A metamaterial-inspired circularly polarized antenna for implantable applications

A novel microstrip-fed metamaterial-inspired antenna is proposed for implantable applications. The designed antenna operates in the Industrial, Scientific and Medical band at a frequency (2.4-2.5) GHz. The implantable antenna comprises of two split ring resonators. The use of metamaterial not only dramatically reduces the size of the antenna, but also improves its gain and bandwidth. Different methods of size reduction with optimum gain and bandwidth are here discussed in detail. The implantable antenna is designed using FR4 substrate which provides better gain, miniature size (84% size reduction), good impedance matching, circular polarization with 3.41% of 3-dB axial ratio bandwidth. Circularly polarized antennas are usually preferred as they reduce polarization mismatch loss. The antenna is 29x28mm(2) in size with 4.86dB gain and 140MHz impedance bandwidth. The design of phantom liquid, the computation of its pH value, and measurement of its permittivity are thoroughly reported. The permittivity of the liquid is found to increase with the pH value. The permittivity of phantom liquid has been validated with 85070E dielectric probe kit. A detailed description of different probes is provided. The measurement results are in good agreement with simulations. Finally, the design of phantom for implantable applications and techniques for size reduction of the same have been described. This reduced size will help to fit antenna in medical devices, providing greater ease for the body movement.