Levitation Breakthrough Achieved in New Study of Acoustic Radiation Force Phenomenon – The Debrief

Scientists from the University of Technology Sydney (UTS) and the University of New South Wales (UNSW) have developed a method that helps fine-tune particle control using ultrasonic waves according to new research, which they believe expands our understanding of the field of acoustic levitation.

The levitation of objects, once a phenomenon seen only in science fiction and fantasy, now represents an area of ​​acoustics with practical applications in multiple fields of research, industries, and even among hobbyists. However, using high intensity sound waves to suspend small objects in the air is nothing new. The theoretical basis for overcoming gravity using acoustic radiation pressure dates back to the 1930s, when researcher Louis King first studied the suspension of particles in the field of a sound wave, and how this demonstrates the force of acoustic radiation exerted against them. .

Later calculations beginning in the 1950s helped refine our understanding of the acoustic radiation force produced by the scattering of sound waves. However, the modern foundations of the science of acoustic levitation draw primarily from the work of superconductivity pioneer Lev. P. Gorkov, who was the first to synthesize previous studies and provide a solid mathematical basis for the phenomenon.

Basically, sound levitation occurs when the propagation of sound produces waves that oscillate but remain fixed in space – otherwise known as standing waves – which can thus be used to suspend a particle in three-dimensional space. In the past, much of our understanding of acoustic levitation relied on the assumption that particles trapped during acoustic levitation are spherical.

Styrofoam sphere levitating above a single beam acoustic levitator (Tatsuki Fushimi/CC 4.0).

However, studies in recent months by researchers at UTS and UNSW have now extended existing theoretical models to also account for particles with asymmetric properties, which the researchers involved say will allow for greater diversity. applications for such technology.

Dr. Shahrokh Sepehrirahnama, Ph.D., of the Biogenic Dynamics Laboratory at the Center for Audio, Acoustics and Vibration at UTS, explains that expanding the models to account for asymmetric particles has been made possible thanks to what is called Willis coupling. This, essentially, refers to the cross-coupling between factors such as velocity and strain, and in the context of the team’s research, has been used “as a measure of asymmetry, capturing the importance of geometric features “.

Such methodology, according to Sepehrirahnama, shows that “asymmetry alters the force and torque exerted on an object during levitation, and shifts the location of ‘entrapment,'” a process which he says “can be used to accurately inspect or sort objects that are smaller than an ultrasonic wavelength.

According to the team’s paper, by “designing the linear properties of an object using metamaterial concepts”, they found that “nonlinear acoustic effects of radiation force and torque can be controlled “.

“We apply our model to a three-dimensional sub-wavelength meta-atom with maximal Willis coupling,” write lead author Sepehrirahnama and his co-authors in the study, “demonstrating that force and torque can be inverted with respect to a symmetric equivalent particle.”

“By considering shape asymmetry in acoustic radiation force and torque, Gorkov’s fundamental theory of acoustophoresis is thus extended,” the researchers write.

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Sepehrirahnama recently said in a press release that his team’s new model “will bring together the two trending fields of non-contact ultrasonic manipulation and meta-materials (materials engineered to have a property not found in nature).” These technologies have several useful applications, including the control and precision manipulation of very small objects, including very sensitive biological materials that can thus be studied without suffering damage from direct contact.

Associate Professor Sebastian Oberst, one of the study’s co-authors, said in a recent statement that many highly sensitive natural objects like insect appendages have yet to be assessed. complete by scientists, largely due to the limitations presented by the apparatus required to maintain them.

“We don’t even have the tools to hold them,” says Oberst. “Touching them can disrupt measurements and using non-contact lasers can cause damage.” Oberst and the team recognize that their newly extended models of acoustic levitation could greatly improve the non-contact analysis methods required for these materials, in addition to contributing to the creation of new materials with new acoustic properties.

The team’s paper, “Willis Coupling-Induced Acoustic Radiation Force and Torque Reversal”, was published in Physical examination letters in October.

Micah Hanks is editor and co-founder of The Debrief. Follow his work on micahhanks.com and on Twitter: @MicahHanks.

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