Johan Engstrand: Fat-Intrabody Communication for Medical Implants and Brain–Computer Interfaces

Abstract

Brain–computer interfaces hold significant promise for restoring function to individuals with neurological disorders and spinal cord injuries. However, the technical evolution of these systems is increasingly challenged by the substantial data throughput requirements of high-density neural recording. Invasive electrode arrays can generate vast amounts of neural data that exceed the capacity of current wireless links, while wired connections introduce infection risks and lifestyle burdens. This thesis explores fat-intrabody communication as an alternative, which utilizes the low-loss dielectric properties of subcutaneous fat. Bounded by skin and muscle, fat tissue acts as a waveguide for microwave signals at gigahertz frequencies. This approach aims to provide the high data capacity necessary for real-time, uncompressed neural data transmission in brain–computer interface applications. Using a three-layer tissue-mimicking phantom (skin–fat–muscle), link performance is characterized with antennas placed against the fat and on the skin at 2.45 GHz. Results show that fat-intrabody communication can support high-order modulation schemes, and a practical transceiver platform, based on commercial off-the-shelf hardware, is developed to quantify data throughput. In phantom experiments with in-body and on-body links, data rates of up to 120 Mb/s are achieved, more than two orders of magnitude higher than previously reported. Beyond performance, security and privacy implications are examined, including signal leakage to external eavesdroppers and the feasibility of in-body covert communication enabled by skin attenuation and friendly jamming. Finally, fat-intrabody communication with on-skin antennas is validated in vivo. This includes an end-to-end closed-loop demonstration of a brain-implanted macaque monkey controlling a prosthetic hand, and measurements on twelve human participants to quantify received signal strength and throughput across multiple body locations, postures, and environmental conditions. Overall, the results show that fat-intrabody communication can provide high-throughput links in realistic scenarios, supporting the case for fat tissue as a communication medium for future implant networks and brain–computer interfaces.