Design of Laser-Induced-Heating Configurations for Generation and Control of Underwater Sound Beams.
Abstract
The dependence of laser generated sound fields on the spatial configuration and the temporal sequencing of laser deposition of heat onto a water surface is examined analytically. The thermoacoustic field equations yields a general strategy by which the optical to acoustic energy conversion efficiency can be increased. The generated underwater sound will propagate obliquely downwards within a narrow beam pattern. Such configuration correspond to the supersonic motion of a corrugated heating pattern over the water surface. Simple analytical models are developed to relate the properties of intermediate and long range sound fields to the parameters characterizing the moving heating configuration and the properties of the laser. It is demonstrated that substantial quantitative insight regarding beam direction and Fresnal region amplitudes can be determined form a two-dimensional model with the rate of heat deposition at any given point described by a time independent part and a part that oscillates sinusoidally with time; the latter also oscillates with the horizontal coordinate that points in the direction of the heating configuration's supersonic motion. An extended analytical model has a moving envelope superimposed on the sinusoidal pattern, with an additional envelope to simulate the beginning and ending of the heat deposition. The width of the resulting acoustic radiation pattern can be controlled by causing the configuration to move over the surface with a time varying speed. In spite of the adverse influence of the pressure release character of the air water interface, it is demonstrated that comparable amplitude sound beams can be created that propagate in nearly horizontal directions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 28, 1987
- Accession Number
- ADA178157
Entities
People
- Hsiao-an Hsieh
Organizations
- Georgia Tech