Radars and visible light are basically the same thing, but with a different wave lenght and energy. So I thought, is this super black fabric pretty much like stealth tech on airplanes, but for our visible light?
>>7950146
Not really, eye/vision is more similar to passive radar. Typical radar is much more similar to echo location.
>>7950166
forgot my pic
Additionally stealth technologies do not simply rely on absorption to hide an object from view, geometry also plays a very important role.
>>7950146
cats and horses are basically the same thing, too, except size and hoof. so I thought, riding cats would allow us getting up that trees?
>>7950184
>geometry also plays a very important role.
of course
also I do realise your point with active/passive radar, but active radar works with the received signal too
I was thinking about how would stealth in visible light spectrum look like, and this was pretty much what I came up with. As it wouldn't be literally invisible, but more like wouldn't return anything that was sent to it.
>>7950146
It could be used like radar stealth tech if you were trying to spot an object against the night sky with a spotlight.
>>7950214
Light works nothing like primary radar because the primary source of light is not the transceiver. Stealth works (in simple terms) by deflecting em to multiple directions so that the volume of the objects appears smaller than it actually is.
There is an RCS equation but its a bit convoluted to repost here. You could only reduce your optical cross section by adapting background radiation to be a part of your figure.
In other words, radar detects objects that generate a return when there is generally nothing. Light is constantly being received from the blue sky or the ground and having an object in front of this disturbs the background image. Light detection is almost the inverse of radar
>>7950184
>>7950426
The difference you're saying is not really a difference in principle. It's just with active radar, you're supplying the light source as well, and there isn't much ambient light. So it's like using a powerful spotlight in the nighttime.
And while "stealth" aircraft technology is more about reflecting the waves away from their source, if there was a material that could absorb radio waves as well as that stuff absorbs visible light, it would make a marvelous stealth coating.
>>7950146
Stealth aircraft are a meme. Radars get much better much faster. Stealth is only useful against prehistoric radar systems.
>>7950455
>And while "stealth" aircraft technology is more about reflecting the waves away from their source, if there was a material that could absorb radio waves as well as that stuff absorbs visible light, it would make a marvelous stealth coating.
It might be for an active radar.
A black object is strikingly clear to a person in a well lit environment. This is the reason why stealth would imply that the object has an inherent property of guiding em radiation.
>is this super black fabric pretty much like stealth tech on airplanes, but for our visible light?
Sorta but no. Even stealth airplanes are still really quite reflective in the radar spectrum, but they are designed such that as little as possible radiation is reflected/scattered back towards the source, instead carefully shaping the airframe to direct these reflections off in a "safe" direction. While stealth airplanes do use radar-absorbent material to some extent, the typical wavelength of radar waves is much longer than the thickness of RAM coating that can actually be applied (mostly due to practical weight constraints), so RAM cannot be relied on to suppress direct specular reflections off the aircraft's surface. What RAM DOES achieve on an airplane is suppression of the running wave, which follows the surface of the aircraft (almost like a waveguide) until it comes upon a sharp corner and scatters. Since this running wave thus follows the surface of the aircraft for several meters, RAM can suppress it and absorb its energy fairly easily.
http://www.microwaves101.com/encyclopedias/radar-cross-section-physics
This super-low albedo black substance is more akin to the anechoic coatings on submarines. Unlike with radar and aircraft, active sonar can have quite short wavelengths (thanks to the dramatically slower propagation speed of sound) and submarines have far less restrictive weight constraints, and so these anechoic coatings (and even specific features within them) can be made many wavelengths thick and can absorb incident sound waves directly, much like this black substance does.
