Miniaturized Circularly Polarized Implantable Antenna for Biotelemetry Applications

This letter presents a miniaturized circularly polarized implantable antenna designed for biotelemetry applications operating in the Medical Implant Communication Service band, spanning 402 MHz to 405 MHz. The proposed antenna features a miniaturized electrical size of 0.01075<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{{0}}\times {\text{0.01075}}\lambda _{{0}}\times {\text{0.0034}}\lambda _{{0}}$</tex-math></inline-formula>. A rectangular spiral loop and V-shaped radiators contribute to miniaturization. The circular polarization property is obtained by implementing an edge-coupled slot, chamfered corners, and a corner feed point configuration. The measured reflection coefficient and axial ratio bandwidths are 8.2% and 4.96%, respectively. The experimental verification is carried out by fabricating the antenna and performing measurements in tissue-mimicking liquid. IEEE safety guidelines confirm the acceptability of the maximum specific absorption rate.