Beamforming approaches for untethered, ultrasonic neural dust motes for cortical recording: A simulation study

Abstract

Abstract-In this paper, we examine the use of beamforming techniques to interrogate a multitude of neural implants in a distributed, ultrasound-based intra-cortical recording platform known as Neural Dust [1]. We propose a general framework to analyze system design tradeoffs in the ultrasonic beamformer that extracts neural signals from modulated ultrasound waves that are backscattered by free-floating neural dust (ND) motes. Simulations indicate that high-resolution linearly-constrained minimum variance beamforming sufficiently suppresses interference from unselected ND motes and can be incorporated into the ND-based cortical recording system.

Blind parallel interrogation of ultrasonic neural dust motes based on canonical polyadic decomposition: A simulation study

“…Although [3] uses mm-scale NDMs, the ND concept has been shown to be scalable to sub-mm scale, which one day could allow to chronically and wirelessly record electro-physiological signals within the brain cortex at a micro-scale pitch [2]. To this end, a large number of free-floating NDMs is implanted in the cortex at a 2mm depth in a grid with a 100 µm pitch, in which each NDM measures action potentials or 'spikes' generated by nearby neuron cells [2], [4]. A grid of 'interrogators' equipped with ultrasound (US) transceiver arrays are attached to the cortex to collect the neural signals measured by the NDMs.…”

“…A grid of 'interrogators' equipped with ultrasound (US) transceiver arrays are attached to the cortex to collect the neural signals measured by the NDMs. The NDMs modulate their recorded neural signal onto a reflected US carrier through passive backscattering, which the interrogator then demodulates and at its turn transmits the result through the skull to an external transceiver based on near-field electromagnetic communication [2], [4].…”

“…In [4], it was demonstrated that this interference can be suppressed by combining transmit (Tx) and receive (Rx) beamforming techniques to target individual NDMs. However, this technique assumes that the NDM positions or the channel characteristics between the individual NDMs and the US transducers can be estimated, which is a non-trivial task in itself.…”

“…We use the canonical polyadic decomposition (CPD) to decompose the tensor in rank-1 terms, and we show that -under certain conditions-each term will only contain the neural signals of a single NDM. This blind CPD-based interrogation scheme allows to read out the entire NDM grid, which is validated on simulated data using the physical ND model described in [2], [4], which has been experimentally validated in [5] and in [6].…”

“…DATA MODEL In this section, we briefly review the ND data/simulation model of [2], [4]. Consider a ND system consisting of a linear grid of K NDMs with a 100µm pitch as shown in Fig.…”