System Concept

Low-power CMOS circuits coupled with ultrasonic harvesting and

backscatter communication can provide a toolset from which to build

scalable, chronic extracellular recording systems.

This paper focuses on the fundamental system design trade-offs

and ultimate size, power, and bandwidth scaling limits of systems

built from low-power CMOS coupled with ultrasonic power delivery

and backscatter communication. In particular, we propose an

ultra-miniature as well as extremely compliant system, shown in Fig.

1, that enables massive scaling in the number of neural recordings

from the brain while providing a path towards truly chronic BMI.

These goals are achieved via two fundamental technology innovations:

1) thousands of 10 – 100 µm scale, free-floating, independent sensor nodes, or neural dust, that detect and report local extracellular electrophysiological data,

and 2) a sub-cranial interrogator that establishes power and communication links with the neural dust. The interrogator is placed beneath the skull and below the dura mater, to avoid strong attenuation of ultrasound by bone and is powered by an external transceiver via RF power transfer. During operation, the sub-cranial interrogator couples ultrasound energy into the tissue and performs both spatial and frequency discrimination with sufficient bandwidth to interrogate each sensing node.

Neural dust can be either an active node, which rectifies or recovers power at the sensing node to activate CMOS electronics for data pre-processing, encoding,

and transmission, or a passive node, which maximizes the reflectivity of the dust as a function of a measured potential. For both schemes, neural dust can communicate the recorded neural data back to the interrogator by modulating the amplitude, frequency, and/or phase of the incoming ultrasound wave.