Date of Award

Summer 2000

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

First Advisor

Jeutter, Dean

Second Advisor

Schneider, Susan

Abstract

The current research work pertains to investigating the modified electrode version of the quartz crystal resonator as chemical sensor in liquid and gas media. The theoretical study of the modified electrode QCR has shown its sensitivity towards the mechanical and electrical properties of a given media. Therefore a practical means of testing these properties was required. The objective of this work has focused on incorporating the sensor device into an electronic circuit, which is portable, efficient, stable and sensitive to the sensing media. Oscillator circuits were built for operation in both the gaseous and aqueous media. The most important emphasis was placed on operating the electronic circuit in liquid media where the acoustic wave undergoes significant damping. The oscillation therefore across the acoustic bulk wave device, under severe damping conditions, was maintained by incorporating an automatic gain control stage. which has been instrumental in understanding various sensing parameters. Extensive experimentation was conducted in regard to testng and fine tuning the electronic circuit. Furthermore, data was collected and analyzed for both the gas and liquid phase. Various film coatings were used to enhance the selectivity by increasing specific sensitivities to exact species. The following film coatings were used PODMA. PEA, PECH, and PDCPZ, and respectively tested for sensitivity and selectivity. These were exposed to the following analytes in varying concentrations: chloroform, tetracloromethane, trichloroethylene, tetrachloroethane, and toluene. It is shown that oscillator circuits designed specifically for sensor applications, can be used more effectively as a reliable tool for data acquisition. The overall results show that the oscillator method provides much better results than those obtained via other methods for this particular application. The detection limits have been significantly lowered with detection limits approaching 500 ppb with 9MHz crystals, thus the experimental results indicate that liquid phase detection utilizing the QCR is feasible.

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