In the development of thermoacoustic energy conversion from heat to electricity, an array configuration of heat engines can yield high acoustic power output. Arrays consisting of multiple thermoacoustic engines have been constructed in such a way that the heat driven acoustic engines radiate sound into a common cavity where a piezoelectric transducer is used to convert acoustic power into electrical signal. Coupling effects between two or more self-sustaining thermoacoustic engines, operating near 2.5 kHz, have been observed and considered in terms of synchronization. Two types of coupling were observed to be present in the system: mass coupling and acoustic coupling. It was found that for a weaker mass coupling, in the absence of acoustic coupling, anti-phase synchronization was observed. In-phase synchronization was observed for stronger mass coupling. To vary the acoustic coupling present in this system, the volume of the cavity, and the separation distance between engines were varied. In-phase synchronization was observed for each combination of two engines tested at every cavity volume and separation distance, however the average phase difference measured between oscillators was not the same for each cavity volume tested. It was found that the cavity volume with 228 cm3 was the only cavity tested to result in synchronization with an average phase difference of approximately zero degrees, and also maintain oscillations in a stable acoustic cavity mode for each array tested. Acoustic pressure amplitude was measured to be proportional to the number of engines in the array when scaled by the amplitude of each single engine operating alone for arrays up to four engines. Since an array consisting of four engines was shown to synchronize and produce coherent sound, the coupling between engines was identified as global coupling. To determine the threshold of frequency difference for synchronization, two coupled engines were detuned. It was found that the threshold frequency difference between devices that would still synchronize in-phase was between 81 Hz and 97 Hz, approximately 3.5% of the operating frequency. For frequency differences of 98 Hz and higher, beating between oscillators was observed.
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