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。

The characteristics of transmitting and receiving sound field of rectangular capacitive micromechanical ultrasonic transducer in silicone oil medium

Compared with the traditional piezoelectric ultrasonic transducer, the capacitive micromachined ultrasonic transducer (CMUT) based on micro-electro-mechanical system (MEMS) micromachining technology has the advantages of wide frequency band, high sensitivity, good consistency, easy integration and so on, and has broad application prospects in medical ultrasonic imaging. Aiming at the rectangular CMUT device developed, this paper carries out theoretical analysis and experimental verification of the sound field characteristics of CMUT emission and reception in silicone oil medium. Firstly, according to the structural characteristics and working principle of CMUT array elements, the directional function analysis model of rectangular CMUT array elements is established according to the directional function theory and Bridge product principle; On this basis, the influence of the number of micro elements and resonant frequency on the directivity of CMUT is analyzed. Finally, the emission and reception characteristics of 7mm×7mm two-dimensional rectangular CMUT in silicone oil medium are experimentally verified. The test shows that the emission directivity curve is basically consistent with the simulation theoretical curve; In addition, the test of CMUT receiving and transmitting directivity shows that the receiving and transmitting directivity is consistent, which verifies the reciprocity of the sound field. The research of this paper has important reference value for the packaging design of CMUT devices and the development of breast ultrasound CT imaging system based on CMUT array.