Impact of Tissue Electromagnetic Properties on Radiation Performance of In-Body Antennas

In-body antennas couple strongly to surrounding biological tissues, thus, resulting in radiation efficiencies well below 1%. Here, we quantify how the permittivity and conductivity, each individually, affect the radiation efficiency of miniature implantable and ingestible antennas. We use a generic pill-sized capsule antenna and a spherical homogeneous phantom with its electromagnetic properties covering the complete range of body tissues. In addition to the phantom surrounded by air, we study the case with a reduced phantom-background contrast (nonresonant case) that allows for decoupling of the obtained results from the phantom shape. The results demonstrate that, for a realistic capsule antenna, the effect of dielectric loading by tissue can partially compensate for the tissue losses. For instance, the gain of the antenna operating in the muscle-equivalent medium is about two times (3 dBi) higher than in the fat-equivalent one, even though the conductivity of muscle is one order of magnitude higher than the one of fat. The results suggest that, in the majority of cases, in-body devices should be designed for and be placed within higher-permittivity tissues with low to moderate losses.