Some questions about Far Infrared diodes

[mistercris]

I'm trying to find out info on these things in a newbie friendly format and having some issues.

I'm trying to find out a few very specific things before I go in (in order to see if they'd work for the project I had in mind).

1) Can they be set up into a "flashlight" like concept? That is, have them emit in a more or less columnar beam?
2) I understand they "heat" some material but not others. Would they warm up glass? Plastic? If the material is translucent, does it's color matter? (For example, how much of a difference would a green tint glass have on things?). 
3) Is there anything special about mounting these things or is it pretty much the same as LEDs?

I'm trying to find ways to heat various things (water, metal, plastic) through an intermediary medium. I'm talking small objects and small amounts of heating here (not trying to heat a room or anything) but do it without affecting the intermediate medium. A good way of thinking about it is imagine a piece of metal in an enclosed glass box. You can shoot a laser through the glass that melts the metal and not the glass (well for short bursts anyway). I want to do something similar but with FIR.
Is it possible?

[mikeselectricstuff]

Induction heating would seem a better option for this

[CatalinaWOW]

There is no simple answer to your question, other than that far infrared diodes that I am aware of are relatively low power and will not heat anything much by radiative transfer. 

For a slightly longer answer, your question breaks into several parts.  First, long wave infrared is not a precisely defined term.  It frequently means radiation with a wavelength from roughly 6 micrometers to roughly 14 micrometers, but other definitions exist.

Second, the transparency of materials varies widely, and often varies widely over this band.  Materials which are relatively transparent a 6 micrometers may be totally opaque at 10 micrometers.  You need to know the wavelength of the diode you propose using, and the specific material you propose for a window to answer your question.  Many plastics are relatively transparent over parts or all of this band, but it varies with the specific mix of plastic.  It is often easier to measure the transmission than to find the exact recipe of a piece of plastic and find transmission measurements made by someone else.  Also relatively transparent does not mean 100%.  70% transmission would not be an unusual value.  If you were to find a source which could do significant heating (10 W as an example), it would deposit significant heat (3 W in the example) in the window.  This isn't necessarily a problem to the window, since you can arrange the beam size to be large as it goes through the window, resulting in low power density.

Third, the absorbtion of materials also varies widely with wavelength and surface treatment.  You will again need to compare your sources wavelength with the proposed target.  But a general comment is that the reason that metals get so hot sitting in the sun is that they are relatively good at absorbing the shorter wavelengths (.3 micrometers to 2 micrometers) that compose most of sunlight while they are poor radiators (which implies poor absorbtion) in the 6 micrometer to 14 micrometer wavelengths where room temperature objects radiate most of their heat.  So your long wave source is unlikely to be an efficient heater of metal targets.

[mikeselectricstuff]

..and if IR is the answer, what's wrong with a simple heater ? Going to be easier and cheaper than any exotic LED.

[mistercris]

Thanks catalinawow, that's the sort of answer I'm looking for. Couldn't find anything (that I understood at least) googling.
Mikeselectricstuff, a normal heater (of any type) isn't what I'm after. Can't have anything in the container other than the thing being heated.
I'm trying to create heat in a container WITHIN a container (if you can visualize it) but doing it remotely vs with a physical connection. I thought of FIR after happening across a description of those IR saunas and how they work. Thought that the concept might carry over.
I also thought of using something like those wireless chargers or induction heaters but I'm not sure if I'm confident playing with that kind of power requirements.
It's not "for" anything just an experiment I'm trying to satisfy my curiosity if it CAN be done with my limited knowledge of electronics.

[evb149]

This has less to do with electronics and more with physics of materials and their absorbtion / emissivity / transmission / loss / heat capacity / conductivity / index of refraction characteristics to a spectrum.

I believe that the other responder that suggested a heater meant, as I was going to say myself, that a FIR diode may be exotic and incapable of the feat.  Actually to be honest I didn't know that there is such a thing as a "readily available" FIR diode out past LEDs and such devices that taper off in the 1000nm give or take region.

Anyway a "heater" as in "as blackbody radiator" aka incandescent bulb or heat lamp with a surface temperature of XXXX Kelvin will emit mostly long wave IR.  That's why normal incandescent light bulbs are so hot and relatively inefficient (in most cases) compared to LEDs, they emit a LOT of LWIR versus the amount of visible they give off.

So a 1 watt flashlight bulb or even something with less power applied will do what it sounds like you're asking for as well as anything else might as a guess without knowing the spectral transmissivity and absorbtivity of your intermediate and end materials.
If you dial down the current a bit until it is just "red hot" or "orange hot" and not "white hot" you'll of course have more LWIR and less visible according to Wein's law and the blackbody emission spectrum of any generic hot object.

Whether the IR is significantly absorbed by your container's "transparent" window materials between the soruce and the object is still unknown.  Of course due to thermal conductivity and convection and such I'd still expect the entire container (inner box and outer shell) to be significantly warmed by any such heat source and application as a generality.

So what the heck is a FIR diode and where do / would you get them? 
Even the ones significantly longer than around 850nm-870nm that used to be more common a few decades back seem to be much less common these days.

And yeah failing doing it with visible light (e.g. 3W white / blue / whatever LED) or LWIR then as the other response said seeing what you can do with kHz/MHz range EM like a phone charging pad or such is about the only next logical consideration.

[mikeselectricstuff]

One of those nice dangerous 1-3w blue laser diodes/pointers  might be an easy option. it will go through glass just fine ( just watch for the reflections)  and be absorbed nicely on a matt black surface.

[KE5FX]

Any IR diode with enough power to cause noticeable heating isn't going to be eye-safe.

[mistercris]

To answer the question, at least as where to get them, ebay and amazon - entering far infrared diode - gets a bunch of hits.
I'd read the marketing wank from one of those IR saunas and then had found those listings on amazon so combining the two bits of info I thought it'd be able to do what I wanted given the small scale I was thinking.
Thanks all, you def saved me a few bucks on parts with your answers! This is why it's worth asking those who know.

[Gregg]

If the purpose to heat a small sample inside a container is to do so in an inert atmosphere, I would consider modifying one of the cheap 858 hot air soldering devices to use nitrogen instead of air.  I don’t know how available nitrogen cylinders are in your country, but the common suppliers are industrial welding and commercial refrigeration outlets.  This would be similar to the way inert gas is used in TIG welding but with a different heat source.  An inexpensive ebay regulator with a flow meter attached would be a good idea to minimize wasting the nitrogen.  A lot of gas flow isn’t necessary except to keep from burning up the heating element.  Carbon dioxide may work, but it is a pretty good refrigerant on its own and may require more heat input.  The beverage industry [beer and soft drinks] uses CO2 as well as paintball etc.  Argon is a staple in TIG welding and for all practical purposes completely inert.

[CatalinaWOW]

Checking the Ebay listings it seems clear that there has been some slippage going back and forth from English to Chinese.

These diodes are far red (usually called near IR).  Some of the listings call them far infrared.

Lots of window materials will transmit this readily, but not all glasses or plastics - you have to check what you are using.  But it is easy, since transmission at these wavelengths is far more available than for longer wavelengths.

Most metals and metal finishes absorb these wavelengths well, so a heating application might work.  May or may not be the best approach depending on the other things going on around your idea.

The ones on Ebay have enough power that eye safety is a real issue.  Since you can't see them real damage can be done without you realizing it.  Keep yourself and other people safe.

[mikeselectricstuff]

It doesn't need to be IR to heat.
As I said, a blue laser is going to be the cheapest & easiest way to get some heat into a glass-enclosed object. Easily enough to set things on fire.

[raspberrypi]

One of those nice dangerous 1-3w blue laser diodes/pointers  might be an easy option. it will go through glass just fine ( just watch for the reflections)  and be absorbed nicely on a matt black surface.

Where do you get one of those in a "laser pointer" format? I have a green one, but you have to focus it and the color of the object you are trying to burn is important. I call it the raciest laser pointer, because I like to aim it at my skin and say its safe, then aim it my friends who are different shades of black and they yell out in pain when I turn it on.

I don't mind spending a hundred bucks on it, but for that kind of money I want to be sure what it is. The green laser was only 10 bucks but the same thing sells as high as 60 or 70 and I don't want to get "burned".

Oh and what are you making? It sounds interesting. LEDs dont put out much power. Ever tried to feel the heat off your TV remote control?

Any more plane crashes near your house?

[mistercris]

catalinawow, you wouldn't happen to have some info on this would you? I had no idea eye safety would be an issue on these things so I would've for sure messed myself up on it. Any links would do (not TOO technical if possible. I can go through the more technical stuff but it's slow going).
At present I'm trying to heat a small item (can be any material frankly as long as it's small) inside a water filled container inside a water filled pot. I was planning on sealing all items but now I'm concerned about reflections off the glass.

[evb149]

What inspired this interest?
What kinds of materials do you have in mind?

Anyway I think it is impossible.  Water has very high thermal conductivity.  So anything touching water even if it generates heat all by itself will efficiently and quickly transfer heat to the water it is touching, and quickly the nearby warmed water will transfer heat toooo the rest of the water.  Similarly  the container that is filled with water will quickly  transfer heat from the water touching the walls of the container inside and out through the walls.
So you cannot have a significant temperature differential between the inner item and the inner water or the outer water that remains effective withouttttt (a) a lot of extra heat input to compensate for the rapid heating of the water (and it cooling the item correspondingly) and (b) the transfer of heat out into the environment.

Take a pebble, heat it to X temperature above ambient, say by placing it into a pot of boiling water.
Remove the hot pebblle and drop it into a container of cool water.
Notice that within a very short time the pebble has drastically cooled and the water has correspondingly warmed.
And that is with a high thermal mass / high specific heat object like rock that also has   not so high thermal conductivity relative to volume.

So..yeah..no.  Not going to effectively happen optically unless you want to go buy an expensive apparatus that can deposit a lot offff heat in a little time and even if you did, I wouldn't    want to be around when you played with it.  Eek.

catalinawow, you wouldn't happen to have some info on this would you? I had no idea eye safety would be an issue on these things so I would've for sure messed myself up on it. Any links would do (not TOO technical if possible. I can go through the more technical stuff but it's slow going).
At present I'm trying to heat a small item (can be any material frankly as long as it's small) inside a water filled container inside a water filled pot. I was planning on sealing all items but now I'm concerned about reflections off the glass.

[CatalinaWOW]

I haven't located any good current summary documents on eye safety, and don't seem to find any of the older ones in my files.  The following links are the best so far.  Although the first is specifically for lasers, the damage to human eyes is not dependent on the coherency of the light, only the intensity.

https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_6.html

This second link gets you to a page where you can download the actual document.

http://ec.europa.eu/social/main.jsp?catId=148&langId=en&pubId=5926&type=2&furtherPubs=yes


The problem with infrared light is has many facets, all related to the fact that your visual system doesn't activate it's protective mechanisms in response to this light.  You don't blink, you don't look away and the iris doesn't shrink down.  Real damage can be done before you realize there is anything to worry about.  The near IR is worse than longer wavelengths because it still focuses very much like visible light, producing the highest energy densities right at the retina.  Longer wavelengths (even 1.5 micrometers helps) tends to focus short of the retina.  The clear gel that fills our eyes is harder to damage than the retina.