Terfenol-D
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Terfenol-D is an alloy of the formula Tb(0.3) Dy(0.7) Fe(1.9), developed in the 1950's at the Naval Ordnance Laboratory in America. It is named after terbium, iron (Fe), Naval Ordnance Laboratory (NOL), and the D comes from dysprosium.
The alloy has an extremely high magnetostriction, up to 0.001 m/m at saturation; it expands and contracts in magnetic field. It sees application in magnetomechanical sensors, actuators, and acoustic and ultrasonic transducers, eg. in the SoundBug device (its first commercial application), or in naval sonar systems.[1]
