An Ultra-Miniaturized Circular Polarized Implantable Antenna With Gain Enhancement by Using DGS and Holey Superstrate for Biomedical Applications

Abstract

In this paper, a new approach is presented for achieving circular polarization (CP) characteristics and gain enhancement of an ultra-miniaturized antenna for biomedical applications. The proposed antenna operates in the frequency of the industrial, scientific, and medical (ISM) bands of 2.4 GHz. The integration of the defected ground structure (DGS), and the Holey supertrate produces a significant gain improvement with the CP characteristic at the desired frequency. As a result, the proposed antenna does not only have an ultra-compact dimension of 2.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2.5$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.28$ </tex-math></inline-formula> mm (8 mm3), but also has CP characteristic, high gain value, and an acceptable radiation efficiency of 0.25 %. The performance of the proposed antenna is tested via numerical and experimental measurement. The designed antenna is fabricated on a low loss, flexible, and biocompatible PCB material, Taconic CER-10 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> = 10.2, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> = 0.0 035). The measurement results assembles a good impedance matching at 2.4 GHz with the bandwidth of 33% and a maximum peak gain of −14.3 dBi. Moreover, the antenna shows a low specific absorption rate (SAR) with the value compliance the IEEE standard safety guidelines. To the best of our knowledge, the proposed CP antenna is the compactest size with high performance and great gain enhancement (approximate 3.2 dBi) compared to previously reported works. Finally, the proposed antenna with the approach and its successful integration is a potential candidate and suitable for biomedical implant applications.