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Goal: We propose a novel wireless fully passive neural recording device for unobtrusive neuropotential monitoring. Previous work demonstrated the feasibility of monitoring emulated brain signals in a wireless fully passive manner. In this paper, we propose a novel realistic recorder that is significantly smaller and much more sensitive. Methods: The proposed recorder utilizes a highly efficient microwave backscattering method and operates without any formal power supply or regulating elements. Also, no intracranial wires or cables are required. In-vitro testing is performed inside a four-layer head phantom (skin, bone, gray matter, and white matter). Results: Compared to our former implementation, the neural recorder proposed in this study has the following improved features: 1) 59% smaller footprint, 2) up to 20-dB improvement in neuropotential detection sensitivity, and 3) encapsulation in biocompatible polymer. Conclusion : For the first time, temporal emulated neuropotentials as low as 63 μVpp can be detected in a wireless fully passive manner. Remarkably, the high-sensitivity achieved in this study implies reading of most neural signals generated by the human brain. Significance: The proposed recorder brings forward transformational possibilities in wireless fully passive neural detection for a very wide range of applications (e.g., epilepsy, Alzheimer's, mental disorders, etc.). [ABSTRACT FROM PUBLISHER]

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 \mu\Vpp) at fneuro>\ 1 kHz. It is also able to read emulated neural signals as low as -70 dBm (200 \mu\Vpp) at fneuro>\ 100 Hz. This is an improvement of up to 22 dB in sensitivity as compared with 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: 1) a subharmonic mixer using an anti-parallel diode pair; 2) a pair of implanted/interrogator antennas with high transmission coefficient \vertS21\vert;and 3) 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. [ABSTRACT FROM PUBLISHER]