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声学超构材料   总被引:2,自引:0,他引:2  
2000年报道的具有局域共振带隙的声学材料是声学超构材料的前身,也是最早实现的声学超构材料.同光学、电磁超构材料一样,近年来声学超构材料也引起了许多学者的研究兴趣.文章介绍了到目前为止声学超构材料的主要研究进展,内容包括含共振单元的声学超构材料的负有效声学参数(包括质量密度、体模量等)的实现,以及不含共振单元的声学超构材料的一些有效声学参数的确定等,最后对声学超构材料的可能应用进行了简单展望.  相似文献   
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声波在一维声子晶体中共振隧穿的研究   总被引:22,自引:0,他引:22       下载免费PDF全文
通过从实验和理论方面对声波在一维声子晶体单晶体和被小的共振腔分开的双晶体中传播时发生的隧穿和共振隧穿现象的研究,观察到了声子晶体单晶体在带隙频率范围内发生的隧穿现象,而对于双晶体样品,在带隙频率范围内出现了很强的共振透射峰.共振发生时,实验测得的群时间很大,但是没有共振时,群速度却很快. 关键词: 声波 声子晶体 隧穿 共振  相似文献   
3.
The Rayleigh identity, based on a multipole expansion theory, is extended to analyse the forces between particles in an electrorheological system. The shear modulus for chains of particles arrayed on a square lattice is calculated. It is found that the modulus increases linearly with the ratio of dielectric constants of the dispersed particles to that of the continuous phase; as the ratio becomes larger, contrary to the expectations from a simple dipole approximation, the modulus would saturate. In the case of conducting particles, the modulus varies with the frequency of the applied field. In a limiting case of perfectly conducting particles, the conductivity is also considered. It is found that the particle-particle forces are extremely sensitive to their separations from each other.  相似文献   
4.
The influences of the configurational disorders on phononic band gaps and on waveguide modes are investigated for the two-dimensional phononic crystals consisting of water cylinders periodically arrayed in mercury. Two types of configurational disorders, relevant to the cylinder position and cylinder size respectively, are taken into account. It is found that the phononic band gap and the guide band are sensitive to the disorders, and generally become narrower with the increasing disorders. It is also found that the waveguide side walls without disorder can significantly prevent the guide modes in the waveguide from influence by the disorders in the crystals to a large amount.  相似文献   
5.
沈平  梅军  刘正猷  温维佳 《物理》2007,36(1):1-6
复合介质的质量密度通常认为是组成它的各种成分的质量密度的体平均值.体平均质量密度常常被用于计算在长波长极限下的声波速度,在此极限下波长比复合介质中的特征尺度要大得多.作者通过严格的数学推导证明,计算(长波长极限下的)波速时所用到的动态质量密度与静态的体平均质量密度有显著的不同.这一发现与最近的实验结果符合得非常好,并且使得声学超常介质的实现成为可能.这两种质量密度之所以不同的物理根源就在于,在波场中复合介质中的各个成分之间有相对的运动.也就是说,隐含的假定——在长波长极限下复合介质中的各个成分必定会全体同相地运动——将不再正确,尤其是当各个成分的声学阻抗之间有较大的差异时.实验和理论显示,对于局域共振声学材料而言,动态质量密度甚至还会变成是负的.文章探讨了这一发现的物理意义,以及它在声学超常介质领域的应用.  相似文献   
6.
王青海  李锋  黄学勤  陆久阳  刘正猷 《物理学报》2017,66(22):224502-224502
基于Su-Schrieffer-Heeger模型,构造了一种一维非线性声子晶体,通过调控外加在声子晶体上的预紧力,可调控声子晶体的拓扑态,从而实现拓扑相变.利用这一效应,把该非线性声子晶体与另一线性声子晶体形成异质结构,可以实现一种新型声学开关:通过调节预紧力即调控非线性声子晶体的拓扑相,可以实现异质结构中界面态从无到有的转变,从而实现了开关效应.利用该效应可望开发新型声学器件,如可调谐振器、可调滤波器、可调隔振器等.  相似文献   
7.
The critical behavior of the dynamical percolation model,which realizes the molecular-aggregation conception and describes the crossover between the hadronic phase and the partonic phase,is studied in detail. The critical percolation distance for this model is obtained by using the probability P∞ of the appearance of an infinite cluster. Utilizing the finite-size scaling method the critical exponents γ/ν and τ are extracted from the distribution of the average cluster size and cluster number density. The influences of two model related factors,i.e. the maximum bond number and the definition of the infinite cluster,on the critical behavior are found to be small.  相似文献   
8.
二维周期性复合介质中弹性波的能带结构   总被引:9,自引:0,他引:9  
用平面波展开方法,研究弹性波在二维周期性复合介质中的传播问题.由 Pb柱体嵌入 epoxy基体组成的复合介质,其弹性波带结构中,存在很大的完全带隙。研究了柱体的横截面形状、组元的体积占有率及复合介质的材料组成等因素对带结构的影响.在C柱体和epoxy基体组成的复合介质中,也观察到完全禁带的出现。但是,相反情况,由epoxy柱体和Pb或C基体组成的材料中,均无完全禁带出现。  相似文献   
9.
Spontaneous rupture of some polymer films upon heating is commonplace. The very criterion for this instability is the system free energy possessing a negative curvature. Within the framework of full frequency-dependent theory of dispersion forces, we have derived the excess free energy of a typical system---polystyrene film deposited on the silicon substrate. The excess free energy, wavelengths and growth rates are calculate and a comparison is made between the accurate results and the approximate results. It is found that the stability of the film can be tuned by the variation of the thickness of the coating and the retardation effects can be significant sometimes.  相似文献   
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