Compact and Broadband Circularly Polarized Implantable Antenna for Wireless Implantable Medical Devices

This letter presents a compact and broadband circularly polarized (CP) implantable antenna for wireless implantable medical devices (WIMDs) in the 2.4 GHz Industrial, Scientific, and Medical band. The proposed antenna consists of a main radiator, a stacked parasitic structure, and a full ground, with its entire dimension of 9.8 x 9.8 x 0.889 mm(3). For size reduction, a modified square ring with a mitered cross inside is adopted as the main radiator. By splitting one arm of the mitered cross, the compactness can be further improved while exciting the potential CP radiation. The stacked parasitic structure not only ensures a satisfactory 3 dB axial ratio bandwidth of 28.7%, but also helps to achieve a -10 dB impedance bandwidth of 30%, with a peak realized gain of -24.7 dBi. The antenna was integrated into two types of dummy WIMDs and analyzed in the human phantoms (scalp and heart) to evaluate its device-level performance and robustness. A fabricated prototype was measured in the minced pork, and the measured results agree with the simulated ones.