A Novel Coupled Piezoelectric Micromachined Ultrasonic Transducer Based on Piston Mode

This article presents a piezoelectric micromachined ultrasonic transducer (pMUT) modified with a piston diaphragm term as piston diaphragm pMUT (PD-pMUT). The transmission sound pressure level (SPL) and the frequency bandwidth of the modified transducer can be remarkably improved by adding a piston diaphragm on the central circular diaphragm. In this work, a lumped model, an acoustic resonance model, and an equivalent circuit model are established to study the multiresonance mechanism. The second resonance peak is contributed by the interference acoustic wave generated between the circular and piston diaphragms. This work demonstrated a simulated far-field average SPL up to 132.2 dB in the single modified piston diaphragm structure and a 28.1%-6-dB frequency bandwidth by theoretical analysis and parameter optimization. The bandwidth is 3.31 times of the traditional pMUT with aluminum nitride (AlN) in air. In addition, the PD-pMUT has a -6-dB frequency bandwidth of up to 66%, which is 1.4 times of traditional pMUT in the liquid-coupled operation. The proposed PD-pMUT provides a new approach for the application of high transmission power and broad bandwidth transducers.