In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and high absorptivity is proposed. The MMA consists of two silver layers separated by a dielectric layer. Its top resonant element is constituted by two concentric ring resonators connected with four strips. Based on electromagnetic field simulation, the proposed MMA has two narrow absorption peaks with an absorption rate of 99.9% at 711 nm and 99.8% at 830 nm, and the corresponding line width of the two absorption peaks are only 9.7 nm and 9.8 nm. The dual-band MMA shows high absorptivity under wide incident angles. The simulated field pattern shows that dual-band perfect absorption is the combined result of the interaction of two concentric ring resonators and unit cell coupling. In addition, the hexapole plasmon mode can be observed at the outer ring at one absorption peak. The narrow plasmon resonance has a potential application in optical sensing, and can be used to measure the concentration of aqueous glucose with two frequency channels. The proposed MMA with high absorptivity is simple to manufacture, and has other potential applications, such as narrow-band filters, energy storage device, and so on.
The widespread use of light emitting diode (LED) based devices makes us inevitably exposed to a blue-enriched environment and brings a potential risk to our eyes. Developing a blue-light-blocking filter with narrow absorbing band, so as to only block harmful blue light (415-455 nm) is highly expected. Here, we create a blue-light-blocking film, consisting of a transparent medium embedded with plasmonic nanoparticles (NPs) that selectively absorb harmful blue light. We present the optimal design based on Mie theory by comprehensive scanning of the parametric space for the NPs, and experimentally demonstrate this concept with a blue-light-blocking film made of silver NPs in a polymer matrix by a simple solvothermal method. For the case of the silver NPs content ~ 0.16 wt%, the film can block harmful blue light ~ 65% at λ0 ≈ 430 nm, while maintaining high transparency for the long wavelength light (λ0 > 500 nm). We also demonstrate that it is possible to correct color cast by optimizing the design of the plasmonic NPs with sharp absorption resonances at yellow waveband. This method has attractive features including simplicity, low cost, non-toxic and scalability to large sizes, which makes it beneficial for blue-light-blocking applications.
Graphene film is a promising thermal camouflage and thermal management material because of its thin, light, flexible structural characteristics and controllable broad-spectrum electromagnetic radiation modulation properties. In this study, a thermal radiation modulator based on multilayer graphene was studied by simulation and an equivalent transmission line model. The physical mechanism underlying the spectral characteristics and the sensitivity of infrared radiation modulation to the number of graphene layers is revealed. Furthermore, to solve the problem of thermal instability in the multilayer graphene-based thermal radiation modulator, a design scheme integrating a thermal radiation modulator and a meta-absorber is proposed. By electrical control of the multilayer graphene, the improved modulator can achieve dynamic emissivity modulation in the wavelength ranges of 3-5 µm and 8-14 µm for adaptive thermal camouflage while maintaining a high emissivity at 5-8 µm for radiative cooling. The compatibility of tunable infrared emission and radiative heat dissipation enables graphene to be used for thermal camouflage in complex environments and at high temperatures. The results not only promote the exploration of advanced thermal camouflage materials or devices but also provide inspiration for the application of graphene in thermal management, thermophotovoltaics, infrared displays and communications.
Anapole states supported by high-refractive-index dielectric nanoparticles have mostly been studied under normal incidence, but this work explores the oblique incidence excitation. For a single silicon nanodisk, as the incident angle (θ) increases, the anapole wavelength undergoes a gradual blueshift, while the wavelength of maximum near-field enhancement remains almost unchanged with increasing E-field enhancement factor (|E/E0|) due to phase retardation effect caused by oblique incidence, and some unique features in field distributions differed from normal excitation are exhibited. In the case of a silicon nanodisk array, the anapole state and near-field enhancement are affected by near-field coupling and the phase retardation effect is weakened. With increasing θ, the anapole wavelength and maximum field enhancement wavelength both blue shift. The y-direction coupling occurs in anapole wavelength and diagonal direction coupling occurs in the maximum field enhancement wavelength. Oblique incident excitation gives us a deeper understanding of anapole state and may have potential applications in nanophotonics.
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