Incomplete-penetration hysteresis losses in transmission line cables

At 77 K, the resistivity of ceramic, high-temperature superconductors grows gradually rather than sharply with increasing current. The critical-state theory of hysteresis losses therefore needs to be modified. This has been done for slab conductors whose resistivity can be taken proportional to a power of the current density. Simple formulas have been derived in the limiting cases of incomplete penetration and full penetration when the losses are driven either by a sinusoidal transport current or a sinusoidal external magnetic field. These formulas can be applied to multilayer transmission line cables once the current distribution within and among the layers has been determined. This distribution has been calculated (in the incomplete penetration limit) by solving Maxwell's field equations. A formula is presented for the dependence of the hysteresis loss on winding angle. The formula is used to determine the optimum winding angle.     

AC losses in a flexible 10 m long conductor model for a HTS power transmission cable

To demonstrate the possibility of manufacturing a HTS power transmission cable with low AC losses, we fabricated a 10 m long cable conductor and a cryosystem. The conductor was wound in a four-layer design out of 2 km Ag/Bi-2223 tapes. We determined a critical current of 5000 A. Loss measurements were performed with an electric method which detects the voltage drop along the conductor with a lock-in technique and a calorimetric method which measures the temperature rise along the conductor. Both methods yield the same low loss values of only 0.8 W/m at 77 K and 2000 A_rms/50 Hz. This is due to the low loss winding scheme we used which assures an equal current distribution in all four layers through transformatoric coupling. We applied the uniform current distribution model and added the nonlinear V–I curve to describe quantitatively the obtained results.     

高温超导YBCO带材的交流传输电流损耗测量

文中对不同频率不同幅值的交变电流下高温超导体YBCO带材的交流传输损耗进行了实验研究。实验在77K下,对Superpower公司生产的SCS4050型号带材采用电测法通过锁相放大器进行了交流损耗值的测量,并将其工作电流为50Hz时的测量结果与Norris矩形模型估算值进行了对比,同时也给出了15Hz到300Hz不同频率下交流损耗测量结果的比较分析。     

Numerical minimization of AC losses in coaxial coated conductor cables

Power cables are one of the most promising applications for the superconducting coated conductors. In the AC use, only small resistive loss is generated, but the removal of the dissipated heat from the cryostat is inefficient due to the large temperature difference. The aim of this work is to minimize the AC losses in a multilayer coaxial cable, in which the tapes form current carrying cylinders. The optimized parameters are the tape numbers and lay angles in these cylinders. This work shows how to cope with the mechanical constraints for the lay angles and discrete tape number in optimization. Three common types of coaxial cables are studied here to demonstrate the feasibility of optimization, in which the AC losses were computed with a circuit analysis model formulated here for arbitrary phase currents, number of phases, and layers. Because the current sharing is practically determined by the inductances of the layers, the optima were obtained much faster by neglecting the nonlinear resistances caused by the AC losses. In addition, the example calculations show that the optimal cable structure do not usually depend on the AC loss model for the individual tapes. On the other hand, depending on the cable type, the losses of the optimized cables may be sensitive to the lay angles, and therefore, we recommend to study the sensitivity for the new cable designs individually.     

Further study on the characteristic impedance of a new transmission line of round conductor and parallel plane with a slit

A conformal transformation for the analysis of a transmission line consisting of a cylindrical conductor placed opposite a slit in an infinite flat plate is developed. The approximate and exact expressions in closed- form of the characteristic impedance for the proposed line based on assuming only a quasi-TEM mode propagating in the line are as exact as the conventional one cited.     

Disorder-induced losses in photonic crystal waveguides with line defects

A numerical analysis of extrinsic diffraction losses in two-dimensional photonic crystal slabs with line defects is reported. To model disorder, a Gaussian distribution of hole radii in the triangular lattice of airholes is assumed. The extrinsic losses below the light line increase quadratically with the disorder parameter, decrease slightly with increasing core thickness, and depend weakly on the hole radius. For typical values of the disorder parameter the calculated loss values of guided modes below the light line compare favorably with available experimental results.     

On the characteristic impedance of a coaxial line with elliptic cone outer conductor and angular strip inner conductor

The expressions of the characteristic impedance of a new kinds of transmission lines—elliptic cone coaxial line are derived. The formulas are based on the TEM and the transformation of the sphero-conal coordinate into two dimension plane. Also themethods using the graphical approximation and taking the geometrical average of the upper and lower bounds to the size of the line are put forward to calculate the characteristic impedance — of the elliptic cone coaxial line.     

Magnetooptical effects in the metal-dielectric gratings

A significant enhancement of the magnetooptical Faraday effect in the bilayer heterostructure of a thin metallic layer pierced by an array of parallel subwavelength slits and a uniform dielectric layer magnetized perpendicular to its plane, is reported. Calculations, based on the rigorous coupled-wave analysis of Maxwell’s equations, demonstrate that in such structures the Faraday effect spectrum has several resonance peaks in the near-infrared range, some of them coinciding with transmittance peaks, providing simultaneous large Faraday rotation enhanced by an order and high transmittance of about 35%. It is shown that the excitation of the quasi-guided TM- and TE-modes in the dielectric layer mostly governs the enhancement of the Faraday rotation.     

螺旋线型三导体脉冲形成线快波抵消方法

针对螺旋线型三导体脉冲形成线的快波振荡问题,提出一种阻抗分两段阶梯变化的螺旋线结构,分析了此类螺旋线快波反射与慢波反射相互抵消快波的条件,给出两段变阻抗螺旋线慢波系数之间的关系式以及匝数密度之比计算方法,通过仿真计算证明该方法能有效消除快波反射对螺旋线输出脉冲的影响。     

Wave reflection and transmission in beams

The vibrational behaviour of beam systems can be expressed in terms of waves of both propagating and near field types. A propagating wave incident upon a discontinuity gives rise to reflected and transmitted waves of both kinds whose amplitudes may be found from well-known reflection and transmission coefficients. In this paper the approach is extended to the case of incident near field waves, reflection and transmission matrices being derived for the cases of a point support and a change in section. Reflection at a boundary and the effects of applied excitations are also considered. It is seen that incident near fields can give rise to substantial propagating components. The application of the results to the analysis of free and forced vibration of beams is then demonstrated. By adopting this approach the effects of the interaction of the near fields with neighbouring discontinuities are fully included.     

螺旋线型三导体脉冲形成线快波抵消方法

针对螺旋线型三导体脉冲形成线的快波振荡问题,提出一种阻抗分两段阶梯变化的螺旋线结构,分析了此类螺旋线快波反射与慢波反射相互抵消快波的条件,给出两段变阻抗螺旋线慢波系数之间的关系式以及匝数密度之比计算方法,通过仿真计算证明该方法能有效消除快波反射对螺旋线输出脉冲的影响。     

Effects of losses on the transmission and reflection in the single-negative materials

In this work, we investigate the angular dependence of transmission and reflection in the single-negative (SNG) materials. We consider a model structure of a SNG bilayer which consists of the epsilon-negative (ENG) and mu-negative (MNG) layers. The wave transmission and reflection properties due to the losses from the ENG and MNG materials are specifically investigated. With the presence of losses in the ENG and MNG materials, some unusual wave properties will be explored and numerically demonstrated.     

线电荷与带有半圆柱凸起的接地导体所形成的电场

利用复数坐标系z上的保角变换,计算长直线电荷与带有半圆柱凸起的接地导体所形成的电场,给出电势和场强分布,并利用软件MATLAB绘制出电场线和等势线(面)图.     

三导体螺旋脉冲形成线的输出特性

采用横电磁波传输理论,分析了三导体螺旋脉冲形成线（PFL）（包含内筒、螺旋中筒和外筒）的脉冲形成过程,给出了螺旋PFL的波阻抗、慢波系数、输出脉冲的平顶波动幅度等特征参数的计算公式。研究表明:三导体螺旋PFL具有与螺旋传输线同样的波阻抗和慢波系数;螺旋PFL的输出脉冲平顶波动,随着慢波系数或负载阻抗的增大而减小。