Characterizing Implant-to-Surface Radio Channels for Brain Computer Interface Applications

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Abstract
Understanding radio-channel characteristics is essential for the design of reliable wireless brain computer interface (BCI) and brain-monitoring systems, where signal propagation is strongly influenced by the complex anatomy of the human head. In this paper, BCI radio-channel characteristics are obtained and analyzed using electromagnetic simulations based on multilayer human-tissue models and validated by measurements performed with a realistic 3D human head phantom. Radio channel analysis is performed considering several scenarios using a flexible implant and an on-body antenna. First, the effect of muscle tissue on channel attenuation is examined by comparing two tissue models with and without a temporalis muscle layer. The sensitivity of the channel parameters to relative antenna positioning is then analyzed by introducing small vertical displacements of the on-body antenna with respect to the implant antenna. Finally, the influence of subcutaneous fat thickness is investigated by considering typical anatomical variations as well as an extreme case representing severe obesity. These studies are done using two practical implant antenna locations, i.e., above the skull and within a shallow cranial recess. The results show that channel characteristics are strongly affected by tissue composition, implant depth, and antenna alignment, with these effects becoming more pronounced at higher frequencies. The findings highlight the importance of accounting for anatomical variability and antenna placement when designing reliable wireless BCI and brain-telemetry systems.

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