A kind of
magnetic sensor that detects
changes in the
strength of a
magnetic field. It consists of a
wire coiled around a
magnet, with a steady
current pumped through. If something
metallic passes close to the magnet, it will effectively become an
extension of the magnet, and change the
permeability within the wire's coils, which will translate into a change in the
impedance of the wire.
Magnetoresistive sensors are found in metal detectors, both the beachcombing kind and the kind you find in airports. Automobile detectors at traffic lights are another example.
They are also popular for use in machinery, where they can count the number of cogs that pass by on a wheel, yet can also stand getting some grease slathered on them.