Electromagnetic radiation location technology for coal and rock failure

As a nondestructive,realtime,noncontact and predictive geophysical monitoring method,the electromagnetic radiation technology plays an important role in evaluating structural stability and stress state of coal and rock,as well as monitoring and early warning on coal and rock dynamic disasters. At present,the time series changes of electromagnetic precursor signals are mainly used for the early warning of coalrock dynamic disasters. The electromagnetic radiation technology has not yet been able to achieve the location of the disaster area. Therefore,it is impossible to guide the precise implementation of prevention and control measures,which restricts the development and application of this technology. In this regard,a systematic study has been carried out on the electromagnetic radiation location technology and method for coal and rock failure. A new type of electromagnetic vector sensor is developed according to the roadway magnetoresistance effect of magnetic multilayer film materials,which lays the foundation for electromagnetic radiation location. The sensor has significant independence in the threeaxis direction,and the response to the cosine of the included angle shows high linearity. The vector characteristics of electromagnetic radiation from coal rock failure are revealed. In the time domain,the threecomponent electromagnetic signals arrive synchronously,and there are obvious differences between the waveforms. In the frequency domain,the dominant frequencies of the signals are the same,and the amplitudefrequency distributions are similar. They can be regarded as the components of the electromagnetic field generated by the main fracture in three orthogonal directions. Based on the process of charge separation and movement when coal and rock failure occur,an equivalent electromagnetic field source model and location equation are established. Then numerical simulation and experimental verification are carried out,and the ideal electromagnetic location effect is obtained. The research is a unique innovation in coal and rock electromagnetic radiation monitoring technology. The technology will enable the development from initially predicting the possibility of a hazard to predicting the area where the hazard will occur. It will promote the upgrading and innovation of coal mine monitoring and early warning technology and equipment for coal mine dynamic disaster,and strongly support the development of intelligent coal mines in China.