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。     

基于ZnO压电薄膜的弯曲振动硅微压电超声换能器的研究

对所研制的硅微压电超声换能器(PMUT)的振动特性进行了研究分析。对硅微压电超声换能的振动膜薄板的厚度相对于薄板的尺度(边长)而言较薄的情况,理论分析与实验结果均表明残余应力对换能器的谐振频率影响较大:不考虑残余应力的理论分析得出的换能器谐振频率与器件的实验测量的结果相差较大,而考虑残余应力的分析给出的谐振频率结果与实验结果是符合的。本文还对所制作的硅微压电超声换能器的谐振频率及导纳进行测量,并给出其等效电路参数。其中振动膜边长为1mm的换能器的谐振频率为71.25 kHz。最后对其进行了简单接收发射实验,测得谐振频率处的接收灵敏度为-201.6 dB(ref 1 V/μPa),发射电压响应约为137 dB(ref 1μPa·m/V)。     

《超声换能器》一书出版

在材料的无损检测、医学诊断、地球物理勘探、电子通讯(如体波延迟线和脉压线)以及许多科学研究中,超声换能器是关键部件之一。为此,改善超声换能器的性能、研制新型的超声换能器是人们十分重视的课题。有关工程技术人员和科研人员迫切希望能找到一本既有超声换能器工作原理又能较全面地反映超声换能器当今水平的著作。值得高兴的是,东南大学无线电工程系袁易全同志在教学和科研工作之余,及时撰写了《超声换能器》一书,以满足我国广大读者的需要。     

直线微动马达箝位超声换能器(PGUT)研究

本文提出一种用于超声微动直线马达的环形三叠片压电箝位超声换能器(Position-Cripped Ultrasonic Transducer,简称:PGUT)。其原理是利用换能器的超声振动产生的表面效应,来实现直线微动马达的箝位或松位。本文给出了这种换能器的共振频率、有效机电耦合系数及实验结果。实验结果表明,PGUT 能迅速、平稳的执行箝位、松位动作,并且具有低工作电压驱动相似文献   

硅油介质中矩形电容式微机械超声换能器发射与接收声场特性研究*

与传统压电式超声换能器相比，基于微机电系统(Micro-electro-mechanical system, MEMS)微加工技术制备的电容式微机械超声换能器（CMUT）具有频带宽、灵敏度高、一致性好、易于集成等优势，在医学超声成像中具有广阔的应用前景。本文针对研制的矩形CMUT器件，开展硅油介质中CMUT发射、接收声场特性的理论分析及实验验证研究。首先，针对CMUT阵元结构特征和工作原理，根据指向性函数理论和Bridge乘积原理，建立了矩形CMUT阵元指向性函数分析模型；在此基础上，分析微元数目以及谐振频率对CMUT指向性的影响规律。最后，针对7mm×7mm二维矩形CMUT在硅油介质中的发射和接收特性进行了实验验证，测试表明发射指向性曲线与仿真理论曲线基本吻合；此外，CMUT接收与发射指向性的测试表明，收发指向性具有一致性，从而验证了声场的互易性。本文的研究对CMUT器件的封装设计以及基于CMUT阵列的乳腺超声CT成像系统的研制具有重要参考价值。     

碳纳米管-聚二甲基硅氧烷的光声特性

碳纳米管-聚二甲基硅氧烷(CNT-PDMS)是一种新型的激光超声换能器(LIU-T)复合材料,具有高频率、宽带宽、高振幅的特性。该复合薄膜可作为高效、鲁棒的超声发射器用于诊断和治疗。纳米复合材料的固有结构提供了独特的热、光学和机械性能,这不仅有利于能量转换,而且对脉冲激光烧蚀具有很好的鲁棒性。PDMS聚合物具有高热弹性系数有利于材料的伸缩从而产生超声。研究了几种不同复合薄膜产生的光声信号特性,测试了不同衬底和水介质条件下的光声信号特性。利用碳纳米材料的高吸光性和PDMS聚合物的高膨胀性制作激光超声换能器,不但降低了材料的厚度,还有望产生高频高强度超声信号。实验用硬玻璃衬底厚度约为1 mm,软薄膜衬底厚度在微米级,水介质条件下的厚度为3 mm。在脉冲激光激励下,水介质下软薄膜条件、硬玻璃衬底、软薄膜衬底涂层端面超声压力分别为2.0, 3.9和5.2 MPa。通过一系列的研究得出了结论:(1)软薄膜衬底(3×3)比硬玻璃衬底(3×3)更具有良好的负脉冲,更适合用在光声空化治疗方面;(2)水介质条件下不利于产生高强度光声信号。总而言之,采用激光超声换能器比压电换能器更具有产生高振福,带宽宽的超声信号的潜力,而且提供了一种没有电子等干扰结构的超声激励新方法,有望成为替代压电换能器的新一代激光超声换能器。这种新方法应用在磁声电成像领域可以大大减少超声激励源的干扰。同时,相对于将CNT混入PDMS中的方法,该方法更具有简单方便节省材料等优点。对于硬玻璃传统型衬底,实现的软薄膜衬底能产生较高的声压5.2 MPa,并且中心频率在5MHz,-6 dB超声带宽也相对较宽接近5MHz,相比于早在2014年实现的CNT-PDMS激光超声换能器产生的4.5 MPa声压,本文方法更具有临床应用前景,应用在磁声电成像等方面具有很好的避免电磁干扰效果。     

变厚度聚焦换能器对声焦域轴向长度影响的研究*

针对不同厚度的病变组织,改变声焦域轴向长度能提高高强度聚焦超声在临床治疗过程中的安全性和有效性。基于多频超声波叠加原理,该文提出了变厚度(多频)聚焦换能器,并设计了两种类型变厚度聚焦换能器。根据瑞利积分法推导了变厚度聚焦换能器声场,计算和分析了变厚度聚焦换能器的声焦域轴向长度,并与等厚度(单频)聚焦换能器声焦域轴向长度进行对比。结果显示,变厚度聚焦换能器中心到边缘的厚度变化趋势与声焦域轴向长度变化相关,中间薄两边厚换能器声焦域轴向长度缩短,中间厚两边薄换能器声焦域轴向长度变长,且实验验证了理论的正确性。研究结果可为变厚度聚焦换能器声场研究和高强度聚焦超声的临床治疗提供参考。     

《超声组件的计算机辅助设计》已在内部发行

由第七一五所教授级高级工程师俞宏沛撰写的《超声组件的计算机辅助设计》小册已于1991年10月在内部发行。 作者俞宏沛同志长期从事换能器的研究与设计工作,在功率超声方面具有丰富的实践经验。他很早就在换能器设计中采用了计算机辅助设计方法,并取得显著成效。该小册5万多字,是俞宏沛同志多年从事功率超声振动组件(换能器、变幅杆和工具头)计算机辅助设计的经验总结。小册中部分内容曾在功率超声     

cMUT阵元的声学分析与环形扫描成像*

电容式微机械超声换能器(cMUT)具有宽带宽、灵敏度高、机械阻抗低和与电子电路集成制造等优点。由于超声换能器声场设计的好坏决定了成像质量的优劣,为了明确阵元参数与辐射声场的关系,该文对不同的阵元参数进行了计算仿真。与压电陶瓷超声换能器的结构不同,cMUT阵元是由多个电容单元(cell)并联构成。因此分析了cell的半径、cell数量、间距、振动频率等阵元参数与辐射声场分布、远近场分界点、辐射声压、指向性的关系,并进行了声轴声压与指向性实验测试验证。理论与实验测试结果基本一致。通过仿真计算,选用一种已制备的指向性强、发射性能好的cMUT单阵元器件对鸡骨进行了环形扫描和成像,实现了对生物体组织横截面的超声CT成像,验证了所制备的cMUT器件的可用性。此研究对工业与医学成像领域具有重要的参考价值。     

向空气中辐射超声波的环形压电换能器

超声压电换能器向空气中辐射超声波的主要缺点是效率低,这是由于压电材料的声阻抗与空气的声阻抗严重失配(差5个数量级)。有两种途径可提高换能器向空气中辐射声波的效率,一是采用多层结构的匹配技术,二是设计高、低声阻抗材料相组合的换能器。作者遵循后一种方法设计并制作了一种新的高效压电换能器。它是将压电圆环埋置在低阻抗的弹性材料(塑料或树脂)中而成的,如图1所示。     

Modeling of circular piezoelectric micro ultrasonic transducer using CuAl<Subscript>10</Subscript>Ni<Subscript>5</Subscript>Fe<Subscript>4</Subscript> on ZnO film for sonar applications

Modeling and theoretical characterization of piezoelectric micro ultrasonic transducer (pMUT) using ZnO film sandwiched between nickel aluminum bronze (CuAl₁₀Ni₅Fe₄) electrodes was reported in this paper. The transducer is targeted to be utilized in sonar applications. Analyses on the model were carried out using finite element method. Model’s dimensional parameters were optimized for desired performance. Simplified technique was proposed to determine transmit and receive sensitivities of the model. As the result, micro ultrasonic transducer model with resonance frequency of 40 kHz was proposed with estimated receive and transmit sensitivities of −93 dB re 1 V/μPa and 137 dB re 1 μPa/V, respectively. Further model validations require actual device fabrication and this will be included in our future works.     

超声换能器并联谐振频率的复合式跟踪方法研究

为了使超声换能器适应变化比较剧烈的负载,本文通过分析超声换能器在并联谐振频率附近工作时的频率特性和实际需求特点,利用变压器初级匹配方法得到了更好的频率特性,并对比了换能器空载和带负荷情况下的阻抗特性曲线,提出了复合式自动频率跟踪方法,空载时找到超声换能器最小电流的对应的频率点,加载过程中利用比例积分微分算法实现频率的快速跟踪。并对超声换能器在不同负载时的功率输出进行了实验,结果表明,复合式频率跟踪方法可以稳定地跟踪到超声换能器的并联谐振频率,能实现超声换能器的功率自调节,对提高换能器的工作效率和负荷适应能力具有实际的指导意义和应用价值。     

Measurement of elastic nonlinearity using remote laser ultrasonics and CHeap Optical Transducers and dual frequency surface acoustic waves

A nonlinear ultrasonic technique for evaluating material elastic nonlinearity has been developed. It measures the phase modulation of a high frequency (82MHz) surface acoustic wave interacting with a low frequency (1MHz) high amplitude stress inducing surface acoustic wave. A new breed of optical transducers has been developed and used for the generation and detection of the high frequency wave. The CHeap Optical Transducer (CHOT) is an ultrasonic transducer system, optically activated and read by a laser. We show that CHOTs offer advantages over alternative transducers. CHOTs and nonlinear ultrasonics have great potential for aerospace applications. Results measuring changes in ultrasonic velocity corresponding to different stress states of the sample are presented on fused silica and aluminium.     

PZT厚膜及高频超声换能器的研究

近年来,基于PZT厚膜的超声换能器研究受到了广泛的重视。本文综述了PZT厚膜制备技术的发展情况,简要介绍了水下声纳和医用超声领域中PZT厚膜型高频超声换能器的应用研制进展。     

Load characteristics of high power sandwich piezoelectric ultrasonic transducers

Based on the equivalent circuit theory, the load characteristics of high power piezoelectric ultrasonic sandwich transducers are studied. Two types of loads are studied. One is liquid load as in ultrasonic cleaning, and the other is solid load as in ultrasonic drilling and machining. The effect of load and structure of the transducer on the resonance frequency of the transducer is analyzed. It is shown that the effect of load on the resonance frequency of sandwich transducers with different structures is different. For liquid load as in ultrasonic cleaning, the effect of the load on the resonance frequency of the sandwich transducer with symmetrical structure is the largest. It is the smallest for the transducer with its displacement node in the back metal cylinder. For solid load as in ultrasonic drilling and machining, the effect of the load on the resonance frequency of the sandwich transducer with its displacement node in the front metal cylinder is the largest. It is also the smallest for the transducer with its displacement node in the back metal cylinder. On the other hand, for some applications, such as ultrasonic drilling, when the lateral dimension of the tool is much less than that of the transducer, its effect on the resonance frequency of the transducer is small. The conclusions are useful in designing vibrating systems for different ultrasonic applications.     

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。     

A new type of high power composite ultrasonic transducer

A new type of high power composite ultrasonic transducer was proposed and studied. The composite transducer consists of a sandwich longitudinal piezoelectric transducer, an isotropic metal hollow cylinder with large radial dimension, and the front and back metal radiation mass. By means of its special structure and Poisson’s effect, the composite transducer can produce vibrations both in its longitudinal and radial directions, and therefore, it can radiate sound waves in three-dimensional space. The electro-mechanical equivalent circuit of the composite transducer was derived and the resonance frequency equation was obtained analytically. Numerical methods were used to simulate the vibration of the composite transducer, and the vibrational displacement distribution, the resonance frequency and the radiation sound field are given. Some composite transducers are designed and manufactured; their resonance frequencies and the radiation acoustic field are measured and compared with the analytical and numerical results. It can be seen that the measured frequencies and acoustic field contour are in good agreement with the analytical and numerical results. It is expected that this kind of composite ultrasonic transducer can be used in more and more power ultrasonic applications, such as ultrasonic cleaning, ultrasonic extraction, ultrasonic sonochemistry and other ultrasonic liquid processing, where high ultrasonic power and large ultrasonic processing space are needed increasingly.