The Research On Transient Electromagnetic Response Of Finite Conductors Based On Orthogonal Dipole Model

Unexploded ordnances refer to ordnances left behind after wars or other military activities,which remain unexploded.These ammunitions pose a great threat to the safety of human life and property.Because of the high effectiveness and the low false-alarm rate of transient electromagnetic methods,this paper aims at studying the basic theories and data processing methods of Transient electromagnetic detection of unexploded ordnances.Firstly,this paper briefly describes the basic principle,the system configuration,the working way and the data processing methods of transient electromagnetic method,on which basis,the portable transient electromagnetic unexploded detector is introduced and the structure and function of the two parts of this system,the sensor and the host,are elaborated.Secondly,this paper focuses on the forward model of the transient electromagnetic responses of finite conductors.We choose the three-dimensional orthogonal dipole model to simulate the target.Then we forward modeling its transient electromagnetic response based on the characteristic response,position,dip angle and etc.of the target.We calculate the time-domain responses,survey line responses and plane responses of the target under different conditions and analyze its response law.By studying the responses of target under different depths,we find that the response amplitude is reduced by an order of magnitude with each 20 cm increase of depth;By setting different dip angle,we find the symmetry of responses: when the dip angle increases from 0° to 45°,the symmetry of the x-and z-components responses of the object deteriorates,and both the symmetrical center and the symmetrical axis shift to the right;When the dip angle get 90°,the symmetry of the response is well.The trend of the plane response is approximately the same as the the survey line response.The detection depth has a great influence on the initial amplitude of the response,and the dip angle determines the symmetry of the plane response.Therefore,the three-component transient electromagnetic response of the target can reflect its position and dip angle information well.In the end,we measured the survey line response and plane response to further verify the calculated results and analyze the accuracy of the dipole model.Compared the measured responses with the calculated responses,we find that with small dip angle ? and enough distance between the target and the detection system,both the amplitude and symmetry of the two results are highly consistent;When the dip angle increases or the detection depth decreases,there is a gap in amplitudes between the measured and calculated results,but their symmetries still match well.Therefore,the forward modeling based on the dipole model can basically reflect the actual transient electromagnetic response of the target.This paper researches the transient electromagnetic response of the target based on the dipole model.The results show that the model can accurately reflect the influence of the position and dip angle of the target on its response,and the theoretical responses are highly consistent with the measured responses.The accuracy and effectiveness of this model are further confirmed.