Subwavelength Chiral Spiral Acoustic Metamaterials for a Robust Topological Acoustic Insulator

Topological acoustic insulators enable sound waves to transmit along the surface without backscattering, which builds a new pathway towards sound wave control. However, a large share of topological acoustic insulators are realized based on special point group symmetry and Bragg scattering mechanism. This method not only exerts a restriction on the unit cell design but also requires the lattice constant to be comparable with the wavelength. In this paper, the chiral spiral acoustic metamaterials are constructed based on an Archimedean spiral structure. This structure enjoys subwavelength characteristics and is easy to construct. Taking advantage of the chirality of the spiral structure topological phases with opposite energy flow direction can be constructed. The edge state is formed at the interface composed of the spiral units sharing different chirality, which does not depend on point group symmetry. The topological transportation on the interfaces shows strong robustness despite sharp corners verified by straight and zigzag waveguides. The topological acoustic insulator with a chiral spiral structure provides a 11el strategy for small acoustic devices with robust sound transmission

Directional Metastable Wetting Evolution of Droplets on Artificial Patterned Microcavity Surfaces

Controllable wetting transition on artificial microtextured surfaces has significant applications in many industrial fields. In this work, the droplet spreading and the directional wetting transition are investigated on the substrate surface with the patterned microcavities. The results show that the macroscopic inward wetting transition from the periphery to the center of the droplet strongly depends on the mesoscopic sequential transition from Cassie to Wenzel state in the microcavities on the substrate surfaces. The semiquantitative relationship between sagging depth of meniscus in the microcavities and the droplet spreading velocity is set up by utilizing scaling-law analysis in terms of mechanical equilibrium of the meniscus. This finding is expected to help to clarify the issues on the mechanism and main affecting factors of the wetting transition on the patterned surface

可重构力学超材料的设计与波动特性研究

力学超材料中的弯曲梁双稳态结构由于其主动调控性强且调控精度高等优点近年来受到广泛关注.文章利用中心受压弯曲梁的不稳定性设计了六角型双稳态结构,首先建立了等效弯曲梁模型,基于梁变形微分方程及能量最低原理探明了结构双稳态特性的产生基理,之后利用有限元数值计算研究了结构几何参数对其整体力学性能的影响,分别得到了具备自恢复及双稳态性能的结构几何参数范围,绘制了几何参数与力学性能之间的相图.同时,可重构结构的可控变形能力有助于调整整体的色散特性,利用数值仿真研究了具备双稳态特性的结构在拉伸和压缩两种构型下的色散关系,对比分析了不同结构几何参数及构型转变对结构产生的带隙位置及范围的影响,之后对由不同构型单胞组成的周期性结构进行了频响分析来验证带隙计算的准确性.通过六角型可重构结构的力学特性、色散特性研究及频响分析表明可以通过结构几何参数的设计实现对结构整体性能的主动调控,为可逆向设计的弹性波超材料结构研究分析提供了一条可靠路径

Wave characteristics of reconfigurable elastic metamaterials based on a multi stable structure

Elastic metamaterials have been considered as important tools for vibration and noise reduction because of their subwavelength bandgaps. However, acritical problem hindering their practical application is the difficulty of constructing an adjustable unit cell that facilitates bandgap tuning. In this study, reconfigurable two dimensional metamaterials based on four curved beams are developed such that they could sustain multi stable configurations. Our calculations and experiments reveal that the developed unit cell can exhibit bidirectional phase transformations to three stable configurations. The three stable configurations have different wave characteristics, allowing for elastic wave propagation to be tuned at the subwavelength scale. Based on this tuneability, a waveguide can be designed and the wave direction of travel can be controlled. This study provides a novel approach for designing reconfigurable elastic wave materials, elastic wave logic circuits, and waveguides

Acoustic edge mode in spiral-based metamaterials at subwavelength scale

Recently, the quantum effect of condensed matter physics is introduced into the acoustic field, which lays a new pathway to manipulate the acoustic wave. However, the acoustic topological insulator based on Bragg scattering requires their lattice constant to be comparable with the wavelength. In this paper, a 11el subwavelength spiral element on the basis of the Archimedean spiral is proposed. Thanks to the central resonator with a slender curved channels scheme, the subwavelength Dirac cone forms in the band structure. The eigenfrequency of the element can be changed by the spiral geometric parameters, which triggers the topological phase transition characterized by opposite valley Chern numbers. The backscattering-immune unidirectional transmission edge state exists at different topological boundaries, suggesting its great robustness even at the sharp bends. Also the topological edge modes along the Z-shaped interfaces are verified by the experiments and the calculation, which provides an effective structure to control the low frequency acoustic wave transmission

Broadband subwavelength tunable valley edge states induced by fluid filling acoustic metastructure

Abstract Topological acoustic insulators demonstrate unusual characteristics in manipulating sound wave, which attract much attention from researchers. However, most of the recent researches are based on passive system, hampering their dispersion tunability. In this paper, a broadband subwavelength tunable fluid filling acoustic topological metastructure is studied. It is composed of perforated cells with tunable water height in the hole, which enables the dispersion of the edge state to be tuned. The inversion symmetry is broken by expanding and shrinking the adjacent holes in the unit cell. Thus, the valley Hall states with opposite Chern number form at the K point in the Brillouin zone. The edge states emerge at the boundary of the different valley Hall phases. The robustness of the edge states is verified by the straight and Z-shaped waveguide. Furthermore, the dispersion of the edge state can be altered continuously by raising and reducing the water height, giving rise to broadband variable topological states, which greatly expands the bandwidth from 40 Hz to 1033 Hz. This work offers a new method to control the topological states and shows great potential for practical application.</p

JUNO Sensitivity on Proton Decay p→νˉK+p\to \bar\nu K^+ Searches

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this paper, the potential on searching for proton decay in $p\to \bar\nu K^+$ mode with JUNO is investigated.The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits to suppress the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar\nu K^+$ is 36.9% with a background level of 0.2 events after 10 years of data taking. The estimated sensitivity based on 200 kton-years exposure is $9.6 \times 10^{33}$ years, competitive with the current best limits on the proton lifetime in this channel

JUNO sensitivity on proton decay p → ν K + searches*

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this study, the potential of searching for proton decay in the $p\to \bar{\nu} K^+$ mode with JUNO is investigated. The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits suppression of the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via $p\to \bar{\nu} K^+$ is 36.9% ± 4.9% with a background level of $0.2\pm 0.05({\rm syst})\pm$$0.2({\rm stat})$ events after 10 years of data collection. The estimated sensitivity based on 200 kton-years of exposure is $9.6 \times 10^{33}$ years, which is competitive with the current best limits on the proton lifetime in this channel and complements the use of different detection technologies