Electrical and Electronic Engineering - Theses

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    Dielectric spectroscopy of biological materials
    This thesis addresses the dielectric spectroscopy of biological materials. The dielectric properties measure the effect of an externally applied electric field on the charge distribution that is specific to a material. An applied electric field induces polarization currents and conduction by drifting and displacing free and bound charges. Dielectric spectroscopy is the science that relates these microscopic mechanisms to the dielectric properties. These dielectric phenomena are determined by and are informative about the biomolecular properties (polarizability, orientation of dipoles), structure, the coupling of electromagnetic energy into materials, and composition of the material. Computer simulations such as molecular dynamics (MD) and density functional theory (DFT) can be used to obtain the dielectric properties. Given the difficulties of related experiments, the computer simulations play an important role in understanding dielectric properties in a wide range of electric fields. This thesis presents a unified theory, utilizing MD and DFT, that is able to determine the frequency-dependent dielectric properties of biological materials in an aqueous solution from their molecular structure alone, using fluctuation method and reaction field approximations. It also presents an external field method to obtain the dielectric properties of biomolecular aqueous solutions without prior knowledge of their static dielectric constant using reaction field approximations. Further, this thesis focuses on coplanar waveguide (CPW) based measurement techniques, since they enable compact sensors to be implemented as part of integrated on-chip systems. The effects of the dimensions of the CPW sensor, properties of test materials, and the methods used for permittivity estimation from scattering parameters, on the estimation of the complex permittivity using electromagnetic 3-D simulation software are analyzed. The measured dielectric properties in 1-30 GHz using on-chip CPW are used to verify the performance of the proposed system. The transmission coefficient method S21 is corrected considering the multiple reflections at the many interfaces in the measurement systems. A new method based on the corrected S21 method, which uses materials with known permittivity as a reference, is proposed to minimize the length dependence of the estimated permittivity. The accuracy of these methods is verified using on-chip CPW measurements in 1-30 GHz. This thesis also presents a method of identifying both chemical species and their volume fractions of binary mixtures using frequency-dependent permittivity, verified using on-chip CPW measurements in 1-30 GHz. Finally, fabrication of an open-ended coplanar waveguide structured probe for the measurement of dielectric properties using microelectromechanical systems (MEMS) technology is presented and performance of the probe is verified.