A Tightly Integrated Multilayer Battery Antenna for RFID Epidermal Applications

For the acceptance of biointegrated devices in daily life, radio systems must be developed, which are minimally invasive to the skin, and they must have ultralow-profile local power sources to support data-logging functionality without compromising shape conformability. This contribution proposes a tightly integrated multilayer battery-antenna system (65 x 23 mm(2)), that is, ultrathin (just 200 mu m), flexible, and lighter than 1 g, making it suitable for epidermal applications. The negative electrode (anode) current collector of the battery is a radio frequency identification tag antenna coated by a conductive polymer (Pedot:PSS) working as anode material. Since the battery is a dynamic device, subjected to discharging, the antenna design must include the variable dielectric properties of the conductive polymer which are here first characterized in the UHF band for real charge/discharge battery conditions. The communication performance of the prototype composite device is hence evaluated through the measurement of the realized gain of the tag antenna (-19.6 dBi at 870 MHz) when it is placed directly onto a volunteer's forearm. The read range of 1.3-3 m is suitable for occasional data download from the epidermal data logger when the user comes close to a reader-equipped gate.