Quantitative and Qualitative Characterization of Liquid Materials - Broadband Reflectometry for Enhanced Diagnostics and Monitoring Applications - page 64

foam-dielectric coaxial
cable (Cellflex LCF78-50JA), contained in the stainless steel outer conductor that
is ground contacted. The 433 mm-long inner conductor of the probe is obtained
removing the same length of the external shield and foam dielectric of the Cellflex
cable.
As aforementioned, to perform a SOL calibration at the exact section where the
sensing element begins (section #2 of Fig. 4.6), a calibration structure reproducing
the internal probe-head portion was specifically realized. This structure terminated
with an N-type connector (thus ensuring the connection to N-type SOL standards).
For the time-domain measurements, the HL1500 unit was used. Comparative fre-
quency domain measurements were performed through the Agilent E8363B VNA,
whose upper operating frequency is 40 GHz. The probe was connected to the TDR
and to the VNA instrument through a 3 m-long RG213 coaxial cable.
The HP85032B N-type SOL standard calibration kit was used for calibration
measurements, both for VNA and TDR measurements. In particular, the SOL kit
standards were connected at the end of the 'calibration structure' (which was con-
nected to the instrument through the 3 m-long cable as well). In this way, all the
parasitic effects caused by the probe-head (and, consequently, also of the cable)
were adequately compensated for.

The probe-head internal portion is made up of a 50 Ω

4.3.3 Experimental Validation of the Method

To assess the method, measurements were performed on stratified liquids, namely
fuel/tap water layered samples. Three samples were considered. All measurements
were performed at room temperature (26 1 ◦ C). The three samples differed in the

relative level of fuel and water, as shown in Table 4.2. First, the apparent dielectric

±

Ta b l e 4 . 2 Reference level of fuel ( H ref
f

) and tap water ( H re w ), for the three considered samples

H ref
f

H ref
w

(mm) (mm)

Sample #1 283 . 0 ± 0 . 5 150 . 0 ± 0 . 5

Sample #2 219 . 0 ± 0 . 5 214 . 0 ± 0 . 5

Sample #3 335 . 0 ± 0 . 5 98 . 0 ± 0 . 5

constant and the levels were estimated through the time-domain approach presented
in the previous section.
Secondly, the dielectric permittivity and the levels were evaluated by resorting
to the proposed TL modeling and optimization procedure. For comparison, this
TL-based approach was applied separately to two sets of data: to the scattering