Increasing the radiation efficiency and matching stability of in-body capsule antennas

International audienceWe propose an approach to increase the operating range and matching stability of in-body ingestible or implantable capsule antennas. It involves using high permittivity biocompatible superstrate on a high-Q narrowband microstrip antenna. In this way, the antenna-body coupling can be significantly reduced, resulting in improved detuning immunity, increased radiation efficiency, and reduced power absorption inside the body. To demonstrate the feasibility of the proposed approach, we designed a mid-ISM band (433 to 434.8) MHz low-profile (85 μm) conformal microstrip antenna loaded with high permittivity ceramic superstrate. We achieved a simulated gain of -20.4 dBi. The radiation efficiency reaches 0.6%, which exceeds the counterparts operating within the same band by at least 3.5 times. The bandwidth is 26 MHz (6%), while the antenna remains matched (S11 < -10 dB) at 434 MHz within a wide range of tissue-equivalent phantoms. To validate the numerical results, we manufactured an antenna prototype and characterized it in terms of reflection coefficient S11. © 2016 European Association of Antennas and Propagation