Vibration and Acoustics Research Group, Laboratory of Science and Technology on Integrated Logistics Support, College of Mechatronics and Automation, National University of Defense Technology, Changsha, Hunan 410073, China.
Ultrasonics. 2013 Sep;53(7):1332-43. doi: 10.1016/j.ultras.2013.03.019. Epub 2013 Apr 8.
Three-dimensional (3D) locally resonant sonic materials (LRSMs) are studied theoretically for purpose of optimising their sub-wavelength performance by coupling resonance and Bragg scattering effects together. Through the study of effective sound speeds of LRSMs, we find that the starting frequency of Bragg scattering can be shifted to sub-wavelength region by softening coats of resonators when the matrix is a low shear-velocity medium. A similar result can be achieved by compressing the lattice constant. By using a layer-multiple-scattering method, we investigate the complex band structure and the transmission spectrum of an LRSM whose Bragg gap is already close to the resonance gap in frequency. The wave fields of the composite simulated by COMSOL are further analysed at several typical frequencies. The result shows that the approaching of two kinds of gaps not only broadens the bandwidth of the resonance gap, but also increases the depth of the Bragg gap since the interaction between resonant modes and scattering waves are enhanced. By varying the shear velocity of coats, we obtain a coupled gap, which exhibits a broad transmission gap in the sub-wavelength region. When the loss of coats is considered, the coupled gap can not only maintain a good sound blocking performance, but also perform an efficient absorption in the low frequency region.
本文从理论上研究了三维（3D）局域共振声子晶体（LRSM），通过将共振和布拉格散射效应耦合在一起，优化其亚波长性能。通过研究 LRSM 的等效声速，我们发现当基体为低切变波速介质时，通过软化共振器的覆盖层，可以将布拉格散射的起始频率转移到亚波长区域。通过压缩晶格常数也可以达到类似的效果。利用多层散射方法，研究了一个已经接近共振频率的布拉格带隙的 LRSM 的复能带结构和透射谱。利用 COMSOL 对复合材料进行了模拟，进一步在几个典型频率下对波场进行了分析。结果表明，两种带隙的接近不仅拓宽了共振带隙的带宽，而且由于共振模式和散射波之间的相互作用增强，布拉格带隙的深度也增加了。通过改变覆盖层的切变波速，得到了一个耦合带隙，在亚波长区域具有较宽的传输带隙。当考虑覆盖层的损耗时，耦合带隙不仅可以保持良好的隔声性能，而且可以在低频区域实现高效吸收。
