Horn-integrated air-coupled PMUT rangefinder for simultaneous sensitivity and detection range enhancement

Abstract

Given the pulse-echo operation mode, the vibration amplitude and the duration time of the piezoelectric micromachined ultrasonic transducer (PMUT) worked under resonance are both positively correlated with the quality factor Q. Therefore, the PMUT-based self-transceiving rangefinders have to face performance trade-off dilemma between the maximum detection distance and the minimum detection blind area. To address this challenge, a specially designed horn-shaped acoustic package is integrated into a quasi-closed PMUT with inherently low Q factor. A lumped-parameter acoustic model and finite element modeling (FEM) method are used for analysis, through which effective enhancement of both of the transmitting and receiving sensitivities of the PMUT can be achieved by optimizing the horn configuration. At the same time, the low Q characteristic can be well maintained, enabling simultaneous detection distance extension and detection blind area reduction. From proof of concept experiment, it can be seen that after the integration of the horn structure, the emission sensitivity and the pulse-echo signal strength of the PMUT can be increased by factors of 2.65 and 7.68, respectively, with a slight decrease in Q factor. As a result, a large detection range covering from 142.9 mm to 6 m with a −6 dB divergence angle of 66° has been successfully demonstrated with a single PMUT driven by a pulsed sinusoidal signal with 72.9 kHz and 40 V_pp, despite its small effective device area of only 0.59 mm². Provided this competitive performance, the current method possesses excellent application perspective in air-coupled ultrasonic sensing applications.