Exploiting Spatial Degrees of Freedom for High Data Rate Ultrasound Communication with Implantable Devices

TL;DR

This paper demonstrates a novel ultrasonic communication method using spatial multiplexing with multiple transducers to significantly increase data rates for implantable medical devices, verified through experiments in mineral oil.

Contribution

The study introduces a spatial multiplexing approach for ultrasonic implants, enabling higher data rates without additional power or bandwidth, validated through experimental proof-of-concept.

Findings

Achieved 250 kbps data rate with two data streams

Successfully separated channels with low bit error rate below 1e-4

Demonstrated robustness to positional offsets

Abstract

We propose and demonstrate an ultrasonic communication link using spatial degrees of freedom to increase data rates for deeply implantable medical devices. Low attenuation and millimeter wavelengths make ultrasound an ideal communication medium for miniaturized low-power implants. While small spectral bandwidth has drastically limited achievable data rates in conventional ultrasonic implants, large spatial bandwidth can be exploited by using multiple transducers in a multiple-input/multiple-output system to provide spatial multiplexing gain without additional power, larger bandwidth, or complicated packaging. We experimentally verify the communication link in mineral oil with a transmitter and receiver 5 cm apart, each housing two custom-designed mm-sized piezoelectric transducers operating at the same frequency. Two streams of data modulated with quadrature phase-shift keying at 125 kbps are simultaneously transmitted and received on both channels, effectively doubling the data rate to 250 kbps with a measured bit error rate below 1e-4. We also evaluate the performance and robustness of the channel separation network by testing the communication link after introducing position offsets. These results demonstrate the potential of spatial multiplexing to enable more complex implant applications requiring higher data rates.