Multi-frequency energy harvesting of acoustic waves in a sonic crystal ring resonator

Abstract Acoustic energy harvesting offers a promising solution for powering wireless sensor networks and Internet of Things devices by converting ambient noise into usable electricity. However, conventional harvesters are limited by the low energy density of acoustic waves and their inherently narrow operating bandwidth. This paper proposes a novel multi-frequency acoustic energy harvester based on a sonic crystal (SC) ring resonator with a line defect. Introducing a line defect into a two-dimensional SC with a complete bandgap forms a waveguide, which is then configured into a closed loop to create a ring resonator supporting multiple resonant modes with strong acoustic confinement. Finite element simulations are conducted to analyze the band structure, acoustic pressure distributions, and electromechanical coupling behavior. Piezoelectric elements placed in high-pressure regions convert the localized acoustic energy into electricity. Results show that the proposed SC ring resonator significantly enhances voltage and power output at multiple discrete frequencies, achieving a maximum power amplification of 85 times compared with the case without the SC structure. In addition, the symmetric ring geometry provides excellent angular adaptability, enabling stable output over a wide range of incident angles. This work offers an effective strategy for multi-frequency, multi-directional acoustic energy harvesting from ambient noise.