Asimina Kiourti, Cedric W.L. Lee, Junseok Chae, and John L. Volakis, The Ohio State University, Arizona State University, USA
Brain implant technology has a strong potential to improve the individual’s well-being. However, current brain implants lack the safety and reliability required for unobtrusive, long-term monitoring of neuropotentials. In this work, we propose a novel technology for safe and reliable neuropotential recorders. Our objectives entail: a) fully-passive operation, implying no active devices/components exist within the implant, b) wireless operation for unobtrusive monitoring with minimal impact to the individual’s activity, c) extremely simple on-board electronics that generate insignificant heat to ensure patient safety, and d) integration of all required electronics in a tiny footprint to minimize trauma.
The implant has a footprint of 15 mm × 16 mm and can detect emulated neuropotentials down to 63 µVpp at 100 Hz – 5 kHz. This corresponds to a significant sensitivity improvement, a factor of 8, over prior work. The neural recorder incorporates several innovations, including a) an anti-parallel diode pair for the sub-harmonic implanted mixer with high conversion efficiency, and b) a pair of highly coupled interrogator and implanted antennas. Specifically, the proposed neurosensing system consists of two sub-systems: a) the fully-passive implant, and b) the external interrogator. The external interrogator sends a carrier of 2.4 GHz to turn on the mixer within the implant. Concurrently, the implant’s electrodes detect the neural signals at fneuro. Subsequently, harmonic mixing occurs to generate the signal at 4.8 GHz ± fneuro. This up-converted signal is then re-transmitted back to the external interrogator and demodulated to recover the neural signals at fneuro.
This is the first ever demonstration of wireless and unobtrusive reading of emulated neuropotentials as low as 63 µVpp. Such low voltage detection implies reading of most neuropotentials generated by the human brain. The highly-sensitive wireless fully-passive neural recorder provides for transformational health-status monitoring possibilities for epilepsy, prosthetics control, Alzheimer’s disease, and many neurological disorders.
Keywords – biomedical telemetry, brain sensor, brain implant, neuropotential recorder, miniaturization, neurosensing, passive circuits, sub-harmonic mixer, wireless circuits.