A wideband, low‐profile, and high‐gain antenna loaded with a dual‐layer metasurface is proposed in this study. The metasurface consists of two metallic layers printed on two dielectric layers, in which each metallic layer contains an array of 4×4 square patch cells. The proposed antenna is fed by an aperture coupled layer under the metasurface. This design makes the antenna work at two different modes with different resonant frequencies close to each other, to enhance the bandwidth. To achieve the best bandwidth performance, a genetic algorithm is adopted to optimise the geometrical parameters of this antenna. This metasurface‐based antenna maintains a low profile of 0.09λ0 at 5 GHz, meanwhile yields wideband characteristics for both the impedance and gain bandwidth. The −10 dB impedance bandwidth of the proposed antenna is about 44% (4.08–6.38 GHz) and the 3 dB gain bandwidth reaches 45% (4.16–6.56 GHz) with a peak realised gain of 11.6 dBi. A prototype of the antenna is fabricated and the measured results demonstrate the authors’ design.
Self-assembled InAs/GaAs quantum dot structures with different cap layers are grown by metal-organic chemical vapor deposition.The structure and optical properties of quantum dots are investigated using atomic force microscopy and photoluminescence.The cap layers sandwiched between quantum dots are composed of a low-temperature layer and a high-temperature layer.The comparative studies on low-temperature cap layer show that In graded InGaAs layer structure improves the uniformity of quantum dots,decreases coalescent islands and enhances photoluminescence intensity.Emission wavelength shifts from 1256.0 nm to 1314.4 nm when the thickness of graded InGaAs low-temperature cap layer increases form 6.8 nm to 12 nm.The research on high-temperature cap layer structure indicates that In graded InGaAs layer can increase photoluminescence intensity.
The photovoltaic effect of a-C: Fe/AlOx/Si based heterostructures prepared by Pulsed Laser Deposition (PLD) and its applications for solar cells were investigated. Thin alumina layer with a thickness of ~2nm was introduced to the interface between carbon and silicon, and the photovoltatic properties, such as open circuit voltage of ~0.33 V and short current density of ~4.5 mA/cm2, were improved dramatically compared with the samples without the insulation alumina layer. This may be related to the improvement of interface quality, where there are lower recombination centers such as defects and traps, which are approved by the C-V measurement. This work may shed light on the carbon/silicon based solar cells.
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