On the Design and Modeling of a Full-Range Piezoelectric MEMS Loudspeaker for In-Ear Applications

MEMS loudspeakers are emerging as very promising solutions to meet the ever-increasing requirements for modern audio devices to become smaller, lighter and potentially more power efficient. The piezoelectric actuation principle, thanks to the relatively large driving force achievable at low voltages, represents the most promising implementation of loudspeakers at the microscale. Despite a significant number of new structures have been proposed in the last years, research work is still needed both at the design level, in order to obtain full-range microspeakers with good sound quality, and at the simulation level, to accurately capture the linear and nonlinear responses of these type of devices. We here propose the design, modeling and characterization of a high performance piezoelectric MEMS speaker for in-ear applications, based on a piston-like movement of the microspeaker central component, connected to the actuators through a set of folded springs. The device features a Sound Pressure Level (SPL) greater than 107 dB from 500 Hz onwards for actuation voltages of 30 Vpp and a compact footprint of 4.5 x 4.5mm(2). A Total Harmonic Distortion (THD) smaller than 1% has also been observed at 1 kHz at 94 dBSPL. Therefore, even if at the prototype stage, the proposed device represents a promising solution towards a new set of high performances piezo-MEMS speakers that do not require further additional closing membranes to minimize acoustic losses. An excellent numerical-experimental matching in terms of SPL was also proved, thus opening the path to a new systematic design procedure for this class of MEMS structures.