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为实现高效太赫兹调控,迫切需要一种高效且成本低的材料。新型钙钛矿材料由于其优异的光电特性,加上钙钛矿制备工艺简单、可大批量生产等优点,非常适合作为太赫兹超材料的活性材料,通过外部激励改变活性材料的属性,可灵活调控太赫兹波。因此,选择新型钙钛矿材料外加光场调控太赫兹,分析在光场作用前(绝缘态)和在光场作用后(金属态)两种状态对单元结构太赫兹宽波段下幅值和相位的影响。设计出光场灵活调控的钙钛矿基1 bit太赫兹编码超表面结构,该结构由有机无机杂化钙钛CH3NH3PbI3(MAPbI3)、聚酰亚胺和铝构成。通过CST仿真结果显示,该超表面结构在光场的调控下能够实现宽谱(0.1、1、2、6 THz)太赫兹波的180°相位差变化,经过超表面编码结构的设计,同一编码序列实现远场波束的变换。研究结果表明,基于光场操控钙钛矿材料的编码超表面为实现灵活的太赫兹波调控提供了新的思路,在太赫兹通信、安检、生物医学成像等方面具有巨大的应用潜力。 相似文献
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超表面是一种人工制造的亚波长结构阵列平面,重量轻,易集成,可实现多种功能,被广泛应用于诸多领域。传统光谱成像系统依赖于色散元件及光程累积相位差实现不同波长的色散与聚焦,无法满足系统集成化需求。不同于传统光学元件依赖电磁波在介质中传播累积相位差,超表面依靠界面相位变化来进行相位调控,可实现十分轻薄的光学系统。研究传输相位型超表面,使用时域有限差分算法(FDTD算法)优化单元结构。将超表面引入光谱成像系统中,通过优化亚波长结构尺寸,进行结构排布,开展超表面光谱成像系统研究,实现多波长色散与聚焦独立调控。利用该方法,扫描不同单元结构参数对相位的影响,依照聚焦的相位分布针对不同波长设计对应的位相分布,仿真实现了一个波段范围为510~720 nm,焦距为2 mm,谱段数为八个的超表面多光谱成像系统。通过电磁仿真软件FDTD solutions和数据处理软件计算全模结构电场的远场分布,并分析了系统的成像性能。相比于传统光栅或棱镜分光结构,超表面光谱成像系统可有效减小系统体积,其超轻、超薄、便携特点解决了现有光谱成像系统的应用局限性,为小型化、轻量化光谱成像系统的研制提供了一种新的解决方案。 相似文献
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以广义斯奈尔定律为理论依据,对五模声学超表面定向反射的基本原理进行了解析推导和理论分析,获得了五模超表面的理想连续物性参数分布,并给出了五模超表面尺寸设计准则;然后将超表面离散,获得离散单胞的密度和体积模量,并以此为目标进行五模微结构设计,采用均匀化理论计算微结构的等效物性参数;最后,进行了水下声场的声波定向反射调控仿真实验,研究了入射波频率对超表面定向反射性能的影响,仿真结果展现了五模超表面宽频有效的声波调控能力以及调控的可靠性和准确性。本文的研究工作为五模声学超表面的设计和物理实现提供理论指导。 相似文献
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设计实现了一种基于双圆弧形金属结构的宽带反射型极化旋转超表面, 在7.9–20.1 GHz的宽频带范围内交叉极化转换率达到99%, 通过改变其结构参数可实现在保持高效的交叉极化转换率的条件下对交叉极化反射相位的自由调控. 基于六种不同结构参数极化旋转超表面结构单元的空间排布设计实现了一维宽带相位梯度超表面, 在宽频带内, 实现了异常反射. 测试了其镜面交叉极化反射率, 与仿真结果基本一致. 仿真计算了x-极化波入射时的电磁场分布和异常反射角度, 与理论计算结果基本一致. 仿真与测试结果均表明这种相位梯度超表面在8.9–10 GHz 和10.0–18.1 GHz的两个宽带频率范围内可分别实现高效的表面波耦合和异常反射. 相似文献
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为实现轻质材料对低频声波的有效调控,在传统对称双锥五模超材料构型的基础上,以引入掺杂材料、飞镖型结构的方式构造了具有局域共振特性的非轴对称五模超材料单胞,通过能带分析发现其具有较宽的单模区域与低频性更优的声子禁带。此外还探究了飞镖结构节点圆半径、锥角和掺杂材料模量对能带结构与品质因数的影响。研究结果表明,单胞品质因数随着掺杂材料杨氏模量的提升而增大,单胞对低频声波的调控能力随着结构对称性的降低而变强。所设计的非轴对称单胞单模区域绝对带宽增大到原来的2.5倍,第一带隙相对带宽提升了57%。这为用于低频声波调控的五模超材料单胞构型设计提供了思路。 相似文献
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《Physics letters. A》2020,384(7):126151
In this paper, we propose an ultra-thin acoustic metasurface constructed of multiply resonant units to manipulate reflected wavefront. As a counterpart to the Helmholtz resonator (with monopolar resonance) and membrane-type resonator (with dipolar resonance), the multiply resonator are used in metamaterials to induce strong quadrupolar resonance. Here we use the multiply resonator as a new kind of building blocks to make acoustic metasurfaces. The used multiply resonant unit is composed of solid materials, and the acoustic metasurface can work in a water background. We demonstrate that the proposed acoustic metasurface achieves good performance in anomalous reflection, focusing, and carpet cloaking. The thickness of the acoustic metasurface is about two orders of magnitude smaller than the acoustic wavelength in water. A design of unit group is further proposed to avoid the phase discretization becoming too fine in such a long-wavelength condition. 相似文献
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《Physics letters. A》2019,383(22):2640-2644
We present a new acoustic metasurface structure to generate the stable acoustic vortex beams with controllable topological charge in the broadening of operating frequency. The proposed acoustic metasurface can dynamically achieve a full span of 360° phase modulation by three simple solutions. Acoustic plane beam and acoustic vortex beam can convert each other based on multi-metasurfaces combination. Potential applications of such phase modulation schemes can be anticipated. 相似文献
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本文给出由压电晶体-液体-各向同性固体组成的分层结构中声反射和声透射的一些理论结果,与不考虑介质压电性的情形相比,反射和秀射声场具有大的复杂性,与晶体取向,界面电边界条件等均有关。 相似文献
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Franck Richecoeur Sbastien Ducruix Philippe Scouflaire Sbastien Candel 《Proceedings of the Combustion Institute》2009,32(2):1663-1670
This article considers the influence of fluctuations in temperature on acoustic resonance characteristics of a combustion chamber. This analysis is concerned with acoustic coupling experienced in high frequency instabilities. Experiments carried out on a multiple injector combustor (MIC) operating with liquid oxygen and gaseous methane are used to simulate on a model scale the situation prevailing in a liquid rocket thrust chamber. External acoustic modulations are generated by periodically blocking an auxiliary nozzle with a rotating toothed wheel. By continuously changing the rotation velocity, it is possible to apply a linear frequency sweep and obtain the response of the system to an external excitation. It is found that the chamber quality factor under hot fire conditions is reduced with respect to the one measured under cold flow conditions. This is shown to be correlated with the level and spatial extension of temperature fluctuations inside the chamber. Temperature fluctuations induce variations in the speed of sound which in turn perturb the eigenfrequencies of the system and modify its response. This effect is modeled in a simplified way by considering a second order dynamical system featuring an eigenfrequency which fluctuates around its mean value. The dynamics is analyzed by making use of simulations and by the method of averaging. It is shown that when the eigenfrequency fluctuates, the system behaves as if it had an augmented level of dissipation and that this induces a reduction in the quality factor. It is concluded that this mechanism could have an important impact on the development of oscillations in liquid rocket engines. 相似文献
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Whilst sonothrombolysis is a promising and noninvasive ultrasound technique for treating blood clots, bleeding caused by thrombolytic agents used for dissolving clots and potential obstruction of blood flow by detached clots (i.e., embolus) are the major limitations of the current approach. In the present study, a new sonothrombolysis method is proposed for treating embolus without the use of thrombolytic drugs. Our proposed method involves (a) generating a spatially localised acoustic radiation force in a blood vessel against the blood flow to trap moving blood clots (i.e., generation of an acoustic net), (b) producing acoustic cavitation to mechanically destroy the trapped embolus, and (c) acoustically monitoring the trapping and mechanical fractionation processes. Three different ultrasound transducers with different purposes were employed in the proposed method: (1) 1-MHz dual focused ultrasound (dFUS) transducers for capturing moving blood clots, (2) a 2-MHz High Intensity Focused Ultrasound (HIFU) source for fractionating blood clots and (3) a passive acoustic emission detector with broad bandwidth (10 kHz to 20 MHz) for receiving and analysing acoustic waves scattered from a trapped embolus and acoustic cavitation. To demonstrate the feasibility of the proposed method, in vitro experiments with an optically transparent blood vessel-mimicking phantom filled with a blood mimicking fluid and a blood clot (1.2 to 5 mm in diameter) were performed with varying the dFUS and HIFU exposure conditions under various flow conditions (from 1.77 to 6.19 cm/s). A high-speed camera was used to observe the production of acoustic fields, acoustic cavitation formation and blood clot fragmentation within a blood vessel by the proposed method. Numerical simulations of acoustic and temperature fields generated under a given exposure condition were also conducted to further interpret experimental results on the proposed sonothrombolysis. Our results clearly showed that fringe pattern-like acoustic pressure fields (fringe width of 1 mm) produced in a blood vessel by the dFUS captured an embolus (1.2 to 5 mm in diameter) at the flow velocity up to 6.19 cm/s. This was likely to be due to the greater magnitude of the dFUS-induced acoustic radiation force exerted on an embolus in the opposite direction to the flow in a blood vessel than that of the drag force produced by the flow. The acoustically trapped embolus was then mechanically destructed into small pieces of debris (18 to 60 μm sized residual fragments) by the HIFU-induced strong cavitation without damaging the blood vessel walls. We also observed that acoustic emissions emitted from a blood clot captured by the dFUS and cavitation produced by the HIFU were clearly distinguished in the frequency domain. Taken together, these results can suggest that our proposed sonothrombolysis method could be used as a promising tool for treating thrombosis and embolism through capturing and destroying blood clots effectively. 相似文献
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Fatma Saad Saoud Jean Claude PlenetMohamed Henini 《Physica B: Condensed Matter》2012,407(6):1008-1013
The structural, electronic and vibrational properties of InN under pressures up to 20 GPa have been investigated using the pseudo-potential plane wave method (PP-PW). The generalized-gradient approximation (GGA) in the frame of density functional theory (DFT) approach has been adopted. It is found that the transition from wurtzite (B4) to rocksalt (B1) phase occurs at a pressure of approximately 12.7 GPa. In addition, a change from a direct to an indirect band gap is observed. The mechanism of these changes is discussed. The phonon frequencies and densities of states (DOS) are derived using the linear response approach and density functional perturbation theory (DFPT). The properties of phonons are described by the harmonic approximation method. Our results show that phonons play an important role in the mechanism of phase transition and in the instability of B4 (wurtzite) just before the pressure of transition. At zero pressure our data agree well with recently reported experimental results. 相似文献