Research On Imaging Of Long Offset Radio Wave Penetration Detection In Big-width Coal Face

With the development of China’s coal mining and exploitation,it need higher and higher geological guarantee to fully mechanized coal face.Currently,radio wave penetration method has become one of the most widely used technologies for exploring geological anomaly bodies within coal face.Because of technology restrictions such as equipment,data acquisition method,data processing and interpretation,exploration results often cannot meet the demands of coal mining for big-width coal faces,so researching on imaging of long offset radio wave penetration detection in big-width coal face has important theoretical and practical significance.On the basis of data collection,theoretica formula derivation,numerical simulation,observation system improvement,field experiment and comparison with disclosed geological data by coal mining,a detailed study has been carried out for long offset radio wave penetration detection in big-width coal face.The main results can be summarized as follow:1)based on the basic formula of electromagnetic wave propagation transmitted by magnetic dipole antenna,a field strength formula of radio wave propagation for coal face is derived,which can be used well for measured field strength values observed from receivers.It has analysed the influence of the variation of absorption coefficient to propagation distance,and also analysed the varying pattern of perspective theoretical field strength curves corresponding to the variation of rock’s absorption coefficient values and the width of coal face,which has provided the theoretical foundation of geological anomaly interpretation for big-width coal face;2)It is put forward that the effective perspective width value for coal face can be calculated by initial field strength H0,absorption coefficient β and background field strength HB with a special instrument and operating frequency;3)A method to calculate H0 and β values is put forward,the H0 values can be calculated from the H data near the transmitter in the transmitting gateway,while βvalues can be calculated from the H0 values and H data observed in the receiving gateway.The calculated results are more reliable than those derived from transmitting or receiving gateway;4)The multi-frequency radio-wave penetration method is put forward for big-width coal face.Through two or more operating frequency detection,the more suitable frequency can be gotten,the results can be used to comprehensively analyze effect degree and area of geological anomalies,which can improve the accuracy degree of radio-wave penetration;5)Field strength increment method is put forward to detect the geological anomalies within a big-width coal face.At each received point,the total field strength value and the background field strength value are observed for calculate field strength increment value.The test in the coal face demonstrates that the method can eliminate the effect of background field strength,and improve the resolution capability of present radio wave instruments for geological anomalies;6)In order to solve the problem of big variation of initial field strength values within a coal face,it is put forward that radio-wave penetration technology with measured initial field strength values to explore the geological structures.It adopts the device of one-transmitter and two-receivers,while one receiver is used to receive the signals near the transmitter in the same gateway to calculate H0 values,the other receiver used to receive the perspective field strength H values in the other gateway.The image of inverted βvalues are more objective to reflect the electrical changes of coal and rock,which can give better images to delineate geological anomalies within a coal face;7)A long offset radio wave detection pattern for big-width working face is given:First of all,through theoretical analysis and known data collection,the possible frequency range and detection methods are estimated.Then the suitable working frequency range and optimum working frequency are determined by multi frequency actual detection.Finally,the results of similar conditions coal faces are detected to achieve the effect of rapid and fine imaging.