Quantitative and Qualitative Characterization of Liquid Materials - Broadband Reflectometry for Enhanced Diagnostics and Monitoring Applications - page 81

the intended purposes. As a matter of fact, the choice of the most appropriate probe
length should guarantee an optimal trade-off of contrasting effects, such as an ad-
equate performance at low frequency and the need to limit the quantity of oil re-
quired for performing the tests. This alternative solution may as well be regarded as
a practical alternative for avoiding the use of the LCR meter for evaluating the static
permittivity.

4.4.2.3 Results on Mixtures of Oils

After the validation of the proposed procedure for quality-control of pure olive
oils, the successive phase was to extend the methodology to more complex systems
(such as mixtures of oils), so as to test the method also for anti-adulteration control
purposes.
On such bases, the proposed procedure was applied for the evaluation of the
Cole-Cole parameters of some mixtures of oils (M1, ..., M4). In particular, to re-
produce some typical adulteration cases, the mixtures were prepared by mixing a
new olive oil with sunflower oil, in different volumetric percentages. Measurements
were performed one single time for each mixture; this was done to mimic a typical
practical case in which the personnel in charge of control have to rely on single-shot
measurements. Summarized results are reported in Table 4.13. Also in this case, it is
apparent that the parameter that is more sensitive to the change in the composition
of the mixture is the relaxation frequency. More specifically, it can be seen that start-
ing from pure olive oil, the relaxation frequency value increases proportionally to
the percentage amount of sunflower oil. On the other hand, the remaining Cole-Cole
parameters do not exhibit significant changes.
On a final note, it is worth noting that results show that the difference in f r for
the considered oil mixtures is of the order of a few MHz (see Table 4.13). This
figure is comparable to the achievable uncertainty for measurements on pure oils,
when single-shot measurements are performed (see Table 4.12). Overall, it appears
that a further minimization of the uncertainty on f r evaluation would be necessary
to make the method more effective. This could be achieved, for example, exploit-
ing enhanced probe geometries, as currently under development. Moreover, suitable

Ta b l e 4 . 1 3 Relaxation frequencies for the olive-sunflower oil mixtures

Mixture Sunflower oil percentage (%) f r

(MHz)

olive oil 0 245

M1 10 250

M2 20 257

M3 30 259

M4 40 263

Sunflower oil 100 295