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Simulation of Discrete Actuators using Magnetic Shape Memory Alloys
|Berta Spasova , Marc C. Wurz , Hans-Heinrich Gatzen|
Leibniz Universitaet Hannover, Institute for microtechnology (IMT), An der Universitaet 2, Hannover 30823, Germany
For further miniaturizing micro actuators, new motor drive schemes are desirable. One novel approach is the use of new materials like Magnetic Shape Memory (MSM) alloys. These materials achieve an elongation of up to 10% when exposed by a sufficiently strong magnetic field. But only the area exposed to a magnetic field strong enough to cause crystal reorientation are being elongated. For the design of discrete MSM-actuators, simulations were conducted by the Finite-Element Method (FEM). The goal of the simulation was to find a setup for an optimized system which exposes an as high percentage as possible of the MSM alloy to the required field. Such a system requires three components: (1) an excitation coil to create a magnetic field which is great enough to exceed the required field strength, (2) a soft magnetic flux guide with a magnetic permeability as high as possible, and (3) a strip of MSM alloy with an appropriate crystalline direction allowing the crystalline transformation resulting in an elongation. Investigations revealed that before the crystalline transformation the relative permeability µr of the material is 7, while after the transformation it is 12. Based on the magnetic data of the MSM material and the soft magnetic alloy (NiFe45/55), a design was modeled and simulated.
So far, we discussed the elongation of the material. For creating a switchable actuator, we also have to look into its contraction. The easiest way to accomplish one is to using two stripes working against each other. For creating a motion in one direction, a first MSM element is extended, to return it to the starting point, a second MSM element compresses it by being extended itself, and vice versa. As a result, a system was created with separate magnetization capabilities for the two stripes. For the design chosen, up to 35% of each MSM stripe is exposed to a sufficiently strong magnetic field for causing an actuation.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Berta Spasova
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 16:37 Revised: 2009-06-07 00:44