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New sonic tractor beam levitates objects using only sound waves

These acoustic fields are the first acoustic holograms that can exert forces on particles to levitate and manipulate them. (Asier Marzo, Bruce Drinkwater, Sriram Subramanian)

We may not have real hoverboards yet, but engineers have just invented a device that can levitate tiny objects using only the power of sound — a sonic tractor beam. Researchers say the technology could create a new generation of touch screens made of millions of moving, 3-D pixels. One day, it could even be used to suspend and manipulate tiny structures inside the human body, clearing blood clots with ease. The seemingly gravity-defying device is described in a paper published Tuesday in Nature Communications.

Here it is in action:

Groundbreaking acoustic holograms create unprecedented manipulation and levitation without ever needing to touch an object. (Video: Courtesy of Asier Marzo, Bruce Drinkwater and Sriram Subramanian © 2015)

Sound waves might not be the be-all and end-all in levitation tech, according to lead study author and Public University of Navarre PhD candidate Asier Marzo.

"I think it is important to explore all the different technologies for contactless manipulation," Marzo told The Post. "In the past, our hands were our main tool to manipulate objects but we need new tools for solving today’s challenges."

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"Different fields can exert forces on remote objects," he explained. "And each field has its advantages and disadvantages. Magnetic levitation is powerful but restricted in reach, not very controllable and limited on the materials that can be levitated. Optical levitation exerts very weak forces, and quantum levitation even weaker ones. Using sound waves has several advantages: sound waves have the best ratio of input power to exerted force. Sound can travel through air, water and human tissue."

If you've ever seen a powerful speaker in action, you know that sound waves can be very forceful. A fun way to make sound waves less invisible is to put some liquid in a speaker cone (preferably over some plastic wrap) and watch the force of sound make it dance.

So in principle, a sonic tractor beam is pretty easy to understand: You just need to tune the super-strong sound waves so that they support the object you want supported.

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Acoustic levitation itself isn't new. In fact, NASA has been using it since the '60s to create artificial gravity for experiments. But unlike previous uses of the technique, the new device doesn't have to completely surround its objects with speakers. Instead, 64 miniature loudspeakers at the base of the object are used to create high-pitched and high-intensity sound waves, surrounding the object with high intensity sound. These sound waves create a force field strong enough to hold objects smaller than a millimeter. By manipulating the speaker output, the researchers can make the object stay still, move, or rotate.

In adjusting the acoustic force fields, the researchers were able to create different "containers" for the manipulated object. They could move it with a finger-like apparatus, set it into a twisting vortex, or keep it within the bounds of a "bottle," for example — all using sound waves.

Sound waves do have a couple of drawbacks. They can't travel through empty space, and they quickly lose much of their force out in the open air. Plus, the frequency of the sound waves determines the object that can be lifted.

"The lower the frequency, the larger the object," Marzo explained. "So for instance if you want to levitate a soccer ball, the necessary sound waves will be dangerous for human hearing."

But while Marzo and his colleagues hope to find a way to safely scale up their tech, they're mainly focusing on tiny applications. They're already working with a company called Ultrahaptics — which was involved in the newly published study — on creating new touch screens with the apparatus.

"We are exploring how to manipulate thousands of particles individually. This would enable the development of 3-D displays composed of millions of levitating particles that act as tangible pixels," Marzo said. He estimates that these could be on the market in less than five years. Meanwhile, he's exploring medical applications as well.

"Sound cannot travel through the void of space, but it can do it through water or human tissue. This potentially enables the manipulation of clots, kidney stones, drug capsules, microsurgical instruments or cells inside our body without any incision," Marzo said.

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