A sandwich pMUT for the amplification of ultrasound transmission and reception

Piezoelectric micromachined ultrasound transducers (pMUTs) are essential for ultrasonic communication as well as energy harvesting and transmission. While pMUTs typically demonstrate lower energy conversion efficiency and narrower bandwidths compared to traditional sandwich ultrasound transducers, their larger counterparts often present size constraints in specific applications. This paper introduces a sandwich pMUT (SpMUT) designed to enhance ultrasound transmission and reception. The SpMUT features a silicon substrate with a scandium aluminum nitride thin film, a dual electrode layer, and a three dimensional printed horn. The horn acts as a mechanical intermediary, amplifying the mechanical strain generated by the piezoelectric layer or an external sound field. Our experiments yielded a fractional bandwidth of −6 dB at 107% with a center frequency of 421 kHz in water. By optimizing the ratio of the horn's back and front diameters, we achieved maximum amplification factors of 8.59 for transmission and 8.1 for reception. The SpMUT shows significant potential for enhanced ultrasound signal amplification in biomedical and nondestructive testing applications.