FONTANA, M.; http://lattes.cnpq.br/6557924427592953; FONTANA, Márcio.
Resumo:
I n this work the characterization and modelling of the optical properties of a vanadium
dioxide sensor ( V 0 2 ) are studied. These sensors present a crystalographic transformation
induced by temperature and exhibit hysteresis. For the modelling of the optical properties
in the phase plan i t was necessary to adapt the classic Preisach model and the adiabatic limit
approximation model. In the Preisach model it was necessary to redefine the elementary
hysteresis operator, to choose a distribution function and to adopt a new interpretation
of the Preisach triangle. In the adiabatic limit approximation model the expression that
represents the adiabatic equilibrium limits was also modified.
An experimental platform was developed to submit the film of V02 to a controlled
temperature variation in order to allow the characterization of its optical properties. The
wiping-out and congruency properties and the accommodation phenomenon were observed
experimentally. The temperature was controlled by using a Peltier module. The linearization
around an operation point made possible the Peltier module to be represented by a
second order linear system with temperature dependent parameters. The model of the
Peltier module was identified for nine operating points and a scheduling PID temperature
controller was designed by the zero-pole cancellation technique.
The distribution function used in the modified Preisach model was determined from the
first-order descending transition curves by using a genetic algorithm. The parameters of
the modified adiabatic limit approximation model were obtained directly from the experimental
data of the major hysteresis loop. The models obtained experimentally were used to
generate hysteresis loops that were compared with the experimental data. The obtained results
are considered satisfactory. However, the developed models reproduce approximately
the hysteresis phenomenon of the film of VQ2. The discrepancies between the calculated
and the experimental data, mainly for the congruency property, can be attributed to limitations
in the numeric implementation of the model, to the film temperature control and
the experimental platform limitations.