Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for High-Resolution Distance Sensing

Abstract

High-frequency airborne ultrasound enables high-resolution distance sensing for various applications, such as robotics, industrial automation, gesture control, and more. This paper presents a 1.5MHz, 12-element 2-D Piezoelectric micromachined ultrasonic transducer (PMUT) array for high temporal and spatial resolution distance sensing in air. Electrical impedance analysis and measured electroacoustic frequency response of the air-coupled PMUT array showed a resonant frequency f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> of 1.5 MHz, an electromechanical coupling factor k<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 4.5%, and a -3 dB fractional bandwidth of 5% centered at 1.5 MHz, with high transmit and receive sensitivities of 70 Pa/V and 0.16 mV/Pa, respectively. Distance measurement on a curved surface using two matched PMUT arrays in pulse-echo proved the feasibility of sensitive and accurate high-resolution distance sensing in demanding scenarios.