ELECTROMAGNETIC FIELDS IN AN N‐LAYER ANISOTROPIC HALF‐SPACE

Geophysics ◽  
1967 ◽  
Vol 32 (4) ◽  
pp. 668-677 ◽  
Author(s):  
Douglas P. O’Brien ◽  
H. F. Morrison
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Plane Wave ◽  
Half Space ◽  
Electric Fields ◽  
Field Measurements ◽  
Large Scatter ◽  
Tensor Impedance ◽  
The Magnetic Field ◽  
Made In

From Maxwell’s equations and Ohm’s law for a horizontally anisotropic medium, it may be shown that two independent plane wave modes propagate perpendicular to the plane of the anisotropy. Boundary conditions at the interfaces in an n‐layered model permit the calculation, through successive matrix multiplications, of the fields at the surface in terms of the fields propagated into the basal infinite half space. Specifying the magnetic field at the surface allows the calculation of the resultant electric fields, and the calculation of the entries of a tensor impedance relationship. These calculations have been programmed for the digital computer and an interpretation of impedances obtained from field measurements may thus be made in terms of the anisotropic layering. In addition, apparent resistivities in orthogonal directions have been calculated for specific models and compared to experimental data. It is apparent that the large scatter of observed resistivities can be caused by small changes in the polarization of the magnetic field.

scholarly journals Discovery of weak magnetic fields in four DZ white dwarfs in the local 20 pc volume

2019 ◽  
Vol 630 ◽  
pp. A65 ◽  
Author(s):  
S. Bagnulo ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Measurements ◽  
Weak Magnetic Fields ◽  
Polluted Atmosphere ◽  
Highly Sensitive ◽  
Cool White Dwarfs ◽  
The Magnetic Field ◽  
Made In

We report the discovery of weak magnetic fields in three white dwarfs within the local 20 pc volume (WD 0816−310, WD 1009−184, and WD 1532+129), and we confirm the magnetic nature of a fourth star (WD 2138−332) in which we had previously detected a field at a 3σ level. The spectra of all these white dwarfs are characterised by the presence of metal lines and lack of H and He lines, that is, they belong to the spectral class DZ. The polarisation signal of the Ca II H+K lines of WD 1009−184 is particularly spectacular, with an amplitude of 20% that is due to the presence of a magnetic field with an average line-of-sight component of 40 kG. We have thus established that at least 40% of the known DZ white dwarfs with an He-rich atmosphere contained in the 20 pc volume have a magnetic field, while further observations are needed to establish whether the remaining DZ white dwarfs in the same volume are magnetic or not. Metal lines in the spectra of DZ white dwarfs are thought to have originated by accretion from rocky debris, and it might be argued that a link exists between metal accretion and higher occurrence of magnetism. However, we are not able to distinguish whether the magnetic field and the presence of a polluted atmosphere have a common origin, or if it is the presence of metal lines that allows us to detect a higher frequency of magnetic fields in cool white dwarfs, which would otherwise have featureless spectra. We argue that the new highly sensitive longitudinal field measurements that we have made in recent years are consistent with the idea that the magnetic field appears more frequently in older than in younger white dwarfs.

scholarly journals Time development of electric fields and currents in space plasmas

2006 ◽  
Vol 24 (3) ◽  
pp. 1137-1143
Author(s):  
A. T. Y. Lui
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Electric Fields ◽  
Time Development ◽  
Space Plasmas ◽  
Simplifying Assumptions ◽  
Electric Fields And Currents ◽  
Definition Of ◽  
The Magnetic Field ◽  
Made In

Abstract. Two different approaches, referred to as Bu and Ej, can be used to examine the time development of electric fields and currents in space plasmas based on the fundamental laws of physics. From the Bu approach, the required equation involves the generalized Ohm's law with some simplifying assumptions. From the Ej approach, the required equation can be derived from the equation of particle motion, coupled self-consistently with Maxwell's equation, and the definition of electric current density. Recently, some strong statements against the Ej approach have been made. In this paper, we evaluate these statements by discussing (1) some limitations of the Bu approach in solving the time development of electric fields and currents, (2) the procedure in calculating self-consistently the time development of the electric current in space plasmas without taking the curl of the magnetic field in some cases, and (3) the dependency of the time development of magnetic field on electric current. It is concluded that the Ej approach can be useful to understand some magnetospheric problems. In particular, statements about the change of electric current are valid theoretical explanations of change in magnetic field during substorms.

Transient behaviour of magnetic and electric fields at any height above an atmospheric duct

2008 ◽  
Vol 86 (9) ◽  
pp. 1103-1107
Author(s):  
O M Abo-Seida ◽  
R J Pirjola
Keyword(s):  
Magnetic Field ◽  
Wave Equation ◽  
Half Space ◽  
Electric Fields ◽  
Transient Behavior ◽  
Transient Behaviour ◽  
Atmospheric Duct ◽  
Vertical Magnetic Dipole ◽  
Spatial Coordinates ◽  
The Magnetic Field

We model the atmosphere by a surface duct underlying a half-space. A derivation is given for the electromagnetic field created by a vertical magnetic dipole, in the half-space above the duct, with an arbitrary time-varying moment. The method used for the solution is essentially based on the application of two functional transforms. Starting from the wave equation for the magnetic field and applying a Laplace transform in time, we obtain a two-dimensional Fourier transform in the horizontal spatial coordinates leading to an integral representation of the solution of the wave equation in the transform space. The transient behavior of the magnetic-field strength at any distance above the duct is determined.PACS Nos.: 41.20Jb, 42.25Bs, 42.25Gy

scholarly journals Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

2016 ◽  
Vol 34 (1) ◽  
pp. 55-65 ◽  
Author(s):  
A. D. M. Walker ◽  
G. J. Sofko
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Electric Field ◽  
Electric Fields ◽  
Magnetic Field Line ◽  
Geomagnetic Field ◽  
Geomagnetic Field Models ◽  
Spatial Derivatives ◽  
Field Lines ◽  
The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

scholarly journals Scattering of field-aligned beam ions upstream of Earth's bow shock

2007 ◽  
Vol 25 (3) ◽  
pp. 785-799 ◽  
Author(s):  
A. Kis ◽  
M. Scholer ◽  
B. Klecker ◽  
H. Kucharek ◽  
E. A. Lucek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Measurements ◽  
Bow Shock ◽  
Ion Distribution ◽  
Parallel Side ◽  
Earth’S Bow Shock ◽  
High Mach ◽  
The Magnetic Field

Abstract. Field-aligned beams are known to originate from the quasi-perpendicular side of the Earth's bow shock, while the diffuse ion population consists of accelerated ions at the quasi-parallel side of the bow shock. The two distinct ion populations show typical characteristics in their velocity space distributions. By using particle and magnetic field measurements from one Cluster spacecraft we present a case study when the two ion populations are observed simultaneously in the foreshock region during a high Mach number, high solar wind velocity event. We present the spatial-temporal evolution of the field-aligned beam ion distribution in front of the Earth's bow shock, focusing on the processes in the deep foreshock region, i.e. on the quasi-parallel side. Our analysis demonstrates that the scattering of field-aligned beam (FAB) ions combined with convection by the solar wind results in the presence of lower-energy, toroidal gyrating ions at positions deeper in the foreshock region which are magnetically connected to the quasi-parallel bow shock. The gyrating ions are superposed onto a higher energy diffuse ion population. It is suggested that the toroidal gyrating ion population observed deep in the foreshock region has its origins in the FAB and that its characteristics are correlated with its distance from the FAB, but is independent on distance to the bow shock along the magnetic field.

scholarly journals Principal Component Gradiometer technique for removal of spacecraft-generated disturbances from magnetic field data

2020 ◽  
Author(s):  
Ovidiu Dragoş Constantinescu ◽  
Hans-Ulrich Auster ◽  
Magda Delva ◽  
Olaf Hillenmaier ◽  
Werner Magnes ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Principal Component ◽  
Field Measurements ◽  
Magnetic Field Data ◽  
Service Oriented ◽  
Sensor Configuration ◽  
Time Required ◽  
First Time ◽  
The Magnetic Field

Abstract. In situ measurement of the magnetic field using space borne instruments requires either a magnetically clean platform and/or a very long boom for accommodating magnetometer sensors at a large distance from the spacecraft body. This significantly drives up the costs and time required to build a spacecraft. Here we present an alternative sensor configuration and an algorithm allowing for ulterior removal of the spacecraft generated disturbances from the magnetic field measurements, thus lessening the need for a magnetic cleanliness program and allowing for shorter boom length. The proposed algorithm is applied to the Service Oriented Spacecraft Magnetometer (SOSMAG) onboard the Korean geostationary satellite GeoKompsat-2A (GK2A) which uses for the first time a multi-sensor configuration for onboard data cleaning. The successful elimination of disturbances originating from several sources validates the proposed cleaning technique.

scholarly journals Tribological Evolution of the Superficial Layer and the Effects of the Magnetic Field to a Non- conventional Treated Steel, During Wear Tests

2018 ◽  
Vol 55 (3) ◽  
pp. 442-446
Author(s):  
Carmen Penelopi Papadatu ◽  
Andrei Victor Sandu ◽  
Marian Bordei ◽  
Ioan Gabriel Sandu ◽  
Sorin Ciortan
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Dry Friction ◽  
Experimental Tests ◽  
Superficial Layer ◽  
Alloyed Steel ◽  
Wear Process ◽  
The Magnetic Field ◽  
Wear Tests ◽  
Made In

The article focuses on the behavior of the non-conventional treated alloyed steel in magnetic field, during the dry wear tests. It is a review of the experimental tests from last years. The thermo-magnetic treatments have been applied before the application of a thermo-chemical treatment in plasma based on diffusion process. The study was made in order to improve the mechanical properties of the alloyed steel during the friction wear. Thermo-magnetic treatment applied before the plasma nitro-carburizing treatment improves the mechanical properties of the material especially in this case, for a steel that has a considerable content of Chromium (1.02%). The behavior was studied using X-Ray diffractometry of the superficial layers during the dry friction of wear process. The wear tests used an Amsler machine, during three hours of wear tests. After each hour of the wear tests the samples have been analyzed. The diffractometric characteristics of the superficial layers obtained after a complex array of thermo-magnetic and thermo-chemical in plasma treatments, the phases distribution, the content of the superficial layers and the behavior of the steel during the wear through dry friction tests, have been considered as criteria.

scholarly journals Attitude Estimation of Underwater Vehicles Using Field Measurements and Bias Compensation

Sensors ◽  
2019 ◽  
Vol 19 (2) ◽  
pp. 330 ◽  
Author(s):  
Nak Ko ◽  
Seokki Jeong ◽  
Suk-seung Hwang ◽  
Jae-Young Pyun
Keyword(s):  
Magnetic Field ◽  
Field Measurement ◽  
Field Measurements ◽  
Underwater Vehicle ◽  
Field Vector ◽  
Attitude Estimation ◽  
Magnetic Field Measurement ◽  
Euler Angles ◽  
Measured Field ◽  
The Magnetic Field

This paper proposes a method of estimating the attitude of an underwater vehicle. The proposed method uses two field measurements, namely, a gravitational field and a magnetic field represented in terms of vectors in three-dimensional space. In many existing methods that convert the measured field vectors into Euler angles, the yaw accuracy is affected by the uncertainty of the gravitational measurement and by the uncertainty of the magnetic field measurement. Additionally, previous methods have used the magnetic field measurement under the assumption that the magnetic field has only a horizontal component. The proposed method utilizes all field measurement components as they are, without converting them into Euler angles. The bias in the measured magnetic field vector is estimated and compensated to take full advantage of all measured field vector components. Because the proposed method deals with the measured field independently, uncertainties in the measured vectors affect the attitude estimation separately without adding up. The proposed method was tested by conducting navigation experiments with an unmanned underwater vehicle inside test tanks. The results were compared with those obtained by other methods, wherein the Euler angles converted from the measured field vectors were used as measurements.

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