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排序方式: 共有328条查询结果,搜索用时 15 毫秒
1.
Daniel Torrent José Sánchez-Dehesa 《Wave Motion》2011,48(6):497-504
We present an analysis of acoustic cloaks based on the homogenization of two fluidlike materials, with an emphasis on periodically layered imperfect cloaks, by removing the singularities of the acoustic parameters required for ideal cloaks. The conditions that material layers should satisfy are systematically analyzed and critically discussed according to their feasibility. 相似文献
2.
《Physics letters. A》2020,384(11):126230
We utilise the pentamode metasurface to realise broadband high-efficiency and controllable asymmetric transmission. The designed metasurface can manipulate the acoustic waves, as expected from the generalised Snell's law, and exhibits unique characteristics such as extraordinary broadband acoustic control, apparent negative refraction, and conversion from the propagating wave to surface mode. The asymmetric transmission features of positive refraction for the forward incidence (FI) and negative refraction for the reverse incidence (RI) can be realised within the range of 2600 Hz to 5600 Hz by controlling the incident angle from 0° to 35° with the transmission efficiency higher than 85.4% for the FI and RI. In addition, by further adjusting the angle of incidence in the range of 25° to 90°, asymmetric transmission characteristics can be expressed as surface wave transmission for the FI and transmitted wave transmission for the RI within the same frequency ranges. 相似文献
3.
《Physics letters. A》2020,384(35):126892
The artificially periodic structures with the bandgap (BG) features provide a fantastic way for elastic wave manipulation. However, omnidirectional control of elastic waves at low-frequency remains a challenge, especially in the engineering application, due to the great different material parameters of the structure's components. In this work, we present the design of a three-dimensional syndiotactic metastructure (STM) and isotactic metastructure (ITM) composed of a single material with the same density and stiffness. A low-frequency broad bandgap occurs in the global band structure of STM. Meanwhile, it also retains the same high-frequency ultra-wide BG as that of ITM. The formation of the low-frequency BG of STM is attributed to the simultaneous activation of rotation and translation modes. The static deformation analysis indicates that STM has a unique translational and rotational coupling mechanism. The frequency response results reveal that the coupling mechanism can also enhance the attenuation of high-frequency BG. 相似文献
4.
Class VII Flextensional Transducers (FTs) have been proposed as a means of overcoming the limitation of very high prestress in Class IV FTs. These transducers are made from shells shaped like dog bone and hence are also known as dog-bone shell transducers. In this work, we report design optimization of a low frequency aluminum shell Class VII FT, resonating at 2.5 kHz, using piezoelectric drive. Two and three dimensional Finite Element Modeling (FEM), with the help of a commercially available package ATILA have been used for the design optimization. Dimensional details of the base model have been adapted from previous literature. Parametric analyses have been done with respect to various aspects like type of rubber, shell height, shell material, etc. in order to optimize the design. Experimental results obtained from an initial prototype are also presented. The results match fairly well with the predicted values. 相似文献
5.
6.
DETERMINATION OF QUADRICEPS FORCES IN SQUAT AND ITS APPLICATION IN CONTACT PRESSURE ANALYSIS OF KNEE JOINT 总被引:1,自引:0,他引:1
While the quadriceps muscles of human body are quite important to the daily activities of knee joints,the determination of quadriceps forces poses significant challenges since it cannot be measured in ... 相似文献
7.
Carbazole‐based liquid single‐crystal elastomers (LSCEs) are valuable fluorescent flexible materials to perform optical mechanotransduction under ambient conditions. Indeed, the covalent incorporation of carbazole derivatives into nematic LSCEs allows to tune their luminescence on demand under mechanical control in a quick and reversible fashion. Specifically, the fluorescence intensity for these materials can be switched back and forth in less than a second. Moreover, such a process can be performed several times without detecting any sign of fatigue in the system. In addition, these materials show excellent resistance to aging; 2 years after their preparation they exhibit the very same mechanofluorescent behavior as when freshly prepared. In fact, the here reported fluorescent systems are highly sensitive; the application of a force of 70 mN decreases the fluorescence in the elastomeric material by 7%. Thus, mechanical forces are attractive external stimuli to modulate the fluorescence of nematic elastomers rapidly and reversibly enabling thereby mechanotransduction.
8.
通过向金溶胶中加入无机盐诱导金纳米粒子自组装,并自然沉降金纳米粒子组装体得到黑金薄膜.研究结果表明,该黑金薄膜在400~1600 nm的宽带范围内表现出很强的吸收能力(>80%),在400~800 nm的可见范围内能达到94%,表现出高光热转换能力和宽波段的高表面增强拉曼散射(SERS)活性. 相似文献
9.
Emmanuel Urandu Mapesa Ludwig Popp Wycliffe Kiprop Kipnusu Martin Tress Friedrich Kremer 《Soft Materials》2014,12(4):S22-S30
Broadband Dielectric Spectroscopy (BDS) is used to probe the molecular dynamics of Type A polymer, poly(cis-1,4-isoprene), when confined in the 1-dimensional (1D) exploring space of thin layers and the 2-dimensional (2D) constraining geometry of unidirectional anodic aluminum oxide (AAO) nanopores. For both cases, it was observed that the structural relaxation remains bulk-like in its mean relaxation rate, although the distribution of its relaxation times is broadened in 2D confinement. Furthermore, the fluctuation of the end-to-end vector is interrupted, with the 1D case being relatively less pronounced. By this clear-cut comparison, it is demonstrated that the effects of confinement on molecular dynamics depend, inter alia, on the dimensionality of the restricting space. 相似文献
10.
It is highly desired to maximize the use of solar light by developing broadband-light-responsive H2 production system in the field of photocatalysis. Herein, a novel PbS/(Pt–TiO2) nanocomposite with efficient and unusual broadband-light-driven H2 production feature is constructed by using infrared-bandgap PbS nanocrystals as sensitizer of Pt-loaded ultrafine anatase TiO2 nanotubes (Pt–TiO2). After optimizing the component ratio, the resultant PbS/(Pt–TiO2) nanocomposite delivers a H2 production activity of 813 and 186 μmol h?1 under ultraviolet (UV)-visible (Vis)-near-infrared (NIR) and Vis-NIR light irradiation, respectively. Moreover, an apparent quantum yield of 38.6%, 26.2%, 2.43%, 3.21%, 2.17%, 0.36%, 0.11% and 0.01% can be attained from the PbS/(Pt–TiO2) nanocomposite illuminated at 350, 420, 550, 700, 760, 850, 950 and 1064 nm monochromatic light, respectively. The intimate interfacial contacts in the PbS nanocrystals decorated ultrafine TiO2 nanotubes, which serve as the support and electron acceptor of PbS nanocrystals, can effectively promote the photoexcited hot electrons transferring from PbS nanocrystals to TiO2 nanotubes before the thermalization losses, and thus causing the efficient Vis-NIR-light-responsive H2 production activity of the PbS/(Pt–TiO2) nanocomposite. These results provide an intriguing application of infrared-bandgap materials to exploit the low-energy photons of the solar light for constructing efficient and unusual broadband-responsive H2 production system. 相似文献