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Idea for Stroboscopic Flat Panel Display

I have this idea for creating a large flat panel display, and wonder if it's feasible.

The basic idea is for the panel to be a thin slab chamber of water or gel. The edges are coated with a reflective mirror surface, so total light reflection keeps light inside the panel. One side is perforated with tiny holes, so the water's surface tension keeps it flat.

Three stroboscope LEDs feed red, green, and blue light in turn into the edge of the slab. These need to be able to provide extremely short duration flashes at precisely

60hz (or greater).

The display is shaped using a row of ultrasonic transducers along one edge of the display. These act as a phased array, concentrating sound waves onto individual pixels. The computer electronics sum up the waveforms of every displayed pixel. As a result, when the strobe flashes, the "active" pixels are places where the sound is concentrated. In these places, water pressure causes the water surface at the perforations to be bumpy. These bumps spoil total internal reflection, and as a result light can escape at the active pixels.

Note that these sound waves only concentrate onto the desired pixels momentarily. This is why a strobe is required. The light "captures" the image at the precise point in time when the sound waves are concentrated as desired. The rest of the time, these sound waves interfere in arbitrary ways. If light were applied continuously, imaging may still be vaguely possible but it will be extremely blurry--each active pixel would have an hourglass shaped halo around it.

The duration of the strobe pulses need to be maybe one microsecond or less, but the brightness needs to be able to illumate the entire panel, if necessary (for a pure white image). Is that feasible? Would multiple LEDs be necessary or better?

I'm not sure what requirements are for the linear transducer array. Assuming a pixel size of around 1mm, the transducers need to operate at at most a 1mm wavelength and need to be at most 1mm wide.

I think this concept could be suitable for inexpensive flat panel displays. Most of the display is simply a water chamber surrounded by bulk glass or plastic. One edge has the ultrasonic transducer array, which I imagine would be the most expensive component. Is there a way to make this component less expensive?

The display itself is naturally transparent. For use as a TV or computer display, you'd want it to be backed by a black coating, of course. For an artistic display, the transparency may be considered a feature rather than a flaw. This panel may be cut to any convex shape (as long as the transducer array has an unobstructed view to all pixels in the active display area).

Ideas? Criticisms?

Isaac Kuo

Reply to
IsaacKuo
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On a sunny day (17 Mar 2007 10:48:58 -0700) it happened "IsaacKuo" wrote in :

I am not 100% sure how your system works, _one_ array of transducers would have problems creating _one_ pixel or one row of pixels in the other dimension. The idea to use fluid is not new, look up 'Eidophore'. In the Eidophore a scanning electron beam was used to manipulate the surface of an oil film. In a vacuum and electron beams can go anywhere fast. So how do you addres coordinate x,y?

Reply to
Jan Panteltje

My idea was to build up an image in time, so that the waves constructively reinforced to create the desired image at the instant the strobe light was flashed.

However, I have since realized that I had the approach all backwards. This approach requires very precise control of the transducers in a highly complex way.

The transducers were doing a very complex job, while the LEDs were doing a very simple repeating job (just strobing periodically).

Instead, the greatly superior approach is to have the transducers do a relatively simple repeating task, while the LEDs do a relatively simple modulated task. The transducers produce sound waves to constructively reinforce on a simple raster scanning pixel, while the LEDs create the image by modulating their brightness levels.

My new refined idea has a different construction. From back to front:

  1. Black rear coating.

  1. Clear reflection coating.

  2. Plastic optical chamber.

  1. Perforated clear mask.

  2. Water chamber.

  1. Clear front wall of water chamber.

The plastic optical chamber is a slab of plastic with a mirrored coating around the edge. It's made of a hydrophobic material. Red, greed, and blue LEDs feed this chamber with light from the edge, where total internal reflection contains the light.

The perforated clear mask is also made of a hydrophobic material. The surface of the water has bumps which poke into the perforations, but these bumps don't touch the optical chamber unless sound vibrations provide sufficient pressure.

The water chamber has maybe a dozen blade shaped sonic actuators spaced across the bottom edge. These form sound waves which constructively reinforce to a raster scanning pixel. Within the currently active pixel, pressure is sufficient to make the water bumps touch the optical chamber. Light leaks out from the chamber at these contact points, and reflects off the curved bump surfaces to deflect the light into a forward cone.

The waveform required for creating the raster scanned pixels is calculated in a straightforward manner. For each pixel, there's a particular time "t" when it should be activated. The required waveform is a spike at time t-d/s, where d is the distance between this pixel and the sonic actuator, and s is the speed of sound in water. By summing up all of the spikes, you get a periodic waveform for each sonic actuator.

This approach vastly simplifies the electronics design task. The Red, Green, and Blue LEDs are simply fed analog amplified signals straight from the VGA cable. The challenge is calculating the transducer waveforms and syncing them up to the incoming hsync and vsync signals.

Isaac Kuo

Reply to
IsaacKuo

On a sunny day (17 Mar 2007 22:28:34 -0700) it happened "IsaacKuo" wrote in :

Perhaps you could make a small prototype to see if any problem some up. A prototype with only a few pixels, and one color.

Reply to
Jan Panteltje

No idea ... but an interesting variation would be to feed audio into the transducers and shine powerful LED or laser light from below (for transmission) or above (for reflection) such that the "picture" gets projected onto a ceiling or wall. You could even put a small amount of oil on top for a thin-film effect.

Hmm, might have to go and try this ...

[...] 
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Michael Brown
Add michael@ to emboss.co.nz - My inbox is always open
Reply to
Michael Brown

Yes, I think this refined design is getting simple enough that I can try it out. My original concept was just excessively complex.

I've currently refined the concept so there's no need for messing with water. There are now only two layers:

  1. Rigid optical sheet of clear plastic edged with mirror coatings and three LEDs.

and

  1. Flexible vibrating sheet of with a frosted inner surface. The edge is supported at 12+ points by vibration actuators.

Instead of sound pressure waves, this sheet is vibrated transversely, like a rubber sheet. The frosted inner surface contacts the optical sheet at a single pixel at a time (raster scanning).

Compared to my earlier concept using water, this is a lot less "fiddly". Unfortunately, the frosted surface will reflect ambient light so the black levels are no better than a front projector. This may be mitigated by using a dark coating, but of course this cuts down on the display's own light also.

Isaac Kuo

Reply to
IsaacKuo

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