Analytical Approach to Matching Layer Design for Electric Field Maximization in Biological Tissues

The electromagnetic waves transmission inside biological tissues can be useful in several biomedical applications, such as rehabilitation and microwave imaging. In this context, an important point is to design a matching layer to enhance the penetration of the electric field into a target tissue. Here we present an analytical method to design a matching layer under the near-field regime, i.e. when the electromagnetic source, as for instance a short dipole antenna, lies in the proximity of the body. In particular, two cases are examined: when the matching layer only consists of a dielectric slab, and when it is composed by a metasurface printed on a dielectric substrate. The proposed approach is based on the wave-transmission chain matrix and on the Schelkunoff's definition of wave impedance to consider the source. The body is modeled as a multilayered planar medium. An optimization procedure based on a stochastic algorithm is applied to determine the parameters of the matching layer which could realize the maximum electric field transmission inside the muscle. These parameters are then used to simulate the overall system with a numerical software. The results show that the matching layer comprising the metasurface is the most effective solution in terms of electric field maximization and dimensions of the substrate.