THE USE OF SPECIAL WAVEFORMS IN THE STUDY OF
LINEAR DIELECTRIC PHENOMENA*
Elizabeth Laverick, B.Sc, Ph.D.
A Paper read before the North-Eastern Section on November
A limited amount of work has been published recently on the use of non-sinusoidal waveforms in
the study of dielectrics, and it would appear that such methods are advantageous in the study of both
linear and non-linear phenomena. In this paper, an attempt has been made to illustrate the usefulness
of these methods. First, an outline is given of the steady field and sinusoidal field methods usually used
in the measurement of dielectric properties, and of the theories which have been advanced to explain the
ensuing results. This is followed by a discussion of the work which has been published recently on the
use of special waveforms in dielectric measurements.
In general, the electrical properties of a
dielectric are described by one quantity, the
permittivity. This may be defined as the ratio
between the electrical capacitances of a con-
denser with the dielectric and with a vacuum as
the medium separating the plates respectively.
For most materials the permittivity is indepen-
dent of the strength of the applied field, for
moderate field strengths, but dependent on tem-
perature, and in the case of sinusoidal fields on
frequency also. The variation of the permittivity
with frequency, and the corresponding absorp-
tion of energy involved, gives rise to the concept
of a complex permittivity,
6 = 6' +76'
where E' and e" depend on frequency, and
proportional to the dielectric loss.
The properties of a dielectric are usually
measured in terms of the permittivity (e', or j e | =
)), and the loss angle (tan 6), over a
wide range of frequencies at a series of discrete
frequencies. Alternatively, these properties may
be measured as a function of temperature. The
variations of dielectric properties with frequency
and with temperature are generally similar in
form. In the case of temperature variations,
however, the range in which the variations
occur is comparatively small, and in practice
* Manuscript received November 27th, 1950.
t Formerly at the Physics Department, Durham University;
now at the Research Laboratories, The General Electric Co., Ltd.,
U.D.C. No. 621.317.335.3 : 621.3.018.7.
a fine control of the temperature is required.
The fundamental problem is to explain the
experimental facts in terms of the actual
mechanism by means of which the absorption of
energy takes place in the dielectric. Dielectric
losses contribute materially to the attenuation of
waves in transmission lines, to insensitive tuning
in resonant circuits, and to insulator breakdown
in some circumstances. They also form the
basis of dielectric heating phenomena.