Shape Memory Alloys
Shape memory alloys change their shape when exposed to temperature variations. A structural transformation governs the shape change. The shape memory alloy Nickel-Titanium (Ni-Ti), commonly referred to as Nitinol, finds applications in various products such as medical devices (e.g. stents, orthodontics), as high work-output actuators, and as fasteners to name.
Ni-Mn-Ga: An MSM Alloy
The alloy of Nickel, Manganese and Gallium (Ni-Mn-Ga) is a magnetic shape memory (MSM) alloy, which deforms over 6% when exposed to a variable magnetic field. The magneto-structural coupling through the magneto-crystalline anisotropy drives this MSM effect. The MSM effect occurs in materials when two conditions are met:
- The material must have a low twinning stress so that twin boundaries are mobile.
- The material must be ferromagnetic with a high magneto-crystalline anisotropy energy.
Multiple twin domains, separated by twin boundaries, can exist within martensitic Ni-Mn-Ga. When sufficient magnetic-field-induced stress is applied to this material, the twin variant that is preferentially aligned to the magnetic field grows at the expense of other twin variants. This change in the crystallographic orientation of the material is caused by a shear deformation process called twinning.
Properties of the MSM Alloy Ni-Mn-Ga
- Large, reversible strains of 6 % can be controlled by a magnetic field.
- Induced strain is stable even when the energy source is removed.
- Full actuation of a sample can occur in less than 1 ms.
- Low twinning stress materials can convert energy from the applied magnetic field with an efficiency as high as 90%.
The MSM Micropump
The MSM micropump utilizes a heterogenous magnetic field from a diametrically magnetized permanent magnet to locally strain the material nearest to the poles of the magnet. The resulting small cavity follows the poles of the magnet as it rotates driven by an electromotor. The MSM micropump captures this motion by placing the material within a microfluidic channel. The MSM micropump operates in both directions, works against a high head pressure, and transports gasses and fluids, thus it is self-priming. The MSM micropump is the ideal solution for many microfluidic tasks in biomedical and microbiological research, in nano-manufacturing, and many other high-tech fields.
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