Like invisible tweezers, sound waves can be used to levitate tiny objects in the air. While DIY acoustic levitation kits can be found online, the technique has important applications for research and industry, including the manipulation of sensitive materials such as biological cells.
New research by scientists at the University of Technology Sydney (UTS), in partnership with the University of New South Wales (UNSW), has shown that to precisely control a particle using waves ultrasound, you have to take into account its shape, and the impact it has on the acoustic field. The research has just been published in the journal Physical Review Letters.
Sound levitation occurs when sound waves interact and create a standing wave, with nodes that can “trap” a particle. The current mathematical foundation of acoustic levitation, Gorkov’s fundamental theory of acoustophoresis, assumes that the trapped particle is a sphere.
“Previous theoretical models only considered symmetrical particles. We have extended the theory to account for asymmetric particles, which is more applicable to real-world experience,” said lead author Dr. Shahrokh Sepehrirahnama from the Biogenic Dynamics Laboratory at the UTS Center for Audio, acoustics and vibrations.
“Using a property called Willis coupling, we show that asymmetry changes the force and torque exerted on an object during levitation and changes the location of ‘entrapment’. This knowledge can be used to precisely control or sort objects that are smaller than an ultrasonic wavelength,” he said.
“In a broader sense, our proposed model based on shape and geometry will bridge the two trend areas of non-contact ultrasonic manipulation and meta-materials (materials engineered to have a property not found in nature),” said he added.
Biogenic Dynamics Lab Director, Associate Professor Sebastian Oberst said the ability to precisely control tiny objects without touching them could allow researchers to study the dynamic material properties of sensitive biological objects such as the wings of an animal. insects, ants and termite legs. (An example of a non-contact vibration test of a bee’s wing and an ant’s leg is shown in the photo above.)
A better understanding of the specific structural dynamics of natural objects – how they vibrate or resist forces – could enable the development of new materials.
Associate Professor Sebastian Oberst
“We know that insects have fascinating abilities – termites are extremely sensitive to vibrations and can communicate by this sense, ants can carry many times their body weight and withstand great forces, and the filigree structure of the wings of honey bees 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, nature-inspired materials for use in industries such as construction, defense or development. of sensors. ”
Researchers have focused on understanding the mechanical properties of termite sensing organs in order to build and innovate hypersensitive vibration sensors. They recently identified structural details of the sub-sex organ, located in the leg of a termite, which can detect 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 disrupt measurements and using non-contact lasers can cause damage,” he says.
“So the far-reaching application of this current theoretical research is to use non-contact analysis to extract new material principles to develop new acoustic materials.”
