液体—压电晶片界面上电边界条件对兰姆波散发的影响

本文对液体－压电晶片结构中,不同电边界条件下叉指换能器所激发的兰姆波传播特性进行了分析研究,给出了不同电边界条件下兰姆波的相速度、叉指换能器激发兰姆波的机电耦合系数与压电晶片的归一化厚度、晶体切向之间的关系曲线,为实际设计中电边界条件的正确选择提供了理论基础。     

压电换能器对兰姆波影响的仿真

0引言兰姆波由于传输距离远、检测范围广,一直是国内外无损检测领域研究的热点。频散现象和模态混叠使兰姆波的传播特性十分复杂。解决办法之一就是通过换能器激发单一的模式[1]。考虑高效和低成本,采用压电换能器激励和接收兰姆波是无损检测的常用方法[2]。传统的兰姆波仿真通常不考虑传感器对兰姆波的影响。本文通过有限元软件COMSOL时域分析兰姆波在铝板中的传播状况,为无损检测提供参考。     

《声学技术》2001年总目录

·论文与报告·液体 压电晶片界面上电边界条件对兰姆波激发的影响马伟方　侯　毅　施文康　邓明晰　 (0 1.1.4)………………………基于恒定束宽波束输出的宽带相干源高分辨测向杨益新　卓　颉　孙　超　朱治富　 (0 1.1.7)……………………………二维涡斑的运动发声刘晓宙　刘应中　缪国平　唐春权　 (0 1.1.10 )……………………………………………………………气介式功率超声复合换能器的声辐射特性研究林书玉　张光斌　 (0 1.1.13)……………………………………………………三维障碍物形状近场反演的一种快速算法尤云祥　缪国平　刘应中…     

超声功率标准换能器铌酸锂压电晶片的设计研究

本文探讨了设计合适的铌酸锂压电晶片以研制高频高效的超声功率标准换能器,该换能器用于毫瓦级超声功率国家基准.论文分析铌酸锂各种切型的压电性能并选择最优切型用于研制标准换能器,给出晶片自由振动时的等效电阻抗和集总参数等效电路,以及晶片厚度和共振频率的关系.用所设计晶片研制出共振频率为18.5MHz的标准换能器,其辐射声导值...     

螺旋叉指电极式压电圆片换能器的有限元分析与实验比较

螺旋叉指电极式压电圆片换能器可以产生面内扭转运动,具有结构简单、加工方便、性能可靠等优点,可用于超声马达、光学扫描、黏度测量等领域;但表面螺旋叉指电极间陶瓷材料的极化方向变化复杂,给换能器的机电耦合分析和优化设计带来极大的难度。利用坐标变换思想与有限元方法,将压电圆片分割成若干子体,通过极化电场分析确定子体局部坐标系以定义材料参数,从而实现复杂极化情况下压电换能器的耦合仿真分析。利用ANSYS有限元软件,优化仿真分析过程,研究了该压电圆片换能器的静态扭转位移径向分布特性和动态导纳频率响应特性,并与实验结果相比较,证实了该方法的可行性和有效性。     

电磁超声兰姆波换能器多目标优化设计

针对电磁超声兰姆波换能器激发的兰姆波存在多模式、频散现象和信号较弱的问题,结合铝合金板材检测背景,提出一种基于＂双交点法＂、＂零斜率准则＂和正交试验设计相结合的电磁超声兰姆波换能器多目标优化设计方法。其中,＂双交点法＂可有效削弱兰姆波多模式现象的影响,＂零斜率准则＂能够有效降低兰姆波的频散现象,而正交试验设计方法可有效提高电磁超声兰姆波信号的幅值。依据所提优化设计方法,对一个在铝板检测中常用的电磁超声兰姆波换能器的9个主要参数进行了多目标优化设计。实验表明,优化后,兰姆波信号中的多模式、频散现象得到显著抑制,而且信号幅值得到明显提升,有效改善了电磁超声兰姆波换能器的工程实用性。     

基于COMSOL的声表面波器件仿真

声表面波器件在通信、传感、射频识别等领域有着广泛的应用.以有限元方法为基础,利用有限元软件COMSOL对声表面波器件进行了仿真.从器件的模型建立入手,按由浅入深的顺序对无电极压电基片、压电基片表面沉积叉指换能器、叉指换能器表面溅射薄膜、薄膜上负载液体的4种结构进行了仿真分析.仿真研究表明:叉指换能器的电极效应会产生正、反特征频率,并且两种频率都随着叉指电极的敷金比与高度增加而向低频偏移;薄膜厚度的增加同样会导致器件频率向低频变化;当器件负载液体用于液体密度检测时,可通过器件频率变化对液体密度的灵敏程度来对薄膜厚度进行优化.其研究结果可以为声表面波器件的设计制作提供依据.     

光纤布拉格传感器兰姆波检测的反射谱分析

传统的兰姆波多采用压电陶瓷换能器激发和接收。建立了新的超声兰姆波无损检测系统,其基本思想是采用布拉格光纤传感器作为兰姆波的接收器。光纤光栅传感的基本原理是通过检测光栅反射的中心波长移动实现对外界参量如超声的测量。超声作用下光纤光栅的反射谱发生变化,对超声作用下光纤光栅的反射谱变化进行了数值分析,结果表明,超声对光栅反射谱的影响与超声波长与光栅长度的比值是高度相关的。只有当这个比值相当大时,反射谱的形状才不会变化而中心波长发生偏移,此时光纤传感器可用来探测兰姆波。这个结论为利用新的兰姆波无损检测系统在布拉格光栅长度的设计和兰姆波波长的选择方面提供了有用的工具。     

宽通带小矩形系数的声表面波滤波器

一、声表面波滤波器的设计 理论分析指出,叉指换能器的频率响应[H(ω)],可由叉指换能器的脉冲响应H(t)通过付里叶交换求得,而叉指换能器脉冲响应H(t)的包络恰好是叉指换能器叉指指端的轨迹。所以叉指换能器的脉冲响应就是叉指换能器的空间图像。这种一一对应的关系可由图1来说明。由此可知,通过对叉指换能器电极指条位置与重迭长度的设计便能控制叉指换能器的脉冲响应,从而也就控制了叉指换能器的频率响应。 在一般情况下,声表面波滤波器中的二个叉指换能器只有一个是设计成加权的,另一个采用简单的宽带形式。此时滤波器的频率响应只取决…     

兰姆波检测参数曲线的应用研究

为了推广应用兰姆波进行无损检测,对兰姆波检测参数曲线进行了研究。通过对兰姆波频率特征方程的对称模式和反对称模式两种情况进行算法分析,用VC++软件加以编程实现,设计了专门用于绘制兰姆波参数曲线的软件,同时依据激励角频散曲线设计了兰姆波换能器的斜楔结构参数,并制作了兰姆波换能器,进而解决了兰姆波检测参数曲线的绘制和应用问题,所绘制的参数曲线适用于不同材质、不同型号的金属薄板兰姆波检测。     

Effect of An Initial Stress on SH-Type GuidedWaves Propagating in a Piezoelectric Layer Bonded on A Piezomagnetic Substrate

Propagation of SH-type guided waves in a layered structure with an invariant initial stress is studied, where a piezoelectric thin layer is perfectly bonded on a piezomagnetic substrate. Both the layer and the substrate possess transversely isotropic property. The dispersion relations of SH waves are obtained for four kinds of different electro-magnetic boundary conditions. The effects of initial stress, thickness ratio and electro-magnetic boundary conditions on the propagation behaviors are analyzed in detail. The numerical results show that: 1) The positive initial stresses make the phase velocity increasing, while the negative initial stresses decrease the phase velocity; 2) The smaller the thickness ratio of a piezoelectric layer to a piezomagnetic substrate, the larger the phase velocity of SH-type guided wave propagating in the corresponding layered structure; 3) The electrical boundary conditions play a dominant role in the propagating characteristics. Moreover the phase velocities for the electrically shorted surface are smaller than that for the open case. The obtained results are useful for understanding and design of the electromagnetic acoustic wave and microwave devices.     

Optimization of SAW-type Surface Wave Ultrasonic Sensors for Ultrasonic SHM

Surface acoustic waves (SAW) are particularly suited for effectively monitoring and characterizing a structure’s surfaces (condition of the surface, coating, thin layer, micro-cracks, etc.), and in some cases it is necessary to permanently keep the sensors on the structures to enable continuous monitoring. This article focuses on the optimization of SAW-type interdigital sensors (or IDT sensors for InterDigital Transducer) because they can largely address this issue. Initially, the ability of piezoelectric materials (lead zirconate titanate [PZT] and Niobate de lithium) to generate SAW is studied by modeling. Then a design of an IDT sensor is defined and optimized for the generation of SAW on a substrate. Parameters such as electrode’s periodicity, thickness of piezoelectric plate, and type of contact between the plate and the substrate, are studied. Finally, experimental results are compared with those obtained by modeling.     

Boundary integral equations from Hamilton's principle for surface acoustic waves under periodic metal gratings

The procedure describes the derivation of boundary integral equations for surface acoustic waves propagating under periodic metal strip gratings with piezoelectric films. It takes into account the electrical and mechanical perturbations, including the effects of mass loading caused by the gratings with an arbitrary shape. First, an integral equation is derived with line integrals on the boundaries within one period. This derivation is based on Hamilton's principle and uses Lagrange's method of multipliers to alleviate the continuous conditions of the displacement and the electric potential on the boundaries. Second, boundary integral equations corresponding to each substrate, piezoelectric film, metal strip, and free space region are obtained from the integral equation using the Rayleigh-Ritz method for admissible functions. With this procedure, it is not necessary to make any assumptions for separation of the boundary conditions between two neighboring regions. Consequently, we clarify the theoretical basis for the analytical procedure using boundary integral equations for longitudinal LSAW modes.     

BIEM solution of piezoelectric cracked finite solids under time-harmonic loading

The time-harmonic behavior of cracked finite piezoelectric 2D solids of arbitrary shape is studied by the nonhypersingular traction boundary integral equation method (BIEM). Plane strain and generalized traction free boundary conditions along the crack are assumed. The system may be loaded at the external boundary by arbitrary mechanical or electrical loads. As numerical example a center cracked rectangular piezoelectric plate under time-harmonic tension and electrical displacement is investigated in detail. The accuracy of the proposed numerical algorithm is checked by comparison with available results obtained by other methods for special cases. Parametric studies revealing the sensitivity of the stress intensity factors (SIFs) on the frequency of the applied mechanical and electrical load, on its coupled and uncoupled character and on the piezoelectric properties of the material are presented.     

Development of a generalized model for analyzing phase characteristics of SAW devices under mass and fluid loading

vA generalized model that integrates the Navier-Stokes equation and coupling-of-modes (COM) model for biosensing SAW devices is developed in this paper. The SAW device is separated into three regions: interdigital transducer (IDT), substrate (delay line), and sensing regions. To evaluate the effects of metal thickness, mass loading caused by bioreaction, and different viscous fluid loading, the sensing region is further divided into three layers: piezoelectric substrate, metal layer, and fluid layer. In contrast to the conventional study, which is focused on the change of phase velocity, this model can evaluate the insertion loss and phase shifts under different sensing conditions. It can be shown that the integration of the COM model can provide guidelines for designing the bio-sensing device such as choosing the proper number of IDT, the width of the overlap, and the thickness of the metal layer. Furthermore, the generalized model can be utilized to evaluate the optimal thickness of the metal layer to achieve the maximum sensitivity.     

Fracture of a piezoelectric material layer bonded by two elastic layers

A piezoelectric material layer bonded by two elastic layers under mechanical and electrical loads is studied. The piezoelectric material layer contains a central crack or two collinear cracks. Both mixed-mode crack and anti-plane crack are considered for the impermeable crack assumption and the permeable crack assumption. The effect of electric boundary conditions on electrical and mechanical field intensity factors are discussed. Some new observations are found.     

Shear horizontal (SH) waves propagating in piezoelectric–piezomagnetic bilayer system with an imperfect interface

This work considers the propagation of shear horizontal (SH) waves in a bilayer system consisting of a piezoelectric (PE) layer and a piezomagnetic (PM) substrate. The interface between the PE layer and the PM substrate is imperfectly bonded. The surfaces of the bilayer system are free of traction, electrically shorted or open and magnetically open or shorted. The exact dispersion equations are derived. The numerical examples are given to illustrate the effects of the electromagnetic boundary conditions, the imperfect interface, the different PE layers and the thickness ratio on the dispersion behaviors. It is found that (a) the electrical boundary conditions dominate the propagation characteristics of SH waves; (b) the imperfect bonding lowers the phase velocities; (c) the thickness ratio and the properties of PE layers have a significant effect on the dispersion behaviors. The obtained results provide a predictable and theoretical basis for applications of PE–PM composites to acoustic wave devices.     

Numerical analysis for piezoelectric crack under varied boundary conditions by optimized hybrid element method

In this article, a piezoelectric hybrid element is presented and optimized by penalty equilibrium approach, and special crack surface element is suggested for exactly implementing the boundary conditions on crack surface. An iteration technique is used to treat one of the electric boundary conditions. Then, a piezoelectric material with crack is numerically studied by the optimized hybrid element method, and the results are compared with the analytical solutions. The stress and the electrical displacement fields with different crack surface conditions are studied, and the influence to those fields arisen by the far field mechanical and electric loading is also studied.     

Rayleigh-Type Wave in A Rotated Piezoelectric Crystal Imperfectly Bonded on a Dielectric Substrate

Propagation characteristics of Rayleigh-type wave in a piezoelectric layered system are theoretically investigated. The piezoelectric layer is considered as a cubic crystal with finite thickness rotated about Y-axis and is imperfectly bonded onto a semi-infinite dielectric substrate. The imperfect interface between the two constituents is assumed to be mechanically compliant and dielectrically weakly conducting. The exact dispersion relations for electrically open or shorted boundary conditions are obtained. The numerical results show that the phase velocity of Rayleigh-type wave is symmetric with respect to the cut orientation of 45。 and can achieve the maximum propagation speed in this orientation. The mechanical imperfection plays an important role in the dispersion relations, further the normal imperfection can produce a significant reduction of phase velocity comparing with the tangential imperfection. Comparing with the mechanical imperfection the electrical imperfection makes a relatively small reduction of phase velocity of Rayleigh-type wave. The obtained results can provide some fundamentals for understanding of piezoelectric semiconductor and for design and application of piezoelectric surface acoustic wave devices.