A nonlinear two-degree-of-freedom electromagnetic energy harvester for ultra-low frequency vibrations and human body motions

Converting the ambient waste energy into electricity has been considered as an effective approach for sustaining low-power devices. One of the key issues is how to generate more electricity from ultra-low frequency excitations that are ubiquitous in our environment. To tackle this problem, this paper presents a two-degree-of-freedom (2-DOF) electromagnetic energy harvester (EMEH) that is realized simply by magnetically levitating a 1-DOF EMEH in a cylindrical housing. Both experiment and simulation exhibit the advantages of the proposed design, including the tunable operating frequencies, improved power output, and extended operating bandwidth. The experimental measurements show that, under a sinusoidal excitation with an amplitude of 0.5g (1 g= 9.8 m/s(2)), nearly 40% increase in the magnitude of the power and 152% increase in the operating bandwidth are achieved by the proposed harvester. Under the hand-shaking induced excitation, the 2-DOF EMEH can enhance the voltage of a capacitor (33 mu F) from 0 V to 5 V within half a second, showing a charging performance much better than that of the 1-DOF EMEH. Moreover, the 2-DOF EMEH successfully sustains the continuous operation of a hygrothermograph using the energy converted from human body motions, demonstrating its potential application in powering some wearable electronics. (C) 2019 Elsevier Ltd. All rights reserved.