Miniaturized Fully-Passive Brain Implant for Wireless Neuropotential Acquisition

We present an 8.7 mm x 10 mm fully passive brain implant, capable of wireless acquisition of neuropotentials down to 20 mu V-pp, viz. three times lower than before. The implant receives a 2.4-GHz carrier signal from the external interrogator and mixes it with the neurosignals having a frequency of f(neuro). The mixing products (4.8 GHz +/- f(neuro)) are then transmitted back to the external interrogator and further demodulated to retrieve f(neuro). Previous work demonstrated a 15 mm x 16 mm wireless and fully passive brain implant, capable of detecting emulated neuropotentials as low as 63 mu V-pp. In this letter, we present a new neurosensing system with the following improved features: 1) 63% smaller implant; 2) 98% smaller interrogator antenna; 3) compliance with the strictest Federal Communications Commission standards for patient safety; 4) elimination of lumped components within the implant to preserve biocompatibility; and 5) three-times sensitivity improvement. This high sensitivity implies reading of most neural signals generated by the human brain.