Design of broadband circularly polarized antenna for implantable and ingested biomedical devices

A broadband circularly polarized antenna for implantable and ingested wireless biomedical devices is designed, by loading the compact double semicircular resonant ring. The high electromagnetic energy is collected to generate and enhance the circular polarization characteristics of the antenna, the impedance bandwidth, and axial ratio bandwidth are improved while the volume is reduced. The size of the antenna is reduced to pi x(5)(2) x 0.635 mm(3) with the same bandwidth requirement by introducing T-shaped capacitive loading branch. The performance of the antennas implanted in different human tissues is compared, and the biological compatibility, radiation characteristics, and safety of the antenna are analyzed. In the simulated skin model, the simulation impedance bandwidth is 24.1%, and the axial ratio bandwidth is 18.4%. Finally, the antenna is fabricated and tested in pork. The impedance bandwidth is 23.8%, and the axial ratio bandwidth is 18.6%. The communication ability is evaluated through the external antenna, and the effective transmission distance is 5.5 m. The designed antenna has a simple structure, strong compatibility, and wide functional bandwidth, which can meet the needs of implantable and ingested biomedical devices in the ISM frequency band.