Design, calibration and experimentation of an epidermal RFID sensor for remote temperature monitoring

An epidermal radiofrequency identification technology (RFID) sensor consists of a flexible antenna provided with a radiofrequency identification and sensing microchip directly stuck over the human skin by means of a sub-millimeter bio-compatible membrane. A compact-size epidermal RFID thermometer is here proposed and extensively experimented concerning its electromagnetic and thermal performance in case of battery-less and battery-assisted configurations. The antenna element embeds a mechanism for a post-manufacturing frequency retuning in order to adapt its response to the specific placement over the body. When attached over the skin, the sensor is readable from up to 0.7 m in battery-less mode and 2.3 m in battery-assisted mode. A calibration procedure improved the accuracy of the IC sensor down to 0.18 °C. The time constant evaluated by the first-order response of the IC to impulse heating (photo-flash) resulted in 4.3 s. The epidermal wireless thermometer was experimented in both supervised applications (manual reading) and in un-supervised architectures where users were continuously monitored by a fixed remote antenna or during the crossing of a surveillance gate. In all the considered cases, the reliability of the interrogation link was experimentally quantified and resulted robust for health monitoring applications in clinical and domestic settings and even for the automatic detection of anomalous temperature peaks of people walking within airports and at country border crossing.