German scientists have made holograms from sound using 3D printed plastic blocks. In a new study, these "acoustic holograms" were found to have the ability to manipulate objects in midair without touching them.
This breakthrough technique can help scientists develop new medical techniques for ultrasound therapies where sound fields can be used to destroy unhealthy cells or tissues inside the body without damaging other healthy cells.
Holograms appear to be two-dimensional images that can turn into 3D scenes when pixels scatter light into different directions. Light waves can create an illusion of depth in holograms.
These new acoustic holograms are made of plastic blocks composed of a special structure. They are built with 3D printers. Scientists 3D printed these structures using layers of material on surfaces, similar to how inkjet printers build layers of ink while printing.
In creating an acoustic hologram, scientists developed a special audio speaker known as a transducer, where 15,000 pixels can be scattered as sound waves to create complex 3D sound fields.
Sound waves can place significant forces on matter. In past studies, researchers have used "acoustic tractor beams" to create elaborate 3D sound fields midair or liquids to push around. This works with the help of multiple transducers. However, in this new study, scientists used only a single ultrasonic sound transducer to generate this 3D acoustic field.
According to the lead author of the study, Peer Fischer from the Max Planck Institute for Intelligent Systems in Germany, instead of using a complex set of transducers, a 3D printed piece of plastic that only cost a few dollars was used.
This new method works by generating 3D sound fields that are 100 times more detailed compared to past techniques. The sound fields can assemble silicone rubber microparticles in water or suspend water drops in the air.
Acoustic holograms could one day help medical doctors in ultrasound fields to take out unhealthy or bad tissues inside the human body.
This new study has been published in the journal Nature.