Conventional Electromagnets Research Articles

Robust Control of a 4-Pole Electromagnet in Semi-Zero-Power Levitation Scheme with a Disturbance Observer

Electromagnetic suspension (EMS) has been widely used in many industrial fields because of various advantages in practical use. The U-type magnets are often used to generate the levitation force in the EMS system. This conventional electromagnet, however, can only control one degree-offreedom. It cannot construct a levitation system solely by itself.A 4-pole type yoke hybrid electromagnet is proposed instead of the usual U-type magnet and its magnetic levitation control is studied in this paper. The basic structure and characteristics of the proposed magnet are described first. Next the control system is designed. Luenberger observer, only using gap sensors, is applied to realize zero-power control. The semi-zero-power control with a disturbance observer is proposed to improve the performance, as well as the robustness, of the control system. Finally, the simulation results and corresponding experiments have been presented.

A microstrip-coil integration on superconducting tunnel junctions for X-ray detection

We report the first demonstration of X-ray detection by using a Superconducting Tunnel Junction (STJ) with a microstrip-coil. The STJ was fabricated based on Nb/Al/AlO/sub x//Nb integration process technology using a 2 /spl mu/m design rule. Magnetic field was applied into the STJ by the microstrip-coil to suppress the dc Josephson current instead of the conventional electromagnet. The output waveform was successfully observed by irradiation of 5.9 keV X-ray under a condition of microstrip-coil current of 20 mA at 0.4 K.

Magnetic Field and Isotope Effects on Photochemistry of Chain-Linked Compounds Containing Benzophenone and Hydrogen-Donor Moieties

The magnetic field effects on the decay kinetics for chain-linked triplet biradicals have been observed by the use of a laser photolysis apparatus with a conventional electromagnet and a pulsed magnet. Biradical lifetimes increase steeply to their maxima from the zero field to ca. 2 T. The biradical decay times tend to decrease gradually with further increase of the magnetic field intensity to 14 T. The decreased lifetimes for triplet biradicals can be explained in terms of spin−lattice relaxation due to hyperfine anisotropy and to g tensor anisotropy.

Migration versus Inversion in Electromagnetic Imaging Technique

One of the most challenging problems in electromagnetic (EM) geophysical methods is developing fast and stable methods of imaging inhomogeneous underground structures using EM data. In our previous publications we developed a novel approach to this problem, using EM migration. In this paper we demonstrate that there is a very close connection between the method of EM migration and the solution of the conventional EM inverse problem. Actually, we show that migration is an approximate inversion. It realizes the first iteration in the inversion algorithm, based on the minimization of the residual field energy flow through the profile of observations. This new theoretical result opens a way for formulating a new imaging condition. We compare this new imaging condition with the traditional one, obtained for simplified geoelectrical models of the subsurface structures. This result also leads to the construction of a solution of the inverse EM problem, based on iterative EM migration in the frequency domain, and gradient (or conjugate gradient) search for the optimal geoelectrical model. However, the authors have found that in the framework of this method, even the first iteration, based on the migration of the residual field, generates a reasonable geoelectrical image of the subsurface structure.

Diagnostics of Fluorocarbon Radicals in a Large-area Permanent Magnet Electron Cyclotron Resonance Etching Plasma

Diagnostics of fluorocarbon radicals and fluorine (F) atom species in a size-scaleable large-area permanent magnet electron cyclotron resonance (ECR) etching plasma employing CF4 and C4F8 gases are carried out. Non-intrusive infrared laser diode absorption spectroscopy and actinometric measurement techniques are used in evaluating the performance of the permanent magnet ECR plasma source and in studying the kinetic processes associated with etching plasma chemistry. Successful measurements of the absolute CF and CF2 radical and F atom densities have been achieved. In particular for C4F8 plasma, enhanced CF and CF2 radical densities which afford higher selectivity in the etching of SiO2 on Si are discussed. At a pressure of 0.4 Pa and an input microwave power of 900 W the CF and CF2 radical and F atom densities in C4F8 plasma were 1.7×1013 cm-3, 6.0×1013 cm-3 and 1.5×1013 cm-3, respectively. These results are also discussed in comparison with results for a conventional electromagnet ECR plasma source.

Magnetic multipole cylinders from mould-injection Nd2Fe14B plastic bonded magnets (abstract)

Mould injection Nd2Fe14B magnetic material of density ρ∼4 g/cc and of an energy product (BH)max∼4 MGOe, has been pressed into the form of cylindrical segments in order to investigate the possibility of preparing cylindrical magnetic multipoles which could be used as magnetic gears. The obtained cylindrical bonded magnet segments have a length of 3 cm and an angle width of φ=90° or φ=45°. These segments are easily magnetized along a radial direction at the angle φ/2, using a conventional electromagnet at a magnetic field of 2 T. Subsequently, the opposite magnetized segments are combined and bonded together with ultrasonic technique. The final result of the above procedure is the formation of a magnetic multipole cylinder which could be used as a magnetic gear. Here, except the preparation technique, we report the maximum torque applied versus the magnetization M of the poles and the distance between the gears. The dependence of the applied torque on the rotational frequency is also examined.

Covariances and invariances of the Beltrami-Maxwell postulates

The newly formulated Beltrami-Maxwell postulates (BMP) for complex-valued time-dependent fields and sources have a richer structure than the commonly used Maxwell postulates (MP) for the real-valued time-dependent fields and sources of conventional electromagnetism. In the paper the Lorentz covariance of the BMP is proved and the transformation rules between inertial frames are provided. Furthermore, their scale invariance are explored, both in isotropic and anisotropic settings, and their conjugate invariance delineated in the context of electromagnetism.

A magnetic suspension system with a large angular range

In order to explore and develop technology required for the magnetic suspension of objects over large ranges of orientation, a small-scale laboratory system, the large-angle magnetic suspension test fixture (LAMSTF) has been constructed at NASA Langley Research Center. This apparatus falls into the category of large-gap, actively stabilized magnetic levitation systems. The hardware comprises five conventional electromagnets in a circular arrangement, each driven from a separate bipolar power amplifier. Electromagnet currents are commanded by a digital control system, implemented on a microcomputer, which in turn derives the position and attitude of the suspended element from an infrared optical system. The suspended element is a cylindrical, axially magnetized, permanent magnet core, within an aluminum tube. The element is ‘‘levitated’’ by repulsive forces, with its axis horizontal, 0.1 m above the top plane of the electromagnet conductor. The element is stabilized in five degrees-of-freedom, with rotation about the cylinder axis not controlled. By mechanical rotation of the sensor assembly, the suspended element can be made to undergo a full 360° rotation about the vertical axis. The controller accommodates the changes in magnetic coupling between the electromagnets and the suspended element by real-time adaptation of a decoupling matrix. This report presents a review of the background to the problem of magnetic suspension over large ranges of orientation. Next, the design and operation procedures adopted for LAMSTF, and the system hardware are described. Finally, some performance measurements are shown, together with illustration that the major design objective—the 360° rotation, has been accomplished.

A novel use of superconducting oxides in a non-contact carrier for VLSI plants

A high-Tc superconductor has outstanding intergrain superconductivity and troublesome intergrain electrical conductivity at the same time. But once we consider to utilize the intergrain characteristic only, neglecting the intergrain conductivity, a new world of applied superconductivity is open before us. An yttrium-family class superconductor by the processing technique by which proper sizes and delicate distribution of precipitates are introduced in the material 1 ). The fishing effect showing the stable floating of superconducting oxide materials has its origin in this strong pinning force. Now in a advanced Japanese VLSI plant a magnetically supported non-contact wafer-carrier is used in order to avoid the production of even traces of fine dust made by the friction of the wheels 2–3 ). In this system the controlled attractive force between conventional electro-magnets and an iron guideway is used. The outstanding fishing effect of a strong pinned yttrium-family superconducting oxide processed by the QMG method can be expected to replace electro-magnets. We testfabricated a magnetically suspended non-contact carrier in the same dimension as a VLSI wafer-carrier currently used, with four QMG processed yttrium-family bulk pellets 4 ). The carrier runs at any controlled speed with a load of under 3 kg, with very high stability in the vertical and lateral positions. It was driven by a linear induction motor. The outline of this system and its carrier will be reported as well as the superconducting levitation performance of the carrier.

Permanent magnet sources for extended interaction klystrons

A major part of the bulk and mass of an extended interaction amplifier resides in its magnetic field source. Both can be considerably reduced by application of novel designs made possible by high-energy product permanent magnet materials such as the samarium–cobalts and neodymium–iron–borides. We compare a structure derived from a hemispherical source design (‘‘magic igloo’’) with several more conventional permanent magnet and electromagnet configurations and find that mass reductions of 50% to 80% are often realized when the hemispherical source replaces any of the others. Such reductions afford considerable performance improvement in radars, radios, and jammers, especially in airborne and ballistic devices. Further compaction results from closer packing of field-sensitive instruments afforded by leakage field reduction in the hemispherical source. Other advantages of the latter as well as drawbacks, are discussed.

Electric field gradient sign determination in low magnetic fields perpendicular to the gamma rays in57Fe Mössbauer spectroscopy

The determination, by Mossbauer57Fe spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a “parallel-magnetic-field-to-the-gamma-rays” configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensitics. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example. Mossbauer experimental results obtained at room temperature for natural pyrite (FeS2) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.

Superconducting Magnetic Separators

The fields available with conventional electromagnets are limited to 2 Tesla by the saturation of iron. In addition, the creation of large field volumes is costly in terms of copper, iron and electric power. For these reasons superconducting separator magnets were proposed as early as 1970. This paper deals with the special requirements of cryomagnets in the mineral processing industry, and the relatively slow rate of replacement of conventional magnets. Finally, the impact of the new high‐temperature superconductors is examined briefly.

The Kaluza-Klein theory and four-dimensional spacetime

The conventional electromagnetism, which includes Maxwell's field equations and the Lorentz force relation, does not provide an explanation of well-known electromagnetic phenomena, such as the Aharonov-Bohm interference effect and the Meissner-Ochsenfeld effect in superconductors. In this paper, it is shown that the Kaluza-Klein five-dimensional theory suggests a simple explanation of these effects on a unified basis.

Macroscopic short-time electrodynamics for conductors

In the macroscopic electrodynamics (MED) of good conductors (metals) based on Ohm's law j=σE, the momentum relaxation time τ=σm/ne2 of the electrons limits the application to electromagnetic (EM) processes with characteristic timest≫τ. An interesting physical difficulty occurs in MED since the EM field damping time τR=ɛ/σ of metals is very small compared with the minimum macroscopic time scale, τR≪τ. Consequently, the damping and propagation of EM waves and pulses in good conductors cannot be correctly described within the frame of conventional MED. New hyperbolic EM wave equations with relaxation and memory are proposed, which no longer exhibit the τR≪τ deficiency. The latter is caused by Ohm's law, which breaks down for short-time processes, due to neglect of electron inertia. The advantages of the proposed and the disadvantages of the conventional EM wave equations for good conductors are discussed in applications.

Time‐domain electromagnetic detection of a hidden target

Numerical modeling of the time‐domain electromagnetic (EM) step response of a vertical tabular target hidden beneath a thin conductive overburden reveals that the target’s presence may be detected only during a well‐defined time window. In a situation where the secondary magnetic field is sensed by an airborne system equipped with horizontal coaxial dipoles, a conductance contrast of about ten between the target and the overburden is needed to ensure target detection. This value will, of course, vary with the size and depth of the target and, to a lesser extent, with the geometry of the system. In general, the time at which the window opens is a function of the geometrical parameters of the target, the height of the system, and the conductance of the overburden. For a given target, its width (defined as the ratio of the time of closure to the time of opening) is only a function of the conductance contrast between the target and the overburden. While the target signal is visible, one observes a maximum value of the target‐to‐overburden response ratio. The time at which this occurs is mainly controlled by the conductance of the target. The presence of the overburden causes the target signal to build up gradually before decaying toward zero. However, once the target signal dominates the overburden response, the signal can be approximated by a simple exponential decay over the time range of interest. The time constant of this decay is determined by the size and conductance of the target. Using this model, it is easy to relate the magnetic field step response calculated here to the response observable with a conventional EM system that transmits a primary field pulse of finite duration and detects the time derivative of the secondary magnetic field.

Experimental Facility for Studying MHD Effects in Liquid Metal Cooled Blankets

The capabilities of a facility, brought into service to collect data on magnetohydrodynamic (MHD) effects pertinent to liquid-metal-cooled fusion reactor blankets, are presented. The facility, designed to extend significantly the existing data base on liquid metal MHD, employs eutectic NaK as the working fluid in a room-temperature closed loop. The instrumentation system is capable of collecting detailed data on pressure, voltage, and velocity distributions at any axial position within the bore of a 2 Tesla conventional electromagnet. The axial distribution of the magnetic field can be uniform or varying with either rapid or slow spatial variations. The magnet gap dimensions, for the uniform field of 2T, are 15.3 cm high × 0.76 m wide × 1.83 m long. NaK was circulated in December 1984 and the magnet was energized in March 1985. Shakedown tests in a round pipe test section are currently underway.

Dependence of the anhysteretic magnetization on uniaxial stress in steel

As part of an investigation into the effects of stress on magnetic properties, the stress dependence of the anhysteretic magnetization of three samples of ferromagnetic constructional steel was measured. Measurements were taken using a specially designed apparatus which enabled small samples to be subjected to uniaxial stresses of up to 3.2×108 Pa while held between the pole pieces of a conventional 2T laboratory electromagnet with a pole gap of 70 mm. In each case, the anhysteretic magnetization decreased under compressive stress but increased slightly under tensile stress at low fields. Compared with hysteresis curves, the anhysteretic has a particularly simple form which can be modeled using an equation given previously. The results allowed the stress dependence of three of the four parameters governing hysteresis to be determined.

Low-temperature, high-pressure apparatus for nuclear-magnetic-resonance experiments

A description is given of a liquid-helium cryostat containing a high-pressure NMR probe, suitable for hydrostatic pressures up to 15 kbar. The tail of the cryostat is designed to fit between the poles of a conventional electromagnet. Hydrostatic helium gas pressure is generated by means of a commercially available two-stage gas compressor. The apparatus is designed for performing nuclear-magnetic-resonance (NMR) experiments on samples subjected to pressure, in a temperature range from 2 to 100 K.

Magnetic enrichment of antibody-secreting cells

Amino acid polymer antigens have been covalently coupled to sheep erythrocytes (SRBC) and these have been used in the high gradient magnetic separation (HGMS) technique to enrich murine lymph node cells which had specific receptors for antigen. The method was rapid and provided excellent cell recovery including the fraction retained on the HGMS column. The system could be operated to enrich preformed rosettes, or as an affinity column when preloaded with antigen-coupled SRBC. A 10-fold enrichment of plaque-forming cells was observed in either mode. The HGMS system employed a conventional electromagnet and the fractionation procedure required about 30 min for a sample of up to 10 8 cells.

Classical Derivation of the London Equations

The London equations, which were proposed as restrictions to conventional classical electromagnetism in order to explain the Meissner-Ochsenfeld effect in superconductors, are derived from familiar classical action integrals. The equations of motion, from which the London equations follow, should apply to some collisionless plasmas. Space and thermonuclear applications are timely and significant.