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A OUTSTANDING MINIATURIZED FREQUENCY SELECTIVE SURFACE BASED ON CONVOLUTED INTERWOVEN ELEMENT
摘要： Based on convoluted interwoven element, a miniaturized frequency selective surface (FSS) with stable band-stop response is proposed in the paper. By extending the four dipoles into the adjacent elements, the equivalent inductance and capacitance are increased, and therefore the proposed FSS realizes promising miniaturization characteristics. The simulation results indicate that the resonant frequency is 1.19 GHz, and the dimension is only 0.027λ0. Compared to traditional crossed elements, the size is reduced by 94.6%. Besides, the FSS has excellent angle-stability under both TE and TM waves. Finally, the proposed FSS is fabricated and measured, and the experiment results prove the satisfactory consistency with the simulation results.
关键词： miniaturized,angle-stability,band-stop response,convoluted interwoven element,frequency selective surface
更新于2025-09-04 15:30:14
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Charge Carrier Polarity Modulation in Diketopyrrolopyrrole–Based Low Band Gap Semiconductors by Terminal Functionalization
摘要： Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP) based D–A molecules having three different terminal groups (amide, ester and dicyano) and studied their electronic properties. Increase in electron acceptor strength from amide to dicyano, leads to a bathochromic shift in absorption. Photoconductivity and field–effect transistor (FET) measurements confirmed that a small increase in acceptor strength can results in a large change in the charge transport properties from p–type to n–type. The molecule with amide group, DPP–Amide, exhibited a moderate p–type mobility (1.3 × 10–2 cm2V?1s?1), whereas good n–type mobilities were observed for molecules with an ester moiety, DPP–Ester (1.5 × 10–2 cm2V?1s?1) and with a dicyano group, DPP–DCV (1 × 10–2 cm2V?1s?1). The terminal functional group modification approach presented here is a simple and efficient method to alter the charge carrier polarity of organic semiconductors.
关键词： FP-TRMC,self-assembly,p-n switch,low band gap,Diketopyrrolopyrrole
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Dual-port dual-band (28/38 GHz) SIW leaky wave antenna for 5G base stations
摘要： This paper presents a novel dual-port dual-band (28/38GHz) substrate integrated waveguide (SIW) antenna with stepped long slots (SLS) for base stations in fifth generation (5G) communication systems. A stepped long slot on the top side of an SIW waveguide with a changing width creates a wide and rotated beam, which is desired in some specific 5G applications. One of the unique advantages of the design is its embedded duplexer separating the 28 GHz and 38 GHz ports at opposite sides of the antenna. A wide impedance bandwidth in both bands is obtained. The realized gain of the antenna is around 11.56 dBi and 12.08 dBi in both bands, respectively. The 6 dB beamwidths are 23o and 16o at 28 GHz and 38 GHz. The structure has good frequency scanning properties and is suitable for sectored base station topologies.
关键词： 5G,dual band antennas,millimeter wave antennas,SIW
更新于2025-09-04 15:30:14
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Ethiopian natural zeolites for photocatalysis
摘要： The combination of zeolites and photochemistry has recently shown excellent results due to the special structure of the zeolites that helps a better use of the solar energy improving the selectivity of the chemical reactions carried out. There are several reports on the preparation of TiO2 confined nanoparticles in synthetic zeolites. However, very few reports are found on the use of natural zeolites. Zeolites are a vast natural resource in Ethiopia that remains unexploited. Their microporous structure can accommodate a wide variety of cations such as sodium, potassium and magnesium among others. The main objective of our work was to test the potential use of the naturally occurring zeolites, with high content in titanium, as photocatalysts. The samples have been characterized by X-ray diffraction (XRD), chemical analysis (ICP-OES), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (UV-Vis) and photocatalytic activities of the samples were tested in photocatalytic degradation of methyl orange (MO).
关键词： Natural zeolite,Photocatalysis,Methyl orange,Band gap energy,TiO2 loading
更新于2025-09-04 15:30:14
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Ultrawide‐Bandgap Amorphous MgGaO: Nonequilibrium Growth and Vacuum Ultraviolet Application
摘要： New ultrawide-bandgap (>6.0 eV) photosensitive materials are in urgent need to meet the requirements of vacuum-ultraviolet (VUV) photodetection applied in deep space exploration. Here, a nonequilibrium growth method is reported to fabricate amorphous MgGaO (a-MgGaO) films with an ultrawide bandgap of 6.0 eV and an ultrashort absorption edge of 206 nm by alloying MgO and Ga2O3. By combining the as-grown films with p-type graphene (p-Gr) which serves as a transparent conductor, a vacuum-ultraviolet photovoltaic detector of p-Gr/a-MgGaO/n-SiC (n-type SiC) is constructed. The device exhibits an excellent VUV spectral selectivity with a VUV (185 nm)/UV (250 nm) rejection ratio exceeding 103, high photoresponsivity (≈10.3 mA W?1) under 0 V bias, and ultrafast response and recovery time of 1.94 μs and 0.6 ms, respectively. The reported nonequilibrium growth method is expected to have tremendous potential in fabricating ultrawide-bandgap oxide compounds, and finally facilitate future deep space exploration.
关键词： nonequilibrium growth,vacuum-ultraviolet photodetection,graphene,band engineering,MgGaO
更新于2025-09-04 15:30:14
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Supervised band selection in hyperspectral images using single-layer neural networks
摘要： Hyperspectral images provide fine details of the scene under analysis in terms of spectral information. This is due to the presence of contiguous bands that make possible to distinguish different objects even when they have similar colour and shape. However, neighbouring bands are highly correlated, and, besides, the high dimensionality of hyperspectral images brings a heavy burden on processing and also may cause the Hughes phenomenon. It is therefore advisable to make a band selection pre-processing prior to the classification task. Thus, this paper proposes a new supervised filter-based approach for band selection based on neural networks. For each class of the data set, a binary single-layer neural network classifier performs a classification between that class and the remainder of the data. After that, the bands related to the biggest and smallest weights are selected, so, the band selection process is class-oriented. This process iterates until the previously defined number of bands is achieved. A comparison with three state-of-the-art band selection approaches shows that the proposed method yields the best results in 43.33% of the cases even with greatly reduced training data size, whereas the competitors have achieved between 13.33% and 23.33% on the Botswana, KSC and Indian Pines datasets.
关键词： supervised learning,neural networks,Hyperspectral images,band selection,filter-based approach
更新于2025-09-04 15:30:14
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Light energy accumulation by cholesteric liquid crystal layer at oblique incidence
摘要： Oblique propagation of light through a planar layer of a cholesteric liquid crystal (CLC) is solved by Ambartsumian’s modified layer addition method. Two cases are considered, namely, the case when dielectric boundaries have a minimum influence on light transmission and the case when the CLC layer is in a vacuum. It is shown that in the first case a total internal reflection can happen for the fast eigen-mode at large incidence angles. New important features of light reflection (transmission) spectra, photonic density of states and accumulated energy density in the CLC layer are studied. The light localisation peculiarities in the CLC layer at oblique incidence is investigated too. It is shown that the light localisation for both the long-wavelength edge mode and the short-wavelength edge mode changes differently when the incidence angle changes. The obtained results can be used in the design of low-threshold lasers, in solar cell systems, in chiral photonics, in systems strongly absorbing light at certain wavelengths and when designing systems with absorption suppression created on the base of absorbing media, etc.
关键词： total internal reflection,Cholesteric liquid crystals,photonic band gap,light localisation
更新于2025-09-04 15:30:14
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Opening a band gap in graphene by C-C bond alternation: A tight binding approach
摘要： In the present work, we consider the electronic properties of graphene with Kekule structure formed from two different C–C bonds in its hexagonal lattice. When the C–C bond alternation was introduced, a small band gap has been opened in the band structure of graphene and it increases linearly by a difference in the bond lengths δ. While the applied strain along the zigzag or armchair direction causes band gap to decrease rapidly to zero, the strain in the other directions can increase the band gap. Interestingly, when the graphene with Kekule structure is strained, its band gap is inversely proportional to the bond length difference δ. Opening a band gap in graphene due to bond alternation and strain can open up new applications in nanoelectronic devices.
关键词： band gap,Kekule structure,strain,tight binding,graphene
更新于2025-09-04 15:30:14
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Optical characterization of nanostructured Ge1???xSnxSe2.5 (x?=?0, 0.3, 0.5) films
摘要： The paper reports the optical properties of thin films of nanostructured Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys. The glassy alloys of Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) were prepared using melt quenching method. Thin films of nanostructured Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys were prepared using physical vapor deposition method. The films were characterized using XRD, EDX and TEM, which confirmed the amorphous nature, composition and formation of nanorods in the samples. Absorption and transmission spectra of thin films were recorded in the spectral range 400–2500 nm to obtain energy band gap, refractive index, extinction coefficient, dielectric constant etc. Results show that refractive index increases while band gap decreases on increase of Sn content in the Ge–Se system. This is due to the increase in density of defect states within band gap. The values of Urbach energy support the obtained results.
关键词： Thin films,Nanostructured glasses,Optical properties,Band gap
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - S-Band Microstrip Bandpass Filter Design Based on New Approach to Coupling Coefficients Calculation
摘要： In this paper, a new approach to bandpass filter design, based on coupling coefficients calculation, introduced in [1], is experimentally verified. S-band (2.7 – 3.1 GHz bandwidth) microstrip bandpass filters of several four-resonator structures for pre-selectors of active phase array radar systems are designed, produced and measured. A conventional parallel-coupled filter is produced and measured for comparison. Measurement results confirm good performance of used approach.
关键词： S-band,open-loop resonator,bandpass filter,microstrip,coupled resonators,active phase array radar,pre-selector
更新于2025-09-04 15:30:14