I am searching for a method to detect the type of metal of something solid and small and thin. The test surface is approx 4x2 cm with a thickness of maybe a few millimeter.
I cannot use magnets in this specific case but I can make direct contact with the surface (using a robot arm or another method) so I thought about using something like electrical conductivity (in uS/cm). I am not even sure if that's possible but according to this https://www.tibtech.com/conductivite.php?lang=en_US there is a big difference between the two possible materials I will face either steel (10,1) or aluminium (36,9).
So I am searching for hardware preferably a digital sensor that can do this using my raspberry pi. Something like an electronic conductivity sensor for solid materials as I only seem to find sensors for use with liquid. Does anyone know of such sensors or another method I can use other then electrical conductivity or magnetism to determine the difference between aluminium and steel.
I also thought of using heat and time measuring the heat conductivity but it has to be low heat as plastic is connected to the metal. Or using an (ultra) high definition camera with proper light and trying to determine it based on color difference. Which seems hard to do and unreliable due to other factors.
Also, if you know of any projects where they do use methods or another metal type detection technique with a raspberry pie, just for educational purposes, please share. As I couldn't find anything actually.
Edit: I found this (https://www.youtube.com/watch?v=B0lrcvT2HRc) again for liquids, but I will experiment to try to make a variant on this. But still, any ideas are welcome.