Abstract
The paper presents a block diagram of the recorder of electromagnetic and acoustic signals. The recorder provides monitoring of electromagnetic and acoustic signals under changing stress-strain state of heterogeneous materials and rocks. The analog amplifier input sensitivity of electromagnetic signals in 4 channels is 10 μV, that of the electromagnetic signal intensity is 10 μ and that of acoustic signals is 50 μV. The operating frequency range of recording is (1÷100) kHz. The averaging of electromagnetic and acoustic signal amplitudes is performed within 1 or 5 seconds. The data on electromagnetic and acoustic emission materials is recorded in digital format in the internal memory of the recorder. The recorder operates off-line within 7 days. Repeated testing of the recorder in natural conditions of the Tashtagol mine showed that the changes in the amplitude and frequency parameters of electromagnetic signals (EMC) indicate the structural damage in mines made of rocks which differ in their electrical properties. Measurements of the intensity of electromagnetic signals enable monitoring the changes in the stress-strain state of rocks during and after blasting and other geodynamic phenomena.
Highlights
Electromagnetic radiation (EMR) occurring in the rocks under mechanical impact has been studied for many years in many countries around the world [1,2,3,4,5,6,7]
Mathematical modeling of mechanoelectrical transformations in dielectrics and the experimental studies showed [8, 9] that monitoring of the electromagnetic emission (EME) and acoustic emission (AE) of heterogeneous materials, including rocks, requires an analog-to-digital instrument to detect and record electromagnetic and acoustic signals in a frequency range of (1÷100) kHz in the internal memory
The frequency ranges for electromagnetic emission detection were found in the study of rock block sizes conducted under the guidance of V.N
Summary
Electromagnetic radiation (EMR) occurring in the rocks under mechanical impact has been studied for many years in many countries around the world [1,2,3,4,5,6,7]. The ratio used for the fundamental wave frequency f = Vз/2L at the average speed of sound in rocks Vз=3000 m/s indicates that the blocks of these sizes emit mostly electromagnetic signals (EMS) in the above frequency range. The laboratory studies showed that the EMS parameters depend on the characteristics of the excitation acoustic signal. This proves that acoustic signals generated by emerging and propagating cracks have a significant effect on the EMS frequency spectrum, which can be observed in conditions of natural rock formation. Variations of the amplitude and duration of the excitation acoustic signal, and changed distance of the electromagnetic signal sensor from the radiating surface cause change in the EMS amplitude-frequency characteristics
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