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A cybersecurity researcher covered a Toyota in an AI-generated pattern to confuse Flock cameras (www.techspot.com)
submitted 1 month ago by to c/technology@lemmy.world
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[–] 3 points 1 month ago (8 children)

You are mixing different types of IR and on top are wrong for both cases too. We have materials for both NIR and thermal IR that absorb or reflect them.

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  • [–] 1 point 1 month ago (7 children)

    I've been wrong before, this wouldn't be the first time. But what part of it was wrong? Genuinely, can you clear it up?

    As far as absorbing IR light, I'm not even sure how that would work, wouldn't it just be emitted again as heat?

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  • [–] 1 point 4 weeks ago (6 children)

    So if we focus on thermal IR: shiny metal surfaces hardly emit or absorb it. A black surface emits and absorbs as much as possible. We quantify this via the emissivity (and also reflectivity, shiny metal is a mirror). Emissivity of 1 = theoretical maximum of a prefect absorber/emitter (both are directly linked), everyday stuff like skin or wood is about 0.95, shiny metal surfaces roughly 0.1, a rusty or painted surface again about 0.95.

    You only emit and absorb the same in thermal equilibrium. If the surface is hotter, it emits more. If it is colder, it absorbs more.

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  • [–] 1 point 4 weeks ago* (5 children)

    So with that last part, I get that in theory, but practically, you can only really absorb IR temporarily, right? Because it all gets released again as heat eventually. Like, say you have a mostly inert object, that isn't creating any meaningful amount of heat. If you hit that object with 10 joules of thermal IR, over time, wouldn't nearly all of that energy be either reflected or emitted off it as IR radiation?

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  • [–] 1 point 3 weeks ago (4 children)

    That is how heat works in general, but that has nothing directly to do with reflecting or absorbing IR.

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  • [–] 1 point 3 weeks ago (3 children)

    I guess it depends on the context, initially I was making comparisons to heat seeking missiles. In that context, one might use the radar absorbent materials to defeat radar guided missiles, but that trick just doesn't work with heat, as you can't "permanently" absorb heat the way you can other kinds of energy. If your vehicle is also generating heat, hiding that is quite difficult.

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  • [–] 1 point 3 weeks ago (2 children)

    You don't need to absorb it, just emit less. Lower the emissivity and the at the same temperature it will appear colder to a thermal camera etc.

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  • [–] 1 point 3 weeks ago (1 child)

    Agreed, that's a great trick, except sometimes emitting less isn't really an option if you need the afterburner to keep running. And in fact, being able to radiate that heat away quickly can be important to avoid parts melting. You can dump heat into the exhaust, but that isn't always helpful. Leaving the only real alternative to just make something else emit more (a flare).

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  • [–] 1 point 3 weeks ago

    That is a very specific and extreme example. Yes, you can not use magic there. At the end of the day, even the exhaust gases themselves emit IR. But you can make sure there is no direct line of sight onto the hot parts

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