The potentiality of composite elastic magnets as novel materials for sensors and actuators
Introduction
In the last few years the number of applications of magnetoelastic materials in different kinds of sensors has been greatly increased. The applications development was going on concomitantly with improving the materials composition and manufacturing technologies to meet current and anticipated requirements of the economic realities of quality, reliability and productivity.
Magnetoelastic materials have been used in delay lines, oscillators, micro actuators, filters and sensors [1], [2], [3], [4], [5], [6]. The last ones are particularly used for position control, measurement of static and dynamic displacements both in industry and medicine. Displacements as little as 0.1 μm can be detected and vibrations with amplitude from 0.1 up to 10 mm can be measured in the frequency range 10–500 Hz.
New sensors based on resonant magnetoelastic waves were proposed recently and they have been optimized using a novel amorphous magnetic alloy, which permits very high amplitude of resonant magnetoelastic waves at zero magnetizing field [7], [8]. Fig. 1 shows the scheme of a sensor based on a magnetoelastic resonator (a) and the comparison with the performances of a standard strain gauge (b). In Table 1 are reported some technical data of the two compared sensors.
The most used magnetoelastic materials are amorphous alloys and composites of rare-earth elements embedded in a non-conductive matrix. Up to date it is possible to produce these materials in film, ribbon or rod shape, depending on the application purposes. In Table 2 are summarized some of the most used magnetoelastic materials and their principal physical, magnetic and elastic parameters.
New scenery in the field of magnetoelasticity is opening with the recent conceived and produced composite materials consisting of magnetic particles uniformly dispersed into an elastic matrix [11]. It is known that in the case of Terfenol-D particles the composite material has better performance than bulk Terfenol-D [12], [13]. On the other hand it was proved that for magnetic particles with asymmetric shape embedded into an elastomer matrix with low value of Young’s Modulus, a coupling between strain and magnetization is active independently of direct magnetostriction. More specific, the material magnetization can be changed due to particles rotation induced by strain and this effect is as strong as the coupling between shape anisotropy and easy magnetization direction [14]. This was named “elastomagnetic effect” to distinguish it from the classical magnetoelastic effects. In the following, we study the possibility to enhance the elastomagnetic effect in composite materials by tailoring both composition and structure, pointing out also the potentiality for applications in sensing devices.
Section snippets
Structure and properties of an elastic magnet
We are investigating a composite elastic magnet consisting of Sm2Co7 micro-particles (average size 20 μm), permanently magnetized, dispersed into a silicone matrix in low volume percentage, so that the composite behaves as an elastic material for relative linear deformations up to about 15%.
In order to obtain an uniform dispersion, without formation of particles chains, the micro-particles are initially demagnetized and then a two-step process is followed.
- 1.
Dispersion of the particles in silicone
Direct elastomagnetic effect
The direct elastomagnetic effect consists in obtaining a deformation in a heterogeneous composite, independently of standard magnetostriction, when an external magnetizing field is applied.
In the following, we consider an elastic magnet as that one above reported, in the absence of any external stress. When a magnetizing field Hz is applied, the magnetic moments are subjected to a mechanical torque that tries to rotate toward z-axis. In a solid material this mechanical torque does not
Final remarks
The possibility to have any desired shape of the sample coupled with the non destructive nature of the silicone matrix make the elastic magnet here presented a very ductile, cheap and stabile sensor for any kind of mechanical deformation. It is intuitive to figure many possible applications of this material, for example we are investigating the effectiveness to cover with a film of this elastic magnet the surface of a panel or a tool in order to have a direct map of their deformation status on
References (14)
Magnetostrictive delay lines and their applications
Sens. Actuators A
(1997)- et al.
Potential application of innovative magnetoelastic resonators for vibration detection
Sens. Actuators A
(2001) - et al.
Coexistence of very soft magnetism and good magnetoelastic coupling in the amorphous alloy Fe62.5Co6Ni7.5Zr6Cu1Nb2B15
J. Magn. Magn. Mater.
(2000) Magnetoelastic properties of a ferroelast within an organo-silicon polymer matrix
J. Magn. Magn. Mater.
(1997)- Z. Kaczkowski, in: L. Lanotte (Ed.), Magnetoelastic Effect and Applications, Elsevier, Amsterdam, 1993, pp....
- et al.
Strain sensitivity of highly magnetostrictive amorphous film for use in microstrain sensors
J. Appl. Phys.
(1999) - et al.
Fabrication of magnetostrictive actuators using rare-earth (Tb, Sm)-Fe thin films
J. Appl. Phys.
(1994)
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