Research On Key Techniques To Analyze The Propagation Properties Of Low-frequency Electromagnetic Wave Based On Dispersive Medium

At present,with the in-depth understanding and cross research on the basic electromagnetic theory and practical underwater environment engineering application,the research on the propagation characteristics of underwater low-frequency electromagnetic wave has attracted the big attention of lots of researchers and scholars in various fields.At the same time,researchers get interested in the research on the electromagnetic characteristics of dispersive medium.Many FDTD methods for dispersive medium have been proposed.Low-frequency electromagnetic waves have a very good long-range propagation capability and can carry more information with less energy attenuation.Usually,it takes 2 to 3 computation periods for the target problem space to reach energy convergence.However,as the frequency of the electromagnetic waves decreases,the wavelength of the electromagnetic waves will inevitably increase and the computation period of the target problem space will become longer,resulting in an increase of the computation time of the target problem space.For the traditional FDTD methods,they use the Yee cellular method to discretize the entire space into many small meshes with equal size.And the finite difference discrete computation formula can simulate the calculated minimum size as a unit cell size.In order to ensure the accuracy of the computation,it's necessary that the unit cell grid size must be small enough.According to the Courant condition,the smaller grid size will lead to the decrease of the unit time interval,which in turn resulting in computation time surge.This shortcoming limits the computation of the underwater low-frequency electromagnetic characteristics in large spaces with complex targets.In this paper,in order to overcome those above problems and obtain an algorithm that has a higher computing speed,less computation time and is suitable for the propagation characteristics of underwater low-frequency electromagnetic waves in large space with complex structural targets,a novel dispersive medium FDTD fast computing technology is proposed based on dispersive medium FDTD method.This method uses a non-magnetic dispersive medium to fill the problem space background and space mediums are modeled with the lossless or lossy Drude mode.The conventional FDTD method is corrected by introduced the operator shift method to obtain the iterative formulas.While satisfying the Courant condition,this method allows a larger unit time interval to be expanded.And the numerical examples have shown the effectiveness of the proposed method with high accuracy.The maximum relative error is 4.8%.The long distance propagation characteristics of the underwater low-frequency electromagnetic waves are given by analysis of the application examples.Next,in order to solve the cumbersome problems of data computation and post-processing of data results and reduce the workload,a software interface of underwater low-frequency electromagnetic calculation and data processing is designed based on the Matlab graphical user interface(GUI).The interface includes four parts: parameters setting,model building,parallel computing and data processing.The data processing includes the conversion of data results and the drawing of the electromagnetic amplitude and phase snapshots.This paper gives the basic introduction to GUI and the detailed design process of the software interface,and how to use the software interface.