In science-fiction productions like "Star Wars" or "Star Trek", holograms naturally make noises. People are seen as 3D characters, what they say is transmitted directly. You can even touch them. In the holodeck in "Star Trek" you can beat yourself. The doctor on board the "USS Voyager" is a hologram.
In reality, this is not possible so far. With a new technology, researchers of science fiction technology come but amazingly close. A group led by Ryuji Hirayama from the University of Sussex in Brighton can produce 3D images while producing sound and a haptic signal. You hear the holograms and feel when you touch them.
This is how it works: In a cuboid, the researchers have attached 256 ultrasound speakers at a distance of 20 centimeters at the top and bottom. The elements, also referred to as transducers, produce a sound pressure sufficient to levitate a small polystyrene ball.
Eimontas Jankauskis
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As the sound pressure changes, the ball moves at extremely high speed on a given path through the room. Their tempo is so high that the human eye does not notice the movement.
Specifically, the system runs at 40 kilohertz. The human eye can no longer resolve images with a frequency of 18 Hertz individually and perceives them as a continuously moving image.
Stimuli for the skin
The system linked the researchers with LED light in different colors. Thus, the bead is illuminated on its path - depending on the position with a different color. This creates a colorful, three-dimensional image in front of the human eye. The system is controlled electronically. "The technology was inspired by old TVs," says Hirayama. Their pictures also flicker so fast that people do not notice it.
The special feature of the new hologram is that you can not only see it, but also feel it and hear it: an infrared sensor registers when a finger approaches. Sound pressure of the ultrasonic speakers is then directed towards the fingertip. A tingling sensation that suggests to the brain to touch the hologram.
Eimontas Jankauskis
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The sound of the hologram is generated by the researchers by using the ultrasonic waves to stimulate the bead to oscillate in an audible frequency range. If you play an audio file, it will be played back via the vibration of the bead. In the prototype of the researchers so far, however, are rather simple sounds.
The system still has weaknesses. It takes a long time to render complicated pictures. In the experiment, the researchers tried around a globe. By the time the globule visited all the points on the object, 20 seconds passed. More complex representations need more time.
Researchers are working to increase the frequency of the system. If they succeed in moving the globules faster, a sharper picture would emerge. Even the hitherto quite rudimentary sound could be improved. In addition, Hirayama and colleagues want to use several globules at the same time in the long term to show more details.