## 2 Design of Unit Cell and Analysis  
The unit cell is designed to operate around 5 GHz. The unit cell is developed with a 1 mm thick FR4 substrate dielectric material. The permittivity (\(\varepsilon\)) and loss tangent (\(\delta\)) are 4.3 and 0.025, respectively. The overall dimensions of the proposed design and the back-side metallic plane are 15 mm \(\times\) 15 mm, respectively. The front face of the substrate is a square patch with the dimensions 13 mm \(\times\) 13 mm as a top layer. The ground plane and top layer are copper with a thickness of 0.035 mm and an electrical conductivity constant is \(\sigma\) = 5.8 \(\times\) 10\({}^{7}\) S/m. This structure is illustrated in Figure 1a,b, with the parameters listed in Table 1. To collect the induced current in the metasurface unit cell, a via is placed 3.25 mm below the center of the patch on the \(y\)-axis with a diameter 1.2 mm, rather than at the center of the patch, because the field strength at the center is zero. The electric field at the center of the metasurface unit cell becomes zero due to the symmetrical configuration of the unit cell, which causes the balanced surface charge distribution around the center. Consequently, no voltage difference is developed between the patch and the ground at this location, and thus no current flows through a via placed at the center. The resistive load, which is a simplified model representing the input impedance of a rectifier circuit according to [PERSON]'s theorem, is placed on the bottom layer to establish an electrical connection between the via and the ground plane, as performed in numerous works concerned with rectenna systems. The ground plane has a circular hole with a little larger diameter than the via. Also, a 50 ohm resistive load is integrated to achieve maximum absorption, based on the structure. This resistive load also collects RF energy. As the first case, two resistor placement models are presented in Figure 1c. The lumped resistor is placed in the \(y\)-axis direction in the first model (Model A). The lumped resistor is placed in the \(x\)-axis direction in the second model (Model B). The evaluation of metasurface unit cell performance was conducted through the use of the CST Microwave Studio 2020 commercial software, similar to the simulation methods described in previous papers found in the literature. In order to create a numerically infinite array, the unit cell's boundary conditions were applied along the x- and y-axes. The electromagnetic (EM) waves emitted through the Floquet port, with a total incident power of 0.5 W at the area of a unit cell, propagate along the \(-\)z direction. In this configuration, a linearly polarized plane wave with normal (vertical) incidence propagates along the \(-\)z direction toward \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Dimension (mm)** \\ \hline s & 15 \\
1 & 13 \\ m & 3.25 \\ d & 1.2 \\ \hline \end{tabular}
\end{table} 
Table 1: Descriptions of the structure parameters. Figure 1: The proposed first case unit cell of metasurface. (**a**) Perspective view. (**b**) Front view. (**c**) Back view for Models A and B. \(\varphi\) defines the polarization angle and \(\varphi_{p}\) defines the geometric angle position of the resistor from the center of the patch. the metasurface unit cell. At a polarization angle \(\varphi=0^{\circ}\) the electric field (E) is oriented along the \(y\)-axis and the magnetic field (H) is along the \(x\)-axis, forming a linearly polarized wave with fields confined in the x-y plane. The polarization angle \(\varphi\) is defined as the angle between the electric field vector and the \(y\)-axis, measured counterclockwise in the x-y plane, and is varied from \(0^{\circ}\) to \(180^{\circ}\) in the simulation. This paper focuses on investigating the polarization character of simple square patches. The data presented is a reflection of the incident wave and voltage on the resistive load. The absorption efficiency is evaluated by \(A=1-\left|S_{11}\right|^{2}\), where \(S_{11}\) is the reflection coefficient.