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Abstract:
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The thesis mainly focuses on material characterization in different
environments: freely available samples taken in planar fonn, biological samples
available in small quantities and buried objects.Free space method, finds many applications
in the fields of industry, medicine and communication. As it is a non-contact
method, it can be employed for monitoring the electrical properties of materials
moving through a conveyor belt in real time. Also, measurement on such systems at
high temperature is possible. NID theory can be applied to the characterization of
thin films. Dielectric properties of thin films deposited on any dielectric substrate
can be determined. ln chemical industry, the stages of a chemical reaction can be
monitored online. Online monitoring will be more efficient as it saves time and
avoids risk of sample collection.Dielectric contrast is one of the main factors, which decides the
detectability of a system. lt could be noted that the two dielectric objects of same
dielectric constant 3.2 (s, of plastic mine) placed in a medium of dielectric constant
2.56 (er of sand) could even be detected employing the time domain analysis of the reflected signal. This type of detection finds strategic importance as it provides
solution to the problem of clearance of non-metallic mines. The demining of these
mines using the conventional techniques had been proved futile. The studies on the
detection of voids and leakage in pipes find many applications.The determined electrical properties of tissues can be used for numerical modeling
of cells, microwave imaging, SAR test etc. All these techniques need the accurate
determination of dielectric constant. ln the modem world, the use of cellular and
other wireless communication systems is booming up. At the same time people are
concemed about the hazardous effects of microwaves on living cells. The effect is
usually studied on human phantom models. The construction of the models requires
the knowledge of the dielectric parameters of the various body tissues. lt is in this
context that the present study gains significance. The case study on biological
samples shows that the properties of normal and infected body tissues are different.
Even though the change in the dielectric properties of infected samples from that of
normal one may not be a clear evidence of an ailment, it is an indication of some
disorder.ln medical field, the free space method may be adapted for imaging the
biological samples. This method can also be used in wireless technology.
Evaluation of electrical properties and attenuation of obstacles in the path of RF
waves can be done using free waves. An intelligent system for controlling the
power output or frequency depending on the feed back values of the attenuation may
be developed.The simulation employed in GPR can be extended for the exploration of the
effects due to the factors such as the different proportion of water content in the soil,
the level and roughness of the soil etc on the reflected signal. This may find
applications in geological explorations. ln the detection of mines, a state-of-the art technique for scanning and imaging an active mine field can be developed using
GPR. The probing antenna can be attached to a robotic arm capable of three degrees
of rotation and the whole detecting system can be housed in a military vehicle. In
industry, a system based on the GPR principle can be developed for monitoring
liquid or gas through a pipe, as pipe with and without the sample gives different
reflection responses. lt may also be implemented for the online monitoring of
different stages of extraction and purification of crude petroleum in a plant.Since biological samples show fluctuation in the dielectric nature with time
and other physiological conditions, more investigation in this direction should be
done. The infected cells at various stages of advancement and the normal cells
should be analysed. The results from these comparative studies can be utilized for
the detection of the onset of such diseases. Studying the properties of infected
tissues at different stages, the threshold of detectability of infected cells can be
determined. |