Sonic crystal noise barriers

室外隔音屏障用于减少来自固定工业厂房、飞机地面操作和道路的噪音干扰。近年来，人们对声波晶体用作隔音屏障的潜力越来越感兴趣。声波晶体得名于光子晶体对光的类似效应。它们由周期性的圆柱体阵列组成，众所周知，由于多次散射，它们在选择的频率上具有很高的衰减。通过假设散射体之间的距离适合整数个半波长，可以找到衰减最大的频率。声波晶体(SCS)的主要优点之一是通过改变柱体之间的距离，可以在一定的频率范围内达到衰减的峰值。SC栅栏的一个优点是其相对的光学透明度。另一种是它对风的相对渗透率，从而减少障碍物引起的湍流和风梯度增强的影响。原则上，如果将SC屏障用作道路两侧的高速公路隔音屏障，其混响应该比实心屏障之间的回响要小。SC屏障的出现也可能会对美学产生相当积极的影响。毕竟，人们对使用SC作为屏障的兴趣始于一项发现，即一个由垂直平行圆柱体组成的‘雕塑’起到了声屏障的作用。我们将考虑各种可能的SC路障设计。除了传统的垂直圆柱阵外，还将通过分析/数值和实验室测量来研究反射平面以上的水平圆柱阵、椭球柱阵和曲线阵的声学性能。将研究如何利用声透镜效应和覆盖来优化SC阵列的设计。交通研究实验室将测试适合道路交通噪声配置的垂直圆柱阵的声学性能，并与简单屏障在各种风条件下的声学性能进行比较。

Outdoor noise barriers are used to reduce noise disturbance from fixed industrial plant, from aircraft ground operations and from roads. Recent years have seen a growing interest in the potential for use of sonic crystals as noise barriers. Sonic crystals take their name from the analogous effects of photonic crystals on light. They consist of periodic arrays of circular cylinders and are known to give high attenuation at selective frequencies as a consequence of multiple scattering. The frequencies of highest attenuation can be found by assuming that an integer number of half wavelengths fits the distance between the scatterers. One of the main advantages of sonic crystals (SCs) is that by varying the distance between the cylinders it is possible to attain peaks of attenuation in a certain range of frequencies. One advantage of an SC barrier would be its relative optical transparency. Another would be its relative permeability to wind, thus reducing the effects of barrier induced turbulence and wind-gradient enhancement. In principle, if SC barriers are used as highway noise barriers on both sides of a road, there should be less reverberation than between solid barriers. The appearance of an SC barrier might also have a rather positive aesthetic impact. After all, the interest in using SCs as barriers started with the discovery that a 'sculpture' consisting of vertical parallel cylinders acted as a sound barrier. Various possible designs of SC barriwers will be considered. In addition to 'conventional' vertical circular cylinder arrays, the acoustical performance of horizontal cylinders arrays above a reflecting plane, ellipsoidal cylinder arrays and curved arrays will be investigated both analytically/numerically and through laboratory measurements. The optimisation of the design of SC arrays making use of acoustic lens effects and coverings will be investigated. The acoustical performance of vertical cylinder arrays in configurations suitable for road traffic noise will be tested and compared with that of a simple barrier in various wind conditions by the Transport Research Laboratory.