The theory of acoustic levitation is being expanded with new research, which also highlights potential applications.
Sound waves, like invisible tweezers, can be used to make small objects float in the air. While DIY acoustic levitation kits are readily available online, the technology has important applications in both research and industry, including the manipulation of delicate materials such as biological cells.
Researchers at the Sydney University of Technology (UTS) and the University of New South Wales (UNSW) have recently shown that in order to precisely control a particle using ultrasonic waves, it is necessary to take into account both the shape of the particle and its influence on the acoustic field. Their findings were recently published in the journal Physical assessment letters.
Sound levitation occurs when sound waves interact to form a standing wave with nodes that can “catch” a particle. Gorkov’s core theory of acoustophoresis, the current mathematical basis for acoustic levitation, assumes that the particle being captured is a sphere.
“Previous theoretical models have only taken symmetrical particles into account. We extended the theory to account for asymmetric particles, which is more applicable to real-world experiences,” said lead author Dr. Shahrokh Sepehrirahnama of the Biogenic Dynamics Lab at the UTS Center for Audio, Acoustics, and Vibration.
“Using a property called Willis coupling, we show that asymmetry changes the force and torque applied to an object during levitation, shifting the ‘catch’ location. This knowledge can be used to identify objects that smaller than an ultrasonic wavelength to accurately control or sort,” he said.
“In a broader sense, our proposed model based on shape and geometry will bring the two trending fields of non-contact ultrasonic manipulation and metamaterials (materials designed to have a property not found in nature) closer together,” he added.
Associate Professor Sebastian Oberst, head of the Biogenic Dynamics Lab, said the ability to precisely control small objects without touching them could allow researchers to study the dynamic material properties of sensitive biological objects such as insect appendages, insect wings or ants, and termite feet. to research. .
“We know that insects have fascinating abilities – termites are extremely sensitive to vibration and can communicate through this sense, ants can carry many times their body weight and withstand considerable forces, and the filigree structure of honey bee wings combines strength and flexibility.
“A better understanding of the specific structural dynamics of these natural objects – how they vibrate or resist forces – could enable the development of new materials, based on inspiration from nature, for use in industries such as construction, defense or sensor development.”
The researchers have focused on trying to understand the mechanical properties of termite sensing organs in order to then build and innovate hypersensitive vibration sensors. They recently identified structural details of the subgenual organ, located in a termite’s leg, that can sense micro-vibrations.
“It is currently very difficult to assess the dynamic properties of these biological materials. We don’t even have the tools to hold them. Touching them can distort measurements and using non-contact lasers can cause damage,” said Associate Professor Oberst.
“So the far-reaching application of this current theoretical research is the use of non-contact analysis to extract new material principles for developing new acoustic materials.”
References: “Willis Coupling-Induced Acoustic Radiation Force and Torque Reversal” by Shahrokh Sepehrirahnama, Sebastian Oberst, Yan Kei Chiang, and David A. Powell, October 17, 2022, Physical assessment letters.
“Low radiodensity μCT scans to reveal detailed morphology of the termite leg and its subgenual organ” by Travers M. Sansom, Sebastian Oberst, Adrian Richter, Joseph CS Lai, Mohammad Saadatfar, Manuela Nowotny, and Theodore A. Evans, July 8, 2022 , Structure and development of arthropods.
The study was funded by the Australian Research Council.
Other researchers who contributed to this study include Dr. David Powell of UNSW and Dr. Yan Kei Chiang of UNSW Canberra.