06 January 2014

New Levitation Device Uses Sound Waves

Image Credit: Thinkstock
University of Tokyo researchers have developed a new technique for levitating objects using sound, allowing the floating objects to be steered in three different directions.

The team wrote in a paper that levitation technology works by offsetting the effect of gravity. Scientists have known that an ultrasound standing wave is able to suspend small particles at its sound pressure nodes.

“Our manipulation system has two original features. One is the direction of the ultrasound beam, which is arbitrary because the force acting toward its [center] is also utilized. The other is the manipulation principle by which a localized standing wave is generated at an arbitrary position and moved three-dimensionally by opposed and ultrasonic phased arrays,” the team wrote in the paper.

The researchers said they were able to confirm that small polystyrene particles were able to be manipulated by their method.

“We examined the stability of the manipulation by measuring the duration of the cyclic movement at different frequencies. The test was conducted using two types of particles, namely expanded- polystyrene spheres of diameters 0.6 mm and 2.0 mm,” they said.

During the experiment, a single particle was set at the third node along one of the acoustic axes from the intersection of the ultrasound beams. They set the sound pressure to 70 percent, and were able to move the tiny particle in several directions.

When it comes to making an object float like something out of a Hollywood film, the researchers say that size matters.

“There are some factors to be considered in choosing the manipulation target, namely the size and material. The size of the manipulation target is determined by the distribution of the potential energy, and a light material is required,” the team said. “The internal force is also an important factor in selecting the material; for example the electrostatic force determines the maximum number of particles that can be at a single node, and the surface tension of the fluid determines the size of droplets that can be levitated.”

The researchers said that their method could be used to create a microgravity-type environment so scientists could study objects in these conditions.

“In conclusion, we have demonstrated an extended acoustic manipulation by which millimeter-sized particles can be levitated and moved three-dimensionally by localized ultrasonic standing waves generated by ultrasonic phased arrays. In addition to the presented examples, we also tested other small objects such as a feather and droplets of alcohol and a colloidal solution.”

The team said they plan to try and manipulate larger particles for future experiments by extending the type of sound wave used.

Now read: Designing an acoustic diode


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