中文摘要：

低频噪声（20～400Hz）的降噪处理仍是工程界的难点问题.为了获得一种新的有效低频降噪方法,结合声子晶体中能带图和超结构中负等效质量密度的相关理论,提出了声子晶体结构低频准禁带（即声子晶体结构在低频范围内存在类似于完全带隙的特性,能够有效地衰减低频范围内的弹性波,但其衰减程度低于完全带隙）的概念.低频准禁带是声子晶体结构的一种低频特性,可以实现小尺寸结构降低低频噪声的目的.利用低频准禁带特性,对离心通风机降噪采用的丝网结构的空气占有率、丝网大小及丝网厚度对低频降噪效果的影响进行理论对比分析,所得的理论分析结果与丝网低频降噪实验结果相吻合.可见,低频准禁带为低频降噪的结构优化设计提供了新的方法和思路.

英文摘要：

Noise reduction in the low-frequency range（20-400 Hz）has always encountered difficulties and troubles in the engineering field. In order to obtain a new and effective low-frequency noise reduction method, the phononic crystal band diagram and the effective mass density theories are combined for the novel concept of the low frequency quasi-bandgap,similar to the complete band gap that can prohibit or attenuate the propagation of elastic waves in the low frequency range. However, the attenuation is different from the complete band gap. Low-frequency quasi handgap is of low frequency characteristics of phononic crystal,and can achieve small sizes of structure to reduce low frequency noise, Through analysis on the effects of air occupancy rate, mesh size and thickness on low frequency noise reduction of centrifugal fan using low-frequency quasi-bandgap theory,we obtain results that coincide with the noise reduction experiments. So, the concept of the low-frequency quasi-bandgap presented in this paper could be useful in potential engineering applications of low-frequency noise reduction.