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A kind of piezoresistive ultrasonic sensor based on MEMS is proposed, which is composed of a membrane and two side beams. A simplified mathematical model has been established to analyze the mechanical properties of the sensor. On the basis of the theoretical analysis, the structural size and layout location of the piezoresistors are determined by simulation analysis. The boron-implanted piezoresistors located on membrane and side beams form a Wheatstone bridge to detect acoustic signal. The membrane-beam microstructure is fabricated integrally by MEMS manufacturing technology. Finally, this paper presents the experimental characterization of the ultrasonic sensor, validating the theoretical model used and the simulated model. The sensitivity reaches −116.2 dB (0 dB reference = 1 V/μbar, 31 kHz), resonant frequency is 39.6 kHz, direction angle is 55°.

The design, fabrication and packaging of a type of MEMS piezoresistive ultrasonic transducer array are introduced. The consistency of the resonance frequency and the sensitivity of the array are tested. Moreover, we detect the directivity and the multi-target identification ability of the array. The results of the consistency of the resonance frequency and the sensitivity show that there is a gap between the practical and theoretical results. This paper analyzes this problem in detail and points out the direction of improvement. As for the directivity, the actual result is consistent with the theoretical one. The results of multiple target distinguishing tests demonstrate that the smallest resolution angle of the array is 5.72° when the distance between the sensor array and measured objects is 2 m.