Optical Wireless Power Transfer for Clothing-Covered Wearables

This paper presents a preliminary study on the use of optical wireless power transfer (OWPT) for supplying power without wires to wearables even when they are covered. System description is first given, then theoretical backgrounds on OWPT systems with covered optical receivers are introduced. Next, experimental results on simple tests for an OWPT are provided, in which the optical transmitter is an LED and the optical receiver is a silicon solar cell. The solar cell is covered by two different materials namely a cotton shirt sleeve and a double-layer paper napkin in order to compare the OWPT performance. It is then shown from experimental results that the transparency, i.e. the optical transmittance, of the paper napkin is much better than that of the cotton shirt sleeve. Lastly, additional experiments are carried out for different numbers of paper napkin layers that evaluate the theoretical optical transmittance formula. It then turns out that the Beer-Lambert law is invalid to capture the efficiency of OWPT in the considering context. The obtained results also give hints for choosing suitable clothing materials and for system design in order to have a high performance OWPT system for clothing-covered wearables.