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Efficient microwave absorption achieved through in situ construction of core-shell Co Fe_(2)O_(4)@mesoporous carbon hollow spheres

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International Journal of Minerals,Metallurgy and Materials 2023年第3期30卷 504-514页

作者： Lianggui Ren yiqun wang Xin Zhang Qinchuan He Guanglei Wu College of Materials and Chemistry&Chemical Engineering Chengdu University of TechnologyChengdu 610059China Institute of Materials for Energy and Environment State Key Laboratory of Bio-fibers and Eco-textilesCollege of Materials Science and EngineeringQingdao UniversityQingdao 266071China

Cobalt ferrite(CoFe_(2)O_(4)),with good chemical stability and magnetic loss,can be used to prepare composites with a unique structure and high *** this study,CoFe_(2)O_(4)@mesoporous carbon hollow spheres(MCHS)with a core-shell structure were prepared by introducing CoFe_(2)O_(4)magnetic particles into hollow mesoporous carbon through a simple in situ ***,the microwave absorption performance of the CoFe_(2)O_(4)@MCHS composites was *** and dielectric losses can be effectively coordinated by constructing the porous structure and adjusting the ratio of MCHS and CoFe_(2)O_(4).Results show that the impedance matching and absorption properties of the Co Fe_(2)O_(4)@MCHS composites can be altered by tweaking the mass ratio of MCHS and CoFe_(2)O_(4).The minimum reflection loss of the Co Fe_(2)O_(4)@MCHS composites reaches-29.7 dB at 5.8 *** addition,the effective absorption bandwidth is 3.7 GHz,with the thickness being 2.5 *** boosted microwave absorption can be ascribed to the porous core-shell structure and introduction of magnetic *** coordination between the microporous morphology and the core-shell structure is conducive to improving the attenuation coefficient and achieving good impedance *** porous core-shell structure provides large solid-void and CoFe_(2)O_(4)-C interfaces to induce interfacial polarization and extend the electromagnetic waves’multiple scattering and ***,natural resonance,exchange resonance,and eddy current loss work together for the magnetic *** method provides a practical solution to prepare core-shell structure microwave absorbents.

关键词： porous core-shell structure microwave absorption interface polarization ferrite structure-controllable

CFD based combustion model for sewage sludge gasification in a fluidized bed

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Frontiers of Chemical Science and Engineering 2009年第2期3卷 138-145页

作者： yiqun wang Lifeng YAN Hefei National Laboratory for Physcial Sciences at the Microscale and Department of Chemical Physics University of Science and Technology of ChinaHefei 230026China

Gasification is one potential way to use sewage sludge as renewable energy and solve the environmental problems caused by the huge amount of sewage *** this paper,a three-dimensional Computational Fluid Dynamics(CFD)model has been developed to simulate the sewage sludge gasification process in a fluidized *** model describes the complex physical and chemical phenomena in the gasifier including turbulent flow,heat and mass transfer,and chemical *** model is based on the Eulerian-Lagrangian concept using the non-premixed combustion modeling *** terms of the CFD software FLUENT,which represents a powerful tool for gasifier analysis,the simulations provide detailed information on the gas products and temperature distribu-tion in the *** model sensitivity is analyzed by performing the model in a laboratory-scale fluidized bed in the literature,and the model validation is carried out by comparing with experimental data from the *** show that reasonably good agreement was *** of temperature and Equivalence Ratio(ER)on the quality of product syngas(H_(2)+CO)are also studied.

关键词： CFD model sewage sludge gasification syngas

FINITE ELEMENT ANALYSIS OF TRASINENT TWO DIMENSIONAL CHANNEL FLOW WITH A SUDDEN EXPANSION

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Chinese Journal of Mechanical Engineering 1999年第4期12卷 270-275页

作者： Gao Dianrong Zhao Yongkai wang yiqun (Yanshan University) Yanshan Univ China

The finite element method is employed to simulate incompressible viscous unsteady flow in two dimensional channel with a sudden expansion. The streamline patterns and the velocity vector plots are presented at different expansion ratios and at different moment. The results obtained have certain significance to analyze the formation of eddies and energy loss in a sudden expansion channel flow and other complex channel flow.

关键词： Sudden expansion channel Finite element method Streamline Velocity Energy loss

EXPERIMENTAL STUDY ON INFLUENCE OF SUPPLIED PRESSURE FLUCTUATION ON OUTPUT ARACTERISTIC OF PRESSURE CONTROL SYSTEM OF ROLLING MILL

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Chinese Journal of Mechanical Engineering 1998年第2期11卷 73-79页

作者： Zhao Jingyi Li Jiutong wang yiqun Yanshan University Yanshan Univ China

The infulence of supplied pressure fluctuation on output accuracy for the electro hydraulic pressure control system of the rolling mill is *** on the bond graph theory and experimental study,the relationship between the variation of system output pressure and the supplied pressure fluctuation and the influence of the system bandwidth on system output pressure are provided.A theoretical base for determining the allowable fluctuation range of pressure and accurate design of constant pressure source system is obtained.

关键词： Pressure fluctuation Pressure control system Bond graph

NOVEL FIBER GRATING SENSOR DEMODULATION TECHNIQUE BASED ON OPTICAL WAVELET FILTERING

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Chinese Journal of Mechanical Engineering 2006年第1期19卷 134-136页

作者： wang yiqun wang Haifang ZHU Dandan QIAO Shuxin CAI Yanan College of Mechanical Engineering Yanshan University Qinhuangdao 066004 China College of Electric Engineering Yanshan University Qinhuangdao 066004 China

The optical wavelet filter is designed. It can filter and choose frequency swiftly. It can realize demodulation of distributed fiber Bragg grating（FBG） measurement system. Its scanning resolution and scanning period depend on wavelet function. Wavelet function is controlled by computer. Compared to conventional scan filter, optical wavelet filtering has some advantages such as simple structure, high scan frequency, high resolution and good linearity. At last, the error of optical wavelet filter scanning procedure is analyzed. Scanning step length refers to the shifting of optical wavelet window＇s central frequency. It affects system precision directly. If scanning step length is different, the measured signal is different. The methods of reducing step length guarantee scanning periodic time are presented.

关键词： Optical wavelet filtering Fiber Bragg grating (FBG) Demodulation Scanning step length

Application of Smith Predictor Based on Single Neural Network in Cold Rolling Shape Control

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Chinese Journal of Mechanical Engineering 2009年第2期22卷 282-286页

作者： wang yiqun SUN FD LIU Jian SUN Menghui XIE Yihan College of Mechanical Engineering Yanshan University Qinhuangdao 066004 China School of Information Science and Technology Tsinghua University Beijing 100084 China

Flatness is one of the most important criterion factors to evaluate the quality of the steel strip. To improve the strip＇ s flatness quality, the most frequently used methodology is to employ the closed-loop automatic shape control system. However, in the shape control system, the shape-meter is always installed at the down way of the exit of the cold rolling mill and can not sense the changes of the strip flatness in the rolling gap directly. This kind of installation results in the delay of the feedback in the control system. Therefore, the stability and response performance of the system are strongly affected by the delay. At present, there is still no mature way to design controllers for systems with time delay. Although the conventional PID controller used in most practical applications has the capability to compensate the delay, the effect of the compensation is limited, especially for the systems with long time delay. Smith predictor, as a compensator for solving this problem, is now widely used in industry systems. However, the request of highly precise model of the system and the poor adaptive performance to the changes of related parameters limit the application of the Smith predictor in practice. In order to overcome the drawbacks of the Smith predictor, a new Smith predictor based on single neural network PID （SNN-PID） is proposed. Because the single neural network is employed into the Smith predictor to improve the controller＇s self-adaptability, the adaptive capability to the varying parameters of the system is improved. Meanwhile, for the purpose of solving the problems such as time-consuming and complicated calculation of the neural networks in real time, the learning coefficient of neural network is divided into several stages as usually done in expert control system. Therefore, the control system can obtain fast response due to the improved calculation speed of the neural networks. In order to validate the performance of the proposed controller, th

关键词： shape control time delay single neural network Smith predictor

Heterostructured CoFe@N-doped carbon porous polyhedron for efficient microwave absorption

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Nano Research 2023年第2期16卷 1859-1868页

作者： Dan Wu yiqun wang Shuanglin Deng Di Lan Zhongning Xiang Qinchuan He College of Materials and Chemistry&Chemical Engineering Chengdu University of TechnologyChengdu 610059China School of Materials Science and Engineering Hubei University of Automotive TechnologyShiyan 442002China

The synthesis of wide bandwidth,thin thickness,and high performance microwave absorbing materials has become a hot topic of current ***-organic frameworks with heterojunctions and porous structures are considered as suitable candidates to meet these ***,heterogeneous CoFe@N-doped porous carbon polyhedron composites were successfully synthesized via Fe^(2+)to replace Co in zeolite imidazole *** dielectric properties of composites were enhanced by the replacement of Fe^(2+),and the synergistic effect of dielectric loss and magnetic loss was *** petal-like lamellar structure increases the travel of electromagnetic(EM)waves,and the formation of porous structures improves impedance ***,a reflection loss of−67.30 dB was obtained at a thickness of 2.88 mm,and an ultrabroad wide effective absorption bandwidth of 8.40 GHz was obtained,covering most of the X-band(8–12 GHz)and the whole Ku-band(12–18 GHz).The radar cross section(RCS)reduction value can reach 29.4 dB·m^(2),which means that the radar detector has a smaller probability of detecting *** work describes the unique advantages of metal ion replacement metal-organic frameworks derived materials in structural design,impedance matching,and performance adjustment,and provides a new reference for the field of electromagnetic wave absorption.

关键词： microwave absorption Fe^(2+)replacement ultrabroad bandwidth heterojunction metal-organic framework(MOF)

Double-kill contribution of high-roughness high-density porous carbon electrodes to mechanically self-sensing supercapacitors

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Nano Research 2024年第7期17卷 6157-6167页

作者： Jue Huang Pengyu Liu yiqun wang Keren Dai Qingyun Dou Yajiang Yin Xiaofeng wang Zheng You Department of Precision Instrument Tsinghua UniversityBeijing 100084China State Key Laboratory of Precision Measurement Technology and Instruments Beijing 100084China Department of Materials Science and Engineering Sun Yat-Sen UniversityGuangzhou 510275China ZNDY of Ministerial Key Laboratory School of Mechanical EngineeringNanjing University of Science and TechnologyNanjing 210094China Qiyuan Laboratory Beijing 100095China

Impact detecting and counting are fundamental functions of fuses used in hard target penetration ***,detection failure caused by battery breakdown in high-g acceleration environments poses a vulnerability for such *** paper introduces a novel supercapacitor that combines energy storage and high-g impact detection,called self-sensing *** deliberately inducing a transient soft short-circuit during shock in the supercapacitor,it is possible to detect external impact by its transient voltage *** realize this concept,firstly,by introducing the contact theory and force-induced percolation model,the electrode strength and roughness are found to have key impacts on the formation of soft ***,to meet the needs for sensitivity and capacity,a high-density porous carbon(HDPC)that combines high mechanical strength and porosity,is selected as a suitable candidate based on the analysis ***,a two-step curing method is proposed to prepare the high-roughness HDPC(HRHDPC)electrode and to assemble the self-sensing *** to the rich specific surface of the electrodes and the high surface strength and roughness conducive to the formation of transient soft short circuits,the self-sensing supercapacitor not only possesses an excellent specific capacitance(171 F/g at 0.5 A/g)but also generates significant voltage response signals when subjected to high-g impacts ranging from 8000g to 31,***,the self-sensing supercapacitor is applied to compose a successive high-g impact counting system and compared to traditional solutions(sensors and tantalum capacitors)in the military *** results show that the self-sensing supercapacitor-based system exhibits advantages in terms of size,power consumption,and counting accuracy.

关键词： supercapacitor self-sensing soft short-circuit impact sensing

Absorption properties and mechanism of lightweight and broadband electromagnetic wave-absorbing porous carbon by the swelling treatment

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International Journal of Minerals,Metallurgy and Materials 2024年第7期31卷 1701-1712页

作者： Jianghao Wen Di Lan yiqun wang Lianggui Ren Ailing Feng Zirui Jia Guanglei Wu College of Materials and Chemistry&Chemical Engineering Chengdu University of TechnologyChengdu 610059China School of Materials Science and Engineering Hubei University of Automotive TechnologyShiyan 442002China Institute of Materials for Energy and Environment State Key Laboratory of Bio-fibers and Eco-textilesCollege of Materials Science and EngineeringQingdao UniversityQingdao 266071China Institute of Physics&Optoelectronics Technology Baoji University of Arts and SciencesBaoji 721016China

Bioderived carbon materials have garnered considerable interest in the fields of microwave absorption and shielding due to their reproducibility and environmental *** this study,KOH was evenly distributed on biomass Tremella using the swelling induction method,leading to the preparation of a three-dimensional network-structured hierarchical porous carbon(HPC)through *** achieved microwave absorption intensity is robust at-47.34 dB with a thin thickness of 2.1 ***,the widest effective absorption bandwidth,reaching 7.0 GHz(11–18 GHz),is attained at a matching thickness of 2.2 *** exceptional broadband and reflection loss performance are attributed to the 3D porous networks,interface effects,carbon network defects,and dipole *** has outstanding absorption characteristics due to its excellent impedance matching and high attenuation *** uniform pore structures considerably optimize the impedance-matching performance of the material,while the abundance of interfaces and defects enhances the dielectric loss,thereby improving the attenuation ***,the impact of carbonization temperature and swelling rate on microwave absorption performance was systematically *** research presents a strategy for preparing absorbing materials using biomass-derived HPC,showcasing considerable potential in the field of electromagnetic wave absorption.

关键词： biomass hierarchical porous carbon dielectric loss electromagnetic wave absorption