I'm trying to design a speed trap for an airsoft BBs. My original idea was to use IR photosensor. But this solution is prone to fail if dirty.
I'm playing with the idea to use a coil on a PCB with hollow centre where a BB would fly through. Can I use change of relative permeability of coil's core to detect proximity of a plastic BB? Would it be practical?
BB's diameter is 6mm and it should fly parallel to PCB coil with hollow center.