摘 要

超声波技术是现代声学领域中一个重要的分支之一，它来源于经典声学理论，并跨学科与材料科学、雷达遥感、固体和流体力学、信号处理以及电子电气等学科相互交叉。其在汽车、航空、生物医学等诸多领域中被广泛地应用，基于超声波技术研制的超声传感器则是实现声电转换的核心部件。随着现代工艺的飞速发展，MEMS技术已经用于研制压电超声传感器并具有诸多优点如宽频带、高灵敏度等，在超声波测距和无损检测等领域越来越受重视，这引起了越来越多的学者的研究。

本文以压电式超声传感器作为研究对象，通过设计传感器的仿真模型并进行仿真分析，对传感器的声场特性、变形特性和频率特性以及加工等方面进行了分析。

（1）针对传统pMUT加工过程会产生残余应力的缺点，提出了使用SOI晶片作为衬底来制造pMUT，由真空腔室内部引起的大气压力补偿残余应力。并详细说明了从衬底到器件的整个加工步骤。与传统pMUT相比，本文设计的模型可以作为一种有效减低残余应力的方法。

（2）针对SOI晶片制造的pMUT设计了仿真模型，并使用COMSOL软件对模型进行了有限元仿真，该模型将直观表征了pMUT的各项特性，并分析了对pMUT性能产生影响的因素，其研究结果将对接下来的传感器结构设计发挥一定的建议作用。

（3）针对亥姆霍兹共振腔的腔体进行仿真分析，仿真主要从腔体的尺寸的方面进行考虑，详细给出了腔的半径和高度以及腔的体积对共振腔谐振频率的影响，还对有限元仿真软件求解器进行了验证。论证结果说明了不同求解器在不同求解情况下的求解效果，这部分的研究结果给下一步设计共振腔型压电传感器提供了理论基础。

（4）结合pMUT和亥姆霍兹共振器的理论设计了一种新的传感器结构，从仿真结果上来看，这种结构更适合工作在较低共振频率上，其具有较大的薄膜响应、声压、声压级以及接收灵敏度，这种结构的传感器的整体性能较传统的pMUT有所提升，并与传统的pMUT有着不同的适用方向，其有望作为压电传感器的一种新的选择。

（5）结合传感器阵列和超声测距理论对汽车自动泊车进行了分析和设想，针对阵列型传感器的结构和等效电路模型进行了分析，提出将诸多传感器按照给出了连接方式连接，其组成的传感器阵列可以提供更大的测距范围。接着设计了测距系统的组成部分，并分析各组成模块的功用以及它们作用的部位。

关键词：压电超声传感器；频率特性；pMUT；亥姆霍兹共振器；声场特性；超声波测距

Abstract

Ultrasonic technology is one of the important branches in the field of modern acoustics. It is derived from classical acoustic theory and interdisciplinary with materials science, radar remote sensing, solid and fluid mechanics, signal processing, and electrical and electronic disciplines. It is widely used in many fields such as automobile, aviation, biomedicine, etc. Ultrasonic sensors based on ultrasonic technology are the core components of acoustic-electrical conversion. With the rapid development of modern technology, MEMS technology has been used to develop piezoelectric ultrasonic sensors with many advantages such as wide frequency band, high sensitivity, etc., and more and more attention has been paid in the fields of ultrasonic ranging and non-destructive testing, which has caused more and more A lot of scholars' research.

In this paper, piezoelectric ultrasonic sensor is taken as the research object. By designing the simulation model of the sensor and performing simulation analysis, the sound field characteristics, deformation characteristics, frequency characteristics and processing of the sensor are analyzed.

(1) In view of the disadvantage that residual stress is generated in the conventional pMUT process, it is proposed to use a SOI wafer as a substrate to fabricate a pMUT, and atmospheric pressure caused by the inside of the vacuum chamber will compensate for residual stress. The entire processing steps from the substrate to the device are detailed. Compared with the traditional pMUT, the model designed in this paper can be used as a method to effectively reduce the residual stress.

(2) The simulation model is designed for the pMUT of SOI wafer manufacturing, and the model is finite element simulation using COMSOL software. The model will visually characterize the characteristics of pMUT and analyze the factors affecting the performance of pMUT. The research results will play a certain suggestive role for the next sensor structure design.

(3) Simulation analysis of the cavity of the Helmholtz resonator. The simulation mainly considers the size of the cavity, and gives the details of the radius and height of the cavity and the influence of the volume of the cavity on the resonant frequency of the cavity. The finite element simulation software solver was also verified. The results of the demonstration illustrate the solution effect of different solvers under different solution conditions. The research results of this part provide the theoretical basis for the design of resonant cavity piezoelectric sensors in the next step, which is the necessary research content.

(4) A new sensor structure is designed based on the theory of pMUT and Helmholtz resonator. From the simulation results, this structure is more suitable for working at lower resonance frequency, which has a larger film response. Sound pressure, sound pressure level and receiving sensitivity, the overall performance of this type of sensor is improved compared with the traditional pMUT, and has a different application direction than the traditional pMUT, which is expected to be a new choice for piezoelectric sensors.

(5) Combining the sensor array and ultrasonic ranging theory to analyze and imagine the automatic parking of the car, analyze the structure and equivalent circuit model of the array sensor, and propose to connect many sensors according to the connection mode. The resulting sensor array provides a larger range of ranging. Then the components of the ranging system are designed, and the functions of each component module and the locations where they act are analyzed.

Key words: piezoelectric ultrasonic sensor; frequency characteristics; pMUT; Helmholtz resonator; sound field characteristics; ultrasonic ranging

目录

第一章 绪论 1

1.1选题背景及意义 1

1.2国内外研究现状 2

1.2.1压电式超声传感器 2

1.2.2电容式超声传感器 6

1.3拟解决的关键性问题 8

1.4主要研究内容及意义 9

第二章 声学理论 11

2.1超声波的基本理论 11

2.1.1声波的分类 11

2.1.2声压 13

2.1.3声速 13

2.1.4声阻抗 13

2.1.5声衰减 14

2.2超声波的反射、折射、散射 14

2.3超声波测距原理 15

2.4常用的超声波测距方法 16

2.5阵列型传感器测距 16

2.5.1阵列型传感器结构 16

2.5.2阵列型传感器等效电路 17

2.5.3超声波测距结构 18

第三章 压电部分 19

3.1 压电理论 19

3.1.1 压电效应 19

3.1.2压电方程 20

3.1.3压电材料的性能参数 21

3.1.4压电材料的种类 23

3.2压电超声传感器 26

3.2.1压电超声传感器的工作原理 26

3.2.2压电超声传感器的基本特性 27

3.2.3传感器的等效电路图 28

第四章 pMUT的设计与仿真 30

4.1pMUT的理论分析 30

4.2pMUT的仿真设计 36

第五章 共振腔型压电超声传感器的设计与建模 43

5.1亥姆霍兹共振腔 44