A High-Sensitivity Fully Passive Neurosensing System for Wireless Brain Signal Monitoring

Abstract

Abstract-A high-sensitivity, fully-passive neurosensing system is presented for wireless brain signal monitoring. The proposed system is able to detect very low power brain-like signals, viz. as low as -82 dBm (50 μVpp) at fneuro > 1 kHz. It is also able to read emulated neural signals as low as -70 dBm (200 μVpp) at fneuro > 100 Hz. This is an improvement of up to 22 dB in sensitivity as compared to previously reported neural signals. The system is comprised of an implanted neurosensor and an exterior interrogator. The neurosensor receives an external carrier signal and mixes it with the neural signals prior to retransmitting to the interrogator. Of importance is that the implanted neurosensor is fully passive and does not require a battery nor rectifier/regulator, but is concurrently wireless for unobtrusive neurosensing with minimal impact to the individual's activity. To achieve this remarkable high sensitivity, the sensing system employed: (a) a sub-harmonic mixer using an anti-parallel diode pair (APDP), (b) a pair of implanted/interrogator antennas with high transmission coefficient, |S21|, and (c) a matching circuit between the implanted antenna and the mixer. This neurosensing system brings forward a new possibility of wireless neural signal detection using passive brain implants.Index Terms-Anti-parallel diode pair (APDP), brain implant, neurosensing, passive, wireless medical telemetry, sub-harmonic mixing.

A Wireless Fully Passive Neural Recording Device for Unobtrusive Neuropotential Monitoring

“…However, to be able to read all neural signals generated by the human brain (see Table I [1], [14]- [16]), further improvement in sensitivity is needed. We also remark that the proof-of-concept implant reported in [13] was big (footprint of 39 mm × 15 mm) and non-biocompatible. Thus, it was unsuitable for realistic applications.…”

“…Our objectives entail: (a) fully-passive implants (no battery, energy harvesting unit, or rectifier/regulator), (b) wireless operation for unobtrusive monitoring with minimum impact to the individual's activity, (c) extremely simple electronics that generate minimal heat, and (d) tiny footprint to minimize trauma [12], [13]. Recently, we demonstrated a proof-ofconcept wireless fully-passive neural recording device with high detection sensitivity [13]. Specifically, in frequencydomain, the implant in [13] could detect emulated brain signals of 200 μV pp at f neuro = 100 Hz, to as low as 50 μV pp at f neuro = 1 kHz.…”

“…Recently, we demonstrated a proof-ofconcept wireless fully-passive neural recording device with high detection sensitivity [13]. Specifically, in frequencydomain, the implant in [13] could detect emulated brain signals of 200 μV pp at f neuro = 100 Hz, to as low as 50 μV pp at f neuro = 1 kHz. In time-domain, the aforementioned device could detect neuropotentials of 670 μV pp at f neuro = 100 Hz, to as low as 200 μV pp at f neuro = 1 kHz.…”

“…In this paper, we build upon our previous work [13] to design a novel wireless fully-passive neural recording device that: (a) has 59% smaller footprint, (b) exhibits up to 20 dB improvement in neuropotential detection sensitivity, and (c) is encapsulated in biocompatible polymer. To mimic realistic implantation scenarios, the device is tested inside a 4-layer (skin, bone, grey matter, white matter) head phantom [17]- [19].…”

System-Level Design of a Full-Duplex Wireless Transceiver for Brain–Machine Interfaces

“…Wireless implantable devices can be powered by two different methodologies: 1) with an un-chargeable battery or energy harvester, or 2) wirelessly from external sources by an antenna or an inductive coil [10][11][12][13][14][15]. Since we target permanent implants for a high number of electrodes, we do not consider the first option.…”