Acoustic Energy Output and Synchronization of Standing-Wave TA (Thermoacoustic) Lasers

TA (Thermoacoustic) lasers were constructed, tested, and characterized for the generation and manipulation of high-amplitude and high-frequency acoustic thermal waves. Pyrex glass tubes with one open end and stacks made of ceramics widely used in automobile catalytic converters were employed to generate TA lasers. Temperature gradients are created across the stack heated by a thin NiCr(nichrome) resistance wire at one end, and cooled at the other end by radiation and heat losses to the ambient air by natural convection. The acoustic waves (TA lasers) were generated for different power input rates, various lengths of glass tubes, stack positions and laser arrangements. For a resonance tube of 100mm, the highest frequency of 914Hz was observed with SPL of 90dB and the power input of 35W. By increasing its length to 200mm, however, there was a decrease in its frequency to 500Hz with maximum SPLs of 112.8 dB for 30mm in ID. Two TA lasers were acoustically coupled through the air mass between their openings when the openings of the two lasers were very close to each other and a phase difference fixed at nearly 180°, generating a much lower sound energy level at the focusing point. When the separation distance between the two lasers exceeded a certain value, synchronization of a TA laser pair could not be achieved.