# Design of a Polarization-Insensitive and Wide-Angle Triple-Band Metamaterial Absorber
## 4 Experiment and Verification  
The sample fabricated by the PCB printing process is shown in Figure 14a, and the experimental facilities and environment are shown in Figure 14b [79; 80; 81; 82; 83; 84; 85; 86]. The absorption performance of the sample is tested using the free space method, with the schematic diagram depicted in Figure 14c. The output port and input port of the vector network analyzer \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref**} & **Absorption** & \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{**Absorptivity**} & **Unit Cell** & \multirow{2}{*}{**Unit Cell Size (mm)**} & **Polarization** & **Angular** \\  & **(GHz)** & & & & **(mm)** & & **Insensitivity** & **Stability** \\ \hline
[72] & 2.5, 5.2, 9.8, & & 90\%, 91\%, 97\%, & 1.6 & 19 \(\times\) 19 & 60\% & 60\% for TE \\  & and 11.0 & & & and 94\% & (0.013\(\lambda_{0}\)) & (0.18\(\lambda_{0}\times 0.18\)) & & and TM \\
[73] & 49, 10, & & 99.53\%, 99.76\%, & 0.8 & 10 \(\times\) 10 & & 45\% for TE and \\  & and 14.05 & & & and 98.71\% & (0.013\(\lambda_{0}\times 0.163\lambda_{0}\)) & & 75\% for TM \\
[74] & 2.4, 5.5, and 7.5 & S and C & & 99.53\%, 99.33\%, & 1.6 & 15.1 \(\times\) 15.1 & 52\% for TE \\  & & & & and 99.90\% & (0.0128\(\lambda_{0}\)) & (0.12\(\lambda_{0}\times 0.12\)) & & and TM \\
[75] & 11.6, 14.04, & & 99.88\%, 99.72\% & 1.6 & 13 \(\times\) 13 & & 60\% for TE \\  & and 16.56 & & & and 96.41\% & (0.0618\(\lambda_{0}\)) & (0.425\(\lambda_{0}\times 0.425\)) & & and TM \\
[76] & 5.86, 6.57, and & & 86.23\%, 92.92\%, & 1.52 & 10 \(\times\) 10 & & 90\% for TE \\  & 8.94 & & & and 82.07\% & (0.029\(\lambda_{0}\)) & (0.19\(\lambda_{0}\)) & & and TM \\
[77] & 4.19, 9.34, & & 99.67\%, 99.48\%, & 0.8 & 8 \(\times\) 8 & & 60\% for TE \\  & and 11.48 & & & and 99.42\% & (0.011\(\lambda_{0}\times 0.11\)) & (0.11\(\lambda_{0}\times 0.11\)) & & and TM \\
[78] & 5.376, 10.72, & & 99.9\%, & 1.6 & 10 \(\times\) 10 & & 30\% for TE \\  & and 12.25 & & & and 99.7\% & (0.028\(\lambda_{0}\)) & (0.179\(\lambda_{0}\)) & & and TM \\  & & & & & \(6\times 7.5\times 7.5\times\) & & \\  & & & & & \(\frac{\sqrt{5}}{2}\times\frac{1}{2}\) = & & & \\ This work & 4.306, 7.479, & & 99.05\%, 99.3\%, & 1.07 & \(\frac{\sqrt{5}}{2}\times\frac{1}{2}\) = & & \\  & and 14.661 & & & and 97.9\% & (0.0154\(\lambda_{0}\)) & & & \\  & & & & & (6\times 0.108\(\lambda_{0}\) \(\times\) & & \\  & & & & & 0.108\(\lambda_{0}\) \(\times\) \(\frac{\sqrt{5}}{2}\times\frac{1}{2}\)) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the proposed work and the other literature works. Figure 13: Absorption efficiency diagram for double-ring structure. (VNA) are connected to the transmitting antenna and receiving antenna, respectively. In this experiment, the distance between the metasurface and the horn antenna was set to 35 cm. The electromagnetic wave emitted by the transmitting antenna is reflected and absorbed on the surface of the sample. The reflected energy is collected by the receiving antenna and input into the VNA to obtain the reflection coefficient \(S_{11}\) curve. Since a layer of copper is laid on the back of the sample, the electromagnetic wave will not pass through the sample; therefore, the reflection coefficient can be used to evaluate the absorption performance [87; 88; 89; 90]. By normalizing the reflection coefficient, the absorption rate can be obtained. Firstly, the measured and simulated absorption diagram of MMA under normal incidence is shown in Figure 15. Due to the limitations of the experimental conditions, the transmitting horn can only emit electromagnetic waves of 4-8 GHz, so only the first two absorption peaks can be tested. From the absorption diagram, it is evident that the fabricated MMA achieved absorption efficiencies of 99.5% at 4.12 GHz and 99.4% at 7.123 GHz, with deviations of 0.11 GHz and 0.28 GHz, respectively.