A wireless charging mechanism for a rotational human motion energy harvester

Abstract

Motion energy harvesting is a sought after alternative to battery powering for implanted and body worn devices. However, the lack of electricity generation at rest is a major concern. This paper describes a previously presented piezoelectric rotational motion harvester, and presents a mechanism for wireless and external actuation of the main rotor of the device through a magnetic reluctance coupling. With this approach, an internal battery or super-capacitor could be recharged during prolonged periods of inactivity. An improved experimental setup uses a stepper motor to accurately prescribe even high actuation frequencies. A single stack and diametrically opposed dual stacks of driving magnets are investigated. It is demonstrated that adding the additional magnet stack is detrimental to the system performance. Furthermore, the system was tested in a horizontal and a gravity-independent vertical arrangement. Power can successfully be generated regardless of orientation. The maximal separation between driving magnets and harvester reached 20 millimeters. Lastly, the device can operate even under misalignment, and the optimal driving frequency is 25 Hertz, at which over 100 microwatts of power were generated for a device with a functional volume of 1.85 cubic centimeters.