Transient electromagnetic fields due to a circular current loop perpendicular or parallel to a conducting half-space

1982 ◽  
Vol 65 (1-2) ◽  
pp. 49-55
Author(s):  
H. J. Tsaknakis ◽  
E. E. Kriezis
Keyword(s):  
Half Space ◽  
Electromagnetic Fields ◽  
Current Loop ◽  
Transient Electromagnetic ◽  
Circular Current

The transient EM step response of a dipping plate in a conductive half‐space

Geophysics ◽  
1992 ◽  
Vol 57 (9) ◽  
pp. 1116-1126 ◽  
Author(s):  
James E. Hanneson
Keyword(s):  
Half Space ◽  
Free Space ◽  
Early Time ◽  
Step Response ◽  
Current Loop ◽  
Late Time ◽  
Electromagnetic System ◽  
University Of Toronto ◽  
Transient Electromagnetic ◽  
Induction Process

An algorithm for computing the transient electromagnetic (TEM) response of a dipping plate in a conductive half‐space has been developed. For a stationary [Formula: see text] current loop source, calculated profiles simulate the response of the University of Toronto electromagnetic system (UTEM) over a plate in a 1000 Ω ⋅ m half‐space. The objective is to add to knowledge of the galvanic process (causing poloidal plate currents) and the local induction process (causing toroidal currents) by studying host and plate currents with respect to surface profiles. Both processes can occur during TEM surveys. Plates are all [Formula: see text] thick with various depths, dips, and conductances. Calculated host and plate currents provide quantitative examples of several effects. For sufficiently conductive plates, the late time currents are toroidal as for a free‐space host. At earlier times, or at all times for poorly conducting plates, the plate currents are poloidal, and the transitions to toroidal currents, if they occur, are gradual. At very late times, poloidal currents again dominate any toroidal currents but this effect is rarely observed. Stripped, point‐normalized profiles, which reflect secondary fields caused by the anomalous plate currents, illustrate effects such as early time blanking (caused by noninstantaneous diffusion of fields into the target), mid‐time anomaly enhancement (caused by galvanic currents), and late time plate‐in‐free‐space asymptotic behavior.

Asymptotic expansions for transient electromagnetic fields

Geophysics ◽  
1982 ◽  
Vol 47 (1) ◽  
pp. 38-46 ◽  
Author(s):  
T. Lee
Keyword(s):  
Half Space ◽  
Electromagnetic Fields ◽  
Asymptotic Expansions ◽  
Free Space ◽  
Layered Structures ◽  
Two Dimensional ◽  
Host Medium ◽  
Transient Electromagnetic ◽  
Axisymmetric Structure ◽  
Transient Voltage

Asymptotic expansions may be derived for transient electromagnetic (EM) fields. The expansions are valid when [Formula: see text] is less than about 0.1. Here l, σ, [Formula: see text], and t are the respective lengths, conductivities, permeabilities of free space and time. Cases for which asymptotic expansions are presented include (1) layered grounds, (2) axisymmetric structure, and (3) two‐dimensional (2-D) structures. In all cases the transient voltage eventually approaches that of the host medium alone, the ratio of anomalous response to the half‐space response being proportional to [Formula: see text]. Here v is equal to 0.5 for layered structures and 1.0 for 2-D or 3-D structures.

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