If you're talking about IR light in the 780-1000 nanometer range (just
beyond visible light) used by most infrared sensors, the concept behind
absorbing any kind of light, including infrared, is to convert it to
heat. The energy has to go somewhere. Don't confuse the much longer
"infrared heat" wavelengths with the wavelengths used for sensors. What
makes something warm in the sun is caused by the longer IR wavelengths.
The color black alone isn't usually enough to absorb infrared. Most
black pigments are black (and therefore absorbing) to visible light.
Their properties are different under short infrared and ultraviolet. If
you have an IR security camera, for instance, you may see black things
(especially cloth) look grayish, even white! They reflect a lot of
near-visible IR light.
Carbon black is the among the most common materials used for absorbing
IR. I would advise against working with the raw material as it's
unhealthy. There are others on the specialty market. For example,
Clearweld makes a coating that is designed for absorbing laser light in
the 940nm to 1064nm range, used for YAG laser cutting -- basically the
same wavelength for most IR sensors. There is no reason why the material
wouldn't absorb non-laser light as well. Go to the Clearweld site for
info. The material isn't black, BTW.
Rubber with carbon black, as found in automobile tires, is a
good IR absorber/diffuser. It's not visible to a SICK LMS LIDAR unit.
Some black chair upholstery fabrics are also extremely good
True enough, though cutting up a car tire for its rubber is probably the
hard way to do it! <g> Most Neoprene is pigmented with carbon black,
though during manufacture a surface sheen may be introduced that causes
some specular reflection. I've found (at the surplus sure) some sheets
of thin Neoprene that are basically a black void to IR. The black rubber
used in those flexible magnetic signs might be a good substiute, and
it's easy enough to find to experiment.
Any ideas which ones? Generally anything woven will show what's behind
it, unlease the weave is very tight. I assume you're talking about some
closed-cell material of some type? I'm always amazed at how some "black"
fabrics, like speaker grille cloth, is basically transparent to IR. (In
my photography days, in the 1970s, we'd have to be careful about what
women wore when taking their pictures. The strobes then didn't use IR
filters, and it wasn't uncommon to get some revealing shots, even if
they wore a dark black sweater. The portrait studio were I worked had a
small warddrobe of tops that weren't IR-transparent. Explaining this to
the customer was the hard part...)
For small areas, one can make an IR absorbing backing using an acetylene
torch (no oxygen burn), or an oil lamp. It eventually rubs off and
collects dirt, though. I had an aromatic oil lamp once and tried this,
but it was real greasy.
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