Piston-Mode pMUT With Mass Load

Abstract

This paper proposes a novel piezoelectric micromachined ultrasonic transducer (pMUT) with a proof mass under the central circular diaphragm to enhance transmission efficiency and fractional bandwidth (FBW) in liquid-coupled operation. Compared with the traditional pMUT, the proposed pMUT has advantages: (1) the resonance frequency of pMUT can be adjusted by proof mass; (2) a large ratio of third-order resonance frequency to first-order resonance frequency can be obtained by an additional proof mass under the circular diaphragm; (3) the mode shape of proposed pMUT changes from Gaussian-like to piston-like, which enables higher transmission sensitivity; (4) the FBW can be improved through a trade-off design. The characteristics of resonance frequency, output power, and FBW of pMUT with different proof mass are analyzed with a piezoelectric layer of $1~\mu \text{m}$ and a structural layer of 5 $\mu \text{m}$ . In this work, the far-field sound pressure is 240.5 Pa/V in water, 49.5 Pa/V higher than the traditional pMUT, benefiting from the piston diaphragm movement. Furthermore, a 23% −6 dB FBW in water is demonstrated by theoretical analysis and parameter optimization. This work provides constructive advice for pMUT for better performance of transmission and resolution.

Keywords

• Piezoelectric micromachined ultrasonic transducer (pMUT)
• piston mode
• mass loading effect
• frequency adjustment
• fractional bandwidth