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Infra-red is more penetrating than visible light. That is why firefighters use infra-red imaging technology in smoke-filled room (where visible light cannot pass at all). That is due to longer wavelength that infra-red has.
I have a opto interrupter, and I need a material to use as the codewheel ( the slotted wheel). Black plastic about 1.5mm works (most common type). White plastic with ~1mm does not work although it does not let visible light pass through.
A thin aluminum foil 0.2mm does not let through IR at all. So I was wondering if this property is true for all metals, especially copper.
Hi, Its possible that your white plastic is NOT passing IR but reflecting it and than it can reach your sensor. Black object absorb IR or other kind of radiation. Don't forget IR radiation is like heat, so if its powerfull it can heat your metal sheet and than it passes even metal .
I wolud not expect copper sheet 0.1mm thick to be infrared transmissive.
How about an old CD?
You can scribe as many lines/slots as you like.
Scratch off (or machine) the silver (opaque) backing to leave yourself a translucent chopper disc.
You can also shallow drill holes around the periphery to the same effect.
Using 2 discs - one stationary - a vernier effect may also be achieved.
I have used them to make very precise encoder discs.
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