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Kapton emissivity in thermal IR

Here's a piece of copperclad with a bit of 3 mil Kapton tape stuck to it,

ftp://jjlarkin.lmi.net/Cool1.JPG

(no, my hand's not that short and pudgy... that's just the angle)

and here's the same scene in the thermal IR:

ftp://jjlarkin.lmi.net/Cool2.jpg

The copper is a near-perfect mirror at these wavelengths, so you can see the reflection of my hand. But the kapton is almost black, so it ignores my hand and displays the actual temperature of the copper.

The ceiling is warmer than my desk, which explains the rest.

Neat: Kapton is also OK in ultra-high vacuum.

John

Reply to
John Larkin
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Cool. I wouldn't have thought it's this much of a difference.

Do you guys hold it on each others heads these days, to see who might have the scary flu?

--
Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

A question - is it that the Kapton emissivity is low for IR or that the Kapton reflectivity at IR is low?

That camaera would sure make a handy fault finding tool for boards.

Reply to
Nutz

The emissivity is high and the reflectivity is low. The sum of E + R always equals 1. You can judge E and R by waving your hand over some material and looking at its temp with an imager or an IR thermometer; if it has low emissivity = high reflectivity, you'll see the reflection of your warm hand change the apparent temperature of the stuff. Which is why IR temperature measurements can be so tricky: you can seriously burn your hand touching a piece of copper or brass that reads room temp on an IR: the IR is seeing the reflection of the room, not the temp of the metal.

It sure does, like when a power supply is caved in and you don't know why. I found a shorted cap like that recently. Too bad they're so expensive.

John

Reply to
John Larkin

age

Is this true? Reflectivity I think I understand. There will be an angular dependence to the reflectivity. Emissivity I'm a bit vague about....ratio of energy radiated to black body radiator at same temperature.

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Is there any angular dependence?

George Herold

Reply to
ggherold

A picture is worth a thousand words ... well in this case,

2 pictures. Nice comparison. Thanks for posting them!

Ed

Reply to
ehsjr

I once used a smear of wet cigarette ashes to get an IR thermograph reading from aluminum.

Cheers! Rich

Reply to
Rich Grise

It's true assuming the surface is opaque. If there's transmittance it's a bit more complicated.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

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