Electric power generation using acoustic helical wavefronts in air

Acoustic Vortices (AV) are able to transfer angular momentum to matter and induce rotation to objects with different geometries. Several applications of this feature has already been reported. However, up to our knowledge, the possibility of generating electric power using this type of wavefronts has not been reported. In this work, we present experimental results on the electric power produced by a small generator coupled to a propeller of four blades that is insonified by an acoustic vortex beam of topological charge + 1. The AV is produced using a multitransducer of 123 commercially available emitters driven with a continuous signal of 20 Vpp at 40 kHz in air. The propeller was located 40 mm far from the multitransducer, perpendicular to the principal axis of the AV. A voltage of 6 mV was observed at the electric terminals. A discussion on the obtained efficiency of the conversion is presented. Also, the possibility of harvesting residual acoustic energy by means of wave-matter exchange of linear and/or angular momentum is discussed. Special attention is paid to non-dissipative processes.