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Magnetic Field Components (magnetic + field_component)

Distribution by Scientific Domains
Physics and Astronomy40%
Engineering40%

Selected Abstracts

Negative permeability around 630 nm in nanofabricated vertical meander metamaterials

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2007
Heinz Schweizer
Abstract We demonstrate a new design of a 3-dimensional meander structure that exhibits negative permeability with a broad bandwidth between 550 nm and 665 nm. The structural design allows for full coupling of the magnetic field component at all angles of incidence. We compare our structure with other metamaterial structures with respect to the series capacitance contributions of the different metamaterials. The investigation of optical metamaterials is carried out combining transmission line analysis with numerical simulations of Maxwell's equations. The analysis is demonstrated for typical split ring structures and the novel 3D meander metamaterial structures. Comparing the resulting scattering parameter spectra as well as the retrieved effective material parameters, we find that transmission line description remains valid for metamaterials at optical frequencies. We find in addition that the longitudinal capacitance is the decisive parameter to achieve negative permeability with a broad bandwidth at optical frequencies. For experimental verification we manufactured split-ring resonator structures and meander metamaterial structures with linewidths down to 30 nm, element sizes down to 100 nm, and periods between 200 nm and 350 nm. For meander metamaterial structures a permeability value of ,1 was achieved within a bandwidth of 50 nm centered at 630 nm. The largest absolute value of ,4.5 was achieved at 650 nm. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The feasibility of electromagnetic gradiometer measurements

GEOPHYSICAL PROSPECTING, Issue 3 2001
Daniel Sattel
The quantities measured in transient electromagnetic (TEM) surveys are usually either magnetic field components or their time derivatives. Alternatively it might be advantageous to measure the spatial derivatives of these quantities. Such gradiometer measurements are expected to have lower noise levels due to the negative interference of ambient noise recorded by the two receiver coils. Error propagation models are used to compare quantitatively the noise sensitivities of conventional and gradiometer TEM data. To achieve this, eigenvalue decomposition is applied on synthetic data to derive the parameter uncertainties of layered-earth models. The results indicate that near-surface gradient measurements give a superior definition of the shallow conductivity structure, provided noise levels are 20,40 times smaller than those recorded by conventional EM instruments. For a fixed-wing towed-bird gradiometer system to be feasible, a noise reduction factor of at least 50,100 is required. One field test showed that noise reduction factors in excess of 60 are achievable with gradiometer measurements. However, other collected data indicate that the effectiveness of noise reduction can be hampered by the spatial variability of noise such as that encountered in built-up areas. Synthetic data calculated for a vertical plate model confirm the limited depth of detection of vertical gradient data but also indicate some spatial derivatives which offer better lateral resolution than conventional EM data. This high sensitivity to the near-surface conductivity structure suggests the application of EM gradiometers in areas such as environmental and archaeological mapping. [source]

Implicit symmetrized streamfunction formulations of magnetohydrodynamics

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008
K. S. Kang
Abstract We apply the finite element method to the classic tilt instability problem of two-dimensional, incompressible magnetohydrodynamics, using a streamfunction approach to enforce the divergence-free conditions on the magnetic and velocity fields. We compare two formulations of the governing equations, the standard one based on streamfunctions and a hybrid formulation with velocities and magnetic field components. We use a finite element discretization on unstructured meshes and an implicit time discretization scheme. We use the PETSc library with index sets for parallelization. To solve the nonlinear problems on each time step, we compare two nonlinear Gauss-Seidel-type methods and Newton's method with several time-step sizes. We use GMRES in PETSc with multigrid preconditioning to solve the linear subproblems within the nonlinear solvers. We also study the scalability of this simulation on a cluster. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Modelling of lossy curved surfaces in the 3-D frequency-domain finite-difference methods

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5 2006
Riku M. Mäkinen
Abstract A conformal first-order or Leontovic surface-impedance boundary condition (SIBC) for the modelling of fully three-dimensional (3-D) lossy curved surfaces in a Cartesian grid is presented for the frequency-domain finite-difference (FD) methods. The impedance boundary condition is applied to auxiliary tangential electric and magnetic field components defined at the curved surface. The auxiliary components are subsequently eliminated from the formulation resulting in a modification of the local permeability value at boundary cells, allowing the curved 3-D surface to be described in terms of Cartesian grid components. The proposed formulation can be applied to model skin-effect loss in time-harmonic driven problems. In addition, the impedance matrix can be used as a post-processor for the eigenmode solver to calculate the wall loss. The validity of the proposed model is evaluated by investigating the quality factors of cylindrical and spherical cavity resonators. The results are compared with analytic solutions and numerical reference data calculated with the commercial software package CST Microwave StudioÔ (MWS). The convergence rate of the results is shown to be of second-order for smooth curved metal surfaces. The overall accuracy of the approach is comparable to that of CST MWSÔ. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Tayler instability with Hall effect in young neutron stars

ASTRONOMISCHE NACHRICHTEN, Issue 1 2009
G. Rüdiger
Abstract Collapse calculations indicate that the hot young neutron stars rotate differentially so that strong toroidal magnetic field components should exist in the outer shell where also the Hall effect appears to be important when the Hall parameter = ,B, exceeds unity. The amplitudes of the induced toroidal magnetic fields are limited by the current-induced Tayler instability. An important characteristics of the Hall effect is its distinct dependence on the sign of the magnetic field. We find for fast rotation that positive (negative) Hall parameters essentially reduce (increase) the stability domain. It is thus concluded that the toroidal field belts in young neutron stars induced by their differential rotation should have different amplitudes in both hemispheres which later are frozen in. Due to the effect of magnetic suppression of the heat conductivity also the brightness of the two hemispheres should be different. As a possible example for our scenario the isolated neutron star RBS 1223 is considered which has been found to exhibit different X-ray brightness at both hemispheres (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]