Sound production via Joule heating has been observed since late 19th century. The term “thermophone” was coined soon after to define an acoustic transmitter, where an alternating electrical current produces surface heat-flux fluctuations and, consequently, pressure waves in the surrounding fluid. Such transducers offer several potential advantages over conventional mechanical devices owing to their design simplicity, lightweight structure and acoustic purity. Moreover, thermophones are a promising technological step in the field of active noise cancellation. The ability to generate sound without mechanical motion enables to place the emitter directly at the noise source rather than at the remote point of observation, resulting in a global destructive interference. Recent theoretical papers predict that for the case of vibrating noise boundary (such as conventional loudspeaker), at the optimal cancellation point, the ratio between the thermal and kinetic energies of the two co-planar sources depends on the heat capacity ratio of the fluid medium that surrounds the acoustic system.
Although electro-thermo-acoustic energy conversion process has been the centerpiece of several studies, there is no clear consensus as to the correct approach to modelling thermophone sound production. This leads to a lack of understanding which structural properties would result in an optimal thermo-acoustic transducer. The present research addresses this gap by implementing state-of-the-art thermophone simulation framework, coupled with extensive experimental campaign, that provide an outlook on the performance impact associated with various thermophone geometrical and physical properties. In following, feasibility of active noise cancellation of a vibrating source is demonstrated in various gaseous media.
