基于FDTD的电磁波在煤中传播特性

摘要

针对矿山灾害事故发生时,逃生通道被堵,被困人员位置难以确定这一难题,以钻孔生命雷达为手段,开展了电磁波在煤矿井下传播规律的研究.采用时域有限差分法(FDTD)建立井下二维空间磁场(TM)模型,利用GprMax和Matlab数值软件对模型进行正演模拟计算.通过理论分析与正演模拟,研究了天线中心频率、激励源、煤质与煤温等条件改变时,反射波的幅值强度与反射系数变化规律,目标的探测时间与分辨率,揭示了电磁波在煤体中的传播规律.研究结果表明:天线中心频率为600 MHz的Ricker激励源是最佳探测方式;电磁波在烟煤中的传播速度最快,褐煤居中,无烟煤最次;电磁波在煤中的传播速度随温度的增加而增大,人体反射波幅值强度则随之减弱;人体反射波幅值强度与探测距离呈对数函数关系,据此提出建立相应数据库;确定了生命雷达与被困人员之间煤体厚度的计算方法.研究结果可为生命雷达系统的研发和现场救援探测数据的解释提供参考与支撑.%In view of mine disastrous accidents,once the escape way is blocked,it is hard to locate the miners trapped in the mines.In this paper,the propagation characteristics of electromagnetic wave in coal mine were studied.The finite-difference time-domain (FDTD) method was used to establish the two-dimensional space magnetic field model,which was calculated based on forward simulation technique of GprMax and Matlab software packages.Through theoretical analysis and numerous simulation,the impacts of frequency of antenna center,excitation source,coal types and coal temperatures on the amplitude intensity of the reflected wave and reflection coefficient were investigated.Coupled with the researches referring to the target detection time and resolution,the propagation characteristics of electromagnetic wave in coals were eventually revealed.The results revealed that the Ricker wave with the center frequency of 600 MHz provided the best way of probing.The propagation velocity of electromagnetic wave was the fastest in bituminous coal and lowest in anthracite with lignite in the middle.The propagation velocity of the electromagnetic wave increased with rising coal temperatures.The amplitude intensity of the reflected wave of the human body was weakened with the increase of coal temperature.Further study indicated that the amplitude intensity of the reflected wave of the human body had a logarithmic function with and the detection distance.The above conclusions were then applied for building a database to help the calculation on the thickness of coal between life radar and trapped personnel.The results of this study provide guidelines for the life radar system research as well as the development and on-site rescue detection data interpretation.