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文章从理论和实验上研究了二维三角晶格声子晶体第二能带具有回波(backward-wave)效应的负折射现象.Bragg散射将第二能带等频线(equifrequency surface)分成两类,它们分别凹向简约布里渊区(BZ)的K点和Γ点,并由此导致了两种不同的回波负折射现象.理论和实验证明,这两类负折射的角度与声波的频率以及入射角的变化关系截然不同,同时在第二能带中,不仅存在回波负折射,还存在回波正折射.这两种折射所具有的回波效应都可以用于通过位相补偿效应来突破衍射极限.上述现象和左手材料中以及声子晶体第一能带中的折射现象是不相同的,揭示了声子晶体,第二能带具有更丰富的物理现象.
In this paper, the negative refraction with backward-wave effect in the second energy band of two-dimensional triangular lattice phononic crystals is theoretically and experimentally studied. The Bragg scattering divides the equifrequency surface of the second energy band into two Which are respectively concave to the K point and the Γ point of the BZ (Brillouin zone), and result in two different negative refraction phenomena. Theoretical and experimental evidences show that the relationship between the two types of negative refraction angle and the sound wave Frequency and angle of incidence change very different, while in the second energy band, there is not only echo negative refraction, there are echo positive refraction. Both refraction with echo effects can be used by the phase compensation Effect to break through the diffraction limit.The above phenomenon and the left-handed material and the phonon crystal in the first band refraction phenomenon is different, revealing phononic crystals, the second band has a richer physical phenomenon.