## 4 Case Study for a Brigade-Level EMP Shelter Using the Finite Integrating Method  
The materials and structure of the building should be identified to estimate and simulate the EMP damage range for the building. The simulation programs used for numerical analysis of buildings can be classified mainly into four methods: the method of moment (MoM), the finite element method (FEM), the finite difference time domain (FDTD), and the finite integrating method (FIM). Among various analysis programs, Feko is a typical commercial numerical analysis program that uses MoM. Although Feko provides robust analyses for large buildings, it requires a lot of analysis time for a system structure mixed with small buildings. The high-frequency structure simulator (HFSS) is based on FEM. Although the HFSS can segment meshes according to their shape, it can perform a suitable analysis of a building, regardless of its shape, based on the high-frequency band numerical analysis method, and provide excellent accuracy. However, for complex or large buildings, the analysis time is longer compared to other programs [26]. SEMCAD is a commercial representative analysis program using the FDTD method that does not require repeated analysis (analysis characteristics of FDTD). Furthermore, the FDTD algorithm is simple and can be implemented efficiently and easily. As not only the building but also the surrounding environment of the building must be considered, the program execution time is long. Furthermore, if the building shape is curved, there is a limitation to linking with other programs. Microwave Studio (MWS) is a commercial program that uses FIM, which is a new analysis algorithm different from conventional methods. MWS is capable of processing curved boundaries and complex shapes. Moreover, it produces analysis results quickly. Therefore, in this study, we used MWS to calculate the EMP protection performance of brigade-level protection facilities and apply the differentiation application measures. Natural shielding efficiency against an EMP was modeled for the computer room among various brigade-level facilities on the ground and underground by assuming that it was an EMP shielding facility. The underground soil condition was classified into dry soil and wet soil, considering the terrain characteristics of South Korea. As the EMP-shielding efficiency of concrete walls varies depending on reinforcement configuration, a standard type of reinforcement configuration (15 cm \(\times\) 15 cm) was assumed. Figure 2 shows the geometric design of the modeled EMP rooms. The EMP shielding rooms comprised office rooms, a communication room, a control room, and an equipment room in a building having dimensions of 13 m \(\times\) 13 m \(\times\) 2.7 m. Among various components of the building, four windows were physically most vulnerable to high-power EMPs. Additionally, the building had one main entrance, which was also vulnerable. For the simulation settings, four bands, i.e., 10 kHz, 10 MHz, 100 MHz, and 500 MHz, were applied among analysis frequencies ranging from 10 kHz to 1 GHz, which were signal characteristics of nuclear EMPs, described in IEC-61000-2-9. Additionally, for demonstrating the maximum intensity of E1 pulses, a 50 kV/m pulse was applied. E-field probes were installed at seven places to identify EMP attenuation characteristics, as shown in Figure 3. As shown in Figure 4, air and soil were modeled to show the radiation of the E1 pulse. Figure 5 shows the waveform and maximum intensity of the E1 pulse. Table 4 shows the input values and material properties for air, dry soil, and wet soil conditions.