Piezoelectric–Electromagnetic Hybrid Energy Harvesting System: When is it Useful?

We investigate the performance of a hybrid energy harvesting system composed of piezoelectric and electromagnetic transducers. We introduce effective figures of merit for the piezoelectric and electromagnetic generators that combine the transducer coupling and resistive loss. The maximum output power of single–transducer and hybrid systems are determined analytically, expressed as functions of effective figures of merit. A solution of the conditions under which a resonant hybrid harvester system with multiple transduction mechanisms can outperform its counterpart that uses a single energy conversion is derived. We also find that there is no benefit to utilizing a hybrid system if one of the two, or both, effective figures of merit exceeds a threshold of ${\mathcal{M}^{\ast}} \approx 2.38$.