Chapter 6 Experimental Mapping Method

174 ENGINEERING ELECTROMAGNETICS
FIGURE 6.3
An example of a curvilinear-square field map.
The side of the square is two thirds the radius
of the circle. N V ˆ 4 and N Q ˆ 8 3:25 26,
and therefore C ˆ 0 N Q =N V ˆ 57:6 pF/m.
and then using (2),
C ˆ NQ
N V
L t
L N
ˆ N Q
N V
…3†
since L t =L N ˆ 1. The determination of the capacitance from a flux plot
merely consists of counting squares in two directions, between conductors and
around either conductor. From Fig. 6.3 we obtain
8 3:25
C ˆ 0 ˆ 57:6 pF=m
4
Ramo, Whinnery, and Van Duzer have an excellent discussion with examples
of the construction of field maps by curvilinear squares. They offer the
following suggestions: 1
1. Plan on making a numberof rough sketches, taking only a minute orso
apiece, before starting any plot to be made with care. The use of transparent
paper over the basic boundary will speed up this preliminary sketching.
2. Divide the known potential difference between electrodes into an equal
numberof divisions, say fouroreight to begin with.
1 By permission from S. Ramo, J. R. Whinnery, and T. Van Duzer, pp. 51±52. See Suggested References at
the end of Chap. 5. Curvilinear maps are discussed on pp. 50±52.