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- 摘要
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Topological aspects of photonic time crystals
摘要： We find topological band structures in photonic time crystals—materials in which the refractive index varies periodically and abruptly in time. When the refractive index changes abruptly, the light experiences time refraction and time reflection, analogous to refraction and reflection in photonic crystals. The interference between time-refracted and time-reflected waves gives rise to dispersion bands, which are gapped in the momentum. We show theoretically that photonic time crystals can be in a topologically nontrivial phase, and calculate the topological invariant associated with the momentum bands, which is expressed in the phase between the forward- and backward-propagating waves. When an interface is generated between two time crystals of different topologies, the Zak phase yields a localized interface state, manifested as a localized temporal peak.
关键词： time reflection,time refraction,photonic time crystals,Zak phase,topological band structures
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Research on a Pyramidal Horn Antenna in W-Band
摘要： In this paper, a pyramid horn antenna is design for millimeter wave radar. The antenna is completely machined out by 3D printing technology, which comprises a horn antenna and a flange with a total size of 25mm × 20mm × 50mm. Its bandwidth can cover W-band(75GHz-110GHz), and its gain is basically greater than 22dBi in the working band. Besides, the horn antenna has an advantage to achieve an excellent direction.
关键词： horn,W-band,high gain,pyramid
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 7th International Conference on Photonics (ICP) - Kuah (2018.4.9-2018.4.11)] 2018 IEEE 7th International Conference on Photonics (ICP) - OFDM Transmission in A Converged 60 GHz MMW RoF over OFDM-PON
摘要： The effect of the optical fiber transmission link on 60GHz OFDM signal in a converged 60 GHz Radio over Fiber and OFDM-PON is investigated. In order to achieve an acceptable performance of the received 60GHz OFDM signal in the OFDM-PON network architecture, a standardized EVM range (2-5%) for most of the modern wireless systems that utilize OFDM waveforms must be implemented. The performance of the converged 60GHz RoF over OFDM-PON achieved a better constellation diagram for the received OFDM signal with optimum RF power of 6dBm thus providing the target range EVM measurement.
关键词： RoF,60GHz Millimetre wave band,EVM,RF drive power,OFDM-PON
更新于2025-09-04 15:30:14
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Synthesis and Characterization of novel Thiophene and Carbazole-based Polymers – Optical and Electrochemical Characterization
摘要： A donor/acceptor series of carbazole copolymers, composed of alternating 2,7-linked 3,6-difluoro-9-(1-octyl-nonyl)-carbazole units and bithiophene repeated units [P1], 5,7-bis(5-bromothiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy) phenyl) thieno[3,4-b]pyrazine repeated units [P2] and bithiophene mixed with thieno[3,4-b]pyrazine repeated units [P3] have been prepared following Suzuki polymerisation procedures. The route of synthesis and characterisation techniques of this novel class of materials, together with their photo-physical and electrochemical properties are presented in this study. The polymers were characterised by 1H NMR, 13C NMR and Elemental Analysis. Molecular weights were estimated using gel permeation chromatography (GPC). The thermal stability behaviour for polymers was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The electronic and photo-physical properties were investigated by use of cyclic voltammetry (CV) and UV-Vis spectroscopy, respectively.
关键词： Conjugated polymer,Organic solar cell,Band gap
更新于2025-09-04 15:30:14
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DUAL-BAND DUAL-SENSE CIRCULARLY POLARIZED SLOT ANTENNA WITH AN OPEN-SLOT AND A VERTICAL STUB
摘要： A new dual-band dual-sense circularly polarized (CP) slot antenna is designed in this paper. The proposed antenna is composed of a rectangle patch and a modi?ed ground plane. By opening a U-shaped open-slot and loading a vertical stub to the ground plane, a dual-sense CP performance is achieved for two frequency bands. A bevel is cut on the patch to improve the impedance matching. The antenna is fabricated on a low-cost FR4 substrate and fed by a coplanar waveguide (CPW) structure. The antenna has been investigated numerically, and a prototype was experimentally measured. Experimental results show that the measured 10-dB return loss impedance bandwidths are 18.3% (2.72–3.27 GHz) for the lower band and 23.7% (4.65–5.90 GHz) for the upper band, and the measured 3-dB axial ratio (AR) bandwidths for the lower and upper bands can be up to 28.4% (2.48–3.30 GHz) and 26.3% (4.63–6.03 GHz), respectively.
关键词： open-slot,vertical stub,slot antenna,dual-band,circularly polarized,dual-sense
更新于2025-09-04 15:30:14
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DESIGN OF NOVEL COMPACT TRI-BAND BANDPASS FILTER WITH CONTROLLABLE FREQUENCIES AND HIGH SELECTIVITY
摘要： This paper presents a compact tri-band bandpass ?lter (BPF) with high selectivity. The proposed ?lter utilizes novel stub-loaded quarter-wavelength resonators and conventional uniform quarter-wavelength resonators. The latter is embedded in the former, and they are separated by a feed line. Due to these quarter-wavelength resonators, the total size is greatly reduced. Moreover, the passband frequencies can be controlled individually. To enhance its selectivity, source-load coupling is employed. For demonstration, an experimental ?lter is implemented. High skirt selectivity and suppression levels are observed in the measured results. The circuit area of the ?lter is 0.17λg × 0.19λg, featuring compact size.
关键词： high selectivity,compact size,stub-loaded quarter-wavelength resonators,tri-band bandpass filter,source-load coupling
更新于2025-09-04 15:30:14
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A high‐selectivity dual‐polarization filtering antenna with metamaterial for 5G application
摘要： A high-selectivity dual-polarization filtering antenna with metamaterial is presented in this letter. The multilayer coupled radiation structure of the antenna determines a filtering function. With the metamaterial layer designed above the antenna, a sharp roll-off rate at high pass band edge and a better out-of-band rejection occurs, thus a better high selective filtering characteristic can be achieved. Simulating the impedance bandwidth and measuring the antenna, (VSWR <2) of the antenna is from 3.25 GHz to 3.85 GHz; meanwhile, the maximum gain can reach 9dBi. The gain of antenna can quickly decrease 43dBi at the high pass band edge from 3.85 GHz to 4.05 GHz and the antenna has an out-of-band rejection level of 27dBi from 4.05 GHz to 5 GHz. The tested results verify our designs and the antenna could be a good candidate for the 5G anti-interference wireless terminal communication system.
关键词： high selectivity,metamaterial,filtering antenna,out-of-band rejection,dual polarization
更新于2025-09-04 15:30:14
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New Insights for Detecting and Deriving Thermal Properties of Lava Flow Using Infrared Satellite during 2014–2015 Effusive Eruption at Holuhraun, Iceland
摘要： A new lava ?eld was formed at Holuhraun in the Icelandic Highlands, north of Vatnaj?kull glacier, in 2014–2015. It was the largest effusive eruption in Iceland for 230 years, with an estimated lava bulk volume of ~1.44 km3 covering an area of ~84 km2. Satellite-based remote sensing is commonly used as preliminary assessment of large scale eruptions since it is relatively ef?cient for collecting and processing the data. Landsat-8 infrared datasets were used in this study, and we used dual-band technique to determine the subpixel temperature (Th) of the lava. We developed a new spectral index called the thermal eruption index (TEI) based on the shortwave infrared (SWIR) and thermal infrared (TIR) bands allowing us to differentiate thermal domain within the lava ?ow ?eld. Lava surface roughness effects are accounted by using the Hurst coef?cient (H) for deriving the radiant ?ux (Φ rad) and the crust thickness (?h). Here, we compare the results derived from satellite images with ?eld measurements. The result from 2 December 2014 shows that a temperature estimate (1096 ?C; occupying area of 3.05 m2) from a lava breakout has a close correspondence with a thermal camera measurement (1047 ?C; occupying area of 4.52 m2). We also found that the crust thickness estimate in the lava channel during 6 September 2014 (~3.4–7.7 m) compares closely with the lava height measurement from the ?eld (~2.6–6.6 m); meanwhile, the total radiant ?ux peak is underestimated (~8 GW) compared to other studies (~25 GW), although the trend shows good agreement with both ?eld observation and other studies. This study provides new insights for monitoring future effusive eruption using infrared satellite images.
关键词： TEI,radiant ?ux,SWIR,crust thickness,TIR,dual-band,Landsat-8,effusive eruption,Hurst coef?cient
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) - Metallic Metasurface Antennas for Space
摘要： In metasurface (MTS) antennas, a surface-wave (SW) is gradually radiated by modulating an equivalent reactance tensor in the aperture plane. Such modulation results in the (-1) indexed Floquet mode entering the visible region, thus becoming a leaky-wave (LW) mode with curvilinear phase-contour. This paper explores the use of a class of metallic MTS in the synthesis of the reactance tensor required to obtain the objective radiation patterns. The absence of dielectric is useful to survive harsh environments in space exploration. The proposed element consists of a metallic cylinder with elliptical cross-section, placed on a ground plane and arranged in a square lattice with sub-wavelength unit-cell side. We have applied this structure in the design of a right-handed circularly polarized antenna, with a broadside pencil beam in the Ka band. The obtained performance has been veri?ed by full-wave simulations. A prototype has been manufactured and measurements will be available at the time of the conference.
关键词： surface waves,leaky waves,metasurfaces,circular polarization,millimeter waves,Ka band
更新于2025-09-04 15:30:14
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Out-of-Band Response for the Coastal Zone Imager (CZI) Onboard China’s Ocean Color Satellite HY-1C: Effect on the Observation Just above the Sea Surface
摘要： The out-of-band (OOB) response is one of the key speci?cations for satellite optical sensors, which has important in?uences on quantitative remote sensing retrieval. In this paper, the effect of OOB response on the radiometric measurements made just above the sea surface is evaluated for the three broad visible bands (i.e., blue, green, and red) of the Coastal Zone Imager (CZI) onboard China’s ocean satellite HY-1C to be launched in September 2018. For the turbid coastal (Case 2) waters whose optical properties are mainly dominated by suspended sediment and colored dissolved organic material, the OOB effect can be neglected (<2%) for all three CZI visible bands. For the phytoplankton-dominated (Case 1) waters which are mainly distributed in the clear open ocean, a signi?cant (>2%) OOB effect was found in the green band over oligotrophic waters (chlorophyll a concentration ≤~0.1 mg/m3), and accordingly a model based on the CZI blue-green band ratio is proposed to correct this effect. The OOB in?uence on the CZI ocean color retrieval is discussed. This research highlights the importance of the comprehensive pre-launch radiometric characterization and the OOB effect correction for the broad band space-borne sensor, in order to achieve a high-quality quantitative ocean product.
关键词： out-of-band response,HY-1,Coastal Zone Imager (CZI)
更新于2025-09-04 15:30:14