallel or normal to rotor or stator chords. From the plots, we have found that, for the most part, there was strong transmission and weak reflection over most of the vane/blade ratio range for the stator. For the rotor, there was little transmission loss.
Radiography by selective detection of scatter field velocity components
NASA Technical Reports Server (NTRS)
Jacobs, Alan M. (Inventor); Dugan, Edward T. (Inventor); Shedlock, Daniel (Inventor)
2007-01-01
A reconfigurable collimated radiation detector, system and related method includes at least one collimated radiation detector. The detector has an adjustable collimator assembly including at least one feature, such as a fin, optically coupled thereto. Adjustments to the adjustable collimator selects particular directions of travel of scattered radiation emitted from an irradiated object which reach the detector. The collimated detector is preferably a collimated detector array, where the collimators are independently adjustable. The independent motion capability provides the capability to focus the image by selection of the desired scatter field components. When an array of reconfigurable collimated detectors is provided, separate image data can be obtained from each of the detectors and the respective images cross-correlated and combined to form an enhanced image.
A compact neutron scatter camera for field deployment
Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.
2016-08-23
Here, we describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metalmore » from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.« less
Research of microwave scattering properties of snow fields
NASA Technical Reports Server (NTRS)
Angelakos, D. J.
1978-01-01
The results obtained in the research program of microwave scattering properties of snow fields are presented. Experimental results are presented showing backscatter dependence on frequency (5.8-8.0 GHz), angle of incidence (0-60 degrees), snow wetness (time of day), and frequency modulation (0-500 MHz). Theoretical studies are being made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: snow layering affects backscatter, layer response is significant up to 45 degrees of incidence, wetness modifies snow layer effects, frequency modulation masks the layer response, and for the proper choice of probing frequency and for nominal snow depths, it appears to be possible to measure the effective dielectric constant and the corresponding water content of a snow pack.
A compact neutron scatter camera for field deployment
Goldsmith, John E. M.; Gerling, Mark D.; Brennan, James S.
2016-08-23
Here, we describe a very compact (0.9 m high, 0.4 m diameter, 40 kg) battery operable neutron scatter camera designed for field deployment. Unlike most other systems, the configuration of the sixteen liquid-scintillator detection cells are arranged to provide omnidirectional (4π) imaging with sensitivity comparable to a conventional two-plane system. Although designed primarily to operate as a neutron scatter camera for localizing energetic neutron sources, it also functions as a Compton camera for localizing gamma sources. In addition to describing the radionuclide source localization capabilities of this system, we demonstrate how it provides neutron spectra that can distinguish plutonium metal from plutonium oxide sources, in addition to the easier task of distinguishing AmBe from fission sources.
Regularization methods for near-field acoustical holography.
Williams, E G
2001-10-01
The reconstruction of the pressure and normal surface velocity provided by near-field acoustical holography (NAH) from pressure measurements made near a vibrating structure is a linear, ill-posed inverse problem due to the existence of strongly decaying, evanescentlike waves. Regularization provides a technique of overcoming the ill-posedness and generates a solution to the linear problem in an automated way. We present four robust methods for regularization; the standard Tikhonov procedure along with a novel improved version, Landweber iteration, and the conjugate gradient approach. Each of these approaches can be applied to all forms of interior or exterior NAH problems; planar, cylindrical, spherical, and conformal. We also study two parameter selection procedures, the Morozov discrepancy principle and the generalized cross validation, which are crucial to any regularization theory. In particular, we concentrate here on planar and cylindrical holography. These forms of NAH which rely on the discrete Fourier transform are important due to their popularity and to their tremendous computational speed. In order to use regularization theory for the separable geometry problems we reformulate the equations of planar, cylindrical, and spherical NAH into an eigenvalue problem. The resulting eigenvalues and eigenvectors couple easily to regularization theory, which can be incorporated into the NAH software with little sacrifice in computational speed. The resulting complete automation of the NAH algorithm for both separable and nonseparable geometries overcomes the last significant hurdle for NAH.
Acoustic reconstruction of the velocity field in a furnace using a characteristic flow model.
Li, Yanqin; Zhou, Huaichun; Chen, Shiying; Zhang, Yindi; Wei, Xinli; Zhao, Jinhui
2012-06-01
An acoustic method can provide a noninvasive, efficient and full-field reconstruction of aerodynamic fields in a furnace. A simple yet reasonable model is devised for reconstruction of a velocity field in a cross section of a tangential furnace from acoustic measurements based on typical physical characteristics of the field. The solenoidal component of the velocity field is modeled by a curved surface, derived by rotating a curve of Gaussian distribution, determined by six characteristic parameters, while the nonrotational component is governed by a priori knowledge. Thus the inverse problem is translated into determination of the characteristic parameters using a set of acoustic projection data. First numerical experiments were undertaken to simulate the acoustic measurement, so as to preliminarily validate the effectiveness of the model. Based on this, physical experiments under different operating conditions were performed in a pilot-scale setup to provide a further test. Hot-wire anemometry and strip floating were applied to compare with acoustic measurements. The acoustic measurements provided satisfactory consistency with both of these approaches. Nevertheless, for a field with a relatively large magnitude of air velocities, the acoustic measurement can give more reliable reconstructions. Extension of the model to measurements of hot tangential furnaces is also discussed.
Acoustic temperature measurement in a rocket noise field.
Giraud, Jarom H; Gee, Kent L; Ellsworth, John E
2010-05-01
A 1 μm diameter platinum wire resistance thermometer has been used to measure temperature fluctuations generated during a static GEM-60 rocket motor test. Exact and small-signal relationships between acoustic pressure and acoustic temperature are derived in order to compare the temperature probe output with that of a 3.18 mm diameter condenser microphone. After preliminary plane wave tests yielded good agreement between the transducers within the temperature probe's ∼2 kHz bandwidth, comparison between the temperature probe and microphone data during the motor firing show that the ±∼3 K acoustic temperature fluctuations are a significant contributor to the total temperature variations.
Robust multiscale field-only formulation of electromagnetic scattering
NASA Astrophysics Data System (ADS)
Sun, Qiang; Klaseboer, Evert; Chan, Derek Y. C.
2017-01-01
We present a boundary integral formulation of electromagnetic scattering by homogeneous bodies that are characterized by linear constitutive equations in the frequency domain. By working with the Cartesian components of the electric E and magnetic H fields and with the scalar functions (r .E ) and (r .H ) where r is a position vector, the problem can be cast as having to solve a set of scalar Helmholtz equations for the field components that are coupled by the usual electromagnetic boundary conditions at material boundaries. This facilitates a direct solution for the surface values of E and H rather than having to work with surface currents or surface charge densities as intermediate quantities in existing methods. Consequently, our formulation is free of the well-known numerical instability that occurs in the zero-frequency or long-wavelength limit in traditional surface integral solutions of Maxwell's equations and our numerical results converge uniformly to the static results in the long-wavelength limit. Furthermore, we use a formulation of the scalar Helmholtz equation that is expressed as classically convergent integrals and does not require the evaluation of principal value integrals or any knowledge of the solid angle. Therefore, standard quadrature and higher order surface elements can readily be used to improve numerical precision for the same number of degrees of freedom. In addition, near and far field values can be calculated with equal precision, and multiscale problems in which the scatterers possess characteristic length scales that are both large and small relative to the wavelength can be easily accommodated. From this we obtain results for the scattering and transmission of electromagnetic waves at dielectric boundaries that are valid for any ratio of the local surface curvature to the wave number. This is a generalization of the familiar Fresnel formula and Snell's law, valid at planar dielectric boundaries, for the scattering and transmission
Hu, Yuxiang; Zhou, Haoran; Lu, Jing; Qiu, Xiaojun
2016-08-01
Beamformers enable a microphone array to capture acoustic signals from a sound source with high signal to noise ratio in a noisy environment, and the linear microphone array is of particular importance, in practice, due to its simplicity and easy implementation. A linear microphone array sometimes is used near some scattering objects, which affect its beamforming performance. This paper develops a numerical model with a linear microphone array near a rigid sphere for both far-field plane wave and near-field sources. The effects of the scatterer on two typical beamformers, i.e., the delay-and-sum beamformer and the superdirective beamformer, are investigated by both simulations and experiments. It is found that the directivity factor of both beamformers improves due to the increased equivalent array aperture when the size of the array is no larger than that of the scatter. With the increase of the array size, the directivity factor tends to deteriorate at high frequencies because of the rising side-lobes. When the array size is significantly larger than that of the scatterer, the scattering has hardly any influence on the beamforming performance.
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.
Axial acoustic radiation force on a sphere in Gaussian field
Wu, Rongrong; Liu, Xiaozhou Gong, Xiufen
2015-10-28
Based on the finite series method, the acoustical radiation force resulting from a Gaussian beam incident on a spherical object is investigated analytically. When the position of the particles deviating from the center of the beam, the Gaussian beam is expanded as a spherical function at the center of the particles and the expanded coefficients of the Gaussian beam is calculated. The analytical expression of the acoustic radiation force on spherical particles deviating from the Gaussian beam center is deduced. The acoustic radiation force affected by the acoustic frequency and the offset distance from the Gaussian beam center is investigated. Results have been presented for Gaussian beams with different wavelengths and it has been shown that the interaction of a Gaussian beam with a sphere can result in attractive axial force under specific operational conditions. Results indicate the capability of manipulating and separating spherical spheres based on their mechanical and acoustical properties, the results provided here may provide a theoretical basis for development of single-beam acoustical tweezers.
NASA Astrophysics Data System (ADS)
Mamou, Jonathan; Oelze, Michael L.; O'Brien, William D.; Zachary, James F.
2004-05-01
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.
2014-09-30
Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 2 annulus offset from the origin in the complex plane. The phase distributions are found to...Complex field, (b) amplitude and (c) phase distributions of ocean acoustic signal propagated over small source-receiver separations in the Gulf of
Towards the optimisation of acoustic fields for ablative therapies of tumours in the upper abdomen
NASA Astrophysics Data System (ADS)
Gélat, P.; ter Haar, G.; Saffari, N.
2013-08-01
The efficacy of high intensity focused ultrasound (HIFU) for the non-invasive treatment of cancer has been demonstrated for a range of different cancers including those of the liver, kidney, prostate and breast. As a non-invasive focused therapy, HIFU offers considerable advantages over other techniques such as chemotherapy and surgical resection, in terms of its non-invasiveness and low risk of harmful side effects. There is, however, a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to induce tissue necrosis at the required foci whilst minimising the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. As such, a common side effect of focusing ultrasound in regions located behind the rib cage is the overheating of bone and surrounding tissue, which can lead to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy are deposited. This is likely to rely on a treatment planning procedure in which optimal source velocity distributions are obtained so as to maximise a dose quantity at the treatment sites, whilst ensuring that this quantity does not exceed a specified threshold at other field locations, particularly on the surface of the ribs. Previously, a boundary element approach based on a Generalised Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data [1]. This work describes the reformulation of the boundary element equations as a least-squares minimisation problem with non-linear constraints. The methodology was subsequently tested at an excitation frequency of 100 kHz on a spherical multi-element array in the presence
NASA Astrophysics Data System (ADS)
Hu, Bo; Yang, Desen; Sun, Yu
2010-06-01
Hybrid near-field acoustical holography (NAH) is developed for reconstructing acoustic radiation from a cylindrical source in a complex underwater environment. In hybrid NAH, we combine statistically optimized near-field acoustical holography (SONAH) and broadband acoustical holography from intensity measurements (BAHIM) to reconstruct the underwater cylindrical source field. First, the BAHIM is utilized to regenerate as much acoustic pressures on the hologram surface as necessary, and then the acoustic pressures are taken as input to the formulation implemented numerically by SONAH. The main advantages of this technology are that the complex pressure on the hologram surface can be reconstructed without reference signal, and the measurement array can be smaller than the source, thus the practicability and efficiency of this technology are greatly enhanced. Numerical examples of a cylindrical source are demonstrated. Test results show that hybrid NAH can yield a more accurate reconstruction than conventional NAH. Then, an experiment has been carried out with a vector hydrophone array. The experimental results show the advantage of hybrid NAH in the reconstruction of an acoustic field and the feasibility of using a vector hydrophone array in an underwater NAH measurement, as well as the identification and localization of noise sources.
Lift-Off Acoustics Prediction of Clustered Rocket Engines in the Near Field
NASA Technical Reports Server (NTRS)
Vu, Bruce; Plotkin, Ken
2010-01-01
This slide presentation presents a method of predicting acoustics during lift-off of the clustered rocket engines in the near field. Included is a definition of the near field, and the use of deflectors and shielding. There is discussion about the use of PAD, a software system designed to calculate the acoustic levels from the lift of of clustered rocket enginee, including updates to extend the calculation to directivity, water suppression, and clustered nozzles.
Investigation of Acoustic Fields for the Cassini Spacecraft: Reverberant Versus Launch Environments
NASA Technical Reports Server (NTRS)
Hughes, William O.; McNelis, Anne M.; Himelblau, Harry
2000-01-01
The characterization and understanding of the acoustic field within a launch vehicle's payload fairing (PLF) is critical to the qualification of a spacecraft and ultimately to the success of its mission. Acoustic measurements taken recently for the Cassini mission have allowed unique opportunities to advance the aerospace industry's knowledge in this field. Prior to its launch, the expected liftoff acoustic environment of the spacecraft was investigated in a full-scale acoustic test of a Titan IV PLF and Cassini simulator in a reverberant test chamber. A major goal of this acoustic ground test was to quantify and verify the noise reduction performance of special barrier blankets that were designed especially to reduce the Cassirii acoustic environment. This paper will describe both the ground test and flight measurements, and compare the Cassini acoustic environment measured during launch with that measured earlier in the ground test. Special emphasis will be given to the noise reduction performance of the barrier blankets and to the acoustic coherence measured within the PLF.
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.
Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.
2010-12-15
In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for {sup 40,42,44,48}Ca with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+{sup 40,42,44,48}Ca systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.
Effective Field Theories from Soft Limits of Scattering Amplitudes.
Cheung, Clifford; Kampf, Karol; Novotny, Jiri; Trnka, Jaroslav
2015-06-05
We derive scalar effective field theories-Lagrangians, symmetries, and all-from on-shell scattering amplitudes constructed purely from Lorentz invariance, factorization, a fixed power counting order in derivatives, and a fixed order at which amplitudes vanish in the soft limit. These constraints leave free parameters in the amplitude which are the coupling constants of well-known theories: Nambu-Goldstone bosons, Dirac-Born-Infeld scalars, and Galilean internal shift symmetries. Moreover, soft limits imply conditions on the Noether current which can then be inverted to derive Lagrangians for each theory. We propose a natural classification of all scalar effective field theories according to two numbers which encode the derivative power counting and soft behavior of the corresponding amplitudes. In those cases where there is no consistent amplitude, the corresponding theory does not exist.
NASA Astrophysics Data System (ADS)
Zhou, Deng
2016-10-01
The dispersion relation of geodesic acoustic modes with a magnetic perturbation in the tokamak plasma with an equilibrium radial electric field was derived. The dispersion relation was analyzed for very low field strength. The mode frequency decreases with increasing field strength, which is different from the electrostatic geodesic acoustic mode. There exists an m = 1 magnetic component that is very low when the radial electric field is absent. The ratio between the m = 1 and m = 2 magnetic components increases with strength of the radial electric field for low Mach numbers.
An improved method for the calculation of Near-Field Acoustic Radiation Modes
NASA Astrophysics Data System (ADS)
Liu, Zu-Bin; Maury, Cédric
2016-02-01
Sensing and controlling Acoustic Radiation Modes (ARMs) in the near-field of vibrating structures is of great interest for broadband noise reduction or enhancement, as ARMs are velocity distributions defined over a vibrating surface, that independently and optimally contribute to the acoustic power in the acoustic field. But present methods only provide far-field ARMs (FFARMs) that are inadequate for the acoustic near-field problem. The Near-Field Acoustic Radiation Modes (NFARMs) are firstly studied with an improved numerical method, the Pressure-Velocity method, which rely on the eigen decomposition of the acoustic transfers between the vibrating source and a conformal observation surface, including sound pressure and velocity transfer matrices. The active and reactive parts of the sound power are separated and lead to the active and reactive ARMs. NFARMs are studied for a 2D baffled beam and for a 3D baffled plate, and so as differences between the NFARMS and the classical FFARMs. Comparisons of the NFARMs are analyzed when varying frequency and observation distance to the source. It is found that the efficiencies and shapes of the optimal active ARMs are independent on the distance while that of the reactive ones are distinctly related on.
Excitation of geodesic acoustic modes by external fields.
Hallatschek, K; McKee, G R
2012-12-14
It is planned to use external magnetic perturbations at acoustic frequencies at the DIII-D tokamak to attempt to drive geodesic acoustic modes (GAM) to modify the turbulent transport. We show that this might not only be possible--despite the well-known electrostatic nature of the GAMs--but might be a viable and efficient method to generate GAMs in magnetically confined plasmas, by developing an elegant analytic method which allows us to couple numerical dynamic equilibrium calculations with massively parallel non-Boussinesq turbulence code runs and yields practical estimates of the effectivity of the method.
Direct-field acoustic testing of a flight system : logistics, challenges, and results.
Stasiunas, Eric Carl; Gurule, David Joseph; Babuska, Vit; Skousen, Troy J.
2010-10-01
Before a spacecraft can be considered for launch, it must first survive environmental testing that simulates the launch environment. Typically, these simulations include vibration testing performed using an electro-dynamic shaker. For some spacecraft however, acoustic excitation may provide a more severe loading environment than base shaker excitation. Because this was the case for a Sandia Flight System, it was necessary to perform an acoustic test prior to launch in order to verify survival due to an acoustic environment. Typically, acoustic tests are performed in acoustic chambers, but because of scheduling, transportation, and cleanliness concerns, this was not possible. Instead, the test was performed as a direct field acoustic test (DFAT). This type of test consists of surrounding a test article with a wall of speakers and controlling the acoustic input using control microphones placed around the test item, with a closed-loop control system. Obtaining the desired acoustic input environment - proto-flight random noise input with an overall sound pressure level (OASPL) of 146.7 dB-with this technique presented a challenge due to several factors. An acoustic profile with this high OASPL had not knowingly been obtained using the DFAT technique prior to this test. In addition, the test was performed in a high-bay, where floor space and existing equipment constrained the speaker circle diameter. And finally, the Flight System had to be tested without contamination of the unit, which required a contamination bag enclosure of the test unit. This paper describes in detail the logistics, challenges, and results encountered while performing a high-OASPL, direct-field acoustic test on a contamination-sensitive Flight System in a high-bay environment.
Coherent anti-Stokes Raman scattering under electric field stimulation
NASA Astrophysics Data System (ADS)
Capitaine, Erwan; Ould Moussa, Nawel; Louot, Christophe; Lefort, Claire; Pagnoux, Dominique; Duclère, Jean-René; Kaneyasu, Junya F.; Kano, Hideaki; Duponchel, Ludovic; Couderc, Vincent; Leproux, Philippe
2016-12-01
We introduce an experiment using electro-CARS, an electro-optical method based on the combination of ultrabroadband multiplex coherent anti-Stokes Raman scattering (M-CARS) spectroscopy and electric field stimulation. We demonstrate that this method can effectively discriminate the resonant CARS signal from the nonresonant background owing to a phenomenon of molecular orientation in the sample medium. Such molecular orientation is intrinsically related to the induction of an electric dipole moment by the applied static electric field. Evidence of the electro-CARS effect is obtained with a solution of n -alkanes (CnH2 n +2 , 15 ≤n ≤40 ), for which an enhancement of the CARS signal-to-noise ratio is achieved in the case of CH2 and CH3 symmetric/asymmetric stretching vibrations. Additionally, an electric-field-induced second-harmonic generation experiment is performed in order to corroborate the orientational organization of molecules due to the electric field excitation. Finally, we use a simple mathematical approach to compare the vibrational information extracted from electro-CARS measurements with spontaneous Raman data and to highlight the impact of electric stimulation on the vibrational signal.
Generalizations of Karp's theorem to elastic scattering theory
NASA Astrophysics Data System (ADS)
Tuong, Ha-Duong
Karp's theorem states that if the far field pattern corresponding to the scattering of a time-harmonic acoustic plane wave by a sound-soft obstacle in R2 is invariant under the group of rotations, then the scatterer is a circle. The theorem is generalized to the elastic scattering problems and the axisymmetric scatterers in R3.
Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave
NASA Astrophysics Data System (ADS)
Solikhov, D. K.; Dvinin, S. A.
2016-06-01
Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.
Acoustic confinement in superlattice cavities
NASA Astrophysics Data System (ADS)
Garcia-Sanchez, Daniel; Déleglise, Samuel; Thomas, Jean-Louis; Atkinson, Paola; Lagoin, Camille; Perrin, Bernard
2016-09-01
The large coupling rate between the acoustic and optical fields confined in GaAs/AlAs superlattice cavities makes them appealing systems for cavity optomechanics. We have developed a mathematical model based on the scattering matrix that allows the acoustic guided modes to be predicted in nano and micropillar superlattice cavities. We demonstrate here that the reflection at the surface boundary considerably modifies the acoustic quality factor and leads to significant confinement at the micropillar center. Our mathematical model also predicts unprecedented acoustic Fano resonances on nanopillars featuring small mode volumes and very high mechanical quality factors, making them attractive systems for optomechanical applications.
NASA Technical Reports Server (NTRS)
Bogdan, Thomas J.; Cattaneo, Fausto
1989-01-01
Motivated by considerations of the interaction between fibril magnetic fields and solar p-modes, the acoustic spectrum of a cylindrical cavity filled with ideal gas in which a number of magnetic flux tubes are embedded is studied. A formalism, based on the T-matrix approach to acoustic scattering, is developed which can be used to determine the eigenfrequencies and eigenfunctions for any arbitrary distribution of flux tubes. For weak scatterers, the frequency shifts and velocity eigenfunctions are calculated using perturbation theory for the cases of a single flux tube and a random distribution of up to 100 flux tubes. The results of this 'exact' approach are used to give a critical appraisal of the predictions of theories based on some form of averaging, such as the one discussed recently by Bogdan and Zweibel (1987).
Influence of confined acoustic phonons on the Radioelectric field in a Quantum well
NASA Astrophysics Data System (ADS)
Long, Do Tuan; Quang Bau, Nguyen
2015-06-01
The influence of confined acoustic phonons on the Radioelectric field in a quantum well has been studied in the presence of a linearly polarized electromagnetic wave and a laser radiation. By using the quantum kinetic equation for electrons with confined electrons - confined acoustic phonons interaction, the analytical expression for the Radio electric field is obtained. The formula of the Radio electric field contains the quantum number m characterizing the phonons confinement and comes back to the case of unconfined phonons when m reaches to zero. The dependence of the Radio electric field on the frequency of the laser radiation, in case of confined acoustic phonons, is also achieved by numerical method for a specific quantum well AlGaAs/GaAs/AlGaAs. Results show that the Radio electric field has a peak and reaches saturation as the frequency of the laser radiation increases.
Thermo acoustic study of carbon nanotubes in near and far field: Theory, simulation, and experiment
NASA Astrophysics Data System (ADS)
Asadzadeh, S. S.; Moosavi, A.; Huynh, C.; Saleki, O.
2015-03-01
Carbon nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic effect of these sound sources both in near and far field regions. Based on two alternative forms of the energy equation, we have developed a straightforward formula for calculation of pressure field, which is consistent with experimental data in far field. Also we have solved full 3-D governing equations using numerical methods. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. However, generation of sound waves in far field is independent of projectors area surface. Energy analysis for free standing Thermo-Acoustic (TA) sound sources show that aerogel TA sound sources like CNT based projectors could act more efficiently compared to the other sources in delivering more than 75% of alternative input energy to the medium gas up to a frequency of 1 MHz.
NATO TG-53: acoustic detection of weapon firing joint field experiment
NASA Astrophysics Data System (ADS)
Robertson, Dale N.; Pham, Tien; Scanlon, Michael V.; Srour, Nassy; Reiff, Christian G.; Sim, Leng K.; Solomon, Latasha; Thompson, Dorothea F.
2006-05-01
In this paper, we discuss the NATO Task Group 53 (TG-53) acoustic detection of weapon firing field joint experiment at Yuma Proving Ground during 31 October to 4 November 2005. The participating NATO countries include France, the Netherlands, UK and US. The objectives of the joint experiments are: (i) to collect acoustic signatures of direct and indirect firings from weapons such as sniper, mortar, artillery and C4 explosives and (ii) to share signatures among NATO partners from a variety of acoustic sensing platforms on the ground and in the air distributed over a wide area.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.
2015-05-01
We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implicationsmore » of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.« less
An effective field theory for coupled-channel scattering
NASA Astrophysics Data System (ADS)
Cohen, Thomas D.; Gelman, Boris A.; van Kolck, U.
2004-05-01
The problem of describing low-energy two-body scattering for systems with two open channels with different thresholds is addressed in the context of an effective field theory. In particular, the problem where the threshold is unnaturally small and the cross section at low energy is unnaturally large is considered. It is shown that the lowest-order point coupling associated with the mixing of the channels scales as Λ-2 rather than Λ-1 (the scaling of the same-channel coupling and the scaling in a single-channel case) where Λ is the ultraviolet cutoff. The renormalization of the theory at lowest order is given explicitly. The treatment of higher orders is straightforward. The potential implications for systems with deep open channels are discussed.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.; Cabrera, B.; Cerdeño, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, P.; Daal, M.; Di Stefano, P. C. F.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, J.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, P.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.
2015-05-18
We examine the consequences of the effective field theory (EFT) of dark matter-nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. Here. we demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. In conclusion, we discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Quantifying truncation errors in chiral effective field theory: NN scattering
NASA Astrophysics Data System (ADS)
Phillips, Daniel; Melendez, Jordan; Wesolowski, Sarah; Furnstahl, Richard; Klco, Natalie; Buqeye Collaboration
2017-01-01
Bayesian procedures designed to quantify truncation errors in perturbative calculations were recently adapted to expansions in effective field theory (EFT). By encoding expectations about the naturalness of EFT coefficients in Bayesian priors, this framework provides a statistical interpretation of the standard EFT procedure where truncation errors are estimated using the order-by-order convergence of the expansion. It also permits exploration of the ways in which such error bars are, and are not, sensitive to assumptions about EFT-coefficient naturalness. The procedure has been applied to chiral EFT calculations of neutron-proton scattering that use the semi-local potentials of Epelbaum, Krebs, and Meißner. This talk describes the Bayesian assignment of truncation errors for the total np cross section at a discrete set of energies, and then considers the extension to a full set of observables and arbitrary energy. This research was supported by the US Department of Energy and the National Science Foundation.
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.
2015-05-01
We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
NASA Astrophysics Data System (ADS)
Cui, Weiwei; Zhang, Hao; Zhang, Hongxiang; Yang, Yang; He, Meihang; Qu, Hemi; Pang, Wei; Zhang, Daihua; Duan, Xuexin
2016-12-01
We present an acoustic microfluidic mixing approach via acousto-mechanically induced micro-vortices sustained by localized ultrahigh frequency (UHF) acoustic fields. A micro-fabricated solid-mounted thin-film piezoelectric resonator (SMR) with a frequency of 1.54 GHz has been integrated into microfluidic systems. Experimental and simulation results show that UHF-SMR triggers strong acoustic field gradients to produce efficient and highly localized acoustic streaming vortices, providing a powerful source for microfluidic mixing. Homogeneous mixing with 87% mixing efficiency at a Peclet number of 35520 within 1 ms has been achieved. The proposed strategy shows a great potential for microfluidic mixing and enhanced molecule transportation in minimized analytical systems.
Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue
Treweek, Benjamin C. Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.
2015-10-28
Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitude and direction, which may enable more accurate noninvasive determination of tissue properties.
Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue
NASA Astrophysics Data System (ADS)
Treweek, Benjamin C.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.
2015-10-01
Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitude and direction, which may enable more accurate noninvasive determination of tissue properties.
Scattering amplitudes over finite fields and multivariate functional reconstruction
NASA Astrophysics Data System (ADS)
Peraro, Tiziano
2016-12-01
Several problems in computer algebra can be efficiently solved by reducing them to calculations over finite fields. In this paper, we describe an algorithm for the reconstruction of multivariate polynomials and rational functions from their evaluation over finite fields. Calculations over finite fields can in turn be efficiently performed using machine-size integers in statically-typed languages. We then discuss the application of the algorithm to several techniques related to the computation of scattering amplitudes, such as the four- and six-dimensional spinor-helicity formalism, tree-level recursion relations, and multi-loop integrand reduction via generalized unitarity. The method has good efficiency and scales well with the number of variables and the complexity of the problem. As an example combining these techniques, we present the calculation of full analytic expressions for the two-loop five-point on-shell integrands of the maximal cuts of the planar penta-box and the non-planar double-pentagon topologies in Yang-Mills theory, for a complete set of independent helicity configurations.
NASA Astrophysics Data System (ADS)
Diaz, Sandra; Chopra, Rajiv; Pichardo, Samuel
2012-11-01
In this work we present a model to calculate the acoustic pressure generated by the interaction of forward and reflected waves in the vicinity of a solid interface and compare it to experimental data. An experimental setup was designed to measure the forward and the combined forward-reflected acoustic fields produced by a solid interface. A 0.785mm-needle hydrophone was used to characterize the acoustic field produced by a 7.29MHz-ultrasound transducer focused at 6cm. The hydrophone was positioned perpendicularly to the sound propagation direction and moved between the transducer and a 9mm-thick acrylic sample using a robotic arm. Simulations were carried out using a modified Rayleigh-Sommerfeld integral that calculates the particle displacement over a reflecting surface. This particle displacement at the boundary of the interface is then used as an acoustic source to obtain the reflected particle displacement. The complex sum of the forward and reflected fields was compared to the experimental measurements. The measurements showed an interference pattern that increased the pressure amplitude in average 10.4% with peaks of up to 25.8%. The proposed model is able to represent the interference pattern produced by the reflected wave with an average absolute error of 3.4+/-0.54% and a maximal error of 5.6%. The comparison between the experimental measurements and the simulations indicates that the presented model predicts with good accuracy the acoustic field generated by ultrasound transducers facing a solid interface. This model can be used to foresee the outcome of therapeutic applications where the devices are used in proximity to a bone interface.
Polymer coating of glass microballoons levitated in a focused acoustic field
Young, A.T.; Lee, M.C.; Feng, I.A.; Elleman, D.D.; Wang, T.G.
1981-01-01
Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, uv-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.
Customization of the acoustic field produced by a piezoelectric array through interelement delays
Chitnis, Parag V.; Barbone, Paul E.; Cleveland, Robin O.
2008-01-01
A method for producing a prescribed acoustic pressure field from a piezoelectric array was investigated. The array consisted of 170 elements placed on the inner surface of a 15 cm radius spherical cap. Each element was independently driven by using individual pulsers each capable of generating 1.2 kV. Acoustic field customization was achieved by independently controlling the time when each element was excited. The set of time delays necessary to produce a particular acoustic field was determined by using an optimization scheme. The acoustic field at the focal plane was simulated by using the angular spectrum method, and the optimization searched for the time delays that minimized the least squared difference between the magnitudes of the simulated and desired pressure fields. The acoustic field was shaped in two different ways: the −6 dB focal width was increased to different desired widths and the ring-shaped pressure distributions of various prescribed diameters were produced. For both cases, the set of delays resulting from the respective optimization schemes were confirmed to yield the desired pressure distributions by using simulations and measurements. The simulations, however, predicted peak positive pressures roughly half those obtained from the measurements, which was attributed to the exclusion of nonlinearity in the simulations. PMID:18537369
Muir, Thomas G; Costley, R Daniel; Sabatier, James M
2014-01-01
Finite element methods are utilized to model and compare the use of both a remote loudspeaker and a vertical shaker in the generation of sound and shear and interface waves in an elastic solid containing an imbedded elastic scatterer, which is resonant. Results for steady state and transient insonification are presented to illustrate excitation, propagation, and scattering mechanisms and effects. Comparisons of acoustic and vibratory excitation of the solid interface are made, with a view towards remote sensing of induced vibratory motion through optical measurement of the ground interface motion above the imbedded inclusion. Some advantages of the acoustic excitation method for exciting plate mode resonances in the target are observed.
Numerical Analysis of the Acoustic Field of Tip-Clearance Flow
NASA Astrophysics Data System (ADS)
Alavi Moghadam, S. M.; M. Meinke Team; W. Schröder Team
2015-11-01
Numerical simulations of the acoustic field generated by a shrouded axial fan are studied by a hybrid fluid-dynamics-acoustics method. In a first step, large-eddy simulations are performed to investigate the dynamics of tip clearance flow for various tip gap sizes and to determine the acoustic sources. The simulations are performed for a single blade out of five blades with periodic boundary conditions in the circumferential direction on a multi-block structured mesh with 1.4 ×108 grid points. The turbulent flow is simulated at a Reynolds number of 9.36 ×105 at undisturbed inflow condition and the results are compared with experimental data. The diameter and strength of the tip vortex increase with the tip gap size, while simultaneously the efficiency of the fan decreases. In a second step, the acoustic field on the near field is determined by solving the acoustic perturbation equations (APE) on a mesh for a single blade consisting of approx. 9.8 ×108 grid points. The overall agreement of the pressure spectrum and its directivity with measurements confirm the correct identification of the sound sources and accurate prediction of the acoustic duct propagation. The results show that the longer the tip gap size the higher the broadband noise level. Senior Scientist, Institute of Aerodynamics, RWTH Aachen University.
Daeva, S.G.; Setukha, A.V.
2015-03-10
A numerical method for solving a problem of diffraction of acoustic waves by system of solid and thin objects based on the reduction the problem to a boundary integral equation in which the integral is understood in the sense of finite Hadamard value is proposed. To solve this equation we applied piecewise constant approximations and collocation methods numerical scheme. The difference between the constructed scheme and earlier known is in obtaining approximate analytical expressions to appearing system of linear equations coefficients by separating the main part of the kernel integral operator. The proposed numerical scheme is tested on the solution of the model problem of diffraction of an acoustic wave by inelastic sphere.
NASA Astrophysics Data System (ADS)
Fan, Tingbo; Chen, Tao; Zhang, Wei; Hu, Jimin; Zhang, Yichuan; Zhang, Dong
2017-03-01
A combined experiment and simulation method was utilized to characterize the acoustic field generated from a strong focused HIFU transmitter. The nonlinear sound propagation was described by the spheroidal beam equation (SBE). The relationship between the source pressure amplitude and excitation voltage was determined by fitting the measured ratio of the second harmonic to the fundamental component of the focal waveform to the simulation result; then the acoustic pressure field generated by the strong focused transducer was predicted by using the SBE model. A commercial fiber optic probe hydrophone (FOPH) was utilized to measure the acoustic pressure field generated from a 1.1 MHz HIFU transmitter with a half aperture angle of 30°. The validity of this combined approach was confirmed by the comparison between the measured results and the calculated ones. The results show that the current approach might be useful to describe the HIFU field.
Wu, Sean F; Moondra, Manmohan; Beniwal, Ravi
2015-04-01
The Helmholtz equation least squares (HELS)-based nearfield acoustical holography (NAH) is utilized to analyze panel acoustic contributions toward the acoustic field inside the interior region of an automobile. Specifically, the acoustic power flows from individual panels are reconstructed, and relative contributions to sound pressure level and spectrum at any point of interest are calculated. Results demonstrate that by correlating the acoustic power flows from individual panels to the field acoustic pressure, one can correctly locate the panel allowing the most acoustic energy transmission into the vehicle interior. The panel on which the surface acoustic pressure amplitude is the highest should not be used as indicative of the panel responsible for the sound field in the vehicle passenger compartment. Another significant advantage of this HELS-based NAH is that measurements of the input data only need to be taken once by using a conformal array of microphones in the near field, and ranking of panel acoustic contributions to any field point can be readily performed. The transfer functions between individual panels of any vibrating structure to the acoustic pressure anywhere in space are calculated not measured, thus significantly reducing the time and effort involved in panel acoustic contributions analyses.
Dexterous manipulation of microparticles using Bessel-function acoustic pressure fields
NASA Astrophysics Data System (ADS)
Courtney, Charles R. P.; Drinkwater, Bruce W.; Demore, Christine E. M.; Cochran, Sandy; Grinenko, Alon; Wilcox, Paul D.
2013-03-01
We show that Bessel-function acoustic pressure fields can be used to trap and controllably position microparticles. A circular, 16-element ultrasound array generates and manipulates an acoustic field within a chamber, trapping microparticles and agglomerates. Changes in the phase of the sinusoidal signals applied to the array elements result in the movement of the Bessel-function pressure field and hence the microparticles. This demonstrates ultrasonic manipulation analogous to holographic optical tweezers. The manipulation limits of the device are explained by the existence of unwanted resonances within the manipulation chamber.
Prediction of the acoustic and bubble fields in insonified freeze-drying vials.
Louisnard, O; Cogné, C; Labouret, S; Montes-Quiroz, W; Peczalski, R; Baillon, F; Espitalier, F
2015-09-01
The acoustic field and the location of cavitation bubble are computed in vials used for freeze-drying, insonified from the bottom by a vibrating plate. The calculations rely on a nonlinear model of sound propagation in a cavitating liquid [Louisnard, Ultrason. Sonochem., 19, (2012) 56-65]. Both the vibration amplitude and the liquid level in the vial are parametrically varied. For low liquid levels, a threshold amplitude is required to form a cavitation zone at the bottom of the vial. For increasing vibration amplitudes, the bubble field slightly thickens but remains at the vial bottom, and the acoustic field saturates, which cannot be captured by linear acoustics. On the other hand, increasing the liquid level may promote the formation of a secondary bubble structure near the glass wall, a few centimeters below the free liquid surface. These predictions suggest that rather complex acoustic fields and bubble structures can arise even in such small volumes. As the acoustic and bubble fields govern ice nucleation during the freezing step, the final crystal's size distribution in the frozen product may crucially depend on the liquid level in the vial.
Full-Field Imaging of Acoustic Motion at Nanosecond Time and Micron Length Scales
Telschow, Kenneth Louis; Deason, Vance Albert; Cottle, David Lynn; Larson III, John D.
2002-10-01
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 employing dynamic holography using photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed capable of operation on the nanosecond time 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 at 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 and performance of these devices. Images of 256x240 pixels are recorded at 18Hz rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level 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.
Recovery of burner acoustic source structure from far-field sound spectra
NASA Technical Reports Server (NTRS)
Mahan, J. R.; Jones, J. D.
1984-01-01
A method is presented that permits the thermal-acoustic efficiency spectrum in a long turbulent burner to be recovered from the corresponding far-field sound spectrum. An acoustic source/propagation model is used 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 technique is applied to a long cylindrical hydrogen-flame burner operating over power levels of 4.5-22.3 kW. The results show that the thermal-acoustic efficiency at a given frequency, defined as the fraction of the total burner power converted to acoustic energy at that frequency, is rather insensitive to burner power, having a maximum value on the order of 10 to the -4th at 150 Hz and rolling off steeply with increasing frequency. Evidence is presented that acoustic agitation of the flame at low frequencies enhances the mixing of the unburned fuel and air with the hot products of combustion. The paper establishes the potential of the technique as a useful tool for characterizing the acoustic source structure in any burner, such as a gas turbine combustor, for which a reasonable acoustic propagation model can be postulated.
Liu, Gang; Jayathilake, Pahala G; Khoo, Boo Cheong; Han, Feng; Liu, Dian Kui
2012-02-01
The complex variables method with mapping function was extended to solve the linear acoustic wave scattering by an inclusion with sharp/smooth corners in an infinite ideal fluid domain. The improved solutions of Helmholtz equation, shown as Bessel function with mapping function as the argument and fractional order Bessel function, were analytically obtained. Based on the mapping function, the initial geometry as well as the original physical vector can be transformed into the corresponding expressions inside the mapping plane. As all the physical vectors are calculated in the mapping plane (η,η), this method can lead to potential vast savings of computational resources and memory. In this work, the results are validated against several published works in the literature. The different geometries of the inclusion with sharp corners based on the proposed mapping functions for irregular polygons are studied and discussed. The findings show that the variation of angles and frequencies of the incident waves have significant influence on the bistatic scattering pattern and the far-field form factor for the pressure in the fluid.
Design of acoustic logging signal source of imitation based on field programmable gate array
NASA Astrophysics Data System (ADS)
Zhang, K.; Ju, X. D.; Lu, J. Q.; Men, B. Y.
2014-08-01
An acoustic logging signal source of imitation is designed and realized, based on the Field Programmable Gate Array (FPGA), to improve the efficiency of examining and repairing acoustic logging tools during research and field application, and to inspect and verify acoustic receiving circuits and corresponding algorithms. The design of this signal source contains hardware design and software design,and the hardware design uses an FPGA as the control core. Four signals are made first by reading the Random Access Memory (RAM) data which are inside the FPGA, then dealing with the data by digital to analog conversion, amplification, smoothing and so on. Software design uses VHDL, a kind of hardware description language, to program the FPGA. Experiments illustrate that the ratio of signal to noise for the signal source is high, the waveforms are stable, and also its functions of amplitude adjustment, frequency adjustment and delay adjustment are in accord with the characteristics of real acoustic logging waveforms. These adjustments can be used to imitate influences on sonic logging received waveforms caused by many kinds of factors such as spacing and span of acoustic tools, sonic speeds of different layers and fluids, and acoustic attenuations of different cementation planes.
Behavior of cylindrical liquid jets evolving in a transverse acoustic field
NASA Astrophysics Data System (ADS)
Carpentier, Jean-Baptiste; Baillot, Françoise; Blaisot, Jean-Bernard; Dumouchel, Christophe
2009-02-01
This paper presents a theoretical and an experimental investigation of low-velocity cylindrical liquid jets submitted to transverse planar acoustic waves. For this purpose, the behavior of a liquid jet traversing the section of a Kundt tube was examined. Experiments reported that the liquid jet could be either deviated from its trajectory or deformed as a succession of lobes oriented in space and whose length and width depend on the jet acoustic environment. Furthermore, for a sufficient acoustic velocity, the jet deformation increases in such proportion that a premature and vivid atomization mechanism disintegrates the liquid flow. Theoretical models are proposed to understand these behaviors. The first one calls out for acoustic radiation pressure to explain the jet deviation. The second one consists in a modal analysis of the vibrations of a jet when submitted to a transverse stationary acoustic field. As a first approach, a simplified two-dimensional model is proposed. This model reports that a sudden exposition of the jet to an acoustic field triggers two jet eigenmodes. One of them induces jet deformations that were not experimentally observed. This part of the solution emerges due to theoretical deficiencies. However, the second mode reproduces the lobe formation and leads to atomization criteria in good agreement with the experimental results. The paper ends with an extension of the mathematical development in three dimensions in order to provide a basis to a more consistent model.
Source fields reconstruction with 3D mapping by means of the virtual acoustic volume concept
NASA Astrophysics Data System (ADS)
Forget, S.; Totaro, N.; Guyader, J. L.; Schaeffer, M.
2016-10-01
This paper presents the theoretical framework of the virtual acoustic volume concept and two related inverse Patch Transfer Functions (iPTF) identification methods (called u-iPTF and m-iPTF depending on the chosen boundary conditions for the virtual volume). They are based on the application of Green's identity on an arbitrary closed virtual volume defined around the source. The reconstruction of sound source fields combines discrete acoustic measurements performed at accessible positions around the source with the modal behavior of the chosen virtual acoustic volume. The mode shapes of the virtual volume can be computed by a Finite Element solver to handle the geometrical complexity of the source. As a result, it is possible to identify all the acoustic source fields at the real surface of an irregularly shaped structure and irrespective of its acoustic environment. The m-iPTF method is introduced for the first time in this paper. Conversely to the already published u-iPTF method, the m-iPTF method needs only acoustic pressure and avoids particle velocity measurements. This paper is focused on its validation, both with numerical computations and by experiments on a baffled oil pan.
NASA Astrophysics Data System (ADS)
Pézerat, C.; Leclère, Q.; Totaro, N.; Pachebat, M.
2009-10-01
This study presents a method of using acoustic holography and the force analysis technique to identify vibration sources from radiated noise measurements. The structure studied is a plate excited by a shaker on which three measurements were performed: the first is a reference measurement of plate velocity obtained by scanning laser vibrometry, the second is based on sound pressure measurements in the near field of the structure, and the third is the measurement of normal acoustic velocities by using a p-U probe recently developed by Microflown Technologies. This was followed by the application of classical NAH, known as pressure-to-velocity holography and velocity-to-velocity holography to predict the plate velocity field from acoustic measurements at distances of 1 and 5 cm. Afterwards, the force analysis technique, also known as the RIFF technique, is applied with these five data sets. The principle is to inject the displacement field of the structure into its equation of motion and extract the resulting force distribution. This technique requires regularization done by a low-pass filter in the wavenumber domain. Apart from pressure-to-velocity holography at 5 cm, the reconstructed force distribution allows localizing the excitation point in the measurement area. FAT regularization is also shown to improve results as its cutoff wavenumber is optimized with the natural wavenumber of the plate. Lastly, quantitative force values are extracted from force distributions at all frequencies of the band 0-4 kHz studied and compared with the force spectrum measured directly by a piezoelectric sensor.
NASA Astrophysics Data System (ADS)
Fujii, Ayaka; Wakatsuki, Naoto; Mizutani, Koichi
2016-01-01
A method of suppressing sound radiation to the far field of a near-field acoustic communication system using an evanescent sound field is proposed. The amplitude of the evanescent sound field generated from an infinite vibrating plate attenuates exponentially with increasing a distance from the surface of the vibrating plate. However, a discontinuity of the sound field exists at the edge of the finite vibrating plate in practice, which broadens the wavenumber spectrum. A sound wave radiates over the evanescent sound field because of broadening of the wavenumber spectrum. Therefore, we calculated the optimum distribution of the particle velocity on the vibrating plate to reduce the broadening of the wavenumber spectrum. We focused on a window function that is utilized in the field of signal analysis for reducing the broadening of the frequency spectrum. The optimization calculation is necessary for the design of window function suitable for suppressing sound radiation and securing a spatial area for data communication. In addition, a wide frequency bandwidth is required to increase the data transmission speed. Therefore, we investigated a suitable method for calculating the sound pressure level at the far field to confirm the variation of the distribution of sound pressure level determined on the basis of the window shape and frequency. The distribution of the sound pressure level at a finite distance was in good agreement with that obtained at an infinite far field under the condition generating the evanescent sound field. Consequently, the window function was optimized by the method used to calculate the distribution of the sound pressure level at an infinite far field using the wavenumber spectrum on the vibrating plate. According to the result of comparing the distributions of the sound pressure level in the cases with and without the window function, it was confirmed that the area whose sound pressure level was reduced from the maximum level to -50 dB was
Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire.
Jean, Cyril; Belliard, Laurent; Cornelius, Thomas W; Thomas, Olivier; Pennec, Yan; Cassinelli, Marco; Toimil-Molares, Maria Eugenia; Perrin, Bernard
2016-10-12
The monochromatic and geometrically anisotropic acoustic field generated by 400 and 120 nm diameter copper nanowires simply dropped on a 10 μm silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both sides of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite difference time domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.
Near- and Far-field Response to Compact Acoustic Sources in Stratified Convection Zones
NASA Astrophysics Data System (ADS)
Cally, Paul S.
2013-05-01
The role of the acoustic continuum associated with compact sources in the Sun's interior wave field is explored for a simple polytropic model. The continuum produces a near-field acoustic structure—the so-called acoustic jacket—that cannot be represented by a superposition of discrete normal modes. Particular attention is paid to monochromatic point sources of various frequency and depth, and to the surface velocity power that results, both in the discrete f- and p-mode spectrum and in the continuum. It is shown that a major effect of the continuum is to heal the surface wave field produced by compact sources, and therefore to hide them from view. It is found that the continuous spectrum is not a significant contributor to observable inter-ridge seismic power.
Beam stresses induced by a turbulent boundary layer and simulated with a reverberant acoustic field
NASA Technical Reports Server (NTRS)
Schutzenhofer, L. A.
1981-01-01
Unsteady pressure fluctuations are a feature of the flow field of an airplane or a space vehicle in atmospheric flight. Undesirable effects of these fluctuations range from internal (cabin) noise to structural fatigue and damage of avionic and ordnance systems. The integrity to withstand these fluctuating loads is established through reverberant room acoustical qualification testing. The purpose of this paper is to develop a methodology of simulating turbulent boundary layer fluctuating pressure loading for a simply supported beam with a reverberant acoustic field. This goal was accomplished using normal mode vibration analysis. The main results were developed in terms of dimensionless quantities such as turbulent boundary layer spectrums, reverberant acoustical field simulation spectrums, and stress response spectrums with parameters: dimensionless fundamental frequency, Mach number, and relative boundary layer displacement thickness.
NASA Astrophysics Data System (ADS)
Bolghasi, Alireza; Ghadimi, Parviz; Chekab, Mohammad A. Feizi
2016-09-01
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz-Kirchhoff-Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall-Novarini model and optimized HKF method. The extended Hall-Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
Active control of acoustic pressure fields using smart material technologies
NASA Technical Reports Server (NTRS)
Banks, H. T.; Smith, R. C.
1993-01-01
An overview describing the use of piezoceramic patches in reducing noise in a structural acoustics setting is presented. The passive and active contributions due to patches which are bonded to an Euler-Bernoulli beam or thin shell are briefly discussed and the results are incorporated into a 2-D structural acoustics model. In this model, an exterior noise source causes structural vibrations which in turn lead to interior noise as a result of nonlinear fluid/structure coupling mechanism. Interior sound pressure levels are reduced via patches bonded to the flexible boundary (a beam in this case) which generate pure bending moments when an out-of-phase voltage is applied. Well-posedness results for the infinite dimensional system are discussed and a Galerkin scheme for approximating the system dynamics is outlined. Control is implemented by using linear quadratic regulator (LQR) optimal control theory to calculate gains for the linearized system and then feeding these gains back into the nonlinear system of interest. The effectiveness of this strategy for this problem is illustrated in an example.
Flow Field and Acoustic Predictions for Three-Stream Jets
NASA Technical Reports Server (NTRS)
Simmons, Shaun Patrick; Henderson, Brenda S.; Khavaran, Abbas
2014-01-01
Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE.
2015-09-30
surrounding these aggregations to identify key parameters related to the distribution and behavior of these animals . These parameters will be used to...large sample size combined with careful measures of swimbladder shape, reproductive condition, stomach fullness, and other independent variables will...allow us to examine the effects of biological variability on acoustic characteristics of these animals . Finally, a number of these individual animals
NASA Astrophysics Data System (ADS)
Hetmaniuk, Ulrich Ladislas
Fast solvers are often designed for problems posed on simple domains. Unfortunately, engineering applications deal with arbitrary domains. To allow the use of fast solvers, fictitious domain methods have been developed. They usually define an auxiliary problem on a rectangle or a parallelepiped. In aerospace and military applications, many scatterers are composed of one major axisymmetric component and a few features. Therefore, the aim of this thesis is to define, for the scattering of acoustic waves, fictitious domain methods which exploit such local axisymmetry. The original exterior problem is first approximated by introducing an absorbing boundary condition on an artificial boundary. A family of absorbing conditions is reviewed. For some simple scatterers, numerical experiments on the position of the artificial boundary reveal that the error induced by the absorbing condition is bounded, as the wave number increases, when the artificial boundary is fixed. Then, for a class of partially axisymmetric scatterers, the truncated computational domain is embedded into an axisymmetric domain. Helmholtz problems are formulated inside this axisymmetric domain and inside each feature. Lagrange multipliers are introduced at the interfaces between the features and the axisymmetric domain to enforce a set of carefully constructed constraints. This formulation is analyzed at the continuous level and is shown to be equivalent to the original one. For the Helmholtz equation defined over the axisymmetric domain, the solution is approximated by truncated Fourier series and finite elements. Properties of this discretization method for the Helmholtz equation are also analyzed on a two-dimensional model problem. Numerical experiments are performed to illustrate the analytical results. For the auxiliary problem inside each feature, classical finite elements are used to approximate the solution. The constraints are enforced pointwise. The resulting algebraic system is solved either
Prediction of sound fields in acoustical cavities using the boundary element method. M.S. Thesis
NASA Technical Reports Server (NTRS)
Kipp, C. R.; Bernhard, R. J.
1985-01-01
A method was developed to predict sound fields in acoustical cavities. The method is based on the indirect boundary element method. An isoparametric quadratic boundary element is incorporated. Pressure, velocity and/or impedance boundary conditions may be applied to a cavity by using this method. The capability to include acoustic point sources within the cavity is implemented. The method is applied to the prediction of sound fields in spherical and rectangular cavities. All three boundary condition types are verified. Cases with a point source within the cavity domain are also studied. Numerically determined cavity pressure distributions and responses are presented. The numerical results correlate well with available analytical results.
Geodesic acoustic modes in tokamak plasmas with a radial equilibrium electric field
Zhou, Deng
2015-09-15
The dispersion relation of geodesic acoustic modes in the tokamak plasma with an equilibrium radial electric field is derived and analyzed. Multiple branches of eigenmodes have been found, similar to the result given by the fluid model with a poloidal mass flow. Frequencies and damping rates of both the geodesic acoustic mode and the sound wave increase with respect to the strength of radial electric field, while the frequency and the damping rate of the lower frequency branch slightly decrease. Possible connection to the experimental observation is discussed.
Mizuno, K.; DeGroot, J.S.; Seka, W. l Drake, R.P.
1991-12-31
We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.1. In high power laser regime, the spectrum become broad, and the {alpha}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations. 20 refs.
Mizuno, K.; DeGroot, J.S. ); Seka, W. . Lab. for Laser Energetics)l Drake, R.P. )
1991-01-01
We have developed 5-channel collective Thomson scattering system to measure the ion acoustic wave excited by the ion acoustic wave decay instabilities. The multichannel collective Thomson scattering technique was established with 4{omega} probe laser beam using GDL laser system at LLE, Univ. of Rochester. We have obtained the ionic charge state Z by measuring the second harmonic emission from the ion acoustic decay instability. The LASNEX computer simulation calculations have been carried out. The experimental results agree very well with the LASNEX computer simulation results with the flux number f=0.1. In high power laser regime, the spectrum become broad, and the {alpha}{gamma} decreases indicating that the turbulent like spectrum is observed. In order to understand the experimental results, we have developed a theory to study absorption of laser and heat transport. This new theory includes the temporal evolution of the heat conduction region. The results agree with flux-limited hydrodynamic simulations. 20 refs.
On reconstruction of acoustic pressure fields using the Helmholtz equation least squares method
Wu
2000-05-01
This paper presents analyses and implementation of the reconstruction of acoustic pressure fields radiated from a general, three-dimensional complex vibrating structure using the Helmholtz equation least-squares (HELS) method. The structure under consideration emulates a full-size four-cylinder engine. To simulate sound radiation from a vibrating structure, harmonic excitations are assumed to act on arbitrarily selected surfaces. The resulting vibration responses are solved by the commercial FEM (finite element method) software I-DEAS. Once the normal component of the surface velocity distribution is determined, the surface acoustic pressures are calculated using standard boundary element method (BEM) codes. The radiated acoustic pressures over several planar surfaces at certain distances from the source are calculated by the Helmholtz integral formulation. These field pressures are taken as the input to the HELS formulation to reconstruct acoustic pressures on the entire source surface, as well as in the field. The reconstructed acoustic pressures thus obtained are then compared with benchmark values. Numerical results demonstrate that good agreements can be obtained with relatively few expansion functions. The HELS method is shown to be very effective in the low-to-mid frequency regime, and can potentially become a powerful noise diagnostic tool.
Acoustic scattering from a finite plate: generation of guided Lamb waves S(0), A(0) and A.
Cité, N; Chati, F; Décultot, D; Léon, F; Maze, G
2012-06-01
In the domain of renewable energies, marine current turbines constitute one of the possibilities of producing electrical energy. Naked-eye inspection, or with the aid of video monitoring systems of these machines to ensure their perfect working order, can be difficult in a turbid environment. Acoustic methods are conceivable. The study focuses on the blades of these machines, by considering rectangular plates. The propagation of Lamb waves in a plate is studied by analyzing experimental time signals obtained from acoustic scattering. These signals are analyzed employing the ray theory. In vacuum, the flexural wave is the A(0) Lamb wave, whilst in water this wave splits in a bifurcation: the A wave with a phase velocity always smaller than the sound speed in water, and the A(0) wave with a phase velocity always higher than the sound speed in water. In the central bandpass of the transducers used in the experiments, mainly the A and S(0) waves exist. However, signals observed in the third harmonic bandpass of the transducers are also analyzed. In order to complement these results, resonance frequencies of the plate studied are calculated taking into account the boundary conditions and compared with the resonance frequencies of the experimental spectra.
The optimization of acoustic fields for ablative therapies of tumours in the upper abdomen
NASA Astrophysics Data System (ADS)
Gélat, P.; ter Haar, G.; Saffari, N.
2012-12-01
High intensity focused ultrasound (HIFU) enables highly localized, non-invasive tissue ablation and its efficacy has been demonstrated in the treatment of a range of cancers, including those of the kidney, prostate and breast. HIFU offers the ability to treat deep-seated tumours locally, and potentially bears fewer side effects than more invasive treatment modalities such as resection, chemotherapy and ionizing radiation. There remains however a number of significant challenges which currently hinder its widespread clinical application. One of these challenges is the need to transmit sufficient energy through the ribcage to ablate tissue at the required foci whilst minimizing the formation of side lobes and sparing healthy tissue. Ribs both absorb and reflect ultrasound strongly. This sometimes results in overheating of bone and overlying tissue during treatment, leading to skin burns. Successful treatment of a patient with tumours in the upper abdomen therefore requires a thorough understanding of the way acoustic and thermal energy is deposited. Previously, a boundary element approach based on a Generalized Minimal Residual (GMRES) implementation of the Burton-Miller formulation was developed to predict the field of a multi-element HIFU array scattered by human ribs, the topology of which was obtained from CT scan data (Gélat et al 2011 Phys. Med. Biol. 56 5553-81). The present paper describes the reformulation of the boundary element equations as a least-squares minimization problem with nonlinear constraints. The methodology has subsequently been tested at an excitation frequency of 1 MHz on a spherical multi-element array in the presence of ribs. A single array-rib geometry was investigated on which a 50% reduction in the maximum acoustic pressure magnitude on the surface of the ribs was achieved with only a 4% reduction in the peak focal pressure compared to the spherical focusing case. This method was then compared with a binarized apodization approach
High amplitude nonlinear acoustic wave driven flow fields in cylindrical and conical resonators.
Antao, Dion Savio; Farouk, Bakhtier
2013-08-01
A high fidelity computational fluid dynamic model is used to simulate the flow, pressure, and density fields generated in a cylindrical and a conical resonator by a vibrating end wall/piston producing high-amplitude standing waves. The waves in the conical resonator are found to be shock-less and can generate peak acoustic overpressures that exceed the initial undisturbed pressure by two to three times. A cylindrical (consonant) acoustic resonator has limitations to the output response observed at one end when the opposite end is acoustically excited. In the conical geometry (dissonant acoustic resonator) the linear acoustic input is converted to high energy un-shocked nonlinear acoustic output. The model is validated using past numerical results of standing waves in cylindrical resonators. The nonlinear nature of the harmonic response in the conical resonator system is further investigated for two different working fluids (carbon dioxide and argon) operating at various values of piston amplitude. The high amplitude nonlinear oscillations observed in the conical resonator can potentially enhance the performance of pulse tube thermoacoustic refrigerators and these conical resonators can be used as efficient mixers.
Deep ocean sound speed characteristics passively derived from the ambient acoustic noise field
NASA Astrophysics Data System (ADS)
Evers, L. G.; Wapenaar, K.; Heaney, K. D.; Snellen, M.
2017-02-01
The propagation of acoustic waves in the ocean strongly depends on the temperature. Low frequency acoustic waves can penetrate the ocean down to depths where few in-situ measurements are available. It is therefore attractive to obtain a measure of the deep ocean temperature from acoustic waves. The latter is especially true if the ambient acoustic noise field can be used instead of deterministic transient signals. In this study the acoustic velocity, and hence the temperature, is derived in an interferometric approach from hydrophone array recordings. The arrays were separated by over 125 km, near Ascension Island in the Atlantic Ocean, at a depth of 850m. Furthermore, the dispersive characteristics of the deep ocean sound channel are resolved based on the retrieved lag times for different modes. In addition, it is shown how the resolution of the interferometric approach can be increased by cross correlating array beams rather than recordings from single-sensor pairs. The observed acoustic lag times between the arrays corresponds well to modeled values, based on full-wave modeling through best-known oceanic models.
Research on Diagnosing the Gearbox Faults Based on Near Field Acoustic Holography
NASA Astrophysics Data System (ADS)
Jiang, W. K.; Hou, J. J.; Xing, J. T.
2011-07-01
The gearbox fault diagnosis was developed for some decades. The current diagnosis techniques were mostly based on analyzing the shell vibration signals especially close to the bearing seat of gearbox. In order to utilize the spatial distribution information of fault signal, the near field acoustic holography (NAH) is employed for the condition monitoring and fault diagnosis of the gearbox in this presentation. The distribution images of sound pressure on the surface of gearbox are reconstructed by NAH, and the feature extraction and pattern recognition can be made by image processing techniques. A gearbox is studied in a semi-anechoic chamber to verify the fault diagnosis technique based on NAH. The pitting and partial broken tooth faults of gears are artificially made on one gear as the fault statuses, and the differences of acoustic images among normal and fault working states under the idling condition are analyzed. It can be found that the acoustic images of gearbox in the three different situations change regularly, and the main sound sources can be recognized from the acoustic images which also contain rich diagnosis information. After feature extraction of the acoustic images, the pattern reorganization technique is employed for diagnosis. The results indicate that this diagnosis procedure based on acoustic images is available and feasible for the gearbox fault diagnosis.
Acoustic Field Associated with Parabolized Stability Equation Models in Turbulent Jets
2013-05-01
discusses linear models of these wavepackets for supersonic turbulent jets based on Parabolized Stability Equations ( PSE ). In the past, results of...comparisons of the PSE models with near-field pressure fields from LES, filtered by means of Proper Orthogonal Decomposition (POD), demonstrate acceptable...fidelity of the model. Finally, the acoustic far-field associated with the PSE wavepackets is computed using a Kirchhoff surface method, capturing
Observing backfolded and unfolded acoustic phonons by broadband optical light scattering.
Maerten, L; Bojahr, A; Bargheer, M
2015-02-01
We use broadband time domain Brillouin scattering to observe coherently generated phonon modes in bulk and nanolayered samples. We transform the measured transients into a frequency-wavevector diagram and compare the resulting dispersion relations to calculations. The detected oscillation amplitude depends on the occupation of phonon modes induced by the pump pulse. For nanolayered samples with an appropriately large period, the whole wavevector range of the Brillouin zone becomes observable by broadband optical light scattering. The backfolded modes vanish, when the excitation has passed the nanolayers and propagates through the substrate underneath.
Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M
2016-04-01
The identification of acoustic sources is critical to targeted noise reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic sources from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent source distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated source location; sources farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped source regions, which is a phenomenon relatively recently reported for full-scale jets.
Chen, Tao; Fan, Tingbo; Zhang, Wei; Qiu, Yuanyuan; Tu, Juan E-mail: dzhang@nju.edu.cn; Guo, Xiasheng; Zhang, Dong E-mail: dzhang@nju.edu.cn
2014-03-21
Prediction and measurement of the acoustic field emitted from a high intensity focused ultrasound (HIFU) is essential for the accurate ultrasonic treatment. In this study, the acoustic field generated from a strongly focused HIFU transmitter was characterized by a combined experiment and simulation method. The spheroidal beam equation (SBE) was utilized to describe the nonlinear sound propagation. The curve of the source pressure amplitude versus voltage excitation was determined by fitting the measured ratio of the second harmonic to the fundamental component of the focal waveform to the simulation result; finally, the acoustic pressure field generated by the strongly focused HIFU transmitter was predicted by using the SBE model. A commercial fiber optic probe hydrophone was utilized to measure the acoustic pressure field generated from a 1.1 MHz HIFU transmitter with a large half aperture angle of 30°. The maximum measured peak-to-peak pressure was up to 72 MPa. The validity of this combined approach was confirmed by the comparison between the measured results and the calculated ones. The results indicate that the current approach might be useful to describe the HIFU field. The results also suggest that this method is not valid for low excitations owing to low sensitivity of the second harmonic.
Popa, Alexandru
2011-08-15
We prove that the analytical expression of the intensity of the relativistic Thomson scattered field for a system composed of an electron interacting with a plane electromagnetic field can be written in the form of a composite periodic function of only one variable, that is, the phase of the incident field. This property is proved without using any approximation in the most general case in which the field is elliptically polarized, the initial phase of the incident field and the initial velocity of the electron are taken into consideration, and the direction in which the radiation is scattered is arbitrary. This property leads to an exact method for calculating the angular and spectral distributions of the scattered field, which reveals a series of physical details of these distributions, such as their dependence on the components of the initial electron velocity. Since the phase of the field is a relativistic invariant, it follows that the periodicity property is also valid when the analysis is made in the inertial system in which the initial velocity of the electron is zero in the case of interactions between very intense electromagnetic fields and relativistic electrons. Consequently, the calculation method can be used for the evaluation of properties of backscattered hard radiations generated by this type of interaction. The theoretical evaluations presented in this paper are in good agreement with the experimental data from literature.
Oba, Roger; Finette, Steven
2002-02-01
Results of a computer simulation study are presented for acoustic propagation in a shallow water, anisotropic ocean environment. The water column is characterized by random volume fluctuations in the sound speed field that are induced by internal gravity waves, and this variability is superimposed on a dominant summer thermocline. Both the internal wave field and resulting sound speed perturbations are represented in three-dimensional (3D) space and evolve in time. The isopycnal displacements consist of two components: a spatially diffuse, horizontally isotropic component and a spatially localized contribution from an undular bore (i.e., a solitary wave packet or solibore) that exhibits horizontal (azimuthal) anisotropy. An acoustic field is propagated through this waveguide using a 3D parabolic equation code based on differential operators representing wide-angle coverage in elevation and narrow-angle coverage in azimuth. Transmission loss is evaluated both for fixed time snapshots of the environment and as a function of time over an ordered set of snapshots which represent the time-evolving sound speed distribution. Horizontal acoustic coherence, also known as transverse or cross-range coherence, is estimated for horizontally separated points in the direction normal to the source-receiver orientation. Both transmission loss and spatial coherence are computed at acoustic frequencies 200 and 400 Hz for ranges extending to 10 km, a cross-range of 1 km, and a water depth of 68 m. Azimuthal filtering of the propagated field occurs for this environment, with the strongest variations appearing when propagation is parallel to the solitary wave depressions of the thermocline. A large anisotropic degradation in horizontal coherence occurs under the same conditions. Horizontal refraction of the acoustic wave front is responsible for the degradation, as demonstrated by an energy gradient analysis of in-plane and out-of-plane energy transfer. The solitary wave packet is
Dynamics of a spherical particle in an acoustic field: A multiscale approach
Xie, Jin-Han Vanneste, Jacques
2014-10-15
A rigid spherical particle in an acoustic wave field oscillates at the wave period but has also a mean motion on a longer time scale. The dynamics of this mean motion is crucial for numerous applications of acoustic microfluidics, including particle manipulation and flow visualisation. It is controlled by four physical effects: acoustic (radiation) pressure, streaming, inertia, and viscous drag. In this paper, we carry out a systematic multiscale analysis of the problem in order to assess the relative importance of these effects depending on the parameters of the system that include wave amplitude, wavelength, sound speed, sphere radius, and viscosity. We identify two distinguished regimes characterised by a balance among three of the four effects, and we derive the equations that govern the mean particle motion in each regime. This recovers and organises classical results by King [“On the acoustic radiation pressure on spheres,” Proc. R. Soc. A 147, 212–240 (1934)], Gor'kov [“On the forces acting on a small particle in an acoustical field in an ideal fluid,” Sov. Phys. 6, 773–775 (1962)], and Doinikov [“Acoustic radiation pressure on a rigid sphere in a viscous fluid,” Proc. R. Soc. London A 447, 447–466 (1994)], clarifies the range of validity of these results, and reveals a new nonlinear dynamical regime. In this regime, the mean motion of the particle remains intimately coupled to that of the surrounding fluid, and while viscosity affects the fluid motion, it plays no part in the acoustic pressure. Simplified equations, valid when only two physical effects control the particle motion, are also derived. They are used to obtain sufficient conditions for the particle to behave as a passive tracer of the Lagrangian-mean fluid motion.
Guided Acoustic and Optical Waves in Silicon-on-Insulator for Brillouin Scattering and Optomechanics
2016-08-01
energy and momentum must be conserved. Consider an incoming optical mode of frequency ωp and a mechanical mode of frequencyΩ. These modes can scatter into...a downshifted optical Stokes wave with frequencyωs = ωp −Ω or an upshifted anti-Stokes wave with frequency ωp +Ω. Momentum conservation, or spatial
Selective Observation of Elastic-Body Resonances via Their Ringing in Transient Acoustic Scattering.
1984-09-12
evident but have not been discussed by him. Subsequent studies of pulse scattering from rigid spheres by Rudgers 3 , or from elastic 4 cylinders by Veksler...Lucite 1.182 2680 1380 1. J. J. Faran, J "" - -’,:. Amer. 23, 405 (1951) 2. R. Hicklinc, J. ,w.L t. Soc. Amer. 34, 1582 (1962). 3. A. J. Rudgers , J
A Simple Acoustic Scattering Model for Ensembles of Rocks and Seashells Lying on the Ocean Floor
2007-11-02
i.e., rocks and seashells lying on the ocean floor. A simplified modeling approach has been adopted that incorporates basic concepts and principles...over the equivalent frequency range. Seashells are represented by water-filled spherical shells. The model predicts scattering strength values for
NASA Astrophysics Data System (ADS)
Fatone, Lorella; Recchioni, Maria Cristina; Zirilli, Francesco
2006-05-01
In this paper we propose a highly parallelizable numerical method for time dependent acoustic scattering problems involving realistic smart obstacles hit by incoming waves having wavelengths small compared with the characteristic dimension of the obstacles. A smart obstacle is an obstacle that when hit by an incoming wave tries to pursue a goal circulating on its boundary a pressure current. In particular we consider obstacles whose goal is to be undetectable and we refer to them as furtive obstacles. These scattering problems are modelled as optimal control problems for the wave equation. We validate the method proposed to solve the optimal control problem considered on some test problems where a "smart" simplified version of the NASA space shuttle is hit by incoming waves with small wavelengths compared to its characteristic dimension. That is we consider test problems with ratio between the characteristic dimension of the obstacle and wavelength of the time harmonic component of the incoming wave up to approximately one hundred. The website: http://www.econ.univpm.it/recchioni/w14 contains animations and virtual reality applications showing some numerical experiments relative to the problems studied in this paper.
Application of ray-born scattering and boundary perturbation methods to acoustic reverberation
NASA Astrophysics Data System (ADS)
Toksoz, M. N.
1992-08-01
This study utilizes ultrasonic water tank modeling to examine three-dimensional scattering trends from a random set of parallel grooves, and compares this with theoretical results obtained from two-dimensional finite-difference calculations. Ultrasonic laboratory modeling is carried out using computer-controlled source and receivers with an aluminum block submerged in a water tank. The block's upper interface is plane for the reference model and grooved for the test model. The grooves measure about one-third the center source wavelength and have a Gaussian distribution with a mean of 1 wavelength and a standard deviation of 1/3 wavelength. This experiment places both the source and receiver at the water's surface with the receiver array in the horizontal plane. The receiver line is then positioned at various angles to grooves. A staggered-grid finite-difference scheme is used for theoretical computations and comparisons with laboratory data. These theoretical results matched experimental data well for both the plane interface and the grooved model. Specifically, this study shows that scattering mechanisms are different for propagation normal to grooves than those parallel to the grooves. In the first case scattering takes place in the form of point diffractors. This causes reduction of the specular reflections. Amplitudes decrease by more than 60 percent, relative to a plane interface, when the incidence angle exceeds 45 degrees. 'Snapshots' of finite-difference synthetics helped to clarify details of scattering. In the second case, where the wave front is parallel to the grooves, scattering takes a form of guided head waves and continuous diffractions giving rise to constructive and destructive interference. This gives the illusion of 'broken' reflectors at depth.
Single and multiple light scattering studies of PDLC films in the presence of electric fields
NASA Astrophysics Data System (ADS)
Wu, Wei
Light scattering from Polymer Dispersed Liquid Crystal (PDLC) films is studied in four major respects: the differential scattering cross-section of a single liquid crystal droplet; the total scattering cross-section and film transmittance; multiple scattering effects; and scattering by absorbing droplets (PDLC doped with dichroic dye). The effects of applied electric field, light wavelength and the liquid crystal droplet size on the scattering behavior are examined. PDLC scattering properties under electric field are described by combining the Anomalous Diffraction Approach (ADA) with PDLC electro-optical response theory. Numerical computation results directly demonstrate how the total scattering cross section relates to the incident light wavelength, the droplet size and the applied electric field. Transmittance measurements are used to study the total scattering cross-section. Analyses of the transmittance characteristics show good agreement with the theoretical predictions. PDLC samples with a practical contrast ratio exhibit strong multiple scattering effects. Studies of the single scattering differential cross section provide a foundation for the modeling and experimental work on the multiple scattering effects. Single scattering characteristics of a bipolar droplet director configuration are derived for a highly symmetric situation. The results offer qualitative explanations for some experimental observations, such as the presence of off-normal maxima and breakdown of rotational symmetry in the scattering pattern. As a novel approach, we propose a multiple scattering model for PDLC based on successive order and Monte Carlo methods. This model, along with ADA and electro-optical response theories, was used to calculate the angular distribution of scattered light and electric field switching response. The predictions demonstrate close quantitative agreement with experimental results. Incorporating complex refractive indices to treat dye- doped PDLC
2015-06-17
sound speeds and densities for both the water column and bottom, in conjunction with a correlated noise field. The acoustic source is described by a...determined here through singular value de- composition of matrices associated with the Green functions and noise distribution, in conjunction with a
Assembly of colloidal molecules, polymers, and crystals in acoustic and magnetic fields.
Yang, Ye; Pham, An T; Cruz, Daniela; Reyes, Christopher; Wiley, Benjamin J; Lopez, Gabriel P; Yellen, Benjamin B
2015-08-26
A dynamically adjustable colloidal assembly technique is presented, which combines magnetic and acoustic fields to produce a wide range of colloidal structures, ranging from discrete colloidal molecules, to polymer networks and crystals. The structures can be stabilized and dried, making them suitable for the fabrication of advanced materials.
Stimulated Scattering of Light from Ion Acoustic Waves in Collisional Multi-species Plasma.
NASA Astrophysics Data System (ADS)
Berger, Richard; Valeo, Ernest
2003-10-01
The dispersion properties of ion acoustic waves (IAW) are sensitive to the strength of ion-ion collisions,especially in multi-species plasma in which the different species have differing charge-to-mass ratios(Bychenkov et al., PRE 51, 1400 (1995)). Here, we consider the modification of the frequency and damping of the fast and slow acoustic modes in a plasma composed of light (low Z) and heavy (high Z) ions. In the fluid limit, kλ_lh <<1, the friction between the two species causes the damping whereas, in the collisionless limit, Landau damping of the light ions provides the dissipation. Collisions between light and heavy ions also affect the nonlinear response(P. W. Rambo, S. C. Wilks, and W. L. Kruer, Phys. Rev. Lett. 79), 83 (1997).. We examine the effects of collisions on the linear evolution of ion waves driven by the ponderomotive force of two light waves within the context of linear parametric instability theory. The simulation of the nonlinear evolution is done with a δ f model that evolves the background(E. J. Valeo and S. Brunner, Bull. Am. Phys. Soc. 46), QP1.137 (2001)., and includes the effects of collisions of light on heavy ions within the Lorentz model. The calculated effect of a small number of high Z ions on SBS in low Z plasmas will be compared with recent experimental results(Suter et al.,private communication). l
Bioacoustic field research: a primer to acoustic analyses and playback experiments with primates.
Fischer, Julia; Noser, Rahel; Hammerschmidt, Kurt
2013-07-01
Acoustic analyses of primate vocalizations as well as playback experiments are staple methods in primatology. Acoustic analyses have been used to investigate the influence of factors such as individuality, context, sex, age, and size on variation in calls. More recent studies have expanded our knowledge on the effects of phylogenetic relatedness and the structure of primate vocal repertoires in general. Complementary playback experiments allow direct testing of hypotheses regarding the attribution of meaning to calls, the cognitive mechanisms underpinning responses, and/or the adaptive value of primate behavior. After briefly touching on the historical background of this field of research, we first provide an introduction to recording primate vocalizations and discuss different approaches to describe primate calls in terms of their temporal and spectral properties. Second, we present a tutorial regarding the preparation, execution, and interpretation of field playback experiments, including a review of studies that have used such approaches to investigate the responses to acoustic variation in calls including the integration of contextual and acoustic information, recognition of kin and social relationships, and social knowledge. Based on the review of the literature and our own experience, we make a number of recommendations regarding the most common problems and pitfalls. The power of acoustic analyses typically hinges on the quality of the recordings and the number of individuals represented in the sample. Playback experiments require profound knowledge of the natural behavior of the animals for solid interpretation; experiments should be conducted sparingly, to avoid habituation of the subjects to the occurrence of the calls; experimenter-blind designs chosen whenever possible; and researchers should brace themselves for long periods of waiting times until the appropriate moments to do the experiment arise. If all these aspects are considered, acoustic analyses
Bioacoustic Field Research: A Primer to Acoustic Analyses and Playback Experiments With Primates
FISCHER, JULIA; NOSER, RAHEL; HAMMERSCHMIDT, KURT
2013-01-01
Acoustic analyses of primate vocalizations as well as playback experiments are staple methods in primatology. Acoustic analyses have been used to investigate the influence of factors such as individuality, context, sex, age, and size on variation in calls. More recent studies have expanded our knowledge on the effects of phylogenetic relatedness and the structure of primate vocal repertoires in general. Complementary playback experiments allow direct testing of hypotheses regarding the attribution of meaning to calls, the cognitive mechanisms underpinning responses, and/or the adaptive value of primate behavior. After briefly touching on the historical background of this field of research, we first provide an introduction to recording primate vocalizations and discuss different approaches to describe primate calls in terms of their temporal and spectral properties. Second, we present a tutorial regarding the preparation, execution, and interpretation of field playback experiments, including a review of studies that have used such approaches to investigate the responses to acoustic variation in calls including the integration of contextual and acoustic information, recognition of kin and social relationships, and social knowledge. Based on the review of the literature and our own experience, we make a number of recommendations regarding the most common problems and pitfalls. The power of acoustic analyses typically hinges on the quality of the recordings and the number of individuals represented in the sample. Playback experiments require profound knowledge of the natural behavior of the animals for solid interpretation; experiments should be conducted sparingly, to avoid habituation of the subjects to the occurrence of the calls; experimenter-blind designs chosen whenever possible; and researchers should brace themselves for long periods of waiting times until the appropriate moments to do the experiment arise. If all these aspects are considered, acoustic analyses
NASA Technical Reports Server (NTRS)
Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.
1985-01-01
A low-turbulence subsonic wind tunnel was used to study the influence of acoustic disturbances on the development of small sinusoidal oscillations (Tollmien-Schlichting waves) which constitute the initial phase of turbulent transition. It is found that acoustic waves propagating opposite to the flow generate vibrations of the model (plate) in the flow. Neither the plate vibrations nor the acoustic field itself have any appreciable influence on the stability of the laminar boundary layer. The influence of an acoustic field on laminar boundary layer disturbances is limited to the generation of Tollmien-Schlichting waves at the leading-edge of the plate.
Field performance of an acoustic scour-depth monitoring system
Mason, Jr., Robert R.; Sheppard, D. Max
1994-01-01
The Herbert C. Bonner Bridge over Oregon Inlet serves as the only land link between Bodie and Hatteras Islands, part of the Outer Banks of North Carolina. Periodic soundings over the past 30 years have documented channel migration, local scour, and deposition at several pilings that support the bridge. In September 1992, a data-collection system was installed to permit the off-site monitoring of scour at 16 bridge pilings. The system records channel-bed elevations at 15-minute intervals and transmits the data to a satellite receiver. A cellular phone connection also permits downloading and reviewing of the data as they are being collected. A digitally recording, acoustic fathometer is the main component of the system. In November 1993, current velocity, water-surface elevation, wave characteristics, and water temperature measuring instruments were also deployed at the site. Several performance problems relating to the equipment and to the harsh marine environment have not been resolved, but the system has collected and transmitted reliable scour-depth and water-level data.
Adaptive plasticity in wild field cricket's acoustic signaling.
Bertram, Susan M; Harrison, Sarah J; Thomson, Ian R; Fitzsimmons, Lauren P
2013-01-01
Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience.
Synthetic-gauge-field-induced Dirac semimetal state in an acoustic resonator system
NASA Astrophysics Data System (ADS)
Yang, Zhaoju; Gao, Fei; Shi, Xihang; Zhang, Baile
2016-12-01
Recently, a proposal of synthetic gauge field in reduced two-dimensional (2D) system from three-dimensional (3D) acoustic structure shows an analogue of the gapped Haldane model with fixed k z , and achieves the gapless Weyl semimetal phase in 3D momentum space. Here, extending this approach of synthetic gauge flux, we propose a reduced square lattice of acoustic resonators, which exhibits Dirac nodes with broken effective time-reversal symmetry. Protected by an additional hidden symmetry, these Dirac nodes with quantized values of topological charge are characterized by nonzero winding number and the finite structure exhibits flat edge modes that cannot be destroyed by perturbations.
Mapping the sound field of an erupting submarine volcano using an acoustic glider.
Matsumoto, Haru; Haxel, Joseph H; Dziak, Robert P; Bohnenstiehl, Delwayne R; Embley, Robert W
2011-03-01
An underwater glider with an acoustic data logger flew toward a recently discovered erupting submarine volcano in the northern Lau basin. With the volcano providing a wide-band sound source, recordings from the two-day survey produced a two-dimensional sound level map spanning 1 km (depth) × 40 km(distance). The observed sound field shows depth- and range-dependence, with the first-order spatial pattern being consistent with the predictions of a range-dependent propagation model. The results allow constraining the acoustic source level of the volcanic activity and suggest that the glider provides an effective platform for monitoring natural and anthropogenic ocean sounds.
Jin, Ru-Long; Yang, Han; Zhao, Di; Chen, Qi-Dai; Yan, Zhao-Xu; Yi, Mao-Bin; Sun, Hong-Bo
2010-02-15
Electro-optic probing of electric fields has been considered as a promising approach for integrated circuit diagnosis. However, the method is subject to relatively weak voltage sensitivity. In this Letter, we solve the problems with electro-acoustic effect. In contrast to the general electro-optic effect, the light phase modulation induced by the acoustic effect is 2 orders of magnitude stronger at its resonant frequency, as we observed in a GaAs thin film probe. Furthermore, this what we believe to be a novel method shows a highly reproducible linearity between the detected signals and the input voltages, which facilitates the voltage calibration.
Acoustic streaming field structure. Part II. Examples that include boundary-driven flow.
Bradley, Charles
2012-01-01
In this paper three simple acoustic streaming problems are presented and solved. The purpose of the paper is to demonstrate the use of a previously published streaming model by Bradley [J. Acoust. Soc. Am. 100(3), 1399-1408 (1996)] and illustrate, with concrete examples, some of the features of streaming flows that were predicted by the general model. In particular, the problems are intended to demonstrate cases in which the streaming field boundary condition at the face of the radiator has a nontrivial lateral dc velocity component. Such a boundary condition drives a steady solenoidal flow just like a laterally translating boundary drives Couette flow.
Bayesian Inversion of Seabed Scattering Data (Special Research Award in Ocean Acoustics)
2012-09-30
and reflection coefficient forward models. APPROACH The data used in this work were collected by Charles Holland, who measured direct -path... shear -wave velocity cs and attenuation αs . The only difference between the seabed model for scattering and reflection calculations is that the first...and density below 5-m depth is likely evidence of a limestone basement, which is known to exist in the region. Figure 5 shows the 1D marginal posterior
Bayesian Inversion of Seabed Scattering Data (Special Research Award in Ocean Acoustics)
2013-09-30
the inversion of measured data. APPROACH The data used in this work were collected by Charles Holland, who measured direct -path scattering1 and...of a sediment layer), sound velocity c, density ρ, and attenuation α. In addition, the basement is assumed to be elastic with a shear -wave velocity...resolution seismic survey of the experimental site. These results seem to indicate a limestone basement, which is known to exist in the region
Bayesian Inversion of Seabed Scattering Data (Special Research Award in Ocean Acoustics)
2011-09-30
APPROACH The data used in this work were collected by Charles Holland, who measured direct -path scattering1 and reflection2 data over a wide...consistent with sand (known to represent the surficial sediments). The high sound speed and density below 5-m depth is likely evidence of a limestone ...basement, which is known to exist in the region. If so, to model the seabed correctly requires extending the forward model to include shear waves in the
NASA Astrophysics Data System (ADS)
Swearingen, Michelle Elaine
2003-10-01
This thesis is a presentation of an analytic model, developed in cylindrical coordinates, for the scattering of a spherical wave off a semi infinite right cylinder placed normal to a ground surface. The model is developed to simulate a single tree and is developed as a first piece to creating a model for estimating attenuation in a forest based on scattering from individual tree trunks. Comparisons are made to the plane wave case, the transparent cylinder case, and the rigid and soft ground cases as a method of theoretically verifying the model. Agreement is excellent for these benchmark cases. Model sensitivity to five parameters is determined, which aids in error analysis, particularly when comparing the model results to experimental data, and offers insight into the inner workings of the model. An experiment was performed to collect real-world data on scattering from a cylinder normal to a ground surface. The data from the experiment is analyzed with a transfer function method into frequency and impulse responses. The model results are compared to the experimental data.
Imaging of transient surface acoustic waves by full-field photorefractive interferometry
Xiong, Jichuan; Xu, Xiaodong E-mail: christ.glorieux@fys.kuleuven.be; Glorieux, Christ E-mail: christ.glorieux@fys.kuleuven.be; Matsuda, Osamu; Cheng, Liping
2015-05-15
A stroboscopic full-field imaging technique based on photorefractive interferometry for the visualization of rapidly changing surface displacement fields by using of a standard charge-coupled device (CCD) camera is presented. The photorefractive buildup of the space charge field during and after probe laser pulses is simulated numerically. The resulting anisotropic diffraction upon the refractive index grating and the interference between the polarization-rotated diffracted reference beam and the transmitted signal beam are modeled theoretically. The method is experimentally demonstrated by full-field imaging of the propagation of photoacoustically generated surface acoustic waves with a temporal resolution of nanoseconds. The surface acoustic wave propagation in a 23 mm × 17 mm area on an aluminum plate was visualized with 520 × 696 pixels of the CCD sensor, yielding a spatial resolution of 33 μm. The short pulse duration (8 ns) of the probe laser yields the capability of imaging SAWs with frequencies up to 60 MHz.
Calculation of electromagnetic fields in the near-field region of a moving scattering object
NASA Astrophysics Data System (ADS)
Vogel, M. H.
1990-07-01
The problem of scattering of electromagnetic fields by perfectly conducting, moving objects is solved with the Lorentz transformation and the plane wave formulation. Apart from the physical optics approximation, the solution is exact. The result is subsequently applied to the special case of monostatic reflection by an object that moves slowly with respect to the velocity of light. The result can be used to predict the time dependent reflection from an aircraft that passes the antenna of a proximity fuze, and the optimum fuze algorithm can be selected.
Characterization of the Acoustic Field in Marine Environments with Anthropogenic Noise
NASA Astrophysics Data System (ADS)
Guan, Shane
Most animals inhabit the aquatic environment are acoustical-oriented, due to the physical characteristics of water that favors sound transmission. Many aquatic animals depend on underwater sound to navigate, communicate, find prey, and avoid predators. The degradation of underwater acoustic environment due to human activities is expected to affected these animals' well-being and survival at the population level. This dissertation presents three original studies on the characteristics and behavior of underwater sound fields in three unique marine environments with anthropogenic noises. The first study examines the soundscape of the Chinese white dolphin habitat in Taiwan. Acoustic recordings were made at two coastal shallow water locations, Yunlin and Waisanding, in 2012. Results show that croaker choruses are dominant sound sources in the 1.2--2.4 kHz frequency band for both locations at night, and noises from container ships in the 150--300 Hz frequency band define the relative higher broadband sound levels at Yunlin. Results also illustrate interrelationships among different biotic, abiotic, and anthropogenic elements that shape the fine-scale soundscape in a coastal environment. The second study investigates the inter-pulse sound field during an open-water seismic survey in coastal shallow waters of the Arctic. The research uses continuous acoustic recordings collected from one bottom-mounted hydrophone deployed in the Beaufort Sea in summer 2012. Two quantitative methods were developed to examine the inter-pulse sound field characteristics and its dependence on source distances. Results show that inter-pulse sound field could raise the ambient noise floor by as much as 9 dB, depending on ambient condition and source distance. The third study examines the inter-ping sound field of simulated mid-frequency active sonar in deep waters off southern California in 2013 and 2014. The study used drifting acoustic recorder buoys to collect acoustic data during sonar
NASA Astrophysics Data System (ADS)
Lu, Wenbo; Jiang, Weikang; Yuan, Guoqing; Yan, Li
2013-05-01
Vibration signal analysis is the main technique in machine condition monitoring or fault diagnosis, whereas in some cases vibration-based diagnosis is restrained because of its contact measurement. Acoustic-based diagnosis (ABD) with non-contact measurement has received little attention, although sound field may contain abundant information related to fault pattern. A new scheme of ABD for gearbox based on near-field acoustic holography (NAH) and spatial distribution features of sound field is presented in this paper. It focuses on applying distribution information of sound field to gearbox fault diagnosis. A two-stage industrial helical gearbox is experimentally studied in a semi-anechoic chamber and a lab workshop, respectively. Firstly, multi-class faults (mild pitting, moderate pitting, severe pitting and tooth breakage) are simulated, respectively. Secondly, sound fields and corresponding acoustic images in different gearbox running conditions are obtained by fast Fourier transform (FFT) based NAH. Thirdly, by introducing texture analysis to fault diagnosis, spatial distribution features are extracted from acoustic images for capturing fault patterns underlying the sound field. Finally, the features are fed into multi-class support vector machine for fault pattern identification. The feasibility and effectiveness of our proposed scheme is demonstrated on the good experimental results and the comparison with traditional ABD method. Even with strong noise interference, spatial distribution features of sound field can reliably reveal the fault patterns of gearbox, and thus the satisfactory accuracy can be obtained. The combination of histogram features and gray level gradient co-occurrence matrix features is suggested for good diagnosis accuracy and low time cost.
NASA Astrophysics Data System (ADS)
Ghislotti, G.; Bottani, C. E.; Mutti, P.; Byloos, C.; Giovannini, L.; Nizzoli, F.
1995-04-01
Brillouin light spectroscopy in p-p backscattering geometry is used to study sagittal surface acoustic phonons in silicon on insulator structures formed on a silicon buffer. The experimental spectra show, near the longitudinal threshold of silicon, two peaks whose physical meaning is discussed by comparison with theoretical cross sections. Calculations of Brillouin cross sections were performed, taking into account both the ripple and elastooptic coupling mechanisms. The peaks originate from two pseudomodes: the first is highly localized in the buried SiO2 layer and the second in the top silicon layer. The dependence of the pseudomode localization and cross section intensity with the parallel wave vector and with the thickness of the top silicon layer are discussed.
Acoustic Resonators for Far-Field Control of Sound on a Subwavelength Scale
NASA Astrophysics Data System (ADS)
Lemoult, Fabrice; Fink, Mathias; Lerosey, Geoffroy
2011-08-01
We prove experimentally that broadband sounds can be controlled and focused at will on a subwavelength scale by using acoustic resonators. We demonstrate our approach in the audible range with soda cans, that is, Helmholtz resonators, and commercial computer speakers. We show that diffraction-limited sound fields convert efficiently into subdiffraction modes in the collection of cans that can be controlled coherently in order to obtain focal spots as thin as 1/25 of a wavelength in air. We establish that subwavelength acoustic pressure spots are responsible for a strong enhancement of the acoustic displacement at focus, which permits us to conclude with a visual experiment exemplifying the interest of our concept for subwavelength sensors and actuators.
Field evaluation of boat-mounted acoustic Doppler instruments used to measure streamflow
Mueller, D.S.; ,
2003-01-01
The use of instruments based on the Doppler principle for measuring water velocity and computing discharge is common within the U.S. Geological Survey (USGS). The instruments and software have changed appreciably during the last 5 years; therefore, the USGS has begun field validation of the instruments used to make discharge measurements from a moving boat. Instruments manufactured by SonTek/YSI and RD Instruments, Inc. were used to collect discharge data at five different sites. One or more traditional discharge measurements were made using a Price AA current meter and standard USGS procedures concurrent with the acoustic instruments at each site. Discharges measured with the acoustic instruments were compared with discharges measured with Price AA current meters and the USGS stage-discharge rating for each site. The mean discharges measured by each acoustic instrument were within 5 percent of the Price AA-based measurement and (or) discharge from the stage-discharge rating.
Integrating Acoustic Imaging of Flow Regimes With Bathymetry: A Case Study, Main Endeavor Field
NASA Astrophysics Data System (ADS)
Bemis, K. G.; Rona, P. A.; Jackson, D. R.; Jones, C. D.
2003-12-01
A unified view of the seafloor and the hydrothermal flow regimes (plumes and diffuse flow) is constructed for three major vent clusters in the Main Endeavour Field (e.g., Grotto, S&M, and Salut) of the Endeavour Segment, Juan de Fuca Ridge. The Main Endeavour Field is one of RIDGE 2000's Integrated Study Sites. A variety of visualization techniques are used to reconstruct the plumes (3D) and the diffuse flow field (2D) based on our acoustic imaging data set (July 2000 cruise). Plumes are identified as volumes of high backscatter intensity (indicating high particulate content or sharp density contrasts due to temperature variations) that remained high intensity when successive acoustic pings were subtracted (indicating that the acoustic targets producing the backscatter were in motion). Areas of diffuse flow are detected using our acoustic scintillation technique (AST). For the Grotto vent region (where a new Doppler technique was used to estimate vertical velocities in the plume), we estimate the areal partitioning between black smoker and diffuse flow in terms of volume fluxes. The volumetric and areal regions, where plume and diffuse flow were imaged, are registered over the bathymetry and compared to geologic maps of each region. The resulting images provide a unified view of the seafloor by integrating hydrothermal flow with geology.
NASA Astrophysics Data System (ADS)
Honeycutt, Rebecca L.; Johnson, Steven J.
1993-04-01
The sound scattering due to an ambient noise field, approximated by a squared cosine function, is considered for infinite rigid and elastic cylinders and rigid spheres. For the cylinders, it is assumed that the acoustic wave front is parallel to the axis of the cylinder (informally incident). For this assumption, a closed form expression for the scattered sound field-to-incident ambient noise field (signal-to-noise) ratio is obtained not only for the cosine squared directivity, but for any arbitrary directivity which can be expressed in terms of a Fourier series. For the sphere, it is assumed that the noise is circumferentially symmetric which leads to a closed form expression for the signal-to-noise ratio due to a cosine squared directivity.
Adaptive Plasticity in Wild Field Cricket’s Acoustic Signaling
Bertram, Susan M.; Harrison, Sarah J.; Thomson, Ian R.; Fitzsimmons, Lauren P.
2013-01-01
Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience. PMID:23935965
Acoustic field interaction with a boiling system under terrestrial gravity and microgravity.
Sitter, J S; Snyder, T J; Chung, J N; Marston, P L
1998-11-01
Pool boiling experiments from a platinum wire heater in FC-72 liquid were conducted under terrestrial and microgravity conditions, both with and without the presence of a high-intensity acoustic standing wave within the fluid. The purpose of this research was to study the interaction between an acoustic field and a pool boiling system in normal gravity and microgravity. The absence of buoyancy in microgravity complicates the process of boiling. The acoustic force on a vapor bubble generated from a heated wire in a standing wave was shown to be able to play the role of buoyancy in microgravity. The microgravity environment was achieved with 0.6 and 2.1-s drop towers. The sound was transmitted through the fluid medium by means of a half wavelength sonic transducer driven at 10.18 kHz. At high enough acoustic pressure amplitudes cavitation and streaming began playing an important role in vapor bubble dynamics and heat transfer. Several different fixed heat fluxes were chosen for the microgravity experiment and the effects of acoustics on the surface temperature of the heater were recorded and the vapor bubble movement was filmed. Video images of the pool boiling processes and heat transfer data are presented.
Hurrell, Andrew M
2008-06-01
The interaction of an incident sound wave with an acoustically impenetrable two-layer barrier is considered. Of particular interest is the presence of several acoustic wave components in the shadow region of this barrier. A finite difference model capable of simulating this geometry is validated by comparison to the analytical solution for an idealized, hard-soft barrier. A panel comprising a high air-content closed cell foam backed with an elastic (metal) back plate is then examined. The insertion loss of this panel was found to exceed the dynamic range of the measurement system and was thus acoustically impenetrable. Experimental results from such a panel are shown to contain artifacts not present in the diffraction solution, when acoustic waves are incident upon the soft surface. A finite difference analysis of this experimental configuration replicates the presence of the additional field components. Furthermore, the simulated results allow the additional components to be identified as arising from the S(0) and A(0) Lamb modes traveling in the elastic plate. These Lamb mode artifacts are not found to be present in the shadow region when the acoustic waves are incident upon the elastic surface.
Near field acoustic holography measurements of carbon nanotube thin film speakers.
Asgarisabet, Mahsa; Barnard, Andrew R; Bouman, Troy M
2016-12-01
Carbon nanotube (CNT) thin film speakers produce sound with the thermoacoustic effect. Better understanding of the physical acoustic properties of these speakers will drive future design improvements. Measuring acoustic properties at the surface of the CNT thin film is difficult because the films, themselves, do not vibrate, are fragile and have a high surface temperature. In order to measure the surface particle velocity and sound pressure level (SPL), near field acoustic holography (NAH) has been used by employing probe microphones. NAH images the acoustic quantities of the source system using the set of acoustic pressure measurements on a hologram parallel to the source surface. It is shown that the particle velocity at the surface of an open-air, double-sided speaker is nominally zero, as expected. However, the SPL distribution is not uniform on the source surface, contrary to common lumped parameter model assumptions. Also, particle velocity and sound intensity distributions on the hologram have been obtained in this study. Finally, measured directivity patterns of the planar CNT speaker are reported.
Antifade sonar employs acoustic field diversity to recover signals from multipath fading
Lubman, D.
1996-04-01
Co-located pressure and particle motion (PM) hydrophones together with four-channel diversity combiners may be used to recover signals from multipath fading. Multipath fading is important in both shallow and deep water propagation and can be an important source of signal loss. The acoustic field diversity concept arises from the notion of conservation of signal energy and the observation that in rooms at least, the total acoustic energy density is the sum of potential energy (scalar field-sound pressure) and kinetic energy (vector field-sound PM) portions. One pressure hydrophone determines acoustic potential energy density at a point. In principle, three PM sensors (displacement, velocity, or acceleration) directed along orthogonal axes describe the kinetic energy density at a point. For a single plane wave, the time-averaged potential and kinetic field energies are identical everywhere. In multipath interference, however, potential and kinetic field energies at a point are partitioned unequally, depending mainly on relative signal phases. Thus, when pressure signals are in deep fade, abundant kinetic field signal energy may be available at that location. Performance benefits require a degree of uncorrelated fading between channels. The expectation of nearly uncorrelated fading is motivated from room theory. Performance benefits for sonar limited by independent Rayleigh fading are suggested by analogy to antifade radio. Average SNR can be improved by several decibels, holding time on target is multiplied manifold, and the bit error rate for data communication is reduced substantially. {copyright} {ital 1996 American Institute of Physics.}
Theory of VHF Scattering by Field-Aligned Irregularities in the Ionosphere.
1986-09-01
A. (1981), "A Global Model for Wideband *HF Skywave Propagation ", in Effect of the Ionosphere on Radiowave Systems, J.M. Goodman Ed., U.S. Government... SCHELL Chief " ’ Electromagnetic Sciences Division FOR THE COMMANDER: LOHN A. RSTZ Plans & Programs Division If your address has changed or if you wish to...SUB-GROUP Field Aligned Scatter Anisotropic Scatter 17 02 1 Auroral Scatter VHF Propagatione -4 20 14 ’." . ~lg. ABSTRACT (Cantino n on reverse if
2011-09-30
the Rayleigh-to-geometric scattering transition is within the frequency band of the WHOI broadband system (e.g., copepods ), and either larger fluid...that numerical abundance of zooplankton was dominated by small copepods that were relatively evenly distributed throughout the water-column...indication in either the MONESS or the VPR that the acoustic scattering layer was correlated to an increased abundance of zooplankton. Small copepods
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.
NASA Astrophysics Data System (ADS)
Michell, R. G.; Grydeland, T.; Samara, M.
2014-10-01
Naturally enhanced ion-acoustic lines (NEIALs) have been observed with the Poker Flat Incoherent Scatter Radar (PFISR) ever since it began operating in 2006. The nearly continuous operation of PFISR since then has led to a large number of NEIAL observations from there, where common-volume, high-resolution auroral imaging data are available. We aim to systematically distinguish the different types of auroral forms that are associated with different NEIAL features, including spectral shape and altitude extent. We believe that NEIALs occur with a continuum of morphological characteristics, although we find that most NEIALs observed with PFISR fall into two general categories. The first group occurs at fairly low altitudes - F region or below - and have power at, and spread between, the ion-acoustic peaks. The second group contains the type of NEIALs that have previously been observed with the EISCAT radars, those that extend to high altitudes (600 km or more) and often have large asymmetries in the power enhancements between the two ion-acoustic shoulders. We find that there is a correlation between the auroral structures and the type of NEIALs observed, and that the auroral structures present during NEIAL events are consistent with the likely NEIAL generation mechanisms inferred in each case. The first type of NEIAL - low altitude - is the most commonly observed with PFISR and is most often associated with active, structured auroral arcs, such as substorm growth phase, and onset arcs and are likely generated by Langmuir turbulence. The second type of NEIAL - high altitude - occurs less frequently in the PFISR radar and is associated with aurora that contains large fluxes of low-energy electrons, as can happen in poleward boundary intensifications as well as at substorm onset and is likely the result of current-driven instabilities and in some cases Langmuir turbulence as well. In addition, a preliminary auroral photometry analysis revealed that there is an
NASA Astrophysics Data System (ADS)
MacAulay, Michael C.; Wishner, Karen F.; Daly, Kendra L.
This research was part of the South Channel Ocean Productivity Experiment (SCOPEX), a multidisciplinary study to investigate the biological and physical processes associated with the very high annual springtime abundance of right whales ( Eubalaena glacialis) in the Great South Channel off New England. Right whales appear to gather there in the spring because of the increased abundance of aggregations of their principal prey, the copepod Calanus finmarchicus. Observations of hydroacoustic scattering were made in relation to the hydrography, whale distributions, and other biological measurements in the vicinity of the Great South Channel during May 1986, March, April and May of 1988, and May and June of 1989. Copepods were detected (at 200 kHz) as a near-surface layer with strong diel changes. In 1989, a second frequency (120 kHz) was used to discriminate between copepod layers (which the 120 kHz detected only weakly) and other targets (which both frequencies detected). Acoustically distinct layers of zooplankton and micronekton were observed, which were often correlated in time and space with the copepod layers. Quantitative estimates derived from the acoustic data indicate that the abundance of zooplankton varied from 1-5 g wet weight m -3 to 18-25 g wet weight m -3 which correlates well with the abundances observed from MOCNESS tows. The acoustic data revealed a complex diel migration of two layers in addition to the copepods. Euphausiids (predominantly Meganyctiphanes sp.) were found in a layer above the bottom, and a mid-water layer may have been due to sand lance ( Ammodytes americanus). The observed biological phenomena appeared to be related to the complex hydrography of the region. A surface thermal front existed at the northern entrance to the channel in 1988 and 1989, with colder vertically mixed water to the south and warmer stratified water to the north. A Fast Fourier Transform analysis for spectral composition and autocovariance shows (a) strong
Intermediate regime of charged particle scattering in the field-reversal configuration.
Shustov, P I; Artemyev, A V; Yushkov, E V
2015-12-01
In this paper, we investigate the charged particle scattering in the magnetic field configuration with stretched magnetic field lines. This scattering results from the violation of the adiabaticity of charged particle motion in the region with the strong gradient of the magnetic field. We consider the intermediate regime of charged particle dynamics, when the violation of the adiabaticity is significant enough, but particle motion is not chaotic. We demonstrate and describe the significant scattering of particles with large adiabatic invariants (magnetic moment). We discuss a possible application of obtained results for description of the peculiarities of pitch-angle diffusion of relativistic electrons in the Earth radiation belts.
Intermediate regime of charged particle scattering in the field-reversal configuration
Shustov, P. I. Yushkov, E. V.; Artemyev, A. V.
2015-12-15
In this paper, we investigate the charged particle scattering in the magnetic field configuration with stretched magnetic field lines. This scattering results from the violation of the adiabaticity of charged particle motion in the region with the strong gradient of the magnetic field. We consider the intermediate regime of charged particle dynamics, when the violation of the adiabaticity is significant enough, but particle motion is not chaotic. We demonstrate and describe the significant scattering of particles with large adiabatic invariants (magnetic moment). We discuss a possible application of obtained results for description of the peculiarities of pitch-angle diffusion of relativistic electrons in the Earth radiation belts.
NASA Astrophysics Data System (ADS)
Liu, Yuxiang; Barnett, Alex H.
2016-11-01
We present a high-order accurate boundary-based solver for three-dimensional (3D) frequency-domain scattering from a doubly-periodic grating of smooth axisymmetric sound-hard or transmission obstacles. We build the one-obstacle solution operator using separation into P azimuthal modes via the FFT, the method of fundamental solutions (with N proxy points lying on a curve), and dense direct least-squares solves; the effort is O (N3 P) with a small constant. Periodizing then combines fast multipole summation of nearest neighbors with an auxiliary global Helmholtz basis expansion to represent the distant contributions, and enforcing quasiperiodicity and radiation conditions on the unit cell walls. Eliminating the auxiliary coefficients, and preconditioning with the one-obstacle solution operator, leaves a well-conditioned square linear system that is solved iteratively. The solution time per incident wave is then O (NP) at fixed frequency. Our scheme avoids singular quadratures, periodic Green's functions, and lattice sums, and its convergence rate is unaffected by resonances within obstacles. We include numerical examples such as scattering from a grating of period 13 λ × 13 λ comprising highly-resonant sound-hard ;cups; each needing NP = 64800 surface unknowns, to 10-digit accuracy, in half an hour on a desktop.
Surface modes and acoustic scattering of microspheres and ultrasound contrast agents.
Falou, Omar; Jafari Sojahrood, Amin; Kumaradas, J Carl; Kolios, Michael C
2012-09-01
Surface modes of spherical objects subject to ultrasound excitation have been recently proposed to explain experimental measurements of scattering from microspheres and ultrasound contrast agents (UCAs). In this work, the relationship between surface modes and resonance frequencies of microspheres and UCAs is investigated. A finite-element model, built upon the fundamentals of wave propagation and structural mechanics, was introduced and validated against analytical solutions (error <5%). Numerical results showed the existence of a systematic relationship between resonance frequencies and surface modes of a 30 μm microsphere driven at 1-70 MHz. On the contrary, for a 100 nm shelled, 4 μm diameter UCA, no clear relationship between the resonance frequencies and the surface modes was found in the frequency range examined. Instead, the UCA exhibited a collection of complex oscillations, which appear to be a combination of various surface modes and displacements. A study of the effects of varying the shell properties on the backscatter showed the presence of peaks in the backscatter of thick-shelled UCAs, which are not predicted by previous models. In summary, this work presents a systematic effort to examine scattering and surface modes from ultrasound contrast agents using finite-element models.
Some general properties of the exact acoustic fields in horns and baffles
NASA Astrophysics Data System (ADS)
Campos, L. M. B. C.
1984-07-01
The propagation of the fundamental, longitudinal acoustic mode in a duct of variable cross-section is considered, and the "Webster" wave equations for the sound pressure and velocity are used to establish some general properties of the exact acoustic fields. The equipartition of kinetic and compression energies is shown (section 2.1) to hold at all stations only for (i) a duct of constant cross-section and (ii) an exponential horn; these are the two cases for which the wave equations for the acoustic velocity and pressure coincide. It is proved (section 2.3) that there are only five duct shapes, forming two dual families, which have constant cut-off frequency(ies): namely, (I) the exponential duct, which is self-dual, and is the only shape with constant (and coincident) cut-offs both for the velocity and pressure; (II) the catenoidal horns, of cross-section S˜cosh 2, sinh 2, which, with their duals (III) the inverse catenoidal ducts S˜sech 2, csch 2, have one constant cut-off frequency, respectively, for the acoustic pressure and velocity. The existence of at least one constant cut-off frequency implies that the corresponding wave equation can be transformed into one with constant coefficients, and thus the acoustic fields calculated exactly in terms of elementary (exponential, circular and hyperbolic) functions; this property also applies to the imaginary transformations of the above shapes, viz., the sinusoidal S˜sin 2 and inverse sinusoidal S˜csc 2 ducts, that have no cut-off frequency, i.e., are acoustically "transparent". It is shown that elementary exact solutions of the Webster equation exist only (section 3.1) for these seven shapes: namely, the exponential, catenoidal, sinusoidal and inverse ducts; it is implied that for all other duct shapes the exact acoustic fields involve special functions, in infinite or finite terms, e.g., Bessel and Hermite functions respectively for power-law and Gaussian horns. Examples of the method of analysis are given by
NASA Astrophysics Data System (ADS)
Hu, Bo; Yang, DeSen; Li, SiChun; Sun, Yu; Mo, ShiQi; Shi, ShengGuo
2012-11-01
One-step patch near-field acoustical holography (PNAH) is a powerful tool for identifying noise sources from the partially known sound pressure field. The acoustical property to be reconstructed on the surface of interest is related to the partially measured pressure on the hologram surface in terms of sampling and bandlimiting matrices, which cost more in computation. A one-step procedure based on measuring of the normal component of the particle velocity is described, including the mathematical formulation. The numerical simulation shows that one-step PNAH based on particle velocity can obtain more accurately reconstructed results and it is also less sensitive to noise than the method based on pressure. These findings are confirmed by an underwater near-field acoustical holography experiment conducted with a vector hydrophone array. The experimental results have illustrated the high performance of one-step PNAH based on particle velocity in the reconstruction of sound field and the advantages of a vector hydrophone array in an underwater near-field measurement.
Determination of the Accommodation Coefficient Using Vapor/gas Bubble Dynamics in an Acoustic Field
NASA Technical Reports Server (NTRS)
Gumerov, Nail A.; Hsiao, Chao-Tsung; Goumilevski, Alexei G.; Allen, Jeff (Technical Monitor)
2001-01-01
Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as in evaporation in a vacuum. The rate at which such a phase transformation occurs depends on the "condensation" or "accommodation" coefficient, Beta, which is a property of the interface. Existing measurement techniques for Beta are complex and expensive. The development of a relatively inexpensive and reliable technique for measurement of Beta for a wide range of substances and temperatures is of great practical importance. The dynamics of a bubble in an acoustic field strongly depends on the value of Beta. It is known that near the saturation temperature, small vapor bubbles grow under the action of an acoustic field due to "rectified heat transfer." This finding can be used as the basis for an effective measurement technique of Beta. We developed a theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave. A numerical code was developed which enables simulation of a variety of experimental situations and accurately takes into account slowly evolving temperature. A parametric study showed that the measurement of Beta can be made over a broad range of frequencies and bubble sizes. We found several interesting regimes and conditions which can be efficiently used for measurements of Beta. Measurements of Beta can be performed in both reduced and normal gravity environments.
Acoustic structures in the near-field from clustered rocket nozzles
NASA Astrophysics Data System (ADS)
Canchero, Andres; Tinney, Charles E.; Murray, Nathan E.; Ruf, Joseph H.
2014-11-01
The plume and acoustic field produced by a cluster of two and four rocket nozzles is visualized by way of retroreflective shadowgraphy. Steady state and transient operations (startup/shutdown) were conducted in the fully-anechoic chamber and open jet facility of The University of Texas at Austin. The laboratory scale rocket nozzles comprise thrust-optimized parabolic contours, which during start-up, experience free shock separated flow, restricted shock separated flow and an end-effects regime prior to flowing full. Shadowgraphy images with synchronized surveys of the acoustic loads produced in close vicinity to the rocket clusters and wall static pressure profiles are first compared with several RANS simulations during steady operations. A Proper Orthogonal Decomposition of various regions in the shadowgraphy images is then performed to elucidate the prominent features residing in the supersonic annular flow region, the acoustic near field and the interaction zone that resides between the nozzle plumes. POD modes are used to detect propagation paths of the acoustic waves and shock cell structures in the supersonic shear layer. Spectral peak frequencies on the propagation paths are associated with the shock cell length, which are responsible for generating broadband shock noise. Aerospace Engineering & Engineering Mechanics.
NASA Astrophysics Data System (ADS)
Amamou, Manel L.
2016-05-01
This paper develops an analytical solution for sound, electromagnetic or any other wave propagation described by the Helmholtz equation in three-dimensional case. First, a theoretical investigation based on multipole expansion method and spherical wave functions was established, through which we show that the resolution of the problem is reduced to solving an infinite, complex and large linear system. Second, we explain how to suitably truncate the last infinite dimensional system to get an accurate stable and fast numerical solution of the problem. Then, we evaluate numerically the theoretical solution of scattering problem by multiple ideal rigid spheres. Finally, we made a numerical study to present the "Head related transfer function" with respect to different physical and geometrical parameters of the problem.
NASA Technical Reports Server (NTRS)
Miura, T.; Chao, C. C.
1980-01-01
The propagation of sound due to a line acoustic source in the moving stream across a semiinfinite vortex sheet which trails from a rigid plate is examined in a linear theory for the subsonic case. A solution for the transmitted sound field is obtained with the aid of multiple integral transforms and the Wiener-Hopf technique for both the steady state (time harmonic) and initial value (impulsive source) situations. The contour of inverse transform and hence the decomposition of the functions are determined through causality and radiation conditions. The solution obtained satisfies causality and the full Kutta conditions. The transmitted sound field is composed of two waves in both the stady state and initial value problems. One is the wave scattered from the edge of the plate which is associated with the bow wave and the instability wave. These waves exist in the downstream sectors. The other is the wave transmitted through the vortex sheet which is also associated with the instability wave. Regional divisions of the transmitted sound field are identified.
James, Kevin R; Dowling, David R
2008-09-01
In underwater acoustics, the accuracy of computational field predictions is commonly limited by uncertainty in environmental parameters. An approximate technique for determining the probability density function (PDF) of computed field amplitude, A, from known environmental uncertainties is presented here. The technique can be applied to several, N, uncertain parameters simultaneously, requires N+1 field calculations, and can be used with any acoustic field model. The technique implicitly assumes independent input parameters and is based on finding the optimum spatial shift between field calculations completed at two different values of each uncertain parameter. This shift information is used to convert uncertain-environmental-parameter distributions into PDF(A). The technique's accuracy is good when the shifted fields match well. Its accuracy is evaluated in range-independent underwater sound channels via an L(1) error-norm defined between approximate and numerically converged results for PDF(A). In 50-m- and 100-m-deep sound channels with 0.5% uncertainty in depth (N=1) at frequencies between 100 and 800 Hz, and for ranges from 1 to 8 km, 95% of the approximate field-amplitude distributions generated L(1) values less than 0.52 using only two field calculations. Obtaining comparable accuracy from traditional methods requires of order 10 field calculations and up to 10(N) when N>1.
A survey of the physical optics inverse scattering identity
NASA Astrophysics Data System (ADS)
Bojarski, N. N.
1982-09-01
An inverse scattering identity relating the characteristic function of a scatterer to the three-dimensional spatial Fourier transform of the augmented far field scattering amplitude is derived by applying the physical optics approximation to the acoustic and electromagnetic direct scattering integral representation. Because this identity requires full scattering data for all frequencies and aspect angles, an integral equation is developed for incomplete scattering data which solves for the unknown characteristic function of the scatterer in terms of the known incomplete scattering data. A regularized analytic closed form solution to this integral equation is obtained, and synthesized numerico-experimental results verifying the solution are presented.
Methods And Systems For Using Reference Images In Acoustic Image Processing
Moore, Thomas L.; Barter, Robert Henry
2005-01-04
A method and system of examining tissue are provided in which a field, including at least a portion of the tissue and one or more registration fiducials, is insonified. Scattered acoustic information, including both transmitted and reflected waves, is received from the field. A representation of the field, including both the tissue and the registration fiducials, is then derived from the received acoustic radiation.
Nuclear forward scattering of synchrotron radiation in pulsed high magnetic fields.
Strohm, C; Van der Linden, P; Rüffer, R
2010-02-26
We report the demonstration of nuclear forward scattering of synchrotron radiation from 57Fe in ferromagnetic alpha iron in pulsed high magnetic fields up to 30 T. The observed magnetic hyperfine field follows the calculated high field bulk magnetization within 1%, establishing the technique as a precise tool for the study of magnetic solids in very high magnetic fields. To perform these experiments in pulsed fields, we have developed a detection scheme for fully time resolved nuclear forward scattering applicable to other pump probe experiments.
Resonant scattering of ultrarelativistic electrons in the strong field of a pulsed laser wave
NASA Astrophysics Data System (ADS)
Lebed', A. A.; Padusenko, E. A.; Roshchupkin, S. P.
2016-02-01
Electron-electron scattering in a strong field of a pulsed laser wave is studied theoretically. Resonant scattering kinematics at the small polar angles for electron ultrarelativistic energy is studied in detail. Compact analytical expressions for the amplitude and the differential cross section for wave elliptical polarization are obtained under resonant conditions. The resonant cross section of electron-electron scattering is shown to decrease sharply with increasing the electron ultrarelativistic energies for weak and moderately strong fields. It was demonstrated that the resonant cross section of electron-electron scattering at wave circular polarization is four times greater than the corresponding cross section at linear polarization. The resonant cross section may exceed the corresponding cross section of a field-free process: by 5-6 orders of magnitude for electron MeV-energy and petawatt optical lasers (PHELIX, Vulcan); and 8-9 orders for multipetawatt laser fields within the femtosecond range (Vulcan10, ELI).
NASA Astrophysics Data System (ADS)
Dukeshire, Andrea
To efficiently model the effect of the airwave in the controlled-source electromagnetics (CSEM) method has historically been a problem of major interest. The methods proposed in this thesis provide a new method of simulating CSEM interactions in the finite-difference time-domain (FDTD) by using the total-field scattered-field (TFSF) formulation. TFSF provides an inherent separation of the total and scattered fields, which allows the proposed method to decompose the CSEM domain into separate simulation runs. By simulating the problem in stages, the process of extracting the response of the scatterer is streamlined. If the increased efficiency options within the proposed method are utilized, the efficiency of single forward simulations can be improved. This method shows potential for computational cost savings, especially in typical CSEM data analysis and reconstruction situations where numerous iterations of various scatterers are required.
Detection and processing of electromagnetic and near-field acoustic signals in elasmobranch fishes.
Kalmijn, A D
2000-01-01
The acoustic near field of quietly moving underwater objects and the bio-electric field of aquatic animals exhibit great similarity, as both are predominantly governed by Laplace's equation. The acoustic and electrical sensory modalities thus may, in directing fishes to their prey, employ analogous processing algorithms, suggesting a common evolutionary design, founded on the salient physical features shared by the respective stimulus fields. Sharks and rays are capable of orientating to the earth's magnetic field and, hence, have a magnetic sense. The electromagnetic theory of orientation offers strong arguments for the animals using the electric fields induced by ocean currents and by their own motions in the earth's magnetic field. In the animal's frame of reference, in which the sense organs are at rest, the classical concept of motional electricity must be interpreted in relativistic terms. In the ampullae of Lorenzini, weak electric fields cause the ciliated apical receptor-cell membranes to produce graded, negative receptor currents opposite in direction to the fields applied. The observed currents form part of a positive-feedback mechanism, supporting the generation of receptor potentials much larger than the input signal. Acting across the basal cell membranes, the receptor potentials control the process of synaptic transmission. PMID:11079385
NASA Technical Reports Server (NTRS)
Parasarathy, R.; Karamcheti, K.
1972-01-01
The Lighthill method was the basic procedure used to analyze the sound field associated with a vortex of modified strength interacting with an airfoil. A free vortex interacting with an airfoil in uniform motion was modeled in order to determine the sound field due to all the acoustic sources, not only on the airfoil surfaces (dipoles), but also the ones distributed on the perturbed flow field (quadrupoles) due to the vortex-airfoil interaction. Because inviscid flow is assumed in the study of the interaction, the quadrupoles considered in the perturbed flow field are entirely due to an unsteady flow field. The effects of airfoil thickness on the second radiation are examined by using a symmetric Joukowski airfoil for the vortex-airfoil interaction. Sound radiation in a plane, far field simplification, and computation of the sound field are discussed.
A sparse equivalent source method for near-field acoustic holography.
Fernandez-Grande, Efren; Xenaki, Angeliki; Gerstoft, Peter
2017-01-01
This study examines a near-field acoustic holography method consisting of a sparse formulation of the equivalent source method, based on the compressive sensing (CS) framework. The method, denoted Compressive-Equivalent Source Method (C-ESM), encourages spatially sparse solutions (based on the superposition of few waves) that are accurate when the acoustic sources are spatially localized. The importance of obtaining a non-redundant representation, i.e., a sensing matrix with low column coherence, and the inherent ill-conditioning of near-field reconstruction problems is addressed. Numerical and experimental results on a classical guitar and on a highly reactive dipole-like source are presented. C-ESM is valid beyond the conventional sampling limits, making wide-band reconstruction possible. Spatially extended sources can also be addressed with C-ESM, although in this case the obtained solution does not recover the spatial extent of the source.
Underwater Acoustic Matched Field Imaging Based on Compressed Sensing
Yan, Huichen; Xu, Jia; Long, Teng; Zhang, Xudong
2015-01-01
Matched field processing (MFP) is an effective method for underwater target imaging and localizing, but its performance is not guaranteed due to the nonuniqueness and instability problems caused by the underdetermined essence of MFP. By exploiting the sparsity of the targets in an imaging area, this paper proposes a compressive sensing MFP (CS-MFP) model from wave propagation theory by using randomly deployed sensors. In addition, the model’s recovery performance is investigated by exploring the lower bounds of the coherence parameter of the CS dictionary. Furthermore, this paper analyzes the robustness of CS-MFP with respect to the displacement of the sensors. Subsequently, a coherence-excluding coherence optimized orthogonal matching pursuit (CCOOMP) algorithm is proposed to overcome the high coherent dictionary problem in special cases. Finally, some numerical experiments are provided to demonstrate the effectiveness of the proposed CS-MFP method. PMID:26457708
Orthogonal acoustic dimensions define auditory field maps in human cortex.
Barton, Brian; Venezia, Jonathan H; Saberi, Kourosh; Hickok, Gregory; Brewer, Alyssa A
2012-12-11
The functional organization of human auditory cortex has not yet been characterized beyond a rudimentary level of detail. Here, we use functional MRI to measure the microstructure of orthogonal tonotopic and periodotopic gradients forming complete auditory field maps (AFMs) in human core and belt auditory cortex. These AFMs show clear homologies to subfields of auditory cortex identified in nonhuman primates and in human cytoarchitectural studies. In addition, we present measurements of the macrostructural organization of these AFMs into "clover leaf" clusters, consistent with the macrostructural organization seen across human visual cortex. As auditory cortex is at the interface between peripheral hearing and central processes, improved understanding of the organization of this system could open the door to a better understanding of the transformation from auditory spectrotemporal signals to higher-order information such as speech categories.
Underwater Acoustic Matched Field Imaging Based on Compressed Sensing.
Yan, Huichen; Xu, Jia; Long, Teng; Zhang, Xudong
2015-10-07
Matched field processing (MFP) is an effective method for underwater target imaging and localizing, but its performance is not guaranteed due to the nonuniqueness and instability problems caused by the underdetermined essence of MFP. By exploiting the sparsity of the targets in an imaging area, this paper proposes a compressive sensing MFP (CS-MFP) model from wave propagation theory by using randomly deployed sensors. In addition, the model's recovery performance is investigated by exploring the lower bounds of the coherence parameter of the CS dictionary. Furthermore, this paper analyzes the robustness of CS-MFP with respect to the displacement of the sensors. Subsequently, a coherence-excluding coherence optimized orthogonal matching pursuit (CCOOMP) algorithm is proposed to overcome the high coherent dictionary problem in special cases. Finally, some numerical experiments are provided to demonstrate the effectiveness of the proposed CS-MFP method.
Visualizing flow fields using acoustic Doppler current profilers and the Velocity Mapping Toolbox
Jackson, P. Ryan
2013-01-01
The purpose of this fact sheet is to provide examples of how the U.S. Geological Survey is using acoustic Doppler current profilers for much more than routine discharge measurements. These instruments are capable of mapping complex three-dimensional flow fields within rivers, lakes, and estuaries. Using the Velocity Mapping Toolbox to process the ADCP data allows detailed visualization of the data, providing valuable information for a range of studies and applications.
2012-08-01
AFRL-RX-WP-JA-2014-0230 INVESTIGATION OF ACOUSTIC FIELDS GENERATED BY EDDY CURRENTS USING AN ATOMIC FORCE MICROSCOPE (POSTPRINT) V...Institute of Physics AIR FORCE RESEARCH LABORATORY MATERIALS AND MANUFACTURING DIRECTORATE WRIGHT-PATTERSON AIR FORCE BASE, OH 45433-7750 AIR... FORCE MATERIEL COMMAND UNITED STATES AIR FORCE NOTICE AND SIGNATURE PAGE Using Government drawings, specifications, or other data included in
Not Available
1987-06-01
The Acoustics site study plan describes a field program which characterizes existing sound levels, determines the area's sound propagation characteristics, and monitors the project-related sound emissions. The plan describes for each study: the need for the study, study design, data management and use, schedule, and quality assurance requirements. These studies will provide data needed to satisfy requirements contained in, or derived from, the Salt Repository Requirements Document. 37 refs., 9 figs., 3 tabs.
Light scattering, field localization and local density of states in co-axial plasmonic nanowires.
Lawrence, Nate; Dal Negro, Luca
2010-07-19
Based on analytical scattering theory, we develop a multipolar expansion method to investigate systematically the near-field enhancement, far-field scattering and Local Density of States (LDOS) spectra in concentric metal-insulator-metal (MIM) cylindrical nanostructures, or coaxial plasmonic nanowires (CPNs). We demonstrate that these structures support distinctive plasmonic resonances with strongly reduced scattering in the far-field zone and significant electric field enhancement in deep sub-wavelength dielectric regions. Additionally, we study systematically the effects of geometrical parameters and dielectric index on the near-field and far-field plasmonic response of CPNs in the visible and near infrared spectral range. Finally, we demonstrate that CPNs provide a convenient approach for engineering strong (almost three orders of magnitude) LDOS enhancement in sub-wavelength dielectric gaps at multiple frequencies. These results enable the engineering of multiband optical detectors and CPNs-based light emitters with simultaneously enhanced excitation and emission rates for nanoplasmonics.
NASA Technical Reports Server (NTRS)
Homicz, G. F.; Moselle, J. R.
1985-01-01
A hybrid numerical procedure is presented for the prediction of the aerodynamic and acoustic performance of advanced turboprops. A hybrid scheme is proposed which in principle leads to a consistent simultaneous prediction of both fields. In the inner flow a finite difference method, the Approximate-Factorization Alternating-Direction-Implicit (ADI) scheme, is used to solve the nonlinear Euler equations. In the outer flow the linearized acoustic equations are solved via a Boundary-Integral Equation (BIE) method. The two solutions are iteratively matched across a fictitious interface in the flow so as to maintain continuity. At convergence the resulting aerodynamic load prediction will automatically satisfy the appropriate free-field boundary conditions at the edge of the finite difference grid, while the acoustic predictions will reflect the back-reaction of the radiated field on the magnitude of the loading source terms, as well as refractive effects in the inner flow. The equations and logic needed to match the two solutions are developed and the computer program implementing the procedure is described. Unfortunately, no converged solutions were obtained, due to unexpectedly large running times. The reasons for this are discussed and several means to alleviate the situation are suggested.
Ben Haj Slama, Rafika; Gilles, Bruno; Ben Chiekh, Maher; Béra, Jean-Christophe
2017-04-01
This research evaluates the use of Particle Image Velocimetry (PIV) technique for characterizing acoustic streaming flow generated by High Intensity Focused Ultrasound (HIFU). PIV qualification tests, focusing on the seeding particle size (diameter of 5, 20 and 50μm) were carried out in degassed water subjected to a focused field of 550kHz-frequency with an acoustic pressure amplitude of 5.2, 10.5 and 15.7bar at the focus. This study shows that the ultrasonic field, especially the radiation force, can strongly affect seeding particle behavior. Large particles (50μm-diameter) are repelled from the focal zone and gathered at radiation pressure convergence lines on either side of the focus. The calculation of the acoustic radiation pressure applied on these particles explains the observed phenomenon. PIV measurements do not, therefore, properly characterize the streaming flow in this case. On the contrary, small particles (5μm-diameter) velocity measurements were in good agreement with the Computational Fluid Dynamics (CFD) simulations of the water velocity field. A simple criterion approximating the diameter threshold below which seeding particles are qualified for PIV in presence of focused ultrasound is then proposed.
Prediction and near-field observation of skull-guided acoustic waves.
Estrada, Hector; Rebling, Johannes; Razansky, Daniel
2017-03-01
Ultrasound waves propagating in water or soft biological tissue are strongly reflected when encountering the skull, which limits the use of ultrasound-based techniques in transcranial imaging and therapeutic applications. Current knowledge on the acoustic properties of the cranial bone is restricted to far-field observations, leaving its near-field unexplored. We report on the existence of skull-guided acoustic waves, which was herein confirmed by near-field measurements of optoacoustically-induced responses in ex-vivo murine skulls immersed in water. Dispersion of the guided waves was found to reasonably agree with the prediction of a multilayered flat plate model. We observed a skull-guided wave propagation over a lateral distance of at least 3 mm, with a half-decay length in the direction perpendicular to the skull ranging from 35 to 300 μm at 6 and 0.5 MHz, respectively. Propagation losses are mostly attributed to the heterogenous acoustic properties of the skull.. It is generally anticipated that our findings may facilitate and broaden the application of ultrasound-mediated techniques in brain diagnostics and therapy.
NASA Astrophysics Data System (ADS)
Arndt, Christoph M.; Severin, Michael; Dem, Claudiu; Stöhr, Michael; Steinberg, Adam M.; Meier, Wolfgang
2015-04-01
A gas turbine model combustor for partially premixed swirl flames was equipped with an optical combustion chamber and operated with CH4 and air at atmospheric pressure. The burner consisted of two concentric nozzles for separately controlled air flows and a ring of holes 12 mm upstream of the nozzle exits for fuel injection. The flame described here had a thermal power of 25 kW, a global equivalence ratio of 0.7, and exhibited thermo-acoustic instabilities at a frequency of approximately 400 Hz. The phase-dependent variations in the flame shape and relative heat release rate were determined by OH* chemiluminescence imaging; the flow velocities by stereoscopic particle image velocimetry (PIV); and the major species concentrations, mixture fraction, and temperature by laser Raman scattering. The PIV measurements showed that the flow field performed a "pumping" mode with varying inflow velocities and extent of the inner recirculation zone, triggered by the pressure variations in the combustion chamber. The flow field oscillations were accompanied by variations in the mixture fraction in the inflow region and at the flame root, which in turn were mainly caused by the variations in the CH4 concentration. The mean phase-dependent changes in the fluxes of CH4 and N2 through cross-sectional planes of the combustion chamber at different heights above the nozzle were estimated by combining the PIV and Raman data. The results revealed a periodic variation in the CH4 flux by more than 150 % in relation to the mean value, due to the combined influence of the oscillating flow velocity, density variations, and CH4 concentration. Based on the experimental results, the feedback mechanism of the thermo-acoustic pulsations could be identified as a periodic fluctuation of the equivalence ratio and fuel mass flow together with a convective delay for the transport of fuel from the fuel injector to the flame zone. The combustor and the measured data are well suited for the validation of
NASA Astrophysics Data System (ADS)
Kim, Yong-Joe; Bolton, J. Stuart; Kwon, Hyu-Sang
2004-04-01
It has been shown previously that the multiple reference and field signals recorded during a scanning acoustical holography measurement can be used to decompose the sound field radiated by a composite sound source into mutually incoherent partial fields. To obtain physically meaningful partial fields, i.e., fields closely related to particular component sources, the reference microphones should be positioned as close as possible to the component physical sources that together comprise the complete source. However, it is not always possible either to identify the optimal reference microphone locations prior to performing a holographic measurement, or to place reference microphones at those optimal locations, even if known, owing to physical constraints. Here, post-processing procedures are described that make it possible both to identify the optimal reference microphone locations and to place virtual references at those locations after performing a holographic measurement. The optimal reference microphone locations are defined to be those at which the MUSIC power is maximized in a three-dimensional space reconstructed by holographic projection. The acoustic pressure signals at the locations thus identified can then be used as optimal ``virtual'' reference signals. It is shown through an experiment and numerical simulation that the optimal virtual reference signals can be successfully used to identify physically meaningful partial sound fields, particularly when used in conjunction with partial coherence decomposition procedures.
A nonlinear model of cell interaction with an acoustic field.
Miller, A D; Subramanian, A; Viljoen, H J
2017-03-14
A theoretical and experimental nonlinear analysis of cellular response/displacement to ultrasound excitations is presented. Linear cell models can predict the resonant frequency (fR∼5MHz), but only a nonlinear analysis can reveal the amount of mechanical energy that couples into the cell and the bifurcation behavior of the cell when it is excited near resonance. The cell dynamics is described by the nonlinear viscoelastic constitutive behavior of the cytoplasm, nucleus and their respective membranes, in the presence of a fluid with an oscillating pressure field. The method of multiple scales is used to derive the amplitude of oscillation of the cytoplasm and nucleus as a function of frequency. A major finding is the existence of multiple solutions for a range of sub-resonant frequencies. At positive detuning (f>fR), the mechanical energy that couples into the cell is small, it is higher at resonance but significantly higher at sub-resonant frequencies in the multiplicity range. Experimentally it was shown when 3.5MHz is approached sub- and supra-resonance and 6.5MHz is approached sub-resonance, gene expression was statistically higher than that when stimulated directly. Thus, there exists an optimal range of frequencies for ultrasound treatment - in the region of multiplicity where deformation and thus mechanical energy coupling is maximized. The ultrasound protocol must be designed to operate at the solution associated with the higher mechanical energy - thus the start-up conditions should be in the domain of attraction of the high energy solution.
Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields
Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin
2015-09-15
A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.
Scattering measurements on natural and model trees
NASA Technical Reports Server (NTRS)
Rogers, James C.; Lee, Sung M.
1990-01-01
The acoustical back scattering from a simple scale model of a tree has been experimentally measured. The model consisted of a trunk and six limbs, each with 4 branches; no foliage or twigs were included. The data from the anechoic chamber measurements were then mathematically combined to construct the effective back scattering from groups of trees. Also, initial measurements have been conducted out-of-doors on a single tree in an open field in order to characterize its acoustic scattering as a function of azimuth angle. These measurements were performed in the spring, prior to leaf development. The data support a statistical model of forest scattering; the scattered signal spectrum is highly irregular but with a remarkable general resemblance to the incident signal spectrum. Also, the scattered signal's spectra showed little dependence upon scattering angle.
Solving outside-axial-field-of-view scatter correction problem in PET via digital experimentation
NASA Astrophysics Data System (ADS)
Andreyev, Andriy; Zhu, Yang-Ming; Ye, Jinghan; Song, Xiyun; Hu, Zhiqiang
2016-03-01
Unaccounted scatter impact from unknown outside-axial-field-of-view (outside-AFOV) activity in PET is an important degrading factor for image quality and quantitation. Resource consuming and unpopular way to account for the outside- AFOV activity is to perform an additional PET/CT scan of adjacent regions. In this work we investigate a solution to the outside-AFOV scatter problem without performing a PET/CT scan of the adjacent regions. The main motivation for the proposed method is that the measured random corrected prompt (RCP) sinogram in the background region surrounding the measured object contains only scattered events, originating from both inside- and outside-AFOV activity. In this method, the scatter correction simulation searches through many randomly-chosen outside-AFOV activity estimates along with known inside-AFOV activity, generating a plethora of scatter distribution sinograms. This digital experimentation iterates until a decent match is found between a simulated scatter sinogram (that include supposed outside-AFOV activity) and the measured RCP sinogram in the background region. The combined scatter impact from inside- and outside-AFOV activity can then be used for scatter correction during final image reconstruction phase. Preliminary results using measured phantom data indicate successful phantom length estimate with the method, and, therefore, accurate outside-AFOV scatter estimate.
NASA Astrophysics Data System (ADS)
Razaz, Mahdi; Kawanisi, Kiyosi; Kaneko, Arata; Nistor, Ioan
2015-12-01
A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20-35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5-3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth-average current velocity components from differential travel times. Zeroth-order Tikhonov regularization, in conjunction with L-curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along-channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.
Effects of Strong Diffraction on the Focusing and Scattering of Acoustic Waves.
1986-06-01
in source level below 1Hz. According to measurements by Kelley et al. (1982), the part of the received WTG signal that was above the noise at the...and wind speed profiles for a period of strong focusing in the planetary boundary layer ...... .. 70 13. Sound-speed profile corresponding to ...into the sound speed, the signal levels at any point fluctuate according to the reaction of the field components to these perturbations. While the
NASA Astrophysics Data System (ADS)
Reinsch, Thomas; Jousset, Philippe; Henninges, Jan; Blanck, Hanna
2016-04-01
Seismic methods are particularly suited for investigating the Earth's subsurface. Compared to surface-measurements , wellbore measurements can be used to acquire more detailed information about rock properties and possible fluid pathways within a geothermal reservoir. For high temperature geothermal wells, however, ambient temperatures are often far above the operating temperature range of conventional geophones. One way to overcome this limitation is the application of fiber optic sensor systems, where only the passive optical fiber is subjected to downhole conditions. Their applicability is thus determined by the operating temperature range of the optical fiber. Choosing appropriate fibers, such sensor systems can be operated at temperatures far above 200°C. Along an optical fiber, the distributed acoustic sensing technology (DAS) can be used to acquire acoustic signals with a high spatial and temporal resolution. Previous experiments have shown that the DAS technology is well suited for active seismic measurements. Within the framework of the EC funded project IMAGE, a fiber optic cable was deployed in a newly drilled geothermal well (RN-34) within the Reykjanes geothermal field, Iceland. Additionally, a >15 km fiber optic cable, already available at the surface, was connected to a DAS read-out unit. Acoustic data was acquired continuously for 9 days. Hammer shots were performed at the wellhead as well as along the surface cable in order to locate individual acoustic traces and calibrate the spatial distribution of the acoustic information. During the monitoring period both signals from on- and offshore explosive sources and natural seismic events could be recorded. We compare the fiber optic data to conventional seismic records from a dense seismic network deployed on the Reykjanes in the course of the IMAGE project. Here, first results from the seismic survey will be presented.
Coherence vortices in Mie scattering of statistically stationary partially coherent fields.
Marasinghe, Madara L; Premaratne, Malin; Paganin, David M
2010-03-29
Points within a fully coherent complex scalar optical field, where the amplitude is identically zero but the optical phase has a jump discontinuity, have been widely investigated by the singular-optics community. More recent researches have extended the domain of singular optics to include partially coherent fields. For example, in coherence vortices the phase of the two-point spectral degree of coherence of a partially coherent field exhibits vortex structure around a point where the magnitude of the spectral degree of coherence vanishes. We show that the spectral degree of coherence of Mie scattered partially coherent statistically stationary electromagnetic fields exhibits a rich set of coherence vortices in both the internal and external fields. Specifically, we look at Mie scattering of a stationary beam from a dielectric sphere and study the formation of coherence vortices and their evolution with both the properties of the scattering sphere, and of the incident partially coherent beam.
Electric Field Light Scattering by Rod-Like Polyelectrolytes in Aqueous Suspensions
NASA Astrophysics Data System (ADS)
Martin, C.; Weyerich, B.; Biegel, J.; Deike, R.; Johner, C.; Klein, R.; Weber, R.
1995-05-01
Static light scattering measurements are presented for rod-like fd-virus particles (L=880 nm, D= 9 nm) subjected to a pulsed alternating electric field in aqueous suspensions at very low ionic strength. In aqueous suspensions the dispersed fd-particles are negatively charged and surrounded by a diffuse Debye counterion cloud. In an external electric field an induced dipole originating from a deformation of the diffuse counterion cloud causes the alignment of the macromolecules. The anisotropic orientation distribution of the particles in the presence of the electric field results in a change of the angular distribution of the scattered light intensity with regard to the isotropic case. The steady-state electric field light scattering effect Δ I/I_0 is measured as a function of the electric field strength and its frequency at a fixed scattering angle. The determination of the anisotropy of the electric polarizability Δα_el of a fd-virus particle at higher electric field strengths, above the Kerr regime, shows a decrease of Δα_el with increasing field. This is interpreted as a destruction of the diffuse Debye cloud in high electric fields. The orientational order parameter has been found to be as large as 0.93 indicating an almost complete particle orientation along the external field at the highest fields. It is also shown that in the frequency regime below 1 kHz electrostatically interacting rods can align perpendicular to the external electric field, whereas at higher frequencies this anomalous behaviour disappears. From the scattered intensity the form-factor and the static structure factor of interacting fd-virus particles have been determined. With increasing fields a substantial increase in the peak height of the static structure factor is found. The data is in good agreement with Monte Carlo simulations using a simple interaction model for the system. The orientation of the macromolecules in the presence of an electric field is affected by the
Angular Spectrum Method for the Focused Acoustic Field of a Linear Transducer
NASA Astrophysics Data System (ADS)
Belgroune, D.; de Belleval, J. F.; Djelouah, H.
Applications involving non-destructive testing or acoustical imaging are more and more sophisticated. In this context, a model based on the angular spectrum approach is tackled in view to calculate the focused impulse field radiated by a linear transducer through a plane fluid-solid interface. It is well known that electronic focusing, based on a cylindrical delay law, like for the classical cases (lenses, curved transducer), leads to an inaccurate focusing in the solid due to geometric aberrations errors affecting refraction. Generally, there is a significant difference between the acoustic focal distance and the geometrical focal due to refraction. In our work, an optimized delay law, based on the Fermat's principle is established, particularly at an oblique incidence where the geometrical considerations, relatively simple in normal incidence, become quickly laborious. Numerical simulations of impulse field are judiciously carried out. Subsequently, the input parameters are optimally selected in order to achieve good computation accuracy and a high focusing. The overall results, involving compression and shear waves, have highlighted the focusing improvement in the solid when compared to the currently available approaches. Indeed, the acoustic focal distance is very close to geometrical focal distance and then, allows better control of the refracted angular beam profile (refraction angle, focusing depth and focal size).
Dark matter effective field theory scattering in direct detection experiments
Schneck, K.; Cabrera, B.; Cerdeno, D. G.; Mandic, V.; Rogers, H. E.; Agnese, R.; Anderson, A. J.; Asai, M.; Balakishiyeva, D.; Barker, D.; Basu Thakur, R.; Bauer, D. A.; Billard, J.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Caldwell, D. O.; Calkins, R.; Chagani, H.; Chen, Y.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; Di Stefano, P. C.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Harris, H. R.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jardin, D. M.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kennedy, A.; Leder, A.; Loer, B.; Lopez Asamar, E.; Lukens, W.; Mahapatra, R.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Morales Mendoza, J. D.; Oser, S. M.; Page, K.; Page, W. A.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Rau, W.; Redl, P.; Reisetter, A.; Ricci, Y.; Roberts, A.; Saab, T.; Sadoulet, B.; Sander, J.; Schnee, R. W.; Scorza, S.; Serfass, B.; Shank, B.; Speller, D.; Toback, D.; Upadhyayula, S.; Villano, A. N.; Welliver, B.; Wilson, J. S.; Wright, D. H.; Yang, X.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.
2015-05-01
We examine the consequences of the effective eld theory (EFT) of dark matter-nucleon scattering or current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral di*erences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.
Imaging of Passive Scalar Fields by Filtered Rayleigh Scattering
NASA Astrophysics Data System (ADS)
Kearney, Sean; Grasser, Thomas; Beresh, Steven; Schefer, Robert
2002-11-01
Filtered Rayleigh Scattering (FRS) is a molecular-filter-based, laser-diagnostic approach for multiparameter flowfield imaging that has been gaining popularity over the past 5-10 years [1]. Advantages of FRS for noninvasive gas-phase imaging include: (1) elimination of particle or chemical seeding requirements, (2) increased optical noise rejection allowing imaging close to walls and in "dirty" laboratory environments, (3) imaging of multiple flowfield parameters with a single diagnostic. In this work, the construction and performance of a FRS optical system for passive scalar imaging at Sandia National Laboratories is presented. Data were obtained in an open lab where no special precautions for the elimination of room particulate were made. Results from nonreacting jets and from a premixed flame are shown. Temperature imaging in a nonreacting, steady calibration jet reveals the precision of the time-averaged FRS thermometry results to be ±20 K, or 4of the characteristic temperature difference, while the single-laser-pulse precision is degraded to approximately ±40-50 K. These results are adequate for combustion thermometry purposes. Relative to the jet temperature measurements, species concentration imaging of a buoyant helium jet displays increased signal dynamic range and further improved precision. Reacting flow measurements from the combustion-product region of a methane-air Hencken-type premixed flame are also presented and a comparison of FRS and coherent anti-Stokes Raman scattering (CARS) experiments to calculated adiabatic-equilibrium product temperatures is made which validates the suitability of our FRS instrument for combustion temperature imaging. [1]G.S. Elliott, N. Glumac, and C.D. Carter, Meas. Sci. Tech., 12, 452, 2001.
Fan, Zongwei; Mei, Deqing; Yang, Keji; Chen, Zichen
2014-12-01
To eliminate the limitations of the conventional sound field separation methods which are only applicable to regular surfaces, a sound field separation method based on combined integral equations is proposed to separate sound fields directly in the spatial domain. In virtue of the Helmholtz integral equations for the incident and scattering fields outside a sound scatterer, combined integral equations are derived for sound field separation, which build the quantitative relationship between the sound fields on two arbitrary separation surfaces enclosing the sound scatterer. Through boundary element discretization of the two surfaces, corresponding systems of linear equations are obtained for practical application. Numerical simulations are performed for sound field separation on different shaped surfaces. The influences induced by the aspect ratio of the separation surfaces and the signal noise in the measurement data are also investigated. The separated incident and scattering sound fields agree well with the original corresponding fields described by analytical expressions, which validates the effectiveness and accuracy of the combined integral equations based separation method.
Mantsevich, S N; Molchanov, V Ya; Yushkov, K B; Khorkin, V S; Kupreychik, M I
2017-04-02
Ultrasound wave reflection from one of the crystal faces is the convenient way to arouse the acoustic beam with a desired propagation direction in acousto-optic cells with collinear and quasi-collinear interaction geometries. The reflection process effects on the ultrasound field amplitude and phase structure. The method to simulate the reflected finite ultrasound beam structure in the case of acoustically anisotropic media is presented in this paper. The investigation is carried on the example of two quasi-collinear acousto-optic cells fabricated on the base of tellurium dioxide crystal. The cells have special geometry that allows to obtain extremely long acousto-optic interaction length and to achieve unprecedented spectral resolution. The influence of reflection process in the acousto-optic diffraction characteristics was also examined.
On an acoustic field generated by subsonic jet at low Reynolds numbers
NASA Technical Reports Server (NTRS)
Yamamoto, K.; Arndt, R. E. A.
1978-01-01
An acoustic field generated by subsonic jets at low Reynolds numbers was investigated. This work is motivated by the need to increase the fundamental understanding of the jet noise generation mechanism which is essential to the development of further advanced techniques of noise suppression. The scope of this study consists of two major investigation. One is a study of large scale coherent structure in the jet turbulence, and the other is a study of the Reynolds number dependence of jet noise. With this in mind, extensive flow and acoustic measurements in low Reynolds number turbulent jets (8,930 less than or equal to M less than or equal to 220,000) were undertaken using miniature nozzles of the same configuration but different diameters at various exist Mach numbers (0.2 less than or equal to M less than or equal to 0.9).
Flow and far field acoustic amplification properties of heated and unheated jets
NASA Technical Reports Server (NTRS)
Maestrello, L.; Bayliss, A.
1981-01-01
The interaction of an acoustic pulse with the experimentally determined mean flow field of a spreading jet is simulated numerically. The simulation is obtained through solving the Euler equations linearized about the spreading jet. The model reveals a small, sustained oscillation long after the original pulse has passed. This remnant is considered a continual shedding of vortices from the nozzle lip, together with the generation of acoustic ripples. IT is shown that the jet also acts as an amplifier of sound. This amplification is traced to the jet's stability characteristics. It is demonstrated that some of the observed differences in the spectra of heated and unheated jets can be attributed to differences in the stability characteristics of the jets.
Far-field acoustic data for the Texas ASE, Inc. hush house
NASA Astrophysics Data System (ADS)
Lee, R. A.
1982-04-01
This report supplements AFAMRL-TR-73-110, which describes the data base (NOISEFILE) used in the computer program (NOISEMAP) to predict the community noise exposure resulting from military aircraft operations. The results of field test measurements to define the single-event noise produced on the ground by military aircraft/engines operating in the Texas ASE Inc. hush-house are presented as a function of angle (0 deg to 180 deg from the front of the hush-house) and distance (200 ft to 2500 ft) in various acoustic metrics. All the data are normalized to standard acoustic reference conditions of 59 F temperature and 70% relative humidity. Refer to Volume I of the AFAMRL-TR-73-110 report for discussion of the scope, limitations, and definitions needed to understand and use the data in this report.
NASA Astrophysics Data System (ADS)
Raczkowska, A.; Gorska, N.
2012-12-01
Puck Bay is an area of high species biodiversity belonging to the Coastal Landscape Park of Baltic Sea Protected Areas (BSPA) and is also included in the list of the World Wide Fund for Nature (WWF) and covered by the protection program "Natura 2000". The underwater meadows of the Puck Bay are important for Europe's natural habitats due to their role in enhancing the productivity of marine ecosystems and providing shelter and optimal feeding conditions for many marine organisms. One of the dominant species comprising the underwater meadows of the Southern Baltic Sea is the seagrass Zostera marina. The spatial extent of underwater seagrass meadows is altered by pollution and eutrophication; therefore, to properly manage the area one must monitor its ecological state. Remote acoustic methods are useful tools for the monitoring of benthic habitats in many marine areas because they are non-invasive and allow researchers to obtain data from a large area in a short period of time. Currently there is a need to apply these methods in the Baltic Sea. Here we present an analysis of the mechanism of scattering of acoustic waves on seagrass in the Southern Baltic Sea based on the numerical modeling of acoustic wave scattering by the biological tissues of plants. The study was conducted by adapting a model developed on the basis of DWBA (Distorted Wave Born Approximation) developed by Stanton and Chu (2005) for fluid-like objects, including the characteristics of the Southern Baltic seagrass. Input data for the model, including the morphometry of seagrass leaves, their angle of inclination and the density plant cover, was obtained through the analysis of biological materials collected in the Puck Bay in the framework of a research project financed by the Polish Government (Development of hydroacoustic methods for studies of underwater meadows of Puck Bay, 6P04E 051 20). On the basis of the developed model, we have analyzed the dependence of the target strength of a single
Acoustic integrated extinction
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
Bragg scattering of light in vacuum structured by strong periodic fields.
Kryuchkyan, Gagik Yu; Hatsagortsyan, Karen Z
2011-07-29
Elastic scattering of laser radiation due to vacuum polarization by spatially modulated strong electromagnetic fields is considered. The Bragg interference arising at a specific impinging direction of the probe wave concentrates the scattered light in specular directions. The interference maxima are enhanced with respect to the usual vacuum polarization effect proportional to the square of the number of modulation periods within the interaction region. The Bragg scattering can be employed to detect the vacuum polarization effect in a setup of multiple crossed superstrong laser beams with parameters envisaged in the future Extreme Light Infrastructure.
Effective field theory for large logarithms in radiative corrections to electron proton scattering
NASA Astrophysics Data System (ADS)
Hill, Richard J.
2017-01-01
Radiative corrections to elastic electron proton scattering are analyzed in effective field theory. A new factorization formula identifies all sources of large logarithms in the limit of large momentum transfer, Q2≫me2. Explicit matching calculations are performed through two-loop order. A renormalization analysis in soft-collinear effective theory is performed to systematically compute and resum large logarithms. Implications for the extraction of charge radii and other observables from scattering data are discussed. The formalism may be applied to other lepton-nucleon scattering and e+e- annihilation processes.
Mishchenko, Michael I; Yurkin, Maxim A
2017-02-01
Although the model of randomly oriented nonspherical particles has been used in a great variety of applications of far-field electromagnetic scattering, it has never been defined in strict mathematical terms. In this Letter, we use the formalism of Euler rigid-body rotations to clarify the concept of statistically random particle orientations and derive its immediate corollaries in the form of the most general mathematical properties of the orientation-averaged extinction and scattering matrices. Our results serve to provide a rigorous mathematical foundation for numerous publications in which the notion of randomly oriented particles and its light-scattering implications have been considered intuitively obvious.
Louis, A. K.
2006-01-01
Many algorithms applied in inverse scattering problems use source-field systems instead of the direct computation of the unknown scatterer. It is well known that the resulting source problem does not have a unique solution, since certain parts of the source totally vanish outside of the reconstruction area. This paper provides for the two-dimensional case special sets of functions, which include all radiating and all nonradiating parts of the source. These sets are used to solve an acoustic inverse problem in two steps. The problem under discussion consists of determining an inhomogeneous obstacle supported in a part of a disc, from data, known for a subset of a two-dimensional circle. In a first step, the radiating parts are computed by solving a linear problem. The second step is nonlinear and consists of determining the nonradiating parts. PMID:23165060
Kusch, Patryk; Mastel, Stefan; Mueller, Niclas S; Morquillas Azpiazu, Nieves; Heeg, Sebastian; Gorbachev, Roman; Schedin, Fredrik; Hübner, Uwe; Pascual, Jose I; Reich, Stephanie; Hillenbrand, Rainer
2017-04-12
Surface-enhanced Raman spectroscopy (SERS) enables sensitive chemical studies and materials identification, relying on electromagnetic (EM) and chemical-enhancement mechanisms. Here we introduce a tool for the correlative nanoimaging of EM and SERS hotspots, areas of strongly enhanced EM fields and Raman scattering, respectively. To that end, we implemented a grating spectrometer into a scattering-type scanning near-field optical microscope (s-SNOM) for mapping of both the elastically and inelastically (Raman) scattered light from the near-field probe, that is, a sharp silicon tip. With plasmon-resonant gold dimers (canonical SERS substrates) we demonstrate with nanoscale spatial resolution that the enhanced Raman scattering from the tip is strongly correlated with its enhanced elastic scattering, the latter providing access to the EM-field enhancement at the illumination frequency. Our technique has wide application potential in the correlative nanoimaging of local-field enhancement and SERS efficiency as well as in the investigation and quality control of novel SERS substrates.
Acoustic anomalies in UPt{3} at high magnetic fields and low temperatures.
Feller, J. R.; Ketterson, J. B.; Hinks, D. G.; Dasgupta, D.; Sarma, B. K.; Materials Science Division; Northwestern Univ.; Univ. of Wisconsin at Milwaukee
2000-11-01
Ultrasound velocity and attenuation measurements were performed on single crystals of the heavy fermion compound UPt{sub 3} in magnetic fields up to 33 T and at temperatures ranging from 2.4 K to below 0.1 K. With longitudinal sound propagated in the crystallographic basal plane, parallel to the applied field, the familiar elastic softening is observed at the metamagnetic transition field H-20.2 T. More complicated structure emerges at low temperatures, including quantum acoustic oscillations and a second velocity minimum at -21.6 T. A weak frequency dependence (dispersion) is observed in the velocity. The ultrasonic data are analyzed using the Landau-Khalatnikov formalism, from which temperature- and field-dependent relaxation times are deduced.
NASA Astrophysics Data System (ADS)
Voie, Arne; Fisher, David; Ahadi, Golnaz; Hölscher, Thilo
2012-11-01
The purpose of this study was to ascertain the effects of the skull on the location, shape and power of the acoustic field produced by a 150 mm radius hemispherical array operating at 220 kHz. We wanted to determine whether phase aberrations were significant at this frequency, the amount of attenuation, and whether CT data could be predictive of the trans-skull field. The effects of five calvaria were evaluated. Acoustic field data and CT scans for each skull specimen were imported into MATLAB® for measurements and visualization in two and three dimensions. We examined the effects of skull density, porosity, thickness, and sonication incident angles, and estimated the relative contributions of longitudinal and shear transmission to the total transmitted power. Power transmission through the skulls varied between 4% and 23% (mean: 12%). The range of focal position shifts was from 0.50 mm to 4.32 mm (mean: 1.95 mm). The 3 dB dimensions of the focused ultrasound (FUS) intensity focal volume increased on average by 39% (low: 4%, high: 122%). The 6 dB pressure focal volume increased by an average of 130 ± 75%. In general, the main effects of the skulls were power reduction, field dispersion and slight shift of focal peak location.
NASA Astrophysics Data System (ADS)
Xu, Xiaodong; Agustin Flores Cuautle, Jose Jesus; Kouyate, Mansour; Bernardus Roozen, Nicolaas; Goossens, Jozefien; Menon, Preethy; Kuriakose Malayil, Maju; Salenbien, Robbe; Nair Rajesh, Ravindran; Glorieux, Christ; Griesmar, Pascal; Martinez, Loïc; Serfaty, Stéphane
2016-03-01
The evolution of the elastic and thermal properties of a tetramethylorthosilicate (TMOS)-based gel that exhibits an extraordinary ringing effect when enclosed in a bottle is investigated during the sol-gel transition. The results demonstrate the feasibility of three proposed experimental methods for monitoring of gels during their formation. The shear stiffening evolution during gelation is monitored by ringing bottle, resonant acoustic spectroscopy and by an ultrasonic technique using piezo electric excitation and detection. The evolution of the longitudinal modulus and the thermal diffusivity of the gel during stiffening are simultaneously determined by a combined photoacoustic and photothermal method based on heterodyne diffraction detection of impulsive stimulated scattering by, respectively, a propagating acoustic wave grating and a decaying thermal expansion grating that were both thermo elastically generated using a pulsed laser. Also, the feasibility of an inverse photopyroelectric method and a hot ball technique to monitor the thermal transport efficiency and thermal impedance of a forming gel by tracking the thermal conductivity, the thermal diffusivity, and the thermal effusivity is demonstrated. The network polymerization and stiffening during the sol-gel transition in TMOS-gel corresponds with substantial changes in the shear acoustic velocity and in all thermal properties, while the longitudinal acoustic velocity is only weakly affected.
Scattering in an external electric field asymptotically constant in time
Adachi, Tadayoshi; Ishida, Atsuhide
2011-06-15
We show the asymptotic completeness for two-body quantum systems in an external electric field asymptotically non-zero constant in time. One of the main ingredients of this paper is to give some propagation estimates for physical propagators generated by time-dependent Hamiltonians which govern the systems under consideration.
The effects of external acoustic pressure fields on a free-running supercavitating projectile.
Cameron, Peter J K; Rogers, Peter H; Doane, John W
2010-12-01
Proliferation of supercavitating torpedoes has motivated research on countermeasures against them as well as on the fluid phenomenon which makes them possible. The goal of this research was to investigate an envisaged countermeasure, an acoustic field capable of slowing or diverting the weapon by disrupting the cavitation envelope. The research focused on the interactions between high pressure amplitude sound waves and a supercavity produced by a small free-flying projectile. The flight dynamics and cavity geometry measurements were compared to control experiments and theoretical considerations were made for evaluating the effects. Corrugations on the cavity/water interface caused by the pressure signal have been observed and characterized. Results also show that the accuracy of a supercavitating projectile can be adversely affected by the sound signal. This research concludes with results that indicate that it is acoustic cavitation in the medium surrounding the supercavity, caused by the high pressure amplitude sound, that is responsible for the reduced accuracy. A hypothesis has been presented addressing the means by which the acoustic cavitation could cause this effect.
Wisniewska, Danuta M; Ratcliffe, John M; Beedholm, Kristian; Christensen, Christian B; Johnson, Mark; Koblitz, Jens C; Wahlberg, Magnus; Madsen, Peter T
2015-01-01
Toothed whales use sonar to detect, locate, and track prey. They adjust emitted sound intensity, auditory sensitivity and click rate to target range, and terminate prey pursuits with high-repetition-rate, low-intensity buzzes. However, their narrow acoustic field of view (FOV) is considered stable throughout target approach, which could facilitate prey escape at close-range. Here, we show that, like some bats, harbour porpoises can broaden their biosonar beam during the terminal phase of attack but, unlike bats, maintain the ability to change beamwidth within this phase. Based on video, MRI, and acoustic-tag recordings, we propose this flexibility is modulated by the melon and implemented to accommodate dynamic spatial relationships with prey and acoustic complexity of surroundings. Despite independent evolution and different means of sound generation and transmission, whales and bats adaptively change their FOV, suggesting that beamwidth flexibility has been an important driver in the evolution of echolocation for prey tracking. DOI: http://dx.doi.org/10.7554/eLife.05651.001 PMID:25793440
Sensitivity of simulated transcranial ultrasound fields to acoustic medium property maps
NASA Astrophysics Data System (ADS)
Robertson, James; Martin, Eleanor; Cox, Ben; Treeby, Bradley E.
2017-04-01
High intensity transcranial focused ultrasound is an FDA approved treatment for essential tremor, while low-intensity applications such as neurostimulation and opening the blood brain barrier are under active research. Simulations of transcranial ultrasound propagation are used both for focusing through the skull, and predicting intracranial fields. Maps of the skull acoustic properties are necessary for accurate simulations, and can be derived from medical images using a variety of methods. The skull maps range from segmented, homogeneous models, to fully heterogeneous models derived from medical image intensity. In the present work, the impact of uncertainties in the skull properties is examined using a model of transcranial propagation from a single element focused transducer. The impact of changes in bone layer geometry and the sound speed, density, and acoustic absorption values is quantified through a numerical sensitivity analysis. Sound speed is shown to be the most influential acoustic property, and must be defined with less than 4% error to obtain acceptable accuracy in simulated focus pressure, position, and volume. Changes in the skull thickness of as little as 0.1 mm can cause an error in peak intracranial pressure of greater than 5%, while smoothing with a 1 \\text{m}{{\\text{m}}3} kernel to imitate the effect of obtaining skull maps from low resolution images causes an increase of over 50% in peak pressure. The numerical results are confirmed experimentally through comparison with sonications made through 3D printed and resin cast skull bone phantoms.
Sensitivity of simulated transcranial ultrasound fields to acoustic medium property maps.
Robertson, James; Martin, Eleanor; Cox, Ben; Treeby, Bradley E
2017-04-07
High intensity transcranial focused ultrasound is an FDA approved treatment for essential tremor, while low-intensity applications such as neurostimulation and opening the blood brain barrier are under active research. Simulations of transcranial ultrasound propagation are used both for focusing through the skull, and predicting intracranial fields. Maps of the skull acoustic properties are necessary for accurate simulations, and can be derived from medical images using a variety of methods. The skull maps range from segmented, homogeneous models, to fully heterogeneous models derived from medical image intensity. In the present work, the impact of uncertainties in the skull properties is examined using a model of transcranial propagation from a single element focused transducer. The impact of changes in bone layer geometry and the sound speed, density, and acoustic absorption values is quantified through a numerical sensitivity analysis. Sound speed is shown to be the most influential acoustic property, and must be defined with less than 4% error to obtain acceptable accuracy in simulated focus pressure, position, and volume. Changes in the skull thickness of as little as 0.1 mm can cause an error in peak intracranial pressure of greater than 5%, while smoothing with a 1 [Formula: see text] kernel to imitate the effect of obtaining skull maps from low resolution images causes an increase of over 50% in peak pressure. The numerical results are confirmed experimentally through comparison with sonications made through 3D printed and resin cast skull bone phantoms.
Wang, Dongdong; Hu, Hanping; Wang, Zedong
2015-02-01
Thermo-acoustic (TA) ultrasound has attracted considerable interest during the last decade for its many advantages over the conventional electro-acoustic ultrasound. In this paper, a general expression of the acoustic pressure field of thermally induced ultrasonic emission from a spherical cavity surface is derived by using a fully thermally-mechanically coupled TA model. The characteristics and regularities of ultrasound from spherical focusing TA emitter can therefore be studied in detail. It is found that, for the TA emission in sphere shell, wideband flat amplitude-frequency response pattern, the most important feature of TA ultrasound in an open space from a technical standpoint, is seriously disrupted by wave interference occurring in spherical cavity. The dependences of sound pressure of TA ultrasound in spherical cavity on the heating frequency, the inner radius of spherical cavity, the location in spherical cavity, and the thickness of TA sample layer, as well as the type and filling pressure of gas in cavity are given and discussed. The currently used planar TA solution is only the special case for spherical cavity with infinite radius of the analytical solution developed in this work, which would be of significance for more comprehensive guide to understanding and using TA ultrasound.
Drake, R.P.; Bauer, B.S.; Baker, K.L. |
1994-03-07
In this project, we advanced knowledge of Ion Acoustic Decay on several fronts. In this project, we have developed and demonstrated the capability to perform experimental and theoretical studies of the Ion Acoustic Decay Instability. We have at the same time demonstrated an improved capability to do multichannel spectroscopy and Thomson scattering. We made the first observations of the time-resolved second harmonic emission at several angles simultaneously, and the first observations of the emission both parallel and perpendicular to the electric field of the laser light. We used Thomson scattering to make the first observations of the plasma waves driven by acoustic decay in a warm plasma with long density scale lengths. We also advanced both the linear and the nonlinear theory of this instability. We are thus prepared to perform experiments to address this mechanism as needed for applications.
Bulanov, Alexey V.; Nagorny, Ivan G.
2015-10-28
Researches of the acoustic effects accompanying optical breakdown in a water, generated by the focused laser radiation with power ultrasound have been carried out. Experiments were performed by using 532 nm pulses from Brilliant B Nd:YAG laser. Acoustic radiation was produced by acoustic focusing systems in the form hemisphere and ring by various resonance frequencies of 10.7 kHz and 60 kHz. The experimental results are obtained, that show the sharply strengthens effects of acoustic emission from a breakdown zone by the joint influence of a laser and ultrasonic irradiation. Essentially various thresholds of breakdown and character of acoustic emission in fresh and sea water are found out. The experimental result is established, testifying that acoustic emission of optical breakdown of sea water at presence and at absence of ultrasound essentially exceeds acoustic emission in fresh water. Atomic lines of some chemical elements like a Sodium, Magnesium and so on were investigated for laser breakdown of water with ultrasound field. The effect of magnification of this lines resolution for salt water in ultrasound field was obtained.
NASA Astrophysics Data System (ADS)
Buică, Gabriela
2017-01-01
We theoretically study the influence of laser polarization in inelastic scattering of electrons by hydrogen atoms in the presence of a circularly polarized laser field in the domain of field strengths below 107 V/cm and high projectile energies. A semi-perturbative approach is used in which the interaction of the projectile electrons with the laser field is described by Gordon-Volkov wave functions, while the interaction of the hydrogen atom with the laser field is described by first-order time-dependent perturbation theory. A closed analytical solution is derived in laser-assisted inelastic electron-hydrogen scattering for the 1 s → nl excitation cross section which is valid for both circular and linear polarizations. For the excitation of the n=2 levels simple analytical expressions of differential cross section are derived for laser-assisted inelastic scattering in the perturbative domain, and the differential cross sections by the circularly and linearly polarized laser fields and their ratios for one- and two-photon absorption are calculated as a function of the scattering angle. Detailed numerical results for the angular dependence and the resonance structure of the differential cross sections are discussed for the 1 s → 4 l excitations of hydrogen in a circularly polarized laser field.
Study on the bubble transport mechanism in an acoustic standing wave field.
Xi, Xiaoyu; Cegla, Frederic B; Lowe, Michael; Thiemann, Andrea; Nowak, Till; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander
2011-12-01
The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller-Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton's second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of
Tunable far-field acoustic imaging by two-dimensional sonic crystal with concave incident surface
NASA Astrophysics Data System (ADS)
Shen, Feng-Fu; Lu, Dan-Feng; Zhu, Hong-Wei; Ji, Chang-Ying; Shi, Qing-Fan
2017-01-01
An additional concave incident surface comprised of two-dimensional (2D) sonic crystals (SCs) is employed to tune the acoustic image in the far-field region. The tunability is realized through changing the curvature of the concave surface. To explain the tuning mechanism, a simple ray-trace analysis is demonstrated based on the wave-beam negative refractive law. Then, a numerical confirmation is carried out. Results show that both the position and the intensity of the image can be tuned by the introduced concave surface.
Review of Numerical Models in Underwater Acoustics, Including Recently Developed Fast-Field Program,
1984-12-15
scope of bringing together researchers in different fields of wave propagation (electromagnetics, optics , seismics, underwater acoustics) to exchange...discussed in this paper. A more detailed description can be found in references ə-10>. The starting point for all the models is the wave equation for a...harmonic point source with time dppendence exp(-iwt), V2*(x’yz) + * ] (x,Y,z) = -6(x-Xo)6(y-yo)6(z-zo ) (1) * *exp(-iwt) (2) At any point (x,y,z) in
Far-field acoustic data for the Texas ASE, Inc. Hush-House, supplement
NASA Astrophysics Data System (ADS)
Lee, R. A.
1982-04-01
This report supplements AFAMRL-TR-73-110, which describes the data base (NOISEFILE) used in the computer program (NOISEMAP) to predict the community noise exposure resulting from military aircraft operations. The results of field test measurements to define the single-event noise produced on the ground by military aircraft/engines operating in the Texas ASE Inc. hush-house are presented as a function of angle (0 to 180 from the front of the hush-house) and distance (200 ft to 2500 ft) in various acoustic metrics.
Measurements of underwater acoustic pressure fields using a scanning laser Doppler vibrometer
NASA Astrophysics Data System (ADS)
Carroll, Gerard P.
2004-05-01
Laser Doppler vibrometers (LDV) are designed to measure structural vibration velocity by sensing the phase shift in the laser signal reflected from a vibrating source. It is known that index of refraction modulations resulting from acoustic pressure distributions along a laser light path will also cause a phase shift. Simpson et al. [J. Acoust. Soc. Am. 99(4), 2521(A) (1996)] have investigated this acousto-optic phase modulation as a possible contaminating effect for underwater LDV vibration measurements. This paper will investigate acousto-optic phase modulations measured by a scanning LDV as a method for measuring pressure radiating from underwater vibrating surfaces. This is done by passing the laser beam through the radiating pressure field and measuring the backscattered laser signal which is reflected off a rigid and retroreflective surface (outside the pressure field). It is shown experimentally, using the average pressure measured with an LDV over a plane in the vicinity of a vibrating structure, that the pressure at a far-field location normal to the plane can be determined.
Perez, Camilo; Chen, Hong; Matula, Thomas J.; Karzova, Maria; Khokhlova, Vera A.
2013-01-01
Extracorporeal shock wave therapy (ESWT) uses acoustic pulses to treat certain musculoskeletal disorders. In this paper the acoustic field of a clinical portable ESWT device (Duolith SD1) was characterized. Field mapping was performed in water for two different standoffs of the electromagnetic head (15 or 30 mm) using a fiber optic probe hydrophone. Peak positive pressures at the focus ranged from 2 to 45 MPa, while peak negative pressures ranged from −2 to −11 MPa. Pulse rise times ranged from 8 to 500 ns; shock formation did not occur for any machine settings. The maximum standard deviation in peak pressure at the focus was 1.2%, indicating that the Duolith SD1 generates stable pulses. The results compare qualitatively, but not quantitatively with manufacturer specifications. Simulations were carried out for the short standoff by matching a Khokhlov-Zabolotskaya-Kuznetzov equation to the measured field at a plane near the source, and then propagating the wave outward. The results of modeling agree well with experimental data. The model was used to analyze the spatial structure of the peak pressures. Predictions from the model suggest that a true shock wave could be obtained in water if the initial pressure output of the device were doubled. PMID:23927207
Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field
Ghosh, Samiran; Ehsan, Z.; Murtaza, G.
2008-02-15
The effects of nonsteady dust charge variations and weak magnetic field on small but finite amplitude nonlinear dust acoustic wave in electronegative dusty plasma are investigated. The dynamics of the nonlinear wave are governed by a Korteweg-de Vries Burger equation that possesses dispersive shock wave. The weak magnetic field is responsible for the dispersive term, whereas nonsteady dust charge variation is responsible for dissipative term, i.e., the Burger term. The coefficient of dissipative term depends only on the obliqueness of the magnetic field. It is found that for parallel propagation the dynamics of the nonlinear wave are governed by the Burger equation that possesses monotonic shock wave. The relevances of the findings to cometary dusty plasma, e.g., Comet Halley are briefly discussed.
NASA Astrophysics Data System (ADS)
Huang, Xue-Feng; Li, Sheng-Ji
2014-04-01
We report an approach to detect near-field nanofluid concentration by scattering Bragg grating evanescent wave (EW). Since the suspended nanoparticles can enhance the scattering intensity of the EW from the thinned and tapered fiber with Bragg grating, the reflectance ratio of Bragg grating is dependent on the corresponding refractive index (RI) of the nanofluid at different nanoparticle volume fraction. A critical reflectance ratio measurement identifies the nanofluid concentration. Theory and simulation of scattering Bragg grating EW was analyzed. The scattering Bragg grating EW fiber sensing probe was designed and fabricated by the wet chemical etching method, and calibration was made by several chemical solutions without suspended nanoparticles. The example application of the nanofluid containing dispersed 40 nm SiO2 nanoparticles demonstrates the feasibility. The reflectance ratio decreases by over 3.2% with the nanofluid concentration increasing from 0.25 wt.% to 4 wt.%, while the temperature disturbance can be negligible.
Biswas, Tutul; Ghosh, Tarun Kanti
2013-01-23
We study the interaction between electron and acoustic phonons in a Rashba spin-orbit coupled two-dimensional electron gas using Boltzmann transport theory. Both the deformation potential and piezoelectric scattering mechanisms are considered in the Bloch-Grüneisen (BG) regime as well as in the equipartition (EP) regime. The effect of the Rashba spin-orbit interaction on the temperature dependence of the resistivity in the BG and EP regimes is discussed. We find that the effective exponent of the temperature dependence of the resistivity in the BG regime decreases due to spin-orbit coupling.
Lee, Seungah; Park, Guenyoung; Chakkarapani, Suresh Kumar; Kang, Seong Ho
2015-01-15
Novel, fluorescence-free detection of biomolecules on nanobiochips was investigated based on plasmonic nanometal scattering in the evanescent field layer (EFL) using total internal reflection scattering (TIRS) microscopy. The plasmonic scattering of nanometals bonded to biomolecules was observed at different wavelengths by an electromagnetic field in the EFL. The changes in the scattering of nanometals on the gold-nanopatterned chip in response to the immunoreaction between silver nanoparticles and antibodies allowed fluorescence-free detection of biomolecules on the nanobiochips. Under optimized conditions, the TIRS immunoassay chip detected different amounts of immobilized antigen, i.e., human cardiac troponin I. The sandwich immuno-reaction was quantitatively analyzed in the dynamic range of 720 zM-167 fM. The limit of detection (S/N=4) was 600 zM, which was ~140 times lower than limits obtained by previous total internal reflection fluorescence and dark field methods. These results demonstrate the possibility for a fluorescence-free biochip nanoimmunoassay based on the scattering of nanometals in the EFL.
Elements of QED-NRQED effective field theory: NLO scattering at leading power
NASA Astrophysics Data System (ADS)
Dye, Steven P.; Gonderinger, Matthew; Paz, Gil
2016-07-01
The proton radius puzzle, i.e. the large discrepancy in the extraction of the proton charge radius between regular and muonic hydrogen, challenges our understanding of the structure of the proton. It can also be an indication of a new force that couples to muons, but not to electrons. An effective field theory analysis using nonrelativistic quantum electrodynamics (NRQED) indicates that the muonic hydrogen result can be interpreted as a large, compared to some model estimates, muon-proton spin-independent contact interaction. The muonic hydrogen result can be tested by a muon-proton scattering experiment, MUSE, that is planned at the Paul Scherrer Institute in Switzerland. The typical momenta of the muons in this experiment are of the order of the muon mass. In this energy regime the muons are relativistic but the protons are still nonrelativistic. The interaction between the muons and protons can be described by a hybrid QED-NRQED effective field theory. We present some elements of this effective field theory. In particular we consider O (Z α ) scattering up to power m2/M2 , where m (M ) is the muon (proton) mass and Z =1 for a proton, and O (Z2α2) scattering at leading power. We show how the former reproduces Rosenbluth scattering up to power m2/M2 and the latter the relativistic scattering off a static potential. Proton structure corrections at O (Z2α2) will be considered in a subsequent paper.
Acoustic pressure waves induced in human heads by RF pulses from high-field MRI scanners.
Lin, James C; Wang, Zhangwei
2010-04-01
The current evolution toward greater image resolution from magnetic resonance image (MRI) scanners has prompted the exploration of higher strength magnetic fields and use of higher levels of radio frequencies (RFs). Auditory perception of RF pulses by humans has been reported during MRI with head coils. It has shown that the mechanism of interaction for the auditory effect is caused by an RF pulse-induced thermoelastic pressure wave inside the head. We report a computational study of the intensity and frequency of thermoelastic pressure waves generated by RF pulses in the human head inside high-field MRI and clinical scanners. The U.S. Food and Drug Administration (U.S. FDA) guides limit the local specific absorption rate (SAR) in the body-including the head-to 8 W kg(-1). We present results as functions of SAR and show that for a given SAR the peak acoustic pressures generated in the anatomic head model were essentially the same at 64, 300, and 400 MHz (1.5, 7.0, and 9.4 T). Pressures generated in the anatomic head are comparable to the threshold pressure of 20 mPa for sound perception by humans at the cochlea for 4 W kg(-1). Moreover, results indicate that the peak acoustic pressure in the brain is only 2 to 3 times the auditory threshold at the U.S. FDA guideline of 8 W kg(-1). Even at a high SAR of 20 W kg(-1), where the acoustic pressure in the brain could be more than 7 times the auditory threshold, the sound pressure levels would not be more than 17 db above threshold of perception at the cochlea.
NASA Astrophysics Data System (ADS)
Xia, Baizhan; Yin, Hui; Yu, Dejie
2017-02-01
The response of the acoustic field, especially for the mid-frequency response, is very sensitive to uncertainties rising from manufacturing/construction tolerances, aggressive environmental factors and unpredictable excitations. To quantify these uncertainties with limited information effectively, two nondeterministic models (the interval model and the hybrid probability-interval model) are introduced. And then, two corresponding nondeterministic numerical methods are developed for the low- and mid-frequency response analysis of the acoustic field under these two nondeterministic models. The first one is the interval perturbation wave-based method (IPWBM) which is proposed to predict the maximal values of the low- and mid-frequency responses of the acoustic field under the interval model. The second one is the hybrid perturbation wave-based method (HPWBM) which is proposed to predict the maximal values of expectations and standard variances of the low- and mid-frequency responses of the acoustic field under the hybrid probability-interval model. The effectiveness and efficiency of the proposed nondeterministic numerical methods for the low- and mid-frequency response analysis of the acoustic field under the interval model and the hybrid probability-interval model are investigated by a numerical example.
Light Scattering Studies of Organic Field Effect Transistors
NASA Astrophysics Data System (ADS)
Adil, Danish
Organic semiconductors hold a great promise of enabling new technology based on low cost and flexible electronic devices. While much work has been done in the field of organic semiconductors, the field is still quite immature when compared to that of traditional inorganic based devices. More work is required before the full potential of organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), and organic photovoltaics (OPVs) is realized. Among such work, a further development of diagnostic tools that characterize charge transport and device robustness more efficiently is required. Charge transport in organic semiconductors is limited by the nature of the metal-semiconductor interfaces where charge is injected into the semiconductor film and the semiconductor-dielectric interface where the charge is accumulated and transported. This, combined with that fact that organic semiconductors are especially susceptible to having structural defects induced via oxidation, charge transport induced damage, and metallization results in a situation where a semiconductor film's ability to conduct charge can degrade over time. This degradation manifests itself in the electrical device characteristics of organic based electronic devices. OFETs, for example, may display changes in threshold voltage, lowering of charge carrier mobilities, or a decrease in the On/Off ratio. All these effects sum together to result in degradation in device performance. The work begins with a study where matrix assisted pulsed laser deposition (MAPLE), an alternative organic semiconductor thin film deposition method, is used to fabricate OFETs with improved semiconductor-dielectric interfaces. MAPLE allows for the controlled layer-by-layer growth of the semiconductor film. Devices fabricated using this technique are shown to exhibit desirable characteristics that are otherwise only achievable with additional surface treatments. MAPLE is shown to be viable alternative to other
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.
Hesford, Andrew J.; Astheimer, Jeffrey P.; Greengard, Leslie F.; Waag, Robert C.
2010-01-01
A multiple-scattering approach is presented to compute the solution of the Helmholtz equation when a number of spherical scatterers are nested in the interior of an acoustically large enclosing sphere. The solution is represented in terms of partial-wave expansions, and a linear system of equations is derived to enforce continuity of pressure and normal particle velocity across all material interfaces. This approach yields high-order accuracy and avoids some of the difficulties encountered when using integral equations that apply to surfaces of arbitrary shape. Calculations are accelerated by using diagonal translation operators to compute the interactions between spheres when the operators are numerically stable. Numerical results are presented to demonstrate the accuracy and efficiency of the method. PMID:20136208
NASA Astrophysics Data System (ADS)
Oh, S. B.; Choi, Y.; Jung, H. G.; Kho, S. W.; Lee, C. S.
2014-12-01
Acoustic microscopy and small-angle neutron scattering were applied to non-destructively evaluate the hydrogen-induced cracking of API steels and to find the initiation time of the crack. The API steels had equiaxed grains with about 4 to 12-μm average grain size along the rolling, sample-normal, and transverse directions. For 5 days of immersion in a sodium-acetic solution with chloride ions (NaCl: CH3COOH: H2O: FeCl2 = 50: 5: 944: 1, pH = 2.7), micro-sized cracks were not formed in the as-received specimen, but they did form in the 7% deformed specimen. Nano-sized cracks were observed in the specimen after 3 days of immersion by small-angle neutron scattering.
Electron-atomic-hydrogen ``elastic" scattering in the presence of a laser field
NASA Astrophysics Data System (ADS)
Li, S.-M.; Chen, J.; Zhou, Z.-F.
2002-05-01
Laser-assisted electron-atomic-hydrogen “elastic" scattering is studied in the first Born approximation. The initial and final states of projectile electron are described by the Volkov wavefunctions; the dressed state of target described by a time-dependent perturbative wavefunction in soft photon approximation. The laser modified cross-sections are calculated in two distinct geometries for laser polarization either parallel or perpendicular to the incident direction of electron. The numerical results shows that the multiphoton cross-sections oscillate by a few orders over the whole scattering angular region. The results for a parallel geometry oscillate more frequently in the intermediate angles; while the results for a perpendicular geometry oscillate more frequently in the forward and backward angles. At large scattering angles, the sum rule of Kroll and Watson is noticeably violated. The laser modification on summed total cross-section increases with field strength, but decreases with field frequency and polarization deviation from the incident direction.
Parametric interference effect in electron-nucleus scattering in the field of two pulsed laser waves
NASA Astrophysics Data System (ADS)
Roshchupkin, S. P.; Lebed', A. A.
2014-09-01
Electron scattering on a nucleus in a field of two unidirectional pulsed laser waves is considered. The parametric interference effect is studied, which manifests in electron scattering within the plane formed by both the direction of laser-wave propagation and the initial electron momentum (the interference region). In this kinematics the electron emits and absorbs photons of both waves in a correlated manner. The distribution of the differential cross section of the final-electron energy for the process of electron-nucleus scattering in the field of two pulsed waves is considered. This distribution in the interference region differs qualitatively and quantitatively from the corresponding distribution in any other geometry. The appearance of the parametric interference effect may be experimentally verified by measuring the energy spectrum of final electrons in the framework of modern research projects, which use sources of pulsed laser radiation (XFEL, ELI, PHELIX).
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.
Reconstruction of an acoustic pressure field in a resonance tube by particle image velocimetry.
Kuzuu, K; Hasegawa, S
2015-11-01
A technique for estimating an acoustic field in a resonance tube is suggested. The estimation of an acoustic field in a resonance tube is important for the development of the thermoacoustic engine, and can be conducted employing two sensors to measure pressure. While this measurement technique is known as the two-sensor method, care needs to be taken with the location of pressure sensors when conducting pressure measurements. In the present study, particle image velocimetry (PIV) is employed instead of a pressure measurement by a sensor, and two-dimensional velocity vector images are extracted as sequential data from only a one- time recording made by a video camera of PIV. The spatial velocity amplitude is obtained from those images, and a pressure distribution is calculated from velocity amplitudes at two points by extending the equations derived for the two-sensor method. By means of this method, problems relating to the locations and calibrations of multiple pressure sensors are avoided. Furthermore, to verify the accuracy of the present method, the experiments are conducted employing the conventional two-sensor method and laser Doppler velocimetry (LDV). Then, results by the proposed method are compared with those obtained with the two-sensor method and LDV.
Spatial correlation of the high intensity zone in deep-water acoustic field
NASA Astrophysics Data System (ADS)
Li, Jun; Li, Zheng-Lin; Ren, Yun
2016-12-01
The spatial correlations of acoustic field have important implications for underwater target detection and other applications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterborne modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth. Project supported by the National Natural Science Foundation of China (Grant Nos. 11434012 and 41561144006).
Remote phonon scattering in field-effect transistors with a high κ insulating layer
NASA Astrophysics Data System (ADS)
Laikhtman, B.; Solomon, P. M.
2008-01-01
In this paper a remote phonon scattering of channel electrons in a field-effect transistor (FET) with a high dielectric constant (κ) insulator in between the gate and the channel is studied theoretically. The spectrum of phonons confined in the high κ layer and its modification by the gate screening is investigated. Only two phonon modes of five participate in the remote electron-phonon scattering. The gate suppresses one of the modes but increases scattering by the other. Numerical results for the channel mobility limited only by remote phonon scattering were obtained for a Si FET with a HfO2 layer and a SiO2 layer in between the channel and metallic gate. A surprising result is the reduction of the mobility compared to the case when the gate screening is absent. The dependence of the mobility on the widths of HfO2 and interfacial SiO2 layers on channel concentration and temperature was studied. The accuracy of the calculations based on the Boltzmann equation is discussed. Finally, a comparison of our results with available experimental data leads to the conclusion that the remote phonon scattering is not the dominating scattering mechanism.
NASA Astrophysics Data System (ADS)
Kurata, Tomohiro; Oda, Shigeto; Kawahira, Hiroshi; Haneishi, Hideaki
2016-12-01
We have previously proposed an estimation method of intravascular oxygen saturation (SO_2) from the images obtained by sidestream dark-field (SDF) imaging (we call it SDF oximetry) and we investigated its fundamental characteristics by Monte Carlo simulation. In this paper, we propose a correction method for scattering by the tissue and performed experiments with turbid phantoms as well as Monte Carlo simulation experiments to investigate the influence of the tissue scattering in the SDF imaging. In the estimation method, we used modified extinction coefficients of hemoglobin called average extinction coefficients (AECs) to correct the influence from the bandwidth of the illumination sources, the imaging camera characteristics, and the tissue scattering. We estimate the scattering coefficient of the tissue from the maximum slope of pixel value profile along a line perpendicular to the blood vessel running direction in an SDF image and correct AECs using the scattering coefficient. To evaluate the proposed method, we developed a trial SDF probe to obtain three-band images by switching multicolor light-emitting diodes and obtained the image of turbid phantoms comprised of agar powder, fat emulsion, and bovine blood-filled glass tubes. As a result, we found that the increase of scattering by the phantom body brought about the decrease of the AECs. The experimental results showed that the use of suitable values for AECs led to more accurate SO_2 estimation. We also confirmed the validity of the proposed correction method to improve the accuracy of the SO_2 estimation.