Graduation Year

2005

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Shekhar Bhansali, Ph.D.

Committee Member

Larry Langebrake, P.E.

Committee Member

Rudy Schlaf, Ph.D.

Committee Member

Babu Joseph, Ph.D.

Committee Member

Kendra Daly, Ph.D.

Keywords

Impedance, oscillator, dielectric, polarization, complex permittivity

Abstract

This work is aimed at developing a high sensitivity salinity (conductivity) sensor for marine applications. The principle of sensing involves the use of parallel plate capacitors, which minimizes the proximity effects associated with inductive measurement techniques. The barrier properties of two different materials, AZ5214 and Honeywell's ACCUFLO T3027, were investigated for use as the insulation layer for the sensor. Impedance analysis performed on the two coatings using Agilent's 4924A Precision Impedance Analyzer served to prove that ACCUFLO was a better dielectric material for this application when compared to AZ5214.
Two separate detection circuits have been proposed for the salinity sensor. In the Twin-T filter method, a variation in capacitance tends to shift the resonant frequency of a Twin-T oscillator, comprising the sensor. Simulations of the oscillator circuit were performed using Pspice. Experiments were performed on calibrated ocean water samples of 34.996 psu and a shift of 410 Hz/psu was obtained. To avoid the problems associated with the frequency drift in the oscillator, an alternate detection scheme is proposed which employs frequency-to-voltage converters. The sensitivity of this detection scheme was observed to be 10 mV/psu.

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