Environmental Engineering Reference
In-Depth Information
5.5.4
Practical Considerations
Preliminary results obtained comparing the traditional and the described methods
highlighted similar performance in terms of estimation of the electrical static con-
ductivity, both for the electrolyte solutions and for the moistened sand samples.
However, it is important to underline that the two proposed approaches are advanta-
geous in two major ways. In fact, the TLM method clearly discovers and compen-
sates for the major parasitic effects that influence the final measurement accuracy.
As for the ICM method, the simple requirement of two capacitance measurements
simplifies and speeds up the entire procedure. Additionally, the addressed metro-
logical validation clearly demonstrates that the uncertainty in the estimation of elec-
trical conductivity through the ICM method is always smaller than (or, at worst,
equal to) the uncertainty related to the traditional C-S method. On such basis, the
described approaches represent a viable way toward a cost-effective and time-saving
TDR monitoring of conductivity for quality control of both liquid and granular
materials.
5.6
Noninvasive Moisture Content Measurements
In some monitoring or diagnostic applications, the noninvasive approach may rep-
resent a stringent requirement. Therefore, with regards to the BMR capabilities to
satisfy such needs, much research effort has been paid to designing and realizing
probes that could guarantee a noninvasive approach. For example, metallic strips
have been investigated as possible surface-TDR probes [58]. Similarly, serpentine-
shaped wires (attached to a planar acrylic pad) have also been considered as a non-
invasive solution for BMR-based moisture monitoring [59].
Starting from these considerations, in this section, the possibility of noninva-
sive moisture monitoring through a suitable combination of BMR with the use of
a microstrip antenna as sensing element is addressed. This method may become
particularly suitable for monitoring applications in which the noninvasive approach
is mandatory (e.g., construction materials, walls, architectonic structures, frescoes,
etc.).
As will be detailed in the following subsections, the dielectric properties of the
considered material are associated to the changes in the reflection scattering param-
eter of the antenna,
S
11
(
, occurring when the antenna is placed in contact with the
surface of the MUT [57]. More specifically, the changes in the resonant frequency
(
f
res
) of the antenna can be associated to the moisture content of the MUT.
The main steps of the adopted method can be summarized as follows:
f
)
•
a microstrip antenna (which can be specifically designed and realized) is placed
on the surface of the MUT, and the TDR waveform of the system (antenna and
MUT) is acquired [see Fig. 5.15];
•
the
S
11
(
of the system is evaluated through the TD/FD combined approach
described in Chapt. 3 [9];
f
)
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