【作者】 张昊；

【导师】 程建春；

【作者基本信息】 南京大学 ， 声学， 2016， 硕士

【摘要】 近些年来,声学人工材料逐渐成为一个研究热点,其中具有梯度折射率的非均匀介质的声波操控问题也得到广泛关注。类似于光学梯度透镜操控光波,声学梯度透镜也可以对声波进行聚焦,由于其在声波操控领域的作用,相关的研究取得了显著的进展。实现声学梯度透镜的一种有效的方法就是利用声子晶体,来调控材料的折射率分布。这种方法的优势在于可避免使用共振单元,有助于拓展工作带宽,并减少声能的损耗。声学梯度透镜的发展证明了声学梯度材料在声波操控方面的潜力,也对其他类型声学器件的设计与应用有很大的推动作用。声波的偏转也是一种重要的操控方式,对宽频声波的全向性偏转操控将具有重要研究意义,并有望在噪声控制、声学成像等领域实现其应用。本文从等效参数理论出发,根据声波偏转2π以下角度时符合的一系列近似条件,提出了基于声学梯度折射率材料的声波偏转器的设计理论,并利用一种可调控等效折射率的声子晶体单元结构加以实现,构建出了一种声偏转器的实际结构。此结构中没有共振单元,因此对宽频有效,而且具有全向性。数值计算证明,这种声偏转器结构可以对沿任意角度入射的声波进行偏转,使之按照预设的轨迹进行传播,并沿预定角度出射。本文分为以下几个部分。第一章是绪论部分,介绍了声子晶体、声学超常材料和声梯度材料的研究背景及其最新研究进展。第二章实理论背景,介绍了伊顿透镜及其近似方法,以及等效参数理论。第三章,根据本文提出的模型的一些近似条件,提出一种通过结构操控等效折射率的方法,并对梯度折射率结构和声子晶体结构的声偏转器进行仿真计算,用有限元模拟对三个特殊偏转角度的梯度折射率结构和声子晶体结构分别做了仿真计算,验证了这种方法的可行性。第四章,利用上一章中提出的声子晶体结构声偏转器的设计方法,制作出声偏转器样品,置于波导板中间模拟二维情况,通过测量波导板间的声场,利用插值算法画出声压分布图,进一步验证这种声偏转器的可行性。第五章,给出了工作总结和对今后的展望。更多还原

【Abstract】 In recent years, more and more attentions have been paid to acoustic artificial structures. And the gradient index (GRIN) media have been attracting increasing attention due to their unique performance. By controlling the parameters of GRIN media, various optical phenomena can be realized, such as bending and convergence. However, acoustic wave is another classical wave whose wave equation is similar with that of electromagnetic counterpart. The concept of acoustic GRIN lens can be proposed according to the theoretical principle of optical GRIN lens. It has been extensively proven that acoustic GRIN media can be realized by selecting the structural parameters of sonic crystals in the direction transverse to the acoustic propagation or employing acoustic metamaterials formed by coiling up space. Thus, acoustic GRIN systems will have the potential to control the acoustic waves, which would have more implications for acoustic devices.In this letter, the study is about the design, construction and characteristics of a circular structure that works as an omnidirectional acoustic deflector of airborne sound, which is able to guide the waves at any refraction angle. This article is divided into the following five sections.In the first chapter, the background and the development of the phononic crystal, acoustic metamaterial and the acoustic gradient index (GRIN) metamaterial are reviewed.In the second chapter, Eaton lens and a retroreflector approximation is introduced.Here derive a more accessible form of the refractive index for any refraction angle with some accuracy using the retroreflector approximation.In the third chapter, a method for retrieving effective properties of locally resonant acoustic metamaterials is showed here. According to this method, a "cell" structure is proposed, of which the effective refractive index can be controlled by the radii of rigid circles. Deflection behavior of GRIN media and our structure is proved using FEM simulations. It can be found that the structure performed as well as GRIN in terms of acoustic deflection. Without loss of generality, this kind of structures is able to deflect acoustic waves by any angles using this method.In the fourth chapter a retroreflector made of resin is placed between two waveguide plates, and pressure field can be measured. The acoustic retroreflector is proved experimentally.In the fifth chapter the main conclusion of this article and prospects for future work are presented.更多还原