Possibilities to realize a negative refraction in chiral composites in in dual-phase mixtures of chiral and dipole particles is studied. It is shown that because of strong resonant interaction between chiral particles (helixes) and dipoles, there is a stop band in the frequency area where the backwardwave regime is expected. The negative refraction can occur near the resonant frequency of chiral particles. Resonant chiral composites may offer a root to realization of negative-refraction effect and superlenses in the optical region.
We consider a novel method of cloaking objects from the surrounding electromagnetic fields in the microwave region. The method is based on transmission-line networks that simulate the wave propagation in the medium surrounding the cloaked object. The electromagnetic fields from the surrounding medium are coupled into the transmission-line network that guides the waves through the cloak thus leaving the cloaked object undetected. The cloaked object can be an array or interconnected mesh of small inclusions that fit inside the transmission-line network.
A possibility to realize isotropic artificial backward-wave materials is theoretically analyzed. An improved mixing rule for the effective permittivity of a composite material consisting of two sets of resonant dielectric spheres in a homogeneous background is presented. The equations are validated using the Mie theory and numerical simulations. The effect of a statistical distribution of sphere sizes on the increasing of losses in the operating frequency band is discussed and some examples are shown.
A new simple equation for the effective permittivity of particle-filled composites is presented. The equation does not involve any free parameters in addition to the volume fraction of inclusions, the semi-axes of ellipsoidal inclusions and the permittivities of materials. Alternatively, instead of semi-axes, the percolation threshold can be used as a parameter. It is derived in a similar manner as the Maxwell Garnett mixing equation, but by including an enhanced background permittivity effect when the volume filling ratio of inclusions increase. The result is a mixing equation which has the Maxwell Garnett mixing equation as a low volume filling ratio limit, but which approaches the Bruggeman mixing equation as the volume fraction of inclusions increases. The mixing equation is compared with classical mixing formulae, and to numerical simulations and measurements from the literature.
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