A two-dimensional (2D) phononic crystal (PC), including a type of linear defect that is composed of third component materials, is proposed in this paper. The sonic guided characteristics of the structure are investigated by combining the plane-wave expansion method and a supercell technique. The results show that there are guided modes in the original band gap when third material-based linear defects are introduced in the two-component PC. The frequency of the guided modes changes with the rotational angle and filling fraction of the linear defect. The frequency distribution is symmetric to the (0, 1) direction. The sonic waveguide characteristics of the PC do not change with the orientation and the type of cross-section of the defect cylinders when the filling fraction is very small. This property has potential application in controlling the guided modes in a 2D PC.
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