The frequency dependence of the complex permittivity (ε∗=ε′-jε″) of Ba0.5Sr0.5TiO3 0.3-μm-thick film is measured up to 110 GHz by using interdigitated capacitors and coplanar waveguides. It is shown that the temperature dependence (from 77 to 373 K) of microwave losses, measured at 20 GHz, is described by a tan(δ)-(ε′)3/2 law. This result indicates distributed electromagnetic wave interactions with the local soft-phonon modes. This conclusion is further confirmed by the satisfactorily fit of the frequency dependence of the complex permittivity by a Cole–Cole function with an exponent β=0.6 and a characteristic time τ=0.21 ps.
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.
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