Microwave Attenuation of Solid Propellant Exhaust Plume in Oblique Orientation

Aim To investigate the effects of the incident orientation on the microwave attenuation. Methods Attenuation allowing microwave signal transmitting in an oblique or vertical direction through the solid propellant exhaust plume was computed, and the experiments were performed utilizing a lab scale solid rocket motor with a fully expanded nozzle. Results The predicted results accord well with the experimental results. Conclusion The microwave attenuation in the oblique path is greater than that in the vertical path.

Rain Attenuation in the Microwave-to-Terahertz Waveband

In recent years, there has been increased interest in the terahertz waveband for application to ultra-high-speed wireless communications and remote sensing systems. However, atmospheric propagation at these wavelengths has a significant effect on the operational stability of systems using the terahertz waveband, so elucidating the effects of rain on propagation is a topic of high interest. We demonstrate various methods for calculating attenuation due to rain and evaluate these methods through comparison with calculated and experimental values. We find that in the 90 - 225 GHz microwave band, values calculated according to Mie scattering theory using the Best and P-S sleet raindrop size distributions best agree with experimental values. At 313 and 355 GHz terahertz-waveband frequencies, values calculated according to Mie scattering theory using the Weibull distribution and a prediction model following ITU-R recommendations best agree with experimental values. We furthermore find that attenuation due to rain increases in proportion to frequency for microwave-band frequencies below approximately 50 GHz, but that there is a peak at around 100 GHz, above which the degree of attenuation remains steady or decreases. Rain-induced attenuation increases in proportion to the rainfall intensity.

Application of Machine Learning Methods on Climate Data and Commercial Microwave Link Attenuations for Estimating Meteorological Visibility in Dusty Condition

Accurately measuring meteorological visibility is an important factor in road, sea, rail, and air transportation safety, especially under visibility-reducing weather events. This paper deals with the application of Machine Learning methods to estimate meteorological visibility in dusty conditions, from the power levels of commercial microwave links and weather data including temperature, dew point, wind speed, wind direction, and atmospheric pressure. Three well-known Machine Learning methods are investigated: Decision Trees, Random Forest, and Support Vector Machines. The correlation coefficient and the mean square error, between the visibility distances estimated by Machine Learning methods and those provided by Burkina Faso weather services are computed. Except for the SVM method, all the other methods give a correlation coefficient greater than 0.90. The Random Forest method presents the best result both in terms of correlation coefficient (0.97) and means square error (0.60). For this last method, the best variables that explain the model are selected by evaluating the weight of each variable in the model. The best performance is obtained by considering the attenuation of the microwave signal and the dew point.

Oxidative Molecular Layer Deposition Tailoring Eco-Mimetic Nanoarchitecture to Manipulate Electromagnetic Attenuation and Self-Powered Energy Conversion

Advanced electromagnetic devices,as the pillars of the intelligent age,are setting off a grand transformation,redefining the structure of society to present pluralism and diversity.However,the bombardment of electromagnetic radiation on society is also increasingly serious along with the growing popularity of"Big Data".Herein,drawing wisdom and inspiration from nature,an eco-mimetic nanoarchitecture is constructed for the first time,highly integrating the advantages of multiple components and structures to exhibit excellent electromagnetic response.Its electromagnetic properties and internal energy conversion can be flexibly regulated by tailoring microstructure with oxidative molecular layer deposition(oMLD),providing a new cognition to frequency-selective microwave absorption.The optimal reflection loss reaches≈−58 dB,and the absorption frequency can be shifted from high frequency to low frequency by increasing the number of oMLD cycles.Meanwhile,a novel electromagnetic absorption surface is designed to enable ultra-wideband absorption,covering almost the entire K and Ka bands.More importantly,an ingenious self-powered device is constructed using the eco-mimetic nanoarchitecture,which can convert electromagnetic radiation into electric energy for recycling.This work offers a new insight into electromagnetic protection and waste energy recycling,presenting a broad application prospect in radar stealth,information communication,aerospace engineering,etc.

Diagnosis of Unmagnetized Plasma Electron Number Density and Electron-neutral Collision Frequency by Using Microwave

The plasma diagnostic method using the transmission attenuation of microwaves at double frequencies （PDMUTAMDF） indicates that the frequency and the electron-neutral collision frequency of the plasma can be deduced by utilizing the transmission attenuation of microwaves at two neighboring frequencies in a non-magnetized plasma. Then the electron density can be obtained from the plasma frequency. The PDMUTAMDF is a simple method to diagnose the plasma indirectly. In this paper, the interaction of electromagnetic waves and the plasma is analyzed. Then, based on the attenuation and the phase shift of a microwave in the plasma, the principle of the PDMUTAMDF is presented. With the diagnostic method, the spatially mean electron density and electron collision frequency of the plasma can be obtained. This method is suitable for the elementary diagnosis of the atmospheric-pressure plasma.

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process.The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured.It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders.The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%.Mechanical properties were controlled by Al2O3 content,dispersion of nano reinforcements and grain size.The optimum hardness and strength properties were achieved through incorporation of 10 wt.%Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles(NPs)at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement.Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time.The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix.The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.

Microwave method based on curve fitting method for high-precision collision frequency diagnosis

In this work,the results of plasma microwave transmission diagnosis were analyzed.According to the attenuation and phase shift of the electromagnetic wave propagating in the plasma,the electron density and collision frequency of the plasma can be diagnosed.Since part of the electromagnetic wave is reflected or diffracted when propagating in the plasma,and is not absorbed by the plasma,and this part of the attenuation is still included in the measured attenuation,the attenuation is distorted.Therefore,a curve fitting method is proposed to remove the attenuation caused by the plasma reflection,thereby improving the accuracy of the diagnosis of the collision frequency.The calibration effect of this method on plasmas with different electron densities and collision frequencies is analyzed,and a diagnostic frequency band with good calibration results is given.The curve fitting method is verified by experiment and simulation.After adopting the newly proposed method,the diagnosis accuracy of collision frequency can be increased by 30%.This method can be widely used in various types of plasma diagnosis and provides a new idea for plasma diagnosis.

Absorption of Microwaves in Low Intensity Eucalyptus Litter Fire

A fuel bed was constructed where various vegetation species could be used as combustion fuel. The fuel bed was equipped with a thermocouple to measure fire temperature and a two-port automatic network analyser to measure microwave scattering parameters in flame medium. The parameters are then used to determine microwave propagation characteristics in fire. The measurements have implications on radio wave communication during wildfire suppression and in remote sensing. The attenuation data also provide an estimation of vegetation fire ionisation and conductivity. Eucalyptus litter fire with a maximum flame temperature of 976 K was set on the fuel bed and X-band microwaves (7.00 - 9.50 GHz) were caused to propagate through the flame. Attenuation of 0.35 - 0.90 dB was measured for microwaves in the frequency range. For the low intensity fire, conductivity was measured to range from 0.00021 - 0.00055 mho/m and electron density was to be the range of 1.83 - 2.24 × 1015 m-3.

Microwave Diagnostics for Studies of Electromagnetic Scattering by Fluorescent Lamp Plasma

This paper rerports a related microwave diagnostic methhod that measures both the electron number density and the electron-neu- tral collision frequency, which are crucial to understand the behavior of microwave traveling in plasma. Arrays of standard commercial fluoresoent lamp placed directly against each other in two rows are used to produce a plasma layer. Attenuations of microwave by plasma layer are studied experimentally in the frequencies of 1--8 C44z using a synthesized signal generator and a spectnnn analyzer. Two wavepolarizations are trader investigation： dectric field of the wave is either parallel （ E -wave） or perpendicular （H-wave） to the fluorescent lamp axis. The electron number density and the electron-neutral collision frequency of fluorescent lamp plasma are obtained by microwave diagnostics, for the purpose of analyzing microwave scattering characteristics by plasma.

基于指数雨胞雨衰模型的微波链路雨强反演方法

为了提高微波链路雨强反演的准确性,基于指数雨胞雨衰模型提出了一种新的微波链路雨强反演方法,并利用瑞典哥德堡市21条微波链路和距链路2 km范围内8个雨量站的实测数据,将指数雨胞雨衰模型与传统幂律模型和ITU-R P.530-16雨衰模型进行了雨强反演对比。结果表明:指数雨胞雨衰模型在雨强反演方面表现优异,决定系数和纳什效率系数均为0.78,平均绝对误差为0.39 mm/h,均方根误差为0.68 mm/h;与幂律模型相比,指数雨胞雨衰模型在准确度和稳定性方面有显著提升,与ITU-R P.530-16雨衰模型相比也有所改进,特别是在短链路和中小雨的雨强反演中表现出明显的优势,对于进一步提升微波链路雨强反演精度和改善降水监测效果具有重要价值。

微波含水率检测技术在复杂油水混合形态下的应用研究

在油水混合物中会出现不同的乳化形态,不同的乳化形态对应的电导率和介电常数也具有显著差异,从而导致通过检测电导率和介电常数值间接测量含水率的测量结果不准确。针对复杂油水混合状态下含水率难以测准的问题,提出一种基于微波技术的复杂油水两相流含水率检测技术,建立了基于微波技术的“油包水”和“水包油”状态分析方法。首先通过检测微波信号穿过不同介质后信号幅值的衰减和相位的偏移,推测油水混合物的含水率值。再利用不同输入功率的微波信号在不同介电常数下功率衰减比不同的原理,来区分油水混合物的乳化状态,优化含水率的测量。室内验证和矿场试验结果表明,该系统可有效区分乳化液的混合状态,通过含水率标定值对实测数据进行修正,最终测量的含水率误差可控制在1个百分点以内,实现了复杂油水混合形态下含水率的高精度测量。

短距离无线微波链路降雨反演模型研究

利用商用微波链路进行降雨反演是一种新型的降雨监测手段,且随着通信技术的发展,高密度的商用微波链路网络可提供更高空间分辨率的降雨空间反演结果。目前,幂律模型被广泛用于研究微波衰减与雨率的关系,该模型对长度超过1 km的链路反演精度较高,但在反演短链路(长度<1 km)雨强时出现显著的降雨强度过高估计问题。针对此问题,本文基于ITU-R P.530-16建议书中长期雨衰减公式,建立了雨强反演模型。在瑞典哥德堡地区对该模型进行了验证,并对比分析了本文模型与幂律模型降雨反演结果。结果表明,相比于幂律模型,本文模型在对短链路进行雨强反演时更稳定、精确,确定性系数提升了55.3%,标准化均方根误差下降了76.2%,累计降雨量误差下降了92.4%。本文研究结果为短链路在反演降雨时出现的过高估计问题提供了一个解决思路。

电离层对月基对地观测平台辐射成像的影响

月基对地观测是一种全新的空间观测手段,其将月球作为搭载平台对地球进行持续长期观测,具有超大可观测范围、高测绘带幅宽、多角度成像、高时间分辨率和长使用寿命等优势。地球电离层位于地表以上至1000 km的高空区域,是影响月基对地观测成像质量的重要因素。为探索月基对地观测平台下热红外及微波辐射传输特性,研究开展了地球电离层对月基对地观测平台热红外和微波辐射成像影响分析的工作,并模拟不同纬度区域月基微波辐射亮温衰减值。首先根据Chapman分布定量化分析电离层电子浓度、折射率变化规律,再结合观测天顶角、碰撞频率等参数计算穿过电离层过程中不同高度处衰减及传输路径,最终采用积分方式获取热红外和微波在电离层中能量衰减量。结果表明,月基对地观测平台热红外和微波成像链路中电离层中造成的能量衰减与碰撞频率、热红外波长和观测天顶角有关,且地球电离层对月基对地观测平台微波成像的影响大于热红外成像的影响。此外,低纬度区域月基微波辐射受电离层衰减影响较大,月基微波亮温值降低约1.304 K;中纬度次之。

脲醛树脂包覆对片状羰基铁粉电磁吸波性能的影响

目的提高片状羰基铁粉(FCI)的吸波性能。方法采用原位聚合法制备脲醛树脂(UF)包覆片状羰基铁粉核壳复合粒子。通过透射电子显微镜(TEM)和X射线衍射仪(XRD)分别对试验前后样品的微观形貌和物相组分进行表征。采用矢量网络分析仪对处理前后片状羰基铁粉在0.5~18 GHz频率范围内的电磁参数进行测试,基于传输线理论对其反射损耗曲线进行拟合分析。结果微观形貌及X射线衍射谱结果表明,成功合成了脲醛树脂包覆片状羰基铁粉复合粒子(FCI@UF)。对测得的电磁参数进行分析,与原始片状羰基铁粉相比,包覆后铁粉介电常数和磁导率的实部、虚部均呈下降趋势,电磁波衰减能力减弱,与空气的阻抗匹配能力增强。反射损耗曲线图中,包覆后铁粉能有效吸收频带变宽(以反射损耗小于‒10 dB的带宽作为有效吸收频带),由3.15GHz变为4.38GHz,在13.84GHz时有最小反射损耗(‒20.64dB),最小反射损耗向高频移动,最小值降低率达41.38%。结论使用脲醛树脂对片状羰基铁粉进行包覆,制备了综合吸波性能更具优势的FCI@UF复合粒子,有效提高了片状羰基铁粉的吸波性能。

基于商用微波链路反演降雨的空间插值方法对比研究

为探究适宜于商用微波链路降雨监测数据的空间插值方法,基于无线微波雨衰特性经验模型,分析不同线状降雨数据转换为点状降雨数据情景下,反距离权重法、克里金法和趋势面法对降雨空间插值的反演精度。研究结果表明:微波链路越密集,条数越多,其趋势的一致性越好;在微波线状数据转换为点状数据的五种情景中,将微波链路以200m为间隔概化为具体的降雨监测点时,空间插值效果较好;趋势面法的空间插值效果较好,反距离权重法次之,克里金法最差。研究结果明晰了线状降雨数据转换为格网型空间数据的原则,为商用微波链路组网构建空间二维雨量场提供了支撑,对提高线状降雨监测产品兼容性具有重要意义。

矿用微波在线水分仪的研究与设计

为了在矿井等有防爆要求的场所实现煤炭水分在线测量,基于煤的水分对微波功率衰减的原理,选择C波段微波,以水分与微波功率衰减的线性关系及煤量补偿方法建立微波测水模型,并对微波发生装置、天线、物位传感器及整体结构进行了矿用防爆设计,研制了矿用微波在线水分仪。经厂内评估测试,矿用微波在线水分仪的设计满足现场需求,测量的均方根误差小于0.5%。文章还对矿用微波在线水分仪在矿井中的实际应用提出了相关建议。

水利工程微波通信技术问题研究及优化策略

微波通信技术作为重要的信息传输手段,在水利工程监控、调度等方面发挥着重要作用。然而,该技术在实际应用中面临着信号衰减、电磁干扰与多径效应、环境因素的影响以及设备老化与维护等问题。为解决这些问题,需要采取一系列优化策略,包括提升信号传输质量、抑制电磁干扰与多径效应、增强通信系统对环境变化的适应能力以及加强设备维护与更新等。这些策略的实施有助于提高水利工程中微波通信技术的稳定性和可靠性,为水利通信的可持续发展提供有力支持。

Rational construction of graphene oxide with MOF- derived porous NiFe@C nanocubes for high-performance microwave attenuation

Exploring lightweight microwave attenuation materials with strong and tunable wideband microwave absorption is highly desirable but remains a significant challenge. Herein, three-dimensional （3D） porous hybrid composites consisting of NiFe nanoparticles embedded within carbon nanocubes decorated on graphene oxide （GO） sheets （NiFe@C nanocubes@GO） as high-performance microwave attenuation materials have been rationally synthesized. The 3D porous hybrid composites are fabricated by a simple method, which involves one-step pyrolysis of NiFe Prussian blue analogue nanocubes in the presence of GO sheets. Benefiting from the unique structural features that exhibit good magnetic and dielectric losses as well as a proper impedance match, the resulting NiFe@C nanocubes@GO composites show excellent microwave attenuation ability. With a minimum reflection loss （RL） of -51 dB at 7.7 GHz at a thickness of 2.8 mm and maximum percentage bandwidth of 38.6% for RL 〈 -10 dB at a thickness of 2.2 mm, the NiFe@C nanocubes@GO composites are superior to the previously reported state-of-the-art carbon-based microwave attenuation materials.

STUDIES OF THE VERTICAL STRUCTURE MODEL AND THE MICROWAVE ATTENUATION OF CLOUDS AND PRECIPITATION OVER TROPICAL OCEAN AREA

Using radiosonde data and other related observations in the TOGA-COARE IOP(from November 1,1992 to February 28,1993),the microwave attenuation of non-precipitating clouds is investigated based on microwave radiative transfer model(MRTM)at the specific frequencies of 6.8,10.65,13.9,19.35,22.235,37.0,85.5 and 90.0 GHz.Besides,utilizing the data of the airborne radar and radiometer at 13.8 GHz in the IOP(Intensive Observation Period),vertical structure models for different types of precipitating clouds are obtained,and also the microwave attenuation of precipitating cloud is studied.Some statistical characteristics of 13.8 GHz microwave path integrated attenuation for stratiform and convective precipitating clouds are presented.The results given here are valuable for the spaceborne microwave remote sensing of precipitation,and the cloud and precipitation attenuation corrections in the spaceborne microwave remote sensing of earth surface over tropical ocean area.

Calculation of thermodynamic parameters of relaxation process using a microwave attenuation method

THE method of determination of thermodynamic parameters of relaxation process——relax-ation time τ,enthalphy ΔH,entropy ΔS and free energy δF——has been established anddeveloped.The mathematical models of the real and imaginary parts of dielectric con-stants ε’(ω,t),ε’’(ω,t)which are expressed by τ,ΔH,ΔS and ΔF are first established.