Holograms aren't just for stage shows anymore. A group of scientists have figured out how to make holograms out of sound waves. What's more, they say they can use these next-generation holograms to levitate and control tiny objects, according to a new study published Tuesday in the journal Nature Communications.
The image holograms you're used to are tricks of light generated by getting light waves to interfere with one another to create the appearance of three-dimensional shapes.
"We took that concept and applied it to sound," said Asier Marzo, a computer scientist at the Public University of Navarre in Pamplona, Spain, and the first author of the study. "If you have a two-dimensional surface that projects different sound waves, you can create any shape from these acoustic fields."
The scientists found that they could program the sound waves to exert a force strong enough to keep objects afloat, like a high-tech fan that keeps a beach ball up in the air. They devised sound holograms whose shapes were really good at handling minuscule styrofoam spheres. The best ones, which looked like paddle-like tweezers, tiny tornadoes and hollow bottles, could rotate, spin and drag objects through space. This is the first time acoustic holograms have been described, according to Marzo, and the first time they've been used in this context.
"The possibility of holding and manipulating particles from a distance with invisible forces is intrinsically exciting," said Marzo. "It can be something dull like levitating the remote control from the table to your hand; or something incredibly sophisticated like tangible displays composed of millions of levitating particles acting as pixels."
For now, the researchers' acoustic holograms can only direct styrofoam spheres that are 1 millimeter, or four hundredths of an inch, in diameter. But the researchers plan to tweak their setup to be able to move a beach ball around. Being able to control objects with sound could be useful in applications as varied as space science and medicine.
Other research groups have used sound to levitate small match sticks, water droplets, and screws (which you can see in the video below). The big advance here, apart from the sound holograms, is the ability to manipulate objects using single-sided sound beams. This, Marzo says, will make biomedical applications, like handling and destroying clots, tumors and kidney stones or delivering medications to specific tissues, more feasible because it reduces the amount of equipment necessary to steer objects, while increasing precision.
We're still years away from being able to apply sound levitation to medicine, Marzo says. It needs to be tested in animals, but he insists this has a better chance at working than older methods.
Previous sound levitation setups, like the one in the video above, surround the particles scientists want to control from at least two sides, like a sandwich. If the object you want to tweak is in your hand or toe, that might work well enough, but if you want to manipulate a molecule or cell in your heart or pancreas, this sandwich approach probably won't work because getting one part of the setup inside the body might be close to impossible. And you need both to work because each panel of "speakers" emits sound waves that collide to form a standing wave with nodes that create an acoustic force that cancels out the force of gravity. They're like a little invisible hammock.
The problem though is that these tiny sound traps don't give scientists a lot of leeway in moving objects. The "hammock" can be moved up and down or side to side, but that's pretty much it. Rotating it or moving an object in three dimensions can be more challenging. The holograms get around that because they help "clasp" the object the scientists want to control.
"We want to move an object wherever we want and rotate it wherever we want," Marzo says. Wannabe sound surgeons should keep tabs on their future work.
Daniela Hernandez is a senior writer at Fusion. She likes science, robots, pugs, and coffee.