# Design of Three-Dimensional Electrical Impedance Tomography System for Rock Samples
## 7 Results
### Rock and Ore Specim Test  
The previous section's model testing verified the system's high accuracy. To evaluate the system's performance in practical measurements of rock samples, a prototype was used to measure a granite specimen obtained through drilling. The physical specimen is shown in Figure 11, presenting a cylindrical shape with a length of 17 cm and a base diameter of 7 cm. Prior to the measurement, the specimen was soaked in water for 24 h and then removed. The immersion of the rock sample in water before testing served multiple purposes:  
1. Extended exposure and storage might have led to the formation of an oxide layer on the sample. This layer could potentially diminish the electrical conductivity of the rocks, influencing the accuracy of electrical parameters. Immersing the rock sample effectively eliminated the oxide layer, ensuring more reliable electrical test results. 2. The electrical conductivity of certain rocks is closely linked to their water content. Soaking the rock samples increased the water content within the rocks, thereby enhancing their electrical conductivity. This was particularly crucial for measuring specific electrical parameters, as wet rocks closely represented actual underground conditions. 3. Rock samples typically exhibit variations in porosity and water absorption properties. Without presoaking the rock samples, different levels of moisture content could lead to variations in measurement results. Uniformly soaking the specimens mitigated this variability, thereby improving the repeatability and accuracy of the measurements. Figure 10: Test result of model II when the potential electrode labeled as 1 is active. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Electrode** & \begin{tabular}{c} **Measured** \\ **Resistance** \\ **(f)** \\ \end{tabular} & \begin{tabular}{c} **Theoretical** \\ **Resistance** \\ **(f)** \\ \end{tabular} & \begin{tabular}{c} **Deviation** \\ **(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Measured** \\ **Phase** \\ **(mrad)** \\ \end{tabular} &
\begin{tabular}{c} **Theoretical** \\ **Phase** \\ **(mrad)** \\ \end{tabular} \\ \hline
1-1 & 1000.08 & 1000 & 0 & \(-61.95\) & \(-62.75\) & 0.8 \\
1-2 & 1998.87 & 2000 & 0.06 & \(-62.50\) & \(-62.75\) & 0.25 \\
1-3 & 2999.94 & 2999 & 0.03 & \(-62.57\) & \(-62.75\) & 0.18 \\
1-4 & 3991.17 & 3999 & 0.20 & \(-62.65\) & \(-62.75\) & 0.10 \\
1-5 & 4988.49 & 4999 & 0.21 & \(-63.08\) & \(-62.75\) & \(-0.33\) \\
1-6 & 5984.06 & 5999 & 0.25 & \(-63.38\) & \(-62.75\) & \(-0.63\) \\
1-7 & 6984.44 & 6999 & 0.21 & \(-63.53\) & \(-62.75\) & \(-0.78\) \\
1-8 & 7984.52 & 7999 & 0.18 & \(-63.47\) & \(-62.75\) & \(-0.72\) \\
1-9 & 8975.54 & 8999 & 0.26 & \(-63.24\) & \(-62.75\) & \(-0.49\) \\
1-10 & 9978.60 & 9999 & 0.20 & \(-63.31\) & \(-62.75\) & \(-0.56\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Complete measurements of model II when the potential electrode labeled as 1 is active. Following the soaking process, the rocks underwent a brief air-drying period. This step aimed to ensure the specimens' surfaces were dry, preventing residual water interference with the measurement results. Due to the cylindrical shape of the specimen, electrode connections were arranged in a circular pattern. At positions 3 cm, 7 cm, 11 cm, and 15 cm (marked in red in Figure 11a), a circular array of electrode connections was established [35], with 24 electrodes in each circle. Among them, the electrodes at positions 3 cm and 11 cm served as potential electrodes, while the other two positions were designated as current electrodes. The grounding electrode was placed at the center of the base [36]. The schematic diagram illustrating the arrangement of electrodes is presented in Figure 12. To enhance electrode-sample coupling, a damp dough was applied at the contact points between each electrode and the specimen. Figure 11b reveals the presence of a noticeable crack in the physical specimen [37]. Figure 11: Granite specimen. (**a**) The red markings indicate the precise positions of the electrodes.