【作者】 高东宝；

【导师】 曾新吾；

【作者基本信息】 国防科学技术大学 ， 物理学， 2013， 博士

【摘要】 声学超材料是近年来理论声学领域发展起来的一个方兴未艾的热点方向。由于声学超材料具有不可替代的声波控制功能，使它成为了众多具有奇异特性的声学功能器件的实现途径之一。基于声学超材料的声学功能器件设计过程也是功能-结构-材料一体化设计过程的典型代表。本文以声学超材料为基础，对多种新型隔声技术进行了理论与实验研究。根据隔声装置的声场特性，将其分为无散射和有散射两种情况。在无散射装置中，声波不但不会进入隔声区域，同时在隔声装置外也不会产生散射波，声隐身衣是其中一个最具代表性的结构。相对的，有散射装置功能比较单一，只具有隔声特性，而隔声装置外侧依然会存在散射波。针对这两方面内容，本文所做工作和取得的重要结果与结论如下：1、在圆柱形声隐身衣层状等效结构的基础上，对“离散-等效”方法进行推广，提出了实现具有弱对称形式的椭圆柱形声隐身衣的实现方法。进而，针对任意形状声隐身衣，提出了一种近似层状等效结构，该结构可由均匀各向同性材料实现，此项工作解决了基于现实材料实现复杂形状声隐身衣的重要问题。2、基于无散射需求，在层状流体介质反射系数的基础上，推导了各向同性介质声场中，质量密度各向异性超材料界面处的参数匹配条件，并进而提出了一种声传感器隐身衣的设计方法。研究发现，在转换声学方法基础上得到的理想声隐身衣，只适合实现传感器密度与背景介质密度相同的传感器隐身衣。弱化声隐身衣是避免这一问题的有效途径之一。可以通过调节弱化系数，实现对任意参数声传感器的隐身。3、基于理论与实验方法，系统研究了带点缺陷的一维Helmholtz腔超材料中缺陷模式的基本特性、能量局域化现象以及不同振动模式下声场和相位分布等问题。缺陷模式对应了局域共振型禁带中的一处非常窄的声通带，并且在此频率下，缺陷单元附近会出现能量集中的现象。缺陷模式的位置受到了缺陷参数的影响，而它又进而会影响到能量局域化的程度。局域化的能量在结构中的分布情况则受到了缺陷单元与完美单元共振频率比的影响。带点缺陷的一维Helmholtz腔超材料中存在多种振动模式，不同的振动模式对应不同的能量分布形式。通过研究相位分布特性，发现该结构中还存在局部负参数形式，且负质量密度不但存在于声禁带中，在缺陷模式引起的声通带中也表存在负参数特性。4、基于Helmholtz腔超材料单元，设计了一种嵌入式的低频宽带隔声装置。埋入平面以下的共振单元却会对平面之上的区域进行隔声，是实现无障碍隔声的一种有效手段。实验结果表明，当Helmholtz腔单元共振时，会将入射声波隔绝在由它所围成的区域外，产生较好的隔声效果。通过在装置内设置多种共振频率的Helmholtz共振单元，可以实现对宽频带进行隔声。综上所述，本文研究了两种不同类型的新型隔声装置的设计与实现方法，并对有散射隔声装置进行了实验研究，无论是理论结果还是实验结果都证明了文中方法的正确性和有效性。这些研究成果为利用声学超材料技术实现新型隔声装置提供了支撑和参考，对推动声学超材料理论与技术走向应用也具有重要意义。更多还原

【Abstract】 Acoustic metamaterial (AMM) is one of the hottest topics in acoustic realm inrecent years. Due to the dramatical property of controlling the propagation path ofacoustic waves, the AMM is considered as one of the most promising materials torealize acoustical functional devices.This dissertation is aimed at providing some methods to investigate new soundinsulation technology with AMMs. Based on the properties of the acoustic scatteringfield, the sound insulation device (SID) can be classified as two kinds, which arescattering case and non-scattering case, respectively. For the case of non-scattering, theacoustic waves neither transmit into the insulation area, nor reflect back into the hostmedium. On the other hand, the function of the scattering device is simpler. Theinsulation shell can only prevent the incident wave penetrating into the inner area, butcan not eliminating the acoustic reflection. The main contents and findings of thisdissertation include:1. On the basis of the layered structure of cylindrical acoustic cloak, therealizability of acoustic cloaks with complex shapes is analyzed. A layeredelliptical-cylindrical acoustic cloak with the same focus is designed based on theeffective medium theory. Furthermore, an approximation approach is proposed forrealizing arbitrarily shaped acoustic cloak. Based on the effective medium theory, thedesigned cloak is a discrete layered structure using homogeneous isotropic materials.The performance of the cloaks is simulated. The results demonstrate that the cloakpossesses properties of low-reflection outside the cloak and wavefront-bending in thecloak shell. In this section, we solve the problem of realizing a complicated shapedacoustic cloak with normal materials.2. Based on the non-scattering parameter-matched conditions on the interfacebetween the isotropic material and the metamaterial with an anisotropic mass density, amethod to design the acoustic scattering cancellation cloak for acoustic sensors isproposed. The cloak is a transparent structure while canceling the scattering of theacoustic sensors which can receive the outside information without any scattering. Thesimulation results indicate that the acoustic cloak designed by transformation acousticsis only suitable for acoustic sensors with an identical mass density equaling to the hostmedium. The reduced cloak is one of the possible approaches to avoid this restriction.Reduction coefficient is introduced to the material parameter expressions, by which theproperties of the sensor cloak are totally changed. The reduced sensor cloaks areadapted to acoustic sensors with arbitrary parameters only by adjusting the values thereduction coefficient. 3. The properties of defect mode, the energy localization effect and the resonantmodes in a one-dimensional Helmholtz resonantor (HR) metamaterial with point defectare researched analytically and experimentally. Defect mode corresponds to a narrowpass band in local resonant forbidden band. At the frequency of the defect mode, energycan be localized around the defect resonator. The frequency of the defect mode isassociated with the defect parameter; however, it can further affect the degree of thelocalized energy. The ratio of the resonant frequencies of defect reonator and perfectreonantor can influence the position of the localized energy in the structure. There aremany resonant modes in the HR metamaterial with point defect. Different modescorrespond to different distributions of the acoustic energy. By studying thedistributions of the phase, local negative parameter is observed. The negative dynamicmass density not only exists in the forbidden band, but also appears in the pass bandbrought by the defect mode.4. A low-frequency wideband SID with inbuilt elements is designed andimplemented. The embedded structure can insulate the incident acoustic energy above it,which is a possible scheme to realize acoustic defence structure with no obstacle. Theexperimental results show that the acoustic energy is reflected by the resonant HRswhen they are resonating, and a large low-frequency area is formed by the rounded HRs.Wideband insulation area can be achieved by introducing much more HRs withgradually changed resonant frequencies.In conclusion, we studied two kinds of new sound insulation devices, and carriedout experiments on the low-frequency wideband sound insulation device. Boththeoretical and experimental results all verified the feasibility of the methods proposedin this dissertation. This work is helpful for realizing new acoustic sound insulationdevices with acoustic metamaterials, and also significative for pushing forword theapplication of the acoustic metamaterial.更多还原