Broadband high-efficiency controllable asymmetric propagation by pentamode acoustic metasurface

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.     

3D syndiotactic elastic metastructure with single-phase material

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.     

Broadband reflective liquid crystal films induced by facile temperature-dependent coexistence of chiral nematic and TGB phase

A wide pitch gradient covering the near infrared region (750.0–2500.0 nm) were facilely obtained by simple controlling temperature difference to LC mixtures with a twist grain boundary (TGB)–N* phase transition. After the pitch gradient formed, the structure of broad reflective bandwidth was fixed through polymerisation of monomers in mixtures by UV irradiation. It was found that the temperature difference between the up and down side of the samples was critical to form wide-pitch gradient distribution. Additionally, the reflection wavelength and bandwidth of films could be adjusted by the applied temperature difference with the widest bandwidth up to 1750 nm. This simple method for the preparation of broad reflective films was expected to be used in the fields like architectural energy conservation or infrared shield.     

Broadband acoustic cloaks based on the homogenization of layered materials

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.     

Design of a type of broadband metamaterial absorber based on metal and graphene

In this paper, we demonstrate a kind of broadband metamaterial perfect absorber using both graphene and metal resonator elements. Through step by step design and simulation, wider absorption band from about 4.22 THz to 7.48 THz with average absorption rate up to 98.21% is achieved in the absorption spectrum. In addition, the absorber has characteristics of polarization insensitivity and wide incident angle due to its inherent rotational symmetry. Moreover, the absorption band can be adjusted by changing the chemical potential of the graphene. The superiorities of broadband, high absorption rate, polarization independent and wide-angle characteristics make it have potential application prospects in electromagnetic wave absorbing, signal sensing and detection, and other optoelectronic devices.     

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.     

Fabrication of PbS nanocrystal-sensitized ultrafine TiO2 nanotubes for efficient and unusual broadband-light-driven hydrogen production

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.     

盐诱导金纳米粒子自组装和沉降制备具有宽波段吸收特性的黑金

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.     

A novel method for measuring optical fiber delay lines based on the optical fiber low-coherence Young's interferometer

According to the principle of double-beam interference imaging using an infrared broadband light source, a novel method based on the optical fiber low-coherence Young's interferometer for the measurement of programmable optical fiber delay line is proposed. By measuring the small length increments of delay fiber through the evaluation of the central positions of zero-order interference fringes, we successfully construct a system with a variety of important functions, such as real-time controlling, measurement and displaying. This system offers the benefit that it can be regulated precisely to generate interference stripes once again after the length of fiber segment changes. When the locations of central stripes are moved to coincide with the original markers, the determination of the corresponding fiber optical delay time becomes really simplified, as just by reading out the tinny displacement of the reference arm. Multiple groups of experimental results demonstrate the outstanding performance of the proposed system since it bears a measuring accuracy of μm and a measuring range from 1 mm to 20 cm.     

Sol-gel preparation and characterization of nanoporous ZnO/SiO2 coatings with broadband antireflection properties

Nanoporous ZnO/SiO₂ bilayer coatings were prepared on the surface of glass substrates via sol-gel dip-coating process. The structural, morphological and optical properties of the coatings were characterized. The refractive indices of ZnO layer and SiO₂ layer are 1.34 and 1.21 at 550 nm, respectively. The transmittance and reflectance spectra of the coatings were investigated and the broadband antireflection performance of the bilayer structure was determined over the solar spectrum. The solar transmittances in the range of 300-1200 nm and 1200-2500 nm are increased by 6.5% and 6.2%, respectively. The improvement of transmittance is attributed to the destructive interference of light reflected from interfaces between the different refractive-index layers with an optimized thickness. Such antireflection coatings of ZnO/SiO₂ provide a promising route for solar energy applications.