Research On Magnetic Induction Through-the-earth Positioning Methods For Long-distance Mine Emergency Rescue

Long-distance mine emergency rescue has an urgent demand for through-the-earth positioning technology.Magnetic induction through-the-earth positioning technology uses lowfrequency magnetic field to locate trapped miners underground.This technology has excellent through-the-earth ability and excellent positioning accuracy.For this reason,several magnetic induction through-the-earth positioning methods for long-distance mine emergency rescue are put forward to improve the ability of finding and locating trapped miners and ensure the life safety of trapped miners.This dissertation focuses on the key issues such as transmission model,positioning methods and noise reduction methods of the magnetic induction through-the-earth positioning methods,which covers the research of magnetic induction through-the-earth transmission distance analysis model,the design of positioning methods based on signal path loss,signal direction,dual-frequency positioning signal,and noise reduction methods based on bandpass filter and discrete Fourier transform.The main works and innovations of this dissertation are as follows:(1)The analytical model of how the main parameters of transmitter antenna coil,transducer sensitivity of the receiver and earth magnetic conductivity affect through-the-earth positioning distance was set up.The approximate relation between the parameters of model and the through-the-earth positioning distance was obtained.Geomagnetic noise was introduced into the model,which makes the results closer to the actual situation.The analysis and simulation results show that the magnetic induction through-the-earth transmission work method has the advantages of stable transmission which can solve the problems such as the large influence of the earth media on through-the-earth positioning distance.The analysis and simulation results show that: under the feasible parameter configuration,the magnetic induction through-the-earth positioning method can penetrate more than 1000 meters of the earth media,which meets the needs of post-accident rescues of underground mine for through-the-earth positioning.(2)Aiming at the application scenario of long-distance mine rescue with single-layer earth medium,this dissertation proposes a three-dimensional magnetic induction through-the-earth positioning method based on the positioning signal direction and path loss.Using the characteristic that the horizontal components of the positioning signals point to the axis of the horizontal loop coil of the underground transmitter,the azimuth of the transmitter coil axis on the ground is determined by intersecting the positioning signal vectors at two triaxial orthogonal receivers on the ground.Taking advantage of the feature that the strength of the positioning signal decreases with the increase of the transmission distance,the position of the transmitter in the vertical dimension is determined.According to the extremely narrow bandwidth of the sinusoidal positioning signals in the spectrum,a Kaiser window bandpass filter with an extremely narrow passband width to reduce the noise of the positioning signals is configured,and positioning signals with mean values close to the ideal values of positioning signals and minimal fluctuations are obtained.A leap from the traditional two-dimensional positioning to three-dimensional positioning is realized by the proposed method.The analysis and simulation results show that: the proposed three-dimensional positioning method and noise reduction method can achieve high-precision through-the-earth positioning with an error of less than 15.9meters at the depth of 1000 meters.(3)Aiming at the application scenario of long-distance mine emergency rescue in multilayered earth media,this dissertation proposes a magnetic induction through-the-earth positioning method based on the signal direction.Using the directional characteristics of the the magnetic field vector of the underground horizontal transmitter coil distributed in the surrounding space,the azimuth of the transmitter coil in the horizontal dimension is obtained through the vector intersection of the horizontal components of the positioning signal vectors in the three-dimensional space.The azimuth of the transmitter coil in the vertical dimension is obtained through the vector decomposition and algebraic transformation of the positioning signal vector.In addition,taking advantage of the extremely narrow bandwidth of the sinusoidal signal in the spectrum,this paper proposes a noise reduction method based on the discrete Fourier transform,which eliminates the influence of noise at other frequency points on the spectrum on the positioning accuracy.The magentic induction through-the-earth positioning method based on signal directions overcomes the influence of multi-layer earth conductivity on positioning accuracy.The analysis and simulation results show that: in the multi-layered earth media,the proposed magnetic induction through-the-earth positioning method based on the signal direction can achieve high-precision through-the-earth positioning with an error of less than 2 meters at the depth of 1000 meters.(4)Aiming at the application scenario of long-distance mine emergency rescue in multilayered earth media,this paper proposes a dual-frequency magnetic induction through-the-earth positioning method.This method uses a loop energized coil placed horizontally underground as the positioning signal transmitter,and uses a three-axis orthogonal magnetic core coil placed on the ground as the receiver.This method first uses algebraic transformation to eliminate the earth conductivity in the expression of the dual-frequency positioning signal,and obtains the transceiver distance function that is not affected by the conductivity of the multi-layered earth media.Then,this paper carries on the vector decomposition to the transceiver distance,obtains the three-dimensional coordinates of the transmitter.The dual-frequency positioning method eliminates the influence of the electrical conductivity on the positioning accuracy.Compared with the single-frequency positioning method,the through-the-earth ability of the dualfrequency positioning method is slightly weaker,but the dual-frequency positioning method can be realized by using a single receiver,which is easier to be deployed and beneficial for underground rescue.The analysis and simulation results show that: the dual-frequency positioning method can achieve high-precision through-the-earth positioning with an error of less than 4 meters at the depth of 1000 meters.(5)Aiming at the application scenario of long-distance mine emergency rescue with multilayered roadway structure,this paper proposes a dual-frequency magnetic induction relay positioning method.Using the roadway receiver as the relay,the roadway rescuers determine the relative position between the dual-frequency transmitter on the ground and the trapped miners underground.The relay location method greatly shortens the distance between the roadway rescuers and the trapped miners,and the smaller portable dual-frequency transmitter coils can be carried by the trapped miners while maintaining the accuracy of ground penetration positioning.The analysis and simulation results show that: the relay positioning method can achieve high-precision through-the-earth positioning with an error of less than 1 meter at the depth of 1000 meters.