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The efficient computation of periodic Green’s functions is discussed here for an arbitrarily directed array of point sources in layered media. These Green’s functions are necessary to formulate boundary integral equations for arrays of scatterers inside a general layered medium, solved with the method of moments in the spatial domain. For this reason, mixed-potential Green’s functions—having a mild spatial singularity—are selected. The case of horizontally oriented dipoles is rather simple and has been previously solved. On the other hand, the case of vertically oriented dipoles (i.e., aligned perpendicular to the layers) is more intricate, since the extracted terms cannot be transformed into well-known Green’s functions. Previous works dealt with arrays of line and point sources, but did not address the critical task of computing the curl of the dyadic potentials, required to treat slot arrays and dielectric inclusions, whose available Floquet series expressions do not converge if the source and observation points lie in the same transverse plane. [ABSTRACT FROM AUTHOR]

Efficient modeling of eddy current testing (ECT) signals is needed in many areas of industry. Design of probes may be improved and interpretation of experimental signals better understood by using dedicated numerical simulation tools, if they are computationally effective and accurate, yet remain simple enough to be applied at an end-user level. A boundary element method (BEM), dedicated to the numerical simulation of ECT signals due to complex narrow cracks within a planar multilayered structure (PMS) and presenting arbitrary orientations, is investigated. The theoretical formulation relies on the calculation of the dyadic Green operator, associated to the PMS, via appropriate vector wave function expansions. Then, the use of the discrete complex image method followed by the application of the generalized pencil of function method is proposed for efficient computation of this operator. Results of the validation of the complete model by comparison with the experimental data acquired in the laboratory-controlled conditions and with data computed by a finite element code are discussed. [ABSTRACT FROM PUBLISHER]

An evolutionary algorithm, the estimation of distribution algorithm (EDA), is used to reconstruct the objects that buried in planar layered media. It is essential that fast forward solvers be used to solve the forward scattering problem for the nonlinear inverse scattering methods, since it can avoid errors by approximation. The EDA is a predominant all-round optimizing method in the macroscopic simulation of evolution process species of nature. Recent studies have shown that the EDA provides better solution for nonlinear problems than the microscopic evolutionary algorithm, such as genetic algorithm (GA) in some cases. The EDA is simpler, both computationally and theoretically, than the GA. We discuss how this can be used to calculate the permittivity and conductivity of the targets. We show preliminary results indicating the potential of reconstruction for buried objects. Compared with other methods, the experiment result shows that the EDA algorithm reduces the number of iteration. [ABSTRACT FROM PUBLISHER]

This paper describes a relatively simple approach to calculating the frequency response for a two-dimensional (2-D) magnetic recording system with a medium that can include an arbitrary number of layers. Each layer may have an arbitrary magnetization direction, anisotropic permeability, and exchange coupling. The approach relies on an initial transformation into the spatial frequency domain and then the use of transmission matrices to relate the fields in the different layers. The approach is general in that it provides a method for finding the field configuration for any set of 2-D magnetic sources embedded in a layered magnetic medium with a linear B-H relationship. Here, we focus on calculating the readback response for a variety of longitudinal and perpendicular recording configurations. Since the permeability may have any wavelength dependence, we can easily include the effect of exchange coupling in the underlayer. [ABSTRACT FROM AUTHOR]