A triple-band metamaterial absorber (MMA) which is composed of a traditional metal-dielectric-metal structure is proposed in this paper, three absorption peaks are located at S-band, C-band and X-band, respectively. The design parameters are obtained by the methods of controlling variables and iterative optimization, and three perfect absorption peaks exceeding 99% are acquired at 3.72 GHz, 5.86 GHz, and 10.54 GHz after numerical calculation and analysis. Subsequently, the impedance matching conditions for absorption are proved through the analysis of equivalent electromagnetic parameters. For the proposed MMA, polarization independent characteristic, which is produced from the symmetry properties of the structure is verified, and it also has a stability of incident angle in both TE and TM modes from the result of the analysis of oblique incident response. In addition, its absorption mechanisms and methods are discussed and analyzed through electromagnetic field and surface current distributions. At the same time, the triple-band absorption performances of the proposed MMA derived from the material losses, 2D microstructure of the top layer and dimension parameters have also been calculated and investigated through the discussing of certain parameters individually. Finally, the absorption performance of the MMA is tested through experiments, and experimental results are basically same as the simulation results. Compared with other studies, the MMA proposed in this paper has higher absorption peaks at the resonance points, and the thickness is only 0.013 times of the longest working wavelength, which has a thinner thickness. The proposed MMA can be utilized in the areas of the decrease of Radar-Cross-Section, electromagnetic shielding, sensing and other applications. 

Design and analysis of a polarization-independent and incident angle insensitive triple-band metamaterial absorber

• In the present work, we investigate the metamaterial based electromagnetic wave absorber using full wave finite element method. • Our model consists of gold-magnesium oxide-germanium-gold-germanium layers and rings-disk shape resonators over top of the proposed structure. • The circular symmetric nature of these resonators, enhance the localized surface plasmon resulting more electromagnetic power absorption occur. • Metamaterials have potential applications such as energy harvesting, hot electrons generation, detectors, imaging, defense, etc. • The average absorption of this model is above 90 % from 12.8 μ m to 17.8 μ m and including 100 % (at 9.1 μ m and 17.8 μ m ). In this paper, we propose a design of metamaterials-based polarization insensitive, broadband electromagnetic (EM) wavebands absorber in the long-wave infrared (LWIR) region. The proposed model consists multilayer of gold-magnesium oxide-germanium-gold-germanium layers from the bottom to the top of the structure. The top surface of our proposed metamaterial structure consists of rings and disk-shape resonators. Using the finite element method, the electromagnetic properties of the metamaterials are investigated in terms of reflectance and absorbance. We find that excitation of localized surface plasmon resonance gives rise to highly localized electromagnetic resonance with the structure. Due to the circularly symmetric nature of the ring resonator, the numerical results show that the proposed design of metamaterial has average absorption (above 90 %) from 12.8 μm to 17.8 μm for both transverse electric (TE) and transverse magnetic (TM) polarization over a wide range of incidence angle. Along with this, it can absorb EM waves completely (100 %) at a particular wavelength of 9.1 μm and 17.8 μm. These results show the proposed model configuration may have wide application in energy harvesting and another optoelectronic area. 

Polarization insensitive metamaterial based electromagnetic multiband absorber in the long-wave infrared (LWIR) region

With continuous development nanotechnology and materials science, wearable electronic devices have being one of the hot points in nanoelectronics and attracted extensive attention in the last years. The devices have...

Fabrication, material regulation, and healthcare applications of flexible photodetectors

Spin coating is widely used to form a uniform film on a solid substrate. Airflow disturbance has been considered as one of the most influential factors of film thickness, especially for spin coating on large area noncircular substrates. However, the exact mechanism of airflow disturbance influence, such as air shear force effect or indirect effects on evaporation, so far, remains ambiguous. In this work, the influence mechanism of airflow disturbance on film uniformity on large rectangular substrates is studied. The experiment with airflow disturbance is artificially introduced and contrasts with the common spin coating conditions. Both numerical simulations and experiments show a causal relationship between airflow disturbances and the uniformity of the spin coating film. The film thickness and airflow field results show that the film uniformity is affected by solvent evaporation and air shear force caused by airflow disturbance. Additionally, evaporation inhibition and airflow disturbance results do not support the proposition that air shear forces can affect film uniformity, but that solvent evaporation is the primary factor affecting film thickness uniformity. These conclusions are beneficial to the understanding of the mechanism of airflow disturbance influence on the film thickness uniformity on large rectangular substrates.

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Influence of Airflow Disturbance on the Uniformity of Spin Coating Film Thickness on Large Area Rectangular Substrates

In this current Special Issue, “Nanocrystalline Materials: Preparation, Structural, Magnetic, Dielectric, Electrical, Optical, Thermal Properties and Applications (Volume II)”, eight original research articles have been published [...]

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Nanocrystalline Materials: Preparation, Structural, Magnetic, Dielectric, Electrical, Optical, and Thermal Properties and Applications (Volume II)

Ultraviolet-visible-near infrared broadband photodetectors have significant prospects in many fields such as image sensing, communication, chemical sensing, and day and nighttime surveillance. Hybrid one-dimensional (1D) and zero-dimensional (0D) materials are attractive for broadband-responsive photodetectors since its unique charges transfer characteristics and facile fabrication processes. Herein, a Si/ZnO nanowires/Ge quantum dots photodetector has been constructed via processes that combined electrospinning and spin-coating methods. A broadband response behavior from ultraviolet to near-infrared (from 250 to 1550 nm) is observed. The responsivity of the hybrid structure increases around three times from 550 to 1100 nm compared with the pure Si photodetector. Moreover, when the photodetector is illuminated by a light source exceeding 1100 nm, such as 1310 and 1550 nm, there is also a significant photoresponse. Additionally, the ZnO NWs/Ge quantum dots heterostructure is expected to be used in flexible substrates, which benefits from electrospinning and spin-coating processes. The strategy that combines 1D ZnO NWs and 0D solution-processed Ge QDs nanostructures may open a new avenue for flexible and broadband photodetector.

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Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

Vortex electromagnetic waves carrying orbital angular momentum (OAM) have been widely discussed for potential applications in wireless communications. Belonging to the Laguerre–Gaussian beams family, such type of waves present a hollow conical shape and divergence characteristics along with a directional radiation. In this paper, an innovative method to produce omnidirectional OAM beams based on spatial transformation is proposed at microwave frequencies. As a proof-of-concept demonstration, a lens with omnidirectional radiation in the horizontal plane is designed and simulated with an incident vortex beam carrying the OAM mode l = +2. The designed lens can be potentially implemented with an all-dielectric medium showing a gradient permittivity distribution. Furthermore, the proposed lens presents good performances over a wide operational bandwidth spanning from 8 to 17 GHz. By converting the directional beam to an omnidirectional one, the proposed method opens the door to the potential development of microwave vortex antenna systems.

A metamaterial lens based on transformation optics for horizontal radiation of OAM vortex waves

We report on the investigation of a high–efficiency, widely tunable femtosecond optical parametric oscillator (OPO) based on a multi–period MgO–doped periodically poled lithium niobite (MgO: PPLN) crystal, pumped by an all–solid–state femtosecond mode–locked Yb: KGW laser at 1030 nm providing 100 fs pulses. With 6 W pump power, the OPO generates 2.68 W of signal power at 1540 nm and 1.2 W of idler power at 3110 nm, which corresponds to the total conversion efficiency adding up to 67.4%. To the best of our knowledge, this is the highest conversion efficiency of a femtosecond OPO. Meanwhile, in order to obtain a broad optical spectrum range, both the grating period and working temperature are tuned, resulting in tunable signals of 1.43–1.78 µm and idlers of 2.44–3.68 µm. This source will be used to generate a femtosecond mid–infrared laser of wavelength range 3.7–6.5 µm and tens milliwatts average power through difference frequency generation (DFG).

Haoxiang Sun

Papers

Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

A metamaterial lens based on transformation optics for horizontal radiation of OAM vortex waves

High–Efficiency, Widely Tunable MgO: PPLN Optical Parametric Oscillator