Designs Of Undersea Bubble Cloud Targets Using Collective Oscillations To Produce Low Frequency Underwater Sound

Bubbles within a cloud can undergo collective oscillations and produce large acoustic emissions at low frequencies (20 to 2 kHz). Using the collective oscillation properties, relatively small targets can be developed for underwater acoustics research and other applications. This proposal presents three designs to produce and contain bubble clouds in a fixed geometry for the purpose of producing low-cost, high-target-strength acoustic scatterers for sonar calibration and decoy design. THe first design is a cylindrical container made of an acoutstically transparent material. A propeller will be used to disperse the bubble sinto a spatially homogeneous distribution. Compressed air or chemical foaming agents can be used as the air supply to produce microbubbles from an underwater bubbler. The second design uses agar gel to stabilize air bubbles grown from decompression of the supersaturated gel. The third design uses polymer additives to suspend and stabilize bubbles injected at the time of target production. The void fraction and bubble size can be adjusted by mass flow rate, size of aerator and degree of supersaturation, depending on the design selected. The acoustic resonance frequency can be tuned by varying the size and number of the injected bubbles (therefore, the void fraction) and the size of the containers. ANTICIPATED BENEFITS: This research effort will lead to the successful development of low-cost bubble cloud targets for commercial applications in sonar calibration, undersea beaconing, environmental simulation, and designs of decoys and countermeasures. The products will benefit researchers as well as manufacturers in the field of ocean acoustics and defense industries conducting underwater acoustics research.