Study On The Influence Of Coal And Rock Electrical Parameters With Different Frequencies At The Radio Wave Perspective

With the increasing intensity of deep mining in coal mines,coal mining enterprises in China are increasingly threatened by water disasters,resulting in serious loss of people's lives and property.In the field of coal mine geological structure detection,it is one of the important prevention and control technical means in "Coal Mine Safety Regulations" and "Detailed Rules for Coal Mine Water Prevention and Control".Among them,the difference of coal and rock electrical parameters is the physical basis of electromagnetic detection.In the past,most of the electrical parameters used by electromagnetic method were measured at a frequency lower than 1KHz.Although a series of theoretical problems of detection have been solved,in actual detection,the frequency used by underground electromagnetic wave detection varies widely.In view of whether there are differences in electrical parameters at different frequencies and whether these differences affect the detection accuracy,the measurement of electrical parameters at different electromagnetic wave frequencies(DC-8MHz)has important theoretical and practical significance for exploring the propagation law of electromagnetic waves and improving the detection accuracy of electromagnetic waves.Therefore,relying on the national key research and development project-"Research on dynamic intelligent detection technology of hidden geological factors causing disasters in coal mines",this paper analyzes the micro-pore structure of coal surface through environmental electronic scanning mirror and nuclear magnetic resonance experiment;The multi-frequency dielectric constant test fixture was developed in cooperation with the manufacturer,and the dielectric constant measurement experiments of coal samples in different areas were carried out,and the variation law of electrical parameters of different coal samples under different frequency conditions was discussed Finally,combined with the electromagnetic wave theory,the influence of the electrical parameters of coal samples on the perspective of wireless electromagnetic waves at different frequencies is analyzed by using conditional experiment method.Through laboratory test,numerical calculation,theoretical derivation and field engineering verification,the following conclusions are obtained:(1)The characteristics of micro-pore structure of coal samples in different areas are different,so are their dielectric constants and resistivity.In the frequency range of 1 k Hz? 8MHz,with 1MHz as the dividing line,the dielectric constant of coal samples in various regions decreases first and then increases with the increase of frequency;With the increase of frequency,the resistivity of coal samples shows a trend of first sharply decreasing,then rapidly increasing to reach the local maximum,then gradually decreasing and infinitely tending to zero.(2)The capacitance first decreases and then increases with the increase of frequency;Before 1MHz,the overall distribution of dissipation coefficient D decreases first and then increases with the increase of frequency.After 1MHz,dissipation coefficient D increases first and then decreases with the increase of frequency.(3)The amplitude attenuation constant of electromagnetic wave increases with the increase of conductivity and frequency of coal bed medium;It decreases with the increase of dielectric constant of coal seam medium,and the change of attenuation constant is faster than that of low frequency electromagnetic wave at high frequency.(4)There are obvious differences in electrical parameters under different electromagnetic wave(DC-8MHz)frequencies,which have a significant impact on wireless electromagnetic wave perspective detection.It has been verified by field detection engineering that the detection accuracy can be improved by using different frequency measurement parameters for correction.