Here's a description more appropriate to plastics. It's interesting to see the transmission-by-wavelength graph for plexiglass there, which has some very fast transitions in it as well as very variable response to the wavelength of interest. It's not a simple low-pass or even bandpass effect (though most of the transparency is in the region of 700 to 2200nm..
https://physics.stackexchange.com/questions/407900/what-plastic-like-materials-allow-ir-to-pass-through-them PIRs and thermal cameras operate at about 10um Common desktop laser cutters operate at about 1000nm (1um) (other wavelengths are used for metal cutting) Remote controls operate at about 700-900nm, bordering on visible light On Tue, Aug 27, 2024 at 7:37 AM Adrian Godwin <[email protected]> wrote: > You can only cut the acrylic with a laser cutter because the material is > somewhat opaque to the laser light. It absorbs it and is melted. If the > material were as clear to IR as it is to visible light, it would be very > hard to cut because the light would pass right through without giving up > any energy to the plastic. > > Yes, opacity to infra-red by materials such as acrylic, some of which are > highly transparent to visible light is well known and very material > dependent. Similar materials that are transparent do exist though - > consider the thin material covering a PIR, or the often apparently black > material covering the IR receiver of a remote control. Some properties are > astonishing. For instance, the silvery metal Germanium which has the > appearance of a mirror to visible light is used as a lens material for > thermal cameras. > > Infra-red covers a very wide band though, of a few decades, and materials > have varied characteristics. In many cases it is possibe to find something > with the properties you need. Refer to articles such as > https://www.edmundoptics.com/knowledge-center/application-notes/optics/the-correct-material-for-infrared-applications/ > for further details. > > > On Tue, Aug 27, 2024 at 3:59 AM <[email protected]> wrote: > >> Yes, I had the same issue with a case made from acrylic I cut with my >> laser cutter. >> >> >> >> Bill v. >> >> >> >> *From:* [email protected] <[email protected]> *On >> Behalf Of *gregebert >> *Sent:* Monday, August 26, 2024 8:29 PM >> *To:* neonixie-l <[email protected]> >> *Subject:* [neonixie-l] PIR Sensors and plastic cases >> >> >> >> To my surprise, the PIR sensor that I had inside a clear-plastic case was >> not detecting any motion. After drilling a large hole for it, no more >> problems. >> >> >> >> Anyone else see this before ? >> >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/6aac8c8b-901f-4a2a-8245-1bddd137c52cn%40googlegroups.com >> <https://groups.google.com/d/msgid/neonixie-l/6aac8c8b-901f-4a2a-8245-1bddd137c52cn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/00ff01daf81c%2482e1a690%2488a4f3b0%24%40gmail.com >> <https://groups.google.com/d/msgid/neonixie-l/00ff01daf81c%2482e1a690%2488a4f3b0%24%40gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CALiMYrskFwgK%2B1bpJ0axc4c%2BxtK3UvKpJkyPX5-NvwFo1ivb-A%40mail.gmail.com.
