Wave localization in two-dimensional porous phononic crystals with one-dimensional aperiodicity

The localization properties of in-plane elastic waves propagating in two-dimensional porous phononic crystals with one-dimensional aperiodicity are initially analyzed by introducing the concept of the localization factor that is calculated by the plane-wave-based transfer-matrix method in this paper. The band structures characterized by using localization factors are calculated for different phononic crystals by altering matrix material properties and geometric structure parameters. Numerical results show that the effect of matrix material properties on wave localization can be ignored, while the effect of geometric structure parameters is obvious. For comparison, the periodic porous system and Fibonacci system with rigid inclusion are also analyzed. It is found that the band gaps are easily formed in aperiodic porous system, but hard for periodic porous system. Moreover, compared with aperiodic system with rigid inclusion, the wider low-frequency band gaps appear in the aperiodic porous system.     

Control analysis of the tunable phononic crystal with electrorheological material

The elastic band structure of a two-dimensional phononic crystal (PC) with electrorheological (ER) material is investigated and the plane-wave-expansion (PWE) method is adopted to solve the problem in this paper. The ER material is used to act as a tunable elastic composite inserts and its material parameter can be changed by the applied electric fields. Variations of the band gaps for the phononic composite system are also calculated with various electric fields and it is found to have a significant effect on the band gaps of the phononic system with ER material inserts. The band gaps of the smart system can be controlled and the acoustic characteristics of the system are also changed by applied different electric fields.     

径向声子晶体隔声特性*

该文构造了由两种匀质材料交替分布的径向声子晶体柱壳模型。首先,针对声波在其中的轴对称传播情况进行了理论分析,建立了声波由内向外传播的传递矩阵,进而导出了声压透射系数和隔声量表达式。采用数值分析的方法系统地讨论了径向声子晶体柱壳的隔声特性,并与单一材质柱壳的传播规律进行对比分析,其次,借助有限元仿真分析的手段对数值结果进行了验证。最后,详细分析了内外流体的特性阻抗对径向声子晶体柱壳隔声特性的影响,得到了相应的参数影响规律。研究表明,径向声子晶体柱壳存在声波带隙,导致其在带隙范围内的隔声效果远远优于单材质柱壳,并且该结构的固有特性突破了质量定律的限制;声波带隙内表面局域态现象出现与否由内外声场和结构场共同决定。     

The band gap and transmission characteristics investigation of local resonant quaternary phononic crystals with periodic coating

In this article, the investigation of the Lamb wave propagation in two-dimensional phononic crystals (PCs) composed of an array of periodic coating on a thin plate is presented. Compared with the traditional PCs usually consist of cylindrical scatters with uniform coatings in their exterior structure, the newly exterior coating structures with periodic alternant arrangement of two different materials are proposed. The band structures are calculated using finite element method. We discover that a complete band gap can be exhibited at low frequency. Furthermore, for a finite PCs plate, the computed transmission and resonance spectra shown an evident resonance nature which can be directly related to formation of the low-frequency gaps. The effects of different material parameters and arrangement mode of coating on the acoustic energy transmission and attenuation are also studied. Finally, the experimental transmission spectrum of the periodic coating PCs are also presented and compared with the numerical results. This study will provide useful support to the design of tuning band gaps and isolators in the low-frequency range.     

新型二维压电声子晶体板带隙可调性研究

设计了一种由涂有硬质材料涂层的柱状压电散射体周期性连接在四个环氧树脂薄板上构成的具有大带宽的新型二维压电声子晶体板,并利用有限元方法计算了该声子晶体板的能带结构、传输损失谱和位移矢量场.研究表明：与二组元材料构成的传统声子晶体板相比,新设计的声子晶体板的第一完全带隙频率更低,并且带宽扩大了5倍;通过在压电体表面上施加不同的电边界条件,可以实现多条完全带隙的主动调控;压电效应对能带结构有很大的影响,并且有利于完全带隙的扩大与形成.基于带隙的可调谐性,分析了可切换路径的压电声子晶体板波导,结果表明可以通过改变电边界条件来限制弹性波能量流.     

含磁电弹夹层的压电/压磁声子晶体带隙特性研究

将具有力电磁耦合性能的夹层引入到压电/压磁声子晶体中,在保持单胞长度为固定值的情况下,分别改变磁电弹夹层的厚度、磁电弹夹层中压电材料的体积分数和磁电弹夹层中压电材料的种类;并利用传递矩阵法和Bloch定理,得到波数k与频率ω的色散关系;通过色散关系图分析不同的磁电弹夹层对压电/压磁声子晶体带隙特性的影响.研究发现:当磁电弹夹层厚度增加时,带隙的中心频率上升,带隙宽度变宽;当磁电弹夹层中压电材料体积分数增加时,带隙中心频率下降,第一带隙宽度变窄,第二带隙宽度增加,第三带隙宽度保持不变;当磁电弹夹层中的压电材料种类不同时,带隙的中心频率和带隙宽度有明显的改变;磁电弹夹层对压电/压磁声子晶体带隙中心频率的影响在高频区比低频区更显著.     

用于汽车压缩机振动噪声控制的声子晶体设计与试验*

针对汽车压缩机低频振动噪声控制难的问题,基于局域共振机理在压缩机外壳设计一种声子晶体结构。借助有限元法,计算声子晶体带隙范围,阐明声子晶体结构参数与在压缩机外壳布置方式选取原因,分析其具备的优势。而后,定制各部分材料组装声子晶体实体并布置于压缩机外壳后端面,搭建压缩机振动噪声台架试验台,选取4个声学场点采集辐射噪声,并记录压缩机本体振动变化情况。进一步,选取某型号汽车搭建压缩机整车振动噪声试验台,在驾驶员座椅右侧靠近人耳处设置声学麦克风采集驾驶室内辐射噪声,并记录压缩机本体振动变化情况。试验结果表明,压缩机外壳安装声子晶体后,在声子晶体带隙频率范围对应转速内,台架与整车试验测得总辐射噪声与压缩机本体各向振动加速度RMS值基本存在改善,且部分转速范围效果显著。本文为汽车压缩机低频振动噪声控制研究提供了新的参考。     

二维复式声子晶体中基元配置对声学能带结构的影响

研究了二维复式声子晶体中基元配置对其声学能带结构的影响,发现当声子晶体的基元配置改变时,声子晶体的不可约布里渊区也会改变,而且部分能带的极值不再在高对称线上.特别地,在某些基元配置下,不可约布里渊区扩大为整个第一布里渊区.因此,对于对称性较高的复式晶格声子晶体,可用通常的方法得到能带结构,而对于对称性较低的复式晶格结构声子晶体,只有采用对整个第一布里渊区进行研究的方法,才能获得可信的能带结构及带隙.     

平板二维声子晶体声波能带结构研究

利用超元胞法,研究由钢板上生长有限长度的钢柱体形成的散射体嵌入环氧树脂基体中所构成的平板二维声子晶体的声波能带结构,分析散射体的几何参数如柱体的高、半径和板的厚度对声波带隙的影响。研究结果表明:(1)这种新型的声子晶体具有很宽的带隙,且带隙出现在低频范围内;(2)散射体的几何参数对带隙的宽度有很大的影响,它们是控制带隙宽度的主要因素。     

Band gap structures for viscoelastic phononic crystals based on numerical and experimental investigation

Many materials used as phononic crystals (PCs) are viscoelastic one. It is believed that viscosity results in damping to attenuate wave propagation, which may help to tune the defect modes or band gaps of viscoelastic phononic crystals. To investigate above phenomenon, firstly, we have extended the application of boundary element method (BEM) to the study of viscoelastic phononic crystals with and without a point defect. A new developed BEM within the framework of Bloch theory can easily deal with viscoelastic phononic crystals with arbitrary shapes of the scatterers. Experimental methods have been put forward based on the self-made viscoelastic phononic crystals. Verified by the experimental results, systematic comprehensive parametric studies on the band structure of viscoelastic phononic crystals with varying factors (final–initial value ratio, relaxation time, volume fraction of scatterers, shapes of scatterers) have been discussed by the numerical simulation. To further address the possibility to change the defect modes, the band structure of viscoelastic phononic crystals with a point defect has been studied based on the numerical and experimental methods. From present research work, it can be found that by adjusting the two viscous parameters combined with considering the effect of volume fraction and shapes, a wider and lower initial forbidden frequency or lower and higher quality factor resonant frequency can be obtained.     

一维准周期结构声子晶体透射性质的研究

提出了一维准周期结构的声子晶体模型.对弹性波通过该一维准周期结构声子晶体的透射系数进行了数值计算，并与周期结构的透射系数进行了比较.计算结果表明，弹性波通过一维准周期结构声子晶体时，同样会有带隙的出现，且带隙所在频率范围与周期结构的情形完全一样，不同的是在准周期结构声子晶体中，带隙内有很强的局域共振模.对此局域模性质的研究有助于声波或弹性波滤波器的制作. 关键词： 准周期结构 声子晶体 局域化     

Collimation and enhancement of elastic transverse waves in two-dimensional solid phononic crystals

In this Letter, we numerically investigate the propagation characteristics of elastic transverse waves emitted by line sources embedded inside two-dimensional (2D) solid phononic crystals (PCs). The results show that collimation and enhancement of elastic transverse waves can be achieved at the band edge frequencies. We find that the collimation effect originates from the flat equifrequency contours (EFCs) at the band edge of appropriately designed 2D solid PCs. It is shown that, in addition to geometric symmetry, appropriate constituent material combination is essential to obtain flat EFCs at the band edge. A highly directional and enhanced elastic transverse wave source with a half power angular width of only 5.6° and an enhancement factor of 530 is realized simply by utilizing a finite-size 2D solid PC structure.     

一维颗粒声子晶体的拓扑相变及可调界面态

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.     

内插扩张室声子晶体管路带隙特性研究

声子晶体管路的带隙特性,可以实现管路系统在特定频率下的噪声控制.利用二维模态匹配法推导出单个内插扩张室元胞的传递矩阵,结合Bloch定理,得到声子晶体管路的能带结构计算方法;验证了二维方法在计算能带结构时的准确性.研究发现,内插扩张室声子晶体管路存在布拉格带隙和局域共振带隙.进一步研究了晶格常数以及内插管长度对能带结构的影响,结果表明,晶格常数主要控制布拉格带隙,而内插管长度对局域共振带隙有较大的影响,并研究了两种参数变化下的带隙耦合.研究结果可以为管路降噪设计提供新的思路.     

Effect of interface/surface stress on the elastic wave band structure of two-dimensional phononic crystals

In the present Letter, the multiple scattering theory (MST) for calculating the elastic wave band structure of two-dimensional phononic crystals (PCs) is extended to include the interface/surface stress effect at the nanoscale. The interface/surface elasticity theory is employed to describe the nonclassical boundary conditions at the interface/surface and the elastic Mie scattering matrix embodying the interface/surface stress effect is derived. Using this extended MST, the authors investigate the interface/surface stress effect on the elastic wave band structure of two-dimensional PCs, which is demonstrated to be significant when the characteristic size reduces to nanometers.     

Phononic crystals containing piezoelectric material

The elastic band structure of a two-dimensional phononic crystal containing piezoelectric material is investigated by the plane-wave-expansion method. Numerical results show that for large filling fraction, the full band gap of this kind of system is enlarged by considering the piezoelectric effect, but for small filling fraction, the influence of the piezoelectric effect is so small that it can be neglected.     

声波在二维固/流声子晶体中的禁带特性研究

采用时域有限差分法(FDTD),分析了声波在二维四方点阵铝/空气组合声子晶体中的禁带特性,并利用实验测试验证了理论分析的正确性.在此基础上研究了两种不同声阻抗率比固(实心圆柱和空心圆管)/流系统声子晶体的禁带特性.对于实心圆柱体,分析了有限尺寸结构声子晶体在传播方向上的层数对声波传播特性的影响,得到了这两种系统在不同填充率下取得最大声波禁带宽度所需的最少层数.同时指出,在低声阻抗率比条件下,对于空心圆管填充物,通过选取适当的半径比,可以获得比实心柱体更宽的方向带隙.     

Transmission mode of one-dimensional phononic crystal based on coupling of total evanescent waves

In order to obtain the transmission properties of one-dimensional phononic crystal under total evanescent waves, we design structure model. Basing on the basic acoustic wave equations and boundary condition as well as the Bloch theory, we study the band structure of one-dimensional phononic crystal. We summarize the properties of the mode based on the coupling of total evanescent waves and explain its physical mechanism. There are three transmission modes in phononic crystal. Based on the coupling of total evanescent waves, the number of perfect transmission peaks is just equal to the number of structure period, and the thickness of period can be much less than the wave length.     

可用于隔声和带隙调控的五模式超材料

为了利用在声学领域极具应用前景的双锥型五模式超材料进行隔声降噪,提出一种双锥宽直径不全同型五模式超材料.利用有限元方法分析了其声子能带结构、各波模相速度、品质因数随结构与材料参数的变化关系,在实用性和稳定性上与窄直径不同型五模式超材料作了比较.宽直径不全同型五模式超材料在保持原始五模式结构单模传输能带的前提下,还产生了更低频、宽带的三维完全带隙,且结构更稳定,重量更轻。双锥型五模式超材料在特定宽直径不同时具有三维完全带隙,品质因数主要由结构参数决定,各材料参数只是不同程度地影响带隙的绝对宽度和位置.研究结果表明双锥宽直径不全同型五模式超材料有望用于带隙调控和隔声。      

Phononic glass: A robust acoustic-absorption material

In order to achieve strong wide band acoustic absorption under high hydrostatic pressure, an interpenetrating network structure is introduced into the locally resonant phononic crystal to fabricate a type of phononic composite material called "phononic glass." Underwater acoustic absorption coefficient measurements show that the material owns high underwater sound absorption coefficients over 0.9 in 12-30?kHz. Moreover, the quasi-static compressive behavior shows that the phononic glass has a compressive strength over 5?MPa which is crucial for underwater applications.