Recording of ultra-low frequency electromagnetic emission during loading of a rock sample

We present a survey of publications devoted to the investigation and analysis of the specific features of recording of the electromagnetic emission detected in the process of loading of the samples of rocks, metals, and composite materials both under laboratory conditions and in the areas of disintegration of rock masses at the sites of mining. The electromagnetic emission observed in the process of destruction of rock samples in the laboratory experiments and under the field conditions can be detected not only in the high-frequency and low-frequency ranges (1000–3⋅10⁶ Hz and 500–1000 Hz, respectively) but also in the very-low- and ultra-low-frequency ranges (200–500 Hz and 0.01–200.00 Hz, respectively). However, the overwhelming majority of the results of experimental studies of rock samples subjected to the action of destructive loads under the laboratory conditions are aimed at measuring the electromagnetic emission in the high-frequency range. An instrumental measuring complex aimed at recording electromagnetic emission in the ultra-low frequency range is described. The composition of this instrumental measuring complex includes magnetic modulation transducers of magnetic induction used as magnetic-field sensors. We describe the procedure of laboratory experiments aimed at recording, by the proposed instrumental measuring complex, electromagnetic signals caused by the action of external loads upon the rock samples. An example of uniaxial loading of a basalt sample is presented. In the course of loading of the analyzed samples, the amplitude of pulses of the electromagnetic emission exceeds the level of background fields caused by the anthropogenic magnetic noise by two orders of magnitude. The high sensitivity of the magnetic modulation transducer of magnetic induction makes it possible to use it for recording the components of magnetic induction in the process of destruction of rock samples in the presence of interference caused by the anthropogenic magnetic noise. The accumulated results are important for monitoring and prediction of the process of cracking prior to mining impacts, as well as for the investigation of the geologic media and the processes of generation of the low-frequency electromagnetic emission in mining areas.