Active Noise Control Using Glow Discharge

First-day spacecraft failures frequently occur as a result of the loads experienced during launch into orbit. These loads include structural vibrations transmitted at points of structural contact, and structural-acoustic vibrations created by the excitation of the payload fairing cavity. Structural control techniques, using piezoelectric actuators, have previously been studied as cost-effective ways of reducing the structural-acoustic vibrations being transmitted into the fairing cavity. These structural control methods, while effective at reducing the sound transmitted into a structure, have not been as effective for controlling acoustic reflections from surfaces. This is due to large impedance mismatches at the solid-fluid interface where control is applied. Recent developments in plasma engineering have made it possible to create a uniform glow-discharge plasma over a surface at one atmosphere (OAUGDP). This creates a thin active layer with almost no impedance mismatch to the surrounding fluid. This thin layer can be used to actuate the air around it much like a speaker. This thesis investigates the use of thin OAUGDP layer over a surface for active noise control. This technology was also combined with structural control methods to produce a single surface capable of both structural and acoustic actuation. Results from all of these tests indicate an ability to reduce noise by as much as 15.9dB at specific frequencies and by 9dB over a broad frequency range. The reductions were not global in nature, but certain qualities of this control method make it attractive for the problem of reducing acoustic loads on payloads during launch. Special thanks are due to Paul Bauer for suggestions over the last year or so that prevented me from electrocuting myself and others, Thanks to my lab partner John for his understanding when electricity did go astray, Thanks to John-Paul Clarke, the best advisor a guy could ask for, Thanks to various friends in Boston for making the last couple of years enjoyable, And finally, thanks to my family, especially my parents, Monty and Pamela, for their support of my education over the last twenty odd years.