## 4 Discussion
### Variation of Impedance during Loading  
Without any load applied, the total impedance (\(Z_{\sigma}\)) equals the initial value (\(Z_{0}\)). The initial value of \(Z_{\sigma}\) may vary depending on the rock type, as indicated in Table 2. When a load is applied to the specimen and the electrodes at both ends are open circuit, the voltage \(U_{\sigma}(t)\) at both ends of the specimen is equal to the potential (\(E_{\sigma}(t)\)). If the relationship between \(U_{\sigma}(t)\), \(I_{\sigma}(t)\), and \(Z_{\sigma}\) follows [PERSON]'s law of complex impedance, then  
\[U_{\sigma}(t)/Z_{\sigma}=I_{\sigma}(t) \tag{29}\]  
In Equation (29), \(Z_{\sigma}\) represents the total microelement impedance of the specimen. The value of the total microelement impedance (\(Z_{\sigma}\)) is closely related to the total resistance (\(R_{\sigma}\)), total capacitance (\(Z_{\sigma}\)), and total inductance (\(Z_{L\sigma}\)) of the specimen. The total microelement impedance (\(Z_{\sigma}\)) of the specimen directly measured using an LCR instrument is listed in Table 2. According to Table 2, as the load (\(P\)) increases, the total microelement impedance (\(Z_{\sigma}\)) of the specimen shows a decreasing trend.  
The aforementioned types of rocks exhibit different dynamic impedance values when subjected to the same level of load (see Table 2). This indicates that  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Load** & **0** & **2** & **4** & **6** & **8** & **10** \\ \hline \multicolumn{8}{c}{8\# Granite sample} \\ \hline \(Z_{\sigma}(t)\) (k\(\cdot\)\(\Omega\)) & 0 & 0.264 & 0.102 & 0.326 & 0.309 & 0.480 \\ \(Z_{\sigma}(0)\) (k\(\cdot\)\(\Omega\)) & 374.0 & 146.0 & 129.0 & 119.0 & 112.0 & 106.0 \\ \(R_{\sigma}\) (k\(\cdot\)\(\Omega\)) & 171.0 & 131.0 & 120.0 & 113.0 characteristics of rocks are correlated with their types. Generally speaking, granite is primarily composed of quartz, feldspar, and mica, with a typically high content of quartz. Sandstone, on the other hand, is mainly composed of sand particles (usually quartz, feldspar fragments, or rock debris), with a sand content usually exceeding 50%. However, the quartz content in sandstone is not as significant as in granite. Research by [PERSON] et al. [28] has shown that the quartz content does not stimulate the activity and intensity of the electromagnetic radiation (EMR) signals generated by rock fracture. Secondly, changes in dynamic impedance involve resistance, capacitance, and inductance. Generally, due to its higher porosity, sandstone typically exhibits higher capacitance values, which, in turn, results in higher dynamic impedance values [35; 36]. This can be reflected in the capacitance measurements from Table 1 and the dynamic impedance measurements from Table 2. Regarding the orientation of minerals, minerals in granite have a certain degree of orientation, but this orientation is usually weak; the sand particles and cementing materials in sandstone may exhibit a stronger orientation, especially in the layered structures formed during the sedimentation process. When subjected to the same level of load, the mineral orientation in sandstone is more disturbed, leading to a more intense reset of the internal particle organization configuration, thereby exhibiting a greater dynamic impedance value. Although there are significant differences between different rock types, this study found that the dynamic impedance of different rock types shows a consistent overall downward trend, which can be generalized to a broader range of rock materials. However, to specifically reveal the correlation between the dynamic impedance characteristics of rocks and specific rock types and their microstructural properties, further research using techniques such as scanning electron microscopy (SEM) and X-ray micro-computed tomography (X-CT) will be required in the future.