| Description |
Thermoacoustics is a field studying the effects of applying heat to particular resonator geometries, resulting in the oscillations of gas and thereby producing sound waves. This field is a rich blend of many other scientific fields: acoustics, thermodynamics, and fluid mechanics. Thermoacoustic engines work on a similar principle as traditional heat engines. The main difference between a traditional heat engine and a thermoacoustic engine is that an acoustic wave drives the thermodynamic process in the latter. These engines are easy to construct, and there are no moving parts, which reduces the mechanical wear and tear. In our case, we fabricated the simpler thermoacoustic lasers to conduct the analysis. In most previous work within this field, different designs were tested and studied for a single laser operation from which extensive experimental data sets were collected and analyzed. Design and operation of a thermoacoustic laser pair is more complicated. Even though there have been a few coupling studies, detailed information about the acoustic field of multiple thermoacoustic lasers is lacking. Hence, an effort was made to study the interaction between the sound waves by acoustically coupling two thermoacoustic lasers. The acoustic coupling was varied using 4 different configurations. First, the lasers were placed parallel to each other, with their open ends separated by a 1 m distance (0o crossing angle). Next, the sound waves of the two lasers were focused at a particular point, with their openings in proximity at a fixed crossing angle (30 or 90o). Finally, the spatial distance between the openings of the 30 and 90o crossing lasers was increased in their own respective angles. The signals were read using three different measuring devices: a sound pressure level meter, a unidirectional microphone or an omnidirectional miniature microphone. The signals read using both microphones were collected, measured, and analyzed. The results proved that coupling between two thermoacoustic lasers was strong enough to allow synchronization (mode-locking) of the sound waves in a particular frequency and phase. The output amplitude of the synchronized signal produced from coupling two thermoacoustic lasers was always less compared to the acoustic amplitude of a single laser, suggesting out-of-phase synchronization. In a few experiments, the signals from the two coupled lasers did not synchronize because of the mistuning of the natural frequencies between them. When this happened, the uncoupled signals beat with the difference in the natural frequency. The amplitude output of the beating signal was greater than that of the single laser only when the two lasers were in-phase. |
