Miniaturized Fully Passive Brain Implant for Wireless Neuropotential Acquisition

We present an <inline-formula><tex-math notation="LaTeX">$8.7\ \text{mm} \times 10\ \text{mm}$</tex-math> </inline-formula> fully passive brain implant, capable of wireless acquisition of neuropotentials down to <inline-formula><tex-math notation="LaTeX">$20\, \mu \text{V}_{\rm{pp}}$</tex-math></inline-formula>, 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 <inline-formula><tex-math notation="LaTeX">$f_{\rm{neuro}}$</tex-math> </inline-formula>. The mixing products (<inline-formula><tex-math notation="LaTeX">$4.8\ \text{GHz}\,\pm \, f_{\rm{neuro}}$</tex-math></inline-formula>) are then transmitted back to the external interrogator and further demodulated to retrieve <inline-formula><tex-math notation="LaTeX">$f_{\rm{neuro}}$</tex-math></inline-formula>. Previous work demonstrated a <inline-formula><tex-math notation="LaTeX">$15\ \text{mm} \times 16\ \text{mm}$</tex-math> </inline-formula> wireless and fully passive brain implant, capable of detecting emulated neuropotentials as low as <inline-formula><tex-math notation="LaTeX">$63\, \mu \text{V}_{\rm{pp}}$</tex-math></inline-formula>. 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.

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