Acoustic energy harvesting using nanotube sheet flutter

T.J. Kang, E.Y. Jang, M.D. Lima, H. Im, R. Ovalle-Robles, T. Kim, R.H. Baughman, Y.H. Kim
Seoul National University, KR

Keywords: carbon nanotube, acoustic energy, harvesting

Summary:

Energy harvesting from the surrounding environment has attracted much interest for diverse applications. One of the most widely available forms of ambient energy is acoustic noise, which is essentially inexhaustible and everywhere, however few research attempts have been made of harvesting acoustic energy. We have fabricated a nanotube sheet flutter to transfer acoustic energy into electrical energy. The flutter simply consists of the nanotube sheet suspended between copper wire electrodes, and the sheet is placed in a homogeneous magnetic field. When a voltage is applied to the sheet, the current flow perpendicular to the magnetic field generates flapping motion of the sheet due to the Lorentz force. The first mode resonance of the flutter is observed at 45 Hz in air. When acoustic waves propagate through air molecules inside the nanotube sheet, the pressure wave provides effective oscillating force for individual nanotubes of the sheet. The flapping motions are responsible for generating a current based on electromagnetic induction. Larger peak-to-peak voltage can be obtained when the frequency of acoustic wave matches with the natural frequencies of the flutter. Moreover, low-magnitude sound pressure is effectively converted to electrical energy with several tens of micro-volts.