二次曲面线圈中的均匀磁场

基于对旋转椭球内部磁场的讨论,采用Matlab数值计算的方法计算了旋转椭球的内部磁场.对于旋转抛物球和双曲球面,用相同方法绕制线圈也能得到均匀的磁场.印证了内部磁场计算的公式,并提出了一种产生大范围均匀磁场的方法.     

旋转二次曲面线圈轴线上的磁场

从普通物理电磁学角度出发,分别讨论了球状、椭球状、旋转抛物面状及双曲面状线圈旋转对称轴线上的磁场问题,最后得到了一个关于旋转二次曲面对称轴线上磁场的普适表达式.     

Polarizability and capacitance of a conducting ellipsoid

Expressions for the polarizability of a conducting ellipsoid and for the capacitance of an isolated conducting ellipsoid are suggested.     

量子棒中弱耦合磁极化子的性质

给出了具有椭球边界量子棒经过坐标变换成球形边界的哈密顿量.采用线性组合算符和幺正变换的方法研究了在抛物限制势下量子棒中弱耦合磁极化子的振动频率和基态结合能随横向和纵向有效受限长度、电子-声子耦合强度、椭球的纵横比以及磁场的回旋频率的变化关系.数值计算结果表明:振动频率和基态结合能随回旋频率的增加而增大,随横向和纵向有效受限长度的减少而迅速增大.基态结合能随耦合强度的增加而增大.振动频率随纵横比的增加而减少.当e′1时,基态结合能随纵横比的增加而增加.e′1时,随着纵横比的减少,基态结合能增大.当e′=1时,基态结合能取稳定的极小值.     

The Ellipsoid Theory of Electromagnetic Radiation from a Moving Source

The ellipsoid theory Is a modification of the ether theory coupled with time dilation. It is not in conflict with any known observational evidence. Certain astronomical evidence, which conflicts with relativity theory, supports the ellipsoid theory. The moon laser experiment will serve as a direct test of the validity of both theories.     

Coarse and Fine Control of the EPR Frequency of a Loop-Gap Resonator Using a Single-Turn Coil with a Varactor Diode Attached

Coarse control and fine control of the resonant frequency of a loop-gap resonator (LGR) operating at an electron paramagnetic resonance (EPR) frequency of ca. 650 MHz were achieved using a single-turn coil with a varactor diode attached (a frequency shift coil). When the distance between the LGR and the frequency shift coil was changed from 15 to 10 mm under the condition of constant voltage to the varactor diode (0 V), a shift of the resonant frequency of the LGR of ca. 20 MHz was observed (coarse frequency control). When the voltage applied to the varactor diode was changed from 0 to 15 V at the same distance between the LGR and the frequency shift coil (10 mm), a shift of the resonant frequency of the LGR of ca. 200 kHz was observed (fine frequency control). There were no significant changes in sensitivity of EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) without and with the frequency shift coil. The EPR sensitivity did not change discernibly when the resonant frequency was shifted by the frequency shift coil. Furthermore, radio-frequency phase adjustment for homodyne detection could be performed by using the frequency shift coil without applying frequency modulation to the carrier wave.     

Anisotropic diffusion of a magnetically torqued ellipsoidal microparticle

We study the dynamics of an overdamped paramagnetic ellipsoidal particle confined above a plane and subjected to an external rotating magnetic field. Without magnetic forcing, the Brownian ellipsoid exhibits a crossover from a short time anisotropic diffusion to a long time isotropic one. Application of an external static or rotating magnetic field enables controlling and varying the crossover time depending on the field frequency and amplitude. We combine analytical results and numerical simulations in order to explore the diffusive properties of the forced ellipsoid.     

Analysis of the Possibility of Creating a Stable Satellite of the Asteroid Apophis as a Homogeneous Triaxial Ellipsoid

Doklady Physics - The problem of creating a stable satellite orbit about the asteroid Apophis as a homogeneous triaxial ellipsoid is investigated. The motion of the spacecraft around the asteroid...     

Is there a collective dielectric resonance?

It is shown that the Maxwell-Garnett equation predicts resonance in a heterogeneous material consisting of ellipsoids embedded in a matrix, even if the ellipsoids are made from a transparent material. It is suggested that the resonance of this type be denoted as collective because it cannot be achieved in a single ellipsoid. However, the problem of applicability of the Maxwell-Garnett equation in the range of ellipsoid concentrations corresponding to the resonance condition remains unsolved.     

Vibration analysis and measurement of a gradient coil insert in a 4 T MRI

High speed switching of current in gradient coils within high magnetic field strength Magnetic Resonance Imaging (MRI) scanners may result in high acoustic sound pressure levels in and around these machines. Many studies have already been conducted to characterize the sound field in and around MRIs and various methods have been investigated to attenuate the noise generated. To characterize the vibration properties of the gradient coil, a modified Finite Element (FE) model was developed according to the dimensional design of an available gradient coil insert and the concentration of the copper windings in the coil. The finite element analysis results were verified through experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Comparisons show that the FE model predicts the vibration properties extremely accurately. Based on the verified FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again verified through experimental vibration testing with the gradient coil insert installed in a 4 T MRI and excited using swept sinusoidal time waveforms. Through a comparison of the vibration signals generated it was found that the vibration resonances, both from the FE model and the experimental vibration testing, shift to higher frequencies after the boundary constraints were applied, as was expected. The predicted vibration response was very close to that measured from the gradient coil insert in operation. The FE modeling procedure that has been developed could easily be used to accurately predict the vibration properties of other gradient coil designs. Furthermore, the vibration analysis results from the FE model could be used in acoustic noise analysis to predict the sound pressure level produced by different types of input current pulse sequences.     

Performance improvement of a high-temperature superconducting coil by separating and grading the coil edge

In this paper, we establish a model to analyze the transport current performance of a high-temperature superconducting (HTS) coil, considering the dependencies of critical current and n-value of an HTS tape on magnetic field and magnetic field angles. This analysis shows that relatively large electric fields appear at the coil’s edges, preventing improvement in the transport current performance of the coil. To solve this problem, in this paper, we propose a graded coil in which several coil edges of different heights are separated and graded. Analysis of its performance shows that the coil’s critical current increases, thus confirming that there exists an optimum coil cross section at which the stored energy and central magnetic field improve 2.1 times and 45%, respectively, compared with a typical rectangular coil that employs the same total length of the HTS tape. It is recommended that these results of the coil should be applied to SMES.     

太阳模拟器中椭球面聚光镜参数的确定

椭球面聚光镜是太阳模拟器设备的重要组成部分,其能量收集的效率决定着太阳模拟系统的能量传递效率,而太阳模拟器光学系统中的椭球面聚光镜参数一直没有理论上的设计依据,结合氙灯的发光特性并通过对MATLAB 中建立的椭球面聚光镜聚光过程数值分析模型给出了椭球面聚光镜包括第一焦距、最大成像放大倍率、包容角范围及前后开口直径的确定依据,并通过在Lighttools 中建立的4种仿真模型验证了理论分析的正确性。第一焦距由光源光中心高确定,最大成像放大倍率由光学积分器相对孔径及椭球镜包容角范围共同确定,椭球镜包容角范围不小于30～120,前开直径口由椭球镜的最大孔径角确定,后开口直径由最小孔径角和光源的径向调节量共同确定。该结论给椭球面聚光镜的设计提供了理论支撑,有利于设计完成高能量收集效率的椭球面聚光镜。     

椭球内反射的几何光学性质

本文讨论椭球的内反射性质。由椭球的一个焦点F_1发射出的光波将在反射过程中与椭球的长轴充分逼近,使焦点F_1所具有的辐射以极狭窄的光束从椭球长轴的一端发射出来。     

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A hybrid structure was adopted for the PF coil of the building HL-2M device. In the process of discharge, there is a strong coupling between the coils, each coil will be subjected to a large electromagnetic force. In this paper, PF coil electromagnetic force is computed by the analytic method under the discharge conditions of the largest I_p =3MA plasma current and various configurations. These calculation results are of reference value for the design of PF coil and its support structure.     

Magnetization curves for a hard superconductor sample in the shape of a general ellipsoid

The critical state model is solved to obtain the virgin and hysteresis magnetization curves for a zero field cooled hard type-II superconductor sample in the shape of general ellipsoid, with the applied magnetic field along one of its principal axes.     

Experimental development of a petal resonator surface coil

A surface coil for MRI was designed and built based on the principles of the petal resonator proposed by Mansfield [J Phys D Appl Phys 21 (1988) 1643]. This resonator coil design was named the petal resonator surface (PERES) coil and is composed of an eight-petal coil array and a central circular coil. A minimum separation of three times the petal coil radius is necessary to significantly decrease the mutual inductance. An analytical function for the PERES Signal-to-noise ratio (SNR) is obtained based on the quasistatic method. Theoretical plots of SNR enhancement yielded 26% and 35% more SNR over the circular coil and phased-array coils. Imaging experiments were first performed using a spectroscopy phantom on a 1.5-T commercial imager. Subsequently, brain images of healthy volunteers were obtained. Clinical MR imager compatibility allows this resonator coil to be used with conventional pulse sequences and imaging protocols. This coil design offers a new alternative to existing surface coils because it significantly increases the SNR.     

Wetting and contact lines of micrometer-sized ellipsoids

We experimentally and theoretically investigate the shapes of contact lines on the surfaces of micrometer-sized polystyrene ellipsoids at the water-air interface. By combining interferometry and optical trapping, we directly observe quadrupolar symmetry of the interface deformations around such particles. We then develop numerical solutions of the partial wetting problem for ellipsoids, and use these solutions to deduce the shapes of the corresponding contact lines and the values of the contact angles, theta(c)(k), as a function of the ellipsoid aspect ratio k. Surprisingly, theta(c) is found to decrease for increasing k suggesting that ellipsoid microscopic surface properties depend on ellipsoid aspect ratio.     

HL-2M极向场线圈电磁力的计算分析

在建的HL-2M装置的PF线圈采用了混合式结构。在放电过程中,线圈之间有很强的电磁耦合,每一个线圈都会受到很大电磁力的作用。采用解析法,在最大I_p=3MA等离子体电流和各种位形的放电条件下,计算分析了PF线圈受到的电磁力。这些计算结果对PF线圈及其支撑结构的设计都是具有参考价值的。     

Studies of a slow-wave Rogowski coil

A Rogowski coil in a conducting shield can be considered as a slow-wave transmission line. By carefully constructing the slow-wave structure in such a way that the distributed capacitance becomes large (on the order of nF) and the coil inductance is at least several microhenries, it is possible to obtain a high-sensitivity (≅1 V/A) Rogowski coil for a pulse duration of up to several microseconds. The design and performance of such a slow-wave Rogowski coil are described. Details of the experimental results for the effects of the terminating resistance on the probe response are also presented. These results agree with theoretical predictions