多匹配层空气耦合压电超声换能器*

该文针对超声无损检测与成像功能空气耦合换能器开展了分析计算和研制。为解决压电材料与空气间巨大的阻抗失配问题,进行了多匹配层设计,并基于有限元技术仿真设计了1-3压电复合材料参数。借助复数压电方程,导出考虑损耗的多匹配层压电复合材料换能器厚度振动等效电路,获得其等效导纳,以此计算电导谱,同时基于有限元技术数值计算相应电导谱,二者有较好的一致性。在此基础上分别设计制作复合压电材料,多匹配层材料以及由此构成的空气耦合超声换能器。换能器的实测电导谱与数值仿真结果一致。进一步的换能器回波信号测试及其谱分析结果表明,所研制的160 k Hz中心频率空气耦合换能器样品有较好灵敏度和带宽。这些结果说明,该文研制的空气耦合超声换能器的初样是成功的。     

水下应用的电容式微机械超声换能器阵列设计

为提高用于水下成像的电容式微机械超声换能器的指向性,文中用ANSYS力电耦合分析法设计了工作频率为400 k Hz的收发一体传感器的结构参数并完成了实验验证。同时研究了阵列设计方法,分析了电容式微机械超声换能器阵列各参数对指向性的影响,完成了从微小敏感单元到阵列的设计,实现了阵列指向性的优化设计。该阵列为16阵元的线阵,阵元间距为1.925 mm,阵元宽度为1.82 mm。进行了水下指向性测试,实验表明该线阵的-3 dB主瓣宽度为5?,最大旁瓣级为-13.5 dB,对称性好。该设计是实现较远距离的探测,提高成像分辨率的前提。     

面向水下应用的电容式微机械超声换能器*

电容式微机械超声换能器具有宽频带和易于制造二维阵列等优势,已经成为一种重要的新型超声换能器。该文针对图像声呐系统对新型超声换能器的迫切需求,提出了一种电容式微机械超声换能器结构和参数,并利用硅微加工技术制备出了该换能器,最后对其主要性能参数进行了测试和分析。测试结果表明该换能器具有发射和接收超声波的功能,中心工作频率为1.965 MHz,6 dB相对带宽达到109.4%,在1 MHz、2 MHz和3 MHz频率时的接收灵敏度分别为-218.29 d B、-219.39 dB和-218.11 dB。该文研制的电容式微机械超声换能器显示出了优秀的宽频带特性,且工作频率和接收灵敏度性能均基本满足了高频图像声呐系统的需求。     

175kHz高频空气超声换能器研制及其特性测量

本文报道了一种用于复杂空气旋涡场参量测量的高频空气超声换能器．在用超声-激光方法研究流场时，它是关键的换能元件。该换能器工作频率为175kHz。由于采用了管状压电元件及特制的伞状反射器，该换能器具有优越的指向性（士2．5°）     

空气耦合超声检测复合材料研究综述*

复合材料普遍具有高比强度、高比刚度、高模量、耐腐蚀等优异性能,广泛应用于飞机机翼、导弹外壳、航空发动机壳体等部位。制造和服役过程中各类缺陷影响复合材料的力学性能和服役性能,必须采用有效的方法准确检测和评估复合材料中各类缺陷。空气耦合式超声检测具有完全非接触、非侵入、无损伤和无需耦合剂的特点,能够很好地运用于复合材料的在线和在位检测。该文就近年来空气耦合超声检测技术的研究现状进行了系统综述,简明扼要地分析和介绍了当前空气耦合超声检测的研究热点及进展,重点介绍了1-3型压电复合材料换能器、信号处理技术、相控聚焦式空气耦合超声检测、超声在复合材料的传播特性及其与缺陷交互作用的研究现状,探讨了空气耦合超声无损检测技术与仪器的发展方向,总结了目前空气耦合超声检测的研究热点问题,最后展望了空气耦合超声检测的发展趋势和应用前景。     

多基元聚焦空气耦合超声换能器*

文中针对空气耦合超声换能器及其在表面缺陷检测中的应用开展了研究。选用1-3型压电复合材料及双匹配层结构来实现超声换能器压电材料与空气之间声阻抗的逐渐过渡,提高压电材料/空气界面的声能量透射率进而提高空气耦合超声换能器的灵敏度。在此基础上研发制作了440 kHz多基元聚焦空气耦合超声换能器,并对其性能进行了测试。其焦距、焦宽及焦深分别为41.44 mm、1.14 mm和20.30 mm,灵敏度和带宽分别为-50 d B和20.2%。测试结果表明该空气耦合超声换能器具有优良的性能,利用该超声换能器可以有效检测材料表面缺陷。     

超声技术的基石——超声换能器的原理及设计

超声换能器是在超声频率范围内将交变的电信号转换成声信号或者将外界声场中的声信号转换为电信号的能量转换器件,它是超声技术中的关键器件,其性能好坏直接关系到超声应用技术的效果和使用范围.由于超声技术的应用范围很广,且超声新技术层出不穷,因而与此对应的超声换能器的种类也很多.文章对不同应用背景下多种类型超声换能器的原理及设计进行了阐述,分析了不同类型超声换能器的性能参数及设计要求,简要总结了超声换能器的性能参数测试方法,并对超声换能器的发展趋势进行了一定的分析.     

超声技术的基石——超声换能器的原理及设计

超声换能器是在超声频率范围内将交变的电信号转换成声信号或者将外界声场中的声信号转换为电信号的能量转换器件,它是超声技术中的关键器件,其性能好坏直接关系到超声应用技术的效果和使用范围.由于超声技术的应用范围很广,且超声新技术层出不穷,因而与此对应的超声换能器的种类也很多.文章对不同应用背景下多种类型超声换能器的原理及设计进行了阐述,分析了不同类型超声换能器的性能参数及设计要求,简要总结了超声换能器的性能参数测试方法,并对超声换能器的发展趋势进行了一定的分析.     

电容式微超声波换能器的设计与电容值测试*

本文设计的微电容超声波换能器(CMUT)是由电容阵列组成的超声波传感器,主要是利用电容的改变来实现能量的转换。是基于硅硅键合技术的MEMS电容式超声传感器,制作的传感器误差小,并且工艺流程简单且能进行量产。在利用E4990A阻抗分析仪对传感器进行C—V测试分析而得出其电容的实际值与理论值的误差仅为1.6%。并且利用该仪器测试传感器电容在工作电压下随频率的变化,得出其在工作电压下,频率为400K的时候电容值为617.67PF,为对传感器进行理论计算提供了重要支撑,并且为后续转换电路的设计提供了数据支撑。     

Medical imaging using capacitive micromachined ultrasonic transducer arrays

We are investigating the use of capacitive micromachined ultrasonic transducers (cMUT's) for use in medical imaging. We propose an ultrasound probe architecture designed to provide volumetric ultrasound imaging from within an endoscope channel. A complete automated experimental system has been implemented for testing the imaging performance of cMUT arrays. This PC-based system includes custom-designed circuit boards, a software interface, and resolution test phantoms. We have already fabricated 1D and 2D cMUT arrays, and tested the pulse-echo imaging characteristics of 1D arrays. Beamforming and image formation algorithms that aim to reduce the complexity of data acquisition hardware are tested via numerical simulations and using real data acquired from our system.     

面向电容式微机械超声换能器器件的32通道收发 电路设计与测试*

针对以电容式微机械超声换能器(CMUT)阵列为探头的超声成像系统,设计了一种兼具现场可编程门阵列(FPGA)控制、脉冲驱动以及微弱电流信号检测功能的电路。利用FPGA产生64路控制信号,控制脉冲信号的频率、脉冲个数、占空比等参数;脉冲电路在FPGA以及直流电压的控制下,产生32路脉冲信号;接收电路通过跨阻放大结构实现32路电流信号检测;32通道收发电路利用脉冲产生芯片内自带的T/R开关进行高压隔离。通过搭建测试平台,对收发电路功能及一致性进行测试,并连接CMUT进行自发自收测试。测试结果表明,32通道收发电路具有良好的一致性,电路可以实现基于CMUT阵列的32通道超声信号的发射,检测回波信号,并对CMUT器件的带宽进行测试。电路具有功能完善,结构稳定的优点,为基于CMUT阵列的超声成像系统的应用提供了硬件支持。     

Imaging using air-coupled polymer-membrane capacitive ultrasonic arrays

Polymer-membrane capacitive ultrasonic linear and 2-D arrays have been fabricated for use in air-coupled imaging. By using arrays as receivers, there is a possibility of much faster imaging as the need for physically moving the receiver to scan a sample can be replaced by electronic multiplexing. In order to utilise this, a through-thickness air-coupled image of a composite plate has been made using a 2-D array as a receiver and a comparatively large planar source in air. This was made possible by the use of a chirp drive signal and cross-correlation on the measured waveform. Larger 2-D arrays with an increased number of elements have been simulated using a small scanned single receiver, and excellent imaging potential demonstrated. In addition two array receivers have been used in conjunction with two methods of post-processing, SAFT and ellipse crossing, to locate objects accurately.     

Electromechanical coupling factor of capacitive micromachined ultrasonic transducers

Recently, a linear, analytical distributed model for capacitive micromachined ultrasonic transducers (CMUTs) was presented, and an electromechanical equivalent circuit based on the theory reported was used to describe the behavior of the transducer [IEEE Trans. Ultrason. Ferroelectr. Freq. Control 49, 159-168 (2002)]. The distributed model is applied here to calculate the dynamic coupling factor k(w) of a lossless CMUT, based on a definition that involves the energies stored in a dynamic vibration cycle, and the results are compared with those obtained with a lumped model. A strong discrepancy is found between the two models as the bias voltage increases. The lumped model predicts an increasing dynamic k factor up to unity, whereas the distributed model predicts a more realistic saturation of this parameter to values substantially lower. It is demonstrated that the maximum value of k(w), corresponding to an operating point close to the diaphragm collapse, is 0.4 for a CMUT single cell with a circular membrane diaphragm and no parasitic capacitance (0.36 for a cell with a circular plate diaphragm). This means that the dynamic coupling factor of a CMUT is comparable to that of a piezoceramic plate oscillating in the thickness mode. Parasitic capacitance decreases the value of k(w), because it does not contribute to the energy conversion. The effective coupling factor k(eff) is also investigated, showing that this parameter coincides with k(w) within the lumped model approximation, but a quite different result is obtained if a computation is made with the more accurate distributed model. As a consequence, k(eff), which can be measured from the transducer electrical impedance, does not give a reliable value of the actual dynamic coupling factor.     

电容MEMS超声换能器研究进展

MEMS(micro-electromechanical systems)超声换能器(MEMS ultrasonic transducer,简称MUT)是采用微电子和微机械加工技术制作的新型超声换能器。与传统超声换能器相比,MUT具有体积小、重量轻、成本低、功耗低、可靠性高、频率控制灵活、频带宽、灵敏度高以及易于与电路集成和实现智能化等特点。是超声换能器的重要的研究方向之一。MUT的研究主要包括压电MUT(piezoelectric MUT,简称PMUT)和电容MUT(capacitiveMUT,简称CMUT)两个方面。本文概述了CMUT研究的发展进程和研究成果,展望了CMUT的研究和应用前景。     

应用于微电容超声换能器的信号处理电路设计*

针对微电容超声换能器的输出信号特征及检测要求,文中设计了换能器的微弱信号处理电路,包括基于跨阻的微弱电流信号检测和多重反馈带通滤波电路。通过搭建水下测试平台,对电路性能及功能进行实际测试,并进行水下测距实验。实验结果表明,该电路可对微电容超声换能器输出的400 k Hz信号进行检测放大与滤波;电路的线性度为0.18%,滤波电路中心频率为396 k Hz,带宽为55 k Hz。该电路可用于CMUT的接收信号处理并应用于超声测距及成像的前端信号处理。     

Study on the high power air-coupled ultrasonic compound transducer

The high power air-coupled compound ultrasonic transducer in flexural vibration is studied. The transducer consists of a sandwich longitudinal piezoelectric transducer and a circular thin plate in flexural vibration. The resonance frequency equation and the equivalent circuit of a circular radiator with clamped boundary condition are derived. The resonance frequency equation and the equivalent circuit of the compound transducer are also obtained. The radiated acoustic field of the circular thin plate radiator is analyzed and the directional pattern is calculated. It can be seen that when the vibrational order of the circular thin plate in flexural vibration is increased, the radiated acoustic field becomes complex.     

The characterization of capacitive micromachined ultrasonic transducers in air

Surface micromachined, capacitive ultrasonic transducers have been fabricated using a low thermal budget, CMOS-compatible process. They exhibit interesting properties for transduction in air at frequencies in excess of 1 MHz, when driven from a standard ultrasonic voltage source. Experiments are described using 1 mm square devices in air, operating in both pitch-catch and pulse-echo modes. The dependence on d.c. bias voltage is examined, together with calibration measurements using 1/8 in. microphones. The radiated beam profile, and the farfield directivity pattern, have been measured for both broad bandwidth and one-burst excitation, using a scanned miniature receiver. A 16 element square array is also presented, which has been used to measure the beam cross-sections from a focussed source.