The potentiality of composite elastic magnets as novel materials for sensors and actuators

doi:10.1016/S0924-4247(03)00133-X

Sensors and Actuators A: Physical

Volume 106, Issues 1–3, 15 September 2003, Pages 56-60

https://doi.org/10.1016/S0924-4247(03)00133-X Get rights and content

Abstract

In the last decade the progress of standard magneto-elastic materials is going toward its physical limits. New horizons are recently opened by the development of artificial composites having both elastic and magnetic properties. The working principle of these elastomagnetic materials is not depending on intrinsic magnetostriction, but on the coupling between magnetic moments of the particles and particles themselves. The possibility to study the physical mechanism that relates the elastic and magnetic properties in the new scenery furnished by composites of magnetic particles in an elastic matrix is very promising from the basic knowledge point of view. On the other side, the potential competitiveness in several applications justifies the increasing efforts to improve the production and to perform technical characterization of these magnetoelastic composites in different experimental conditions.

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 H_z is applied, the magnetic moments are subjected to a mechanical torque $m → × B →$ that tries to rotate $m →$ 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

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The potentiality of composite elastic magnets as novel materials for sensors and actuators

Abstract

Introduction

Section snippets

Structure and properties of an elastic magnet

Direct elastomagnetic effect

Final remarks

Sens. Actuators A

Sens. Actuators A

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Strain sensitivity of highly magnetostrictive amorphous film for use in microstrain sensors

J. Appl. Phys.

Fabrication of magnetostrictive actuators using rare-earth (Tb, Sm)-Fe thin films

J. Appl. Phys.