Bi-Phasic Quasistatic Brain Communication for Fully Untethered Connected Brain Implants

Abstract

Wireless communication and powering in a brain implant for freely moving subjects has been a research area of paramount importance in the recent past due to the multitude of medical, neuroscientific and societal applications that it can unveil. Unfortunately, traditional electromagnetic (EM) fields are significantly absorbed in the brain tissue, making it imperative to explore alternative modalities of signal transfer. Recently investigated ultrasonic, optical and magneto-electric modes of communication/powering suffer from large transduction losses when converting electrical energy to other forms of energies (and vice versa) during field transduction, leading to high end-to-end system loss (> 80 dB). To solve the challenge of powering and communication in a brain implant with low end-end channel loss, we present Bi-Phasic Quasistatic Brain Communication (BP-QBC), which achieves < 60 dB worst-case end-to-end channel loss at a channel length of ~55 mm, by using Electro-quasistatic Signaling that avoids transduction losses due to no field-modality conversion. BP-QBC utilizes dipole coupling based signal transmission within the brain tissue using differential excitation in the transmitter (TX) and differential signal pick-up at the receiver (RX), and uses electroquasistatic (EQS) signaling for low-leakage and low-power. Understanding that the EQS signal transfer through the brain channel occurs through AC electric fields, while the primary source of power consumption is due to galvanic DC currents arising from the finite conductivity of brain tissues, we propose to block the DC current paths through the tissue using a DC-blocking capacitor without significantly affecting the bi-phasic AC communication at EQS frequencies. The power consumption in the BP-QBC TX is only 0.52 μW at 1 Mbps (with 1% duty cycling), which is within the range of harvested power from an external wearable to the brain implant through the EQS brain channel, and is ~41× lower than traditional Galvanic Human Body Communication at 1 MHz. Furthermore, unlike optical and ultrasonic techniques, BP-QBC does not require sub-cranial interrogators/repeaters as the EQS signals can penetrate through the skull and has enough strength due to the low loss channel. Such low end-to-end channel loss with high data rates enabled by a completely new modality of brain communication and powering has deep societal and scientific impact in the fields of neurobiological research, brain-machine interfaces, electroceuticals and connected healthcare.