Orphée Cugat

Magnetic micro-actuators and systems (MAGMAS)

Magnetic interactions provide outstanding performances for powerful integrated micro-actuators. This paper explains how magnetic interactions involving permanent magnets, currents, and various magnetic materials remain very effective and even improve as dimensions are reduced. The technological problems that have slowed the development of magnetic micro-actuators and systems (MAGMAS) are progressively being solved. As long as materials scientists continue to develop better thick-film patterned permanent magnets compatible with microsystem technologies, MAGMAS will have a promising future.

Magnetostrictive-piezoelectric composite structures for energy harvesting

In this paper, harvesters coupling magnetostrictive and piezoelectric materials are investigated. The energy conversion of quasi-static magnetic field variations into electricity is detailed. Experimental results are exposed for two macroscopic demonstrators based on the rotation of a permanent magnet. These composite/hybrid devices use both piezoelectric and magnetostrictive (amorphous FeSiB ribbon or bulk Terfenol-D) materials. A quasi-static (or ultra-low frequency) harvester is constructed with exploitable output voltage, even in quasi-static mode. Integrated micro-harvesters using sub-micron multilayers of active materials on Si have been built and are currently being characterized.

Magnetic planar micro generator

A prototype of an axial-flux permanent magnet electromagnetic generator was recently built in LEG in collaboration with LETI. The /spl phi/ 8 mm planar generator consists of a permanent magnet disc rotor cut out of bulk SmCo/sub 5/ or NdFeB and a silicon stator with electroplated three-phase planar coil. The machine was driven at speeds up to 260 000 rpm on hybrid magneto-pneumatic bearings. This mm-scale planar generator is compatible with mm-scale gas turbines. The article evaluates its integration for the generation of electrical power, using compressed air presently. The first prototype of micro-turbo-generator driven by compressed air delivers an electric output power of 14.6 mW at 58 000 rpm.

Autonomous, Low Voltage, High Efficiency, CMOS Rectifier for Three-Phase Micro Generators

The paper reports on the design, fabrication and testing of a fully integrated, low voltage rectifier for three-phase micro-generators. Focus is applied to the design of a stand-alone rectifier for three-phase AC inputs in the range of 1-3.3 V, 5-500 mA at 10-100 kHz. Specific low powering issues such as low-voltage rectification, self-powering, automatic start-up and anti-parasitic protection are clearly presented. These issues have been solved thanks to original designs and concepts realized using CMOS 0.35 mum technology. The measurements on the fabricated mu-rectifier coupled to a three-phase micro-generator indicate its full functionality and high conversion efficiency, up to 90 %.

Deformable mirror using magnetic membranes: application to adaptive optics in astrophysics

An alternative approach to more compact deformable mirrors for adaptive optics is developed. A thin and flexible reflective membrane is coated with a magnetic layer and locally deformed by the field created by an array of planar microcoils. This novel technology should enable higher resolution with smaller, lighter integrated mirrors. Several complementary modelling tools are used to study the electromagnetic, mechanical, magneto-mechanical and thermal behaviour of the device. A first prototype of O 30 mm mirror with a matrix of permanent magnets and an array of 25 microcoils is under construction.

Planar brushless magnetic micromotors

Novel planar magnetic micromotors and microgenerators of active diameter 8 mm were developed, delivering estimated torques of 100 muN.m at speeds in excess of 140 000 r/min. Such high performances are due to an innovative use of deep lithography and silicon etching for the fabrication of the stator coils. The hybrid design of the micromotors combines a pair of double-layer three-phase stator coils and a disc-shaped SmCo rotor with eight or 15 axial pairs of poles, all enclosed in a case fabricated using watch-industry micromachining

Anisotropy of easy-plane Y2Fe17, Y2Fe17N3 and Sm2Fe17

Abstract The magnetocrystalline anisotropy of the easy-plane compounds Y 2 Fe 17 , Y 2 Fe 17 N 3 and Sm 2 Fe 17 are measured. To simplify the analysis of the magnetisation data, the metallic powders are aligned in a magic cylinder device. Based on the Sucksmith-Thompson method, K 1 and K 2 are determined between 4.2 K and room temperature. The values are used to separate the transition metal anisotropy contribution from the rare-earth contribution in Sm 2 Fe 17 .

Design and modelling of permanent magnet micro-bearings

A model of micro-dimensioned permanent magnet bearings for micromotors is proposed. 2D and 3D modelling and simulation of scaled-down classical structures were carried out using 3 complementary computation methods. Their application to thick-film magnets technology is considered.

Practical and Theoretical Investigations of a Rotating Coilless Actuator Using the Inverse Magnetostrictive Effect

In this paper, we present a novel rotating actuator based on the interaction of a permanent magnet with a magnetostrictive soft ribbon submitted to mechanical stress. The direction and magnitude of the stress generates a directional magnetic anisotropy (easy axis) in the soft ribbon. A nonzero angle between the polarizing magnet and the induced easy axis results in a torque between the two: hence the magnet being free to rotate aligns itself with the easy axis. A demonstrator of this principle was made using a Nd-Fe-B magnet above a disk cut from an iron-based amorphous ribbon glued between two unidirectional piezoelectric actuators. The analytical model takes into account the magnetic domains and assumes a magnetization mechanism of both coherent rotation and domain-wall displacement, with a uniaxial anisotropy induced by the applied stress.

Magnetic micro-actuators & systems (MAGMAS)

In this paper, the magnetic interaction, scale reduction laws and the implication of scale reduction on magnetic interactions are described. The role of micro-magnets and micro-coils was presented. Finally, panorama of todays MAGMAS and their potential applications were presented.