Ultrasonic Piezoelectric Mems Speakers for In-Ear Applications: Bubbles-Like and Pistons-Like Innovative Designs

MEMS speakers are attracting increasing interest thanks to their reduced size, low cost and power efficiency. Research work is still needed in terms of Sound Pressure Level (SPL) improvement at low frequency and of Total Harmonic Distortion (THD) reduction to obtain devices competitive with the non-MEMS counterparts. In this work, two innovative PZT-driven MEMS speakers for in-ear applications are designed and simulated. They consist of arrays of mechanical structures excited through PZT patches properly designed that do not need any protecting membrane. Thanks to the resonance frequency in the ultrasonic regime, they represent a very promising solution for the design of high fidelity and high-performance speakers. The ultrasonic resonance of the mechanical structure indeed guarantees a flat and high SPL at low frequencies and a moderate intrinsic THD.