An Ultra-Miniaturized Antenna Using Loading Circuit Method for Medical Implant Applications

Abstract

In this paper, an ultra-miniaturized implantable antenna is proposed for biomedical applications, which operates in frequency of the industrial, scientific, and medical bands of 2.4 GHz. The miniaturization of the proposed antenna is obtained by using a meander line as radiating patch, introducing a $1.2~\Omega $ chip resistor, and two pairs of a rectangle slot are etched on the ground plane to expand the antenna impedance bandwidth. The antenna has an ultra-compact size with a width and length of 2.5 mm and a thickness of 0.64 mm (the total dimension of $2.5 {\mathrm {mm}} \times 2.5 {\mathrm {mm}} \times 1.28 {\mathrm {mm}}^{3}$ ). To validate the antenna structure, the optimal design is fabricated and experimentally measured. A low loss, flexible, and biocompatible PCB material, Taconic CER-10 ( $\varepsilon _{r} = 10.2, \sigma = 0.0 035$ ) is adopted as both the substrate and superstrate. The experiment results imply that the proposed antenna produces a good impedance matching at 2.4 GHz with a bandwidth of 16.6% and a maximum peak gain of −18.3 dBi. In addition, to further prove the performance of the designed biomedical implantable antenna, the effects of a coaxial cable and the simulations in the environment of the human tissue models (head, arm, and leg) are established. The antenna provides a low specific absorption rate (SAR) with the value compliance the IEEE standard safety guidelines. To the best of our knowledge, the proposed antenna is the smallest dimension (in width and length) with high performance compared to previously reported works. Thus, the antenna is a potential candidate and suitable for the biomedical applications.