Environmental Engineering Reference
In-Depth Information
Fig. 3.8
Picture of an Agi-
lent E8361C VNA [6].
The FDR approach is often used for the dielectric spectroscopy of materials and
for impedance characterization of electronic devices and components. In particular,
a VNA used in conjunction with a dielectric probe kit can be employed to charac-
terize the dielectric behavior of materials. However, it is important to point out that,
although these are well-established experimental setups, their application is far from
being universal, and often specific solutions must be designed.
3.4
TD/FD Combined Approach
The adoption of the TD/FD combined approach allows taking advantage of the ben-
efits of both the approaches. In particular, estimating the frequency-dependent scat-
tering parameter starting from TDR measurements, can help disclosing useful infor-
mation that is masked in time domain (e.g., single or multiple dielectric relaxation)
[21]. This strategy is regarded as a powerful tool for guaranteeing simultaneously
low cost and portability of the instruments, and measurement accuracy. The
S
11
(
)
of the monitored system can be calculated as the ratio between the discrete Fourier
transformation (DFT) of the reflected signal and that of the input signal [22]:
f
DFT
[
r
(
t
)]
S
11
(
f
)=
(3.11)
DF T
[
v
0
(
t
)]
where
v
0
(
is the input function, which should be the unaltered signal generated by
the TDR instrument and propagating (along the cable) up to the section where the
S
11
(
t
)
is being measured [29].
This approach provides reliability and adequate measurement accuracy, although
relying on relatively-inexpensive TDR instrumentation.
In this regard, it is worth mentioning that, unlike VNAs, portable and affordable
TDR instruments (with wide operating frequency range) are commonly available on
the market. For example, for the time being, the cost of portable TDR modules with
a frequency bandwidth of 10 GHz and of 2 GHz is approximately 7000 USD and
3500 USD, respectively.
f
)
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