Underwater acoustic energy harvesting using an ePTFE waterproof acoustic-permeable membrane and helmholtz piezoelectric resonator

Abstract Underwater wireless power supply is crucial for the long-term operation of distributed sensors and Internet of Underwater Things (IoUT) nodes, yet practical implementation is hindered by severe acoustic impedance mismatch at water–structure interfaces and low energy conversion efficiency. In this work, a waterproof underwater acoustic energy harvester integrating a porous expanded polytetrafluoroethylene (ePTFE) acoustic membrane, a Helmholtz resonant cavity, and a bimorph piezoelectric cantilever array is proposed. The ePTFE membrane acts as a waterproof acoustic coupling layer, whose hydrophobic surface and microporous structure prevent water infiltration and, by adjusting the porosity, can tune the acoustic impedance, thereby reducing interfacial reflection and efficiently transmitting acoustic energy into the air-filled cavity. The Helmholtz cavity amplifies local acoustic pressure near the piezoelectric array, enhancing electromechanical conversion. Finite element simulations and laboratory water-tank experiments show that the 10 cm cavity with a 25 μm ePTFE membrane produces a peak open-circuit voltage of 7.8 V at 4.8 kHz and 1 m, a local field-enhancement location in the present tank. Under the same condition, a 6800 μF capacitor is charged to 3.96 V in 34.1 s (53.2 mJ; 1.56 mW average storage power), and the stored energy drives 50 LEDs. These absolute values are tank-conditioned, not free-field metrics, and demonstrate intermittent micro-power supply in a confined underwater field. This work provides a feasible design strategy for non-contact underwater acoustic energy harvesting with enhanced output performance, enabling long-term operation of low-power IoUT nodes.