| The Transient Electromagnetic Method (Transient Electromagnetic Method) is akind of time domain Method, Used for mineral exploration, engineering exploration,and so on. The purpose of the transient electromagnetic method is to interpretation andanalysis the secondary field docking received signal, and analysis the distribution ofunderground medium. Modeling method is the foundation of inversion.Multidimensional forward and inversion problem is a in dire need of transientelectromagnetic field problem to be solved. The blind range of detection is concentratedin less than20m; signal is concentrated in early phase. The study of the entire signal forthe transient electromagnetic (including the emission current in the shutdown process aswell as the completion of the relevant section of early and late signal), and more focuson shut off in the middle and late, during the shutdown and shut off early signal less.Transient electromagnetic receive coil early signal serious influenced by distributionparameters,shape of send current waveform and displacement current, and has firstfield and the second field aliasing problem during the current turned off, which wasthe main causes of difficulties about the early signal. This thesis analyzes the transientelectromagnetic method of modeling research status and the theory, On this basis, thisthesis study the following:①.This thesis innovative introduce Ansoft Maxwell3D to the transientelectromagnetic method in the forward modeling, compared with widely used softwarein the forward modeling simulation EMMA. Contrast the simulation from an ideal halfspace of medium, at the same time, from point of view of common medium (such as thelow resistance sphere anomaly and layered medium)，Confirmed the feasibility andvalidity of modeling simulation about Ansoft Maxwell used in transientelectromagnetic.②.To analyze the characteristics of secondary response during the current beshutoff. Field-circuit hybrid simulation with magnetism and electric property mediabased on Ansoft Maxwell3D, analyzing additive effect in shutoff in the case ofMagnetic/Electronic media. Simulation and experimental results confirmed that theelectrical medium voltage in the early shutdown of the transient electromagneticresponse to the existence of a variable number process, magnetic media does not existsign changing process, the use of this feature can guide the classification of electricaland magnetic geologic exploration. ③.Field Road hybrid simulation, combined with the equivalent model of transientelectromagnetic coil, the change of the receiving coil parameters on the transientelectromagnetic response of the entire signal, the change of coil inductance caused bymedium. Analysis showed that the coil parameters has the significant impact of theduring shutdown and the early signs, medium magnetic causes the greater influence ofcoil inductance, positive significance simulation method for the effective conduct of theprobe design and experimental.④.Transient electromagnetic modeling somewhere in the air-raid shelter, buildtransient electromagnetic prototype system, and to carry out the experiment. Thesimulation effectively guided the experiment carried out with the improvement of theinversion method, the apparent resistivity imaging well reflected in the distribution ofunderground air-raid shelters.This thesis puts forward field and circuit hybrid modeling of TEM，and themethods of forward modeling and the analysis of transient electromagnetic whole signalfeature. They are used in instruction of detection devices design, the correction andinversion of shut off period and early signal, improving the shallow detection and finedetection precision. |
