Miniaturized Fully Passive Brain Implant for Wireless Neuropotential Acquisition

We present an 8.7 mm × 10 mm fully passive brain implant, capable of wireless acquisition of neuropotentials down to 20 μV
_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 × 16 mm wireless and fully passive brain implant, capable of detecting emulated neuropotentials as low as 63 μVpp . 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.