Electromagnetic response and homogenization of grids of ferromagnetic microwires

Abstract

This contribution presents an analytical formulation for the electromagnetic response of grids of ferromagnetic microwires, where the electromagnetic fields produced by the structure are found by means of the local field method. In addition, a circuit analogy is introduced for a better understanding of the grid response, where a single ferromagnetic microwire is modeled as an impedance-loaded wire, and the transmission-line approach is used for the whole grid. Moreover, the homogenization of the structure is considered to provide more physical insight into internal polarizations of the grid. Contrary to the previous experiments of left-handed transmission in grids of ferromagnetic microwires, it is found that such structures can be modeled as artificial dielectric slabs with a frequency dispersive permittivity.

A Novel DNG Medium Formed by Ferromagnetic Microwire Grid

“…1) with the following specifications [16,17]: radius a = 1 µm, conductivity σ = 6. response of the medium. The imaginary part of μ zz , φφ and μ ρρ is positive with a large value which represents huge losses inside the medium.…”

“…Variation in effective permittivity and effective permeability is shown with respect to the operating frequency in the range of 5-15 GHz. In order to validate the results of the proposed analysis, a comparison is done with the results available in [17] for T M z polarization at an angle of incidence θ 0 = 90 • .…”

“…As discussed in [17], the optimum value of the thickness of unit cell is equal to the diameter of the microwires 2a, while the width and height are kept equal to the spacing among the microwires d. The effective permittivity and permeability of the ferromagnetic microwire grid structure are reported in [17] for the normally incident T M z polarized uniform plane wave. In [17], effective medium properties are evaluated by assuming the microwires of the grid as made up of impedance loaded perfect electric conductors (PEC) and equivalent sheet current density is calculated. Then, polarization and effective medium properties are obtained by applying homogenization.…”

“…According to the effective medium theory, volume of the whole medium is divided into unit cells identical in shape and size. Each unit cell is chosen such that it contains one scatterer [17]. Geometry of such unit cell is shown in Fig.…”

“…Then, polarization and effective medium properties are obtained by applying homogenization. The approach in [17] is limited for the case of normal incidence and T M z polarization only. In this paper, a method for the evaluation of effective permittivity and permeability is reported which enables us to evaluate the effective permittivity and permeability of the medium for any arbitrarily polarized uniform plane wave incident obliquely.…”