Optimal Frequency of Shallow-Implanted Antennas for Brain–Machine Interfaces

The optimal operating frequency of shallow-implanted antennas is critical for achieving efficient wireless communication in brain-machine interface (BMI) applications. This paper presents an analytical study of shallow-implanted antennas using planar body models, with closed-form expressions that characterize the dependence of maximum radiation gain on implantation depth, surrounding tissue properties, operating frequency, and implant dimensions. The analysis reveals that shallow implants benefit from reduced propagation losses at higher frequencies while mitigating excessive near-field losses at lower frequencies, thereby favoring operation in the several gigahertz range. Numerical simulations using an anatomical head model validate the analytical predictions, confirming that higher-frequency bands, such as those employed in implantable impulse-radio ultra-wideband (IR-UWB) devices for intracranial neural sensing, improve the implant's radiation performance while simultaneously enabling high-data-rate communication. These findings provide practical design guidance for shallow brain implants and support the advancement of next-generation, high-performance wireless BMI systems.