Surface-Mounted Parallel-Plate Coupler for Cylindric Dielectric Waveguides

Surface-mounted parallel-plate capacitors (PPCs) can be used as transducing elements in wireless communication, for example, in human-body-dedicated applications, such as healthcare monitoring or activity tracking, which require robust wireless communications and user-convenient implementation. In this context, PPCs are an attractive element due to their mobility, noninvasive positioning, and small form factors. Moreover, they are relatively easy to analyze with a simple design. This work studies the use of PPCs on dielectric, cylindrical waveguides as a precursor to the relatively complex electromagnetic environment that the human body is. The electromagnetic fields surrounding PPCs placed on a dielectric medium are described theoretically. This theory involves a combination of surface waves, inductive coupling, and quasi-static coupling between PPCs. In dielectric (cylindric) waveguides, the material’s dimensions and frequency of excitation dictate whether propagation of certain modes can occur. This article shows, on one hand, that these modes can be excited by a surface-mounted waveguide coupler such as PPCs, and on the other hand, that the associated propagation is governed by modal characteristics.