Date of Graduation

5-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

El-Ghazaly, Samir M.

Committee Member

Hanna, Victor F.

Second Committee Member

Naseem, Hameed A.

Third Committee Member

Yu, Shui-Qing "Fisher"

Fourth Committee Member

Balda, Juan C.

Keywords

Pure sciences; Applied sciences; Carbon nanotubes; Composite material; Dielectrophoresis; Microwave characterization; Mode matching technique; Nano-particles

Abstract

This work includes the microwave characterization of carbon nanotubes (CNTs) to design new CNTs-based high frequency components. A novel developed method to extract the electrical properties over a broad microwave frequency band from 10 MHz to 50 GHz of carbon nanotubes (CNTs) in a powder form is performed. The measured scattering parameters (S-parameters) with a performance network analyzer are compared to the simulated one obtained from an in-house computed mode matching technique (MMT). An optimized first order gradient method iteratively changes the unknown complex permittivity parameters to map the simulated S-parameters with the measured one until convergence criteria are satisfied. The mode matching technique accurately describes waveguide discontinuities as both propagating and evanescent modes are considered allowing an error less than 5% on the extracted permittivity over a broad frequency range. The very large values obtained at low frequencies of carbon nanotubes permittivity are explained theoretically and experimentally based on the percolation theory. The powder composed of semiconducting and conducting CNTs illuminated by an electromagnetic field is seen as series of nano-resistance-capacitance which significantly increase the real and imaginary parts of the complex effective permittivity until the percolation threshold is reached. Based on experimental results different CNTs-based composites material are engineered to design novel microwave components for possible electromagnetic compatibility (EMC) applications.

As the extraordinary properties of the carbon nanotubes exist along their axis, the second part of this work is oriented on the alignment and the deposition of carbon nanotubes using a dielectrophoresis (DEP) technique. Micro/nano-electrodes are fabricated using a lift-off process consisting of photo-lithography and electron-beam lithography techniques where the carbon nanotubes suspended in an aqueous solution are attracted in the gap between the electrodes by applying an AC bias voltage. After burning the conducting carbon nanotubes an observed photocurrent with aligned semiconducting CNTs is used to develop high frequency photo-device prototypes.

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