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.

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