Environmental Engineering Reference
In-Depth Information
In additional use of this method rely upon the availability of information about the
dielectric properties of the contaminated soil. Development of such information has
formed a focus of research by many authors around the world over several years
[7-9]
.
This study focuses on the factors affecting the dielectric response of soil-water-heavy
metal mixture at low frequency ranges. In this paper, the complex permittivity of soils
was measured at the frequency range of 100 kHz-1 MHz by means of using LCR
meters. The effects of measurement frequency, heavy metal type and concentration
on the dielectric response were evaluated by analyzing the complex permittivity of
specimen at low frequencies.
Complex Permittivity and Polarization
When a capacitor containing material is connected to a sinusoidal voltage source,
all materials including soils have a loss current component which is in phase with
the applied voltage
[10]
. The partially out-of-phase response of the materials due to
the existence of the loss currents can be well described in terms of the complex
permittivity (e*). The relative complex permittivity, which is normalized with respect
to the permittivity of free space, can be represented by Eq.
1
[10]
. In common
usage, the word “relative” is frequently dropped (ASTMD150).
e
e ee
e
==−
(1)
*
′
i
′′
o
In Eq.
1
, e
o
is the permittivity of the free space (e
o
= 8.85 × 10
-12
F/m) and i denotes
an imaginary number. The real part of the complex permittivity (e¢) is commonly
called the permittivity or dielectric constant of a material and represents the
capacitive behavior or polarizability of the material. The imaginary part (e”) is
called the loss factor and represents the energy losses due to polarization and
conduction
[11, 12]
. In the permittivity measurement, losses due to polarization and
conduction are measured together
[13]
. Hence, the effective imaginary permittivity
(e
eff
”) becomes Eq.
2
:
s
′
=+
(2)
′′
e
e
eff
ew
o
where s is zero-frequency current (DC) conductivity, w is the angular frequency
(w = 2pƒ) and ƒ is the frequency. When an electric field is applied to a medium,
some charges are bound, yet these positive and negative charges can move locally
relative to each other, which results in a polarized medium. The polarizability of
the medium is represented by permittivity. In other words, permittivity is a measure
of the extent to which the electrical charge distributed in a material can be polarized
by the application of an electric field. The spectral response of permittivity with
frequency captures the various polarization mechanisms
[14, 15]
.
