Electromagnetic limits to radiofrequency (RF) neuronal telemetry

Abstract

The viability of a radiofrequency (RF) telemetry channel for reporting individual neuron activity wirelessly from an embedded antenna to an external receiver is determined. Comparing the power at the transmitting antenna required for the desired Channel Capacity, to the maximum power that this antenna can dissipate in the body without altering or damaging surrounding tissue reveals the severe penalty incurred by miniaturization of the antenna. Using both Specific Absorption Rate (SAR) and thermal damage limits as constraints, and 300 Kbps as the required capacity for telemetry streams 100 ms in duration, the model shows that conventional antennas smaller than 0.1 mm could not support human neuronal telemetry to a remote receiver (1 m away.) Reducing the antenna to 10 microns in size to enable the monitoring of single human neuron signals to a receiver at the surface of the head would require operating with a channel capacity of only 0.3 bps.

Figure 1. Simplified models of realistic microscopic antennas occupying approximately the same volume: dipole on the left, loop on the right.

Figure 2. Maximum Channel Capacity at 2 GHz as a function of antenna diameter for the human head case with receive antenna at the surface of the head.

Transmitting antennas: Red = dipole, Blue = loop, dashed Black = loop with permeable core.

Figure 3. Maximum Channel Capacity at 3 GHz as a function of antenna diameter for the case of a mouse head experiment with a receiver 10 cm away.

Transmitting antennas: Red = dipole, Blue = loop, dashed Black = loop with permeable core.