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In this study, an efficient and accurate staggered-grid finite-difference time-domain method to solve the two-dimensional (2-D) first-order stress–velocity elastic-wave equation is proposed. In the conventional implementation of the staggered-grid finite-difference (SGFD) method, the same SGFD operator is used to approximate the spatial derivatives. However, we propose a numerical method based on the mixed SGFD operators that are more efficient but similar in accuracy when compared with a uniform SGFD operator. We refer to the proposed method as the nonbalanced SGFD numerical scheme that combines the high-order SGFD operators with the second-order SGFD operators. The suitability of the proposed scheme is verified by dispersion analysis. Through SGFD modeling and reverse-time migration examples, we demonstrate that the proposed nonbalanced scheme offers a similar level of accuracy with a lower computational cost compared with the time-consuming conventional SGFD method.

Scars are a type of fibrous tissue that typically forms during the wound healing process to replace damaged skin. Because studies have indicated a high correlation between scar stiffness and clinical symptoms, assessing the mechanical properties of scar is crucial for determining an appropriate treatment strategy and evaluating the treatment’s efficacy. Shear wave elastography (SWE) is a common technique for measuring tissue elasticity. Because scars are typically a few millimeters thick, they are thin-layer tissues, and therefore, the dispersion effect must be considered to accurately estimate their elasticity. In this study, high-frequency ultrasound (HFUS) elastography was proposed for estimating the elastic properties of scars by using the Lamb wave model (LWM). An external vibrator was used to generate elastic waves in scar tissue and skin, and the propagation of the elastic waves was tracked through 40-MHz ultrafast ultrasound imaging. The elasticity was estimated through shear wave models (SWMs) and LWMs. The effectiveness of using HFUS elastography was verified through phantom and human studies. The phantom experiments involved bulk phantoms with gelatin concentrations of 7% and 15% and 2–4-mm-thick thin-layer 15% gelatin phantoms. The studies of three patients with eight cases of scarring were also conducted. The phantom experimental results demonstrated that the elasticity estimation biases for the thin-layer mediums were approximately −36% to −50% and 3% to −9% in the SWMs and LWMs, respectively, and the estimated shear moduli were 12.8 ± 5.4 kPa and 74.8 ± 26.8 kPa for healthy skin and scar tissue, respectively. All the results demonstrated that the proposed HFUS elastography has a great potential for improving the accuracy of elasticity estimations in clinical dermatological diagnoses. [ABSTRACT FROM AUTHOR]

High-order staggered-grid finite-difference (SFD) schemes are preferred in elastic wave simulation for geophysical problems because they decrease the accumulation of error from grid dispersion. However, most SFD approaches reach high-order spatial but limited temporal accuracy. To tackle the issue, we develop a novel temporal and spatial high-accuracy elastic SFD scheme by selectively modifying the spatial operators of the original SFD stencil. This modification has three main advantages. First, it facilitates the design of a new SFD stencil with temporal and spatial accuracies to arbitrary even-order by a Taylor-series expansion method. Second, it helps boost the accuracy further by implementing a linear optimization method. Third, the new selectively modified SFD (SMSFD) stencil needs fewer float-point operations (FPOs) than the existing temporal high-order SFD stencil. We compare our new SMSFD scheme with spatial high-order and temporal–spatial high-order SFD schemes and show that our new elastic SMSFD scheme possesses better accuracy and stability and requires fewer FPOs than these methods. [ABSTRACT FROM AUTHOR]

Elastic least-squares reverse-time migration (ELSRTM) yields subsurface high-resolution elastic images from multicomponent seismic data. For ocean bottom seismic (OBS) acquisitions, both pressure and displacement components are measured using four-component (4C) modern receivers. However, these 4C data cannot be effectively simulated and migrated using conventional ELSRTM approaches due to the limitation of the standard elastic wave equation. For this reason, we propose a new ELSRTM method based on a modified acoustic-elastic coupled (AEC) equation. Owing to this equation, either the prediction or the migration of OBS 4C data can be implemented using a one-time wavefield simulation. Incorporation with a perturbation imaging condition, the proposed method can invert for P- and S-wave velocity and density and generate amplitude-preserving images. Besides, it can provide subsurface impedance reflectivity models by stacking the obtained multi-parameter images. In the least-squares migration, a preconditioned conjugate gradient algorithm is implemented based on a multi-parameter diagonal Hessian. Numerical experiments on an uncorrelated layer model and a portion of the Southern Yellow China sea model can demonstrate the effectiveness of this method on improving imaging resolution and accelerating convergence rate. [ABSTRACT FROM AUTHOR]

Theoretical study of the effect of uniaxial pressure on the propagation characteristics of plate modes as Lamb and SH waves in a lithium niobate plate is carried out. A change in the effective crystalline symmetry, as well as the effective elastic constants under the pressure influence, has been derived. The controlling coefficients describing the pressure influence on the plate modes’ phase velocities are calculated for the various applications of uniaxial pressure. The uniaxial pressure influence on the hybridization of the elastic waves is discussed. [ABSTRACT FROM AUTHOR]

For oil and gas exploration, seismic wave propagation in coupled acoustic, elastic, poroelastic, and even anisotropic media is a valuable aspect. However, it is a challenging task to deal with the interfaces of the coupled model. In order to tackle the specific issue, a unified numerical scheme is developed, which is based on the discontinuous Galerkin method. The acoustic, elastic, poroelastic, and anisotropic elastic wave equations are unified into a first-order velocity–stress system. The numerical simulation at the interfaces in the coupled model is conveniently handled by the Godunov flux without any extra operations. Numerical results from the coupled acoustic–elastic and acoustic–poroelastic model are compared with the analytic solutions. In addition, the rates of convergence from different orders are analyzed, which demonstrates the accuracy of the proposed numerical scheme. The surface waves at the fluid–solid interface are studied. Moreover, the proposed scheme is applied to a more complex coupled model, including the coupled acoustic–elastic–poroelastic model and the coupled acoustic–anisotropic elastic model. The corresponding results demonstrate that the proposed numerical scheme is capable of dealing with the coupled model. [ABSTRACT FROM AUTHOR]

Objective: Estimating the elasticity distribution in the cornea is important because corneal elasticity is usually influenced by corneal pathologies and surgical treatments, especially for early corneal sclerosis. Because the thickness of the cornea is typically less than 1 mm, high-resolution ultrasound elastography as well as the Lamb wave model is required for viscoelastic property estimation. In the present study, an array high-frequency ultrasound (HFUS) elastography method based on ultrafast ultrasound imaging was proposed for estimating the viscoelastic properties of porcine cornea. Methods: The elastic wave was generated by an external vibrator, after which the wave propagation image was obtained using a 40-MHz array transducer. Viscoelasticity estimation was performed by fitting the phase velocity curve using the Lamb wave model. The performance of the proposed HFUS elastography system was verified using 2-mm-thick thin-layer gelatin phantoms with gelatin concentrations of 7% and 12%. Ex vivo experiments were carried out using fresh porcine cornea with artificial sclerosing. Results: Experimental results showed that the estimated elasticity was close to the standard value obtained in the phantom study when the Lamb wave model was used for elasticity measurement. However, the error between the standard elasticity values and the elasticity values estimated using group shear wave velocity was large. In the ex vivo eyeball experiments, the estimated elasticities and viscosities were respectively 9.1 ± 1.3 kPa and 0.5 ± 0.10 Pa·s for a healthy cornea and respectively 15.9 ± 2.1 kPa and 1.1 ± 0.12 Pa·s for a cornea with artificial sclerosis. A 3D HFUS elastography was also obtained for distinguishing the region of sclerosis in the cornea. Conclusion: The experimental results demonstrated that the proposed HFUS elastography method has high potential for the clinical diagnosis of corneal diseases compared with other HFUS single-element transducer elastography systems. [ABSTRACT FROM AUTHOR]

Transmission of information using ultrasonic elastic waves on existing metallic pipes provides an alternative communication option across physical barriers in a highly partitioned industrial complex, such as a nuclear facility. This work investigates the feasibility of the transmission of digital images over metallic pipes. Ultrasonic communication systems for transmission of images on a nuclear-grade stainless steel pipe were assembled for bench-scale demonstration. Information carriers in this system are refracted shear waves transmitted and received with piezoelectric transducers (PZTs) operating at 2-MHz nominal frequency. The refraction and propagation of ultrasonic shear waves were modeled with COMSOL software. An amplitude shift keying (ASK) communication protocol for image transmission was developed and implemented in the GNURadio software-defined radio (SDR) environment. Digital information was converted to analog ultrasonic signals using Red Pitaya electronic boards. The performance of the ASK protocol is evaluated at the output of every block in the GNURadio program by monitoring the transmission of select characters. Using the ASK communication protocol, the transmission of the 32-KB image was demonstrated at 2-Kbps bitrate across 6-ft-long stainless steel pipe. Preliminary evaluation of ultrasonic communication on the piping of a nuclear facility, such as signal transmission on bent pipes, was performed with COMSOL computer simulations. [ABSTRACT FROM AUTHOR]

Magnetic resonance elastography (MRE) offers a noninvasive solution to visualize the mechanical properties of soft tissue, but the study suffers from expensive magnetic resonance scanning. Moreover, translating MRE wave images into soft tissue elasticity is a nontrivial issue for clinical professionals and healthcare practitioners. An interactive system—OpenMRE—is thus developed with the aid of ImageJ for numerical MRE study. It is comprised of two comparatively independent toolkits, namely MREA for simulation and MREP for interpretation. MREA mainly deals with the forward problem of MRE, and provides a numerical platform to determine the propagation and distribution of specially designed elastic wave. It is possible to numerically study some state-of-the-art paradigms including multisource and multifrequency MRE. The resultant wave images are interpretable in MREP that is designed for the inverse problem of MRE. It consists of the algorithms for phase unwrapping, directional filtering, and elasticity reconstruction. In a word, OpenMRE offers the MRE community a convenient and well-functioning system for interactive MRE study. [ABSTRACT FROM AUTHOR]

A thorough study of elastic waves in waveguides, taking into account the full tensorial nature of the stiffness tensor, is presented in the context of stimulated Brillouin scattering. Various approximations of the elastic wave equation used in the stimulated Brillouin scattering literature are implemented and their validity and applicability are discussed. The developed elastic wave mode-solver is also coupled with an electromagnetic counterpart to study the influence of elastic anisotropies on Brillouin gain. [ABSTRACT FROM AUTHOR]

Railgun performance requires a low-resistance electric gliding contact between the rails and the armature. The electromagnetic forces, which accelerate the launch package (0.7 to 3 kg mass) up to more than 2000 m/s, are acting on the rails as repulsive forces. Therefore, the rails of the NGL60 electromagnetic gun, with caliber 60 $\times$ 60 mm2, are held in their position by an arrangement of discrete steel bolts, further by beams and plates made of glass fiber reinforced plastic, as well as by stiffening metal plates. The highly dynamic electromagnetic forces generate stress waves and elastic rail deformation that might contribute to contact transition between the rails and the armature. If the rail deformation enters the plastic domain, the rail geometry may be altered in an unfavorable way for subsequent shots. For our numerical investigation, we used the multiphysics finite-element computation code LS-DYNA to simulate a railgun projectile launch with a moving armature by injecting an electric current into the rails. It is therefore possible to study the dynamic deformations during the launch and get insight in the dynamic stress states. The material models for the rails and for the armature take into account elastic-plastic stress-strain behavior as well as strain rate sensitivity. We expect to simulate launch dynamics with higher accuracy than previously presented models with a nonmoving armature. The principal objective of the study is to show that this procedure is capable of effectively optimizing the structural behavior of the rails inside the barrel. [ABSTRACT FROM AUTHOR]

Porous materials are ubiquitous in the subsurface formations of the earth where acoustic and seismic waves are used for remote sensing. However, it is not well understood how the dissipation and the dispersion of poroelastic waves are caused by the viscoelastic and viscous properties of the constituents such as solid grains and pore fluid and by the viscoelastic dissipation of the solid frame, as well as the viscodynamic coupling of the pore fluid to the solid frame due to its global and local flows relative to the solid grains. Such attenuation mechanisms have seldom been incorporated in subsurface sensing simulations, although they can be very important to applications. In this paper, we propose a complete attenuation model, including both full stiffness and viscodynamic dissipation, for poroelastic media in seismic wave simulations. Completely based on a generalized Zener model, the effects associated with physical dissipation and frequency-dependent dispersion are accurately simulated by a finite-difference time-domain algorithm. Verifications with analytical solutions show the accuracy, efficiency, and flexibility of our method. Numerical results demonstrate that the attenuation of Biot’s model in the sediment of the seafloor has significant effects on acoustic wave scattering from complex geologic structures. [ABSTRACT FROM AUTHOR]

This paper reports on the proof-of-concept demonstration of an approach for the synthesis of a through package charging and authenticating communication link enabled by GHz-range aluminum nitride (AlN) piezoelectric transducers. The acoustic link is formed by two thickness-mode acoustic transducers placed on the two sides of a packaging substrate. The link leverages the enhancement of energy transfer that occurs at resonance; 1- \mu \textm -thick (2.7 GHz) and 6- \mu \textm -thick (500 MHz) AlN acoustic links are demonstrated showing substantial enhancement of power transfer efficiencies (PTE) when using thicker AlN substrates. PTEs of −8 dB at 2.7 GHz and −2 dB at 500 MHz are measured for transducers’ size of 1\times 100\times 100~\mu \textm^3 and 6\times 100\times 100~\mu \textm^3 through 700- and 500- \mu \textm -thick silicon substrates, respectively. The experimental values are in very close agreement with the analytical model of the acoustic link. The potential misalignment between the two transducers is the main limitation of this approach. To overcome this challenge, acoustic phased arrays are devised to enable steering of the transmitted beam. Preliminary results on the steering capability demonstrate about 8 dB of improvement in PTE via a two-element array when dealing with a 100- \mu \textm misalignment. This paper is the first step toward the development of next-generation high-efficiency and micro-scale power transfer units that could energize chips through packages. [2017-0010] [ABSTRACT FROM AUTHOR]

In this paper, we formulate an integer linear programming (ILP) to perform multicast routing and spectrum assignment (MRSA) in elastic optical networks, which serves jointly a set of multicast requests. In this formulation, all physical layer restrictions including modulation level assignment, maximum number of multicast capable nodes (MCNs), and maximum splitting degree (MSD) of MCNs, are considered. In addition, we modify the proposed joint ILP to serve multicast requests one-by-one, which is referred to as a separate ILP. Furthermore, we present three heuristic algorithms for MRSA, namely distance-based MRSA (DMRSA), congestion-based MRSA (CMRSA), and mixed CMRSA/DMRSA, which are applicable in both static and dynamic operation scenarios. In CMRSA and DMRSA, the link length and the amount of occupied spectrum are considered as the cost function of multicast routing, respectively; and in mixed CMRSA/DMRSA, a combination of normalized link length and normalized occupied spectrum is considered as the cost function. The comparison of ILPs and heuristic algorithms in static operation reveals that the joint ILP, as the benchmark, gives the optimum solution while has the most computational complexity. Furthermore, the separate ILP has lower complexity at the cost of consuming slightly more spectrum. Unless the DMRSA method, which has the worst performance, the gap between the other two heuristic algorithms and the ILPs is negligible. Furthermore, simulation results of dynamic operation scenarios reveal that mixed CMRSA/DMRSA outperforms other two heuristics algorithms in terms of blocking probability. [ABSTRACT FROM PUBLISHER]

This paper presents the theory of the $k$ -space method generalized to model elastic wave propagation in heterogeneous anisotropic media. The $k$ -space methods are promising time integration techniques giving, in conjunction with collocation spectral methods, accurate and efficient numerical schemes for problems in heterogeneous media. In this paper, the $k$ -space operator is derived in a spatially continuous form using the Fourier analysis of the displacement formalism of elastodynamics. An efficient numerical algorithm is then constructed by applying a Fourier collocation spectral method, leading to define the discrete $k$ -space scheme. The proposed method is temporally exact for homogeneous media, unconditionally stable for heterogeneous media, and also allows larger time steps without loss of accuracy. Implementation of the method is discussed in detail. The method is validated through a set of numerical tests. The numerical results show the efficacy of the method compared with the conventional schemes. [ABSTRACT FROM PUBLISHER]

Acousto-optic interaction in optomechanical crystals allows unidirectional control of elastic waves over optical waves. However, as a result of this nonlinear interaction, infinitely many optical modes are born. This paper presents an exact formulation of a coupled mode theory for interaction between elastic and photonic Bloch waves moving along an optomechanical waveguide. In general, an optical wavefront is strongly diffracted by an elastic wave in frequency and wave vector, and thus infinite modes with different frequencies and wave vectors appear. We discuss resonance and mode conversion conditions and present a rigorous method to derive coupling rates and mode profiles. We also find a conservation law which rules over total optical power from interacting individual modes. We present application examples to the theory to optomechanical waveguides and cavities, as well as non-reciprocal transmission of light and optomechanical switches. [ABSTRACT FROM PUBLISHER]

This paper presents a high-voltage impulse generated using piezoelectric materials by an elastic wave. The impact method was a high-pressure gas gun with projectiles and the type of stress wave was an elastic wave. The results were different from the previous method using high explosive (shock wave). The charge release phenomenon that cannot be explained by the piezoelectricity theory occurred as under shock wave. But pulse duration is longer than the transit time of wave and the piezoelectricity phenomenon also occurred in the time of pulse generation. This complex phenomenon cannot be explained by the previous research under the stress wave experiments or conventional piezoelectricity theory. [ABSTRACT FROM PUBLISHER]

In this study, modeling approaches for porosity in layered media are presented and compared. First, an effective-medium model is used to account for the frequencydependent attenuation of the elastic waves. The effective-medium model is based on a single-scattering approach, i.e., it neglects multiple-scattering effects. Then, the effective-medium model is compared in time-domain finite element simulations. The numerical model allows the study of the scattering of the elastic waves on randomly distributed spherical cavities and also accounts for multiple-scattering effects. The models are compared to investigate the validity of the effective-medium model approach. The calculated reflected laminate responses and transmission spectra from the two models show a good agreement. [ABSTRACT FROM PUBLISHER]

The dynamic behavior of the railgun housing including the rails is of great importance for the system performance. The transient loading (magnetic pressure) may have a negative influence on the sliding electrical contact required for this acceleration technology. Therefore, the analysis of the displacement of the inner rail surfaces due to elastic waves is of great importance. The French-German Research Institute of Saint Louis (ISL) is operating several railguns with housings characterized by an open barrel design allowing for innovative diagnostic techniques. The repelling forces between the rails are countered using discrete steel bolts. The rails are mounted to bars made from composite material. In the past, we presented the experimental and numerical findings concerning the dynamic behavior of such railguns in single shot mode. In this paper, we present for the first time 3-D finite element calculations concerning the dynamical behavior of the ISL RApid FIre RAilgun operating in multishot mode. Multishot scenarios with fire rates of 50 Hz are considered and particular attention is paid to the question if the dynamical behavior of the railgun is influenced by preceding shots. [ABSTRACT FROM PUBLISHER]

Kirchhoff plate equations are examined for flexural plate wave sensors with a polymeric substrate that is mechanically similar to the polymer sensing layers commonly used in mass loading and gas sensing applications. The new analytical derivations for sensitivity are examined both experimentally and through finite element analysis (FEA). For substrates with a large in-plane stress, the behavior of the sensor is consistent with other gravimetric sensors based on flexural plate waves. In the case of low stress, the influence of variations in substrate stiffness and stress significantly outweigh the effects of mass loading in sensor frequency response. Experimental results using a poly(vinyl alcohol) sensing layer and poly(vinylidene fluoride) substrate are compared with analytical and FEA models, and demonstrate good adherence. The FEA models are also used to illustrate the relevant influences of mass loading, variations in substrate stiffness, and stress on the sensor response. [ABSTRACT FROM PUBLISHER]

The elastic waves generated by traditional meander- line coil electromagnetic acoustic transducers (EMATs) propagate in two directions, overlapping the echo signals from defects with the same distances, and the defect echo signal is hard to distinguish from the edge-reflected signal when the EMATs are near the edge of a specimen. In this paper, a unidirectional EMAT with two meander-line coils is proposed. A finite element model is used to simulate the directivity of the Rayleigh and shear vertical waves generated by these EMATs. Six transducers are fabricated using the printed circuit technique. The unidirectional Rayleigh wave and shear vertical wave are tested, and the results agree well with the simulation. [ABSTRACT FROM AUTHOR]

The interaction of waves with materials could include multiple physics (multiphysics), depending on the properties of waves and materials. For microwave illumination on elastic media, the electromagnetic (EM) and mechanic processes exist simultaneously and are coupled together. To exactly describe the involved process with interaction of microwave and induced elastic wave, the coupled Maxwell's equations and elastic wave equations should be solved. Although such coupled equations have been derived earlier but they are in partial differential equation (PDE) form. The solutions for the equations are then only based on finite difference method (FDM) or finite element method (FEM) in addition to analytical approaches. In this work, we first derive coupled integral equations for governing the process from its PDE counterpart. The derivation is based on the Huygens' equivalence principle and extinction theorem by recognizing that the excitation of elastic wave is EM force and the induced elastic wave will be a new excitation source to affect the EM in return. The coupled integral equations is solved using Nyström method in first time and some basic results from numerical examples for microwave illumination on piezoelectric materials are presented. [ABSTRACT FROM AUTHOR]

Transcranial ultrasound imaging is limited by poor acoustic windows and skull induced distortions to the beam. Shear waves in the skull have a better impedance match with longitudinal waves in water and thereby produce a more coherent focus inside the skull. This study presents work on an imaging technique that utilizes shear-wave propagation through the skull. The pulse-echo lateral distortion introduced by the skull was analyzed by imaging a point scatterer behind ex vivo human craniums at 1 MHz. Brightness images of the target obtained with either shear-mode or conventional longitudinal-mode transmission in the bone were assessed to quantify lateral resolution. As compared to longitudinal-mode transmission, it was found that the use of shear-mode resulted in improved localization along the propagation (depth) axis at the expense of degraded lateral resolution. The signal-to-noise ratio (SNR) limitations introduced by severe attenuation of shear-waves in the skull were overcome with frequency modulated (FM) coded excitations. This gain in SNR was exchanged with resolution and used for compensation of frequency-dependent attenuation in the skull, resulting in a greater than 20% improvement in lateral resolution for both modes of transcranial transmission. The results are an important step towards enhancing the quality of transcranial sonography. [ABSTRACT FROM AUTHOR]

The article focuses on the developments in the pressure wave propagation (PWP) procedure. It is examined that in the case of complex materials, exhibiting either a divergent electric field or a heterogeneous structure, PWP is not due only to the presence of space charges and other spurious contributions should be included. It is determined that at the end of the correction method, the signal can be treated as if it had been obtained from a uniform planar material. Moreover, it is found that as far as the spatial resolution is concerned, a change in the measuring setup is required.

An effective way to generate localized narrow-band low-frequency shear waves within tissue noninvasively, is by the modulated radiation force, resulting from the interference of two confocal quasi-CW ultrasound beams of slightly different frequencies. By using approximate viscoelastic Green's functions, investigations of the properties of the propagated shear-field component at the fundamental modulation frequency were previously reported by our group. However, high-amplitude source excitations may be needed to increase the signal-to-noise-ratio for shear-wave detection in tissue. This paper reports a study of the generation and propagation of dynamic radiation force components at harmonics of the modulation frequency for conditions that generally correspond to diagnostic safety standards. We describe the propagation characteristics of the resulting harmonic shear waves and discuss how they depend on the parameters of nonlinearity, focusing gain, and absorption. For conditions of high viscosity (believed to be characteristic of soft tissue) and higher modulation frequencies, the approximate shear wave Green's function is inappropriate. A more exact viscoelastic Green's function is derived in k-space, and using this, it is shown that the lowpass and dispersive effects, associated with a Voigt model of tissue, are more accurately represented. Finally, it is shown how the viscoelastic properties of the propagating medium can be estimated, based on several spectral components of the shearwave spectrum. [ABSTRACT FROM AUTHOR]

The use of block overlapping and time windowing in the estimation of the frequency response functions (FRFs) of linear systems is considered. The systems are subjected to stationary white random excitation, and there is no external noise. The sources of errors for the bias and variance of the frequency response are identified to be due to the Fourier transforms of the transient terms or end effects that arise due to nonperiodic signals. Using a pure time delay as an example for the system, it is shown that there is a limit to the improvement achievable in reducing the variance as the block overlap is increased. [ABSTRACT FROM AUTHOR]

This paper presents an experimental method of determining the elastic bar's transfer functions in the form of formulas. The method is based on the two-point measurement of the elastic strain waves propagating inside the bar, the spectral analysis of these waves, and making use of the general solution of the equation of movement of the bar in the frequency domain. The determined transfer functions of the bar are used for impulsive strain waveform reconstruction by means of deconvolution in the frequency domain and for the validity check of the reconstruction. The application of this method to the reconstruction of impact pressure waveforms is presented. [ABSTRACT FROM AUTHOR]

This paper presents the propagation characteristics of the shear horizontal surface acoustic wave (SH-SAW) in ZnO (0°, 90°, ψ) (11 ¯2 0) textured ZnO films. ZnO (0°, 90°, 0°) film/interdigital transducer (IDT) electrode/silica glass substrate structures were fabricated by RF magnetron sputtering. Experimental results demonstrate that SH-SAW was clearly excited in these structures. We also theoretically estimated the electromechanical coupling coefficient K2 in the ZnO (0°, 90°, ψ) film/silica glass substrate structure. The theoretical results show that the IDT electrode/ZnO (0°, 90°, 55°) film/silica glass substrate structure had a relatively high K2 value of 3.4%. Moreover, the shear horizontal displacement component of the SH-SAW in this structure is much larger than the transverse and longitudinal displacement components. This structure could be used in SH-SAW sensors for evaluating the electrical properties of liquids. [ABSTRACT FROM AUTHOR]

We present a method for formulating the design problem of maximizing the transduction efficiency of a magnetostrictive patch-type transducer as a topology optimization problem. Unlike existing methods based on magnetic analysis alone, our method is based on a coupled magnetomechanical analysis. It employs a quasi-static magnetomechanical transduction model relating applied magnetic field and induced stress in a magnetostrictive patch to facilitate design optimization. For the generation of a specific elastic wave mode, not only the patch shape but also the state of patch-waveguide bonding should be optimized simultaneously. We therefore developed a modified topology optimization formulation. The optimal results are consistent with physical intuition and some existing experimental findings for the case of torsional and longitudinal waves in a cylindrical waveguide. [ABSTRACT FROM AUTHOR]

The mechanics of the friction drive of a surface acoustic wave motor were investigated by means of contact mechanics theory. As a means to control the contact condition, the motor's slider had projections on its frictional surface. Assuming the projection was a rigid circular punch and the slider body was an elastic half-space allowed application of contact mechanics formulae to the analyses of the friction drive. Because the projection contacted the Rayleigh wave vibration, the projection's responses were considered dynamic; thus, the dynamics were also analyzed in the same framework of contact mechanics formulae. Moreover, the analyses were applied to measurements of the projection's displacement to examine the detailed mechanics during the friction drive. We calculated the contact/frictional forces based on the measurement and indicated the necessity of further investigation of the surface acoustic wave motor's friction drive, because the usual friction law was unable to explain the measurement. [ABSTRACT FROM AUTHOR]

An experiment for studying the shear wave speed in ocean-bottom sediment using Scholte pulse waves was conducted on a shelf in the East China Sea. To generate Scholte pulse waves, we developed a new electromagnetic induction source, which was placed at 100-m depth on the seafloor and was remotely controlled on board through a 1000-m-long cable. A Scholte pulse propagating in sandy sediment was then measured using a couple of geophones placed on the seafloor at a distance of 100 m from the source. The dispersion property of the Scholte waves was obtained by applying a multiple filter technique (MFT) to the observed waves. We then obtained the shear wave speed structure, i.e., the depth dependency of the shear wave speed in the sediment, by applying an inversion method based on a genetic algorithm (GA). The estimated speed was about 100 m/s near the bottom and increased with depth. The power was a close match to the estimated depth-speed profile, as reported previously by Hamilton [E. L. Hamilton, Geophysics, vol. 41, pp. 985-996, 1976]. [ABSTRACT FROM AUTHOR]

Spatial resolution is a key parameter for the measurement of any distribution. In the case of space charge distribution measurements, it is difficult to compare technique performances since each technique has its own resolution definition most of the time. In this paper the resolution, in terms of position accuracy and charge discernment, is determined on the basis of a unique definition for the thermal, the pressure-wave-propagation and the electro-acoustic methods and their derived techniques. It is shown that spatial resolution is similar throughout the sample in the case of the pressure-wave-propagation or the electro-acoustic methods, except if attenuation and dispersion of elastic waves are important, but decreases as the charge position inside the sample in the case of thermal method. Elastic wave methods are therefore preferable for a given signal to noise ratio as soon as the sample thickness is larger than twice the sound velocity times the excitation rise time. [ABSTRACT FROM AUTHOR]

This study reports the phase detection of the two-port flexural plate wave (FPW) sensor for designing and integrating the miniature system and provides a comprehensive methodology for portable using in the biosensor applications of severe acute respiratory syndrome coronavirus (SARS-CoV). The miniature system mainly utilizes the concept of the frequency divider that involves a divider, a time-based oscillator and a gate to reduce the high frequency, and the FPW sensor is fabricated using microelectromechanical systems (MEMS) technologies for producing a potable biosensing detector. The results demonstrate that the insertion loss decreased about -1.15% dB/degC, and the phase delay was about 2.05deg/(1000 cP). The phaseshift resolution was about 10 mV per degree, and the original frequency of 4.2 MHz was divided by 100 to reduce the frequency to 42 kHz. The SARS-CoV could be detected via the S protein binds to the human angiotensin-converting enzyme 2 (hACE2) as a functional receptor, which would cause the phase delay due to the combining of the antibody with the antigen. Therefore, the feasibility studies provide the information that phase detection is an appropriate low-cost technology via frequency divider for fabricating of the miniature biosensors. [ABSTRACT FROM PUBLISHER]

In this work, the dispersion curves of elastic waves propagating in electrical cables and in bare copper wires are obtained theoretically and validated experimentally. The theoretical model, based on Gazis equations formulated according to the global matrix methodology, is resolved numerically. Viscoelasticity and attenuation are modeled theoretically using the Kelvin-Voigt model. Experimental tests are carried out using interferometry. There is good agreement between the simulations and the experiments despite the peculiarities of electrical cables. [ABSTRACT FROM AUTHOR]

The article offers information on the use of a turbo space division multiple access techniques for the uplink of multi-carrier code division multiple access systems wherein the sent signals experience strong nonlinear distortion effects. The signal is sent by mobile terminal to a nonlinear operation with a clipping device which decreases the envelope fluctuations. The results of the performance reveals that the offered receiver structures can get good performances with linear transmitters.

After introducing our previous study of bouncing instability of a flying head slider, we numerically investigated slider dynamics in the near-contact region taking the root-mean-square value and frequency roll-off factor of the micro-waviness as parameters by using 2-degrees-of-freedom slider model, random micro-waviness model and lubricated rough-surface-contact characteristics model. We found that the slider exhibits self-excited bouncing vibration with a frequency close to the lower pitch frequency under small microwaviness but tends to exhibit forced vibration with a resonant frequency in the upper pitch mode as the amplitude of microwaviness increases. If the amount of microwaviness and destabilized sources are reduced sufficiently, there is a contact sliding condition without self-excited and forced bouncing vibration. [ABSTRACT FROM AUTHOR]

This study focuses on the inverse scattering of objects embedded in a homogeneous elastic background. The medium is probed by ultrasonic sources, and the scattered fields are observed along a receiver array. The goal is to retrieve the shape, location, and constitutive parameters of the objects through an inversion procedure. The problem is formulated using a vector integral equation. As is well-known, this inverse scattering problem is nonlinear and ill-posed. In a realistic configuration, this nonlinear inverse scattering problem involves a large number of unknowns, hence the application of full nonlinear inversion approaches such as Gauss-Newton or nonlinear gradient methods might not be feasible, even with present-day computer power. Hence, in this study we use the so-called diagonalized contrast source inversion (DCSI) method in which the nonlinear problem is approximately transformed into a number of linear problems. We will show that, by using a three-step procedure, the nonlinear inverse problem can be handled at the cost of solving three constrained linear inverse problems. The robustness and efficiency of this approach is illustrated using a number of synthetic examples. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication results of surface acoustic wave (SAW) devices operating at frequencies up to S GHz. In previous work, we have shown that high acoustic velocities (9 to 12 km/s) are obtained from the layered AlN/diamond structure. The interdigital transducers (IDTs) made of aluminium with resolutions up to 250 am were successfully patterned on AlN/diamond-layered structures with an adapted technological process. The uniformity and periodicity of IDTs were confirmed by field emission scanning electron microscopy and atomic force microscopy analyses. A highly oriented (002) piezoelectric aluminum nitride thin film was deposited on the nucleation side of the CVD diamond by magnetron sputtering technique. The X-ray diffraction effectuated on the AlN/diamond-layered structure exhibits high intensity peaks related to the (002) AlN and (111) diamond orientations. According to the calculated dispersion curves of velocity and the electromechanical coupling coefficient (K²), the AlN layer thickness was chosen in order to combine high velocity and high K². Experimental data extracted from the fabricated SAW devices match with theoretical values quite well. [ABSTRACT FROM AUTHOR]

The analysis and precise calculation of reflection and scattering of Rayleigh wave by electrodes is important for surface acoustic wave (SAW) device models, especially for SAW identification (ID) tag design. We present a source regeneration method, which utilizes Green's function combined with finite-element method (FEM)/boundary-element method (BEM) to obtain accurate values of reflection, transmission, and scattering coefficients in a direct way. We take one electrode as the reflector on 128° YX-LiNbO3 substrate to show the result as an example. The results are very accurate and are obtained with short computing time. The new analysis way shows its powerful ability for other advanced discussion of SAW devices. [ABSTRACT FROM AUTHOR]

This article analyzes the propagation modes of ultrasound waves inside an electrical cable in order to assess its behavior as an acoustic transmission channel. A theoretical model for propagation of elastic waves in electric power cables is presented. The power cables are represented as viscoelastic-layered cylindrical structures with a copper core and a dielectric cover. The model equations then have been applied and numerically resolved for this and other known structures such as solid and hollow cylinders. The results are compared with available data from other models. Several experimental measures were carried out and were compared with results from the numerical simulations. Experimental and simulated results showed a significant difference between elastic wave attenuation inside standard versus bare, low-voltage power cables. [ABSTRACT FROM AUTHOR]

The need for high-frequency, wide-band filters has instigated many developments based on combining thin piezoelectric films and high acoustic velocity materials (sapphire, diamond-like carbon, silicon, etc.) to ease the manufacture of devices operating above 2 GHz. In the present work, a technological process has been developed to achieve thin-oriented, single-crystal lithium niobate (LiNbO3) layers deposited on (100) silicon wafers for the fabrication of radio-frequency (RF) surface acoustic wave (SAW) devices. The use of such oriented thin films is expected to favor large coupling coefficients together with a good control of the layer properties, enabling one to chose the best combination of layer orientation to optimize the device. A theoretical analysis of the elastic wave assumed to propagate on such a combination of material is first exposed. Technological aspects then are described briefly. Experimental results are presented and compared to the state of art. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) resonators on lithium tantalate (LiTaO3) and lithium niobate (LiNbO3) are investigated. The amplitude of the acoustic fields in the resonators are measured using a scanning laser interferometer. The amplitude profiles of the surface vibrations reveal the presence of distinct acoustic beams radiated from the transducer region of the SAW resonators and propagating with low attenuation. We suggest that this radiation is generated by the charges accumulating at the tips of the finger electrodes. The periodic system of sources, namely oscillating charges at the fingertips, generates Rayleigh-wave beams in the perpendicular and oblique directions. Green's function theory is used to calculate the coupling strength and slowness of the Rayleigh waves on 42°Y-cut LiTaO3 and Y-cut LiNbO3 substrates as a function of the propagation direction. Furthermore, the propagation angles of the Rayleigh-wave beams as a function of frequency are calculated. The computed angles are compared with the measured ones for both the LiTaO3 and LiNbO3 substrates. [ABSTRACT FROM AUTHOR]

In a fluid-loaded, semi-infinite axisymmetric rod, a free shear stress boundary condition on the circular cross-sectional end introduces complicated, nondispersive waves in the solid. They are composed of a pulse wave, which has the same waveform as the transmitted one and travels at speed c1, and different kinds of pulse trains, each of which travels along the rod at the speed of either c1 or √c2, where C1 and c2 are the propagating speeds of the longitudinal and transversal bulk waves, respectively. Furthermore, one can conclude from the solutions to the boundary conditions that c1 and √2c2 are the only phase speeds of nondispersive waves. Frequency equations associated with these waves are established, and the solutions are solved and discussed analytically and numerically. The acoustic field in the fluid is also fully discussed, and it is more complicated than a single outgoing Hankel function as described for an infinite rod. The acoustic energy coupling between the solid and the fluid and the end reflection and transmission are quantified as well. In the end, experimental examinations of the echo spectra, using an aluminum rod immersed in the water and air, fully confirm the numerical solutions to the frequency equations. [ABSTRACT FROM AUTHOR]

Elastic waves are considered as a contributing factor to solid armature transition in guide rail launchers. The transient elastic waves in the rails of electromagnetic launchers are studied as well as the normal contact pressure between the rails and the armature. We have shown that, due to the interference of elastic waves, the contact pressure between the armature and rail will change dramatically as the armature goes through the critical velocity. This paper explores the effects of transverse magnetic pressure on the trailing arms of a "C"-shaped armature. [ABSTRACT FROM AUTHOR]

In this paper, a new nondestructive testing method using elastic waves for imaging possible voids or defects in concrete structures is proposed. This method integrates the point-source/point receiver scheme with the synthetic aperture focusing technique (SAFT) process to achieve the effect like scanning with a phase array system. This method also is equipped with large functioning depth because of the high-energy feature that elastic waves usually possess over traditional ultrasound. Both numerical simulations and experimental tests were carried out to explore the capabilities of this method in revealing single or multiple defects implied in a matrix material. The results from numerical simulations indicate that this method can clearly reveal the number of the voids or defects, their locations, and front-end profiles. The influence of the accuracy of the wave velocity determination on the resultant image also was evaluated in this study. Furthermore, the effects of the types of the responses to be recorded and the wavelength of the introduced waves also were evaluated so that very good resultant images may be obtained. Both the results from the numerical simulations and the experimental tests indicate that this elastic-wave-based method exhibits high potential in inspecting the defects of in-situ concrete structures by imaging. [ABSTRACT FROM AUTHOR]

In the framework of transduction, nondestructive testing, and nonlinear acoustic characterization, this article presents the analysis of strongly nonlinear vibrations by means of an original numerical algorithm. In acoustic and transducer applications in extreme working conditions, such as the ones induced by the generation of high-power ultrasound, the analysis of nonlinear ultrasonic vibrations is fundamental. Also, the excitation and analysis of nonlinear vibrations is an emergent technique in nonlinear characterization for damage detection. A third-order evolution equation is derived and numerically solved for extensional waves in isotropic dissipative media. A nine-constant theory of elasticity for isotropic solids is constructed, and the nonlinearity parameters corresponding to extensional waves are proposed. The nonlinear differential equation is solved by using a new numerical algorithm working in the time domain. The finite-difference numerical method proposed is implicit and only requires the solution of a linear set of equations at each time step. The model allows the analysis of strongly nonlinear, one-dimensional vibrations and can be used for prediction as well as characterization. Vibration waveforms are calculated at different points, and results are compared for different excitation levels and boundary conditions. Amplitude distributions along the rod axis for every harmonic component also are evaluated. Special attention is given to the study of high-amplitude damping of vibrations by means of several simulations. Simulations are performed for amplitudes ranging from linear to nonlinear and weak shock. [ABSTRACT FROM AUTHOR]

Acoustic radiation force impulse imaging has been used clinically to study the dynamic response of lesions relative to their background material to focused, impulsive acoustic radiation force excitations through the generation of dynamic displacement field images. Dynamic displacement data are typically displayed as a set of parametric images, including displacement immediately after excitation, maximum displacement, time to peak displacement, and recovery time from peak displacement. To date, however, no definitive trends have been established between these parametric images and the tissues' mechanical properties. This work demonstrates that displacement magnitude, time to peak displacement, and recovery time are all inversely related to the Young's modulus in homogeneous elastic media. Experimentally, pulse repetition frequency during displacement tracking limits stiffness resolution using the time to peak displacement parameter. The excitation pulse duration also impacts the time to peak parameter, with longer pulses reducing the inertial effects present during impulsive excitations. Material density affects tissue dynamics, but is not expected to play a significant role in biological tissues. The presence of an elastic spherical inclusion in the imaged medium significantly alters the tissue dynamics in response to impulsive, focused acoustic radiation force excitations. Times to peak displacement for excitations within and out- side an elastic inclusion are still indicative of local material stiffness; however, recovery times are altered due to the reflection and transmission of shear waves at the inclusion boundaries. These shear wave interactions cause stiffer inclusions to appear to be displaced longer than the more compliant background material. The magnitude of shear waves reflected at elastic lesion boundaries is dependent on the stiffness contrast between the inclusion and the background material, and the stiffness and size of the inclusion dictate when shear wave reflections within the lesion will interfere with one another. Jitter and bias associated with the ultrasonic displacement tracking also impact the estimation of a tissue's dynamic response to acoustic radiation force excitation. [ABSTRACT FROM AUTHOR]

Depending on its electrical-to-mechanical energy conversion process, the torque on a traveling wave ultrasonic motor (TWUM)'s shaft is not directly proportional to a measurable electrical variable, such as current or voltage. But it is derived from a complicated process at the stator/rotor interface. The load torque is thus quite unknown, and this can be a disadvantage in applications in which a torque limitation is required or a torque measurement is needed. The aim of this article is to come up with a straightforward torque estimator on a TWUM. For that purpose, the motor is modeled; this modeling leads to different estimator strategies. More specifically, we chose a strategy for which a speed sensor is useless, relying only on the stator's resonant behavior. The parameters of the motor needed for the estimator are measured afterward, and some nonlinearities are identified and taken into account. Several experimental trials then are carried out to check the performance of the estimator. A claw actuated by a TWUM is presented because this is a typical application in which the knowledge of the torque helps guarantee the safety of the device. [ABSTRACT FROM AUTHOR]

Nanocrystalline diamond (NCD) is a promising material for the fabrication of highly sensitive flexural-plate-wave (FPW) sensors. The design of FPW sensors requires the determination of the mechanical properties of a vibrating thin-film membrane. In this paper, a method to investigate the mechanical resonance of NCD membranes is presented. Membranes with lateral dimensions in the millimeter range and 1.2-mum thick were excited in air by a loudspeaker, and the resonance mode shapes were recorded optically with a stroboscopic interferometer. The resonance frequencies helped in determining directly the mechanical parameter of interest for the design of diamond-based FPW devices and the residual stress in the NCD layer. This method allows the rapid investigation of prototype materials without requiring an integrated transduction system and can be applied to analyze structures with the actual dimensions of FPW sensors. The experimental results are used to assess the sensing properties of FPW devices with NCD membranes, which are enhanced with respect to classical materials such as silicon-based materials [ABSTRACT FROM PUBLISHER]