Diffraction-free propagation of acoustic bean through solid-fluid periodic lattice

摘要: We propose a simple solid-fluid layered structure where narrow Gaussian acoustic beam propagates practically without spreading. It is demonstrated that the coefficient (so-called diffraction coefficient), which defines rate of linear spreading, vanishes if certain relation between frequency and direction propagation hold. Unlike nonspreading “light bullets” recently proposed in optics, monochromatic signal can propagate diffraction-free regime sophisticated modulation. In experiment with steel-water we observe ~ 100 kHz at distance 1m. Such long-range collimation accompanied by negative phase velocity refraction, anomalous dispersion, very strong anisotropy effective mass density.