A New Wireless Power Transmission (WPT) System for Powering Wireless Sensor Networks (WSNs) in Cavity-Based Equipment

Abstract

We introduce a new cavity-based wireless power transmission (WPT) system that could be applied to any cavity-based equipment regardless of its shape and size. The proposed scheme provides uniform and selective powering modes. In either powering mode, the field is isotropic, which removes the WPT-restrictions on placement and orientation of the energy harvester. The design process has three main steps, randomness creation, frequency selection, and waveform generation. We validate the proposed scheme in a lab lyophiliser’s (freeze-drier) chamber. First, we create a random electromagnetic environment using mechanical stirring. Then, we evaluate this randomness in terms of the average to minimum power ratio. To select an appropriate frequency for the WPT system, we consider randomness and power uniformity. To maintain randomness, we extract the lowest usable frequency of the chamber using a Goodness of Fit test; this is found to be 6 GHz. As for the power uniformity, we plot the standard deviation (STD) of a large sample of the received powers at different locations. This plot is used to select the frequency based on an arbitrary uniformity level in terms of STD. At 6 GHz a 2.5 dB standard deviation is calculated. To enable the selective powering mode, we propose the electromagnetic time reversal (EMTR) technique. We show that EMTR can, theoretically, focus 97% of the energy on 0.5λ-diameter area in an ideally random environment.