Design of air-coupled capacitive micromachined ultrasonic transducer

The theoretical method of air-coupled capacitive micromachined ultrasonic transducer(CMUT) was established to analyze the influence of CMUT structure parameters on its performance parameters. A CMUT array composed of 16 elements was designed according to the theoretical analysis and the background of non-destructive testing. And it was fabricated by silicon on insulator(SOI) wafer bonding process. Each element of the array contains 16 circular CMUT sensitive cells with a radius of 400 μm and a center frequency of 230 kHz. The CMUT transmitting and receiving transient simulation model was established to obtain the transmitting sound pressure and the receiving sensitivity of the CMUT at the different excitation voltages. And the experimental results showed the accuracy of the simulation model.Finally, the performance of CMUT was compared with commercial piezoelectric air-coupled ultrasonic transducer by experiments. The experiment results showed that the transmitting sound pressure and receiving sensitivity of CMUT were the same order of magnitude as that of commercial transducer. And the CMUT can successfully stimulate and receive the A0 modal Lamb wave in the aluminum alloy plate.