Harnessing vibration energy by inverted fork harvester with electromagnetic and piezoelectric effects

In this study a hybrid scheme for harnessing vibration energy is proposed, which incorporates both electromagnetic and piezoelectric effects into a bi-stable fork-shaped harvester to increase the harvesting efficiency. This harvester consists of a fork-shaped inverted beam, three tip magnets and an iron-core coil, it can realize jumping between potential wells within a broadband frequency range. Under base excitations, the fork-shaped structure oscillates and jumps between potential wells, making the magnetic flux through the coil change dramatically and thus generating large electric output. Meanwhile, the piezoelectric material bonded to the root of fork-shaped structure deflects greatly and generates electric output through piezoelectric effect. This combination of electromagnetic and piezoelectric effects can promote the harvesting performance significantly. Theoretical analyses and simulations are carried out. The validation experiments are conducted. The experiment results prove that the hybrid energy harvester owns a wide working frequency band. The system can execute jumping between potential wells under weak random excitations and generates large outputs. For a random excitation with power spectral density (PSD) of 0.065 g²/Hz, the electromagnetic root mean square (RMS) power can reach 2.626 mW.