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KelvinAll®
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Energen’s products are based on our patented magnetic “smart” materials (MSM) technology. “Smart” refers to the fact that the material changes its properties in response to an external force, and magnetic smart materials (MSM) are materials that deform in response to a magnetic field. Other examples of smart materials include piezoelectrics, which respond to electricity, and shape memory alloys (SMA) (temperature).
Using our unique expertise in MSM, we have developed a proprietary and patented material, Kelvin All®, which we use to make precision, high force actuators and motors that are controlled by a magnetic field, rather than an electrical signal or other force. The key attribute of KelvinAll is its operating temperature range. Competing materials operate reliably at either room temperature and above, or work at -170°C and below. KelvinAll is the only materials that operates predictably, reliably, and repeatably over the entire temperature range from absolute zero to 125°C, with minimal change in sensitivity. Its temperature versatility enables the most challenging scientific applications and saves money for the customer: Only Energen can supply an extremely sophisticated, nanometer resolution motion control system to operate in a vacuum at a temperature of 2K (-456 ˚F), yet verify its performance with a few simple room temperature tests.
Other important attributes of KelvinAll are low-voltage operation and affordability. Piezoelectric materials require 100 to 1000 V to operate - which can cause arcing in a vacuum environment. KelvinAll can require as little as 10 V for the same application.
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The cryogenic terbium-dysprosium-zinc alloy shown in Figure 1 can operate at low voltage, but costs over 6 times as much to fabricate as KelvinAll. Furthermore, it cannot be tested at room temperature, resulting in added development time and cost.
MSM are capable of applying more force than any other smart material and can do so with high resolution, repeatably and reliably when controlled properly. For example, with MSM, we could lift a car with nanometer precision. MSM respond rapidly to changes in magnetic field, enabling high payload active vibration control. A bulky motor can be bolted onto an MSM vibration control system, and the MSM will move opposite the load in real time to cancel the vibrations.
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General Properties of KelvinAll®
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Mechanical Properties:
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Young's Modulus:
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30GPa
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Acoustic Velocity:
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1790 m/s
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Tensil Strength:
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30 MPa
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Compressive Strength:
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700 MPa
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Density:
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9250 kg/m3
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Thermal Properties:
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Thermal Expansion:
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12 ppm/K
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Specific Heat:
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0.35 kJ/kg-K
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Thermal Conductivity:
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10-13 W/m-K
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Electrical Properties:
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Resistivity:
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58 x 10-8 W-m
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Curie Temperature:
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380C
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Relative Permeability:
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7-11
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Geometry
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Cylinders and disks to 50mm diameter and 300mm long
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Laminations to reduce eddy currents available
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Special geometries available upon request
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Behavior of KelvinAll® Actuators
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Energen’s KelvinAll® actuators are designed to deliver reliable performance from near absolute zero to above room temperature. Since these actuators are devices that convert electrical into mechanical energy, it should not be surprising that mechanical loads on the actuators affect their electrical performance. The force and stroke capability of KelvinAll® actuators are influenced by the absolute load and the stiffness against which the actuators move.
This variation is a result of the mechanism of magnetostriction. From a macroscopic point of view, magnetostriction includes two distinct processes:
1. the rotation of magnetic domains to align with the applied magnetic field; and
2. the migration of domain walls and the growth of domains.
These two mechanisms result in a distortion of the crystal structure, which manifests itself as a macroscopic elongation of the magnetostrictive object.
A compressive force along the direction of the applied magnetic field “squeezes” the magnetic domains and causes them to flatten in a direction perpendicular to the applied force. The rotation and alignment of these domains is proportional to the applied magnetic field. Figure 1 shows the effect of compressive force on stroke as a function of current (magnetic field).
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Effect of load stiffness
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The stiffness of the load also affects the available stroke. As the load becomes stiffer, more magnetic energy is needed to induce the domain rotation. Figure 2 illustrates the effect of load and stiffness on the performance of KelvinAll actuators.
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