Bandwidth Enhancement and SPL Flattening in MEMS Piezoelectric Speaker Array via Stiffness-Modulated Triangular Diaphragm Design

Abstract

To overcome the intrinsic narrowband limitation of high-Q MEMS piezoelectric speakers, a stiffness-modulated multi-resonant array strategy is proposed to broaden the effective acoustic bandwidth. By locally modifying the boundary stiffness of triangular cantilever diaphragms through etched grooves of different lengths, the resonant frequencies of individual speaker units are intentionally distributed within a target frequency band. A theoretical framework based on single-degree-of-freedom resonance modeling is established to analyze the phase–frequency behavior of each unit and to clarify how appropriate resonance spacing suppresses inter-unit phase mismatch. The analysis reveals that closely spaced resonances confine the phase transition regions, thereby preventing destructive interference of volume displacement between adjacent units and enabling constructive superposition over a wider frequency range. Finite element simulations incorporating an IEC 711 ear-coupler model validate the resonance allocation mechanism and predict broadened acoustic response. Experimental measurements under 1 V_rms AC excitation with 15 V DC bias demonstrate an SPL exceeding 120 dB across 12.5–18 kHz, confirming the effectiveness of the proposed resonance-dispersion design. This work provides a physically grounded strategy for rationally allocating resonant frequencies in multi-unit MEMS speaker arrays and offers a practical route toward wideband high-SPL acoustic transducers.[2025-0173]