Airborne ultrasonic vortex generation using flexible ferroelectrets

Abstract

Abstract-Cellular ferroelectrets exhibit interesting electromechanical-acoustical characteristics. Their recent appearance and remarkable properties open up new possibilities for the design and development of ultrasonic transducers. In particular, the feasibility of fabricating ultrasonic vortex generators using ferroelectret films is demonstrated in this work. To this end, a transducer prototype was built by gluing the material onto a tangential-helical surface (outer diameter: 40 mm, pitch: 3.45 mm). Experimental results agree well with the theoretical estimation of the pressure and phase of the acoustic field in the near field and far field, which corroborates the potential of ferroelectrets to customize special acoustic fields. Furthermore, the proposed fabrication procedure is inexpensive and represents a new alternative for exploring and analyzing the special characteristics of acoustical helical wavefronts.

Orbital Angular Momentum Waves: Generation, Detection, and Emerging Applications

“…The difference is that the optoacoustic conversion efficiency of this SPP is very low, and this device requires high-energy short pulse excitation. In addition to passive SPPs, active sound sources with spiral thickness [53], [54] are used to generate acoustic vortices. The dimensions of those spiral structures are generally dozens of wavelengths and their large volume limits the application in low frequency sound waves.…”

Acoustic Rotational Manipulation Using Orbital Angular Momentum Transfer

“…Such a singularity is locally described by a phase dependence of the pressure field of the form expði'Þ, where ' is an integer called the topological charge [7], and is the azimuthal angle. Since then, several works were dedicated to the production of AVs [7][8][9][10][11], their description [2,12], and the study of their propagation properties [2,9,13]. A few experiments that demonstrate acoustic OAM transfer from AVs to matter have been reported, which exploit either the finite angular deviation of absorbing torsional pendulums immersed in air [14][15][16] or the transient angular deviation of an absorbing fisk immersed in water [17].…”

Formation of high-order acoustic Bessel beams by spiral diffraction gratings

“…Phase dislocations using a single source were first proposed by Nye and Berry [20]. The acoustic analog of the optical SPP has also been proposed [21,22], consisting of a transducer with a surface properly deformed to create the helicoidal beam. This method is restricted to a single operating frequency.…”