## 4 Laboratory Experiment Verification of space state Transformation
### Experiment Procedure  
The PROTEM47 transient electromagnetic instrument is shown in Figure 9. The PROTEM47 transient electromagnetic instrument could observe three components at the same time, and could also measure a single component separately. The turn-off time is one of the important technical indicators of the transient electromagnetic instruments. If the turn-off time is long, shallow signals are lost, the intensity of the secondary field weakened and the detection effect directly affected. The turn-off time of the device depends on the performance of the transmitting, the size of the transmitting current, and the size of the transmitting coil. Theoretically, the turn-off time of the PROTEM47 could be as short as 0.5 \(\upmu\)s. In terms of coil design, the coil is made of copper metal wire, and its shape is square, as shown in Figure 10. The coil size was selected according to different requirements. In the indoor experiment, the width of the transmitting coil and the receiving coil were both 5 cm, the number of turns of the transmitting coil and the receiving coil were both 30 turns, the diameter of the transmitting coil and the receiving coil were both 0.51 mm, and the transmitting current was 0.5 A.  
Figure 10: The type of the transmitting coil and the receiving coil. (**a**) Copper metal wire; (**b**) Coil of a certain size. Figure 9: The PROTEM47 transient electromagnetic instrument. The main content and process of this experiment were as follows:  
1. The half space state: In the similarity experiment, only the saline medium was used to simulate the three-dimensional uniform half space medium. According to the conductivity and volume of the saline medium, a suitable amount of solid salt was added, and the saline height was set to the half-height of the container. After the liquid surface was calm, the transmitting coil and the receiving coil were placed 5 cm above the surface of the saline solution. The plane of the coil system was parallel to the surface of the solution. The transient electromagnetic response data were measured and recorded. 2. The full space state: Similar to the response experiment in the half space state, the saline medium was used to simulate the three-dimensional uniform full space medium. According to the conductivity and volume of the saline medium, an appropriate amount of solid salt was added, and the saline height was set to the height of the container. After the liquid surface was calm, the transmitting coil and the receiving coil were placed in the center of the solution space, and the plane of the coil system was parallel to the solution surface. The transient electromagnetic response data were measured and recorded. 3. The 3/4 space state: Similar to the response experiment in the half space state, only the saline medium was used to simulate the three-dimensional uniform 3/4 space medium. In the lower-left corner of the model space, the air bag was placed and fixed to take up a quarter of the space. After the conductivity of the saline medium was adjusted to the design value, and the liquid surface was calm, the transmitting coil and receiving coil were placed in the center of the solution space, and the plane of the coil system was parallel to the solution surface. The transient electromagnetic response data were measured and recorded. 4. Judgment of critical distance in the 3/4 space state: Based on the experiment of no abnormal body response in 3/4 space state, the transmitting coil and receiving coil were moved 0.1 m, 0.2 m, 0.3 m, 0.4 m, and 0.5 m, in turn. The transient electromagnetic response data were measured and recorded. Taking the 3/4 space state as an example, the preparation process of the experiment is described in detail. According to the schematic diagram in Figure 8, a polypropylene water tank with a certain water pressure resistance was selected as the experimental container, and EPE pearl cotton foam board was selected as the high-resistance filler.