An RFID-Based Closed-Loop Wireless Power Transmission System for Biomedical Applications

This brief presents a standalone closed-loop wireless power transmission system that is built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader (TRF7960) operating at 13.56 MHz. It can be used for inductively powering implantable biomedical devices in a closed loop. Any changes in the distance and misalignment between transmitter and receiver coils in near-field wireless power transmission can cause a significant change in the received power, which can cause either a malfunction or excessive heat dissipation. RFID circuits are often used in an open loop. However, their back telemetry capability can be utilized to stabilize the received voltage on the implant. Our measurements showed that the delivered power to the transponder was maintained at 11.2 mW over a range of 0.5 to 2 cm, while the transmitter power consumption changed from 78 mW to 1.1 W. The closed-loop system can also oppose voltage variations as a result of sudden changes in the load current.

I. Introduction

Passive radio-frequency identification (RFID) tags and certain implantable microelectronic devices (IMDs) such as cochlear implants do not include batteries due to cost, size, weight, safety, and lifetime limitations. Inductive power transmission provides these devices with the required power on a continuous basis [1], [2]. In these systems, wireless power transmission across a pair of loosely coupled coils is preceded by a power amplifier (PA) in the external unit and followed by an efficient rectifier in the implanted unit to provide the IMD with an unregulated supply [3].