Attractive Shapes

Materials scientists have long played with “shape memory alloys,” metals that shift between one shape and another when heated or cooled to just the right temperature. But so far, real-world applications have been limited, because controlling the alloy’s shape with temperature is often difficult and inefficient. Now, researchers have found a way to accomplish the same shape-memory tricks using magnets rather than temperature-an advance that could make possible efficient, less clunky moving parts for machine components in aircraft, automobiles or even robots.

Materials scientists Bob O’Handley of MIT and Kari Ullakko from the Helsinki University of Technology in Finland reasoned that an alloy of nickel, manganese and gallium might respond to a magnetic field with a change of shape. When the researchers expose a sample of the new alloy to a magnetic field about two or three times stronger than that generated by a refrigerator magnet, the material becomes rubbery and expands. When the researchers remove the field, a spring pushing on the alloy causes it to revert to its original shape. By alternating the magnetic field at high speed, the researchers can repeat the cycle several thousand times per minute. “It sort of looks like a heart beating very quickly,” says O’Handley.

Adding magnetic control, researchers believe, will make shape memory alloys much more practical to use. “There’s a great deal of promise in these [magnetically controlled] materials,” says the University of Minnesota’s Thomas Shield, who also studies shape memory alloys. O’Handley, for example, envisions using the alloy to make lightweight mechanical parts in airplane wing flaps. A lump of the new material wrapped in a magnetic coil could raise and lower a flap on cue, replacing today’s heavy hydraulic systems that require a central pump and multiple oil lines running to the flaps.