Effect Of Mutual Inductance Research Articles

Parallel imaging methods for phased array MRI*

Abstract Two parallel methods for magnetic resonance imaging (MRI) using radiofrequency (RF) phased array surface coils, named spatial local Fourier encoding (SLFE) and spatial RF encoding (SRFE), are presented. The MR signals are acquired from separate channels across the coils, each of which covers a sub-FOV (field-of-view) in a parallel fashion, and the acquired data are combined to form an image of entire FOV. These two parallel encoding techniques can accelerate MR imaging greatly, yet associated artifact may appear, although the SLFE is an effective image reconstruction method which can reduce the localized artifact in some degrees. By the SRFE, RF coil array can be utilized for spatial encoding through a specialized coil design. The images are acquired in a snapshot with a high signal-to-noise ratio (SNR) without the costly gradient system, resulting in great saving of cost. Both mutual induction and aliasing effect of adjacent coils are critical to the success of SRFE. The strategies of inverse so...

A high-torque low-speed multiphase brushless machine-a perspective application for electric vehicles

This paper presents the design, analysis, simulation, and modeling of a high-torque low-speed multiphase permanent-magnet brushless; machine. The machine fits an in-wheel motor arrangement to be used for electric vehicle applications. This paper presents issues regarding the high-level modeling comprised of a transient model in conjunction with their corresponding experimental evaluation. Analysis was made to combine the modeling efforts with the expected behavior concerned with mutual inductance and armature reaction effects, so as to have realistic simulation results verified by the experimental setup. Comprehensive experimental results corroborate the work.

SQUID microscope read-out on a Josephson junction array

LTC Josephson junction arrays (JJA) have recently gained interest as a model for the study of magnetization in superconductor materials. The presence of paramagnetic Meissner effect in such devices when field-cooled makes them an excellent candidate to discriminate between the different explanations given for such phenomenon. On the other hand, the understanding of the JJA physics is not simple due to the interplay between the non-linear behaviour of Josephson devices and the mutual induction effects in large JJA. The use of a SQUID microscope (SSM) to catch the magnetic image of the array is a distinctive feature of the experiment. So a study of SQUID read-out based on the actual JJA magnetic behaviour is needed in order to have a correct picture of what is going on. In this paper, using a simple way to reconstruct the complex array far-field viewed by the SQUID, we study how the flux read-out is dependent on array resolution, distance, tilting and noise for the typical situations in which arrays are found.This paper was presented at the 8th International Superconductive Electronics Conference, Osaka, Japan, 19–22 June 2001

Effect of mutual inductance on the pulsed current amplification of magnetic flux compressors

The reusable linear magnetic flux compressor is an ideal pulsed power supply for the electric gun. Based on the theoretical analysis of the model of the reusable linear magnetic flux compressor, which was completed by the authors, it is found that the pulse transformer not only can extend the application field of this flux compressor, but also can increase the current amplification. In order to verify this result, the authors used the computer code RMFC-I to perform some numerical experiments. The results of these numerical experiments show the same conclusion.

Mutual inductance effects in rf driven planar Josephson junctions arrays

In this paper we investigate the behavior of moderate size two-dimensional classical arrays of Josephson junctions in presence of an external oscillating field. We have included in the model the effects due to mutual inductance terms, and we have employed an explicit set of differential equations. We have found that the discretization parameter βL - i.e. the coupling term due to the inductance of the loops - is the most important parameter to determine the height of the Shapiro steps for a given amplitude and frequency of the rf-bias. The amplitude of the Shapiro steps in the case of zero frustration as a function of the coupling term shows a remarkable minimum for intermediate values when we retain all terms of the full model with mutual inductances, while the limits for very large and very small values of βL they are the same of the single Josephson junction. For the case of frustration 1/2 the Shapiro step becomes smaller in the rigid limit (i.e., small βL as expected for the XY model, and tends to the limit value of the single junctions for the decoupled case (i.e., large βL).

Simulation of a Nonideal Saddle Coil on Toroidally Symmetrical Magnetic Confinement Experiments

A method for modeling the time-varying magnetic geometry in a low-aspect-ratio tokamak is developed. The model includes mutual inductance effects of an arbitrarily shaped (toroidally symmetric) conducting shell, poloidal field (PF) coils, a saddle coil with finite gap resistance, and a single element, distributed plasma current. The plasma current distribution is specified using EFIT results and remains unchanged during the simulation, while the magnitude of the plasma current is ramped up linearly over time. The resulting simulation code is used to predict power supply requirements and tracking capabilities of an arbitrarily chosen feedback mechanism employed to operate the PF coils of the tokamak.

High Temperature Superconducting Microwave Filters

The design philosophy of high temperature superconducting high Q filter, is discussed. The special design considerations associated with HTS thinfilms such as the effects of kinetic inductance and mutual inductance, film thickness effects, power handling capability, interfacing and packaging techniques etc are discussed. Material selection for the substrate, and HTSC thinfilm fabrication techniques are addressed. Taking the above considerations into account, high Q microwave filters are designed and analyzed. Experimental results of a C-band filter (1% BW) designed on MgO substrate using YBa2Cu3O7-5 thinfilm are presented.

Dynamical Induction ofs-Wave Component ind-Wave Superconductor Driven by Thermal Fluctuations

We investigated the mutual induction effects between the d-wave and the s-wave components of order parameters due to superconducting fluctuation above the critical temperatures and calculated its contributions to paraconductivity and excess Hall conductivity based on the two-component stochastic TDGL equation. It is shown that the coupling of two components increases paraconductivity while it decreases excess Hall conductivity compared to the cases when each component fluctuates independently. We also found the singular behavior in the paraconductivity and the excess Hall conductivity dependence on the coupling parameter which is consistent with the natural restriction among the coefficients of gradient terms.

Quantization and Squeezed State of Two L-C Circuits with Mutual-Inductance

It is pointed out that the quantum mechanical Hamiltonian of two L-C circuits with mutual-inductance is equivalent to a pair of harmonic oscillators with a kinetic coupling term. We then diagonalize the Hamiltonian. It is shown that instantaneously switching on the external sources may result in a two-mode squeezed state of the system, which actually arises from the effect of mutual-inductance. The quantum fluctuation for the case of l1c1 = l2c2 is analysed and it is found that the current fluctuation in the circuits increases with the increment of the mutual-inductance.

Active cancellation of mutual inductance in split-coil thin-film heads

The consequences of using split-coil thin-film inductive heads for the recording process were investigated. The heads studied have two separate coils (the head is a four-terminal device); this allows the number of turns in the write and read process to be optimized independently. Unfortunately, at high frequencies the effect of mutual inductance between the coils offsets the potential reduction in the write inductance. The mutual inductance was characterized using both recording and impedance measurements. We demonstrate a novel, active technique for reducing the effect of the mutual inductance.

Three-dimensional Josephson-junction arrays: Static magnetic response

In this work we present a simple three-dimensional Josephson-junction array model: a cube with twelve junctions, one on each edge. The low-field magnetic response of the system is studied numerically for arbitrary directions of the applied field. In this model the magnetic energy of the circulating currents is taken into account by introducing an effective mutual inductance matrix. The lower threshold field for flux penetration is determined in a closed analytic form for field directions perpendicular to one cube side. {copyright} {ital 1998} {ital The American Physical Society}

Theory and application of array coils in MR spectroscopy.

The theory and application of array coils are reviewed in the context of phased array spectroscopy. The optimization of the signal-to-noise ratio from an array of coils is developed by considering the efficiency of a phased array transmit coil. This approach avoids the need to consider noise correlation, and should be useful in future considerations of transmit phased array coils for MR spectroscopy. Methods to characterize array coil performance, including fields and coupling are briefly summarized, along with methods to minimize the effects of mutual inductance. The signal-to-noise advantages of array coils over single coils are examined for both planar and cylindrical arrays. Numerical simulations of planar arrays of 2 x 2, 4 x 4 and 8 x 8 elements and constant overall dimension are compared to a single coil of the same size. The results demonstrate a significant improvement in sensitivity near the array coil. Although the benefits of the array decrease as a function of distance from the array, the array sensitivity never drops below that of a single coil with the same overall dimensions, or that of a single element of the array. Similar results are obtained for a sixteen element cylindrical array, which is compared to a standard quadrature birdcage coil using both computational methods and phantom measurements. The phased array techniques reviewed are demonstrated with proton spectroscopic images of the brain.

The Interpretation of Geomagnetic Field Reversal on the Basis of Fluctuation Growth by Using Disk Dynamo Model.

Based on the viewpoint of fluctuation growth, we analyze and discuss the geomagnetic field reversal, focusing on a three-disk dynamo model, mainly on the effect of mutual inductance on dynamic behaviors. If mutual inductance is large, which means strong interaction between neighboring disks and their associated circuits, then a very slight fluctuation of electric current is found to be greatly enhanced after a short incubation time. On the contrary, after a long incubation time, fluctuation growth is very slow when mutual inductance is small. Therefore the degree of interaction is related to the length of incubation time: the stronger the interaction, the shorter incubation time. The analogy between the disk dynamos and the geomagnetic field reversal patterns implies slight fluctuations are greatly enhanced during the period for the past 25 Ma, whereas fluctuation growth is very slow during the period of the Cretaceous Superchron, implying that mutual inductance is dependent on time. Hence, disk dynamo calculations including time dependence of mutual inductance are found to explain geomagnetic field reversal pattern qualitatively. From the mathematical viewpoint, numerical solutions for time dependent mutual inductance is found to be obtained by frequency modulation (FM) over those for time independent mutual inductance.

Mutual-inductance effects of an input inductor on a three-phase switch-mode converter

The control parameters of three-phase AC-to-DC switch-mode converters are usually related to the phase inductance of the input inductor. Previously the mutual inductances of the input inductor have been formerly neglected. A control scheme including the influences of the mutual inductances is presented to correct the mis-estimation of the control parameters. A prototype of a 4-5 kW indirect current-controlled AC-to-DC converter is implemented to verify this proposed scheme. The theoretical analysis is finally verified from the simulation results and the testing data.

Aharonov-Bohm effect induced by mutual inductance for an array of mesoscopic rings.

The effect of mutual inductance on the persistent currents in N mesoscopic rings placed periodically on a plane is investigated. The persistent currents for the situations with mutual inductance between the nearest-neighbor rings are calculaed in detail. We find that while the self-inductance suppresses the persistent current, the effect of the mutual inductance is to enhance it. For example, for a metal ring (Au or Cu) of length ${\mathit{L}}_{0}$=1 \ensuremath{\mu}m and cross-section A=0.02\ifmmode\times\else\texttimes\fi{}0.02 \ensuremath{\mu}${\mathrm{m}}^{2}$, the persistent current due to the self-inductance is ${\mathit{I}}_{\mathit{L}}$=0.2${\mathit{I}}_{0}$ where ${\mathit{I}}_{0}$ is the persistent current without the self-inductance. For a pair of rings, the contribution of the persistent current due to the mutual inductance is about 10%. The results can be understood as entirely due to self-consistency of the equilibrium properties in the nanostructure.

Theoretical analysis of a relaxation oscillation SQUID

Describes the theoretical analysis of oscillation modes produced in a relaxation oscillation SQUID (ROS). It is made clear what kind of oscillation modes are produced in ROS in relation to circuit parameters of the SQUID from the viewpoint of relaxation oscillation. Emphasis is placed on mapping of oscillation modes to design the ROS. Furthermore, the effect of mutual inductance between the load impedance and SQUID to the oscillation frequency is analyzed. >

Simplified equations for the interaction of nearly parallel vortex filaments

New simplified asymptotic equations for the interaction of nearly parallel vortex filaments are derived and analysed here. The simplified equations retain the important physical effects of linearized local self-induction and nonlinear potential vortex interaction among different vortices but neglect other non-local effects of self-stretching and mutual induction. These equations are derived systematically in a suitable distinguished asymptotic limit from the Navier–Stokes equations. The general Hamiltonian formalism and conserved quantities for the simplified equations are developed here. Properties of these asymptotic equations for the important special case involving nearly parallel pairs of interacting filaments are developed in detail. In particular, strong evidence is presented that for any filament pair with a negative circulation ratio, there is finite-time collapse in a self-similar fashion independent of the perturbation but with a structure depending on the circulation ratio. On the other hand, strong evidence is presented that no finite-time collapse is possible for perturbations of a filament pair with a positive circulation ratio. The present theory is also compared and contrasted with earlier linear and nonlinear stability analyses for pairs of filaments.

Analysis of Magnetic Shielding Effects for Thin-Film Inductors

Issues related to magnetic shielding effects are discussed for inner-coil type thin-film inductors with closed magnetic circuits. The relationship between magnetic shielding effects, mutual inductance, and proximity effects are investigated using the finite integral equation method. The results show that obvious shielding effects occur in the inductors and that the mutual inductance is not influenced by the shielding effects.

磁気シールド効果を考慮した薄膜インダクタの特性解析

Issues related to magnetic shielding effects are discussed for inner-coil-type thin-film inductors with closed magnetic circuits. The relationship between magnetic shielding effects, mutual inductance, and proximity effects is investigated by using the finite integral equation method. The results show that obvious shielding effects occur in the inductors and that the mutual inductance is not influenced by the shielding effects.

An asymptotic theory for the nonlinear instability of antiparallel pairs of vortex filaments

Simplified asymptotic equations describing the nonlinear dynamics of perturbed pairs of parallel vortex filaments are derived and analyzed here. The derivations are general enough to allow for vortices of unequal strength, but emphasis here is on the antiparallel vortex pair. The simplified asymptotic equations account for both the internal effects of self-induction and self-stretching for each filament and also the external effects of mutual induction that lead to a nontrivial coupling of the perturbations of the two filaments. When these nonlinear equations are linearized at the unperturbed filament pair, the linearized stability theory of Crow [AIAA J. 8, 2172 (1970)] is recovered in a systematic fashion. The asymptotic equations are derived in a novel singular limit at high Reynolds numbers through assumptions similar to the authors’ recent theories [Physica D 49, 323 (1991); ibid. 53, 267 (1991); Phys. Fluids A 4, 2271 (1992)] for the dynamics of a single perturbed vortex filament. Through the Hasimoto transform [J. Fluid Mech. 51, 477 (1972)], these equations become two coupled perturbed nonlinear Schrödinger equations for a pair of filament functions. A series of numerical solutions of the asymptotic equations exhibits several new phenomena in the nonlinear instability of pairs of antiparallel vortex filaments.