| Wireless power transmission is used in a variety of applications including medical devices and consumer electronics. Surgical placement of implantable medical devices (IMDs) has limited precision, and after implantation the device can move over time. Accurate knowledge of the position of IMDs allows better interpretation of data gathered by the devices, and may allow wireless power to be focused on the IMD thereby increasing power transfer efficiency. Existing positioning methods require device sizes and/or power consumption which exceed the limits of in-vivo mm-sized IMDs applications. A novel implant positioning scheme by sensing the back-scattered electromagnetic (EM) field is proposed to overcome those disadvantages and hence is considered ideal for power and area constrained IMDs and suitable for wearable devices. First, the external transmitting (TX) coil of a wireless power transfer link is replaced by an array of smaller coils. Second, back-scattered electromagnetic field is measured between each coil in the TX array and the implanted receiving (RX) coil. Third, spatial variation in that field is used to estimate the location of the implanted device. This method does not increase the hardware or power consumption in the IMD. 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 mm. Different on-chip implementation for measuring the back-scattered EM field and their trade-offs are described. Power and data communication ranges for backscattering systems is also investigated and compared using RFID as an example. Finally, conclusions are presented. |
