Air-coupled capacitive micromachined transducer array for non-contact Lamb wave detection.

Capacitive micromachined ultrasonic transducer (CMUT) has shown the potential for the air-coupled application due to its good acoustic match with air. Therefore, air-coupled guided wave detection technology based on CMUT array has a good application prospect in structure detection. In this paper, a 16-element CMUT array for air-coupled guided wave detection is designed and fabricated by the silicon-on-insulator (SOI) wafer bonding process. All the CMUT cells have the same geometric parameters with circular and sealed membrane. Each element has good consistency in impedance and transceiver performance. In addition, the transmit performance was improved by a third through impedance matching. The resonant frequency is 207 kHz at 150 DC voltage and − 6 dB main lobe width of the sound beam is 9.4°. The emission beam can be steered by programmable driving circuit. So different modes of guided wave can be excited without adjusting the tilt angle of the transducer. This will reduce the interference caused by the movement of device in the experiment. After that, the air-coupled guided wave detection experiment was carried out by two CMUT arrays. The results show that the CMUT array can well excite the single mode Lamb wave in aluminum plate and composite plate, and receive the leaky Lamb wave. Besides, the defect can be identified by the variation of the received signal amplitude. Thus, the position of the defect can be located and the approximate size of the defect can be predicted. In general, it is proved that the CMUT has ability for the air-coupled Lamb wave detection by the non-contact guided wave detection experiment and the comparison experiment with commercial air coupling probe. [Display omitted] • A 16-element CMUT array for air-coupled guided wave detection is designed and fabricated by SOI wafer bonding process. • Each element has good consistency by acoustic and electrical properties test and the performance is improved by impedance matching. • The CMUT can excite the single mode Lamb wave in plate and receive the leaky Lamb wave,。Besides, the defect can be identified. [ABSTRACT FROM AUTHOR]