Dispersion and negative refractive of acoustical waves in heterogeneous media
Realization conditions and parameters of heterogeneous media under which the effect of the sound wave negative refraction, resulted from multiple resonant scattering by hollow and porous spherical inclusions inserted in water, were analyzed. The frequency ranges of transparency windows, in which effective compressibility and density take negative values when the relative level of radiative losses is low were calculated. A phononic crystal in the form of a periodic rhombic structure with a large filling factor, made up of steel cylinders, is investigated. The dispersion characteristic of the crystal is found experimentally and the upper Brillouin zone structure which has negative dispersion while the crystal has negative refraction is constructed.