Implant Position Estimation Via Wireless Power Link

Wireless power transmission is widely used in implantable medical devices (IMDs). Surgical placement of IMDs has limited precision, and after implantation, the device can move over time. Accurate knowledge of the IMD´s position enables better interpretation of data sensed by the device and may allow wireless power to be focused on the IMD, thereby increasing power transfer efficiency and enabling greater implant depth. Existing positioning methods require device sizes and/or power consumption that exceed the limits of in vivo millimeter-sized IMD applications. We have previously proposed a novel implant positioning scheme by sensing the backscattered electromagnetic (EM) field to overcome those disadvantages, which is hence considered ideal for power- and area-constrained IMDs and suitable for wearable devices. This paper briefly reviews the previously proposed localization scheme and reports the progress of this research. Specifically, different approaches to realize this scheme are discussed and compared. Localization experiments in free space are then demonstrated, and the accuracy is shown on the order of millimeters. Different on-chip implementation procedures of measuring the backscattered EM field and their tradeoffs are described. Finally, conclusions and the future plan are presented.