Hybrid Solution for Enhanced Energy Harvester from Torsional Vibration

Kinetic energy harvesting arouses practical interest for wireless sensor nodes and autonomous or quasi-autonomous measurement systems. In particular, motion and vibration present potential energy sources and, by using a suitable transducer, a mechanical to electrical conversion can be pursued. The most common approach concerns a linear/nonlinear oscillator able to collect energy by using a mass-spring-damper architecture (i.e. cantilever resonator, bridge structure, etc.), suitable to work along a preferential axis. Very often, in real-world applications, the motion also appears as angular displacements and rotating vibration manly focalized at low frequency, less than 100 Hz (i.e. motion induced by human body, fluid movements, vortices, etc.). Several solutions have been presented in literature, mostly based on frequency up-conversion to increase the performance of the device and complex solutions. The aim of the present paper is to describe a comprehensive strategy for efficiently harvesting energy from torsional motion, a hybrid solution has been pursued to increase the performance of the entire system. The device is able to work also in presence of very low frequency sources, it can operate over a broad range of frequencies, and it is able to operate in non-resonant condition with a self-rectified output voltage. A prototype has been designed, fabricated and an experimental characterization campaign has been also accomplished to collect the measures needed to demonstrate the validity of the proposed technique.