An analysis of the coupling effect for a hybrid piezoelectric and electromagnetic energy harvester

This paper investigates the influence of the electromechanical coupling effect on the performances of a hybrid piezoelectric and electromagnetic energy harvester. For a common hybrid energy harvester, we derive an accurate analytical solution and get expressions for the resonant frequency shift, output power, amplitude and conversion efficiency. Then, based on various degrees of coupling effect, the performance of the harvester is studied with different load and excitation frequency, and compared with piezoelectric-only and electromagnetic-only energy harvesters. The results show that the bigger the coupling coefficient, the greater the resonant frequency shift, output power and conversion efficiency. In the weak coupling and medium coupling, the performances of the hybrid energy harvester are better than those of the two separate energy harvesting techniques; however, the hybrid energy harvester does not increase the power and conversion efficiency in contrast with the piezoelectric-only and electromagnetic-only energy harvester in strong coupling. In addition, the optimal load resistance of the hybrid energy harvester is related to the strength of the coupling effect; moreover, the optimal load resistance of the electromagnetic harvesting element for the hybrid harvester is bigger than that of the electromagnetic-only harvester in the medium and strong coupling. Through analysis of the results, ways of boosting the performances of the hybrid energy harvester are found.