Passive UHF RFID near field link budget for implanted sensors

The precise estimation of the communication range for a passive wireless implanted sensor is an essential system design parameter in medical telemetry research. Path loss measurements between an RFID reader antenna and an implanted biosensor at UHF band were performed in an anechoic chamber representing two scenarios: depending on whether the reader is worn by a medic within 1 meter distance from the implant or by the patient in a shirt pocket. Near-field measurements in the first scenario proved that a passive RFID communication link can be established within 0.46 m for the considered subcutaneous implant. As the gain of the implanted antenna is quite low, the impact of the feeding cables on the results of the second scenario have been estimated by simulations of the measurement set up embedded. This uncertainty is due to the radiation and reflection coming from the feeding cables and it increases with the distance between the two antennas. A methodology is presented to estimate this uncertainty for a proper link-budget estimate.