Optical holograms have come a long way—even bringing Tupac and Michael Jackson back from the dead. But a new type of hologram developed by researchers at the Max Planck Institute in Stuttgart, Germany, takes a different approach to holography, using sound waves to produce 3-D images in water and levitate small objects, Sarah Kaplan reports for The Washington Post. Their research appears in the journal Nature.
“It's just like” the holograms you've seen in "Star Trek," co-author of the study Peer Fischer tells Kaplan. “Only we don't generate an image using light—we do it with sound.”
To produce the holograms, the researchers compute how strong and what phase acoustic waves need to be in order to push around small microparticles of silicon floating in a tank of water. They then use a 3-D printer to create a plastic plate that they place over a speaker. The plate transmits the sound waves at various strengths and phases, creating what is essentially a 3-D acoustic picture in the water. The sound waves then push the silicon beads together to form an image that lasts as long as the tone plays.
In one of their first tests they created a plate that produces Picasso’s peace dove. They also created an acoustic hologram that counts from one to three.
The researchers also used the 3-D printed plates to push small polymer dots and boats around the surface of the water and even suspend drops of water in midair using the acoustic waves. That is something other researchers accomplished last year using a large array of speakers. But Fischer’s team was able to levitate the objects using just one speaker and a 3-D printed plate, which they say is the equivalent of 20,000 small sound transducers.
“Instead of using a rather complex and cumbersome set of transducers, we use a piece of plastic that cost a few dollars from a 3-D printer,” Fischer tells Charles Q. Choi at LiveScience. “With an incredibly simple approach, we can create extremely complex, sophisticated acoustic fields that would be difficult to achieve otherwise.”
Kaplan reports that the technique has many more serious applications than bringing pop stars back from the dead. It could be used to move samples around a petri dish without touching (and potentially contaminating) them. Choi writes that it could help improve the resolution of ultrasonic images, improve treatment of kidney stones or be shaped to attack unhealthy tissues while preserving healthy cells. The next step is to try and produce animated holograms instead of the static images created by the current plastic plates.