| Cranially implanted sensors and electrodes have been used in practice for several years; their applications range from the recording of neural signals for use in Brain-Computer Interfaces to help the disabled, to the treatment of diseases and conditions ranging from Parkinson's disease, multiple sclerosis, depression, etc. Current communication methods with implants, however, are lacking; they run the gamut from physical, percutaneous connections that increase the risk of infection, to wireless links that are slow and uncomfortable for patients.;The present work focuses on the characterization of the effects of the human head on communication with cranially implanted antennas for its eventual use in improving current communication methods. A realistic human head model with frequency dependent tissue characteristics is used to obtain a transfer function that describes the magnitude and phase of an electromagnetic wave as it propagates through the human head over both frequency and depth into the skull; this data is obtained for multiple energy entry angles. The technique used to obtain transfer function measurements consists of taking the ratio of the electric fields at the receiver and transmitter and is developed through analysis of ultra-wideband transmit/receive antenna systems; verification for this technique is provided.;After the transfer function data described above is obtained, we posit a communication model to approximate the transfer function magnitude. This approximation takes the form of a modified log-distance, log-frequency path loss model and fits the data quite well. The final approximation describes the path loss of an electromagnetic wave over both frequency and distance for all simulated orientations.;Lastly, simulations are presented for communication from a cranially implanted dipole antenna. The received power of an external antenna -- whose position is varied in both distance (from the head), as well as location (around the head) -- is captured and plotted. We finally show that the transfer function that was obtained for all perpendicular communication through the head is able to, in most cases, correctly predict the results of these received power simulations. |
