British and Japanese engineers have created a volumetric display based on acoustic levitation. A small ball is responsible for displaying the image in it, which is moved along the working area by ultrasonic emitters and illuminated by a high-speed projector. In addition, the device can play sounds, as well as create a tactile response when the user brings his finger to the display, say the authors of the article in Nature.
Since science fiction often uses volumetric displays that float in the air, engineers have long been working on creating such technologies in real life. As a rule, volumetric screens work due to optical effects. For example, among such developments are the Canadian light field screen for teleconferencing and the American 3D desktop screen, which works thanks to a lenticular raster.
However, such technologies create the effect of volume inside the screen, but do not give the impression that the image is floating in the air. For this effect, engineers several years ago suggested using acoustic levitation. It works because an array of ultrasonic transducers creates standing waves and stable areas of low and high pressure, capable of fixing small objects, such as polystyrene balls. British engineers have already used this effect, fixing in the air an array of balls that can turn in the desired color towards the observer, or hanging a small translucent piece of fabric onto which the image is projected.
In the new work, engineers led by Sriram Subramanian of the University of Sussex have created a screen in which a single spherical particle is capable of creating a three-dimensional color image in real time. The device is based on two arrays of ultrasonic emitters (16 by 16), located opposite each other: below and above the working area. An LED projector is also mounted on the top side of the emitter array.
The principle of operation of the display is based on the fact that the device quickly moves the area of reduced pressure, in which the polystyrene ball levitates, and illuminates it with a color that changes depending on the position of the ball in space. In the demo, you can see that the display allows you to see the torus knot and butterfly flapping in real time. More impressive examples can also be seen in the video, such as a levitating model of the Earth, however, these frames were shot at a much slower shutter speed and the person is unable to see them with the naked eye.
Experiments have shown that the display can accelerate the ball up to 3.75 meters per second on a straight line and up to 0.75 meters per second when it draws edge and corner details in the image.
In addition to displaying 3D images, the display is also capable of producing sound audible to a person and producing a tactile response. For this, the sound parameters on the emitters are adjusted in such a way that, in addition to the main trap used to levitate the ball, form another area with a changed pressure on the side of it. By placing a finger in it, the user can feel the response of the screen.
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The authors note that the characteristics of the image visible to the naked eye, including size, can be improved by using a more accurate particle motion model as well as a brighter projector. In addition, a more accurate model will allow to allocate a larger fraction of the emitter's duty cycle to the secondary trap, and thereby enhance the tactile response.
There is another technology for creating a volumetric image in the air, developed by Japanese engineers. They suggest using laser emitters for this, which create glowing plasma microdroplets in the air. By moving the glow area, the prototype device is able to create small volumetric figures right in the air, and you can touch them with your finger.
Grigory Kopiev