Acoustic energy-harvesting meta-surface by coupling a nonlinear Helmholtz resonator and an auxetic structure

Traditional acoustic energy-harvesting devices, constrained by their linear operating mechanisms, struggle to simultaneously achieve broadband capture of low-frequency sound waves and efficient electromechanical conversion. This study proposes a novel acoustic energy-harvesting meta-surface (AEHMS) capable of achieving acoustic energy collection through the coupling of a nonlinear Helmholtz resonator and an auxetic structure. This meta-surface exhibits subwavelength characteristics (thickness ∼ λ/12), with its core design philosophy centred on achieving physical cascading and synergy between acoustic and elastic functions: The Helmholtz resonator (HR) leverages its nonlinear acoustic response at high throat amplitudes (characterized and optimized via the Melnikov method) to broaden the acoustic energy capture bandwidth and surpass the energy input limits of linear systems; while the auxetic structure leverages its unique geometric deformation properties to convert the resonator-concentrated acoustic energy into high-density, uniformly distributed elastic strain energy, significantly enhancing the electromechanical conversion efficiency of piezoelectric materials. Experimental results demonstrate that at a centre frequency of 250 Hz and 100 dB sound pressure level, this AEHMS achieves an open-circuit voltage of 1.33 V (31 times higher than that of conventional piezoelectric beams) and an output power of 56.64 µW. This device has pioneered a novel theoretical approach for developing highly efficient, ultra-thin low-frequency acoustic energy-harvesting devices.