MEMS-Based Inductively Coupled RFID Transponder for Implantable Wireless Sensor Applications

In this paper, we present the development of an inductively coupled mini RFID transponder using MEMS technology for implantable wireless sensor applications. The transponder (approximately 25 mm³ in volume) consists of a small solenoid inductor with a high-permeability magnetic core (dia.=750 mum), a chip capacitor and a RFID chip. They are integrated onto a micromachined SU8 polymer substrate and it is operated in the frequency range of 13.56-27 MHz. Voltages up to 4 V were obtained at a small 0.5 muH transponder coil from a 2.2-muH reader coil at 5 mm distance based on a resonant magnetic coupling mechanism. The assembled transponder was tested using a commercial RFID reader at 13.56 MHz and successful communication was established at a distance of 10 mm.