Theconvolutionaldiferentiatormethodfornu┐mericalmodelingofacousticandelasticwave┐fields

Based on the techniques of forward and inverse Fourier transformation, the authors discussed the design scheme of ordinary differentiator used and applied in the simulation of acoustic and elastic wavefields in isotropic media respectively. To compress Gibbs effects by truncation effectively, Hanning window is introduced in. The model computation shows that, the convolutional differentiator method has the advantages of rapidity, low requirements of computer′s inner storage and high precision, which is a potential method of numerical simulation.

A novel method for investigation of acoustic and elastic wave phenomena using numerical experiments

The emergence of new types of composite materials,the depletion of existing hydrocarbon deposits,and the increase in the speed of trains require the development of new research methods based on wave scattering.Therefore,it is necessary to determine the laws of wave scattering in inhomogeneous media.We propose a method that combines the advantages of a numerical simulation with an analytical study of the boundary value problem of elastic and acoustic wave equations.In this letter we present the results of the study using the proposed method:the formation of a response from a shear wave in an acoustic medium and the formation of shear waves when a vertically incident longitudinal wave is scattered by a vertical gas-filled fracture.We have obtained a number of analytical expressions characterising the scattering of these wave types.

The Propagation, Excitation and Coupling of Acoustic Waves in Phonon Band-gap Materials

Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.

A Modified Monte Carlo Model of Speckle Tracking of Shear Wave Induced by Acoustic Radiation Force for Acousto-Optic Elasticity Imaging

A modified Monte Carlo model of speckle tracking of shear wave propagation in scattering media is proposed. The established Monte Carlo model mainly concerns the variations of optical electric field and speckle. The two- dimensional intensity distribution and the time evolution of speckles in different probe locations are obtained. The fluctuation of speckle intensity tracks the acoustic-radiation-force shear wave propagation, and especially the reduction of speckle intensity implies attenuation of shear wave. Then, the shear wave velocity is estimated quantitatively on the basis of the time-to-peak algorithm and linear regression processing. The results reveal that a smaller sampling interval yields higher estimation precision and the shear wave velocity is estimated more efficiently by using speckle intensity difference than by using speckle contrast difference according to the estimation error. Hence, the shear wave velocity is estimated to be 2.25 m/s with relatively high accuracy for the estimation error reaches the minimum （0.071）.

Efficient Computational Approach for Predicting the 3D Acoustic Radiation of the Elastic Structure in Pekeris Waveguides

Ocean boundaries present a significant effect on the vibroacoustic characteristics and sound propagation of an elastic structure in practice.In this study,an efficient finite element/wave superposition method(FE/WSM)for predicting the three-dimen-sional acoustic radiation from an arbitrary-shaped radiator in Pekeris waveguides with a lossy seabed is proposed.The method is based on the FE method(FEM),WSM,and sound propagation models.First,a near-field vibroacoustic model is established by the FEM to obtain vibration information on a radiator surface.Then,the WSM based on the Helmholtz boundary integral is used to pre-dict the far-field acoustic radiation and propagation.Furthermore,the rigorous image source method and complex normal mode are employed to obtain the near-and far-field Green’s function(GF),respectively.The former,which is based on the spherical wave decomposition,is adopted to accurately solve the near-field source strength,and the far-field acoustic radiation is calculated by the latter and perturbation theory.The simulations of both models are compared to theoretical wavenumber integration solutions.Finally,numerical experiments on elastic spherical and cylindrical shells in Pekeris waveguides are presented to validate the accuracy and efficiency of the proposed method.The results show that the FE/WSM is adaptable to complex radiators and ocean-acoustic envi-ronments,and are easy to implement and computationally efficient in calculating the structural vibration,acoustic radiation,and sound propagation of arbitrarily shaped radiators in practical ocean environments.

Low-frequency laboratory measurements of the elastic properties of solids using a distributed acoustic sensing system

In recent decades,low-frequency(LF)experiments based on the forced-oscillation(FO)method have become common practice in many rock physics laboratories for measuring the elastic and anelastic properties of rocks.However,the use of the electronic displacement sensors in traditional acquisition systems of FO devices such as conventional capacitive transducers or strain gauges seriously limits both the efficiency and productivity of LF measurements,and,due to the limited contact area of the displacement sensors with a sample under test,increases the requirements for sample homogeneity.In this paper,we present the first results obtained in the development of a new laboratory method elaborated to measure the elastic properties of solids.The method is a further development of the FO method where traditional data acquisition is replaced by acquisition based on fiber-optic distributed acoustic sensing(DAS)technology.The new method was tested in a laboratory study using two FO setups designed for measurements under uniaxial and confining pressures.The study was carried out on a sample made from polymethyl methacrylate(PMMA)and an aluminium standard,first under uniaxial pressure at FO frequencies of 1,10,30,60 and 100 Hz,and then under confining pressure at an FO frequency of 1 Hz.Both uniaxial and confining pressures were equal to 10 MPa,and the strain in the PMMA sample in all measurements did not exceed 4×10^(-8).The performance of DAS acquisition was compared with the measurements conducted at a strain of 1×10^(-6) using the traditional FO method based on the use of semiconductor strain gauges and the ultrasonic method.The results of the DAS measurements are in good agreement with the FO measurements carried out using semiconductor strain gauges and with the literature data.

PROPAGATION OF SURFACE ACOUSTIC WAVES IN PRESTRESSED ANISOTROPIC LAYERED PIEZOELECTRIC STRUCTURES

The propagation of surface acoustic waves in layered piezoelectric structureswith initial stresses is investigated. The phase velocity equations are obtained for electricallyfree and shorted cases, respectively. Effects of the initial stresses on the phase velocity and theelectromechanical coupling coefficient for the fundamental mode of the layered piezoelectricstructures are discussed. Numerical results for the c-axis oriented film of LiNbO_3 on a sapphiresubstrate are given. It is found that the fractional change in phase velocity is a linear functionwith the initial stresses, and the electromechanical coupling factor increases with an increase ofthe absolute values of the compressive initial stresses. The results are useful for the design ofsurface acoustic wave devices.

Propagations of Rayleigh and Love waves in ZnO films/glass substrates analyzed by three-dimensional finite element method

Propagation characteristics of surface acoustic waves（SAWs） in ZnO films/glass substrates are theoretically investigated by the three-dimensional（3D） finite element method. At first, for（11ˉ20） ZnO films/glass substrates, the simulation results confirm that the Rayleigh waves along the [0001] direction and Love waves along the [1ˉ100] direction are successfully excited in the multilayered structures. Next, the crystal orientations of the ZnO films are rotated, and the influences of ZnO films with different crystal orientations on SAW characterizations, including the phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency, are investigated. The results show that at appropriate h/λ, Rayleigh wave has a maximum k^2 of 2.4% in（90°, 56.5°, 0°） ZnO film/glass substrate structure; Love wave has a maximum k^2 of 3.81% in（56°, 90°, 0°） ZnO film/glass substrate structure. Meantime, for Rayleigh wave and Love wave devices, zero temperature coefficient of frequency（TCF） can be achieved at appropriate ratio of film thickness to SAW wavelength. These results show that SAW devices with higher k^2 or lower TCF can be fabricated by flexibly selecting the crystal orientations of ZnO films on glass substrates.

A novel type of transverse surface wave propagating in a layered structure consisting of a piezoelectric layer attached to an elastic half-space

The existence and propagation of transverse surface waves in piezoelectric coupled solids is investigated, in which perfect bonding between a metal/dielectric substrate and a piezoelectric layer of finite-thickness is assumed. Dis- persion equations relating phase velocity to material con- stants for the existence of various modes are obtained in a simple mathematical form for a piezoelectric material of class 6mm. It is discovered and proved by numerical examples in this paper that a novel Bleustein-Gulyaev （B-G） type of transverse surface wave can exist in such piezoelectric cou- pled solid media when the bulk-shear-wave velocity in the substrate is less than that in the piezoelectric layer but greater than the corresponding B-G wave velocity in the same pie- zoelectric material with an electroded surface. Such a wave does not exist in such layered structures in the absence of pie- zoelectricity. The mode shapes for displacement and electric potential in the piezoelectric layer are obtained and discussed theoretically. The study extends the regime of transverse sur- face waves and may lead to potential applications to surface acoustic wave devices.

Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

When a surface acoustic wave （SAW） propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coemcient is ~alculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.

Transformation method and wave control

Transformation method provides an efficient way to control wave propagation by materials.The transformed relations for field and material during a transformation are essential to fulfill this method.We propose a systematic method to derive the transformed relations for a general physic process,the constraint conditions are obtained by considering geometrical and physical constraint during a mapping. The proposed method is applied to Navier＇s equation for elastodynamics,Helmholtz＇s equation for acoustic wave and Maxwell＇s equation for electromagnetic wave,the corresponding transformed relations are derived,which can be used in the framework of transformation method for wave control.We show that contrary to electromagnetic wave,the transformed relations are not uniquely determined for elastic wave and acoustic wave,so we have a freedom to choose them differently.Using the obtained transformed relations,we also provide some examples for device design,a concentrator for elastic wave,devices for illusion acoustic and illusion optics are conceived and validated by numerical simulations.

Tensile Shock Physics in Compressible Thermoviscoelastic Solid Medium

This paper addresses tensile shock physics in thermoviscoelastic (TVE) solids without memory. The mathematical model is derived using conservation and balance laws (CBL) of classical continuum mechanics (CCM), incorporating the contravariant second Piola-Kirchhoff stress tensor, the covariant Green’s strain tensor, and its rates up to order n. This mathematical model permits the study of finite deformation and finite strain compressible deformation physics with an ordered rate dissipation mechanism. Constitutive theories are derived using conjugate pairs in entropy inequality and the representation theorem. The resulting mathematical model is both thermodynamically and mathematically consistent and has closure. The solution of the initial value problems (IVPs) describing evolutions is obtained using a variationally consistent space-time coupled finite element method, derived using space-time residual functional in which the local approximations are in hpk higher-order scalar product spaces. This permits accurate description problem physics over the discretization and also permits precise a posteriori computation of the space-time residual functional, an accurate measure of the accuracy of the computed solution. Model problem studies are presented to demonstrate tensile shock formation, propagation, reflection, and interaction. A unique feature of this research is that tensile shocks can only exist in solid matter, as their existence requires a medium to be elastic (presence of strain), which is only possible in a solid medium. In tensile shock physics, a decrease in the density of the medium caused by tensile waves leads to shock formation ahead of the wave. In contrast, in compressive shocks, an increase in density and the corresponding compressive waves result in the formation of compression shocks behind of the wave. Although these are two similar phenomena, they are inherently different in nature. To our knowledge, this work has not been reported in the published literature.

Serpentinites of the Ural: Mineralogical Features, Petrophysical Properties and Subduction Processes

The article presents the results of study of composition, structure and properties of three genetic types of serpentinites from Ural: developed by chromite-bearing ultrabasic rocks, by metamorphic zones of carbonate rocks and within the zone of weathering of ultrabasic rocks. The samples were selected from deposits, located along the Main Ural Fault - the Paleozoic subduction zone (named GUR). Peculiarities of microstructure, chemical composition and properties of serpentinites formed in different geological conditions were investigated and their comparative study was held. Three groups of serpentinites with oriented and non-oriented structure, which formed by different protholites, were devided: mantle, lithosphere and crust.

Mineralogical Features and Properties of Serpentine as Indicator of the Deep Earth Subduction Processes

The article presents the results of study of composition, structure and properties of three genetic types of serpentinite, developed by chromite-bearing ultrabasic rocks, by metamorphic zones of carbonate rocks and within the zone of weathering of ultrabasic rocks. The samples were selected from deposits, located along the Main Ural Fault-the Paleozoic subduction zone （named GUR）. Peculiarities of microstructure, chemical composition and properties of serpentinites formed in different geological conditions were investigated and their comparative study was held. They were devided three groups of serpentinites with oriented and non-oriented structure which formed by different protholites： mantle, lithosphere and crust.

二维声学黑洞应用于压电振动能量收集

声学黑洞(acoustic black hole,ABH)效应可以产生强烈的能量集中,能够将高频率低振幅的低品质振动能量转化为高振幅的高品质振动能量,从而便于利用。提出并研究了一种环形二维声学黑洞压电能量收集装置。有限元分析结果表明,环形二维ABH结构能在宽频域内显著提高能量收集效率。搭建了环形二维声学黑洞压电能量收集器试验测试平台,通过试验验证了仿真结果的正确性。与经典二维ABH结构相比,环形二维ABH结构具有更好的能量收集效率和结构强度。分析了压电片几何尺寸等因素对装置能量收集效率的影响,得到了能获得较高输出功率的几何尺寸范围,并进行了正交试验设计,研究了截断厚度、压电片尺寸、中央平台直径、幂指数等多因素的综合影响。

声学双曲构型超材料的负折射特性研究

声学双曲超材料是具有双曲色散特性的人工材料,具有极强的各向异性,其负折射特性是研究实现高分辨率聚焦型超透镜的理论依据。针对远场噪声源识别受制于0.5倍波长声波瑞利衍射识别分辨率问题,结合声学超材料对声波的优异调控效果,引进可以实现亚波长超分辨率成像的双曲超材料,利用其负折射特性设计了一种用于工作频率为2 271.5 Hz的声学双曲结构。分析了该构型的双曲结构色散特性及负折射特性,结果表明声波在该双曲超材料中传播的群速度方向垂直于波矢,并沿着色散曲线的法线方向。本文的研究为实现对声波和弹性波的任意调控,以及噪声源的聚焦定位、识别放大等提供了一定的设计参考。

基于声辐射力脉冲成像的诊断模型对胆道闭锁患儿肝纤维化的应用价值

目的分析基于声辐射力脉冲成像(ARFI)定量参数建立的无创诊断模型对胆道闭锁患儿肝纤维化的诊断价值。方法回顾性收集100例接受ARFI检查并行肝门-空肠吻合术(Kasai’s)治疗及肝组织活检的胆道闭锁患儿,男42例,女58例,平均年龄(68.79±8.79)d。根据活检病理结果分为肝纤维化组(71例)和非肝纤维化组(29例)。依据Metavir分级标准将肝纤维化分为5级:F0(29例)、F1(31例)、F2(24例)、F3(11例)、F4(5例)。2组临床资料和ARFI定量参数的比较采用t检验或χ^(2)检验;采用单因素方差分析比较肝纤维化不同分级间的剪切波速度(SWV)。采用多因素Logistic回归分析影响胆道闭锁患儿发生肝纤维化的独立危险因素,并构建基于ARFI定量参数的无创诊断模型。采用受试者操作特征(ROC)曲线评价模型的诊断效能,计算其曲线下面积(AUC)。结果肝纤维化组血清中性粒细胞(NEUT)、总胆红素(TBIL)、层黏蛋白(LN)、透明质酸(HA)、Ⅲ型前胶原(PCⅢ)、Ⅳ型胶原(Ⅳ-Col)浓度,以及SWV均高于非肝纤维化组(均P<0.05)。多因素Logistic回归分析结果显示,SWV、血清TBIL及LN、HA、PCⅢ、Ⅳ-Col浓度高是影响胆道闭锁患儿发生肝纤维化的危险因素(均P<0.05)。基于SWV的无创诊断模型诊断胆道闭锁患儿发生肝纤维化的最佳临界值为1.75 m/s,敏感度、特异度、准确度、阳性预测值、AUC分别为93.15%、70.09%、90.25%、88.80%、0.922。结论基于ARFI定量参数建立的无创诊断模型,可较为准确地诊断出胆道闭锁患儿是否存在肝纤维化,且具有较高的应用价值。

恒频声学二极管的设计及特性研究

声学二极管能控制声波仅在一个方向有效传输在反方向无法传播,在通信技术中具有广泛的应用,然而目前大多数的声学二极管设计是基于非线性效应使系统只通过新的高次频率并阻止原频率的传输.本文利用不对称结构与弱非线性声子晶体的组合,提出了一种一维声二极管模型,实现弹性波的不对称传输,并保持频率不变.该模型由左端的变幅杆和右端的非线性弹簧质量链组成,理论分析表明,该声学二极管具有与电子二极管相同的正向和反向特性,并通过有限元仿真验证了该模型的有效性.

Coupled method of finite and dynamic infinite elements for simulating wave propagation in elastic solids involving infinite domains

This paper deals with the coupled method of finite and dynamic infinite elements for simulating wave propagation in elastic and viscoelastic solids involving infinite domains.This method can be used to simultaneously simulate material complexities in the near field and the infinite extent of the far field.Based on the governing equations of wave motion in two-dimensional and three-dimensional elastic/viscoelastic solids,the mass and stiffness matrices of the dynamic infinite element have been derived.The proposed two-dimensional dynamic infinite element can be used to simulate both the P-wave and the SV-wave propagation within the element,while the proposed three-dimensional dynamic infinite element can be used to simultaneously simulate the Rayleigh wave,P-wave and S-wave propagation within the element.The related simulation results have demonstrated that the coupled method of finite and dynamic infinite elements can be accurately used to simulate,both physically and computationally,wave propagation in elastic/viscoelastic solids involving infinite domains.Thus,this method provides an advanced scientific tool for dealing with both scientific and engineering problems involving infinite domains.