Self-Tuning UHF Epidermal Antennas

Epidermal sensors based on Radiofrequency Identification are suitable to be attached onto the skin like a thin and flexible plaster and allow collecting biophysical parameters with a high level of comfort for the user. When working in the UHF band (860-960 MHz), the on-skin antenna performance (impedance matching and the corresponding read distance) is strongly dependent on the region of the human body where it is attached and by the body mass of the user. The self-tuning UHF epidermal RFID tag, based on a multi-state RFID IC, is a placement-robust RFID skin device that can automatically and dynamically modify its internal impedance depending of the boundary condition seen by the antenna. The epidermal sensor, also capable to measure skin temperature, preserves a realized gain variation of \pm 2.5 dB for applications in the same part of the body of some volunteers. It provides a read distance of more than 1 m in the whole worldwide RFID band (860-960MHz), with 60% of probability, for any considered positions and users and up to 90% of probability in case of application on abdomen or arms.