THE ELECTROMAGNETIC FIELD WITHIN A DISCONTINUOUS CONDUCTOR WITH REFERENCE TO GEOMAGNETIC MICROPULSATIONS NEAR A COASTLINE

1963 ◽  
Vol 41 (3) ◽  
pp. 484-495 ◽  
Author(s):  
J. T. Weaver
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Plane Surface ◽  
Low Frequency ◽  
Magnetic Component ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Magnetic Vector ◽  
Plane Normal ◽  
Frequency Approximation

The two-dimensional problem of a low-frequency, plane-polarized electromagnetic wave incident on a semi-infinite conducting medium with a plane surface is treated for the case when the medium has a discontinuity, the regions on either side of a plane normal to its surface being of different conductivities. Arguments are given to show that it is reasonable to assume, as a low-frequency approximation, that the tangential magnetic field is constant on the surface of the conductor. With the aid of this approximation, solutions are obtained for the two cases when (i) the magnetic vector (H polarization) and (ii) the electric vector (E polarization) is always parallel to the trace of the discontinuity.The model is discussed with reference to the behavior of geomagnetic micropulsations near a coastline, particular attention being paid to the E-polarization solution which contains a magnetic component normal to the surface of the conductor. The amplitude of this component at the surface is shown to increase sharply as the region of the discontinuity is approached, thus providing an explanation of the enhanced Z magnetic component in the micropulsation field observed at coastal stations.

Data Acquisition and Processing of Weak Low-Frequency Magnetic Signals

2011 ◽  
Vol 65 ◽  
pp. 299-302 ◽  
Author(s):  
Shou Qiang Men ◽  
Christian Resagk
Keyword(s):  
Magnetic Field ◽  
Data Acquisition ◽  
Fourier Transforms ◽  
Low Frequency ◽  
Fast Fourier Transforms ◽  
Two Dimensional ◽  
Calibration System ◽  
Magnetic Field Sensors ◽  
Data Acquisition And Processing

A simple calibration system for magnetic field sensors was designed, and experiments were carried out to calibrate two-dimensional fluxgate sensors and a sensor ring composed of eight fluxgate sensors. Fast Fourier Transforms and trapezoidal numerical integrals were applied to deal with the raw signals. It is found that it is not suitable to apply fast Fourier Transforms only to deal with signals with several peaks close to each other, but trapezoidal numerical integrals should also be used in combination with the FFT method.

Sufficient Symmetry Conditions for Isotropy of the Elastic Moduli Tensor

1987 ◽  
Vol 54 (4) ◽  
pp. 772-777 ◽  
Author(s):  
R. M. Christensen
Keyword(s):  
Elastic Moduli ◽  
Fiber Composite ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Axial Deformation ◽  
Space Network ◽  
Plane Normal ◽  
Rank Tensor ◽  
Three Space

Symmetry conditions are found that assure isotropy of the fourth rank tensor of elastic moduli. Crystallography provides the answer to this problem in the two-dimensional context, namely one axis of three-fold symmetry assures the isotropy of properties in the plane normal to the axis. The present work provides the answer in the three-dimensional problem: 6 axes of five-fold symmetry are sufficient to give isotropy of the elastic moduli. An important restriction must accompany the present result. The derivation is given in the special form appropriate to low density materials which have a microstructure that transmits load according to the axial deformation of a space network of material distributed into micro-struts. The corresponding fiber composite idealization is that of a fiber dominated system, it therefore follows that if the fibers take the 6 specific orientations in three-space then isotropy is obtained.

scholarly journals Surface impedance of electromagnetic field excited by a grounded horizontal antenna in the Earth–ionosphere waveguide

2019 ◽  
pp. 181-189
Author(s):  
E. D. Tereshchenko ◽  
P. E. Tereshchenko
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Surface Impedance ◽  
Low Frequency ◽  
Wave Impedance ◽  
Skin Layer ◽  
Skin Depth ◽  
Plane Waveguide ◽  
The Earth ◽  
Horizontal Antenna

Analytical formulas for the tangential components of extremely-low-frequency (ELF) electromagnetic field in the Earth–ionosphere plane waveguide excited by a grounded linear horizontal antenna are obtained. The behavior of surface impedance is studied as a function of electrodynamic characteristics of the waveguide and the distance from the source. It is shown that surface impedance coincides with the plane wave impedance on the Earth’s surface at distances from the source larger than the skin depth provided that the skin layer is thinner than double the waveguide’s height. The influence of the ionosphere on the amplitude of the ELF and lower-frequency magnetic field and, thus, on the impedance at the distances shorter than two ionospheric heights is theoretically substantiated. This type of effect was observed in the experiments conducted on the Kola Peninsula where the low conductivity of the Earth allowed the detection of the effect of the ionosphere on the amplitude of the magnetic field in the low-frequency band.

scholarly journals Intensity of Extremely Low-frequency Electromagnetic Fields Produced in Operating Rooms during Surgery at the Standing Position of Anesthesiologists

2009 ◽  
Vol 111 (2) ◽  
pp. 275-278 ◽  
Author(s):  
Jang Ho Roh ◽  
Deok Won Kim ◽  
Sung Jin Lee ◽  
Ji Young Kim ◽  
Sung Won Na ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Operating Room ◽  
Electromagnetic Fields ◽  
Low Frequency ◽  
Standing Position ◽  
Operating Rooms ◽  
Operating Room Personnel ◽  
Sample Number ◽  
Extremely Low Frequency

Background Numerous electronic devices have been introduced into operating rooms. Although little is known about the relationship between exposure to electromagnetic fields and health hazards, several studies have demonstrated causal relationships between electromagnetic fields exposure and various symptoms, cancers, and other diseases. Methods This study was approved by the Institutional Review Board. The intensity of extremely low-frequency electromagnetic fields was measured during surgery with the extremely low-frequency electromagnetic field strength measurement system at the standing position of anesthesiologists in 18 operating rooms and analyzed with EMDEX analysis and graphical program (EMCALC 95; ENERTECH, Campbell, CA). Results The average measurement duration per operating room per day was 7.41 +/- 0.70 h (mean +/- SD). The average sample number of measurements was 888.11 +/- 82.75 per operating room. The average magnetic field was 5.83 +/- 5.23 milliGuass (mG) (range, 0.10-33.80 mG), with 70% of these levels 2 mG or greater. Conclusions The authors' results indicate that anesthesiologists in operating rooms are exposed to extremely low-frequency electromagnetic field levels that exceed magnetic field intensity of 2 mG recommended by the Swedish Board for Technical Accreditation for production by computer monitors and detected 30 cm from them. It currently is not clear if this exposure has health effects on anesthesiologists and other operating room personnel.

ON AXIALLY SYMMETRIC ELECTRIC CURRENT INDUCED IN A CYLINDER UNDER A LINE SOURCE

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 971-974 ◽  
Author(s):  
Shri Krishna Singh
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Short Note ◽  
Cylindrical Wave ◽  
Wave Functions ◽  
Static Case ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Axially Symmetric ◽  
Infinite Line

An infinite conducting cylinder excited by an infinite line current located outside the cylinder is a useful model in the interpretation of electromagnetic prospecting data. Several authors, with geophysical applications in mind, have considered the problem of the source being parallel to the axis of the cylinder (Wait, 1952; Negi et al., 1972). In the latter paper, the cylinder is surrounded by a shell; conductivity of both the cylinder and the shell is a function of radius. The secondary fields are written in the form of an infinite series of cylindrical wave functions. This solution is then specialized to the quasi‐static case. For reasons not explained, the authors neglect the n = 0 term. In this short note, computed results are presented which show that the contribution from the n = 0 term (corresponding to an axially symmetric electric current induced in the cylinder causing a transverse secondary magnetic field outside) is significant and must be taken into account for the two‐dimensional problem.

A New Look at Sound Generation by Blade/Vortex Interaction

1985 ◽  
Vol 107 (2) ◽  
pp. 224-228 ◽  
Author(s):  
J. C. Hardin ◽  
J. P. Mason
Keyword(s):  
Low Frequency ◽  
Initial Position ◽  
Sound Pulse ◽  
Two Dimensional ◽  
Vortex Interaction ◽  
Dimensional Problem ◽  
Sound Generation ◽  
Blade Vortex Interaction ◽  
Vortex Velocity

As a preliminary attempt to understand the dynamics of blade/vortex interaction, the two-dimensional problem of a rectilinear vortex filament interacting with a Joukowski airfoil is analyzed in both the lifting and nonlifting cases. The vortex velocity components could be obtained analytically and integrated to determine the vortex trajectory. With this information, the aeroacoustic low-frequency Green’s function approach could then be employed to calculate the sound produced during the encounter. The results indicate that the vortex path deviates considerably from simple convection due to the presence of the airfoil and that a reasonably sharp sound pulse is radiated during the interaction whose fundamental frequency is critically dependent upon whether the vortex passes above or below the airfoil. Determination of this gross parameter of the interaction is shown to be highly nonlinearly dependent upon airfoil circulation, vortex circulation, and initial position.

RADIATION FROM A SOURCE NEAR A PLANE INTERFACE BETWEEN AN ISOTROPIC AND A GYROTROPIC DIELECTRIC

1964 ◽  
Vol 42 (11) ◽  
pp. 2153-2172 ◽  
Author(s):  
S. R. Seshadri ◽  
A. Hessel
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Surface Waves ◽  
High Frequency ◽  
Free Space ◽  
Line Source ◽  
Low Frequency ◽  
Plane Interface ◽  
Magnetic Current ◽  
Asymptotic Evaluation

The radiation from a line source of magnetic current situated in free space near a plane interface between a semi-infinite free space and a semi-infinite gyrotropic dielectric is investigated for the case in which the gyrotropic axis is parallel to the line source. In addition to the space waves, it is found that in general two unidirectional surface waves are excited along the interface. The dispersion relations for the space and the surface waves are thoroughly examined. Both surface waves have different high-frequency cutoff but no low-frequency cutoff. The characteristics of these surface waves are investigated. An asymptotic evaluation of the total electromagnetic field is carried out for a particularly simple choice of the source frequency. For this frequency, the dependence of the efficiency of excitation of the surface waves on the distance of the source from the interface is determined. The radiation patterns are plotted for various values of the static magnetic field and the position of the source.

scholarly journals Kalibracja małej anteny pętlowej

2020 ◽  
pp. 109-116
Author(s):  
Paweł Szczupak ◽  
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Field ◽  
Anechoic Chamber ◽  
Helmholtz Coil ◽  
Loop Antenna ◽  
Magnetic Component ◽  
Small Loop

The article presents examples of calibration of a small loop antenna, witch can be used to measure the magnetic component of the electromagnetic field. The source of such a field may be, for example, lightning. There are many methods of calibration a loop antenna. Two of them are presented below – using test antenna with is calibrated and with known parameters, and using a homogenous magnetic field generated inside Helmholtz coil. Measurements using the first method were carried out in the anechoic chamber of the EMC laboratory.

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