# Study on the Absorbing Properties of V-Doped MoS2
## 3 Result and Discussion
### Analysis of Absorbing Mechanism  
Attenuation characteristics are a key factor influencing the absorbing properties of materials [32]. Specifically, the ability of a material to efficiently convert EM waves into thermal energy and other forms of energy through conduction loss and dielectric loss is referred to as EM wave attenuation characteristics. As shown in Figure 6a, VMSA exhibits higher electrical conductivity than VMS, which is attributed to the annealing treatment resulting in increased V doping concentration and reduced oxidized impurities \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Sample** & **RL\({}_{min}\) (dB)** & **d (mm)** & **f (GHz)** & **Bandwidth (GHz)** & **EAB (GHz)** & **d (mm)** & **RL (dB)** & **f (GHz)** \\ \hline VMS-30 & \(-28.17\) & 5.10 & 18.00 & 1.27 & 2.40 & 5.46 & \(-25.09\) & 16.81 \\ VMS-40 & \(-32.24\) & 1.78 & 12.20 & 3.23 & 4.40 & 1.43 & \(-26.22\) & 15.60 \\ VMS-50 & \(-7.40\) & 1.38 & 11.60 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ VMSA-40 & \(-9.64\) & 1.45 & 11.40 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ \hline \end{tabular}
\end{table} 
Table 1: Parameters of absorbing properties. Figure 5: The EAB of (**a**) VMS-30, (**b**) VMS-40, (**c**) VMS-50, and (**d**) VMSA-40. with low-conductivity. The high conductivity of VMSA also leads to an increase in its conduction loss capability. Additionally, the total attenuation capacity of EM waves can be quantified by the attenuation coefficient as shown in Equation (9). Generally, a higher attenuation coefficient indicates a stronger capacity for EM wave absorption [33]. As depicted in Figure 6b, the attenuation coefficients of the VMS-30, VMS-40, VMS-50, and VMSA-40 samples increase with frequency in the range of 2-18 GHz. Moreover, the attenuation coefficient rises with increasing filler content. For example, the loss capacity of VMS-50 is stronger than that of the other samples, while VMS-30 exhibits the weakest loss capacity. Notably, when the filler content is 40 wt%, the attenuation coefficient of the annealed sample (VMSA-40) is higher than that of the unannealed sample (VMS-40), indicating that annealing enhances the material's loss capacity. However, the absorption performance of VMS-50 and VMSA-40 is not ideal, primarily because impedance matching is another critical factor in determining comprehensive absorption performance. Impedance matching refers to the degree of similarity between the material's characteristic impedance and that of free space [34]. It is worth noting that the impedance matching (\(|Z_{in}/Z_{0}|\)) discussed herein is derived from transmission line theory and calculated based on the complex permittivity and permeability, rather than measured through electrochemical impedance spectroscopy (EIS). When the material's characteristic impedance (evaluated using Equation (7)) is closer to the impedance of free space, EM waves can reflect less at the interface and penetrate deeper into the material. Ideally, when the coating's characteristic impedance matches that of free space, EM waves can enter the material directly without reflection [35; 36]. Therefore, excellent absorbing materials should possess both strong attenuation characteristics and good impedance matching [37]. As shown in Figure 6c-f, it is evident that the impedance matching of VMS-30 is the largest in the area close to 1, and the impedance matching of VMS-40 is close to 1. However, after annealing at a filling ratio of 40 wt%, the impedance matching decreases, and no areas close to 1 are observed. When the filling ratio is further increased to 50 wt%, areas with impedance matching close to 1 are virtually absent. Consequently, the comprehensive absorption performance of VMS-50 and VMSA-40 is the worst, with RL\({}_{min}\) values higher than -10 dB. Although VMS-30 has good impedance matching, its loss capacity is weaker than that of VMS-40, resulting in lower comprehensive absorption performance.