changing electric field orientation (for novel PDLC shutters)

Discussion in 'General Electronics Chat' started by Firstname Lastname, Jan 14, 2018 at 2:52 AM.

  1. Firstname Lastname

    Thread Starter New Member

    Nov 2, 2017
    2
    0
    So I brought this up somewhere else but I guess it's better suited as a discussion rather than a question with a simple answer.

    PDLC stands for polymer dispersed liquid crystal and it's a material used in smart windows or smart films that can go from opaque state to transparent state. In transparent state the light transmittance is over 80%. I'm sure you've seen or heard about it before. That said, there are older technologies for achieving similar things. PDLC approach is fast, relatively cheap and needs 60 VAC to work.

    Now let's go to a technology used in other things, LCD shutters.
    LCD with polarizers is used for screens and optical shutters but because it uses polarizers it block over 50% of the unpolarized light. The advantage over PDLC is it needs much lower and safer DC voltage to work and can change from transparent to opaque state much faster (<8 ms vs 100 ms).
    This makes it usable for fast switching applications such as screens, projectors or stereoscopic shutter glasses. But again, it blocks 50% of unpolarized light.

    Wouldn't it be nice to have the polarizer-less feature of PDLC but the fast switching speeds of LCDs? Well, apparently you kind of can, but I'm baffled why nobody has made a product using this technique yet.Could have been the price drop of high power LED backlights for monitors, TVs, especially 3d TVs, or could be the death of the 3d TV fad where polarizer shutter glasses were used. Or maybe in practice it's much harder to implement than it seams.

    There are two ways to increase PDLC switch speed,
    1) increase voltage, up to 400 VAC which is undesirable especially for portable device screens or shutter glasses
    2) using custom conductor geometry and switching the electric field orientation instead of creating and destroying an electric field. https://www.researchgate.net/public...iquid_crystal_using_field_oriented_addressing

    According to the above paper,

    You need to change the orientation of an electric field from one angle to another. Setup is similar to an ordinary capacitor. There’s an insulator material in the middle and two electrodes on both sides of the material.

    [​IMG]

    Electrodes are typically ITO PETs or ITO coated glass and the insulator is the PDLC layer.

    But unlike a capacitor the purpose is to change the orientation of the electric field flowing through the insulator.
    The paper describes using “two finger electrodes” on one side which is not clear to me and all I can guess is it requires one more electrode and custom electrode geometry on one side of the setup, which is possible by etching. However I’m not sure what shape is needed just by reading the paper. So there are actually 3 electrodes, 1 in one side, two in the other. But the paper makes it quite clear the whole point is just to change the orientation of the electric field relative to the insulator from perpendicular to parallel.

    [​IMG]

    [​IMG]

    What geometry is needed for the “finger” electrodes? The 2d cutout diagram from the paper doesn't really show it to me, need a diagram from top view, not cutout from the side.
    [​IMG]

    My guess is this is the "two finger electrode geometry":

    [​IMG]

    Someon told me it's as simple as "if the plane is negative and all fingers are positive, field is perpendicular. If fingers A are all positive and B negative, field is parallel".

    Is this all there is to it?

    I have gotten some ITO PETs for etching and etching is pretty standard, HCl doesn't seem to affect PET.
    Just need to source some PDLC mixture, but would like some opinions if it's worth a try first because PDLC isn't cheap because is only sold in large quantities.

    My own goal is to make better shutter glasses for my portable 3d ready video projector. The 50% brightness cut with LCD glasses makes them unviewable at decent screen sizes. But you could use the same technique for other projects.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    7,572
    1,644
    It may be (I'm no expert on this), but if it is important to maintain the same field strength then presumably either (a) the inter-finger spacing would have to match the PDLC layer thickness or (b) the peak/rms voltage would need to be changed to account for any mismatch.
     
Loading...