Wireless power recharging for implantable bladder pressure sensor

This paper presents a wireless power recharging system design for implantable bladder pressure chronic monitoring application. The power recharging system consists of an external 4-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 further encloses an ASIC with a programmable charging current and logic control capability, a 3-mm-diameter 12-mm-long rechargeable battery, and two ferrite rods. The ferrite rods are employed to improve the quality factor of the implantable coil. For a constant charging current of 100 ¿A, an RF power of 2.4 mW needs to be coupled into the implantable microsystem through tuned coil loops. With the two coils aligned coaxially or with a tilting angle up to 30°, an external RF power of 7W or 25W is required, respectively, for a large coupling distance of 20 cm at an optimal frequency of 3 MHz.