Using ultrasound to move a tiny illuminated ball pixel creates a 3D visual effect...
18 November 2019

Interview with 

Peter Christopher, Centre for Molecular Materials, Photonics and Electronics, Cambridge University


R2D2 Droid from Star wars


Here’s a story from a long, long time ago in a galaxy far, far away! If you’ve ever wanted a 3D holographic-style display like the one Princess Leia uses in Star Wars, you may be in luck. Researchers in the UK and Japan have invented a device that uses sound waves to produce a 3D video, audio and interactive touch display. And one of the best parts - no flimsy red and green glasses to wear! Nadeem Gabbani asked Peter Christopher, from the Centre for Molecular Materials, Photonics and Electronics at Cambridge University, to take him through how the new gadget works…

Nadeem - "Help me, Obi Wan Kenobi. You're my only hope." Most of us can remember hearing those famous words and watching - and marveling - as R2D2 projects, in 3D, Princess Leah's plea for help to Luke Skywalker and Ben Kenobi in the first Star Wars blockbuster. It was all very futuristic. But now the future is here! Sort of. Scientists have created a new type of device that uses sound waves to produce 3D video, audio, and an interactive touch experience, all without the use of glasses or additional equipment. Peter Christopher researches similar technologies at the University of Cambridge.

Peter - For many, many years people thought that wouldn't be possible. Then in the last few years we've begun to see people taking steps towards having 3D displays, and full 3D displays as opposed to the tricks that are used to make things appear 3D inside a 3D cinema or on a 3D television.

Nadeem - The display itself is about the same size and shape as a microwave, but with the door removed. And this where the magic happens: the display actually uses sound waves to produce an image.

Peter - The technology these guys are using is very clever. They are taking effectively a speaker wall, a very small speaker wall, and a second one matching it, and are using that to form a standing wave. So I don't know if you've ever been to the beach where there isn't much of a current, and you throw a log or a ball out to sea, you'll see that the waves will go up and down but the ball will stay still. And with clever manipulation of the waves you can actually move the ball around without actually moving the material.

Nadeem - The display works on the same principle but moves the ball faster than the human eye is able to resolve, producing a persistent image. To add colour, the ball is illuminated with colour LEDs at distinct points during its travel corresponding to the colour of the same point in the image it's trying to reproduce, just as if it were a pixel. This is a very interesting approach for making 3D images. But why are they using sound rather than light?

Peter - I hate to say this, 'cause obviously they're my competition, but I think acoustic technology makes more sense in the short term. The wavelengths of light that people can use is much, much, much smaller, which requires you to control light on the scale of nanometres; whereas if you use acoustic, or sound-based technology, you only have to control it on millimetres.

Nadeem - And how small is a nanometre?

Peter - So a nanometre is ten to the minus nine of a metre, which translates to about ten atoms.

Nadeem - But then how do they reproduce sound? The speakers in the display vibrate at a frequency of 40 kilohertz, or 40,000 times a second - well outside the range of human hearing.

Peter - The ultrasound waves used for controlling the ball are very high frequency, much higher frequency than you can hear. And the scientists are using a technique known as pulse width modulation to superimpose a much lower-frequency sound wave on top, not in an entirely dissimilar way to, say, your old FM radio you would have as a kid.

Nadeem - Cleverly, the system is not just able to simultaneously reproduce images and audio, but also feedback through tactile touch. This works in a similar way to the image production except instead of a ball being trapped and moved, it would be your finger. This new type of display could enable a whole new range of applications which require a 3D interaction between the user and the content, such as entertainment, training, or gaming, for example.

Peter - I believe the technology is impactful primarily because the image is actually in space. So if you go to a 3D cinema or have a 3D television in your home, or you use an Oculus Rift or other heads-up display; if you use those technologies they're using tricks to trick your eyes into thinking you're seeing a 3D object. This technology is cool because it's a step towards having the first truly 3D displays, as opposed to ones that only look 3D under a very specific set of circumstances. This technology is also very cheap in comparison to 3D cinemas and you could do that for hundreds, rather than hundreds of thousands, of pounds.

Nadeem - So it sounds like what was once “a long time ago in a galaxy far, far away”, is now very much within reach.



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