非Bragg禁带中的缺陷态

Defect states in the non-Bragg band gaps

通过在周期柱状声波导中引入缺陷结构,研究了非Bragg禁带中的缺陷态。与传统Bragg禁带中的缺陷态相比,非Bragg禁带中的缺陷态具有完全不同的特性,所透射的缺陷模包含复杂的高阶横向模式,其形成与波导中的非Bragg共振密切相关。数值模拟表明缺陷态的频率与引入缺陷的几何尺寸有关,当缺陷长度变长时,非Bragg缺陷态与Bragg缺陷态一样向低频移动。而缺陷的半径变化时,非Bragg缺陷态却表现出完全不同的特性,随缺陷半径的变大而向高频移动。非Bragg缺陷态的这一反常变化与其模式结构密切相关,对非Bragg缺陷态的研究工作必将为声选频、滤波等器件的研制提供重要参考。

A defect state in the non-Bragg band gaps is investigated by introducing a straight tube into a cylindrical waveguide with periodic rectangular boundaries.The non-Bragg defect state,containing the more complex high-order guided wave modes,is quite different from that in the well-known Bragg gaps.The numerical simulation indicates that the frequency of the non-Bragg defect modes relies on the geometric parameters of the introduced defect.It moves to the low frequency region as the length of the introduced tube increases.But when the radius gets larger,the frequency of the non-Bragg defect mode goes to the high-frequency side.These results will contribute a lot to the development of the acoustical instruments.