Periodic Reporting for period 1 - RMES (Rotational mechanical effects of sound)
Reporting period: 2022-09-01 to 2024-08-31
The problem that is solved in the project is to find a way to demonstrate experimentally rotational mechanical effects of sound that can be used in the field of acoustic contactless manipulations. This field is important for society as used practically in rheology, medical imaging and other medical applications. The overall objectives of the project are to set an experimental pathway to benefit from the orbital angular momentum of sound for novel options to manipulate matter without contact. In conclusion, a versatile ultrasonic vortex source operating in the air at 100 kHz frequency was developped ; the first-time experimental demonstration of acoustic radiation torque from vortex beam redirection in a pure conversion regime of orbital angular momentum transfer was realised ; the existence of acoustic spin carried by acoustic vortex beams was unveiled experimentally.
At the beginning of the project the task was to develop and construct a certain torsional pendulum as a matter for detecting rotational mechanical effects of sound. As a result, a pendulum was created in the form of a disk on a wire, which is able to rotate around an axis passing along the wire. The next task was to develop and assemble an optical system for detecting rotation, since these are angles of rotation not visible to the naked eye. As a result, a system was assembled that allowed the camera to record the shift of the laser beam reflected from the pendulum when the pendulum itself was turning at a small angle. The next task was to assemble a complete experimental setup for detecting rotational mechanical effects of sound and conduct experiments in the amount necessary for the set of statistics. As a result, an experimental setup was assembled, consisting of a sound source, namely source of an ultrasonic vortex, a torsional pendulum, system for installing and moving the pendulum in the ultrasound area, and an optical system for rotation detection. A series of experiments were conducted with two types of acoustic vortex. The first results were obtained on the acoustic torque acting on the pendulum.
The results were actively exploited by our internship students in January (internship on «Visualising temperature distribution and sound waves with Schlieren optics») and in the summer of 2023 (internship on « Acoustic drone» and internship on « Waves in the deep water regime»)
The intermediate results were disseminated in a form accessible to the general public at the annual public event «la Nuit Européenne des Chercheur.e.s 2023» on September 29. The intermediate results were also presented to the scientific society, namely to «Société Française d'Acoustique», at the event «Les journées jeunes chercheurs d’Acoustique Physiques (JJCAP)» on October 26-27, 2023.
Then the other type of a torsional pendulum was developped and constructed. It is the so-called wireless pendulum where instead of the wire there were used the magnetic carpet and the disk made of a pyrolytic carbon, material that is capable of levitating in a magnetic field. A spiral phase plate, which generates an acoustic vortex when reflecting plane acoustic waves, was attached to the disk. An acoustic torque on this system was detected too by the rotation of the pendulum relative to the axis of rotation when exposed to acoustic waves.
Very useful exploitation of the final results was made by internship students in the spring and summer of 2024 during internships on «Study of the orbital motion of objects under the influence of acoustic vortex waves» and «Optical visualization of the phase and amplitude structure of an acoustic vortex».
To summarize, rotational mechanical effects of sound were detected and measured in two different independent experimental ways by using completely different equipment and processing of the data. The sound with a vortex structure was produced directly by the ultrasound transducer with 8 channels in the first experimental setup and not directly by the reflection of the ultrasound plane waves by the spiral phase plate generating an acoustic vortex beam in the second experimental setup. The rotational effect was detected on the pendulums in both cases but in the first case it was a disk on a wire and in the second case it was a wireless pendulum with a magnetic carpet.
The final results were disseminated at the event «Laboratoire Ondes et Matière d’Aquitaine day 2024» on July 7, 2024.
The results were actively exploited by our internship students in January (internship on «Visualising temperature distribution and sound waves with Schlieren optics») and in the summer of 2023 (internship on « Acoustic drone» and internship on « Waves in the deep water regime»)
The intermediate results were disseminated in a form accessible to the general public at the annual public event «la Nuit Européenne des Chercheur.e.s 2023» on September 29. The intermediate results were also presented to the scientific society, namely to «Société Française d'Acoustique», at the event «Les journées jeunes chercheurs d’Acoustique Physiques (JJCAP)» on October 26-27, 2023.
Then the other type of a torsional pendulum was developped and constructed. It is the so-called wireless pendulum where instead of the wire there were used the magnetic carpet and the disk made of a pyrolytic carbon, material that is capable of levitating in a magnetic field. A spiral phase plate, which generates an acoustic vortex when reflecting plane acoustic waves, was attached to the disk. An acoustic torque on this system was detected too by the rotation of the pendulum relative to the axis of rotation when exposed to acoustic waves.
Very useful exploitation of the final results was made by internship students in the spring and summer of 2024 during internships on «Study of the orbital motion of objects under the influence of acoustic vortex waves» and «Optical visualization of the phase and amplitude structure of an acoustic vortex».
To summarize, rotational mechanical effects of sound were detected and measured in two different independent experimental ways by using completely different equipment and processing of the data. The sound with a vortex structure was produced directly by the ultrasound transducer with 8 channels in the first experimental setup and not directly by the reflection of the ultrasound plane waves by the spiral phase plate generating an acoustic vortex beam in the second experimental setup. The rotational effect was detected on the pendulums in both cases but in the first case it was a disk on a wire and in the second case it was a wireless pendulum with a magnetic carpet.
The final results were disseminated at the event «Laboratoire Ondes et Matière d’Aquitaine day 2024» on July 7, 2024.
The progress of the project beyond the state of the art is to explore experimentally new facets of the rotational mechanical effects of sound based on the use of acoustic vortex beams, which are characterized by a helical wavefront bearing on-axis phase singularity. Expected results of the project are to get quantitative experimental data consistent with the theoretical model for the torque generated by the acoustic vortex. Potential impacts of the project relate to the development of medical methods of elastography using acoustic vortices as ultrasound elastography is a reliable tool for medical diagnostics in order to identify pathologies that cause tissue stiffness disorders. The advantage of the proposed method is that the acoustic vortices make it possible to cover a larger area compared to the already used methods of ultrasound elastography.