Acoustic assisted actuation of Ni-Mn-Ga ferromagnetic shape memory alloys

Ferromagnetic shape memory alloys (FSMA) have been shown in recent work to exhibit large magnetic field induced strains. The material generally requires a large threshold field (of order 3-4 kOe) to initiate the strain. Thus, the power requirements are large and actuators based on these materials could tend to be large. This thesis reports on the effect on the actuation properties of Ni-Mn-Ga single crystals of the use of a sinusoidal stress wave generated by a piezoelectric stack actuator. The piezoelectric drive causes a time varying stress wave in the FSMA that resolves as a shear across the twin-boundaries and aids the twin boundary in overcoming defect-related obstacles. The FSMA shows increased strain and a reduction in threshold field. The effect is most pronounced for crystals showing large initial threshold fields which are associated with high defect strengths or concentrations. For crystals with a large threshold, 4.7 kOe, actuated at 1 Hz, the piezoelectric drive reduces the threshold field by as much as 21% for a piezoelectric driven at 5 kHz and 20 Vrms. As a result of this large threshold reduction, strain output can be more than doubled for magnetic drive amplitudes near the threshold field.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Peterson, Bradley William

Advisor dc:contributor.advisor

• Samuel M. Allen.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/37584

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/37584