Research On Transient Electromagnetic Detection Device In Mine Hole And Its Characteristics

With the increasing demand for fine detection in coal mines,the research pace of borehole geophysical exploration is gradually accelerated in the industry,so the borehole transient electromagnetic(TEM)emerges as the times require.It is necessary to study the response characteristics of TEM to abnormal body.In this paper,the self inductance,mutual inductance and equivalent inductance of single and double dipole transmitting coils are derived theoretically.At the same time,according to the Simulink circuit simulation module of MATLAB,the equivalent circuit model of transmitting coil is built.Through the response characteristics of primary field(transmitting current),it is determined that the influence of inductance on transmitting current is better than other parameters under the same condition The number(resistance,capacitance)is even greater.When the 90 ° space angle between the coils is found out,the mutual inductance can be reduced to the greatest extent,and the inductance of the system can be reduced indirectly,so as to effectively improve the current emission effect and avoid the detection accuracy problem caused by the mutual inductance between the receiving coil and the transmitting coil.In order to explore the response law of transient electromagnetic in the hole,the response characteristics of single dipole and double dipole transmitting coils are simulated through numerical experiments and physical experiments.Based on the two kinds of coil emission modes,the lane hole detection mode and hole hole detection mode in the underground hole of coal mine are compared and studied.For the tunnel hole detection mode(the transmitting coil is in the front of the tunnel and the receiving coil is in the hole),the simulation shows that the magnetic field strength of the single dipole transmitting coil is greater than that of the double dipole transmitting coil at the same distance from the source field,so the single dipole transmitting coil is recommended for this detection mode.Hole hole detection mode(both transmitting coil and receiving coil are in the hole).Through software simulation and physical experiments,the response characteristics of single dipole transmitting coil and double dipole transmitting coil are determined when there is an abnormal body.The radial component signal of single dipole transmitting coil will have positive or negative characteristics when there is an abnormal body,while the radial component signal of double dipole transmitting coil will have positive or negative characteristics when there is an abnormal body These changes are related to the relative position of the abnormal body.From the results of numerical and physical experiments,the position of the extreme point of the response signal is the location of the abnormal body,but in the positioning accuracy,the double dipole is more accurate than the single dipole,and the signal characteristics are more obvious.On this basis,we developed a dual dipole transmitting coil hole transient electromagnetic instrument,and carried out outdoor experiments,analyzed the signal characteristics of each component of the actual data,which can well correspond with the indoor physical simulation signal,and then accurately determined the location of the abnormal body according to the response law,and completed the performance test of the device coil.