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A Novel Transmitting Module Self-Monitoring Protection System Based On MEMS Sensors and Actuators
摘要： Design, fabrication, and measurements of a novel transmitting module self-monitoring protection system are presented in this letter. Such a system is based on micro-electromechanical systems (MEMS) sensors and actuators for monitoring and protecting the microwave amplifier circuit. The transmitting module self-monitoring protection system consists of the RF MEMS switches, the directional coupler, and the MEMS power sensors. When the microwave amplifier circuit is at an abnormal state ("open," "short," or "overload"), the transmitting module self-monitoring protection system can isolate the microwave amplifier circuit out of order and reconfigure the transmitting module into impedance matching within 36 ms. When the microwave amplifier circuit is at the overload state, the error between the set switching power and the actual switching power is less than 9%. The measured results agree well with the theory.
关键词： Microelectromechanical systems (MEMS) power sensor,microwave amplifier circuit,RF MEMS switch,self-monitoring protection
更新于2025-09-23 15:22:29
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Growth Condition-Oriented Defect Engineering for Changes in Au–ZnO Contact Behavior from Schottky to Ohmic and Vice Versa
摘要： ZnO has the built-in characteristics of both ionic and covalent compound semiconductors, which makes the metal–ZnO carrier transport mechanism quite intricate. The growth mechanism-centric change in ZnO defect density and carrier concentration also makes the contact formation and behavior unpredictable. This study investigates the uncertainty in Au–ZnO contact behavior for application-oriented research and the development on ZnO nanostructures. Herein, we explain the phenomenon for how Au–ZnO contact could be rectifying or non-rectifying. Growth method-dependent defect engineering was exploited to explain the change in Schottky barrier heights at the Au–ZnO interface, and the change in device characteristics from Schottky to Ohmic and vice versa. The ZnO nanorods were fabricated via aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. For further investigations, one ACG sample was doped with Ga, and another was subjected to oxygen plasma treatment (OPT). The ACG and Ga-doped ACG samples showed a quasi-Ohmic and Ohmic behavior, respectively, because of a high surface and subsurface level donor defect-centric Schottky barrier pinning at the Au–ZnO interface. However, the ACG-OPT and MAG samples showed a more pronounced Schottky contact because of the presence of low defect-centric carrier concentration via MAG, and the removal of the surface accumulation layer via the OPT process.
关键词： oxygen plasma treatment,nanorod,ZnO,crystal defects,microwave,metal-semiconductor contact
更新于2025-09-23 15:22:29
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Microwave Photonic Devices Based on Liquid Crystal on Silicon Technology
摘要： This paper reviews the recent developments in microwave photonic devices based on liquid crystal on silicon (LCOS) technology. The operation principle, functions and important specifications of an LCOS based optical processor are described. Three microwave photonic devices, which are microwave photonic notch filters, phase shifters and couplers, reported in the past five years are focused on in this paper. In addition, a new multi-function signal processing structure based on amplitude and phase control functions in conjunction with a power splitting function in a commercial LCOS based optical processor is presented. It has the ability to realize multiple time-shifting operations and multiple frequency-independent phase shifting operations at the same time and control multiple RF signal amplitudes, in a single unit. The results for the new multi-function microwave photonic signal processor demonstrate multiple tunable true time delay and phase shifting operations with less than 3 dB amplitude variation over a very wide frequency range of 10 to 40 GHz.
关键词： phase shifters,optical signal processing,filters,true time delays,microwave photonics
更新于2025-09-23 15:22:29
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Microwave-assisted hydrothermal synthesis of BiOCl/Bi2WO6 nanocomposites for the enhancement of photocatalytic efficiency
摘要： In this research, BiOCl/Bi2WO6 nanocomposites were successfully synthesized by a microwave-assisted hydrothermal method. Phase, morphology and optical properties of the as-synthesized products were investigated by X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and photoluminescence (PL) spectroscopy. The as-synthesized products were BiOCl/Bi2WO6 nanocomposites composed of Bi2WO6 microflowers mixed with BiOCl nanoplates. The photocatalytic properties of BiOCl/Bi2WO6 nanocomposites were estimated through photodegradation of rhodamine B and salicylic acid as organic models in wastewater. The 80 wt% BiOCl/Bi2WO6 nanocomposites presented the highest photocatalytic efficiency and were certified for the lowest photonic emission by PL analysis. There was a trivial loss of activity even after four re-cycle tests. A mechanism for photocatalysis by BiOCl/Bi2WO6 nanocomposites was also proposed.
关键词： BiOCl/Bi2WO6 nanocomposites,Photocatalysis,Microwave-assisted hydrothermal synthesis
更新于2025-09-23 15:22:29
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Axiolitic ZnO rods wrapped with reduced graphene oxide: Fabrication, microstructure and highly efficient microwave absorption
摘要： Axiolitic Zinc oxide/reduced graphene oxide (ZnO/r-GO) hybrid was achieved by a facile one-step hydrothermal route in this work. The axiolitic ZnO rods with uniform size were equally implanted in r-GO nanosheets. The composites exhibit prominent microwave absorption performance with the Min. RL of -55.7 dB for a thickness of merely 2.0 mm and effective absorption bandwidth covering the whole Ku band, which benefits by the introducing of axiolitic ZnO rods and constructing distinct structures. The synergistic effect of dipole polarization, interface polarization and conductivity manifestly boost the microwave attenuation capacity. The results indicated that the axiolitic ZnO/r-GO hybrid is a promising candidate for application in the field of microwave absorption, electromagnetic interference shielding, communication and safety information, etc.
关键词： polarization,microwave absorption,reduced graphene oxide,axiolitic ZnO rods
更新于2025-09-23 15:22:29
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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) - Bowtie Antenna TRM Design for Biomedical Imaging Using Electromagnetic Time Reversal Technique
摘要： Microwave based imaging has been extensively examined for biomedical imaging and research is still ongoing to attain best imaging systems. Examination and detection of dielectric property differences of biological tissues has been examined over a wide range of frequencies for such applications. This paper looks at the design of a wide dual band Bowtie time reversal mirror (TRM) for biomedical imaging using electromagnetic time reversal technique resonating at 2.45 GHz and 5.2 GHz.
关键词： microwave imaging,microstrip bowtie antenna,time reversal mirrors,Electromagnetic time reversal
更新于2025-09-23 15:22:29
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Angle-of-Arrival Measurement System Using Double RF Modulation Technique
摘要： A new technique for determining the angle of arrival (AoA) of an RF signal is presented. It is based on a cascaded modulator structure, where continuous wave light from an optical source is modulated by an incoming RF signal twice. The AoA of an RF signal can be determined by the system output RF signal power. The proposed structure is capable for measuring the AoA of both narrow and broadband RF signals. This overcomes the limitation in all previously reported photonics-based AoA measurement systems, which are applicable to either a single-frequency RF signal or a broadband RF signal. It also does not involve electrical components and high extinction ratio modulators, which are required in reported structures. Experimental results are presented that show an AoA measurement range of 0° to over 65° with errors of less than 1.9° for a microwave signal at 2.65 and 12.62 GHz. Results also show that the system is capable to measure the AoA of a pseudorandom binary sequence signal at a microwave frequency.
关键词： notch filters,Direction-of-arrival estimation,phased arrays,microwave photonics
更新于2025-09-23 15:22:29
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Bond theory, Terahertz spectra and dielectric studies in donor-acceptor (Nb-Al) substituted ZnTiNb <sub/>2</sub> O <sub/>8</sub> system
摘要： As a donor and acceptor separately, Nb5+ and Al3+ are used to substitute Ti4+ in the ixiolite ZnTiNb2O8 system for the first time. The dielectric responses in the terahertz range of this system are initially studied based on the data from terahertz time-domain transmitted spectroscopy. Combined with ligand field theory, the formation of a secondary phase of ZnAl2O4 is reasonably explicated. Then, the origins of the lower dielectric loss and the terahertz wave absorption coefficient are determined to be the high chemical bond covalency and effective phase control. For the composition of ZnTi0.85(Al0.5Nb0.5)0.15Nb2O8 sintered at 1180 °C, a low dielectric loss (< 5×10-3 @ 0.5 THz) and absorption coefficient (< 10 cm-1 @ 0.5 THz) are obtained, which make this kind of material propitious for developing terahertz dielectric devices.
关键词： complex chemical bond theory,covalency,microwave and terahertz,dielectric properties,donor-acceptor substituted
更新于2025-09-23 15:22:29
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Distributed Measurement of Polarization Mode Coupling in Polarization Maintaining Fibers Using Microwave Photonic Filter Technique
摘要： Polarization mode coupling (PMC) is a detrimental effect that limits the polarization maintaining performance of polarization maintaining fibers (PMF). In this paper, we propose and demonstrate a novel method based on a principle similar to that of a microwave photonic filter (MPF) for the PMC distribution measurement. By regarding the PMF with PMC taking place as an MPF and measuring its transfer function in frequency domain, we are able to identify the intensities and locations of PMC events along PMFs. After detailed theoretical analysis and numerical simulations, validation experiments have been conducted on four PMF segments with rotational splicing between each other to manually generate PMCs. The measurement results of PMC positions and strengths are in accordance with the preset values. With a frequency scanning step of 16 MHz and a range of 14.4 GHz, such method can achieve a spatial resolution of 30 m and a measurement range of 27 km. The proposed method is suitable for the measurement of PMCs along PMFs up to tens of kilometers.
关键词： microwave filters,optical fibers,microwave photonics,Optical fiber polarization
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 - Physics-Based Modeling of Active-Passive Microwave Covariations for Geophysical Retrievals
摘要： Combined active-passive remote sensing has the potential for capturing the relative advantage of each sensing approach in geophysical retrievals. One cornerstone of combined active-passive microwave sensing is the modeling of the covariation of active and passive signals, which arise from equivalent sensitivities of both sensor types to changes in geophysical properties. In this research contribution, we propose a physics-based active-passive combination of active and passive microwave observations based on Kirchhoff’s law of energy conservation. This allows establishing a physics-based forward model as well as a fully data-driven, single-pass retrieval methodology for active-passive microwave covariation. The forward model and the retrieval approach are adaptable to different sensor characteristics (incidence angle, frequency & polarization). The theoretical (forward model) as well as applied (retrieval method) physics-based covariation framework is tested with SMAP (LL) and SMAP/Sentinel-1 (LC) data to reveal potentials and constraints for active-passive microwave sensing. As a result of the conducted study, a linear functional relationship between active and passive microwave observations (e.g. assumed for the SMAP mission) is confirmed, if higher-order scattering can be omitted.
关键词： microwave covariation,active-passive microwave sensing,Sentinel-1,SMAP,multi-frequency
更新于2025-09-23 15:21:21