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Thread: “smart glass”, maximum possible switch speed?

  1. #1
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    Default “smart glass”, maximum possible switch speed?

    "Smart glass" is just a marketing term for a glass or plastic film with some chemical applied to it that can be made to either pass light / be transparent under certain conditions or become opaque or reflective.

    These smart glasses can be categorized into Passive and Active types. Passive cannot be controlled manually as they do not react to electrial stimuli but to other things such as heat or lighting.

    Active "smart glasses" change their state from mostly transparent to mostly opaque or reflective by electrical stimulation.

    Active ones themselves can be divided further into 3 types: Electrochromic, Suspended Particle Device Technology (SPD) and Polymer Dispersed Liquid Crystal Switchable Technology (PDLC).
    You can google how each works, but the general idea is electrochromic is slow especially for bigger sizes such as used for large windows.

    I want to find out how fast the SPD or PDLC types can switch between on to off and off to on (on meaning opaque or reflective and off meaning transparent).
    If they can be made to switch at 0.008 seconds they could act as a nice fast noiseless optical shutter for various applications that could switch their state at 120 Hz rate.
    The only place I found about the switching state was a website selling commercial films to be applied on office windows and the site mentioned 0.05 seconds which is far from the 0.008, however do note it is not a scientific paper but a website and the speed beyond that shouldn't matter for the use case and could also be a limitation caused by the control board, not the physics of the materials involved.

    I couldn't find any scientific paper on this. Is there any info how fast SPD and PDLC smart glasses or films can be made to switch their states? Right now I'm not even sure if the size of the glass or film matters. For most shutters it would be 1/10th or 1/100th of an office window size, so if size matters it could make a huge difference for other applications such as shutters/light blockers or reflectors in optical systems.

    https://www.youtube.com/watch?v=SaZWW5nASZk&t=5s

    LCD shutters use polarizers which reduces the transmitted light/ brightness to about 50% (of unpolarized light). Most smart glasses on the other hand are above 80% range.
    Last edited by Yerkat; 12-08-2017 at 09:33.

  2. #2
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    Here's a paper describing a switching speed for PDLC at 0.00256 seconds, and 0.00065 seconds to relax. Holographic recording material variation on PDLC (HPDLC) is more than ten times faster. One could make a fast switching beamsplitter for collimated and polarized light with >95% diffraction efficiency, but it would be very expensive to do it.

    https://www.researchgate.net/publica...ted_addressing

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    Are those speeds for the standard method of switching or the "Field Oriented Addressing" method (didn't quite get it) they propose in the paper?
    I'm going to get a sample and try out but the fastest camera I have is only 240 Hz, won't be very clear how/if it works as a 120 Hz shutter with the standard 60V AC voltage.

    Want to build a polarization-free shutter glasses. I'll be the test subject as its AC voltage.
    But I can see this useful for other fun projects, such as selectively blocking sections of a video projection split by relay mirrors and projected onto a rotation projection screen for creating a volumetric display, in cost of resolution, of course.
    Last edited by Yerkat; 12-09-2017 at 06:07.

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    Bumpety bump. I order one big sheet to test. But still, are the speeds in the above paper for the standard method of switching or the "Field Oriented Addressing" method (didn't quite get it).

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    I believe the latter.

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    Can you read ahead of the data to switch slightly before you need it? If it’s a 120hz switch yea no but if the switch is for a shutter on a projector it might work. Ie if the switch is not needed all the time this could work.

    I read what I write and the old kiss theory hits me in the face..... never the less it’s an idea so I didn’t erase it.

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    I'm all for performing experiments with PDLC film, I already ordered a large sheet to test on. But I'll need some help and advice.
    One paper in engrish mentioned using very high voltages (360-720V) to increase the transition speed. I don't think that's practical for shutter glasses or even shutters in small equipment such as in a laser projector. I can link to it but its pay to view.
    The paper Eidetic linked to discusses a different approach to speed things up, "Field-Oriented Addressing", which I'd be down to test out but they use some terms that I can't find anywhere else and is just hard to follow for me. What on earth is a "pixel electrode"? They say there are two electrodes on the back reflective film and one regular ITO electrode in the front side, but in the illustration it looks more like a row of electrodes instead grouped into two. For a shutter you'll need both sides to be transparent conductors. If this approach is possible with that, I could source the materials and try, otherwise this approach will not work for shutters.

    Using a 3 electrode pixel electrode (Fig. 1) it is possible to
    generate a horizontal and a vertical electric field. One transmis-
    sive indium tin oxide (ITO) electrode is on the cover glass and
    two Al finger electrodes (electrode A and B) are on the back
    plane of the display. The ITO electrode has a fixed potential.
    When electrode A and B have the same potential different from
    the potential of the ITO electrode there will be a vertical elec-
    tric field across the cell gap of the display. When the difference
    in potential between electrode A and the ITO electrode and be-
    tween electrode B and the ITO electrode are the same in mag-
    nitude but with opposite sign, the electric field in the cell gap
    between electrode A and B will have a predominant horizontal
    component. In this way it is possible to switch between a hor-
    izontal and a vertical electric field in the cell gap between the
    finger electrodes.
    Quote Originally Posted by kecked View Post
    Can you read ahead of the data to switch slightly before you need it? If it’s a 120hz switch yea no but if the switch is for a shutter on a projector it might work. Ie if the switch is not needed all the time this could work.
    Not sure if I follow. For an active shutter glasses, you need 120Hz show/hide all the time, synced with left and right eye images projected or displayed. For a 3d movie there's a constant stream of left and then right frames.
    Last edited by Yerkat; 12-16-2017 at 05:31.

  8. #8
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    The paper I linked was just to show a typical switching speed for PDLC. I have no idea if it's appropriate for what you're looking to do.

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    It is very much appropriate as long as it can be made to work with a transparent (ITO) conductor film rather than an aluminum. I just can't understand what two electrodes they are talking about in their graph and text.

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    Okay, with the help of a science advisor we figured out what finger electrodes meant and their arrangment.


    ITO coated glass and PET film can be etched like a PCB. Maybe even conductive transparent ink painted on a PET film with a inkjet printer which will be faster and less messy, but I haven't verified this.

    I also managed to find a very low res but highspeed (1000 fps) camera for testing the results.

    One thing left to be able to perform the tests is how to apply the PET films to the PDLC.
    The smart films and glasses already come with the ITO coated glss/film glued to the PDLC in the middle.
    There are companies which sell PDLCs in liquid form. http://www.alibaba.com/product-detai...12514ba38T4ElL
    Or maybe it will be cheaper or easier to remove the original PET films with the ITOs from an existing cheap PDLC smart film and applying new etched ones without damaging the PDLC layer, somehow.
    Any ideas and suggestions?

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