A Current-Switching Communication Technique for Miniaturized Medical Implants

Miniaturization of the medical implants is a key requirement for minimally-invasive surgery, while battery and antenna are the main bottlenecks. Wireless power transfer (WPT) is required to minimize or eliminate the battery, but the conventional inductive or capacitive WPT needs to implant a large inductor or capacitor to realize a relatively high efficiency. Based on the WPT, backscattering communication is widely used in medical implants due to its low power and low hardware cost. In conventional backscattering, the inductive or capacitive antenna of the implant should be large to improve the signal-to-noise ratio (SNR). In this work, we propose a new current-switching technique for the communication of medical implants. To avoid the use of antennas, the body tissue is utilized as the power-transfer medium, where a current loop is formed between the implanted and the external electrode pairs. The data of the medical implant controls its input impedance, and then switches the current loop, resulting in a data-modulated current in the external device. In this way, the external device can sense the data, achieving a high communication SNR without implanted antenna. A prototype is implemented to validate the proposed technique, where the implanted electrodes are as small as 200µ×200µm. Operating at 406 MHz of the standard medical band, the measurement shows that the signal-to-blocker ratio (SBR) achieves -35.7 dB, resulting in a high communication SNR of 21.9 dB at a data rate of 10 Mbps.