Performance evaluation of compact FSS-integrated flexible monopole antenna for body area communication applications

This article presents a compact wearable antenna integrated with a novel frequency selective surface (FSS) made of textile materials. The antenna can be applied in wearable health monitoring applications aimed at the 2.45-GHz Industrial Scientific and Medical (ISM) band. An array of 4 x 4 octagonal slot-shaped FSS (106 x 106 mm(2)) superstrate enhances the performance of the modified Koch curve planar monopole antenna (44.85 x 39 mm(2)). The Jeans substrate prototype with the overall dimensions of 1.128 lambda(0) x 1.128 lambda(0) x 0.319 lambda(0) covers the bandwidth of 2.45-GHz ISM band from 2.24 to 2.76 GHz (S11 <= -10 dB). The band rejection and reflective nature of the proposed FSS suppress the back radiation and improves the antenna's gain by -20 dB and 6.3 dBi, respectively. The specific absorption rate (SAR) level is reduced to 0.445 W/kg from 24.995 W/kg with a higher reduction rate of 98.21%. Many literature reports produced higher gain and lower SAR but exhibited reduced efficiency when the antenna is placed near the human body. The wearable antenna's frequency response tends to vary under bending conditions for narrowband antennas. Wide-band monopole antennas produce omnidirectional radiation pattern which tends to affect human body tissues. So stable polarization-insensitive FSS is placed behind the antenna to enhance the antenna's gain and avoid back radiation. The proposed antenna exhibits stable performance under bending conditions with fractional bandwidth of 22.2%, gain of 8.83 dBi, and produces a better efficiency of 91.30% when the antenna is positioned in the vicinity with human body models. The experimental validation shows that the proposed antenna is a promising candidate for wireless body area networks.