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Firstly, a black body in physic mean a body that absorb 100% energy at all frequency, it is very different from RAM designed to absorb radar energy at a narrow frequency range. In theory, you can make a Salisbury screen with 100% absorption at very narrow frequency, angle. You make a Salisbury screen by placing a thin sheet with same wave impendence as air (377 ohms/sq resistance) on top which allow radio wave to entered the RAM structure without being reflected back right at the surface, the sheet transform the short circuit at the back material into open circuit at the sheet, when the impendence of the sheet is 377 ohms/sq there is no reflection because load is matched. Yes, I know Salisbury isn't used on airplane typically because of the bulkiness and narrow band, but I just thought it is interesting to mentionSecondly, the second chart isn't about absorption, it is sort of reflection coefficient. Let say you have a radar beam hitting your RAM, a 0.1 reflection coefficient mean 10% of the beam reflected away right from the top RAM surface and 90% entered the RAM to be absorbed. The absorption then can be -10 db, -20 dB ..etc then the left over energy will reflect a second time when they hit the metal surface underneath the RAM.
Firstly, a black body in physic mean a body that absorb 100% energy at all frequency, it is very different from RAM designed to absorb radar energy at a narrow frequency range. In theory, you can make a Salisbury screen with 100% absorption at very narrow frequency, angle. You make a Salisbury screen by placing a thin sheet with same wave impendence as air (377 ohms/sq resistance) on top which allow radio wave to entered the RAM structure without being reflected back right at the surface, the sheet transform the short circuit at the back material into open circuit at the sheet, when the impendence of the sheet is 377 ohms/sq there is no reflection because load is matched. Yes, I know Salisbury isn't used on airplane typically because of the bulkiness and narrow band, but I just thought it is interesting to mention
Secondly, the second chart isn't about absorption, it is sort of reflection coefficient. Let say you have a radar beam hitting your RAM, a 0.1 reflection coefficient mean 10% of the beam reflected away right from the top RAM surface and 90% entered the RAM to be absorbed. The absorption then can be -10 db, -20 dB ..etc then the left over energy will reflect a second time when they hit the metal surface underneath the RAM.
