Wireless energy harvesting using time reversal technique: An experimental study with numerical verification

Fully embedded devices and portable devices located in inaccessible areas may be constrained in terms of service lifespan due to limitations in battery capacity. Furthermore, conventional electromagnetic-based wireless charging may be difficult due to environmental interference. Thus, in this article, we present a method that can remotely charge such devices through piezo-generated stress waves that propagate along the structure hosting the device to be charged. However, in order to fully utilize such a conduit for transmitting energy, the dispersive and scattering nature of solid materials should be overcome. As a way to overcome this obstacle, the method innovatively applies the time reversal technique for use in energy harvesting. Through the time reversal technique, the energy transmitted by external actuators, instead of dispersing unhelpfully around the device, can be focused tightly at the energy harvesting component of the device. The method was successfully demonstrated on a copper pipe using four piezoelectric transducers. It was further found that time-reversed signals from multiple actuators can linearly superimpose to increase the amount of energy focused on the energy harvester, thus potentially solving problems related to distance and the signal attenuating properties of the material in the hosting structure. The method was also modeled and simulated using the finite element method through the commercial FE-package Abaqus. Results from both experiment and simulation matched well, thus demonstrating the viability of the wireless energy harvesting method.