Energy harvesting from acoustic sources

Abstract

While energy harvesting from a variety of ambient sources (vibration, light, and wind) has been demonstrated and sensing and communication applications to exploit those sources have been developed, acoustic energy as an ambient source has not received much attention. The reason for this comes down to the basic physics of how much energy is available within an acoustic field. For airborne sounds, the energy density in sound fields that are perceived by humans to be quite loud (e.g., 80 to 160 dB, or ∼0.2 Pa to ~2 kPa) actually represent an extremely low available energy source. In consequence, means must be taken to intensify an acoustic response, for example, through resonance, but even so, available energy remains limited. The exception to this issue in airborne sounds is the sound field that exists inside of an operating jet aircraft engine. The situation is quite different, however, when one considers pumped and pressurized fluid systems, where acoustic pressure variations due to the operation of pumps and other devices may reach into the mega-Pascal (MPa) range. Energy harvesting from such a fluid-borne acoustic source is feasible for powering sensors and wireless communication systems and has been successfully demonstrated.