Measurement And Analysis On Transient Electromagnetic Characteristic Response Of Finite Conductors

Physical information of limited conductors on the ground or in the ground such as shape,structure can be obtained by inverting their transient electromagnetic responses.To make inversion and identification of these limited conductors accomplish,the most important step is to establish the relationship between these characteristics information and their transient electromagnetic responses.Based on the basic theories of transient electromagnetic method,this paper sets up a system to measure the characteristic response on finite conductors through analyzing the theoretical response of the spheres and the dipole model,and select a number of typical objects to measure their characteristic response.Finally,the measure results were systematically analyzed.First of all,this paper describes in detail the basic working process of transient electromagnetic method and the basic theory of characteristic responses.By introducing the basic principles of Maxwell's equations and transient electromagnetic method,describes in detail the entire working process of the detection system on characteristic response.A finite conductor is equivalent to an anisotropic three-dimensional dipole in order to analyze its characteristic response.According to the attenuation characteristics of the theoretical characteristic response on the sphere,a parametric characteristic response model of the characteristic response on a general finite conductor is established,and use the least squares fitting algorithm to extracts the model parameters.Secondly,this paper describes the measurement theory of characteristic responses,and designs its measurement system.According to the analytic formula of the dipoles response,the emission loops that can ensure all parts of the target being uniformly motivated are designed,and the uniformity of its emission field can reach 97%.What's more,based on the MATLAB software,this paper carries out the background response rejection and other measurement data processing.After the original secondary field voltage signals are processed by the system,the error between the measured response and the theoretical response is no more than 10%.By deriving and calibrating the test,a more accurate final characteristic response value is obtained.Finally,the characteristic responses of 21 typical targets are measured,and the influence of physical parameters such as length,outer diameter,wall thickness,shape,and volume of the finite conductor on its characteristic response is analyzed.The experimental results show that the spherical object with complete symmetry structure has only one characteristic response,which is a power function in the early stage and exponentially decays in the late stage.The target object with a certain length-diameter ratio about the axis symmetry has two characteristic responses,and the magnitude and the decay rate of the response on early stage are mainly affected by the length and thickness of the target body.The change of the late decay time constant is mainly related to the outer diameter.The target bodies with no symmetrical structure have three characteristic responses and the parameters are significantly different.