Propagation of Radio-Frequency Electromagnetic Fields Emitted by Surface-Mounted Parallel-Plate Couplers Along Human Limbs

Wearables on human limbs commonly require wireless connections with other body-worn devices. These links can be established using radio-frequency electromagnetic fields emitted by parallel-plate capacitors (PPCs) as transducing elements. The propagation of the electric (E-) fields emitted by such PPCs on the surface of human limbs is studied by simulations with a stratified, lossy, dielectric cylinder as a limb model. In contrast to currently existing models, this analysis demonstrates that this propagation depends strongly on propagating modes within the lossy dielectric waveguide and that this is associated with an optimal frequency band of operation for such wireless links, which is tied to cut-off frequencies for propagation along the cylindrical waveguide and the radiation efficiency of the PPC, which is also dependent on the limb size. A channel-loss model in the 0.1-1 GHz frequency range is determined based on the simulations. This model is validated using channel loss measurements using a PPC placed on the limbs of three human subjects.