Out of the realm of 'Star Wars': Scientists develop sonic tractor beam

Researchers create a sonic tractor beam, capable of lifting small objects.

Courtesy of Asier Marzo, Bruce Drinkwater and Sriram Subramanian
The research team has created three-dimensional acoustic fields with shapes such as fingers, twisters and cages. These acoustic fields are the first acoustic holograms that can exert forces on particles to levitate and manipulate them.

Tractor beams may seem like the stuff of science fiction, but in recent years, they have moved out of the realm of "Star Trek" and "Star Wars." Last year, physicists created a long-distance optical tractor beam that can repel and attract objects. Now, an international team of scientists has developed a sonic tractor beam that can actually lift small objects.

Using high-amplitude sound waves, the researchers generated an acoustic hologram that can pick up small objects, as described in a paper published Tuesday in the journal Nature Communications. 

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

"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." he said.

Study co-author Bruce Drinkwater, a mechanical engineer, told Live Science, ”We've all experienced the force of sound – if you go to a rock concert, not only do you hear it, but you can sometimes feel your innards being moved.” He said, "It's a question of harnessing that force."

The frequency of the sound waves determines what the mysterious ray can pick up. 

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

He also told Smithsonian, “To pick up a beach ball-sized object would require 1,000 Hz. But that enters the audible range, which could be annoying or even dangerous to the human ear.”

Fictitious tractor beams can carry people and even spaceships. But this sonic tractor beam likely doesn’t have the same abilities.

“The power required to lift a human would probably be lethal,” said Marzo. “If you apply too much ultrasound power to a liquid, you will create microbubbles.” As most of a human body is water, this method likely won’t be safe.

Still, this creation could be groundbreaking. 

“Here we have managed to control the sound to a degree never previously achieved,” Dr. Drinkwater said in a news release

Marzo said: "It was an incredible experience the first time we saw the object held in place by the tractor beam. All my hard work has paid off, it's brilliant."

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