In this letter, we show numerically and experimentally that a positional disorder of a collection of absorbing electromagnetic wave resonators operating in the long wavelength regime dramatically enhances the absorption bandwidth. The demonstration is performed by using single-size ring-shaped thin metal pieces periodically or randomly positioned onto a back-grounded dielectric layer. For periodic array, an optimum in the periodicity is pointed out with a narrow bandwidth, while the increasing influence of coupling effects for resonators in close vicinity explains a three-fold bandwidth enhancement in the case of positional disorder.
We report on a negative-zero-positive metamaterial based on an omega-type microstructure with special attention on the nonvanishing group velocity for a zero refractive index. We first investigate the dispersion characteristics by full wave analysis, by stressing the necessary conditions of equality between the electric and magnetic plasma frequencies which are characteristic of the dispersion of the effective permittivity and permeability. Also, tuning of the gapless transition frequency between the left and right-handed dispersion branches was analyzed when the permittivity of the host substrate is changed. Last, we demonstrate experimentally the balanced composite character of the dispersion by frequency and angle-resolved transmission measurements, carried out at centimeter wavelengths on slabs and wedge-type prototypes, respectively.
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