## 3 Results
The result indicated that the SE varied as a function of frequency; however, the average measurement was determined to be 64.57 dB. The electromagnetic shielding performance of the specimen was measured with a 30-um-coating of the core-shell paste on the aluminum baseplate. The results indicate that SE increases to an average of 77.27 dB as shown in Figure 6. As SE is expressed in dB, the shielding rates were determined to be 90, 99, 99.9, 99.99, and 99.999% for 20, 40, 60, 80, and 100 dB, respectively. As a value of 40 dB or more is close to 100%, the SE of the core-shell paste used in this study can be considered excellent. This cause may be due to characteristics of a core-shell structure made of a material with high electrical conductivity. The electrical conductivity of copper is known to be 5.98 \(\times\) 10\({}^{7}\) and that of silver is known to be 6.30 \(\times\) 10\({}^{7}\). This high electrical conductivity of copper and silver makes it easy to increase EM reflection, so it can be judged that the performance of EM shielding has improved. Furthermore, the core-shell structure is a structure in which a copper metal with a high degree of oxidation is coated on the inside and silver with a low degree of oxidation on the outside, thereby protecting the oxidation of the copper metal. Therefore, since it is smooth to maintain electrical conductivity for a long period of time, it may be used as a material capable of improving electromagnetic wave shielding characteristics. It is also more advantageous with respect to price than Ag powder, depending on the characteristics of cheap copper. According to these characteristics, if the process is combined with a simple spraying process, the composite material for an electromagnetic wave shielding coating film could have a great effect. Additionally, core-shell nanoparticles have garnered special scientific interest as they exhibit certain unique properties owing to their design, core geometry, shell, and the combination of core and shell materials. Particularly, the core-shell nanostructures are effective because of their optimal morphology, adjustable pore size (nanoparticles with porous shell), and free space between the core and shell, which imparts more stability under harsh environments [39]. Therefore, they have been used in \begin{table}
\begin{tabular}{c c} \hline
**Location** & **Sheet Resistance (\(\Omega/\square\))** \\ \hline
1 & 0.1309 \\
2 & 0.1410 \\
3 & 0.1254 \\
4 & 0.1321 \\
5 & 0.1387 \\ \hline \end{tabular}
\end{table} 
Table 2: Measurement of sheet resistance using a four-point probe. multiple fields, including medicine, engineering, electronics, and material science [40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51]. Although core-shell nanostructures are small, they are dominant entities with high thermal and chemical stabilities, low toxicity, high solubility, and high permeability to specific target cells [39]. Based on previously reported results, the properties of nanostructures vary depending on the core-shell particle size, shape, and material. In the future, a comparative analysis of SE should be performed according to the coating thickness of the core-shell paste and the wt% of the core-shell powder, and further studies on the oxidation resistance of the core-shell should be conducted.