Ventilated acoustic energy harvester based on Friedrich–Wintgen bound state in the continuum

In this work, we design and fabricate a ventilated acoustic energy harvester based on Friedrich–Wintgen bound state in the continuum (BIC), whose operating frequency can be programmed by tuning the geometry of a bridging coupling tube. By intentionally breaking the symmetry-protected BIC condition, the structure supports quasi-BIC that converts propagating sound into a strongly confined resonant state with a high quality factor, enabling efficient acoustic energy localization. We achieve acoustic-to-electric conversion by placing a piezoelectric composite sheet (PCS) at the location where the acoustic energy is localized. Meanwhile, the acoustic fields on the two sides of a PCS are out of phase, producing a push–pull excitation that enhances acoustic-to-electric conversion. Numerical simulations and experimental results consistently show peak output voltages of 217.2 mV at 1204 Hz and 314.0 mV at 1301 Hz under an incident sound pressure of 1 Pa. The proposed open and fabrication-friendly design provides a simple and effective solution toward ventilated acoustic energy harvesting, with potential for deployment in ventilation-demanding environments.