Electromagnetic parameter retrieval from inhomogeneous metamaterials. Phys Rev E 71:036617

Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708, USA.
Physical Review E (Impact Factor: 2.29). 04/2005; 71(3 Pt 2B):036617. DOI: 10.1103/PhysRevE.71.036617
Source: PubMed


We discuss the validity of standard retrieval methods that assign bulk electromagnetic properties, such as the electric permittivity epsilon and the magnetic permeability mu, from calculations of the scattering (S) parameters for finite-thickness samples. S-parameter retrieval methods have recently become the principal means of characterizing artificially structured metamaterials, which, by nature, are inherently inhomogeneous. While the unit cell of a metamaterial can be made considerably smaller than the free space wavelength, there remains a significant variation of the phase across the unit cell at operational frequencies in nearly all metamaterial structures reported to date. In this respect, metamaterials do not rigorously satisfy an effective medium limit and are closer conceptually to photonic crystals. Nevertheless, we show here that a modification of the standard S-parameter retrieval procedure yields physically reasonable values for the retrieved electromagnetic parameters, even when there is significant inhomogeneity within the unit cell of the structure. We thus distinguish a metamaterial regime, as opposed to the effective medium or photonic crystal regimes, in which a refractive index can be rigorously established but where the wave impedance can only be approximately defined. We present numerical simulations on typical metamaterial structures to illustrate the modified retrieval algorithm and the impact on the retrieved material parameters. We find that no changes to the standard retrieval procedures are necessary when the inhomogeneous unit cell is symmetric along the propagation axis; however, when the unit cell does not possess this symmetry, a modified procedure--in which a periodic structure is assumed--is required to obtain meaningful electromagnetic material parameters.

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    • "In the microwave regime, these negative permittivities may be achieved using arrays of inductively loaded thin wires, which can be implemented in printed-circuit form [12], [14]. Although homogenization of such metamaterials can be carried out through field averaging [15] or inversion of the scattering properties of a metamaterial sample [16], these approaches have difficulty modeling strong spatial dispersion [17], bianisotropy [18], and non-TEM propagation, all of which may be observed in thin-wire media. This is further complicated in cylindrical geometries. "
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    ABSTRACT: This paper presents experimental verification of below-cutoff transmission through miniaturized waveguides whose interior is coated with a thin anisotropic metamaterial liner possessing epsilon-negative and near-zero (ENNZ) properties. These liners are realized using a simple, printed-circuit implementation based on inductively loaded wires, and introduce an HE$_{11}$ mode well below the natural cutoff frequency. The inclusion of the liner is shown to substantially improve the transmission between two embedded shielded-loop sources. A homogenization scheme is developed to characterize the liner's anisotropic effective-medium parameters, which is shown to accurately describe a set of frequency-reduced cutoffs. The fabrication of the lined waveguide is discussed, and the experimental and simulated transmission results are shown to be in agreement.
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    • "Parameter retrieval is an important method to characterize the EM properties of the effective media and commonly used by researchers. There are some available methods in the literature for determining the electromagnetic properties of metamaterials [14] [15] [16] [17] [18] [19]. "
    Optik - International Journal for Light and Electron Optics 09/2015; DOI:10.1016/j.ijleo.2015.09.162 · 0.68 Impact Factor
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    • "Recently, instead of parasitic elements, metamaterials have been investigated as spatial decoupling resonators [14]–[18]. However, the planar antennas in [12], [17], and [18] exhibited a high mutual coupling level and narrow bandwidth. "
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    ABSTRACT: One-dimensional electromagnetic bandgap (1-D EBG) and split ring resonator (SRR) structures were inserted between two closely located monopole antennas to suppress mutual coupling. The 1-D EBG and SRR structures in these planar multiple antennas function as a reflector and wave trap, respectively. With the effect of these two structures, the mutual coupling between the two antennas is reduced by more than 42 dB and the back lobes are reduced by 6 dB. Thereby, the radiation efficiency of the antenna is also improved. The two fabricated antennas with 0.19λ 0 spacing exhibit mutual coupling (S 21 , S 12) of less than −30 dB from 2.43 to 2.54 GHz. A minimum correlation coefficient of 0.002 and maximum radiation efficiency of 82% are also demonstrated. Index Terms—Electromagnetic bandgap (EBG) materials, isolation technology, multiple-input multiple-output (MIMO) antennas, mutual coupling, split ring resonator (SRR).
    IEEE Transactions on Antennas and Propagation 09/2015; 63(9):4194-4198. DOI:10.1109/TAP.2015.2447052 · 2.18 Impact Factor
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