金刚石/ZnSe结构中瞬态热栅场的有限元法分析

利用有限元法分析计算了脉冲激光激发瞬态热栅在金刚石薄膜/ZnSe衬底双层结构中的三维温度场分布及变化。通过比较不同厚度金刚石薄膜样品的温度场分布,结果显示金刚石薄膜的厚度对样品中温度场的分布有较大影响,随着薄膜厚度的增大,峰值温度提高并且二次加热现象更加明显。     

Manipulated localized surface plasmon resonances in silver nanoshells coated with a spherical anisotropic layer

<正>The influences of the anisotropy of the outer spherically anisotropic(SA) layer on the far-field spectra and nearfield enhancements of the silver nanoshells are investigated by using a modified Mie scattering theory.It is found that with the increase of the anisotropic value of the SA layer,the dipole resonance wavelength of the silver nanoshell first increases and then decreases,while the local field factor(LFF) reduces.With the decrease of SA layer thickness, the dipole wavelength of the silver nanoshell shows a distinct blue-shift.When the SA layer becomes very thin,the modulations of the anisotropy of the SA layer on the plasmon resonance energy and the near-field enhancement are weakened.We further find that the smaller anisotropic value of the SA layer is helpful for obtaining the larger near-field enhancement in the Ag nanoshell.The geometric average of the dielectric components of the SA layer has a stronger effect on the plasmon resonance energy of the silver nanoshell than on the near-field enhancement.     

用于汽车低频振动控制的局域共振声子晶体*

低频振动的控制是评估汽车舒适性的重要指标。针对汽车板件结构的低频振动控制问题,提出了一种基于局域共振机理的新型准二维声子晶体板。其结构由单侧复合圆柱共振单元周期排布在基板上构成。通过有限元方法得到了该结构的带隙特性,并结合其振型和传输谱分析了低频完全带隙的形成机理。研究表明,不同形式的板振动模式与圆柱共振单元的局域共振模式相互耦合形成面内带隙与面外带隙,两者叠加形成完全带隙。进一步研究发现,通过改变结构的材料和尺寸参数可以将共振带隙调节到满足实际应用要求的极低频范围,可在低于100 Hz的频段形成完全带隙,并可在更宽的频带内抑制z方向振动的弯曲波,为声子晶体在车身板件减振中的实际应用提供了依据。     

二维声学系统中的拓扑相变及边界传输

拓扑声学的发现产生了一种可以有效抑制反射的声学边界传输态,不仅让人们重新认识了声传输现象,也扩展了声学新原理功能器件的研究领域。文章将介绍二维系统中拓扑声学的基本概念以及一些拓扑非平庸体系。主要关注利用背景流体构造的声类量子霍尔效应,利用共振耦合环形波导构造Floquet拓扑绝缘体,声类量子自旋霍尔效应以及声谷霍尔效应等。     

Manipulation of extraordinary acoustic transmission by a tunable bull’s eye structure

Extraordinary acoustic transmission （EAT） has been investigated in a tunable bull＇s eye structure. We demonstrate that the transmission coefficient of acoustic waves can be modulated by a grating structure. When the grating is located at a distance of 0.5 mm from the base plate, the acoustic transmission shows an 8.77-fold enhancement compared to that by using a traditional bull＇s eye structure. When the distance increases to 1.5 mm, the transmission approaches zero, indicating a total reflection. Thus, we can make an efficient modulation of acoustic transmission from 0 to 877%. The EAT effects have been ascribed to the coupling of structure-induced resonance with the diffractive wave and the waveguide modes, as well as the Fabry-Perot resonances. As a potential application, the modulation of far-field collimation is illustrated in the proposed bull＇s eye structure.     

基于相位调控的超高透射声学超表面及其应用*

声学超表面可以灵活有效地对声波进行调控,实现多种新颖的现象和功能,在诸多声波调控领域有潜在的应用前景。该文引入了一种镀膜型迷宫结构单元,可以提供全范围(0~2π)的突变相位,具有高效的透射率(~100%)和较好的鲁棒性。基于相位调控,可利用镀膜型迷宫结构单元构建出超高透射超表面,实现异常声折射、声聚焦、声束沿任意凸轨迹弯曲传播以及声成像等应用。     

声学Mie共振及其应用

Mie共振是基于Mie散射理论的共振散射现象,起源于单极、偶极、四极、八极和更高的多极振子所引起的辐射叠加。近年来,人工产生的声学Mie共振得到了越来越多的关注。由于声学Mie共振具有多种共振模式,基于Mie共振的声学超构材料体现出许多独特的声学特性,有望被应用到低频声波强反射、负折射、彩虹俘获、指向性声辐射、超常声波透射等众多领域当中。     

点缺陷阵列对声子晶体波导定向辐射性能的影响

将点缺陷阵列应用于声子晶体波导,提出一种具有高定向辐射性能的复合声子晶体波导. 基于有限元法的数值分析表明,附加到声子晶体波导表面的点缺陷阵列可激发出作为次级声源的谐振模. 谐振模辐射的声波与波导出射端口直接辐射的声波相互干涉,可以使声子晶体波导的法向辐射声压提高161.21%、发散角减小85.35%. 当点缺陷的数目增大到一定程度后,波导的定向辐射性能不再有明显的改善. 该研究为改善波导的定向辐射性能提供了一种新方法. 关键词： 声子晶体波导 点缺陷 谐振模 定向辐射     

Extraordinary Resonant Scattering in Imperfect Acoustic Cloak

We present a systematic study on the extraordinary resonant scattering in imperfect acoustic cloak by means of acoustic scattering theory. Analysis results demonstrate that the resonances are inevitable due to the perturbation to the ideal clo~k, and specific resonance modes are excited by specific order waves. The strength of resonance is determined by the magnitude of perturbation and each order wave＇s sensitivity to the perturbation. Further studies reveal the unique scattering characters of different resonance modes.     

One-dimensional $\mathcal{PT}$-symmetric acoustic heterostructure

The explorations of parity-time ($\mathcal{PT}$)-symmetric acoustics have resided at the frontier in physics, and the pre-existing accessing of exceptional points typically depends on Fabry-Perot resonances of the coupling interlayer sandwiched between balanced gain and loss components. Nevertheless, the concise $\mathcal{PT}$-symmetric acoustic heterostructure, eliminating extra interactions caused by the interlayer, has not been researched in depth. Here we derive the generalized unitary relation for one-dimensional (1D) $\mathcal{PT}$-symmetric heterostructure of arbitrary complexity, and demonstrate four disparate patterns of anisotropic transmission resonances (ATRs) accompanied by corresponding spontaneous phase transitions. As a special case of ATR, the occasional bidirectional transmission resonance reconsolidates the ATR frequencies that split when waves incident from opposite directions, whose spatial profiles distinguish from a unitary structure. The derived theoretical relation can serve as a predominant signature for the presence of $\mathcal{PT}$ symmetry and $\mathcal{PT}$-symmetry-breaking transition, which may provide substantial support for the development of prototype devices with asymmetric acoustic responses.