(This article is sponsored by The Boston Group)

Magnetostriction is a dimensional change of a magnetic smart material (MSM) caused by a change in its magnetic state. Magnetostriction arises from a reorientation of the atomic magnetic moments. When the magnetic moments are completely aligned, saturation occurs after which increasing the applied magnetic field will produce no further magnetostriction. The amount of magnetostriction at saturation is the most fundamental measure of MSM material.

For applied fields below saturation, the magnetostriction is approximately linear. MSM devices become valuable to industry and science when they can be precisely controlled to repeatedly and reliably position objects within very close tolerances. Their linear behavior is the basis for the development of precision MSM devices including actuators, stepper motors, position sensors, valves and acoustic transducers. One advantage of MSM devices comes from the ability to provide a large force through a small displacement. The force capability of such a device depends on the Young’s modulus of the magnetostrictor and its cross sectional area. Another advantage is that a MSM device can provide motion in both directions unlike a solenoid that can only pull and thus requires a separate return mechanism. Furthermore, having no moving parts, a MSM actuator is inherently a more reliable, and more precise positioning device.

The modern era of magnetostriction began in 1963 when strains approaching 1% were discovered in the rare earth materials, terbium (Tb) and dysprosium (Dy), at cryogenic temperatures. Since then many materials have been shown to exhibit magnetostrictive behavior including several materials at room temperature.

Currently, low temperature MSMs are being tested for a number of space and other low temperature applications. One example is NASA's Next Generation Space Telescope project.

Over the years, advances in magnetostrictive science have led to commercial viability. A new family of magnetic smart materials with high saturation strain and desirable mechanical properties demonstrate excellent performance for both room temperature and cryogenic actuator applications. Energen, Inc. uses these high performance MSMs in its actuators and linear stepper motors.

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