Matching Layer Design for Far-Field and Near-Field Penetration Into a Multilayered Lossy Media

The remarkable spreading of medical devices relying on electromagnetic (EM) fields stimulates a deeper analysis of their interactions with the human body. The electric field generated by a radio-frequency (RF) source, such as an antenna, can be transmitted inside biological tissues and used in disease treatment, rehabilitation, and noninvasive imaging. In this context, it is important to facilitate the penetration of the electric field inside tissues. Matching layers (MLs) consisting of dielectric media or impedance surfaces provide an approach to maximize the field penetration. However, the presence of a source in close proximity to the body complicates the EM analysis and the design of such a structure. Here, we analyze an analytical method based on the wave-transmission-chain matrix and the wave-impedance concept, as defined by Schelkunoff for near-field sources. Examples of the usefulness of this approach in designing an ML that could improve the penetration of the electric field inside tissues are presented. The results obtained analytically are finally compared with those of a full-wave solver, showing good agreement.