Albert McKeon

Apr 26th 2019

It’s Not Fiction: Sound Wave Technology Levitates Objects


It’s usually the stuff of movies. A superhero or villain has the ability to move objects through telekinesis. Who can forget tiny Yoda lifting a large X-wing fighter, using only his mind?

Science fiction recently became a reality of sorts when two professors of engineering used sound wave technology to levitate objects. It wasn’t sleight of hand or a flight of fancy, but rather a result of manipulation through a system the professors call “holographic acoustic tweezers” (or HAT). Their system creates ultrasonic sound waves that, in turn, independently move particles in a 3D space.

Compared to the fictional Yoda’s Jedi skills, the professors’ experiments are small in scale, but, for now, that’s the point. They hope the acoustic power of their tweezers will enhance microsurgery, replacing potentially intrusive holographic optical tweezers with a tool that could perform medical procedures without touching a patient. As for manipulating larger objects, they envision HAT-enabled creations like a physical hologram that hangs in mid-air.

Using Sound to Manipulate Styrofoam Balls

Professors Bruce Drinkwater, of the University of Bristol in England, and Dr. Asier Marzo, of Universidad Publica De Navarra in Spain, didn’t need manipulation to turn heads with their groundbreaking paper published last year in the Proceedings of the National Academy of Sciences.

As described by ScienceDaily, in their experiments the professors essentially turned up the volume of ultrasonic waves, creating a sound field strong enough to move small objects but at a pitch too high for humans to hear. “We applied a novel algorithm that controls (two arrays) of 256 small loudspeakers, and that is what allows us to create the intricate, tweezer-like, acoustic fields,” Marzo said.

Each array is connected to a computer that controls the sound. In between the speaker arrays sits, at ground level, a reflective surface where the tiny experimental objects are placed, according to Playing with the volume of sound, the professors can control the movement of the objects. They manipulated as many as 25 Styrofoam balls no larger than 3 millimeters in diameter in the experiments highlighted in their paper.

Possible Uses for Microsurgery and Large 3D Displays

In that paper, the professors express their hope that HAT replaces what was also a novel invention 20 years ago: HOT, or holographical optical tweezers, which can build 3D microstructures or be used in medical procedures. The drawback of optical lasers is that, as a University of Bristol news service article explains, they travel only through transparent media, making them difficult to use on applications that involve biological tissue.

Unlike optical lasers, as the university article noted, ultrasound can safely and non-invasively penetrate biological tissue, as seen during pregnancy scans and kidney stone treatment.

“Optical tweezers are a fantastic technology,” Drinkwater said in the article, “but (are) always dangerously close to killing the cells being moved. With acoustics we’re applying the same sort of forces but with way less energy associated. There’s lots of applications that require cellular manipulation and acoustic systems are perfect for them.”

Indeed, Drinkwater and Marzo hope HAT becomes a valuable tool for microsurgery. In an attempt to prove HAT could replace HOT in something as delicate as surgery, the professors attached two millimetric polystyrene spheres to thread and, powered by the sound of HAT, attached the thread to fabric.

The professors told the university news service that they are aiming to manipulate water particles and, ultimately, biological tissue. “Now we have more versatility,” Drinkwater said. The technology creates “multiple pairs of (non-invasive) hands to move things and perform complex procedures. It opens up possibilities that just weren’t there before.”

Beyond medicine, this new form of sound wave technology could help architects, military planners and other professionals who need to see how constructed objects interact in different surroundings. Such a use isn’t as far-fetched as Star Wars characters manipulating objects. Drinkwater envisions the acoustic tweezers someday creating more intricate sound fields, which could allow tangible pixels larger than Styrofoam balls to levitate and form a physical hologram in mid-air.