h a l f b a k e r yFewer ducks than estimates indicate.
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Windows with switchable opacity have been around for a while. These use a layer of liquid crystal between two panes of glass which can be activated by an electric current.
I propose a window with switchable reflectivity. This would be useful for cars when sitting in the sun to prevent overheating.
The
two panes of glass would each have a corner cube array etched into the inner surface. Each corner cube would be a few millimeters width/depth. By total internal reflection, the corner cube array would act like a retroreflector looking from the outer (flat) surface.
When the panes of glass are separated, each side of the glass would become retro-reflective. When the panes of glass are brought together (by linear actuators) the corner cubes arrays of each inner surface would fit together perfectly, essentially making a single pane of glass and thus transparent.
Alternatively, a liquid (with the same refractive index as the glass) could fill the gap between the panes to make the window transparent, and then removed (with a pump or increasing the separation of the panes) to make the window retro-reflective. The corner cubes arrays would be coated in a hydro-phobic material to improve the removal of liquid.
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Would press-fitting the cubes against each other stop them retro-reflecting? |
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Good question. I've seen a video of two glass prisms being placed together to extinguish the total internal reflection; I'll see if I can find it. All the corner cube surfaces might need a thin layer of fluid (e.g. a gel) to ensure optical continuity. |
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I like it! Manufacturing (large-scale) might be tricky, but a test rig for acrylic shouldn't be too hard to do (thinking: make individual cube-point units from metal, assemble into mold, pour in polymer). |
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Note that the higher the refractive index glass, the more effectively this would work. For glass with a refractive index of 1.5, the critical angel would be 42°, so light more than 3° from perpendicular would not be retro-reflected. For glass with a refractive index of 1.8, the critical angle would be 34°, so light more than 11° from perpendicular would not be retro-reflected. |
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Nice, if it were possible to incorporate this into an after-market tint package you'd clean up. |
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