A General-purpose Configurable RFID Epidermal Board with a Two-way Discrete Impedance Tuning

Current advances of the Radiofrequency Identifi- cation (RFID) technology can boost the emerging class of bio- integrated skin devices exploiting low-power (even passive) wire- less communication and sensing interfaces. This work describes a small-size (3cmx3cm) flexible UHF RFID board conceived for the rapid laboratory experimentation and suitable to multi-purpose monitoring of physical parameters (e.g. temperature and sweat) over the skin and/or over clothing layers and medical plasters. An engineered open-loop antenna is coupled with a two-way discrete (four states) tuning circuit to compensate the frequency shifts that occur in real applications due to the intrinsic variability of the human body. The capability of the tuning mechanism to down/up-shift the operating frequency and to restore the default state is validated by means of both numerical simulation and measurements over some volunteers in realistic conditions.