Compact Conformal Tattoo-Polymer Antenna for On-Body Wireless Power Transfer

Abstract A tattoo-polymer loop antenna is proposed for designing a wearable rectenna that can be used for on-body wireless power transfer. The proposed antenna can be easily printed on a piece of flexible tattoo paper and transformed onto a PDMS substrate, making the entire antenna structure conformal to human body. Here, a layer of frequency selective surface (FSS) is inserted in between the antenna and human tissue for improving the radiation performance. The FSS layer has successfully reduced the loading effects of the tissue, and it can improve the antenna gain as much as 13.8 dB. Also, the operating frequency of the rectenna is not affected much by deformation. To maximize the RF-DC conversion efficiency, a matching loop, a matching stub, and two coupled lines are integrated with the antenna for tuning the rectenna so that a wide bandwidth (~ 24%) can be achieved. The proposed rectenna design is simple as it does not require the use of any matching networks. Measurement results show that the proposed rectenna can achieve a maximum conversion efficiency of 59.0% with an input power of 5.75 µW/cm2. The efficiency can even exceed 40% for a low input power of 1.0 µW/cm2 with a 20 kΩ resistive load.