Research On Fast Calculation Method Of Electromagnetic Scattering Of Underground Targets Based On ACA

The electromagnetic calculation of underground targets is always the key point and the most difficult part in the research of electromagnetics.The research on the nondestructive detection technology of underground pipelines is of great significance for ensuring pipeline facilities and construction safety.The underground pipeline problem is an important part of the underground target problem,and the underground pipeline is the essential infrastructure of the modern city.The nondestructive detection of underground pipelines usually uses the reflection and scattering information of electromagnetic waves to realize the recognition,location and imaging of the target.The detection technology is not mature enough in numerical calculation and theoretical analysis.Therefore,the research on numerical simulation and analysis of electromagnetic scattering from underground targets is of great significance.The traditional method of moment based on the surface integral equation has been widely used because of its high accuracy.The computation cost of the moment method is too expensive for the large size scattering of multiple targets.In order to quickly and efficiently calculate the electromagnetic scattering from underground targets,we add a fast algorithm to the scattering calculation of traditional moments method to improve the computation efficiency.For multi-objective electromagnetic scattering problems,the impedance matrix obtained by integral equation has low rank characteristics.For large low rank matrices,the adaptive cross approximation(ACA)algorithm can greatly compress storage and reduce computing time.In addition,an improved ACA algorithm is proposed to accelerate the calculation of the impedance matrix of the coupling between targets which are not too far apart: the ACA method based on the H structure.This article has confirmed that this method can stably improve the computing speed and compress the storage memory.First of all,this article briefly introduces the integral equation method to solve the electromagnetic scattering problem and the method of moments used to solve the integral equation.When the traditional method of moment is used to calculate the scattering problem of large size,the efficiency of the calculation is very low.The proposed multi-level fast multipole algorithm(MLFMA)makes the moment method get great development in the field of electromagnetic scattering.In addition,this paper studies the electromagnetic mutual interaction based on the connection strategy in different cases,and gives a detailed formula deduction.Secondly,a fast algorithm,adaptive cross approximation method,is introduced in this paper,and the basic principle and implementation process of this method are described in detail.According to the low rank characteristic of the coupling action impedance matrix block between the targets,the electromagnetic scattering of the compound target is speeded up by the moment method combined with the ACA algorithm.A numerical example is given to verify the accuracy of the proposed method compared with the traditional moment method based on MLFMA,and significantly improve the computation efficiency and reduce the computation memory consumption.Finally,this paper further improves the adaptive cross approximation method,and proposes a hybrid method of ACA and MLFMA based on H structure combined with multilevel fast multilevel submethod.In view of the relatively large distance between targets and relatively small distance,both far-field and near field exist at this time.The hybrid method of ACA and MLFMA combined with H structure can effectively accelerate computation.The feasibility and efficiency of the method are verified by a numerical example.