## 3 Selection of Materials for Wearable Antennas
### Flexible Substrate Material for Wearable Antennas
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Ref.** & **Materials** & \begin{tabular}{l} **Dielectric** \\ **Constant** \\ \end{tabular} & \
\begin{tabular}{l} **Frequency** \\ **Range** \\ \end{tabular} & **Loss Tangent** &
\begin{tabular}{l} **Substrate** \\ **Height** \\ \end{tabular} \\ \hline
[61] & Flamnel & 1.7 & 2-20 GHz & 0.025 & – \\ \hline
[62] & Polyester & 1.44 & 2.6-5.8 GHz & 0.0045 & 2.85 mm \\ \hline
[47] & Polyurethane & 1.28 & 2.38-6 GHz & 0.016 & 2.4 mm \\ \hline
[63] & Fleece & 1.60 & 2.45 GHz & 0.0400 & 3 mm \\ \hline
[64] & Felt & 1.38 & 2.6-3.95 GHz & 0.023 & 3.5 mm \\ \hline
[65] & Tween & 1.69 & 2.6-3.95 GHz & 0.0084 & – \\ \hline
[66] & Perspex & 2.57 & 2.6-3.95 GHz & 0.008 & - \\ \hline
[57] & Moleskin & 1.51 & 2.6-3.95 GHz & 0.02 & 3 mm \\ \hline
[55] & Cordura/Lycra & 1.5 & 2.6 GHz & 0.0093 & 1.6 mm \\ \hline
[67] & Quartzes fabric & 1.95 & 2.6 GHz & 0.0004 & 1.3 micron \\ \hline
[68] & Cotton & 1.58 & 2.4 GHz & 0.115 & 0.7 mm \\ \hline
[69] & Jeans & 1.68 & 2.4 GHz & 0.05 & 2.5 mm \\ \hline
[68] & Silk & 1.5 & 2.45-5.8 GHz & 0.012 & 0.254 mm \\ \hline
[32] & PTEE & 2.1 & 2.6-5 GHz & 0.0004 & 6 mm \\ \hline
[70] & Panama & 2.12 & 2.4-5.8 GHz & 0.018 & 1.6 mm \\ \hline
[71] &
\begin{tabular}{l} Rogers Duroid \\ RO3003 TM \\ \end{tabular} & 3 & 2.45 GHz & 0.001 & 2.4 mm \\ \hline
[72] & PDMS & 2.65 & 2.45 GHz & 0.02 & 2.5 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Flexible substrates’ material for flexible wearable antennas. Figure 5: Various types of flexible substrates for nonconductive materials. author designed and constructed an antenna from denim, excluding the SMA connector. The antenna, loaded with right rectangular slots and strip lines, reduced its size by 75% compared to the reference antenna. The antenna consistently achieved a radiation efficiency of 79% and a bandwidth of 15% [73]. For an author's jeans-based UWB MIMO, the proposed construction employed denim. Two inverted unformed stubs were attached to the partially etched ground on the antenna's rear to improve port isolation. A 50 \(\times\) 35 mm\({}^{2}\) universal wideband multiple-input multiple-output antenna operated from 1.83 to 13.82 GHz [74]. An author proposed a flexible PDMS antenna where the antenna covered 3.43-11.1 GHz with a 59.9% bandwidth. Changing bending angles changed the bandwidth by less than 1% [75]. It implied a flexible, wide-band antenna. The first coplanar waveguide-fed planar monopole on a Kapton polyimide substrate worked at 2.27 to 5.27 GHz and was 56 mm wide, 56 mm tall, and 0.11 mm thick [69]. For a possible ultra-wideband (UWB) denim textile antenna, the design antenna covered the FCC's UWB range (3.1-10.6 GHz) and had a 118.68 percent bandwidth (2.96-11.6 GHz). Frequently, its 3.5 \(\times\) 10 \(\times\) 1 mm\({}^{3}\) dimension yielded a 5.47 dB peak gain [68] which operated at 7.3 GHz. This antenna had a maximum average SAR of 10 g in open space, and on flat ground, the 2.45 GHz ISM band was 90 percent below the standard [32]. The antenna measured a mere 51 \(\times\) 45 \(\times\) 0.785 mm. A 10 \(\times\) 10 mm rectangular slot enhanced return loss and gain. The substrate materials and design frequencies were subject to variation with a 2.45 GHz semi-flexible wearable antenna for industrial, scientific, and medical band applications [44; 53; 72; 73].