| Description |
Inertial energy harvesting from human motion enables self-powered sensing capabilities for wearable applications. It not only allows 24/7 continuous mobile clinical health monitoring but also helps improve user experience for wearable commercial electronics by reducing battery maintenance. The inherent limitation of utilizing human motion as the source for energy harvesting is that it only provides excitations with very low and irregular frequencies, which is incompatible with conventional resonant energy harvesters. Frequency up-conversion is a commonly applied strategy to tackle this issue by transforming the low-frequency input motion into a high-frequency actuation of the transducer. In terms of piezoelectric energy harvesters, plucking a cantilever beam is one technique that applies such a strategy. Compared to the conventional translational proof mass, a rotational proof mass has no inherent motion limit. In addition, a rotational system with an eccentric weight responds to excitations in all directions. These characteristics cater to the multidirectional human motion with large amplitudes. This project investigates the potentials, and limitation, of eccentric-rotor-based inertial wearable energy harvesting systems with the objective of determining the maximum extractable energy from human motion at various body locations and the underlying principles and design parameters needed to approach the maximum power. This is achieved with a generalized viscous-damped rotational energy harvester model that predicts the theoretical upper bound power. In addition, extensive characterization work is iv conducted on electromagnetic microgenerators in existing commercial off-the-shelf watches made by Seiko and Kinetron for benchmarking. A distributed analytical model for magnetically plucked piezoelectric beams is derived and experimentally validated to study different magnetic plucking configurations. Finally, this project delivers several energy harvester prototypes utilizing custom microfabricated piezoelectric beams through a series of iterations with design-model-fabrication-characterization cycles, demonstrating the feasibility of wearable piezoelectric energy harvesting. |
