Dual-Frequency Piezoelectric Micromachined Ultrasonic Transducers via Beam-Membrane Coupled Structure

Dual-frequency piezoelectric micromachined ultrasonic transducers (pMUTs) are attractive for ultrasonic imaging, which can meet the requirements of large detection depth and high resolution simultaneously. In this letter, we propose a dual-frequency pMUT via beam-membrane coupled structure. The beam-membrane coupled pMUTs (BM-pMUTs) inherently have two fundamental resonant frequencies, corresponding to in-phase and out-of-phase modes. The dual-electrode design is utilized to compensate the sensitivity of out-of-phase mode, hence the BM-pMUTs maintain high sensitivity for both two operation modes. Experimental results show that the optimal transmitting sensitivities of BM-pMUTs are 18 nm/V at 103 kHz and 26 nm/V at 220 kHz when characterized in oil, as well as the optimal receiving sensitivities are 572.1 mV/MPa at 103 kHz and 581.8 mV/MPa at 220 kHz.