SPL and THD improvement of a cantilever-diaphragm piezoelectric MEMS loudspeaker with Double-S actuators
Qincheng Zheng, Ke Cao, Xudong Ma, Ning Deng, Hao Chen, Yulang Cheng, Yao Lu, Huikai Xie
Abstract
Piezoelectric MEMS loudspeakers based on cantilever diaphragms have demonstrated promising electroacoustic efficiency and low-frequency sound pressure level (SPL). However, their total harmonic distortion (THD) significantly increases near the first resonant frequency, and high-frequency SPL (above 10 kHz) rapidly decreases due to the resonance frequency and bandwidth limitations, severely affecting sound quality. This work presents a piezoelectric MEMS loudspeaker featuring a 2.7 µm-thick sputtered PZT film, comprising a cantilever diaphragm and four sets of Double-S actuators. The first resonance frequency of the cantilever diaphragm is 3.2 kHz, and the Double-S actuators introduce an additional resonance frequency at 21.3 kHz, addressing the issues of insufficient high-frequency SPL and poor THD performance. Testing on a 711-ear simulator reveals that, under 1-3 Vpp excitation, incorporating the Double-S actuators leads to an average SPL increase of 23 dB and an average THD reduction of 80% that remains below 0.6% across the 3.2-20 kHz range. Thus, both SPL and THD performance in the mid- to high-frequency range are improved. This work paves the way for the development of high-fidelity piezoelectric MEMS loudspeakers, offering new opportunities to improve sound quality and extend the frequency range for in-ear applications.