A semiconductor for detecting metal.

I Know that this have be done lots of times, so I was hoping that will be easy for you guys.

I need a semiconductor for detecting metal without a magnet, it is for detecting the speed of the back wheel of my kids speedway bike. I will use a small microprocessor (STM32) for the data handling afterwards.

Any ideas.

Best regards.

I don't believe that you'll find "a semiconductor" for this purpose. Inductive proximity sensors (based on eddy currents) are the usual method.

Photo electric sensors can be used by using Infrared transmitter and receiver.