## 2 Experimental
### Measurement of Shielding Effectiveness (SE)  
There are many EMI shielding mechanisms, but EMI shielding is largely caused by reflection, absorption, multi-reflection, or internal reflection mechanisms. Generally, electromagnetic reflection is typical. In metallic materials, when electromagnetic waves traveling in a certain direction pass through the shielding material, electromagnetic waves are reflected due to the difference in impedance between the medium through which electromagnetic waves pass on the surface of the material. In addition, there is an electromagnetic absorption mechanism in which electromagnetic waves such as conductive loss, dielectric loss, and magnetic loss are absorbed, converted into thermal energy, and then lost in the electromagnetic absorption. Most of these electromagnetic wave absorption mechanisms occur in carbon-based and magnetic-based materials. In addition, when the material is non-uniform or thick, there is an electromagnetic multi-reflection or electromagnetic internal reflection mechanism in which electromagnetic waves are transmitted in a completely different direction along the material without transmitting the material by electromagnetic scattering. To improve the shielding performance according to such a mechanism, a material with excellent permittivity, permeability, or high conductivity should be selected. In addition, the EMI shielding method using reflection may be determined by the material and the frequency of the incident but may be largely divided into a single-layer metallic shield and a multi-layer metallic shield. The single-layer metallic shield shielding method  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Features** & **Contents** \\ \hline State & Solid \\ Appearance & Powder \\ Particle size & 2.0 \(\upmu\)m, 4.0–4.4 \(\upmu\)m, 6.0 \(\upmu\)m \\ Particle shape & Spherical \\ Specific surface area & 0.40 m\({}^{2}\)/g \\ Bulk density & 4.2 g/m\({}^{3}\) \\ Purity & 99.9\% \\ Alternate Name & Silver-coated copper powder \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties of the core-shell powder.  
Figure 1: Schematic of the core-shell paste spraying process.  
refers to the aforementioned reflection loss, abortion loss, multi-reflection loss, and internal reflection loss. The multiple shielding effect may increase the shielding effect by adjusting the impedance and thickness of the shielding plates. In conclusion, to improve the EMI shielding effect, a material with excellent permittivity, permeability, or high conductivity should be used. To measure SE, the geometry of the specimen was prepared as depicted in Figure 2 according to the standard ASTM D 4935. Figure 3 illustrates the electromagnetic shielding measurement equipment that was used to analyze the SE of the proposed material; the measurement was obtained in the range of 1.5 to 10 GHz.  
Equation (1) indicates the calculation of SE, and the electromagnetic shielding measurements in this study were obtained using the same equation. The reference specimen without the electromagnetic shielding material was used in the electromagnetic shielding measurement to obtain a reference value. Additionally, the SE of the specimen coated with the electromagnetic shielding material was measured for comparative analysis.  
\[\mathrm{SE}=20 log\frac{V_{2}}{V_{1}}(\mathrm{dB}) \tag{1}\]  
\(V_{1}\): Received voltage when the shielding material is present. \(V_{2}\): Received voltage in the absence of the shielding material.