Galvanic-Coupled Trans-Dural Data Transfer for High-Bandwidth Intracortical Neural Sensing

A digital-impulse galvanic coupling as a new high-speed trans-dural (from cortex to the skull) data transmission method has been presented in this article. The proposed wireless telemetry replaces the tethered wires connected in between implants on the cortex and above the skull, allowing the brain implant to be 'free-floating' for minimizing brain tissue damage. Such trans-dural wireless telemetry must have a wide channel bandwidth for high-speed data transfer and a small form factor for minimum invasiveness. To investigate the propagation property of the channel, a finite-element model is developed, and a channel characterization based on a liquid phantom and porcine tissue is performed. The results show that the trans-dural channel has a wide frequency response of up to 250 MHz. Propagation loss due to micromotion and misalignments is also investigated in this work. The result indicates that the proposed transmission method is relatively insensitive to misalignment. It has approximately 1-dB extra loss when there is a horizontal misalignment of 1 mm. A pulse-based transmitter application-specific integrated circuit (ASIC) and a miniature printed circuit board (PCB) module are designed and validated ex vivo with a 10-mm-thick porcine tissue. This work demonstrates a high-speed and miniature in-body galvanic-coupled pulse-based communication with a data rate up to 250 Mb/s with an energy efficiency of 2 pJ/bit and has a small module area of only 26 mm2.