Metal Annulus Research Articles

Resonances and circuit theory for the interaction of metallic disks and annuli with an electromagnetic field.

To understand the nature of the electromagnetic resonances of finite metallic surfaces, we formulate a rigorous and rapidly convergent circuit theory for the interaction of a metallic disk and a metallic annulus with an electromagnetic field. Expressions for the current induced and the resonance condition are derived. A new understanding of the nature of the resonances is obtained. For half of the resonances we find a divergent electric field at the edge of the disk, even though it is smooth in shape. For the disk, we compare with previous results using vector spheroidal wave functions and found good agreement for the resonance condition. Our approach can be generalized to other finite surfaces.

Theoretical analysis on the role of annular metallic shapes for microwave processing of food dielectric cylinders with various irradiations

A theoretical analysis has been carried out to analyze efficient microwave assisted heating processes of food cylinders with various shapes of metallic annuli in presence of lateral and radial irradiation. Lateral irradiation represents the sample incident at one direction with source at infinity whereas the radial irradiation represents the situation where the sample is incident with microwave radiations from co-axial cylindrical cavity at infinity. A generic finite element method has been used to obtain computational mesh for all shapes of metallic annulus and Galerkin finite element method has been used to solve electric field and energy balance equations. Influence of metallic annulus has been illustrated for three representative sample lengths or regimes (I, II and III) as a function of wave number ( N w ). Sample radius with regime I is smallest and largest sample radius corresponds to regime III. In general, power absorption due to lateral irradiation is larger for regime I whereas identical power with lateral or radial irradiation or larger power absorption with radial irradiation corresponds to regime II in absence of metallic annulus. The metallic annuli are found to enhance power absorption or heating rate for specific aspect ratios of both bread and beef samples. The aspect ratios are defined as the ratio of the dimension of metallic annulus and outer radius of the food sample. Lateral irradiation is found to give larger heating rates especially for regimes II and III for bread samples (low dielectric loss), but radial irradiation gives smaller degree of thermal runaway. On the other hand, radial irradiation gives significantly large heating rates with minimal thermal runaway for beef samples (high dielectric loss) with all regimes. It is interesting to observe that the metallic annuli enhance two to three times microwave power for beef samples involving regimes II and III. Various shapes of metallic annuli are also found to play dominant role either to focus or to optimize heating effects.

Efficient processing of oil–water emulsions confined within 2D cylinders with various microwave irradiations: Role of metallic annulus

Abstract Extensive studies have been carried out to investigate the role of metallic annulus on efficient microwave processing of oil–water emulsions confined within 2D cylinders in the presence of lateral/radial irradiations. A preliminary study has been carried out via average power within a sample vs. sample diameter to estimate microwave power absorptions for various o/w and w/o emulsions with specific fractions of the dispersed phase (ϕ) in the absence of metallic annulus. Based on those studies, various regimes (sample dimension) have been identified for each emulsion (o/w or w/o) based on appropriate length scales. Two types of metallic annular configurations have been considered such as circular and square annuli for further analysis via average power vs. aspect ratio (a) distribution for each regime. Based on that study, suitable aspect ratios have been chosen to carry out detailed analysis on spatial power and temperature distributions for each regime with metallic annuli. Finally, optimal heating strategies have been recommended based on two significant factors such as ‘large heating rate’ with ‘minimal thermal runaway’ for various regimes of o/w and w/o emulsions. It is observed that average power absorptions show greater intensification due to metallic annulus for most of the regimes of o/w emulsions than that for corresponding regimes of w/o emulsions due to lateral and/or radial irradiations. However, in general, for regimes with smaller diameters (for both o/w and w/o samples) radial irradiation is favored, whereas for large regimes, lateral irradiation is favored as the optimal heating strategies.

Design of a giant magnetostrictive motor driven by elliptical motion

Recently, rare earth giant magnetostrictive materials (GMM) have drawn a lot of attention. Their applications are developing quickly owing to their unique features, especially at room temperature, such as giant strain coefficient, efficient electric(magnetic)-mechanical transformation ability, and so on. In this paper, a design model for magnetic and mechanical energy coupling and transformation, so-called coupled field iteration, is firstly described through the finite element method (FEM), including the calculation of magnetostrictive force, which is analyzed through the local application of the virtual work principle. Then a prototype of single GMM actuator is designed and comparison between the calculated deformations and experiment measurements is exhibited. Based on these results, a new motor is designed and fabricated by combining two single actuators with a metallic annulus. The metallic annulus is vibrated in elliptical motion mode, which is driven by the two actuators with specific input current pattern. Finally the elliptical motion is validated by the experiments.

Magnetorotational Instability in Liquid Metal Couette Flow

Despite the importance of the magnetorotational instability (MRI) as a fundamental mechanism for angular momentum transport in magnetized accretion disks, it has yet to be demonstrated in the laboratory. A liquid sodium αω dynamo experiment at the New Mexico Institute of Mining and Technology provides an ideal environment to study the MRI in a rotating metal annulus (Couette flow). A local stability analysis is performed as a function of shear, magnetic field strength, magnetic Reynolds number, and turbulent Prandtl number. The latter takes into account the minimum turbulence induced by the formation of an Ekman layer against the rigidly rotating end walls of a cylindrical vessel. Stability conditions are presented, and unstable conditions for the sodium experiment are compared with another proposed MRI experiment with liquid gallium. Because of the relatively large magnetic Reynolds number achievable in the sodium experiment, it should be possible to observe the excitation of the MRI for a wide range of wavenumbers and to further observe the transition to the turbulent state.

Imaging micro-well proportional counters fabricated with masked UV laser ablation

The micro-well detector is a gas-proportional counter similar to the CAT (Bartol et al., J. Phys. III 6 (1996) 337) and WELL detectors (Bellazzini et al., Nucl. Instr. and Meth. A 423 (1999) 125). The micro-well is a cylindrical hole formed in the polymer substrate of commercially fabricated copper-clad flexible printed circuit board by UV laser ablation. The micro-wells are drilled at GSFC's UV laser-ablation facility. The cathode is a metal annulus that surrounds the opening of the well. The anode is a metal pad that fills the bottom of the well. Advantages of this topology include intrinsic two-dimensional sensing, thick robust electrodes, and large localized image charge on the cathodes. We have fabricated 5 cm×5 cm micro-well detectors with segmented anodes (1-d) and with both anodes and cathodes segmented (2-d), and have demonstrated: • stable, proportional operation at gas gains in excess of 30,000 in Ar- and Xe-based gases; • FWHM energy resolution of 20% at 6 keV in P-10; • preliminary 1-d spatial resolution of ⩽150 μm (rms) in P-10; and • the capability of MWDs to produce 2-dimensional images. We report on the design, fabrication, and testing of 1-d, 2-d, and pixelized micro-well detectors.

Magnetorotational instability in a rotating liquid metal annulus

Although the magnetorotational instability (MRI) has been widely accepted as a powerful accretion mechanism in magnetized accretion discs, it has not been realized in the laboratory. The possibility of studying MRI in a rotating liquid metal annulus (Couette flow) is explored by local and global stability analysis. Stability diagrams are drawn in dimensionless parameters, and also in terms of the angular velocities at the inner and outer cylinders. It is shown that MRI can be triggered in a moderately rapidly rotating table-top apparatus, using easy-to-handle metals such as gallium. Practical issues of this proposed experiment are discussed.

Facial nerve antidromic recordings in patients with Bell's palsy.

Antidromic facial nerve action potentials have been recorded noninvasively from the tympanic membrane (TM) of patients with Bell's palsy. A standardized approach has been developed in normal subjects that involves differential recording between the TM and adjacent canal wall. A metal annulus on the tip of an ear speculum served as the reference electrode. The speculum was held in place by an adjustable headband. A conductive sponge electrode inserted through the speculum served as the active TM electrode. In clinical trials, nerve potentials recorded from the paralyzed side were abnormal in all patients tested, indicating that nerve pathology could be monitored with this technique. Abnormalities were evident at the first test, within the first day of paralysis for some patients, and well in advance of any abnormality in the electroneuronography (ENoG) response. There appeared to be a relationship between specific waveform abnormalities (e.g., increased peak latency, waveform temporal dispersion, decreased area) and the tendency for a patient to recover from paralysis. These observations suggest that the technique described could serve as a means for early prognosis, at a stage in which nerve damage could still be effectively treated.

In-Plane Torsion Testing of Sheet Metal

In this paper, the ‘in-plane’ torsion testing of sheet metal is examined. The test itself was first proposed by Marciniak in order to ascertain the work hardening behaviour and fracture strain of sheet metals. In the original work, the analysis was based on the assumption that the material was rigid-work hardening. The present work attempts a more rigorous solution, assuming the material to be elastic-work hardening. A finite-element approximation is employed to calculate the stress and strain distribution across the sheet metal annulus at various stages in the deformation process. A comparison is made between the results from the finite-element method and those based on a rigid-work hardening material. For certain annulus geometries, excellent agreement is obtained between both sets of results.

The flow of polycrystalline lead under simple shear at higher temperatures

The flow of polycrystalline lead has been investigated in detail by the method of simple shear, as used by Andrade & Jolliffe, at temperatures from 27 to 80 °C and also at 150 °C. Pre­liminary work on the variation of stable grain size with temperatures has shown that at 150 °C there are very few grains to the thickness of the metal annulus subject to shear, which is why this temperature is distinguished from the others. The range of temperature of the detailed measurements appears to be one of particular significance. The t 1/2 formula followed, as strain increases, by a t 1/3 formula, which has been shown to represent in detail the transient flow at 27 °C, has proved to be valid at all the higher temperatures and the laws governing the variation of the constants of the formulae with stress and temperature have been determined. At temperatures approaching 80 °C the flow so expressed is accompanied by a small flow linear with time, the laws of which have been determined. This linear flow has been traced to grain boundary slip, which is not involved in the t 1/2 and t 1/3 flow. Particular attention has been paid to stage III of the flow, in which the metal has the properties of a non-Newtonian fluid. The constant rate of flow has been expressed in terms of a function of the velocity and temperature which is linear with stress. It has been shown that at a certain transition stress the slope of the line changes abruptly. This transition stress is a simple function of the temperature. Photomicrographs showing the deformation of the surface grains, which with the method employed, but not with the method of tensile stress, is held to be typical of the behaviour of internal grains, have thrown some light on the processes associated with the various stages of flow. An intermittent grain boundary migration has been established at higher temperatures. The results obtained by the method of simple shear are compared with the results of tests carried out by the usual method of tensile stress with rods or wires, from which they differ in certain significant respects, such as the conditions leading to recrystallization and the accompanying effects.