## 4 Experiments
### Impact of Different Depth, Length, and Width of Corrosion Defects on the Test Results  
To investigate the impact of corrosion defect depth on the results of electromagnetic ultrasonic SH0 wave detection in flat steel, we selected specimens No. 2 and No. 3. In order to do this, we placed the electromagnetic ultrasonic transducer at points A, B, C, D, E, and F to detect the corrosion defects of 30 mm and 60 mm in length in both specimens. The relationship between the amplitude of the echo signal and the depth of the defect is shown in Figure 13a. Figure 12: (**a**) Echo signals at different distances and (**b**) end-face echo signal. Similarly, we placed the EMAT at three points G, H, and I of specimen No. 4 and three points J, K, and L of specimen No. 5. We then detected the corrosion defects of varying lengths and widths and obtained the echo amplitude versus the length and width of the corrosion defects, as depicted in Figures 13b and 13c, respectively. The experimental results are consistent with the simulation results, indicating that an increase in the depth and length of a corrosion defect leads to an increase in the defect echo signal. In contrast, the width of the corrosion defect has almost no effect on the amplitude of the echo signal. The impact of defect depth or length on signal growth is relatively small, as shown in both simulation and experimental results, indicating high simulation model accuracy and good consistency with experimental results. Therefore, we conclude that electromagnetic ultrasonic guided waves are suitable for detecting corrosion defects in grounding flat steel transmission towers. Furthermore, the size of corrosion defects can be evaluated using the relationship between the echo amplitude and the defect. When considering multiple artificial defects in a single sample during an experiment, it follows that the received signal of the transducer will contain multiple echo signals, impeding accurate assessment of the experimental results. Hence, we analyzed the propagation of ultrasonic guided waves in grounded flat steel using an F-point inspection of specimen No. 3 as an illustrative example. As shown in Figure 14, when the electromagnetic ultrasonic transducer is at point F for detection, the ultrasonic guided waves encounter three defects in succession during propagation, resulting in three propagation paths labeled 1, 2, and 3. Due to the varying distances between the transducer and each defect and the constant wave velocity of the electromagnetic ultrasonic SH0 wave, the echo signals from each defect appears at different times in the received signal of the transducer. Therefore, by analyzing the diagram's guided wave propagation paths and transducer signal reception, we can quickly identify the echo signal required for quantitative detection at point F as the number 2 echo. Consequently, in practical testing the position of defects or flat steel surfaces can be determined by analyzing the guided wave velocity and propagation time. However, distinguishing between defects and welded joints requires further analysis with actual construction drawings or excavation inspections. Therefore, to avoid the influence of welded joints, detection is usually carried out by excavating at the four corners of the square-frame-type grounding electrode, as shown in Figure 14b. Figure 13: (**a**) The relationship between the amplitude of the guided wave and the depth of corrosion defects, (**b**) the relationship between the amplitude of the guided wave and the length of corrosion defects, and (**c**) the relationship between the amplitude of the guided wave and the width of corrosion defects. Field detection was carried out on several pole towers with grounding flat steel. According to experimental results, electromagnetic ultrasonic non-destructive testing technology can effectively detect transmission tower grounding flat steel defects and accurately detect corrosion defects in flat steel.