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This study investigates the nondiffractive propagation of sound waves in two-dimensional sonic crystals consisting of rectangular rods with a slit. The plane wave expansion method is used to calculate the equifrequency surfaces of sonic crystals with a square lattice. At certain frequencies, straight contour lines in the equifrequency surfaces are found. That frequency is strongly dependent on the geometric sizes of the rectangular rods. Further, the nondiffractive propagation of the sound wave can be realized for omnidirectional incident angles, and the properties can be applied to design novel acoustic devices.
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Wu et al. (2008) studied this question.
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