High-quality acoustic energy harvesting via topology-optimized quasi-bound states in the continuum.

Harvesting energy from ambient sound offers a sustainable power solution for distributed sensors and intelligent devices, yet the inherently low energy density of acoustic waves severely limits conversion efficiency. Overcoming this bottleneck requires confining sound with minimal radiation leakage to maximize electromechanical coupling. Here, we introduce a topology-optimized waveguide-resonator structure that exploits bound states in the continuum (BICs) to achieve high-quality acoustic resonance for efficient energy harvesting. The optimized geometry enforces symmetry-protected confinement, resulting in strong pressure localization and amplification at target frequencies while mitigating dissipative loss. Numerical eigenmode and frequency-response analyses demonstrate ultra-narrowband high-Q resonances with dramatically enhanced energy concentration within the optimized cavity-cluster. Experimental validation confirms that the proposed BIC-enabled harvester delivers a substantial increase in output voltage and power density. This work establishes BIC physics as a new paradigm for compact acoustic energy harvesters and offers a generalized design strategy for next-generation self-powered systems requiring high performance at low-frequency excitation.