## 5 Conclusions  
Due to the advantages of fast, accurate, and wide detection range, ultrasonic guided wave technology is used for defect detection of various materials. Based on this, we analyzed the dispersion and guided wave structure of electromagnetic ultrasonic SH waves, studied the attenuation characteristics and inverse and transmission of ultrasonic SH waves in flat steel, and explored the relationship between defect size and the echo signal of flat steel, reaching the following conclusions. (1) Compared with other higher-order SH waves, the wave structure of SH0 waves is more straightforward and does not disperse when propagating in grounded flat steel. In practical engineering structural defect detection, using SH0 waves can reduce the interference of clutter signals generated by mode conversion, reduce detection complexity, and make the detection signal easier to analyze and identify. (2) When neglecting the ambient temperature and pressure around the grounded flat steel without considering the attenuation effect of the soil around the flat steel on the  
Figure 14: (**a**) Ultrasonic guide path and received signal during the test on specimen No. 3 and (**b**) square-frame-type grounding electrode of transmission tower. Figure 15: (**a**) Grounding lead wire inspection of 35 kV steel pipe tower and (**b**) detection of grounding flat steel of 220 kV transmission tower. absorption of the guided wave, the attenuation coefficient of the SH0 wave in grounded flat steel is only 0.0016 dB/mm, which confirms the feasibility of long-distance detection of grounded flat steel with SH0 waves. The amplitudes of transmitted and reflected waves are different due to the different lengths of flat steel defects; as the defect length increases, the amplitude of the reflected waves gradually increases, while the amplitude of the transmitted waves gradually decreases. The increase in the reflected waves (decrease in the transmitted waves) gradually decreases and stabilizes during the process in keeping with the defect length (from small to large). (3) For the same corrosion defect, the farther the detected distance is, the smaller the echo signal amplitude is. Flat steel corrosion defect reflected echo amplitude increases with increasing defect depth and length, while the change of defect width has little effect on the SH0 wave reflected echo amplitude. We used Q235 flat steel for transmission tower grounding devices as the test material. Due to financial constraints, there were few sample materials, the number of experiments was limited, and the experimental data were little. We hope that the data from this study can provide a new method for corrosion detection of power system grounding devices to replace traditional methods such as manual excavation, electromagnetic field analysis, and network nodes. The proposed method can provide a basis for locating and quantitatively detecting defects in transmission tower grounding devices as well as for estimating the operation lifetime of transmission tower grounding devices. In order to further improve the detection accuracy of ultrasonic guided waves, achieve accurate detection and determination of the degree and location of rusting of flat steel, and promote the application of this detection method, further research can be carried out in the following areas. (1) Further research on the irregularity of defect shape, randomness of defect location, and attenuation characteristics of the soil on ultrasonic waves to measure the degree of roughness due to corrosion, calculate the attenuation component caused by the propagation distance on the ultrasonic guided wave signal, and use it to compensate for the actual detected echo signal amplitude while excluding the influence of detection distance on the detection signal. (2) Conduct long-term corrosion monitoring on grounded flat steel in transmission towers to establish an assessment system for the working life of grounded flat steel.