## 2 Materials and Methods  
### Electrophysical Analysis Model  
Electromagnetic radiation will be produced in the process of compressive deformation and failure of rock. Figure 1 depicts a schematic diagram of a compression loading system with a rock specimen. The internal particles of the rock are not randomly distributed; rather, they are arranged in regular arrays, forming different structures. Both extrusion and shear deformation can change the structural configuration of the rock. Rock is cemented by mineral particles of different sizes, which are essentially composed of atoms. An atom consists of an atomic nucleus and electrons that orbit around it at high speed. In the absence of external forces, the rock appears uncharged and lacks electrical and magnetic properties. However, when an external compression load (\(P\)) is applied, the particles inside the rock are compressed or sheared, leading to a change in their structural configuration, known as particle structural configuration reset. During this process, the originally balanced electrons dissociate from the atomic nucleus and undergo polarization, as shown in Figure 2.  
Figure 1: Schematic diagram of loading sample (1. framework of pressure testing machine; 2. loading plate; 3. insulation plate; 4. electrode; 5. sample).  
In Figure 2, the polarized electrons try to neutralize the positively charged cations in their free state. This physical phenomenon is the electric effect caused by the load on the specimen, which is called the piezoelectric effect. The schematic diagram of the current generation (\(I\)) is shown in Figure 2. Current (\(I\)) can be obtained by integrating the infinitesimal current density (\(i\)) on the cross-section of the specimen. It is expressed as:  
\[I=\iint idS_{m} \tag{1}\]  
In Formula (1), \(S_{m}\) represents the microelement area of the cross-section in the specimen, measured in square meters (m\({}^{2}\)). The electromagnetic signal (\(B\)) emitted by the specimen is produced by current, measured in Teslas (T). The current, denoted as \(I_{\sigma}\), is generated under the action of the load and is measured in amperes (A).  
The electromotive force generated by the specimen, whether DC or AC, is expressed by \(E_{\sigma}\), then  
\[E_{\sigma}=\int Edl \tag{2}\]  
In Equation (2), \(E\) represents the electromotive force on a small length of the specimen under compression load, measured in volts (V). A potential difference, denoted as \(U_{\sigma}\), exists at both ends of the specimen, as illustrated in the piezoelectric effect circuit model in Figure 3. The value of \(U_{\sigma}\) can be determined through measurement or calculation and is expressed in volts (V).  
Since the loading device is a metal body, the electromotive force gathered at both ends of the specimen is equivalent to the short circuit of the conducting body, namely \(U_{\sigma}\) = 0 in Figure 4. During the loading process, displacement charge will continuously accumulate on the surfaces at both ends of the specimen. Under normal circumstances, the greater the pressure, the more displacement charge passes through the column of the loading device, and the greater the current flowing through the upper and lower plates, as shown in Figure 4 of the equivalent circuit model of the specimen under compression load. Assume that the current (\(I_{\sigma}\)) in Figure 4 flows from one end of the electromotive force (\(E_{\sigma}\)) and flows to the other end of the electromotive force (\(E_{\sigma}\)) through impedance (\(Z_{\sigma}\)). The current (\(I_{\sigma}\)) will excite the magnetic field (\(B\)), that is, the electromagnetic signal radiated by the specimen. Therefore, in the field of electricity, this is clearly a problem of  
Figure 3: Circuit model of piezoelectric effect.  
Figure 2: Physical model of loaded sample.  
finding the system's response at zero input. When there is no compression load (\(P\)), the input excitation (\(E_{\sigma}\)) of the circuit shown in Figure 4 is zero.