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Large, intelligent fliers would spell the end of HALO (high altitude – low opening for parachute jumps, often called HALO), jumps and the beginning of dragon-riding Navy SEALs. Obviously, only a klutz would pass up the opportunity to have something that cool, however, there is a slight problem, called early-warning systems.

Now, polar bears are already handling infrared cameras well, though it's somewhat uncertain if it could work in the air since they're reflecting their environment like a mirror.

For RADAR, we have two options:

  1. Dielectric heating or other ways of converting electrical energy to another.
  2. Electric insulators.

Electrical insulators should be the most useful for us, but which biogenic material would have the highest (ohmic?) resistance?

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    $\begingroup$ (Dried) wood. Wool. Hair. Leather. Feathers. They are all excellent insulators. (Basically, any biogenic material provided it has been dried and no longer contains water.) (And the words "dielectric" and "insulator" mean the same thing.) (And how would insulators help with radar?) $\endgroup$ – AlexP Feb 19 at 3:12
  • $\begingroup$ @AlexP They don't reflect it. $\endgroup$ – Mephistopheles Feb 19 at 8:41
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    $\begingroup$ They do or they don't reflect it, depending on the specific radar and the specific insulator. If you can see stuff it is because it reflects some electromagnetic waves, which happen to fall within the frequency range to which your eyes are sensitive: and you can see insulators just fine. Some frequencies used for radar, especially longer wave radar (= decimetric waves) do indeed pass through insulators almost undisturbed; other radar frequencies have no problem getting reflected by some insulators. (Materials interact funny with high frequency electromagnetic waves.) $\endgroup$ – AlexP Feb 19 at 13:41
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    $\begingroup$ what does an electrical insulator have to do with hiding from radar? $\endgroup$ – John Feb 19 at 18:51
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Here's an image generated by a millimetre wave radar imaging system pointed at a pair of animals wearing some biogenic insulating materials.

mm-wave imaging of clothed humans

Note that it does them little good.

Here's a paper about using millimeter wave radar to track sheep, who are well known to wear thick biogenic insulating materials at various times of the year. The paper references other papers which also use mm-waves to track animals.

I suggest that attempting to electrically insulate your would-be stealth organisms is not going to help you as much as you think.

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For radar, you do not need (or want) insulating material - what matters is the reflectivity or opacity at radar frequencies, not the dielectric properties. The best way is to reflect the beam somewhere in the empty space, without scattering it. That means you need to cover yourself with flat reflective (i.e. metal) surface(s).

Something like this: enter image description here

(image thanks to wikimedia)

Note the sharp angular surfaces, making sure the beam is not scattered back to the radar.

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  • $\begingroup$ I thought you want to absorb as much of it as possible by trapping it. $\endgroup$ – Mephistopheles Feb 19 at 20:16
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    $\begingroup$ @Mephistopheles that's harder, with RF stuff, but desirable if possible. Reflective stealth like the F117 uses can be beaten if you have additional receivers in other locations which can detect and interpret the scattered signal. $\endgroup$ – Starfish Prime Feb 20 at 14:06
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Noise cancelling headphones. Well, bodyphones. I mean, you want to make it so that the "noise" received from the outside enters and simply disappears. This means it is converted into local energy by being actively cancelled out by the opposite phase signal. This can be done by making a metamaterial that has a 'negative permittivity' - instead of being an insulator, which lets the signal through without reflecting or blocking it, the material actively cancels out the signal.

Spurious signals. Depending on your "metamaterial", there may be a delay before it starts actively cancelling the signal, which could be a blip on someone's very sensitive radar. But imagine you had a chameleon which concealed its own outline even as it displayed a blip on its body that zooms off to one side. Would your eyes follow the chameleon, or the blip? Similarly, you could try to confuse the radar by sending back "reflections" at times of your own choosing, to seem like you are further away and moving away fast. That said, quantum encryption is a thing now, and I imagine the military has ways of talking to itself to see if the photons it sent are 100% consistent with the coupled photons it examined. If they plot the percent consistency between their blip and the returns and there is a peak at a point where the reflection seemed weak but the consistency was higher, I imagine you're up for company.

Reflecting planes. The person who posted the stealth bomber can't be wrong - yes, directing the signal away from the radar seems like a good idea. Still, if you can have flying elephants I wonder if your adversaries have a bunch of Mickey Mouse satellites capable of looking for stray radar reflections when asked.

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