互易法校准压电型声发射传感器的研究与实现

声发射传感器的校准是实现声发射定量技术的前提,依据电声换能器互易原理,在计算互易常数的基础 上,建立了适用于压电型声发射传感器表面波和纵波互易的校准系统。通过设置特定的激励信号波形,依据接收 电压信号与激励电流信号之间的时间延迟,准确获取电流信号与电压信号对应的特征值,实现了声发射传感器的表面波和纵波互易校准。由于传感器的尺寸效应,传感器在高频时的表面波速度灵敏度低于纵波灵敏度,不确定度评定结果表明,声发射传感器速度灵敏度的互易法校准不确定度为1. 2 dB。     

平面波耦合腔中热传导和声泄漏对低频互易校准的影响

针对低频耦合腔互易校准中存在的热传导和声泄漏问题,通过理论计算和不同长度耦合腔的系列实验研究,探讨其对互易校准结果的影响规律。首先阐述了互易校准原理及电容传声器低频时的频响特征,传声器均压孔在声场外时,低频声压灵敏度随着频率降低而逐渐增加;其次,对发射传声器-耦合腔-接收传声器构成的耦合腔系统中的热传导修正因子进行计算,结果表明,随着耦合腔长度变长,热传导修正因子变小,不确定度分量变小;通过不同长度的耦合腔组成的互易校准系统研究声泄漏的影响并探讨其优化方案,实验结果表明,10 mm和15 mm耦合腔对互易校准结果影响较小,重复性高,该实验结果与传声器的低频响应特性一致。     

宽带噪声相关法校准低频发射换能器

本文介绍了一种校准低频发射换能器的噪声相关法,并将该法校准结果与纯音脉冲声法的校准结果作了比较和分析。     

非刚性管中换能器灵敏度的测量方法研究

为实现非刚性管中的换能器低频灵敏度校准,提出了基于互易常数修正的管中灵敏度校准方法。首先,基于管中非刚性边界条件和声压的方程进行了互易常数的推导及修正,并围绕管中互易常数的修正开展了仿真分析,得到测量频率段互易常数的修正值;其次,搭建实验系统开展了基于互易法的管中换能器的灵敏度测量研究。研究表明,管中互易常数的修正使互易换能器灵敏度值更加接近自由场互易法测得的灵敏度值。在0.5~4kHz 频率范围,补偿后的互易换能器灵敏度级最大起伏为-1.41dB,极大改善了未修正的测量情况,与自由场测量值的误差较小,符合声学计量要求。通过对实验与仿真进行对比分析,验证了该方法的有效性和准确性。     

基于自易校准技术的柱面会聚波超声功率测量研究

基于自易校准技术研究了柱面会聚波超声功率的测量方法。首先从定义柱面会聚波的互易常数、自由场发送电流响应及电压灵敏度等电声特性参数开始,重点讨论了反射系数及衍射修正系数的计算方法,推导了凹圆柱面聚焦换能器声功率自易测量计算的表达式。然后,将实测结果与辐射力法的测量结果比较取得很好的一致性。通过实验证明了自易校准法应用于柱面会聚波超声功率测量的合理性和可行性。     

实验室标准传声器前腔体积的测量方法研究

实验室标准传声器的前腔体积(包括等效体积)是耦合腔互易校准声压灵敏度的主要不确定度分量.为了控制前腔体积与等效体积引入的不确定度分量,应用声学方法测量实验室标准传声器的前腔体积,分别利用有源耦合腔结合系列哑头空腔的方法和多个平面波耦合腔的方法对LS1P和LS2P传声器的前腔体积与等效体积之和进行测量.实验结果表明,有源耦合腔法和多个平面波耦合腔法均能有效测量实验室标准传声器的前腔体积,且测量结果具有较好的一致性.前腔体积的精确测量实现了实验室标准传声器声压灵敏度的高精度校准.     

电容传声器声中心的测量及其对互易校准的影响

为研究LS1、LS2及WS3等典型电容传声器声中心位置的准确值,基于自由场传声器声中心位置的测量理论,利用声学分析仪、消声箱和适调放大器等组成的声中心位置测量系统分别测量LS1、LS2及WS3型电容传声器的声中心位置。将测试结果与已公布的相应类型传声器声中心位置数据进行比较,得出声中心位置对自由场互易校准结果影响不可忽视,且在进行传声器自由场互易校准前,需要对参与互易校准的每只传声器的声中心位置进行测量确定。     

脉冲法测量空气声隔声的多通道置换校正

首先介绍利用脉冲法测量构件空气声隔声量的原理。利用多通道测量系统根据脉冲法进行空气声隔声量测量时需保证各通道响应的一致性。本文提出一种通过置换声源室和接收室的测量通道,以校正通道间的响应差异,得到可靠的测量结果的方法。通过验证实验表明了该方法的有效性。该方法降低了对测量设备的要求,对利用脉冲法测量空气声隔声技术的推广和应用具有重要参考价值。     

电容式传声器自由场互易校准数据处理系统设计

基于LabVIEW和Matlab软件开发平台设计了传声器自由场互易校准数据处理系统,该系统可以有效提取电转移阻抗信号,计算声中心和灵敏度级,并通过软件测试证明了系统的可行性.     

声发射传感器表面波灵敏度的比较法校准

声发射传感器的校准是声发射技术的重要课题,基于表面波的比较法校准是声发射传感器校准中的常用方法,其原理简单,校准效率高,适用于声发射传感器的日常校准。本文针对比较法校准,优化了校准中使用的声发射源和声场,构建了完整的声发射传感器比较法校准系统,编写了相应的校准程序,实现了传感器表面波灵敏度的校准,并具有较好的重复性和稳定性。     

Calibration of a focusing transducer and miniature hydrophone as well as acoustic power measurement based on free-field reciprocity in a spherically focused wave field

The free-field transmitting voltage response at the pressure focus of a spherically focusing transducer was defined and calibrated based on the reciprocity theorem of a free-field spherically focused acoustic wave. The acoustic power, the radiation conductance, and the pressure at the pressure focus were derived and measured accordingly from the transmitting current response on the imaginary mirror symmetric spherical surface of the radiating surface. A miniature hydrophone was calibrated by the self-reciprocity of the spherically focusing source. Comparison results show that the measured acoustic power deviation between the reciprocity method and the radiation force balance method are within +/- 5% for two air-backed focusing transducers at 1.53 MHz and 5.27 MHz, respectively, and the maximum deviation of a hydrophone calibration between the new method and the free-field plane wave reciprocity method is within 1.4 dB in the frequency range from 1 MHz to 2 MHz in experiments.     

Critical examination of ultrasonic transducer characteristics and calibration methods

This study systematically determined the transmission and receiving sensitivities of over twenty transducers. Four types of sensitivities were evaluated for both transmission and receiving sensitivities. These are found to be different from each other and the reversibility or reciprocity conditions exist only in exceptional cases. Using their observed behavior as the basis, we critically examined the calibration methods developed to characterize them, including those based on laser interferometry and the acoustic reciprocity principle. Serious flaws in some of the reciprocity methods are uncovered, which can be rectified by using the Hill--Adams method. Four procedures emerged as workable calibration methods for contact ultrasonic and acoustic emission transducers. However, current experimental uncertainties limit the upper frequency to 2 MHz.     

Particle sizing by quantitative acoustic emission

Two methods of particle sizing using an acoustic method are presented. The technique relies on the detection and measurement of elastic waves arising from impact of the particles with a small target plate. The acoustic impact signal, as measured from a high fidelity piezoelectric transducer, is characterised by the first wave arrival (compression wave) amplitude and risetime. A theoretical approach, based upon Hertzian impact theory and elastic wave propagation theory, is developed and used to determine the relationship between the impact dynamics of the particle and the acoustic signal. The first method of particle sizing relies upon amplitude measurements alone but requires accurate system calibration and full knowledge of the particle impact velocity, incident angle and coefficient of restitution. The velocity measurements were determined using a laser Doppler technique. The second approach for particle sizing incorporates risetime measurement and only depends very weakly upon the compression wave amplitude, thus minimizing the need for accurate absolute calibration. Knowledge of the impact velocity, incident angle, and coefficient of restitution were not required.Spherical particles of glass in the size range 35 to 140 µm diameter were dropped onto an aluminium target plate at an incident velocity of 8.1 m/s and angle to the surface normal of 0°, 40°, and 61°. The two acoustic methods were used to size the particles, and the results were compared to the particle size distributions obtained from video microscope measurements. The first sizing method undersized the smaller particles by 20% to 30% and oversized the larger ones by 5% to 10%. However, the second approach gave much smaller errors and consistently undersized all sizes of particle by just a few percent. This undersizing was understood in terms of some plasticity in the target that occurred during particle impact.     

Reciprocity calibration of impulse responses of acoustic emission transducers

By means of reciprocity calibration in Rayleigh-wave and longitudinal-wave sound fields, frequency characteristics of amplitude and phase of absolute sensitivity of acoustic emission transducers were measured on the basis of the newly derived complex reciprocity parameters, and the impulse responses were obtained through inverse Fourier transform. Calibration results were confirmed with supplemental experiments in which the fracturing of a pencil lead was utilized for the source of elastic waves. Impulse responses of acoustic emission transducers to both the Rayleigh-wave and longitudinal-wave displacement velocities were determined by means of purely electrical measurements without the use of mechanical sound sources or reference transducers.     

Minimizing the Effects of Reflections by Using a Virtual Pulse Method, for Free-Field Reciprocity Calibration

The National Metrology Institute of Japan has developed a free-field reciprocity calibration system for type WS3 microphones as acoustic standards in the airborne ultrasonic range between 20 and 100 kHz, because numerous instruments radiate airborne ultrasound. Precise calibration of these microphones requires minimizing the influence of sound reflected from the objects such as absorbing wedges and supporting rods within the acoustic chamber. To minimize this influence, we applied the virtual pulse method, which is a signal processing technique used in the audible frequency to airborne ultrasonic range. Experimental and analytical results validated this method. Use of this method in the calibration of type WS3 microphones will decrease the calibration uncertainty in the free-field sensitivity level.     

动态力校准中力传感器端部等效质量测量方法研究

力传感器端部等效质量是动态力校准中的重要部分,其测量误差会对动态力校准产生较大影响。本文通过了解力传感器结构,确定力传感器端部等效质量的构成,并简单介绍了四种测量端部等效质量的方法。最后,利用两次配重消去法进行实验,将不同配合不同工况下得到的结果进行对比分析,说明该方法可以较好的解决测量端部等效质量问题。     

Transformation of domain integrals to boundary integrals in BEM analysis of shear deformable plate bending problems

In this paper two techniques, dual reciprocity method (DRM) and direct integral method (DIM), are developed to transform domain integrals to boundary integrals for shear deformable plate bending formulation. The force term is approximated by a set of radial basis functions. To transform domain integrals to boundary integrals using the dual reciprocity method, particular solutions are employed for three radial basis functions. Direct integral method is also introduced in this paper to evaluate domain integrals. Three examples are presented to demonstrate the accuracy of the two methods. The numerical results obtained by using different particular solutions are compared with exact solutions. Received 27 January 1999     

Radial integration boundary element method for acoustic eigenvalue problems

In this paper, the radial integration boundary element method is developed to solve acoustic eigenvalue problems for the sake of eliminating the frequency dependency of the coefficient matrices in traditional boundary element method. The radial integration method is presented to transform domain integrals to boundary integrals. In this case, the unknown acoustic variable contained in domain integrals is approximated with the use of compactly supported radial basis functions and the combination of radial basis functions and global functions. As a domain integrals transformation method, the radial integration method is based on pure mathematical treatments and eliminates the dependence on particular solutions of the dual reciprocity method and the particular integral method. Eventually, the acoustic eigenvalue analysis procedure based on the radial integration method resorts to a generalized eigenvalue problem rather than an enhanced determinant search method or a standard eigenvalue analysis with matrices of large size, just like the multiple reciprocity method. Several numerical examples are presented to demonstrate the validity and accuracy of the proposed approach.     

Effect of a ferroelectric inversion layer on the temperature characteristics of SH-Type surface acoustic waves on 36 degrees Y-X LiTaO (3) substrates

The temperature coefficient of delay of the SH-type surface acoustic wave on 36 degrees Y-X LiTaO(3) substrates with a ferroelectric inversion layer is theoretically analyzed and it is shown that the temperature characteristics can be improved by an electric-field short-circuiting effect of the domain boundary. The experimental results of the temperature coefficient of delay agree well with the theoretical. The minimum value of measured temperature coefficients of delay is 12.6 ppm/ degrees C for the metallized surface case, which is about one-third of that in a 36 degrees Y-X substrate with no inversion layer. Experimental results on the phase velocity and the electromechanical coupling factor of the SH-type surface acoustic wave are also presented and compared with the theoretical.