Open Hardware: Towards a Fully-Wireless Sub-Cranial Neuro-Implant for Measuring Electrocorticography Signals

Abstract

Implantable invasive neuronal interfaces to the brain are an important keystone for many interesting future medical applications. However, entering this field of research is difficult since such an implant requires components from many different fields of technology. Beside the required amplifiers, analog-digital-converters and data processing, the complete avoidance of wires is important because it reduces the risk of infection and prevents long-term bio-mechanical problems. Thus, means for wireless transmitting data and energy are also necessary.We present a module, containing the necessary components for wireless data transfer and inductive powering for such implantable neural systems, and its base station. They are completely built of commercial off-the-shelf (COTS) components and the design files are available as Open Hardware / Open Source. The data is transmitted via Microsemi ZL70102 transceivers and custom Tx/Rx antennas for bidirectional communication using frequencies in the MICS band, with a maximal data rate of 515 kbit/s. The energy is transmitted via a wireless inductive energy-link based on the Qi standard. On the implant site a handwound litz wire coil harvests energy from the magnetic field and delivers, over a short distance, more than enough inductive power to the fully implantable unit.Based on this wireless module we also present a fully wireless neuronal implant for simultaneously measuring electrocorticographic (ECoG) signals at 128 locations from the surface of the brain. The implant is based on a flexible printed circuit board and is aimed to be implanted under the skull. 1The application-specific integrated circuit (ASIC) was designed in-house and allows to adapt the data processing of the implant to changing user-defined parameters.

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“…Also a lot of small projects were developed in different laboratories including both recording and stimulation options [2,4,9,16,27].…”

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“…The ultimate goal in the future is to develop a medial implant allowing intracortical stimulation. The challenges of building such a fully implantable wireless system [82,83,84,85,86,87], [88,89] arise from the necessity to obey multiple constraints: the height is restricted, especially if the implant should be placed between the skull and the brain [90] for improving long term stability. Here, possible pressure to the brain tissue is an additional problem [91,92,93].…”

“…The best way to supply the internal components with power is not determined yet (e.g. [82,102,103,104,105]). For the wireless transfer of data two different approaches can be taken: 1.)…”

“…Data transfer via radio-frequency transmissions (e.g. [82,102,106,107,108,109,110,111,112,113,114,115,116,117]). 2.)…”