## 3 Results  
The unit cell and dimensions of the structure are shown in Figure 2a,b where the dimensions of the steel bar are 18 mm in length and 8 mm in diameter. The sizes and the material parameters for the simulations are the same as the experimental ones. The negligible free-space path loss was not considered in simulations. The simulated result is shown in Figure 2c,d; it can be seen from Figure 2c that the absorptivity of concrete without metamaterial absorber is about 0.1, which is low. When the metamaterial absorber is introduced into concrete as in Figure 2b, the absorptivity at 9.82 GHz reaches 98%, as shown in Figure 2d. These results indicate that the EMW absorbance is caused by metamaterial structure. In the experiment, we measured S-parameter curves of metal plane reflector for S11 and free-space path without samples for S21 which are named S11 cal and S21 cal, respectively. The measured S11 and S21 with the metamaterial absorber as sample were named S11 sam and S21 sam, respectively. Considering the loss of the environment (e.g., air), the two S-parameters need to be subtracted, and the final S-parameter is S = Ssam \(-\) Scal. Then, absorptivity can be calculated by Equation (1). The simulated and experimental results are shown in Figure 3. There are small differences between the measured and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cement** & **Sand** & **Stone** & **Water** \\ (**kg/m3**)** & **(kg/m3**)** & **(kg/m3)** & **(kg/m3)** \\ \hline
408 & 576 & 1169 & 200 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mix proportions of the concrete. Figure 2: The designed metamaterial absorber and simulation results: (**a**) unit cell of the steel bar structure, in the simulations, the EMW k is incident to the \(y\)-axis, with magnetic field H parallel to the \(z\)-axis, and electric field E parallel to the \(x\)-axis; (**b**) unit cell of the metamaterial absorber within the concrete; (**c**) simulated absorptivity spectrum of concrete without metamaterial absorber; and (**d**) simulated absorptivity spectrum when a = 2.50 mm, \(\varepsilon=150\). simulated results which are caused by tolerances in the manufacture and environmental disturbance in experiment, et al. Figure 3a demonstrates the absorption both in simulated and experimental results. The effect of polarization angles \(\varphi\) and incident angles \(\theta\) for transverse electric (TE) and transverse magnetic (TM) waves on the absorbance of the absorbers at 9.82 GHz are studied and the results are shown in Figure 3. The results indicate that the EMW absorption is insensitive to polarization because the absorption rate does not change with \(\varphi\) varying in the range of 0-75\({}^{\circ}\), as shown in Figure 3b. For the TE mode, the absorption at 9.82 GHz decreases gradually with the increasing of \(\theta\) from 0\({}^{\circ}\) to 75\({}^{\circ}\), and reaches 90% when \(\theta\) = 75\({}^{\circ}\), and the results are shown in Figure 3c. For the TM mode, the absorption at 9.82 GHz decreases from 98 to 50% with the increasing of \(\theta\) from 0\({}^{\circ}\) to 75\({}^{\circ}\), which is shown in Figure 3d. When the TE wave is obliquely incident to the designed metamaterials absorber, the electric field direction is always parallel to the surface of the absorber; however, the angle between the magnetic field and the surface of the absorber increases with the increasing of incident angle, resulting in a decrease in absorption. The TM wave shows similar results with the TE wave. The simulation and experimental results demonstrate the good absorption performance of the designed absorbing concrete with wide incident angle. To clarify the origin of the EMW absorption, the energy density of electric field and magnetic field at 9.82 GHz when a = 2.5 mm was studied, and the results are shown in Figure 4. Figure 4a,c show the cross-sectional E-field and H-field distribution in the y-z plane and x-z plane, respectively.