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I would like to use the MLX90640 far infrared thermal sensor array on a car as a "night vision" camera. Since glass blocks thermal radiation I have to install it outside the cabin. Is it possible to make the sensor waterproof while still keeping its thermal sensitivity?

I know that water blocks IR so there will be no thermal imaging when the sensor is wet but the idea is rather to protect the sensor from damage and wait till it dries out for further imaging.

I think there may be 2 ways to protect the sensor:

  1. waterproof coating
  2. waterproof housing

Unfortunately I have no idea on practical realization of either of those.

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  • \$\begingroup\$ There is a special glass for that - Germanium. \$\endgroup\$ – Marko Buršič Sep 10 '18 at 19:50
  • \$\begingroup\$ I wonder whether some king of coating that is used for waterproofing electronics may work here. \$\endgroup\$ – Kozuch Sep 10 '18 at 20:10
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    \$\begingroup\$ Sapphire is my favorite and, in this particular device's case, would be appropriate. Your sensor (difficult to find this data in the datasheet itself) responds to 800 nm to 2500 nm. Which is fine (almost perfect, in fact) used with sapphire. Very durable stuff, too. \$\endgroup\$ – jonk Sep 10 '18 at 20:43
  • \$\begingroup\$ @jonk Thanks. Would you mind sharing where you found the spectral response? Because indeed I can not find it in the official datasheet. \$\endgroup\$ – Kozuch Sep 10 '18 at 21:07
  • \$\begingroup\$ @Kozuch Here. Though, as I'm sure you will point out, this doesn't specifically identify the product you named. But it does provide me with the likelihood sufficient for adding a comment. I would have considered a full answer based upon some experience if I actually had been able to get a clear specification in your datasheet (or elsewhere) that noted your device supports exactly this range. Since I couldn't find it, I left this as a comment. \$\endgroup\$ – jonk Sep 10 '18 at 21:21
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There are a variety of common materials that are available to be used as enclosures or windows for an enclosure i.e. Calcium Fluoride (CaF2, Fused Silica (FS),Germanium (Ge),Magnesium Fluoride (MgF2), Sapphire, Silicon (Si),Sodium Chloride (NaCl) to name a few. There are also IR transparent plastics. I had a similar application years ago and I started down the same path as you have, but when I started to go through all of the time in engineering and research I went with a commercially available IR camera with an IP66 rating.

If yours is a labour of learning, then Google "IR transparent materials" and in turn use them as a "window" to your enclosure for your selected sensor it would be the best place to start.

I looked very quickly on the spec sheet for your chip and I didn't notice what wavelength of IR it is the most sensitive to. You would have to ensure the "window" material is efficient in that range.

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