Broadband Acoustoelectric Conversion Based on Oriented Polyacrylonitrile Nanofibers and Slit Electrodes for Generating Power from Airborne Noise.

Electrospun nanofiber acoustoelectric devices typically have a bandwidth in the range of 100-400 Hz, which limits their applications. This study demonstrates a novel device structure with tunable acoustoelectric bandwidth based on oriented electrospun polyacrylonitrile (PAN) nanofibers and slit electrodes. When the PAN nanofibers were arranged perpendicular to the slits, the devices had a much wider bandwidth than their parallel counterparts, while the latter had a bandwidth similar to that of randomly oriented nanofibers. In all devices, the electrical outputs follow a similar trend with the slit aspect ratio. However, the slit number only affected the electrical output without changing the bandwidth characteristic. We further showed that both the slit electrode and the oriented nanofiber membranes played a role in tuning the frequency response. Under sound, the vibration of the electrode caused the slit to be misaligned on both sides. The anisotropic tensile properties of the oriented nanofiber membranes allowed the fibers to stretch differently depending on their angle of alignment with the slits. Those perpendicular to the slits received more intense stretching, contributing to a wider bandwidth. The wider bandwidth increases the electrical output, especially when harvesting multifrequency sound. A 4 × 3 cm device made of five-slit electrodes (slit width × length, 2 mm × 30 mm) with PAN nanofibers perpendicular to the slits showed a bandwidth of 100-900 Hz and electrical outputs of 39.85 ± 1.34 V (current output 6.25 ± 0.18 μA) under 115 dB sound conditions, which is sufficient to power electromagnetic wireless transmitters. When one such slit device was used as a power supply and another as a sound sensor, they formed a completely self-powered wireless system that could detect sounds from various scenarios, such as high-speed trains, airports, highway traffic, and manufacturing industries. The energy can also be stored in lithium-ion batteries and capacitors. We hope that such novel devices will contribute to the development of highly efficient acoustoelectric technology for generating electrical energy from airborne noise.