Originally Posted by
metabike
I am a traffic engineer by trade - detector loops work by inductance, i.e. ferrous metals cause a change in the inductance and "tell" the signal controller that there is a vehicle there. If you are riding an all-carbon bike, you are SOL as far as ever getting a loop to detect you.
Inductive loops only need conductive material to work, not ferrous metals. Maybe you are thinking of magnetic sensor or magnetometer? Most bicycle rims and many frames are are aluminum, which is non-ferrous, but aluminum is a conductor. Carbon fiber is also a conductor so my guess would be that a CF wheel and frame might be able to trigger a light, but I don't know the conductivity of carbon fiber.