## 1 Introduction  
In the design, construction, operation, and maintenance of tunnel, subgrade, rock slope, and mining projects, it is often necessary to fully utilize the compressive properties of rocks [1, 2]. In-depth research on the mechanical laws and response characteristics of rocks under compressive loading is particularly crucial for averting geological disasters. Rocks exhibit nonlinear stress and strain changes and generate various physical signals when subjected to external compressive load [3, 4, 5, 6, 7]. By utilizing these physical signals to obtain dynamic precursor information of rock failure, geological disasters can be predicted, and the impact of geological disasters can be minimized to the greatest extent [8, 9, 10, 11]. When rocks undergo changing compressive stress, free charges move and generate electromagnetic signals. The advantage of electromagnetic signals is their fast propagation speed, which makes the electromagnetic signal monitoring method a key means of predicting dynamic rock disasters [12]. To take advantage of the electromagnetic signals emitted by rocks under pressure, scholars began to explore the laws of these signals as rocks are subjected to external compressive loads. In the early stage, [PERSON] et al. [13], [PERSON] et al. [14], and [PERSON] et al. [15], respectively, reported the electromagnetic radiation (EMR) events of rock under external compression loads[PERSON] [PERSON] and [PERSON] [16] observed the changes in the electric field before complete failure of rock under uniaxial loading conditions with different strain rates[PERSON] [PERSON] et al. [17] detected EMR signals during granite fracture failure, and [PERSON] et al. [18] confirmed that rocks radiate electromagnetic signals in a certain area before and after peak stress. In addition, [PERSON] et al[PERSON] [19] also studied the acoustic emission (AE) and EMR characteristics of concrete and rock samples during laboratory compression tests, and verified that AE and EMR signals are the precursors of concrete and rock collapse. [PERSON] et al. [20] conducted experiments to record the electromagnetic radiation (EMR) and acoustic emission (AE) signals of granite samples under constant strain rate loading, finding that the onset time of EMR coincided with that of AE, and concluding that electromagnetic wave emissions were associated with microcracks in the samples[PERSON] [PERSON] et al[PERSON] [21] noted that as cracks continued to propagate, EMR amplitude increased; when crack propagation ceased, EMR pulse amplitude decayed. [PERSON] et al. [22] investigated a new technique for detecting high-frequency EMR signals emitted by rock microcracks to anticipate the initial stage of mine roof collapse. When analyzing the example results of EMR and low-frequency AE before the roof collapse in Moonee Colliery, it was found that abnormally high EMR was detected more than 1 h before the roof collapse, which had a significant time advantage compared with the first indicator of low-frequency AE. [PERSON] et al. [23] conducted tests on coal rocks to analyze the characteristics of low-frequency electromagnetic radiation signals (1 kHz) during sample fracture failure, and theoretically established the relationship between EMR signals and staged fractures. The above research confirms that rocks emit electromagnetic signals when subjected to pressure, and these signals are closely associated with the progression of rock damage. However, the mechanism of electromagnetic radiation from compressed rocks remains a perplexing issue. Scholars have made great efforts to explore the underlying mechanisms behind the electromagnetic radiation emitted by rocks under the action of external compressive loading. [PERSON] et al. [24] discovered the phenomenon of granite emitting electromagnetic waves in 1985 and discussed the process of generating electric dipole moments from the perspectives of contact electrification and piezoelectric electrification. [PERSON] et al.