The core problem faced by coal mining is coal rock identification. In order to improve the accuracy of coal rock identification, this paper proposes that radar antenna frequency and detection height have an impact on the identification accuracy of coal rock interface. First of all, using matlab simulation, simulation results show that under different frequencies, the identification accuracy of air-coal seam interface increases with the increase of frequency, but the identification of coal rock interface only in the frequency is low only partial error. Secondly, under different detection heights, the identification accuracy of air-coal seam interface becomes more and more accurate with the increase of detection height, but in this experiment, the identification accuracy of the coal-rock interface is the same, which cannot be ruled out because of the insufficient experimental data, the problem still needs to be verified by a large number of experiments. The above research shows that the antenna frequency and detection height of ground penetrating radar have a certain impact on the identification of coal and rock.
In order to study the factors affecting the identification accuracy of coal-rock interface with ground penetrating radar, the finite-difference time-domain (FDTD) method is used to study the law of dust interference, water content of medium and dirt separation under different conditions. The excitation source is 900MHz Blackman-Harris pulse, and Mur twodimensional absorption boundary conditions are adopted to establish different radar forward modeling models. The simulation results show that: Air dust can absorb or scatter the energy of radar signal. The relative dielectric constant of air is set to 1, 2, 2.5, and the corresponding electrical conductivity is 1Ms/m, 4Ms/m, 10Ms/m. The results show that the amplitude of reflected wave decreases successively, and the accuracy of radar system detection decreases gradually. With the increase of coal water content, the energy of reflected wave decreases. The relative dielectric constant of coal seam is set as 3, 4 and 6. The results show that the amplitude of reflected wave decreases successively, which limits the detection range of radar system. When there is interference near the coal wall interface, the reflected wave of the coal wall interface and the reflected wave of the air-coal wall interface are superimposed, which brings challenges to the accurate identification of coal rock interface.
KEYWORDS: General packet radio service, Antennas, Mining, Ground penetrating radar, Dielectrics, Radar, Electromagnetic radiation, Signal processing, Radio propagation, Data processing
The research and application of coal-rock interface identification technology is an important part of the intelligent system construction of fully mechanized mining face. Through the automatic identification of coal-rock interface, the cutting height of shearer drum can be adjusted in time to avoid the problems of "under-cutting" and "over-cutting". At present, the research of coal-rock interface identification technology is widely carried out. This paper mainly proposes a coal-rock interface identification method based on ground penetrating radar. Considering the installation and identification accuracy of GPR under actual working conditions, the forward detection method of GPR is proposed. The GPR is installed on the coal mining machine and emits high-frequency electromagnetic waves in front of the coal wall. Due to the different dielectric constants of coal and rock, the characteristics of the received direct waves are also different. By comparing the characteristics, the cutting medium of the current sampling point can be determined, and the interface curve of coal and rock can be obtained by curve fitting.
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