Research Of Transmission For Tunnel Transient Electromagnetic Method

Tunnel transient electromagnetic method is expanding the application of transient electromagnetic method.It starts works in the underground space closest to the target,with sensitive response, flexible devices,high efficiency features and so on.It plays a import role to the blind ore exploration in metal mines, the adverse geological position in coal tunnels,the tunnel prediction.From the Maxwell equation, derived transient magnetic dipole field of the whole space layered media, calculated typical geological models. From the theory and experiments,analyzed the possibility to survey geological information by means of frequency conversion measurement and all time TEM. Studied the characteristics of improved RCD network shut-off technique,quasi-resonant shut-off technique and series RC network shut-off technique.Created a new transmitting technology called combined transmitting technolog. Studied the influences from responses of behind plates to responses of front plates,when they were stimulated by square transmitting antenna, multi-angle transmitting antenna and rectangle superimposed transmitting antenna.The results show that:The whole space responses are different from half-space responses, the actual measurements can not be ignored, it is necessary to develop transmitting special antenna in order to weak Induced secondary field from the rear. Frequency conversion measurement and all time TEM are easy to measure into current turn-off time,which causes early data aberration,so they can't be used in tunnel.The author proposed combined transmitting technolog.It uses small inductance antenna to obtain a short turn-off delay, measuring shallow geological information;It uses high inductance antenna to measuring distance geological information. Tht experiments showed that combined transmitting technolog is effective. Tht experiments showed that the anti-interference ability of square transmitting antenna, multi-angle transmitting antenna and horizontal rectangle superimposed transmitting antenna is poor,but the 120°and 90°rectangle superimposed transmitting antennas can effectively distinguish the response from front geological bodies.