M.S. Thesis Defense

by

Cheong Chan

Advisor: Prof. Mitchell L.R. Walker

Experimental Investigation Fast Plasma Production for the VAIPER Antenna

9:30 - 10:30 AM, Tuesday December 5, 2017

Weber Space Science and Technology Building

Room 200A

Abstract:

Very low frequency (VLF) transmission with a range from 3 to 30 kHz is used for communications and navigation due to its ability to penetrate deeply into conductors like salt water (large skin depth) and its ability to diffract around obstacles like mountains. These features are enabled by its long wavelengths (10 to 100 km). However, traditional antennas that radiate efficiently at these long wavelengths require physical lengths of 3 to 50 km. Due to physical limitations of antenna construction, VLF radiation is usually generated with electrically short antennas (100s of meters) that thermally dissipate a significant fraction of the input power. This inefficiency is due to the signal reflecting at the end of the electrically-short antenna and interfering with the subsequent part of the signal.

This work, Very-short Antennas via Ionized Plasmas for Efficient Radiation (VAIPER), proposes a technique to combine a fast-switching plasma and a special signal modulation scheme to circumvent the limitation of traditional antennas. The idea is to use the plasma as a conducting medium for the antenna. By selectively turning on and off the plasma, we can suppress the reflected signal from an electrically short antenna. In theory, this method will greatly improve the transmission efficiency of VLF antenna of a given length. The upper frequency limit of this technique is the speed at which the plasma can be modulated. The challenge is to find a method to produce a plasma compatible with the VAIPER scheme that is also scalable to larger sizes.

For this Master’s thesis, I conducted a preliminary experimental study of fast plasma ignition times and characterization under varying conditions. This project is a collaboration between the Prof Mitchell Walker’s High Power Electric Propulsion Lab (HPEPL) in Aerospace Engineering and Prof Morris Cohen’s group in Electrical and Computer Engineering at the Georgia Institute of Technology.

Committee:

Prof. Mitchell L. R. Walker, School of Aerospace Engineering

Prof. Wenting Sun, School of Aerospace Engineering

Prof Morris Cohen, School of Electrical and Computer Engineering