大振幅平面声波在多层介质中的传播

本文用逐级近似法就一维情况下分析了大振幅平面声波在多层介质的界面上发生反射和透射的传播特性。在二级近似下计算了精确到二阶小量的二至三个界面各层的反射波和透射波的二次谐波，并推广至几个界面，得到一些规律性的结果。从拉格朗日坐标下的一级近似和二级近似的波动方程式出发，假定声波在多层介质中传播在各个界面仍是连续的，即各层界面的边界条件由界面两侧的压力平衡和质点速度相等来决定，由此求得各层界面在二级近似下的二次谐波的反射波和透射波。计算结果表明，二级近似下的反射波和透射波均由两部分组成，一部分是由一级反…     

声波在多层介质中传播的四端参数模型应用分析研究

声波在两种介质的交界面透射和反射时 ,借鉴机械四端参数法 ,利用声学边界条件 ,引入了四端参数矩阵 ,建立四端参数模型。通过对四端参数矩阵的分析 ,探讨了在简谐平面波垂直入射的条件下 ,声波在多层介质中的传播特性 ,并推导出声透射系数和声反射系数的一般计算公式。     

周期加筋板中的弯曲波传播

本文采用波动分析法分析了周期加筋板中的弯曲波传播，推导了周期加筋板的波传播方程，分析了振动频率和平面弯曲波入射角对传播常数的影响。研究表明：平面弯工波以某一角度入射周期加筋板时，随着频率的变化，会交错的出现弯曲波传递的穿透频段和阻塞频段；周期加筋板没有明显的穿透频段。本文的研究为周期加筋板应用于结构声传递途径的控制提供了理论基础。     

层状生物介质中二阶反射波的研究

层状生物介质中二阶反射波的研究章瑞铨冯绍松（中科院上海声学实验室上海·２０００３２）１引言大振幅平面声波在生物介质中传播的非线性效应已日益引起人们重视［１］。近年来，已有研究表明，表征非线性效应特性的非线性参数与生物组织的结构与病变有关［２］。因此，...     

层状三元周期结构的带隙计算

对于层状三元周期结构的带隙分析和研究目前还属空白。基于声子晶体理论,将层状三元周期结构简化为一维声子晶体结构,并利用集中质量法,分析了材 料密度与材料阻尼比变化对第一带隙的影响。研究表明,材料密度的改变对第一带隙产生较大影响;材料阻尼比的变化对第一带隙影响不明显。研究结论为层状三元结构带隙设计提供了理论依据。     

声波由粘弹性介质向流体介质入射情况下的声反射分析

在研究含腔体的结构的声学特性时,会遇到声波从粘弹性介质向流体介质入射的情况。主要研究了声波从粘弹性介质向流体介质斜入射情况下的声反射特性,分析表明：反射声波中有横波和纵波同时存在,纵波声压反射系数随入射角度的增大逐渐增大,横波的声压反射系数随入射角度的增加先增大后减小,在垂直入射时只有纵波,而没有横波存在。这些结论为进一步研究带空腔结构的声学特性打下了基础。     

非线性声波方程的几种解法对比

在医学诊疗领域及微、介观损伤的无损检测行业中,经常需要对介质的材料非线性系数进行表征,以得到局部区域更加精细的力学性能变化.文章在简述各向同性固体和理想流体介质中的非线性声波方程的基础上,证实了它们具有相同的形式,这表明它们的解也应具有相同的形式和性质.介绍了求解非线性声波方程的五种方法,包括有限差分、有限元、摄动法、...     

空气中周期管阵列的声波禁带研究

本文以不锈钢管正方形排列在空气中形成的二维声子晶体为对象,使用平面波展开法计算并通过实验测试的方法,分析了该二维声子晶体的声波禁带,讨论了晶格常数对声波禁带的影响.结果表明,随着晶格常数的减小,ΓX方向禁带宽度增加,禁带上下边界频率增大.     

应用于热声机械的声波平面传递装置

应用于热声机械的声波平面传递装置,由柔性部分和刚性片部分组成.通过引入柔性结构,将传递声波所必需的弹性部分和惯性部分分开,实现刚性片的平面运动,从而达到声波的平面传递.依据弹性部分的不同形式,声波平面传递装置有3种形式:弹性膜型、折环型和弹性环型.将这种装置应用于热声机械中,可以大大改善热声系统中声波传递的性能,拓展热...     

声波在弹性圆管内的传播理论

设一无限长弹性圆管其内外半径分别为ａ和ｂ，穿孔率ε＝ａ／ｂ，边界条件为：内界面（ｒ＝ａ）为自由面，应力为零；外界面（ｒ＝ｂ）是静止的，或是刚性的，既无位移，又无切应力。建立圆柱坐标，它的振动方程式为：式中ｕｒ、ｕｚ分别为径向ｒ和轴向ｚ的振动位移，λ和μ为材料的拉密系数。它的特征方程可表达为复波数κ的复杂的超越函数。假设材料的λ近似为实数，其值比μ要大两个数量级；ε＜０．５，同时κ·ａ＜＜１，即在低频或小穿孔率条件下，该特征方程的一阶近似解为：ｋ＝ｋＬ·１＋·（）二阶近似解的形式同一阶，所不同的是…     

Aberration in nonlinear acoustic wave propagation

Theory and simulations are presented indicating that imaging at the second-harmonic frequency does not solve the problem of ultrasonic wave aberration. The nonlinearity of acoustic wave propagation in biological tissue is routinely exploited in medical imaging because the improved contrast resolution leads to better image quality in many applications. The major sources of acoustic noise in ultrasound images are aberration and multiple reflections between the transducer and tissue structures (reverberations), both of which are the result of spatial variations in the acoustic properties of the tissue. These variations mainly occur close to the body surface, i.e., the body wall. As a result, the nonlinearly generated, second harmonic is believed to alleviate both reverberation and aberration because it is assumed that the second harmonic is mainly generated after the body wall. However, in the case of aberration, the second harmonic is generated by an aberrated source. Thus the second harmonic experiences considerable aberration at all depths, originating from this source. The results in this paper show that the second harmonic experiences similar aberration as its generating source, the first harmonic.     

Ferroelectrically active acoustic wave propagation

The ferroelectrically active acoustic wave equation including electrostriction effects is derived from nonlinear constitutive equations of stress and electric displacement for ferroelectric materials exhibiting significant electrostrictive strain. Electrically controllable acoustic wave propagation is predicted by solving the equation as a function of various acoustic variables, e.g., wave excitation, polarization, dc bias, etc. As examples, the elastic, piezoelectric, and ferroelectric acoustic waves and the electromechanical coupling factors are computed as a function of wave propagation in the [100]-[010] plane of BaTiO3 under thickness excitation mode.     

Terahertz wave propagation in one-dimensional periodic dielectrics

We demonstrate the temporal evolution of terahertz (THz) wave propagation in one-dimensional periodic dielectrics. Distributed Bragg reflectors and a resonant cavity are investigated: The structures involve air gaps interleaved between polymer films. Transmitted and reflected broadband THz waves are measured by means of THz time-domain spectroscopy. The experimental results agree well with transfer matrix calculations.     

Magnetic wave propagation in a periodic medium

The propagation of magnetic waves in an infinite medium with a periodic dielectric constant is studied as a simplified example to evaluate the applications of periodic structures. Specifically, the use of those structures for filtering and distributed feedback is investigated, and a new scheme for the generation of magnetic waves using drifting charges and a distributed feedback configuration similar to DFB lasers is studied in some detail.     

非对称周期结构中耦合波的传播特性

为了揭示周期结构中纵向波和弯曲波的耦合作用,设计了对称和非对称周期结构。考虑子结构中的纵向和弯曲耦合运动,利用导纳法和传递矩阵法,得到了周期单元的传递方程。由于结构中存在多种波的耦合作用,在求解周期单元的传播系数时将出现变态矩阵,采用波型分组法,求得了周期结构中多种波型的传播系数。推导了半无限长和有限长周期结构在纵向力、横向力和弯矩作用下的动态响应。数值计算结果表明,对称周期结构中纵向波和弯曲波的带隙结构相互独立;非对称周期结构中纵向波和弯曲波的耦合明显改变了两种波的带隙结构,只有在两种波阻带重叠的频段内结构上的振动响应才存在衰减。     

Elastic wave propagation in a microstructured acoustic fiber

Elastic wave propagation along the structure of hollow cylinders in a linear isotropic medium is investigated. The multipole method for modeling elastic waves propagation in such structures is formulated and implemented. Using the multipole method, dispersion dependencies of the structures (microstructured fibers) containing 3, 6, and 7 hollow cylinders are calculated. Comparison with wave dispersion properties along one cylinder is made. Also, an approximate physical model based on an equivalent coaxial waveguide and multipole method is proposed. Exploiting this model, wave dispersion of the wave propagating along a structure with 18 hollow cylinders is calculated. Validation of the model is also proposed.     

Guided acoustic wave propagation for porcelain coatingcharacterization

In this paper a measurement technique to obtain dispersion curves for guided acoustic modes in porcelain-coated steel is described. The measurement is performed with two angled ultrasonic longitudinal transducers in a pitch catch configuration by employing an immersion technique. Phase velocities for the guided modes are selected through the variation of the angle formed by the transmitter beam with the surface normal vector. The excitation signal of the transmitting transducer is a narrow band pulse. For each phase velocity, the guided mode frequencies are recovered by evaluating the frequency minima of the reflection coefficient     

Dispersion relations for SH-wave propagation in periodic piezoelectric composite layered structures

Propagation behavior of horizontally polarized shear waves (SH-waves) in a periodic piezoelectric-polymeric layered structure is taken into account. The layered structures are consisted of piezoelectric thin films bonded perfectly with polymeric thin films alternately. The phase velocity equations of SH-waves propagation in the periodic layered piezoelectric structure are obtained for the cases of wave propagation in the direction normal to the interface and along the interface, respectively. Filter effect of this kind of structure and the effects of volume fraction and shear modulus ratio of piezoelectric layer to polymeric layer on the phase velocity are discussed in detail, respectively. One set of piezoelectric thin film--polymeric thin film multilayer system (PZT-5H piezoelectric ceramics--polythene) is chosen to show the numerical simulation, basic properties of SH-waves propagation in this particular structure are revealed.     

Love wave propagation in layered magneto-electro-elastic structures with initial stress

Summary An analytical approach is taken to investigate Love wave propagation in layered magneto-electro-elastic structures with initial stress, where a piezomagnetic (piezoelectric) material thin layer is bonded to a semi-infinite piezoelectric (piezomagnetic) substrate. The magneto-electrically open and short conditions are applied to solve the problem. The phase velocity of the Love wave is numerically calculated for the magneto-electrically open and short cases, respectively. The effect of the initial stress on the phase velocity and the magneto-electromechanical coupling factor are studied in detail for piezomagnetic ceramics CoFe₂O₄ and piezoelectric ceramics BaTiO₃. We find that the initial stress has an important effect on the Love wave propagation in layered piezomagnetic/piezoelectric structures.     

粘性联结的层状固体媒质中兰姆波的传播

在复合材料中 ,当有粘弹体存在时 ,粘弹体的粘性会对波的传播造成一定影响。早期的 Thomson-Haskell矩阵以面波描述板层中的场 ,而面波的幅值在各个方向都是常数 ,因此它们不能描述在一衰减媒质中反射或透射波的衰减。本文中引入体波衰减的模型 ,即 Kelvin- Voigt的粘弹性描述 [1] ,该方法导致了一个复数波数。其实部描述了波的传播 ,而虚部则描述波的衰减。1　基本理论传递矩阵可以描述弹性波在包含任意多层的层状媒质中的传播特性 [2 ] 。1.1　无限弹性固体中的波对图 1所示的计算模型 ,其运动位移方程用矢量形式可表示为 :　　 ρ 2 U …