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The stages are considered in incorporating the radio frequency range in electromagnetic field parameter standards. The problems then involved are considered, together with the methods of solution and results obtained. The history of electromagnetic field standards is closely related to research in two metrological centers: VNIIFTRI and NIST. 相似文献
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The historical aspect of the origin and development of the metrology of radio-frequency electromagnetic fields is considered, beginning with Hertz's experiments. The first electric field strength standards in the 30–300 MHz frequency band are described. The results obtained are analyzed and estimated from the modern point of view. 相似文献
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The role of the measurement standards of a radio-frequency electromagnetic field in an international system of calibration of measuring instruments is considered. The calibration and measurement capabilities of VNllFTRI in this domain are listed.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 31–35, January, 2005. 相似文献
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K. Yu. Sakharov 《Measurement Techniques》2004,47(10):994-997
Information on how to construct and improve the State Special Standard of the units of pulsed electric and magnetic field strengths are presented. The need and possibility of extending the time range of the standard in order to ensure uniformity of measurements of the parameters of very short pulses of electromagnetic fields having a pulse length of down to 10-10 sec are considered.Translated from Izmeritelnaya Tekhnika, No. 10, pp. 33–35, October, 2004. 相似文献
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《IEEE transactions on instrumentation and measurement》1963,12(3):134-138
Rather than a comprehensive survey of the field, highlights of the progress in microwave standards and measurement methods are given. Power, attenuation, impedance or reflection coefficient, noise, phase shift, and field strength are covered. Microwave frequencies are assumed to start at 1 Gc and extend upwards, including coherent electromagnetic energy in the spectrum of visible light, approximately 400-800 Tc. A discussion of the intercomparisons of power standards of different nations is followed by a report on newly developed power measuring devices and techniques. Some methods of measuring the power of lasers are given. The present status of attenuation measurements and standards is indicated, giving ranges and accuracies of calibrations at the National Bureau of Standards, Boulder, Colo. New types of standards for millimeter and submillimeter waves and for attenuation of laser beams are mentioned. Impedance standards and measuring techniques are discussed, as well as 2-port measurements and the development of greatly improved coaxial connectors. The recent development of phase shift standards and measurement techniques in the United States is summarized. The essential lack of microwave field strength standards is noted and small progress is reported. 相似文献
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静磁场在材料生产过程中的应用研究评述 总被引:15,自引:0,他引:15
在材料电磁过程研究中,静磁场尤其是强磁场材料科学是当今世界的研究热点。本文从静磁场作用下生成的洛仑兹力和磁化力两个角度系统地归纳总结了静磁场技术在材料生产领域的应用原理和实践。对静磁场下的洛仑兹力,主要介绍了流体流动、波动和对流控制、电磁振动及电磁超声波等方面的研究现状;对强磁场下的磁化力,主要介绍了其在相变、结晶配向、磁悬浮、磁对流等方面的研究进展。最后对强磁场材料科学的研究趋势和发展前景做了展望。 相似文献
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Zhihao ZHAO Jianzhong GUI Jie DONG Beijiang ZHANGThe Key Laboratory of Electromagnetic Processing of Materials Ministry of Education P.O. Box Northeastern University Shenyang ChinaPh.D. candidate 《材料科学技术学报》2005,21(1):75-78
The horizontal direct chill (HDC) casting process is a well-established production route for aluminum alloy ingot but the ingot may suffer from macrosegregation sometimes. In order to control the defect, a low frequency electromagnetic field has been applied in HDC casting process and the relevant influence has been studied. The results show that application of low frequency electromagnetic field can reduce macrosegregation in HDC casting process; and two main parameters of electromagnetic field density and frequency, have great influences on the solution distribution along the diameter of ingot. Moreover, the mechanisms of reduction of macrosegregation by electromagnetic field have been discussed. 相似文献
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应用感应加热理论,利用麦克斯韦方程组和温度微分方程,建立了电磁场与温度场耦合的有限元数学模型,使用有限元分析软件ANSYS对热金属气压成型工艺中的电磁感应加热过程进行了模拟与分析。模拟结果表明:随着电磁感应线圈电流频率的提高,在相等的加热时间内,金属钢管的升温速度不断增加,且最终达到的温度也进一步升高。随着电磁感应线圈电流密度的增加,在相等的加热时间内、相同的电磁感应线圈电流频率下,金属钢管的升温速度不断增加,加热效率得到有效提高,且最终达到的温度也逐步升高。随着金属钢管与线圈的间隔增加,金属钢管内、外表面的温度均逐渐降低;外表面温度的降低趋势越来越平缓,而内表面温度的降低趋势则不断加剧。 相似文献
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电磁场技术在半固态合金加工中的应用促进了制备工艺的开发和创新,也为获得高质量的半固态合金制品提供了保障。电磁场引起的半固态合金熔体流动状态和性质对合金元素传输、晶粒长大、温度场分布、凝固组织等均有重要影响。主要综述了电磁场对半固态合金流动行为的影响、数值模拟技术在解析半固态合金流动行为中的应用等方面的研究进展,并结合笔者的研究经历介绍了电磁场搅拌技术在半固态合金浆料制备中的应用、熔体流动对半固态合金凝固组织的影响,以及在半固态合金熔体流动特性研究中的新发现。在这些研究工作的基础上,着重综述了应用商业软件和数学建模对半固态合金熔体中电磁场作用引起的流动行为进行模拟、仿真所做的工作和取得的成果。最后,对电磁场技术在半固态合金加工中的应用以及电磁场作用下半固态合金熔体流动特性对半固态合金凝固组织影响的研究进展进行了总结,并对其发展前景和主要发展方向进行了展望。 相似文献
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Compression waves propagating through molten metals are contributed to degassing accelerating reaction rate,removing exclusions from molten metals and refining solidifcation structures during metallurgical processing of materials,In the present study ,two electromagnetic methods are proposed to generate intense compression waves directly in liquid metals.One is the simultaneous imposition of a high frequency electrical current filed and a static magnetic field ;the other is that of a high frequency magnetic field and a static magnetic field ,A mathematical model based on compressible fluid dynamics and electromagnetic fileds theory has been developed to derive pressure distri-butions of the generated waves in a metal.It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force,And the frequency is the same as that of the imposed electromagnetic force,On the basis of theoretical analyses ,pressure change in liquid gallium was examined by a pressure transducer under various conditions.The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations.Moreover,the effect of the generated waves on improvement of solidification structures was also examined .It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy ,This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments. 相似文献
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Results from a study of a transportable electric field strength standard are presented. A measurement formula for the standard in the form of a product of three functions, an amplitude function, a frequency function, and a correction function, is obtained. The limits of the working range of measurement of the electric field strength with respect to amplitude and frequency are determined. The random measurement error of the electric field strength is experimentally estimated. 相似文献
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The electromagnetic compatibility of electric vehicles is not only the important technology issue in researches,development and industrialization of electric vehicles,but also the key research area of ... 相似文献
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S. M. Abo-Dahab 《先进材料力学与结构力学》2018,25(4):319-334
In this article, we investigated an effect of external magnetic field on the propagation of surface waves in a perfect electrically conducting fiber-reinforced anisotropic general viscoelastic media of rational and higher orders with voids in a rotating medium. The general surface wave speed is derived to investigate effect of electromagnetic field and rotation on surface waves in the presence of voids and viscosity. Boundary conditions are applied to obtain the secular equation for generalized types of waves. Particular cases of Stoneley, Love and Rayleigh waves are derived. The results obtained are more general in the sense that some earlier published results are obtained from our result as special cases. In the absence of voids, the results for viscoelasticity of order zero are in good agreement with the fiber-reinforced materials. Also by neglecting the reinforced elastic parameters, the results reduce to a well-known isotropic medium. It is observed that surface waves cannot propagate in a strong initially applied electromagnetic field and rotation. Numerical results for particular cases have been obtained and displayed graphically. The results indicate that the effects of voids, anisotropic, fiber-reinforcement, rotation and electromagnetic field are very pronounced and applicable for the phenomena. 相似文献
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In this paper, the axial-flux permanent magnet driver is modeled and analyzed in a simple and novel way under three-dimensional cylindrical coordinates. The inherent three-dimensional characteristics of the device are comprehensively considered, and the governing equations are solved by simplifying the boundary conditions. The axial magnetization of the sector-shaped permanent magnets is accurately described in an algebraic form by the parameters, which makes the physical meaning more explicit than the purely mathematical expression in general series forms. The parameters of the Bessel function are determined simply and the magnetic field distribution of permanent magnets and the air-gap is solved. Furthermore, the field solutions are completely analytical, which provides convenience and satisfactory accuracy for modeling a series of electromagnetic performance parameters, such as the axial electromagnetic force density, axial electromagnetic force, and electromagnetic torque. The correctness and accuracy of the analytical models are fully verified by three-dimensional finite element simulations and a 15 kW prototype and the results of calculations, simulations, and experiments under three methods are highly consistent. The influence of several design parameters on magnetic field distribution and performance is studied and discussed. The results indicate that the modeling method proposed in this paper can calculate the magnetic field distribution and performance accurately and rapidly, which affords an important reference for the design and optimization of axial-flux permanent magnet drivers. 相似文献
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电磁场对高速钢与45钢感应摩擦焊接的影响 总被引:1,自引:0,他引:1
利用电磁场对金属材料产生的"场致效应",调节摩擦焊接表面的温度场,以改善异种金属摩擦焊接组织及性能.研究了外加电磁场对W6Mo5Cr4V2高速钢和45钢摩擦焊缝显微组织、合金元素扩散及焊接接头力学性能的影响.结果表明,摩擦加热阶段施加电磁场使45钢近缝区铁素体的数量减少;而在顶锻阶段施加电磁场,使45钢侧铁素体数量有所增多.同时,在顶锻阶段施加电磁场作用时,主要合金元素C、Cr、W的扩散区宽度明显增大.在顶锻阶段采用较短的电磁场施加时间和较低的感应电流强度,可以提高W6Mo5Cr4V2高速钢和45钢摩擦焊接头的抗拉强度. 相似文献