电容式微机械超声换能器（CMUT）设计及其封装技术研究

发布时间：2018-06-18 15:45

本文选题：CMUT + 结构设计　；参考：《中北大学》2017年硕士论文

【摘要】：基于表面微加工工艺制作的电容式微机械超声换能器具有结构简单、自身噪声低、高机电耦合系数、高分辨率、高灵敏度、宽频带、与介质阻抗匹配性好等优势,从被提出以后就得到广大科研人员的关注,其在海底资源勘探、水下地形地貌探测以及医疗成像等领域有着广泛的应用前景,因此对CMUT展开理论分析和基础应用研究,有着极其重要的科研价值。主要研究内容如下:(1)根据不同分析内容,建立了3种CMUT模型。在振动模型中,计算圆形振动薄膜的振动位移方程;通过平行板电容模型研究了CMUT的塌陷电压、机电耦合系数、接收灵敏度、发射声压等参数;在等效电路模型中,详细分析了有效电容、机械阻抗等参数。(2)应用COMSOL Multiphysics建立了CMUT微元有限元模型。根据特征频率分析,确定了CMUT微元薄膜半径、薄膜厚度参数;通过机电耦合分析研究电极厚度、电极半径与塌陷电压的关系,确定电极结构参数;在静态分析中,研究薄膜在标准大气压下的位移和应力变化情况,得出CMUT空腔高度。CMUT参数确定后,通过模态分析和谐响应分析去验证所设计CMUT结构参数的正确性,并根据瞬态分析研究CMUT在交直流信号激励下的振动位移和速度。(3)指向性是CMUT在远场的重要特性之一,推导出CMUT微元、CMUT阵元和CMUT阵列指向性函数,并详细分析CMUT结构参数对CMUT阵列指向性的影响,随之确定CMUT阵元中的微元个数、CMUT阵元间距。根据声场理论,推导CMUT微元、CMUT阵元和CMUT阵列的声场声压分布公式。(4)在平行板电容模型,静电力在CMUT的工作中发挥着不可替代的作用,由于静电力具有非线性,使得CMUT在发射过程中存在非线性特性。为了消除、抑制CMUT的非线性,采用去除直流偏置电压,以消除谐波分量;采用改变激励信号类型,根据功率谱抑制效果,选用双极性脉冲;依据倍角公式,采用线性和非线性补偿方法,消除二次谐波分量。(5)根据实际应用情况,本文研究CMUT芯片的封装方法并设计封装结构,并根据声学理论,详细分析CMUT外壳封装的材料选择、结构参数、应力大小、透声系数,最终实现CMUT的水密封装。搭建CMUT实验系统,对所设计的CMUT的发射性能、接收性能、指向性和带宽性能进行测试,测试结果表明,设计的CMUT阵列能够满足水下成像要求。
[Abstract]:The capacitive micro mechanical ultrasonic transducer based on the surface micromachining technology has the advantages of simple structure, low self noise, high electromechanical coupling coefficient, high resolution, high sensitivity, wide frequency band and medium impedance matching. There are extensive applications in the fields of detection and medical imaging, so the theoretical analysis and basic application of CMUT expansion are of great value. The main contents are as follows: (1) 3 kinds of CMUT models are established according to the content of different analysis. The board capacitance model has studied the CMUT collapse voltage, the electromechanical coupling coefficient, the receiving sensitivity, the acoustic pressure and so on. In the equivalent circuit model, the effective capacitance, mechanical impedance and other parameters are analyzed in detail. (2) the finite element model of CMUT microelement is established by using the COMSOL Multiphysics. According to the characteristic frequency analysis, the radius of the CMUT microelement film is determined. The thickness of the film, the relationship between the electrode thickness, the radius of the electrode and the collapse voltage are studied by mechanical and electrical coupling analysis, and the parameters of the electrode structure are determined. In the static analysis, the displacement and stress change of the thin film at the standard atmospheric pressure are studied, and the.CMUT parameters of the CMUT cavity height are determined and verified by the modal analysis and the analysis of the harmonic response. The correctness of CMUT structure parameters is designed, and the vibration displacement and velocity of CMUT under AC and DC signal excitation are studied by transient analysis. (3) directivity is one of the important characteristics of CMUT in far field, CMUT microelement, CMUT element and CMUT array directivity function are derived, and the influence of CMUT structure parameters on the directivity of CMUT array is analyzed in detail. According to sound field theory, the sound pressure distribution formula of CMUT microelement, CMUT element and CMUT array is derived according to the theory of sound field. (4) in parallel plate capacitance model, static electric power plays an irreplaceable role in the work of CMUT, because the electrostatic force has nonlinearity, it makes the CMUT nonlinear in the launching process. In order to eliminate and suppress the nonlinearity of CMUT, remove the DC bias voltage to eliminate the harmonic component; use the change of the excitation signal type, select the bipolar pulse according to the power spectrum suppression effect, use the linear and nonlinear compensation method to eliminate the two harmonic components according to the angle formula. (5) according to the actual application, this paper studies C The packaging method of MUT chip is designed and the package structure is designed. According to the acoustic theory, the material selection, structure parameters, stress size, sound permeability coefficient of the CMUT enclosure are analyzed in detail, and the CMUT's watertight encapsulation is finally realized. The CMUT experimental system is built to test the designed CMUT performance, receiving performance, directivity and bandwidth performance. The results show that the designed CMUT array can meet the requirements of underwater imaging.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB552

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