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- microwave photonics
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- Inner Mongolia University
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Preparation of BiOI microspheres in 2-propanol/ethylene glycol by microwave method with high visible-light photocatalytic activity
摘要： BiOI microspheres were synthesized by using mild conditions under microwave irradiation and applying short reaction times. The effect of the reaction medium in the final morphology of BiOI was revised modifying the relative concentrations of 2-propanol and ethylene glycol (EG) used as solvents. The as-prepared samples were characterized by X-ray powder diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, N2 adsorption–desorption isotherms and photoluminescence measurements. The photocatalytic activity of BiOI was evaluated in the oxidation reaction of nitric oxide (NO) under visible-light irradiation. In particular, the samples with morphology of 3D flower-like microspheres prepared with EG showed the highest activity for NO removal (83%), maintaining its performance after several photocatalytic cycles. Besides the morphology of BiOI samples, the high photocatalytic activity was associated with the large surface area and the low rate of charge recombination observed in samples prepared with EG. The use of scavenger agents allowed to determine the predominant participation of holes (h+), electrons (e?) and superoxide ion (·O2?) in the reaction mechanism of the NO oxidation.
关键词： NOx,Microwave,Photocatalysis,BiOI
更新于2025-09-23 15:21:21
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Ultrathin Flexible Carbon Fiber Reinforced Hierarchical Metastructure for Broadband Microwave Absorption with Nano Lossy Composite and Multi-scale Optimization
摘要： The implementation of thin structure for broadband microwave absorption is challenging due to requirement of impedance match across several frequency bands and poor mechanical properties. Herein, we demonstrate a carbon fiber (CF) reinforced flexible thin hierarchical metastructure (HM) composed of lossy materials including carbonyl iron (CI), multiwall carbon nanotube (MWCNT) and silicone rubber (SR) with thickness of 5mm and optimal concentration selected from twelve formulae. Optimization for the periodical unit size is applied and impacts of structural sizes on absorption performance is also investigated. An effective process combining the vacuum bag method and the hand lay-up technique is used to fabricate the HM. Experimental reflectivity of the absorber achieves broadband absorption below -10dB in 2-4GHz and 8-40GHz. Full band in 2-40GHz is covered below -8dB. Yielding stress of the HM is increased to 24MPa with attachment of CF while the fracture strain of the composite reaches 550%. The soft HM is suitable to adhere to curved surface of objects needed to be protected from microwave radiation detection and electromagnetic interference. Enhanced mechanical properties make it possible for further practical applications under harsh service environment such as ocean and machines with constant vibration.
关键词： broadband microwave absorption,hierarchical metastructure,dielectric-magnetic lossy material,flexible,mechanical properties
更新于2025-09-23 15:21:21
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Multi- and single-step in-situ microwave annealing as low-thermal-budget techniques for solution-processed indium–gallium–zinc oxide thin films
摘要： In this study, low-thermal-budget in-situ microwave annealing of solution-processed indium–gallium–zinc oxide (IGZO) thin films was investigated as a potential alternative to the conventional high-thermal-budget annealing process. The low-temperature baking and high-temperature post-deposition annealing of the solution-processed IGZO film were continuously performed using the same microwave equipment, leading to a reduced heat treatment processing time and temperature. We compared the electrical characteristics of IGZO thin film transistors (TFTs) produced using single- and multi-step in-situ microwave annealing methods with those of TFTs manufactured via the conventional annealing method and found that the proposed single-step microwave annealing method yielded TFTs with electrical characteristics better than those of the TFTs fabricated using the multi-step and conventional annealing methods. In addition, the reliability was evaluated by conducting positive and negative gate bias stress tests, in which the IGZO TFTs manufactured using the proposed heat treatment method proved superior to those fabricated via the conventional heat treatment method. We investigated the effects of heat treatment on the composition and energy band structures of the IGZO films by performing X-ray photoelectron spectroscopy analysis and found that the proposed in-situ microwave annealing method is more effective than the conventional method in solution processing.
关键词： low thermal budget,indium-gallium-zinc oxide,Microwave,solution process
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Evaluation of the Vegetation Optical Depth Index on Monitoring Fire Risk in the Mediterranean Region
摘要： Monitoring live fuel moisture content (LFMC) in Mediterranean area is of great importance for fire risk assessment. LFMC has extensively been estimated based on optical remote sensing data. But the latter can be affected by atmospheric effects. As a complementary data source, microwave data can be used as they are relatively insensitive to atmospheric effects. Yet further evaluations are needed to investigate the potential of microwave observations to monitor LFMC. In this study, we assess the capability of long-term microwave vegetation optical depth (VOD) to capture the temporal variability of in situ measured LFMC in 14 Mediterranean shrub species in southern France during 1996-2014. Microwave-derived VOD at X band (VODX-15) displayed a high sensitivity to LFMC with correlation coefficients of 0.56. Similar evaluations were made using four optical indices computed from the Moderate Resolution Imaging Spectrometer (MODIS) data including normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), visible atmospheric resistant index (VARI), normalized difference water index (NDWI). The comparisons showed that VARI performs better than VODX-15 and other optical indices with highest median of correlation coefficients of 0.65. Overall, this study shows that passive microwave-derived VOD, are efficient proxies for LFMC of Mediterranean shrub species and could be used along with optical indices to evaluate fire risks in the Mediterranean region.
关键词： vegetation optical depth,fire risk,microwave remote sensing,live fuel moisture content
更新于2025-09-23 15:21:21
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Design of a Compact GaN MMIC Doherty Power Amplifier and System Level Analysis With X-Parameters for 5G Communications
摘要： This paper presents a monolithic microwave integrated circuit Doherty power amplifier (DPA) operating at sub-6 GHz for 5G communication applications by a 0.25-μm gallium nitride high-electron mobility transistor process. A compact impedance inverter and output matching of the DPA are achieved using a transmission line network and shunt capacitors. Also, the size ratio of power cells in the main and auxiliary amplifiers is optimized for a high efficiency at output power backoff (OPBO). The measured peak output power (Pout) and the 1-dB compression point (P1 dB) are 38.7 and 32.1 dBm, respectively, at 5.9 GHz. The power-added efficiency at 6-dB OPBO is up to 49.5%. Without digital predistortion (DPD), the DPA can deliver an average Pout of 23.5 dBm with error vector magnitude (EVM) <?28 dB and 21.5 dBm with EVM <?32 dB for 64-quadrature amplitude modulation (QAM) and 256-QAM signals, respectively. The measured X-parameters are employed to further investigate the DPA nonlinear characteristics and verify the accuracy of conventionally used power amplifier characterization/measurement methods for system-level design and testing applications. The simulated results based on the X-parameters also indicate that the average output power can be enhanced up to 25.7 dBm with DPD for 256-QAM.
关键词： 5G communication,monolithic microwave integrated circuit (MMIC),X-parameters,power-added efficiency (PAE),power amplifier (PA),Doherty,gallium nitride (GaN)
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A First-Order Radiative Transfer Model for Global Soil Moisture Retrievals Under Vegetation Canopies
摘要： SMAP and SMOS missions estimate soil moisture using a zeroth-order radiative transfer model, the τ-ω model. Its simplifying assumption of a weakly scattering vegetation medium is insufficient in the presence of woody biomass, greater than 30% of the land surface. Here, a simplified first-order radiative transfer equation for use in retrieval algorithms is proposed. The inclusion of first-order scattering increases sensitivity to soil moisture especially for wet surfaces. The recently developed multi-temporal dual channel algorithm (MT-DCA) is implemented over Africa using both the τ-ω model and the proposed first-order equation with SMAP 36 km gridded brightness temperature measurements as inputs. The algorithm finds large changes in soil moisture mean and standard deviation in areas with woody vegetation and little change elsewhere. This implies that inclusion of first-order scattering can significantly change mean soil moisture retrievals and increase their temporal variability in regions with woody biomass.
关键词： Soil moisture,passive microwave radiometer,first-order scattering,SMAP
更新于2025-09-23 15:21:21
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UV-Induced Crosslinking of Poly[2-(2’-Norbornenyl)-2-Oxazoline]s
摘要： A 2-oxazoline monomer bearing a norbornenyl functionality in the side-chain was prepared from the reaction of 5-norbornene-2-carbonitrile and 2-ethanol amine. This monomer could be successfully polymerized using a 2-oxazolinium-based macroinitiator that was in-situ generated from the methyl cation-initiated oligomerization of 2-ethyl-2-oxazoline. This polymer could be subjected to polymeranalogous reactions involving the alkene groups of the norbornenyl side-chains: A proof-of-concept was established by utilizing the polymers in photoresists that were crosslinked by thiol-ene reactions involving bisfunctional thiols. Photoinitiators for the UV-induced thiol-ene reaction were required in catalytic amounts only. After development, the resists exhibited reproduction of the geometric patterns with a resolution of 30 μm.
关键词： cationic polymerization,polymer photochemistry,microwave-assisted polymerization,poly(2-oxazoline)s,photoresist,thiol-ene reaction
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Multi-Frequency Microwave Resonance Cavity for Nondestructive Core Plug Measurements
摘要： This work describes the theory, design and testing of a multi-frequency microwave cavity. The cavity measures the complex permittivity of core plugs of rocks, consolidated soil or sea ice. The core plugs can have commercially available diameter dimensions (0.02 meters - 0.038 meters) and for maximum height of 0.055 meters. The cavity measures the complex permittivity at five resonant frequencies between 1 GHz and 3.5 GHz of the TM0np mode. An infrared temperature sensor measures the temperature of the core plug under testing. This cavity allows for a more accurate characterization of the core composition. Initial complex permittivity measurements of six different shale core plugs were conducted. Results show that permittivity spectra can be correlated to the clay content and total organic content (TOC) of the shales. The latter is a function of the maturity of the rock. Moreover, initial results indicate the importance of water and salinity on shale samples.
关键词： sea ice,dielectric measurement,geology,Permittivity measurement,soil,well logging,geophysical measurement,microwave measurements
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Cold Cathode Based Microwave Devices for Current and Future Systems
摘要： We report ongoing efforts to achieve reliable field emitter (FE) cathode operation for high current electron beam generation in RF microwave devices. These efforts include testing of cold cathode traveling wave tubes, high average power cathode-only testing, and evaluating cathode emission variation over long operating periods in a microwave device vacuum environment. Finally, looking toward future needs, emittance reduction is being addressed to allow cold cathode operation in the mm-wave frequency regime.
关键词： field emitter array,TWT,traveling wave tube,microwave amplifier,cold cathode,vacuum electronics
更新于2025-09-23 15:21:21
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - General Conditions to Realize Exceptional Points of Degeneracy and Applications
摘要： We explore the emergence of exceptional points of degeneracy (EPDs) that denote a coalescence of multiple eigenmodes in coupled-mode structures. We establish the general conditions that lead to observing EPDs of different orders in various coupled systems, either uniform (non-periodic) or periodic. EPDs can be found in lossless systems as well as in systems with gain-loss balance. Also, we provide examples of potential applications of structures with EPDs that help improve the performance of devices, like sensors, oscillators, etc., at microwave and optical frequencies.
关键词： exceptional points of degeneracy,optical frequencies,microwave frequencies,EPDs,gain-loss balance,oscillators,lossless systems,coupled-mode structures,sensors
更新于2025-09-23 15:21:21