Study Of Characteristic Of Electromagnetic Wave Attenuation In Frequency Domain In Coal-Rock Medium

The apparent characteristics of mine production is the underground operation, affected by geological conditions, geological structures and coal seam constructure, and the disaster such as coal dust, methane, fire, water and roof collapse are liable to occur under the mining process and seriously imperil the mining safety and life of miners. The radio wave penetration method is one of the common physical detection methods in mine and can effectively detect the geological abnormity such as the gas-logged zone, water-bearing body and igneous rock corrosion and so on in the working face. Therefore it is of improtant theoretical and realistic value to study the response character of the radio wave transmitting in coal-rock medium and geological abnormity.This paper studied the characteristic of electromagnetic wave attenuation separately in time and frequency domainin in coal-rock medium and geological abnormity, through the forward simulation of the radio wave penetration. Several of representative models were carried the forward simulation of the radio wave penetration through the finite-difference time-domain method with the Matlab language and the time-domain response waveform and field intensity spacial distribution were obtained. The forward simulation manifested that the amplitude of received signal which crossed the low resistance abnormity was diminished and the amplitude of received signal which crossed the high resistance abnormity was increased, at the same time the field intensity in abnormity was different from the around. The paper numerically simulated the centroid frequency downshift in frequency domain. The numerical simulation manifested that the centroid frequency of received signal happened zero-shifting and proved the theory of centroid frequency downshift is right. Spectrum analyse was made and the average attenuation coefficient from the source to received point was calculated separately using the intensity attenuation method and the centroid frequency downshift method to the two models which abnormal body is square. That the changed span of average attenuation coefficient calculated by centroid frequency downshift method was larged than by intensity attenuation method displayed that the centroid frequency downshift method was...