Design and Development of an External Processing Unit for Wireless Power and Data Transmission to Miniaturized Neural Implants for Reverting Blindness

For decades, the investigation of brain functionalities has been a point of care for neuroscientists. The accelerated progress of knowledge of the neural motor system and the significant advances in nano- and micro-technology have led to solid growth in implantable devices technology. Despite the promising prospects of these devices, most of these implants still face limitations due to the bulky implant, the wiring, the limited number of channels, and the invasiveness of the surgical procedure, which cause significant risks for the patient and may cause the failure of the implant. The next generation of implantable neural devices aims to build battery-free, miniaturized, and wirelessly powered implants to achieve a new approach for neural interfaces, thus developing innovative implantable neural prostheses to restore impaired or lost neurological functions. Ultra-miniaturized and wirelessly powered devices, freely distributed in the human brain, are the cornerstone of Neural Dust. Starting from this concept, the ongoing research project in which my master’s thesis is inserted aims to develop an innovative CMOS-based cortical neuroprosthesis to restore vision by stimulating the visual cortex through penetrating and intracortical microelectrodes. This work, carried out in Bio/CMOS Interfaces group at Integrated Circuits Laboratory (EPFL, Neuchâtel), has focused on the design and optimization of the External Processing Unit (EPU) for such cutting-edge cortical prostheses. The EPU includes the: i) video-capturing unit; ii) image processing system; and iii) radiofrequency (RF) base station for simultaneous power and data transfer through an innovative 3-coils inductive link. The transmitter coil was designed and fabricated, focusing on the power transmission and bandwidth trade-off. The adopted solution is based on an L-type impedance matching circuit, and the optimization has been achieved with coils of different shapes and sizes. The printed circuit board (PCB) of the RF base station has been designed and manufactured starting from the work of Barbruni et al. [1] and Barbara Gentile [2]. The system generates an amplitude-modulated RF signal at 433,92 MHz by deploying the amplitude-shift keying (ASK) modulation technique and can deliver 32 dBm combined with a data rate up to 10Mbps and a modulation index of 15.7%. The acquisition and processing of the images and the information delivery to the PCB have been programmed to be synchronous to ensure the real-time operation of the entire process flow. Each frame is captured from a webcam and processed in real-time with a segmentation algorithm implemented in MATLAB software and sent via UART to the RF base station, ensuring data modulation. Finally, validation experiments were conducted on the completed system setup. Based on the satisfactory results, the project concluded with the design and manufacturing of a plastic package for the entire EPU. The latter can wirelessly transmit information regarding the activation and the intensity of the stimulation of each active pixel of each frame toward the implanted free-floating CMOS-based units in real-time.