Performance of epidermal RFID dual-loop tag and on-skin retuning

Originally introduced by the material science community, the epidermal electronics is now collecting interest also among antenna engineers for the potentiality to achieve thin and flexible sensing transponders that are suitable to application over the epidermis. Unlike conventional wearable antennas, which are generally decoupled by the lossy human body by means of spacers or shielding sheets, epidermal tags need to be placed at a very close touch with the skin thus providing poor communication capabilities. This paper investigates, by means of a detailed numerical and experimental study, the performance of an epidermal dual-loop tag for UHF radiofrequency identification (RFID) depending on the specific placement over different parts of the human body and for a variety of volunteers. An on-body tuning mechanism is also introduced and demonstrated in real applications at the purpose to improve the tag response and hence to enable the use of a same tag layout for all the UHF-RFID bands and for several placement loci.