Making a telemetry system implantable: Challenges and opportunities in antenna design

Design of a proximity coupled implantable planar inverted F-antenna (I-PIFA) is presented. It's to be operated in the Australian 900MHz ISM band (915-928MHz). This antenna, integrated to an existing Radio Frequency Identification (RFID) tag, will be implanted under the skin of rats for medical research. The main purpose of this wireless telemetry system is to transmit the extracted physiological signals and indicators from the body of the rat to an external RFID reader connected to a computer. The total volume of the antenna is 9.25mm×8mm×3.2mm and the larger ground plane of the RFID circuit board is utilized to improve the performance of the antenna. A skin-fat-muscle planar tissue model has been developed to represent the immediate environment around the antenna, which has been coated with a bio-compatible material. The simulations have shown that the effect of rat skin and the bio-compatible coating on antenna matching is significant. Yet with the conservative antenna design proposed here that has a nominal 10dB return loss bandwidth of 15%, the antenna remain matched over the entire ISM band even if the dielectric constants of the rat skin and bio-compatible coating change over a wide range.