Multi frequency perspective fine detection of radio wave for thin coal areas in fully mechanized coal face

The large area of thin coal area in the fully mechanized coal mining face is difficult to be detected accurately by the single frequency perspective detection of radio wave, which seriously affects the efficient and safe production of coal face. In order to detect the occurrence of thin coal area more precisely, a method of multi frequency perspective detection of radio wave is put forward. Taking coalface 1610A of Zhangji mine of Huaihe Energy Group as the research object, according to the geological conditions, four frequency(0.088, 0.158, 0.365 and 0.965 MHz) perspective detection are selected to delineate the thin coal area, and the relationship among the perspective field strength value, absorption coefficient value and working frequency is analyzed. The results show that with the increase of working frequency, the value of perspective field strength generally shows a downward trend, and the value of absorption coefficient shows an upward trend; with the detection of the same frequency, the lower the thinning degree of coal seam, the higher the value of perspective field strength, the lower the value of coal rock absorption coefficient; thin coal area with high thinning degree is reflected in multiple frequency detection results, while thin coal area with low thinning degree is only reflected in high frequency. The range of two thin coal areas delineated by multi frequency detection is consistent with the verification of mining exposure, which proves that multi frequency detection can effectively identify and delineate the influence range of different thinning areas, and realize the fine detection of the thinning area of coal seam. The Fresnel zone of radio wave with frequency ≥ 0.965 MHz is narrow, and the energy propagates nearly linearly, which can identify two thin coal areas 10 m apart in the strike. Using radio wave multi frequency detection can realize the fine detection of large-scale geological abnormal area in the working face.