Theory, Design and Development of Resonance Based Biosensors in Terahertz and Millimeter-wave
Year: 2009
Type: dissertation
Abstract: Recent advances in molecular biology and nanotechnology have enabled scientists \nto study biological systems at molecular and atomic scales. This level of sophistication \ndemands for new technologies to emerge for providing the necessary sensing \ntools and equipment. Recent studies have shown that terahertz technology can provide \nrevolutionary sensing techniques for organic and non-organic materials with \nunprecedented accuracy and sensitivity. This is due to the fact that most of the \nmacromolecules have vibrational and/or rotational resonance signatures in terahertz \nrange. To further increase the sensitivity, terahertz radiation is generated and \ninteracted with the bio-sample on a miniaturized test site or the so-called biochip. \nFrom the view point of generation and manipulation of terahertz radiation, the \nbiochip is designed based on the same rules as in high frequency electronic chips \nor integrated circuits (IC). By increasing the frequency toward terahertz range, \nthe conventional IC design methodologies and analysis tools fail to perform accurately. \nTherefore, development of new design methodologies and analysis tools is \nof paramount importance for future terahertz integrated circuits (TIC) in general \nand terahertz biochips in particular. \n \nIn this thesis, several advancements are made in design methodology, analysis \ntool and architecture of terahertz and millimeter-wave integrated circuits when used \nas a biochip. A global and geometry independent approach for design and analysis \nof the travelling-wave terahertz photomixer sources, as the core component in a \nTIC, is discussed in details. Three solvers based on photonic, semiconductor and \nelectromagnetic theories are developed and combined as a unified analysis tool. \n \nUsing the developed terahertz photomixer source, a resonance-based biochip \nstructure is proposed, and its operation principle, based on resonance perturbation \nmethod, is explained. A planar metallic resonator acting as a sample holder and \ntransducer is designed, and its performance in terms of sensitivity and selectivity is \nstudied through simulations. The concept of surface impedance for electromagnetic \nmodeling of DNA self-assembled monolayer on a metal surface is proposed, and its \neffectiveness is discussed based on the available data in the literature. \n \nTo overcome the loss challenge, Whispering Gallery Mode (WGM) dielectric \nresonators with high Q factor are studied as an alternative for metallic resonator. \nThe metallic loss becomes very high at terahertz frequencies, and as a result of \nthat planar metallic resonators do not exhibit high Q factor. Reduced Q factor \nresults in a low sensitivity for any sensor using such resonators. Theoretical models \nfor axially and radially layered dielectric resonators acting on WGM are presented, and the analytical results are compared with the measured data. Excitation of \nWGM through dielectric waveguide is proposed, and the critical coupling condition \nis explained through analytical formulation. The possibility of selecting one resonance \namong many for sensing application is also studied both theoretically and \nexperimentally. \n \nA high sensitivity sensor based on WGM resonance in mm-wave and terahertz is \nproposed, and its sensitivity is studied in details. The performance of the proposed \nsensor is tested for sensing drug tablets and also liquid droplets through various \nmeasurements in mm-wave range. The comprehensive sensitivity analysis shows \nthe ability of the proposed sensor to detect small changes in the order of 10−4 in \nthe sample dielectric constant. The results of various experiments carried out on \ndrug tablets are reported to demonstrate the potential multifunctional capabilities \nof the sensor in moisture sensing, counterfeit drug detection, and contamination \nscreening. The measurement and simulation results obtained in mm-wave hold \npromise for WGM to be used for sensing biological solutions in terahertz range \nwith very high sensitivity.
Source: UWSpace (University of Waterloo)
Author: Mohammad Neshat
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2186271701