Specifications

University of Pretoria etd – Combrinck, M (2006)
Transmitter loop
Thin, conductive sheet with
conductance Siemens.
S
t=t
1
t=t
2
t=t
3
Figure 2-3 Equivalent current filaments (images) for a conducting thin sheet at
various times after current interruption in the transmitter loop (after Nabighian
and Macnae, 1991).
The emf induced in a loop which is located in the horizontal plane, with a small dipole
source located at its centre, is given by Kaufman and Keller (1983) as:
()
()
[]
plate. conductive the and loops the between distancevertical
[S] plate thin the of econductanc
[s] time
loop[m] receiver large the of radius
loop (small)r transmitte the ofmoment dipole magnetic
where
(2.3)
=
=
=
=
=
=
=
++
+
−=
d
r
d
h
S
t
r
Sr
t
M
h
h
Sr
M
emf
s
s
s
0
0
2
0
0
2
2
21
23
2
5
µ
τ
τ
τ
The quasi-stationary (derivative of) magnetic field transient response of a central-loop, step
current system over a thin conducive sheet can be calculated from equation 2.3 by applying
the principle of reciprocity (i.e. in any system the same emf will still be measured if the
transmitter and receiver geometries are interchanged). Making the late time approximation
10