Electromagnetic induction (eddy currents) in a conducting half‐space in the absence and presence of inhomogeneities: A new formalism

1990 ◽  
Vol 68 (12) ◽  
pp. 5995-6009 ◽  
Author(s):  
Satish M. Nair ◽  
James H. Rose
Keyword(s):  
Half Space ◽  
Electromagnetic Induction ◽  
Eddy Currents ◽  
New Formalism

Electromagnetism

2012 ◽  
Author(s):  
Charles M. Epstein
Keyword(s):  
Energy Flow ◽  
Electromotive Force ◽  
Electromagnetic Induction ◽  
Magnetic Stimulation ◽  
Eddy Currents ◽  
Flow System ◽  
Human Beings ◽  
Induced Voltage ◽  
Secondary Currents ◽  
Primary Current

This article elucidates on the concept of electromagnetism and electromagnetic induction with a view to explaining the theory of magnetic stimulation, used to cure diseases in human beings. Magnetic stimulation follows the principles of electromagnetism. A changing primary current induces secondary currents, which are called eddy currents, in the nearby conductors (human tissue in this case). The strength of the electric field is measured by its electromotive force (emf), which in turn, is measured in volts. The changing primary current also gives rise to an induced voltage in the primary loop itself. The essential circuitry of a magnetic stimulator is composed of three elements, the capacitor, inductance of the stimulation coil, and a switch to connect them. This article also explains the process of the energy flow system through the inductor-capacitor system, applying this principle to the biphasic TMS pulse.

scholarly journals Mathematical modeling on the propagation of guided elastic waves

2020 ◽  
Vol 11 (2) ◽  
pp. 135-139
Author(s):  
Sara Teidj
Keyword(s):  
Cross Section ◽  
Elastic Waves ◽  
Electromagnetic Induction ◽  
Eddy Currents ◽  
Composite Plates ◽  
Arbitrary Cross Section ◽  
Train Derailment ◽  
The Subject ◽  
Wave Propagation In Waveguides ◽  
Inspection Techniques

AbstractThe main cause of train derailment is related to transverse defects that arise in the railhead. These consist typically of opened or internal flaws that develop generally in a plane that is orthogonal to the rail direction. Most of the actual inspection techniques of rails relay on eddy currents, electromagnetic induction, and ultrasounds. Ultrasounds based testing is performed according to the excitation-echo procedure [1]. It is conducted conventionally by using a contact excitation probe that rolls on the railhead or by a contact-less system using a laser as excitation and air-coupled acoustic sensors for wave reception. The ratio of false predictions either positive or negative is yet too high due to the low accuracy of the actual devices. The inspection rate is also late; new numerical method has been developed in this context: The semi-analytical finite element method SAFE. This method has been applied in the case of anisotropic media [2], composite plates [3] and media in contact with fluids [4]. This method has been used successfully for several structures and especially in the case of beams of any cross-section such as rails that are the subject of this work and we were interested in wave propagation in waveguides of any arbitrary cross-section in the case of beams or rails.

The effect of a conductive half‐space on the transient electromagnetic response of a three‐dimensional body

Geophysics ◽  
1985 ◽  
Vol 50 (7) ◽  
pp. 1144-1162 ◽  
Author(s):  
William A. SanFilipo ◽  
Perry A. Eaton ◽  
Gerald W. Hohmann
Keyword(s):  
Half Space ◽  
Free Space ◽  
Eddy Currents ◽  
Three Dimensional ◽  
Vertical Component ◽  
The Body ◽  
Electromagnetic Response ◽  
Loop Current ◽  
Transient Electromagnetic ◽  
Space Response

The transient electromagnetic (TEM) response of a three‐dimensional (3-D) prism in a conductive half‐space is not always approximated well by three‐dimensional free‐space or two‐dimensional (2-D) conductive host models. The 3-D conductive host model is characterized by a complex interaction between inductive and current channeling effects. We numerically computed 3-D TEM responses using a time‐domain integral‐equation solution. Models consist of a vertical or horizontal prismatic conductor in conductive half‐space, energized by a rapid linear turn‐off of current in a rectangular loop. Current channeling, characterized by currents that flow through the body, is produced by charges which accumulate on the surface of the 3-D body and results in response profiles that can be much different in amplitude and shape than the corresponding response for the same body in free space, even after subtracting the half‐space response. Responses characterized by inductive (vortex) currents circulating within the body are similar to the response of the body in free space after subtracting the half‐space contribution. The difference between responses dominated by either channeled or vortex currents is subtle for vertical bodies but dramatic for horizontal bodies. Changing the conductivity of the host effects the relative importance of current channeling, the velocity and rate of decay of the primary (half‐space) electric field, and the build‐up of eddy currents in the body. As host conductivity increases, current channeling enhances the amplitude of the response of a vertical body and broadens the anomaly along the profile. For a horizontal body the shape of the anomaly is distorted from the free‐space anomaly by current channeling and is highly sensitive to the resistivity of the host. In the latter case, a 2-D response is similar to the 3-D response only if current channeling effects dominate over inductive effects. For models that are not greatly elongated, TEM responses are more sensitive to the conductivity of the body than galvanic (dc) responses, which saturate at a moderate resistivity contrast. Multicomponent data are preferable to vertical component data because in some cases the presence and location of the target are more easily resolved in the horizontal response and because the horizontal half‐space response decays more quickly than does the corresponding vertical response.

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