M.S. Thesis Presentation by Toby R. Lentz
Wednesday, September 5, 2001

(Dr. Peter Rogers, advisor)

"Design and Testing of a Low Frequency, Water-Filled Sound Exposure Chamber"

Abstract

Military scuba divers often risk exposure to high-amplitude sound fields during hull inspections, mine countermeasure procedures, and shore assaults, typically from sources such as active sonar pulses and underwater explosions.  In addition, civilian recreational divers may face the possibility of an encounter with high-amplitude sound fields while engaged in shallow water diving.

In order to maintain safe and secure diving environments, it is necessary to determine basic tissue damage mechanisms and acceptable sound exposure limits.  The design of a chamber for testing small animals to explore these criteria was developed and implemented.  The design of the chamber was driven by several conditions: pressure levels in the chamber must be sufficiently high to cause tissue damage, the chamber must produce an incident plane wave, and the chamber must produce pure pressure and pure velocity incident waves to determine the potential damage mechanisms in animals.

 The design of this chamber involved an investigation into the possible implementation of an active mass control system that would lower the effective masses of the piston sources.  This control involves feedback from accelerometers mounted on the rear face of the force actuators into the piston drive signals.  The system resonance will be effectively shifted to higher frequencies, allowing for damage measurements at frequencies previously masked by the fundamental chamber resonance.