Standing-to-traveling wave transition in piezoelectric thermoacoustic energy harvesters

Thermoacoustic systems generate high amplitude sound pressure waves from a thermal input, which can then be harvested via piezoelectric transducers. While a promising concept, current thermoacoustic energy harvesters suffer inherent design limitations which result in: (1) low acoustic power output and simple construction or (2) a reasonable output in a significantly large apparatus (i.e. low power density). The challenge is centered around the working gas oscillations being predominantly standing waves which exhibit a pressure-velocity time phasing that is detrimental to the energy output of such harvesters. The goal of this work is to induce temporal phase adjustments in the excited acoustic waves inside a sealed cavity, thus boosting the amount of useful acoustic power which can be effectively scavenged. By employing open and closed-loop feedback control in a thermoacoustic tube with dual sensing and actuating piezoelectric transducers located at two opposing ends, it is shown that the traveling wave portion of the resultant wave dynamics can be significantly increased with a relatively low level of power pumped into the system. As a result, the controlled device outperforms a conventional one of the same size and configuration and approaches the maximum theoretical potential of thermoacoustic energy harvesting.