Ultrasound for Data Transfers from Deep Implants: an Experimental Comparison Between Binary-Frequency-Shift-Keying and On-Off-Keying with Backscatter Modulation

Implantable devices need to communicate information to the outside world. For deep-seated miniaturized implants ultrasound communication can be favourable. However, implants need to operate during movement, and the selected communication scheme should be assessed accordingly. In this work, we implemented a simple protocol to transfer data packets based on On-Off-Keying (OOK) and Frequency-Shift-Keying (FSK) by backscatter modulation in ultrasonic communication links for deep implants. We then used it to compare FSK vs OOK encoding regarding the bit error rate during continuous ultrasound power transfer, and while moving, in a water tank setup. Our experiment shows, that sub-millimeter movements can have severe effects on OOK communication, but not for FKS. Therefore, FSK can allow for backscatter communication from deep implants regardless of their position and involved movements. The protocol can also be adapted to other backscatter modulation schemes in the future.