Analysis of Impedance Characteristics for Electrically Small Implantable Antennas in Lossy Medium

The design principles of implantable antennas are very different from those in free space. To achieve low reflection coefficients, high radiation and transmission efficiency, the insulation layer between the antenna and the lossy medium is essential. The paper analyzes the variation of wave impedance especially in human tissues, and finds that magnetic dipoles are more easily matched to human tissues than electric dipoles for small antennas. In addition, the paper studies the effect of the electrical properties of the insulating layer on antenna matching, and it is shown that the insulation layer with high relative permittivity and low loss is beneficial to reduce reflections and improve the antenna's radiation efficiency. Through theoretical analysis and numerical simulation, the validity of the conclusion is verified, which provides theoretical guidance for designing antennas in lossy medium.