Wireless power recharging for implantable bladder pressure chronic monitoring

This paper presents a wireless power recharging system design for implantable bladder pressure chronic monitoring application. The power recharging system consists of an external 6-turn 15-cm-diameter powering coil and a silicone-encapsulated implantable spiral coil with a dimension of 7 mm × 17 mm × 2.5 mm and 18 turns, which encloses a 3-mm-diameter 12-mm-long rechargeable battery, two ferrite rods, an ASIC and a tuning capacitor. The ferrite rods are employed to improve the quality factor of the implantable coil. For a constant charging current of 100 μA, an RF power of 700 μW needs to be coupled into the implantable microsystem through tuned coil loops. With the two coils aligned coaxially or with a tilting angle of 30° and 6 cm offset in coils axes, an external power of 3.5W or 10W is required, respectively, for a large coupling distance of 20 cm at an optimal frequency of 3 MHz. The ASIC implemented in a 1.5 μm CMOS process can provide on-chip rectification for an incoming RF signal and generate a scalable charging current with logic control capability for battery recharging.