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1.
By using of the multiple scattering methods, we study the negative refraction imaging effect of solid acoustic waves by two-dimensional three-component phononic crystals composed of coated solid inclusions placed in solid matrix. We show that localized resonance mechanism brings on a group of flat single-mode bands in low-frequency region, which provides two equivalent frequency surfaces (EFS) close to circular. The two constant frequency surfaces correspond to two Bloch modes, a right-handed and a left-handed, whose leading mode are respectively transverse (T) and longitudinal (L) modes. The negative refraction behaviors of the two kinds of modes have been demonstrated by simulation of a Gaussian beam through a finite system. High-quality far-field imaging by a planar lens for transverse or longitudinal waves has been realized separately. This three-component phononic crystal may thus serve as a mode selector in negative refraction imaging of solid acoustic waves. 相似文献
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Focusing of sound in a 3D phononic crystal 总被引:1,自引:0,他引:1
We present a combined experimental and theoretical study of phonon focusing phenomena in a pass band above the complete band gap in a 3D phononic crystal. Wave propagation was found to depend dramatically on both frequency and incident direction. This propagation anisotropy leads to very large negative refraction, which can be used to focus a diverging ultrasonic beam into a narrow focal spot with a large focal depth. The experimental field patterns are well explained using a Fourier imaging technique, based on the 3D equifrequency surfaces calculated from multiple scattering theory. 相似文献
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利用多重散射理论分析了钢/水声子晶体平板成像过程.发现平板成像中的散射波会聚具有散射通道特征.对于确定的声源位置,不同入射角信号对应不同的通道;耦合进入通道的信号强度也不相同.小角度入射波能较强地耦合进入通道;大角度入射波在入射表面受到强烈散射,较弱地耦合进入通道.非理想成像情况下,不同入射角信号通过平板成像的位置不同,因而形成像差.声源位置改变,对应的通道亦随之改变.散射通道与声子晶体的各向异性能带结构和多重散射密切相关. 相似文献
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Berrier A Mulot M Swillo M Qiu M Thylén L Talneau A Anand S 《Physical review letters》2004,93(7):073902
We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area. 相似文献
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Shasha Peng Xuefei Mei Pei Pang Manzhu Ke Zhengyou Liu 《Solid State Communications》2009,149(17-18):667-669
The focus behaviors of acoustic wave through 8-fold-symmetry phononic quasicrystals have been observed experimentally in this paper. By measuring the field distributions in the image plane, we obtain an elongated image of a point source which has a similar result with phononic crystals. The negative refraction index was measured in two different ways which are very consistent with each other. These properties make the phononic quasicrystals (PQCs) promising for application in a range of phononic devices. 相似文献
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A two-component thin-layer acoustic superlattice (one-dimensional phononic crystal), in which one of the layers of the superlattice period is near the proper ferroelastic phase transition, is considered. The necessary conditions under which a bulk elastic wave incident on the outer surface of the superlattice excites a refracted wave with negative acoustic refraction (at the fundamental or multiple frequency) have been determined. 相似文献
9.
E. A. Vinogradov V. G. Veselago V. I. Golovanov K. F. Shipiliv 《Physics of Wave Phenomena》2010,18(1):27-29
A phononic crystal in the form of a periodic rhombic structure with a large filling factor s=0.86, made up of steel cylinders in the air, is investigated. Under excitation of the crystal from the depth of the structure
by a point acoustic radiator, the dispersion characteristic of the crystal is obtained and the band structure is constructed
in the upper (reduced) Brillouin zone which has negative dispersion while the crystal has negative refraction. The second
derivative of the dispersion dependence differs from zero. The resolution of the flat lens was as high as λ/3 near the edges of the band. Structures like this may be effective nonlinear converters of acoustic waves. 相似文献
10.
Negative refraction in two-dimensional photonic crystals 总被引:1,自引:0,他引:1
M. Qiu S. Xiao A. Berrier S. Anand L. Thylén M. Mulot M. Swillo Z. Ruan S. He 《Applied Physics A: Materials Science & Processing》2005,80(6):1231-1236
We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index neff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths. PACS 42.70.Qs; 41.85.Ct; 42.30.Va 相似文献
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A three-dimensional bicontinuous photonic crystal of a bcc lattice with all-angle negative refraction that can be achieved at optical frequencies by interference lithography is proposed. A numerical simulation of the focusing imaging of a slab of this crystal was performed to verify the property of all-angle negative refraction. The dependence of the negative-refraction frequency range on the threshold of photoresist development and on the dielectric constant is also discussed. 相似文献
13.
《中国科学:物理学 力学 天文学(英文版)》2020,(8)
The study of topological semimetals hosting spin-1 Weyl points(WPs) beyond Dirac points and WPs has attracted a great deal of attention. However, a spin-1 Weyl semimetal that exclusively possesses spin-1 WPs in a clean frequency window without being shadowed by any other nodal points is yet to be discovered. This study reports a spin-1 Weyl semimetal in a phononic crystal. Its spin-1 WPs are touched by two linear dispersions and an additional flat band and carry monopole charges(-2,0,2) or(2,0,-2) for the three bands from the bottom to the top. They result in double Fermi arcs, which occur between the first and second bands, as well as between the second and third bands. Further robust propagation is observed against the multiple joints and topological negative refraction of the acoustic surface arc wave. The results of this study create the basis for the exploration of the unusual properties of spin-1 Weyl physics on a macroscopic scale. 相似文献
14.
波状结构二维光子晶体近场亚波长成像的研究 总被引:7,自引:5,他引:2
研究了波状结构二维光子晶体(2DPC)在红外波段的负折射近场成像,对其等频面进行了分析,指出波状结构二维光子晶体无法实现负折射远场成像的原因在于缺少与入射介质等频面相匹配的光子晶体圆形等频面,所用的矩形等频面使波状膜层二维光子晶体不可避免地具有各向异性特征,进而将成像限制在近场范围内。采用时域有限差分(时域有限差分)方法模拟了不同厚度的波状结构二维光子晶体近场成像效果,当厚度为两倍栅格常量时,单光源的成像分辨力为0.28λ,达到亚波长分辨效果。分辨力随着光源逐渐远离近场范围而降低,而像点的位置基本不随光源距离和光子晶体厚度的变化而改变。双光源的成像模拟进一步验证了波状结构二维光子晶体的近场亚波长成像能力,分辨力达到0.35λ,但成像质量受光子晶体厚度变化的影响较大。 相似文献
15.
We have studied the propagation of a surface acoustic waves (SAW), in a structure constituted by a 2D phononic film (a few micrometers thick and having lattice constants of a few hundreds of micrometers in the two directions of the propagation plane) deposited onto a homogeneous semi-infinite substrate. First, we have calculated the dispersion relations of the acoustic modes by using a plane waves expansion method. We found that the surface branch exhibits both the folding effect and a band gap for the propagation along some particular directions. This is a very interesting result which demonstrates that the effects related to the existence of the band gap (sound velocity dispersion, diffraction, refraction, ultrasound tunneling, etc.) can all appear, even if the thickness of the phononic film is much less than the penetration depth of the SAW. Then, we used an all-optical technique to monitor the spectral content of the SAW propagating along the GammaX direction in the reduced Brillouin zone. We show that a wave with frequency in the stop band, is destructively diffracted after it propagates through less than ten periods. Finally, we report on measurements of the Rayleigh wave phase velocity and we show that the transit time is independent of the distance traveled inside the phononic crystal, suggesting that tunneling trough the sample is involved. 相似文献
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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. 相似文献
17.
Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized Si/Si{0.4}Ge{0.6} superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal. 相似文献
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Using an exact Mie scattering solution, this paper investigates the mode conversions during the Mie scattering of a single bi- or one-component sphere in unbounded epoxy. Then the formation mechanism of the first complete gap in the corresponding tri- or bi-component phononic crystal is investigated by the multiple-scattering method. It is shown that the heavy density of the scatterer plays an essential role in the Mie resonance and the formation of the gaps for both types of the phononic crystals. For the tri-component phononic crystal, the gap is mainly induced by the Mie resonance of the single scatterer. For the bi-component phononic crystal, the transverse wave (by mode-conversion during the Mie scattering under a longitudinal wave incidence) is modulated by the periodicity and governed by the Bloch theory, which induces the gap cooperatively. 相似文献
19.
The problem of subwavelength imaging via a photonic crystal slab lens made of two-dimensional (2D) square arrays of parallel dielectric cylinders in air is studied and discussed theoretically. The finite-difference time-domain method is employed to investigate the unique features of imaging by such lens. We confirm earlier findings that a photonic crystal slab lens can provide the imaging of a point source. By analysing the transmission properties of the proposed structure, we demonstrate that inside the all-angle negative refraction, there are some favourable directions for waves to travel. We show that the surface termination of the photonic crystal is a key parameter to obtain a good quality image. The super-resolution of two sources separated by a distance less than the wavelength is also considered. It is shown that the achievable resolution is limited by the slab length. 相似文献
20.
We have theoretically studied the negative refractive behavior and the focusing effect in a two-dimensional square-lattice photonic crystal made of air rods in a dielectric background. Detailed explanations are given for the effect of the negative refraction, and the imaging of the plano-concave lens is shown by the use of a wave vector diagram formalism. The typical negative refractive behavior is demonstrated by considering the Bloch mode with the wave vector inside the first Brillouin zone, because only those wave vectors inside the first Brillouin zone of multiple Brillouin zones have a definite meaning. The single propagating beam is analyzed by the use of the wave vector diagram formalism following the folding of the wave vectors. Good-quality focusing of a plane wave can be realized by using a photonic crystal plano-concave lens, while a plane wave is formed by a point source placed at the focal point. Our results are in good agreement with the experimental ones shown for a negative-index plano-concave lens by Vodo et al. [Appl. Phys. Lett. 86 (2005) 201108]. Finally, we also have shown the focusing behavior of a plane wave and a Gaussian pulse by a plano-concave lens structure with high-index modulation instead of air in the concave region. 相似文献