pre-printThis paper explores a subdermal RFID antenna at 918 MHz. The antenna, made from ink encapsulated in thin sheets of biocompatible PET, is designed to be implanted in the fat layer just below the skin, with the muscle acting as a lossy ground plane. The antenna is a patch that uses a T-slot for matching. Three materials are tested - aluminum tape, ELCOAT ink, and inkjet printing. The effect of antenna conductivity and the properties of the fat/skin and muscle layers are explored. The ELCOAT ink performs very similar to the aluminum, but the inkjet printing creates a very thin layer that is subject to skin depth effects. This RFID antenna provides a good proxy for next generation work on subdermal antennas. It demonstrates that the fat layer can sufficiently insulate the antenna to enable subdermal applications, and that the muscle acts like a sufficient ground plane, but without the challenges of a PEC ground plane very near the antenna. The antenna could also be used on the skin surface if the impedance is properly tuned
