Microstrip Excitation of Magnetostatic Surface Waves: Theory and Experiment

A model is developed for excitation of magnetostatic surface waves (MSSW) with microstrip transmission lines. Energy carried away in MSSW propagating perpendicular to the microstrip is related to electromagnetic (EM) energy propagating along the microstrip line by an equivalent radiation resistance. Supporting experimental results are in excellent agreement with predictions derived from this model.     

Analysis of Interdigital Surface Wave Transducers by Use of an Equivalent Circuit Model

Immittance, transfer, and scattering characteristics are studied for acoustic surface wave transducers of the interdigital electrode form. Linear network models are used to represent the transducer as a chain of identical three-ports which are acoustically in cascade but electrically in parallel. Transducer operation at acoustic synchronism is described theoretically and compared to current experimental data for transducers operating at 100 MHz and fabricated on lithium niobate. Favorable lithium niobate configurations for efficient, broad-band transducer operation are given. Scattering characteristics as a function of electric load are discussed. Low values of acoustic reflection loss are predicted theoretically and observed experimentally when the electric load and transducer capacitance are in resonance. The frequency dependence of transducer radiation immittance is studied, and the response is found to be analogous to the response of an endfire antenna array.     

基于角谱法分析圆形活塞声源近场声特性

圆形活塞的声辐射应用较广,大多数超声检测应用中所用的声源,都可视为活塞式辐射器。利用角谱法分析了传播波和倏逝波在声场轴线上的分布与空间位置、声源半径及辐射频率间的关系,通过比较两种波的声压幅值确定了倏逝波的有效传播距离。利用近场声全息(NAH)理论计算了倏逝波在换能器近场空间的声压分布,并对结果进行误差分析。仿真结果表明,基于空间傅里叶变换的角谱法和NAH法均可准确反映圆形活塞辐射近场声压呈现数衰减的分布规律。     

高频压电复合材料球形换能器仿真设计

该文仿真设计了一种高频压电复合材料球形换能器,利用COMSOL软件建立了有限元模型,计算了换能器的声辐射特性,分析了不同压电陶瓷材料、不同基元尺寸对换能器声辐射特性的影响。仿真分析结果表明,球形高频换能器具有高频、宽带及可全向辐射声波等特性,能广泛应用于水声探测与成像发射换能器及其阵列。     

Magnetically tunable wideband magnetostatic-surface-wave filter using Ga-YIG film

The characteristics of a magnetically tunable wideband filter utilising the property of a pass bandwidth of magnetostatic surface waves (MSSW) are given. The pass bandwidths of MSSW obtained experimentally through the Ga-YIG slab having the saturation magnetisation, 1100 Gs and the ordinary transducers consisting of wire antenna vary from 230 to 55 MHz for the operation frequency, 1 to 8 GHz, corresponding to the external static magnetic field. These results could fully be explained by the theory. Loaded Q values of this filter vary from 20 to 270 at the same frequency range as above.     

Liquid velocity measurement using interdigital transducers

A system for measuring the velocity of a flowing liquid is presented using three interdigital transducers, one of which is used for the radiation of the compressional wave into the liquid. The velocity is estimated from the measurement of the output voltage corresponding to the phase difference between two output signals detected at the output transducers, mounted on the same surface opposite to the surface with the input transducer.     

Experimental Distinction Between Crossed-Field and In-Line Three-Port Circuit Models for Interdigital Transducers (Short Papers)

The crossed-field and in-line Mason circuit models for interdigital surface-wave transducers give opposite predictions for the dependence of acoustic reflection coefficients on electric load resistance for purely resistive loads. Experiments described herein show that the crossed-field model correctly describes the reflections for YX quartz, ST-X quartz, and YZ lithium niobate substrates. A low-resistance load minimizes reflections for transducers with double electrodes operating at the fundamental synchronous frequency. For single electrode transducers, optimum reflection suppression may call for a load resistance comparable to the transducer impedance.     

基于格林函数声表面波换能器的分析

以准静态近似为前提,采用格林函数法对声表面波换能器进行分析。推导了声表面波换能器激励电压与表面电荷之间的关系,计算了加载单位激励电压时换能器上的静态电荷分布并与有限元法计算结果进行比较。格林函数法的换能器的分析可用来为声表面波器件设计优化进行参数计算,及为其建模提供精确的数据。     

Generation of Bleustein?Gulyaev and bulk-shear waves by interdigital transducers on a piezoelectric ceramic

Theoretical predictions are made of the piezoelectric generation of Bleustein?Gulyaev and bulk-shear waves by interdigital transducers on p.z.t.-4 ceramic. Variation with frequency and number of periods of each transducer is studied for both metallised and free-external-surface regions. Bulk-wave radiation patterns for the two sets of electrical boundary conditions are also studied.     

宽带声光器件声场仿真研究

该文根据亥姆霍兹 基尔霍夫积分定理，建立了两片矩形换能器在声光晶体中的声场分布模型，并利用MATLAB数值模拟中心频率为100 MHz的矩形换能器在氧化碲晶体中的声场分布，实现声场可视化。结果表明，与单片换能器声场分布相比，两片换能器的结构使声光器件的布喇格带宽增大了11 MHz。仿真结果为理解声场变化和试验结果提供了理论依据。     

ADCP压电换能器及其校准方法研究进展

声学多普勒流速剖面仪(ADCP)在海洋学中应用广泛,是目前最主要的流速流量测量设备,其关键部件是压电换能器,用以发射和接收声学信号。该文结合ADCP仪器自身的发展,梳理了ADCP压电换能器及其阵列的研究进展,并对压电换能器及ADCP的校准方法进行简要概述。     

基于空间冲激响应的圆形换能器辐射声场研究

基于空间冲激响应的稳态声压场理论,从选取距离函数出发,建立了单阵元圆形平面换能器声场中任一场点处的基于傅里叶变换的冲激响应声场模型,该模型适用于声场中的任意位置。并运用Matlab仿真了换能器的轴向与径向声压分布,且在圆形换能器冲激响应的声压分布实验系统上进行验证,实验结果与仿真得到的声压场具有很好的一致性。实验验证表明,仿真结果可准确反映圆形换能器的空间辐射声场分布。该方法计算快捷,对于优化圆形换能器设计参数及提高超声成像检测分辨率有重要参考意义。     

考虑介损的压电陶瓷开路输出电压研究

该文以PZT-5H为代表的d_(33)模式压电换能器为研究对象,推导实际开路输出电压与荷载频率的关系,并分析考虑了介质损耗影响的必要性。通过设计验证性试验,并采用有限元模拟法,分别在不同换能器结构(单片和多片堆栈)、不同荷载幅值、不同加载频率条件下验证预测值与试验值的吻合程度。结果表明,压电陶瓷实际开路输出电压在低频荷载条件下随荷载频率的增大呈非线性增长,而在高频荷载条件下随荷载频率增长缓慢,理论公式预测值与试验值吻合良好。该文推导的压电陶瓷开路输出电压公式可用于实际压电陶瓷开路输出电压的预测分析。     

宽带组合式水声换能器设计研制及应用

通用宽带换能器（含低频到高频）一般是将不同类型的换能器进行组合使用,单个换能器独立设计再组合成阵,其综合体积及质量均大,且安装后其性能指标受影响(如换能器开角变小等)。该文在分析当前国内外宽带换能器研究现状基础上,结合小型遥控无人潜水器（ROV）搭载探测需求,提出具体设计指标要求。将复合棒换能器与数个压电陶瓷圆环进行开放式一体化组合设计,在满足小型ROV安装要求的基础上,实现了发射3～100 kHz、接收1～100 kHz的超宽频带覆盖范围,且开角不小于70°。水池及湖上实航实验结果表明,研制的换能器与仿真设计相符,实航测量结果与国内外相关结论一致性较好,具有广泛的工程实用价值。     

提高压电换能器导纳圆测量精度的方法研究

不同压电换能器的动态电阻、电容、电感和静态电阻、电容的值不同,这些参数均可从其对应的导纳圆中得到.分析了导纳圆测量中的两个重要影响因素:A/D转换器的量化误差、测量电阻.为提高导纳圆的测量精度,量化误差不变时不同的压电换能器需选择不同的测量电阻以保证所测量的两路正弦信号有适当的幅值比和相位差.测量电阻的值为压电换能器动态电阻值的0.15～3.5倍时,导纳圆半径的相对误差小于0.5％,测量电阻为动态电阻的0.7倍时导纳圆的相对误差最小.     

锥形结构超声阵列换能器研究

传统外形构造的换能器难以适应水下高速运动。因此,在头部为圆形或椭圆形的普通阵列式换能器基础上,该文设计了一种锥形结构的超声阵列式换能器,其可适用于水下高速航行器。通过有限元仿真确定了阵元尺寸与阵列构造,分析了换能器整体的声场分布,研制换能器样机并测试其电声性能。样机测试结果与仿真结果呈现出较好的一致性,换能器指向性与发射电压响应满足使用需求。结果表明,此种换能器结构具有实际的可行性。     

一种频率可调超声波发生器设计

不同清洗物所需的清洗频段不同,需要接入的超声波换能器也不同。为了提高超声波发生器对不同频段换能器的适应性,设计了一种由上位机进行频率给定、锁相环电路进行频率跟踪的闭环控制系统。整个系统由STM32主控制器产生脉冲宽度调制(PWM)脉冲信号,控制EXB841优化驱动电路,驱动高频全桥逆变电路;通过阻抗匹配和输出电流的检测,保证作用于换能器输出的功率值最大。同时对于不同频段的超声波换能器,需要调整给定输入,保持发生器在频率基准值的一定范围内进行频率跟踪。超声波换能器测试样机工作频率点为28.8 kHz,最大功率1 500 W,将本系统接入后谐振频率保持在28.8 kHz左右,输出功率近似为最大值。经测试,该系统对于工作频率点为20~40 kHz的超声波换能器都具有较好的适应性。     

B-scan based acoustic source reconstruction for magnetoacoustic tomography with magnetic induction (MAT-MI)

We present in this study, an acoustic source reconstruction method using focused transducer with B-mode imaging for magnetoacoustic tomography with magnetic induction (MAT-MI). MAT-MI is an imaging modality proposed for noninvasive conductivity imaging with high spatial resolution. In MAT-MI, acoustic sources are generated in a conductive object by placing it in a static and a time-varying magnetic field. The acoustic waves from these sources propagate in all directions and are collected with transducers placed around the object. The collected signal is then used to reconstruct the acoustic source distribution and to further estimate the electrical conductivity distribution of the object. A flat piston transducer acting as a point receiver has been used in earlier MAT-MI systems to collect acoustic signals. In this study, we propose to use B-mode scan scheme with a focused transducer that gives a signal gain in its focus region and improves the MAT-MI signal quality. A simulation protocol that can take into account different transducer designs and scan schemes for MAT-MI imaging is developed and used in our evaluation of different MAT-MI system designs. It is shown in our computer simulations that as compared to the earlier approach, the MAT-MI system using B-scan with a focused transducer allows MAT-MI imaging at a closer distance and has improved system sensitivity. In addition, the B-scan imaging technique allows reconstruction of the MAT-MI acoustic sources with a discrete number of scanning locations, which greatly increases the applicability of the MAT-MI approach, especially when a continuous acoustic window is not available in real clinical applications. We have also conducted phantom experiments to evaluate the proposed method, and the reconstructed image shows a good agreement with the target phantom.     

基于1-3压电复合材料宽带超声换能器研究

电声转换效率与换能器带宽是评价聚焦超声换能器性能的重要指标。传统压电陶瓷制备的聚焦超声换能器,其电声转换效率与换能器带宽偏低。该文采用实验结合仿真模拟的方式,通过研究1-3压电复合材料中压电相的体积比、环氧相改性、调控匹配层阻抗与匹配层厚度对换能器性能的影响,开发了一种基于1-3压电复合材料的聚焦超声换能器,实现了82.3%的电声转换效率与140 kHz的换能器带宽。结果表明,与同等规格的传统压电陶瓷聚焦超声换能器相比,该超声换能器的两项指标分别提升了105%与250%,这为大功率聚焦超声换能器的设计开发提供了参考与指导。     

Frequency response of an interdigital transducer for excitation of surface elastic waves

Excitation of elastic waves in a piezoelectric solid by an interdigital transducer, in terms of a simplified model, has been analyzed using Lamb's integral solution. The transducer generates three types of disturbances propagating at the velocities of irrotational, equivoluminal, and Rayleigh waves. While the amplitudes of the former two waves diminish as the three-half power of the distance from the transducer, that of the latter does not decay with distance on the surface. Dependence of particle displacement of the waves on electric fields, number of electrodes, electrode width, and wave numbers has been derived. It has been shown that a conventional interdigital transducer, in which all the electrode widths and all the spacings are respectively equal among themselves, can respond to fundamental and odd harmonic excitations, but not to the even harmonics. Means to improve the insertion loss and the bandwidth of the transducer are discussed. A flat overall frequency response can be synthesized by parallel operation of two or more transducers, the fundamental frequencies of which are properly staggered.