A low-profile flexible planar monopole antenna for biomedical applications
Md. Shazzadul Islam, S. M. Kayser Azam, A. K. M. Zakir Hossain, Muhammad Ibn Ibrahimy, S. M. A. Motakabber
Abstract
This article proposes a low profile planar monopole antenna on flexible substrate. The antenna is designed with an elliptical slot inserted in a rectangular patch by utilizing the coplanar waveguide (CPW) feeding technique on a polyimide substrate. The proposed antenna operates within 7–14 GHz (S11 < − 10 dB) with a minimum return loss is observed as low as – 58 dB by simulation, whereas the entire X-band is covered by the – 20 dB bandwidth while maintaining an excellent VSWR of almost 1. Also, the antenna exhibits an average gain of 4 dBi while the average radiation efficiency is 92%. The maximum SAR of the proposed antenna for 1 g mass is below 1.0 W/Kg throughout the entire bandwidth. To observe flexibility, four different bending conditions of the antenna have been analyzed. For experimentation, the antenna has been realized as a prototype by using a low-cost fabrication process. The measurement reveals that the prototype has a −10 dB bandwidth of 5.4 GHz. During In-Vivo test, over the variation of 0 ∼ 3 mm distance between the antenna-prototype and the human chest/chicken breast tissue, the best performance is obtained at 3 mm in terms of the return loss. One of the significant features of the proposed design is its measured average and peak gain of 4.4 dBi and of 6.33 dBi respectively with a measured average efficiency of 65%. The proposed antenna has a compact size of 13 × 13 mm2 (0.35λg×0.35λg), and its performance remains nominally constant even under different bending conditions which makes the antenna suitable for biomedical imaging applications. A new figure-of-merit has been introduced to evaluate the overall performance based on different antenna key parameters. The fabricated antenna would contribute to the future biomedical research by utilizing X-band frequencies.