Date of Award

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering

First Advisor

Kurt E. Oughstun

Abstract

Electromagnetic transient waves are pulsed events that occur when there is an abruptchange in the typical steady-state conditions on a transmission line. Digital pulses on integrated circuits and a lightning strike on overhead power lines are some examples of transient voltage pulses. Although transients occur within a very short time duration, they can propagate over long distances; much farther than a slowly-varying envelope signal can propagate. Lingering effects of transients can be damaging to electrical equipment if they are not properly mitigated. Despite the negative effects of transients, certain designed transient pulses may be used to an advantage in remote sensing applications, such as that found in Time Domain Reflectometry (TDR). TDR analysis is a method that makes use of pulse propagation on transmission lines in order to identify and locate any abrupt changes to the line characteristics. Applications include identifying moisture content in soil and detecting damage on printed circuit boards. Accurate identification of damage and other material changes is complicated by transmission line losses, such as attenuation, dispersion, and frequency-dependent circuit parameters. Dispersion and frequency-dependent losses result in different frequency components of the wave propagating at different velocities, which introduces a spreading effect on the wave as it propagates down the line. The effective dielectric constant of the transmission line and surrounding media influences the losses that create the distortion. Material properties and line geometry determine the value of the effective dielectric constant, and they may be identified through a detailed analysis of the reflected pulse. A detailed study of the behavior of pulse propagation on dispersive attenuative transmission lines is presented in this dissertation. Models of three different types of transmission lines are extended in order to compare the effects of material properties and line geometry on transmission properties. These include the coaxial cable, single microstrip, and coupled microstrip models. A numerical model is developed in order to calculate the effects of voltage propagation on a particular transmission line that contains impedance changes. A trapezoidal envelope pulse is considered because of its typical use in digital applications. TDR techniques are then performed with the trapezoidal envelope pulse in order to identify the locations of a change in medium properties. Historically, the group velocity of the pulse is used to perform TDR analysis, but it does not accurately account for the distortion of the pulse in a dispersive and attenuative media. The energy centrovelocity is used here as an alternative to the group velocity. The accuracy of the use of energy centrovelocity in TDR is analyzed.

Language

en

Number of Pages

154 p.

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