## 3 Optical Properties Measurement
### Results of Measurement  
Figure 2 shows the spectrophotometer (Cary 5000, Agilent Technologies, Santa Clara, CA, USA) used to measure the optical properties of the specimens in this study. Spectrophotometers use a light source to illuminate a sample with light in the Ultraviolet (UV) to near-infrared (NIR) wavelength range. The instruments measure the light absorbed, transmitted, or reflected by the sample at each wavelength [18]. \begin{table}
\begin{tabular}{c c c c c c} \hline
**No.** & **1** & **2** & **3** & **4** & **5** \\ \hline Wire diameter & 25 μm & 25 μm & 25 μm & 25 μm & 27 μm \\ \hline Knitted type & Atlas & TUCH & Double-Atlas & Atlas & Atlas-Atlas \\ \hline Number of twists & 1 EA & 1 EA & 1 EA & 1 EA & 3 EA \\ \hline OPI & 36 & 36 & 18 & 10 & 12 \\ \hline Configuration & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Mesh specimen by knitting characteristics. Figure 2: Diffuse reflectance accessory showing the optics. In this study, the spectral measurement range of the instrument was 300-2500 nm, and a Cary 5000 two-channel spectrophotometer was equipped with an integrating sphere accessory known as the sample holder compartment, which is available for specular reflection measurements [19]. Figure 3 shows representative results (Specimen 5) of the optical property spectrum of the measured mesh fabric. For all the specimens, including Specim 5, the transmittance was measured to be over 80%, which was confirmed to be owing to the characteristics of the mesh in which pores were formed. Additionally, the absorptivity remained below 0.1 over the entire spectral range, and the reflectance did not exceed 0.15. The optical properties of all specimens are quantified in Table 3 by calculating the average values at 5 nm intervals over the measured wavelength range, and the graph is shown in Figure 4. The absorptivity was calculated using the following equation:  
\[R+T+A=1, \tag{1}\]  
where \(R\) is reflectance, \(T\) is transmittance, and \(A\) is absorptivity. From the measurements on Specimens 1-5, we confirmed that the transmittance generally decreased as the OPI increased when the specimen was in a standard state. However, there was no absolute inverse relationship between the OPI and transmissivity, and the two cases described later can be confirmed by comparing the results of the optical characterization of each specimen performed in this study. First, the transmittance of Specim 3 (18 OPI) is 0.84, which is approximately 0.04 lower than that of Specim 1 (36 OPI), despite having a lower OPI. This indicates that Specim 3, characterized by a  
Figure 3: Example of spectral optical characteristics (Specimen 5). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{3}{c}{**Description**} & \multirow{2}{*}{\(\boldsymbol{\alpha}\) *} & \multirow{2}{*}{\(\boldsymbol{\rho}\) *} & \multirow{2}{*}{\(\boldsymbol{\tau}\) *} \\ \cline{2-2} \cline{5-6}  & **Knitted Type** & & & & & \\ \hline
1 & Atlas & 36 & & 0.03 & 0.08 & 0.89 \\ \hline
2 & TUCH & 36 & & 0.05 & 0.11 & 0.84 \\ \hline
3 & Double-Atlas & 18 & & 0.04 & 0.11 & 0.85 \\ \hline
4 & Atlas & 10 & & 0.05 & 0.02 & 0.93 \\ \hline
5 & \multirow{2}{*}{Atlas-Atlas} & \multirow{2}{*}{12} & Standard state & 0.07 & 0.13 & 0.81 \\ \cline{3-5} \cline{5-6}
5-1 & & & & & & \\ \cline{3-5} \cline{5-6}
5-2 & & & & & & \\ \cline{3-5} \cline{5-6}
5-3 & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Experimental result of mesh specimen optical properties. double-weave structure, had a higher density than regular fabrics, resulting in reduced light transmittance. Second, the transmittance of Specim 5 (12 OPT) was 0.81, which was lower than those of Specimens 1, 2 (36 OPT), and 3 (18 OPT), which had higher OPI. This indicates that Specim 5 was the only specimen composed of 3 ply wires, and the transmittance decreased as the reflected area increased compared with a single wire.