Development of a Novel Simultaneous Information and Power Transfer System to Inductively Address Miniaturized Neural Implants

Implantable medical devices have experienced a major development in the past years due to the super-miniaturization of mechanical structures and electronic circuits. Among the most innovative medical technologies, "Neural Dust" and "Body Dust" are two key concepts in the field of neural bio-implants for brain recording and spreadable bio-electronics for marker sensing respectively. Moreover, neurostimulation is a promising method to address several neurological and mental disorders. Toward this end, the project carried at Medtronic Chair in Neuroengineering (EPFL, Genève) and Integrated Circuits Laboratory (EPFL, Neuchâtel) aims to restore the sense of vision in blind patients. Brain implantation is challenging and the main target is to design a device less invasive as possible. To accomplish the minimal invasive intention, the best course of action is to send power and data from an external transmitter, avoiding the introduction of wires that easily lead to scarring and infections. In this work, a printed circuit board has been designed, fabricated and characterized starting from the study of Barbruni et al. [1] and optimizing it, redesigning the schematic around the components and inserting a microcontroller to exploit its serial peripheral interface. The PCB is a radiofrequency transmitter operating at 433.92 MHz with an amplitude-shift keying modulator that modulates the amplitude accordingly to the digital data, received from image processing, to individually address the implanted CMOS μelectrodes with the correct intensity. In addition to the PCB, a study of the 3-coil inductive link has been done with electromagnetic simulations, in particular to discover the best shape for the implanted secondary coil: the resonator. The coil with the highest quality factor, i.e. capability to boost electromagnetic field, was found to be a circular coil with 9 mm of diameter and 4 mm wide, encapsulated in biocompatible polydimethylsiloxane (PDMS). The resonator was consequently fabricated in cleanroom with 200 μm of encapsulating PDMS and then tested to verify the match with simulations. Moreover, some transmitting coils were printed to further test the transmitter. The results are promising, the PCB output is the expected one with small attenuations that have been adjusted in a new PCB design. The shape of the resonator with highest quality factor was found, the feasibility of its fabrication was confirmed and the measurements have proved that the simulations are reliable. [1] Barbruni et al. «A 20 Mbps, 433 MHz RF ASK Transmitter to Inductively Power a Distributed Network of Miniaturised Neural Implants». In: 2021 IEEE International Symposium on Medical Measurements and Applications (MeMeA). June 2021