Energy harvesting — the extraction of energy from the local environment for conversion to electrical power — is of particular interest for low power wireless devices such as body or machine mounted sensors. Motion and vibration are a potential energy source, and can be exploited by inertial devices, which derive electrical power by the damping of the relative movement of a proof mass mounted in a frame attached to the moving host. Inertial devices using linear motion of the proof mass, which have been extensively studied and developed, have a maximum power output limited by the internal travel range of the proof mass. In the current paper, the potential power of devices using rotating proof masses, powered by linear or rotational host motion, is analysed. Two new operation modes are introduced: rotationally resonant devices, and devices driven by continuous rotation. In each case the maximum achievable power densities are estimated, and these are compared with equivalent expressions for devices with linear proof mass motion where appropriate. The possibility of using actively driven, gyroscopic structures is then introduced, and the potential power of such devices is considered. By avoiding the linear displacement limit and the limited mass of conventional devices, it is shown that increases in obtainable power are possible if parasitic damping is minimized, particularly for cases of low linear source amplitude. Finally, issues of implementation are discussed, with an emphasis on microengineered devices.
RF Energy Harvesting System and Circuits for Charging of Wireless Devices Using Spectrum Sensing