NU 2009-109 

Inventors

Xuexi Zhang

David C. Dunand*

Peter Mullner

Markus Chmielus

Cassie Witherspoon 

Short Description

Polycrystal memory foam for less expensive, more stable actuators 

Abstract

Magnetic shape memory alloys (MSMAs) are a field of active materials that enable fast, large-strain actuators. Single crystal shape-memory alloys have thus far been utilized; very high (~10%) magnetic-field-induced strains (MFIS) for single-crystal nickel-manganese-gallium (Ni-Mn-Ga) alloys have been measured. However, Ni-Mn-Ga single crystals are brittle and difficult to prepare, thus limiting their commercial potential. Randomly textured, fine-grained, polycrystalline Ni-Mn-Ga alloys are easier to manufacture, but result in near-zero MFIS. Northwestern inventors have overcome these performance limitations by synthesizing the alloy as a polycrystalline foam structure. The foam permits single crystallinity deformation to extend over longer distances, resulting in greater field induced strain (2-4%)‚ i.e., the foam changes shape in strong magnetic field. This development will allow for the manufacture of actuators using polycrystals, which are less restrictive to produce than the single-crystal variety. 

Applications

• Long-stroke actuators (aerospace, automotive, and biomedical devices)
• Sensors
• Magnetic cooling systems
• Energy devices

Advantages

• Inexpensive casting process
• Actuation stroke 100 times that of piezoelectric actuator materials, but with comparable response time
• Compact, lightweight, and robust

IP Status

Issued US Patent No. 8,586,194