EP1399938A1

EP1399938A1 - Magnetic actuator with reduced response time

Info

Publication number: EP1399938A1
Application number: EP02758514A
Authority: EP
Inventors: Claire Divoux; Pierre Gaud; Jérôme Delamare
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2001-06-25
Filing date: 2002-06-24
Publication date: 2004-03-24
Anticipated expiration: 2022-06-24
Also published as: EP1399938B1; FR2826504B1; DE60202769D1; FR2826504A1; WO2003001548A1; US6859122B2; DE60202769T2; US20040246082A1

Abstract

Magnetic actuator comprising a closed magnetic circuit (26) for guiding a magnetic flux. The magnetic circuit (26) comprises a fixed magnetic piece (30, 31, 32) with a yoke (30) and a mobile piece (22) magnetically connected to each other and more or less to a main pole gap (29), defined by at least one section (28) of the mobile piece (22) and the yoke (30). Within the pole gap (29) the flux is retained by being established essentially transverse to the mobile piece (22). The fixed piece (30, 31, 32) comprises means for retaining flux (40), which, together with the mobile piece (22), defines an auxiliary pole gap (38) in which the flux is established laterally to the mobile piece (22). The flux is retained on either side of the principal pole gap (29), on one side by means of the yoke (30) and on the other side jointly by the mobile piece (22) and the means (40) for retaining flux using that section (28), which contributes to defining the principal pole gap (29). The auxiliary pole gap (38) has a dimension in the sense in which the magnetic flux is established which is minimal at the level of at least one region of the section (28), contributing to the definition of the principal pole gap (29).

Description

MAGNETIC ACTUATOR WITH REDUCED RESPONSE TIME

DESCRIPTION

TECHNICAL AREA

The present invention relates to magnetic actuators whether they are miniature or of larger size. We speak of micro-actuators when they are miniature. The production of such actuators uses techniques for machining mechanical structures, micromachining or techniques used in microelectronics.

These actuators are used in particular to produce electrical, optical, power, high frequency relays, switches, but also to produce pumps, valves, motors. By switch is meant a device with several contacts which can close separately while the relay has only one or more which close at the same time. These contacts can be in the open or closed position.

Electromagnetic relays and switches, miniaturized or not, are widely used in many applications such as transmission or reception telecommunications, optical telecommunications, automatic test equipment, automotive, aeronautics and electronic devices General public.

Pumps, valves, motors can be used in wide fields of application and in particular microbiology, medicine, optics etc. STATE OF THE PRIOR ART

The actuators of known types include a fixed magnetic part 1 and a mobile magnetic part 2 which cooperate. The fixed magnetic part 1 is magnetically connected to the mobile magnetic part.

Reference is made to FIG. 1 which shows an example of a magnetic actuator of the known type with a single air gap.

The fixed magnetic part 1 and the mobile magnetic part 2 form a magnetic circuit 6 closed on itself capable of guiding a magnetic flux. The fixed magnetic part 1 and the mobile magnetic part 2 are stacked one on the other. The magnetic circuit 6 cooperates with means 7 for generating the magnetic flux. The fixed magnetic part and the mobile magnetic part 2 each have a portion 12, 8 respectively, helping to define an air gap 9 so that a force can be exerted on the portion 8 of the mobile part 2 for the move under the effect of the magnetic field.

In the air gap 9 the magnetic flux is established transversely to the portion 8. In this example, the fixed magnetic part 1 comprises a base or yoke 10 which is extended by a first magnetic stud 11 and by a second magnetic stud 12. The second magnetic pad 12 contributes to delimiting the air gap 9.

The yoke 10 is magnetically connected to the mobile magnetic part 2 via the first stud 11. It also has the role of mechanically holding the mobile magnetic part 2 relative to the fixed magnetic part 1. The fixed magnetic part 1 and the magnetic part mobile 2 extend one above the other, in substantially parallel planes when one actuator is in the open position. The magnetic circuit 6 in closed loop comprises, one after the other, in one of the directions of flow of the magnetic flux: the yoke 10, the first magnetic stud 11, the mobile part 2, the air gap 9 and the second magnetic stud 12. Its reference 6 schematizes the path traveled by the magnetic flux during its crossing of the various elements which compose it.

The movable magnetic part 2 is in the example of an arm with a support end

13 connected to the first magnetic stud 11 and another free end which corresponds in the example to the portion 8 contributing to delimit the air gap 9.

In electrical relays, the free end serves as an electrical contact whether the arm is made of electrically conductive material or whether the arm is equipped with an electrical contact. No electrical contact has been shown.

The means 7 for generating the magnetic flux can include one or more coils surrounding one or more parts of the fixed magnetic part 1 and / or of the mobile magnetic part 2 and / or possibly one or more permanent magnets. When an electric current flows in one of the windings a magnetic flux is produced. It is materialized by the closed loop with arrows.

In the example of Figure 1, a coil 7 has been shown around the first magnetic pad 11. Several coils could be used, they could be around the yoke 10, around the second magnetic pad 12 or even around the magnetic part mobile 2.

In such a magnetic circuit 6, a compromise must be found between the cross-sections of the flow of its different parts: that of the part moving magnetic 2, that of the fixed magnetic part

I and that of the air gap 9.

We seek to obtain a large induction value at the air gap 9 so that the force which will be exerted on the movable magnetic part 2, at the portion 8, is large.

This requires that the magnetic flux available in the air gap 9 is large. The magnetic flux available in the air gap 9 corresponds to that which is guided by the magnetic circuit 6 on either side of the air gap 9. The maximum magnetic flux which can be guided by a piece of magnetic material depends on the material magnetic and cross-section of the part.

In the unsaturated state of the magnetic material, the larger the section, the lower the magnetic losses and in the saturated state of the magnetic material, all the magnetic flux generated cannot be contained and the excess of magnetic flux corresponds to the losses, it cannot be guided by the magnetic material and it contributes very little to the force.

The section of the magnetic circuit 6 can be substantially uniform over its entire length. In this case the mechanical performance of the actuator is poor. Generally, the section of the mobile magnetic part 2 is smaller than that of the fixed magnetic part 5 for mechanical reasons. In fact, it is sought that the stiffness of the movable part 2 is not too great for it to be able to bend easily. One of the ways to reduce the stiffness of the mobile part is to reduce its section. This reduction in the section of the mobile part is to the detriment of the possibility of passage of the magnetic flux in the mobile magnetic part, which results in a reduction in the force at the level of the air gap and increased response time of the mobile part.

There are other types of magnetic actuators in which there are several air gaps. In these types of actuator, the main air gap is the one which is delimited by transverse surfaces in the direction of movement of the mobile magnetic part. In these configurations there is at least one other air gap which will be qualified as auxiliary.

Figure 2 illustrates a micro relay in top view. This micro-relay is produced in planar form and no longer in stacked form. It has been described in the article: "Fully Batch Fabricated Magnetic Microactuators Using A Two Layer LIGA Process" by B. ROGGE, J. SCHULZ, J. MOHR, A. THOMMES and W. MENZ in TRANDUSCERS '95 - EUROSENSORS IX pages 320 to 323.

It now comprises, on a common support 3, the fixed magnetic part 1 and the mobile magnetic part 2. The mobile magnetic part 2 corresponds to a free end 17 of a mobile arm 5, the other end 13 of which is a fixed support end of the support 3. The arm 5 and the fixed magnetic part 1 are located one next to the other substantially in the same plane, parallel to the plane of the support 3. The movement takes place in the plane of the arm 5 and of the fixed magnetic part 1.

The free end 17 ends with a movable electrical contact 16 intended to come against a fixed electrical contact 15 carried by the support 3.

The fixed magnetic part 1 in this example comprises a yoke 10 secured to one side of a magnetic stud 12 which contributes to delimiting the main air gap 9 with the movable magnetic part 2. On the other side, the yoke 10 is secured a magnetic extension 14, in this example in the form of an arm, which comes opposite with the magnetic stud 12. This magnetic stud 12 and the magnetic extension 14 delimit an auxiliary air gap 18. The magnetic circuit 6 then comprises the yoke 10, the first magnetic pad 12, the second air gap 18, the magnetic extension 14 and bypass the air gap 9 and the movable magnetic part 2. The low rigidity of the arm 5 implies a low restoring force which therefore slows down the movement in repulsion of the arm.

It is clear that the operation of this micro-relay is not optimum, the force exerted on the mobile part is very limited. As before, the magnetic circuit 6 cooperates with means 7 for generating the magnetic flux. They have been represented by a winding around the cylinder head 10 and another around its extension 14. Also known from patent application O-97/39468 is an electrical relay as shown in FIGS. 3A and 3B. These two figures are not on the same scale.

Instead of being of planar construction, this relay is of stacked construction. We find the fixed magnetic part 1 and the mobile magnetic part 2 which cooperate. The movable magnetic part 2 is a portion of a larger movable part 5, but the latter is only sketched in the figures. It lacks its connection to a fixed element which can for example be a support on which the fixed magnetic part 1 would rest. The reason for this absence is that the connection to the fixed element does not play any magnetic role.

The fixed magnetic part 1 comprises, in this example, a yoke 10 which is extended, in a central zone, by a central magnetic stud 12 contributing to delimiting with the mobile magnetic part 2 the main air gap 9. It is assumed that the mobile magnetic part 2 corresponds substantially to the hatched part of FIG. 3A and that it takes the form of a plate. The cylinder head 10 is also integral, on either side of the central stud 12, with two magnetic extensions 14 which project towards the mobile magnetic part 2. These extensions 14 end opposite, close to the mobile magnetic part 2, they each contribute to delimiting with the mobile magnetic part 2 an auxiliary air gap 18.

The magnetic circuit 6 then comprises, following one another, the yoke 10, one of the extensions 14, the auxiliary air gap 18, the mobile magnetic part 2, the main air gap 9 and the central magnetic stud 12. The extensions 14 allow only better guidance of the magnetic flux in the vicinity of the mobile magnetic part 2. This is the only means of guiding the flux and there is creation of an additional air gap. There is no direct flow guidance means.

The magnetic flux which circulates in the magnetic circuit 6 follows two closed loops which meet in the central stud 12. These two loops are symmetrical if the magnetic circuit is symmetrical with respect to a median axis passing through the central stud 12 in the direction of the movement.

In this example, the mobile magnetic part 2 is electrically conductive, it plays the role of an electrical contact which when it approaches the central stud 12 under the effect of the induced force closes an electrical circuit. This electrical circuit ends with two fixed contacts 15 inserted between the central magnetic pad 12 and the mobile magnetic part 2. These fixed electrical contacts increase the size of the air gap.

As before, the magnetic circuit 6 cooperates with means 7 for generating the magnetic flux. They have been represented by a winding surrounding the central magnetic stud 12.

In this configuration, the magnetic flux in the main air gap 9 is not optimum, because when one seeks to close the actuator, the magnetic flux being in the cylinder head 10 is well guided towards the extensions 14, but all that flow does not pass through the movable magnetic part 2 towards the main air gap 9, significant flow leaks occur between the extensions 14 and the cylinder head 10, through the central stud 12, without passing through either the magnetic part mobile 2 nor by the main air gap 9.

STATEMENT OF THE INVENTION

The object of the present invention is to produce an electromagnetic actuator the force of which is applied to the movable part and the speed is increased compared with conventional actuators and which avoids damping of the movable magnetic part. Such an actuator makes it possible to have a large displacement force while retaining a reduced section in the mobile part so that it has mechanical properties compatible with the reduction of the mechanical response time.

To achieve this, the present invention provides a magnetic actuator having a closed magnetic circuit, capable of guiding a magnetic flux, this magnetic circuit comprising a fixed magnetic part with a yoke and a movable magnetic part magnetically linked together and moreover, at least a main air gap delimited by at least a portion of the movable magnetic part and by the yoke and in which the magnetic flux closes by establishing itself substantially transversely to the movable magnetic part. The fixed magnetic part further comprises flux recovery means which contribute to delimiting with the mobile magnetic part, an auxiliary air gap in which the magnetic flux is established laterally to the mobile magnetic part, the magnetic flux being contained on both sides. 'other of the main air gap on one side by the cylinder head and on the other jointly by the mobile magnetic part and by the flow recovery means via the portion helping to delimit the main air gap, the auxiliary air gap having a dimension in the direction of establishment of the flow which is minimum at the level of at least one zone of the portion contributing to delimit the main air gap.

At least a first magnetic stud makes it possible to mechanically and magnetically connect the cylinder head to the mobile magnetic part.

At least one second magnetic pad contributes to delimiting the main air gap, this magnetic pad being obtained either from the cylinder head or from the mobile magnetic part. Advantageously, this magnetic pad is made of a hysteresis material.

At least one other magnetic pad makes it possible to mechanically and magnetically connect the cylinder head to the flow recovery means. The actuator comprises means for generating the magnetic flux in the closed magnetic circuit, these means for generating the magnetic flux being able to be produced by at least one winding.

To avoid unwanted lateral displacements of the mobile magnetic part, it can generally take the form of at least one arm with one or several non-parallel branches, connected together at the level of the portion contributing to delimit the main air gap.

The flow recovery means can generally take the form of at least one arm with one or more branches.

The moving magnetic part could take the form of a star with several branches.

To avoid the appearance of parasitic forces on the portion which contributes to delimiting the main air gap, it is preferable that the flux recovery means have, in the direction of movement of the movable magnetic part, a thickness greater than that presented by the movable magnetic part in the direction of movement, so that the auxiliary air gap is delimited by surfaces which remain opposite during displacement.

To limit the flow of direct leakage between the flux recovery means and the other fixed parts of the closed magnetic circuit, it is preferable that, knowing that the main air gap is defined by two opposite surfaces, the first belonging to the portion of the movable magnetic part and the second belonging to the yoke, the first surface is greater than the second surface and protrudes around the second surface.

In order for damping to be effectively avoided, it is possible that the dimension of the auxiliary air gap, in the direction of establishment of the magnetic flux, is almost maximum near the portion contributing to delimiting the main air gap and that it decreases the further we go.

The movable magnetic part can comprise at least one through opening, in the direction of a displacement, in the movable magnetic part so as to further reduce the damping.

The actuator may be of the stacked type, the cylinder head forming a first level and the assembly formed by the flux recovery means and by the mobile magnetic part a second level.

To limit flow leaks, it is preferable that at least one of the levels has an oblong shape which is substantially rounded at its two ends. For the same purpose, it is preferable that the two levels overlap. At least one of the levels can have at least one through central opening.

The actuator can be substantially symmetrical with respect to a median plane passing through the movable magnetic part substantially perpendicular to the direction of movement.

The actuator can be used to close or open an electrical circuit. The portion contributing to delimit the main air gap may include at least one electrical contact intended to contact at least one other electrical contact when the actuator is closed.

According to another embodiment, the mobile magnetic part can end with at least one electrical contact offset with respect to the portion contributing to delimit the main air gap, this electrical contact being intended to contact at least one other electrical contact when the actuator is closed.

The electrical contact can be electrically isolated from the movable magnetic part.

The mobile magnetic part can be made of an electrically conductive magnetic material. The present invention also relates to a method for producing a magnetic actuator. It includes the following steps:

- etching in a substrate of a box to be filled with a magnetic material to make a yoke of a fixed magnetic part,

deposition of a first dielectric layer on the substrate with the yoke, etching of at least one box to delimit means for generating a magnetic flux, and deposition of said means,

- deposition of a second dielectric layer on the first layer,

- Etching of boxes through the two layers reaching the yoke to delimit at least a first magnetic pad and at least a second magnetic pad, the second pad helping to define at least one main air gap, depositing the first and second magnetic pads in the boxes ,

depositing a sacrificial layer on the second dielectric layer and etching the sacrificial layer to release the first magnetic pad and ensure separation between a mobile magnetic part and means for recovering flux from the fixed magnetic part deposited subsequently, deposit on the sacrificial layer of magnetic material to produce the mobile magnetic part and the flux recovery means, then etching of the magnetic material to delimit them, elimination of the sacrificial layer under the movable magnetic part to release it and create the main air gap.

The present invention also relates to a relay comprising a magnetic actuator thus defined.

The present invention also relates to a switch comprising at least one magnetic actuator thus defined so as to present several main air gaps.

The present invention also relates to a pump comprising a magnetic actuator thus defined, in which the mobile magnetic part is integral with a membrane helping to delimit a cavity for circulating a fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear on reading the description which follows, illustrated by the attached figures.

Figure 1 (already described) shows a longitudinal section of a known magnetic actuator.

Figure 2 (already described) shows a top view of another known magnetic actuator. Figures 3A and 3B (already described) respectively show in longitudinal section and in top view a third known magnetic actuator.

FIGS. 4A to 4D respectively show a top view, in longitudinal section along the axis BB, in longitudinal section along the axis CC, in bottom view, a magnetic actuator according to the invention.

FIGS. 5A to 5D show a top view of the magnetic actuators according to the invention, equipped with means to avoid damping of the mobile magnetic part during its movement.

FIGS. 6A and 6B show respectively in top view and in bottom view, a magnetic actuator according to the invention, with limited leakage flow.

FIGS. 7A and 7B show a solid magnetic actuator, FIG. 7C a magnetic actuator symmetrical with respect to a median plane of the mobile magnetic part, substantially perpendicular to the direction of movement and FIG. 7D a magnetic actuator produced in microtechnologies.

FIGS. 8A to 8D show a longitudinal section and top views of a magnetic actuator with high mechanical stability in torsion.

Figures 9A and 9B show respectively in top view and in longitudinal section, an electrical relay according to the invention. FIGS. 10A to 10C show different variants of the electrical contact of an actuator according to the invention.

Figures 11A and 11B are respectively a top view and a sectional view of an electrical switch according to the invention.

Figures 12A and 12B are respectively a top view and a sectional view of a pump according to one invention.

FIGS. 13A to 13F show different stages of manufacturing an actuator similar to that of FIG. 8A. DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

FIGS. 4A to 4D respectively show a top view, in cross section along the axis BB, in cross section along the axis CC, in bottom view a magnetic actuator according to the invention. Such an actuator can for example be a micro-relay usable in particular in portable telephone devices. It is achievable in microtechnology with stacked layers. In this configuration, the closed magnetic circuit 26, capable of guiding a magnetic flux, is shown diagrammatically by the arrows in bold. It comprises a fixed magnetic part 21 and a mobile magnetic part 22 magnetically connected to each other. The fixed magnetic part 21 comprises a substantially flat cylinder head or base 30 which is extended on one side by a first magnetic stud 31 intended to magnetically connect the fixed magnetic part 21 and the mobile magnetic part 22. It is extended on the other side by a second magnetic pad 32 which contributes to delimiting a main air gap 29 between the fixed magnetic part 21 and a portion 28 of the mobile magnetic part 22. It further comprises flux recovery means 40 which will be detailed later.

The mobile magnetic part 22 is in the form of a substantially planar arm having an end 33 of support integral with the first magnetic stud 31 and ending in a free end. In this example, the free end corresponds to the portion 28 which contributes to delimiting the main air gap 29. This portion 28 has a maximum amplitude during a movement of the mobile magnetic part 22. This portion 28 is located opposite of the second stud magnetic 32, the force generated during actuation is applied to this portion.

The first magnetic pad 31 also has a role of mechanical anchoring of the mobile magnetic part 22 to the fixed magnetic part 21. This anchoring can be done by embedding or by articulation. The first magnetic pad can be made entirely of magnetic material or only partially.

The second magnetic pad 32 which contributes to delimiting the main air gap 29 can have a role of electrical contact in the application of an electrical relay.

It is possible to produce the second magnetic pad in a hysteresis material, for example it can be produced by an electrolytic deposition of a cobalt alloy. This embodiment makes it possible to obtain a stable state of the actuator.

The two magnetic studs 31, 32 are located at the two ends of the yoke 30. In the main air gap 29 the magnetic flux closes by establishing itself transversely to the plane of the mobile magnetic part 22.

According to a characteristic of the invention, the fixed magnetic part 21 comprises flux recovery means 40, magnetically connected with the cylinder head 30 which delimit with the mobile magnetic part 22 at least one auxiliary air gap 38 in which the magnetic flux s' establishes laterally to the movable part 22. In this example, the magnetic connection between the yoke 30 and the flux recovery means 40 is made by means of the first magnetic stud 31.

Means for generating magnetic flux

27 can be produced by one or more windings placed around the closed magnetic circuit 26. One or several permanent magnets can be provided in addition or in place of the windings.

In Figures 4, the means for generating the magnetic flux are not shown, for the sake of clarity, but they are visible in Figures 5 described later. They can be placed around the cylinder head, magnetic studs, flux recovery means or even the moving magnetic part, if they do not hinder movement. In the example of FIGS. 4, the flow recovery means 40 are shown as an arm with two branches 41, substantially flat with one end

40.1 not magnetically connected and one support end

40.2 magnetically and mechanically connected to the yoke 30 via the first magnetic stud 31. The flux recovery means 40 are situated substantially in the same plane as the mobile magnetic part 22.

The two branches 41 are joined at the two ends of the arm 40. The two branches delimit a space in which the mobile magnetic part 22 takes place. In fact in this example, the mobile magnetic part 22 and the flux recovery means 40 are integral of the same first magnetic pad 31, but several pads could be present. The flux recovery means 40 surround the fixed magnetic part 22 and the lateral auxiliary air gap 38, which they help to define, borders the mobile magnetic part 22 from its built-in bearing end 33 to the portion 28 contributing to delimit the main air gap 29.

The flux recovery means 40 cooperate with the mobile magnetic part 22. They recover part of the magnetic flux established in the main air gap 29 which, when the mobile magnetic part 22 is in a saturated state, cannot be guided by it. This may be the case when the main air gap 29 is small, when the relay is being closed for example, in particular for thin film materials deposited by electrolytic means for example, for which the value of the induction at saturation is low.

In Figures 4 the circulation of the magnetic flux has been shown. The magnetic flux which is established in the auxiliary air gap 38 is directed substantially transversely to that which is established in the main air gap 29 and therefore substantially transversely to the movement.

By making an analogy with an electric circuit, the closed magnetic circuit 26 thus produced comprises a section comprising the flux recovery means 40 and the mobile magnetic part 22 mounted in parallel, this section being in series with another section comprising the first pad. magnetic 31, the yoke 30, the second magnetic pad 32 and the main air gap 29 mounted in series.

The flux recovery means 40 make it possible to increase the section of the magnetic circuit in the part corresponding to the mobile magnetic part and therefore to guide a magnetic flux greater than that which could be guided in the absence of the recovery means. These flux recovery means 40 are used before, during and after the movement of the mobile magnetic part 22.

It is then possible to give the magnetic mobile part 22 a section adapted to the desired mechanical stresses without fear that it will saturate, because saturation is no longer synonymous with reduced force exerted on the portion 28 contributing to delimit the main air gap 29 and long response time. Thanks to the presence of the flux recovery means 40, for a low main air gap 29, the magnetic flux which is established therein can be increased and the force which is also exerted. There is less magnetic flux that cannot be guided due to saturation.

For a larger main air gap, the reluctance of the magnetic circuit 26 is reduced by the magnetic elements put in place and the gain in magnetic flux and force are appreciable. Remember that the reluctance of a magnetic circuit is the equivalent of the resistance of an electrical circuit.

In all cases, the gain in magnetic force results in a reduction in the mechanical switching time.

The distance between the mobile magnetic part 22 and the flux recovery means 40 characterizes the auxiliary air gap 38. It can be substantially constant as shown in FIG. 4A. However, it is preferable to adjust it to adjust the flow passage and optimize the force exerted on the portion at maximum amplitude 28 and avoid damping. It is preferable that the dimension D1 of the auxiliary air gap 38, in the direction of establishment of the magnetic flux, is minimum at the level of at least one zone of the portion 28 contributing to delimiting the main air gap.

Still with the aim of optimizing the value of the force exerted on the mobile magnetic part 22, it is preferable to limit the appearance of parasitic forces between the flux recovery means 40 and the mobile magnetic part 22.

When establishing a magnetic flux in two magnetic elements, forces linked to reluctant effects tend to align the two magnetic elements in the direction of induction magnetic. If the flux recovery means 40 and the movable magnetic part 22 have the same dimension in the direction of movement, during actuation, there is an offset between them, this offset may lead to the surfaces delimiting the auxiliary air gap 38 are no longer opposite. The mobile magnetic part 22 then undergoes a Lorentz force which opposes its displacement and which can disturb the operation of the actuator. To avoid this phenomenon, it is preferable that the flux recovery means 40 have, in the direction of movement, a thickness El greater than that E2 of the movable magnetic part 22 so that the surfaces delimiting the auxiliary air gap 38 remain opposite.

It is also preferable to limit the flow of direct leakage between the flux recovery means 40 and the other fixed parts of the closed magnetic circuit 26, in particular the second magnetic pad 32.

The main air gap 29 is delimited by the portion 28 of the movable magnetic part 22 which has a surface SI and by the second magnetic pad 32 of the yoke 30 which has a surface S2 opposite the surface SI. To limit the leakage flux, it is possible that the surface S1 is larger than the surface S2 and that it protrudes around the surface S2. The surface S1 exceeds the surface S2 by a distance PI. The magnetic flux contained in the recovery means 40 then more readily passes into the portion 28 of the mobile magnetic part 22 than into the second pad 32.

We are now interested in Figures 5A and 5B which are two variants, in top view, of a magnetic actuator according to the invention. These figures are comparable to FIG. 4A as regards the overall shape of the mobile magnetic part 22 and of the magnetic flux recovery means 40.

FIG. 5A shows the means for generating the magnetic flux 27 in the form of one or more coils 27.1 to 27.3. There are a large number of possibilities for arranging and carrying them out. In this example, there is a coil 27.1 around each of the studs 31, 32, a coil 27.2 around the arm forming the movable magnetic part 22 and a coil 27.3 around each of the branches 41 of the flow recovery means 40.

It is assumed that the windings 27.1 associated with the pads 31, 32 are spiral windings. This type of winding, compatible with micro-technologies, is easy to perform. The windings 27.2, 27.3 around the arm and the branches have been shown of the solenoid type. One or more windings 27.4 of the latter type for example, can be associated with the cylinder head 30 as illustrated in FIG. 6B.

To further reduce the response time of the actuator according to the invention, it is preferable to provide means to avoid damping of the mobile magnetic part 22 during its movement. These means promote an escape of the air located in the main air gap 29 when the displacement of the mobile magnetic part 22 has the effect of reducing the main air gap 29.

These means 42.1 may consist in providing along the mobile magnetic part 22 one or more first zones Z1 at which the magnetic flux recovery means 40 are more distant than in one or more second zones Z2.

To optimize the force exerted on the portion 28 which delimits the main air gap 29 and avoid the damping of the mobile magnetic part 22, the auxiliary air gap 38 has a dimension in the direction of establishment of the magnetic flux which is minimum at the level of at least one zone of the portion 28 contributing to delimiting the main air gap 29. It is therefore greater in at least one zone outside said portion 28.

In the example of FIGS. 5A and 5B, the mobile magnetic part 22 is an arm which ends in the portion 28, the latter being enlarged relative to the width of the arm. The distance D2 between the flux recovery means 40 and the movable magnetic part 22 is almost maximum near the portion 28 and it decreases the further we go. At the level of the portion 28 the distance D1 is minimal as we have seen previously. In FIGS. 5A, 5B, the minimum dimension D1 exists all around the portion 28.

If the size of the auxiliary air gap is substantially constant, air may remain trapped at the movable magnetic part 22, which dampens its movement.

These means for promoting escape can also consist in providing the mobile magnetic part 22 with through openings 42.2 in the direction of movement. This configuration is illustrated in FIG. 5B in combination with the adjustment of the distance between the mobile magnetic part 22 and the flux recovery means 40. There are a series of openings 42.2 along the arm from the end of support 33 towards the portion 28 and two series of openings along the portion 28.

Figures 5C and 5D show two other configurations of the auxiliary air gap 38, they are derived from Figures 5A and 5B. It can be seen that the mobile magnetic part 22 risks moving laterally in the plane of the auxiliary air gap 38 to come into contact with the flux recovery means 40, due to mechanical instability due to magnetic forces existing between the mobile magnetic part 22 and the flux recovery means 40. The mobile magnetic part 22 may come to block against the flow recovery means 40. This generates a malfunction and wear of the actuator.

It is possible, to avoid this drawback to increase the dimension D3 of the auxiliary air gap 38, on either side of the movable magnetic part 22, at the level of the portion 28 contributing to delimiting the main air gap 29. By against, at the end of the mobile magnetic part 22, at the end of the arm, the dimension D4 of the auxiliary air gap, in the direction of establishment of the magnetic flux, remains minimal.

In these FIGS. 5, it is assumed that the first magnetic pad 31 and the second magnetic pad 32 come from the mobile magnetic part 22 instead of being from the fixed magnetic part 21. The flux recovery means 40 are always connected magnetically and mechanically to the yoke 30 by the first magnetic pad 31. The second magnetic pad 32 then forms part of the portion 28 of the movable magnetic part 22. The main air gap is delimited by the second magnetic pad 32 and by the portion of the cylinder head which is opposite with this second magnetic stud. Still with a view to optimizing the force exerted on the portion 28, it is sought to limit the flow leaks in the magnetic circuit 26 in particular between its different stacked levels. Flow leaks are due to the length of the magnetic circuit, the cross-section of the magnetic material and the shape effects of the circuit. In materials in thin layers, leaks are greater than in solid materials.

It is however possible, in order to limit the form effect, to give the cylinder head 30 (which corresponds to a first level of the actuator) and / or the assembly formed by the mobile magnetic part 22 and the recovery means flow 40 (which corresponds to a second level of the actuator) an oblong shape substantially rounded at its two ends. Figures 6A and 6B are top and bottom views respectively of an actuator according to the invention.

It is also possible, always for the same purpose, to overlap the two levels. In the example of FIGS. 6, the cylinder head 30 exceeds the whole mobile magnetic part 22-flux recovery means 40 over a large part of its periphery. It is also possible to provide at least one through opening on at least one of the levels to reduce the facing surfaces. In the example, the cylinder head 30 is provided with a large opening 43 which is substantially central. This configuration is not limiting, others are possible.

We will now see another example of a relay according to the invention. It is assumed that the relay was produced by conventional technologies for assembling and machining mechanical structures as opposed to micro-technologies. Such a relatively massive relay is particularly suitable for high powers. This relay is shown in top view in Figure 7A and in section in Figure 7B. We find the fixed magnetic part 21 with the yoke 30 magnetically and electrically connected to the mobile magnetic part 22 via the first holding pad 31. The second pad 32 which contributes to delimiting the main air gap 29 is massive. The means for generating the magnetic flux 27 are produced by a coil arranged around the second pad 32. The movable magnetic part 22 is an arm with a support end 33 connected to the first pad 31 and a free end forming the portion 28 which comes in opposite the second pad 32 to delimit the main air gap 29.

The flow recovery means 40 are produced by a solid arm mechanically and magnetically connected by one of its ends 35 to the cylinder head 30 by means of a third stud 34. Like the other two studs, this third stud 34 is a protrusion relative to the cylinder head 30. It could be envisaged that this third stud 34 comes from the flow recovery means 40 instead of being part of the cylinder head.

The other end 36 of the arm is not magnetically connected, it comes close to the mobile magnetic part 22 and contributes with the latter to delimit the auxiliary air gap 38. In the previous configurations, the mobile magnetic part and the means flow recovery were directed substantially in the same direction while in this configuration their directions are substantially perpendicular. Their magnetic connection points with the cylinder head are distinct.

It is assumed that in this configuration the mobile magnetic part 22 and the second magnetic pad 32 are electrically conductive and form part of an electrical circuit which is open when the actuator is open and which is closed when the actuator is closed .

The actuator according to the invention can be symmetrical with respect to a median plane P passing through the mobile magnetic part 22 substantially perpendicular to the direction of movement (materialized by a double-pointed arrow). It is thus possible to produce a switch. FIG. 7C illustrates this configuration. The mobile magnetic part 22 is now connected by its support end 33 to a cylinder head with two branches 30.1, 30.2 substantially parallel and this connection is made by two first studs 31.1, 31.2 in the extension of one another. It is the same for the flow recovery means 40. They are each magnetically connected to a branch 30.1, 30.2 of the cylinder head 30 via two third studs which are not visible in FIG. 7C but which are in the extension one on the other.

There is also a pair of second studs 32.1, 32.2 in the extension of one another, opposite, each of them contributing to delimit a main air gap 29.1, 29.2 with the mobile magnetic part 22. These air gaps are arranged in the extension of one another, on either side of the mobile magnetic part 22. The portion 28 of the mobile magnetic part 22 is the seat of a force which is exerted in one direction or in the other, so as to move the mobile magnetic part 22 towards one of the second pads 32.1 or towards the other 32.2. The means for generating the magnetic flux have been shown in the form of two coils 27.1, 27.1, one 27.1 allowing the flux to settle in one 28.1 of the main air gaps and the other 27.2 allowing the flux of s' establish in the other main air gap 28.2. The windings 27.1, 27.2 each encircle one of the second pads 32.1, 32.2.

If the second magnetic pads 32.1, 32.2 are made of a hysteresis material, two stable states of the actuator can be obtained. FIG. 7D illustrates a relay having substantially the same structure but produced in micro- technology. We start from a substrate 70, for example made of silicon. An opening 71 is etched in the substrate to make the means for generating the magnetic flux 27 in the form of a spiral winding. It is filled with conductive material. An electrically insulating layer 72 is deposited on one of the faces of the substrate 70 at the level of the spiral winding. At least one pair of holes 73 are drilled through the substrate 70, they are filled with conductive material to make two electrical contacts 75 intended to be electrically connected when the magnetic actuator is closed.

Other holes 74 are drilled through the substrate 70 and the insulating layer 72 to produce the pads 31, 32, 34. They are filled with magnetic material. Care has been taken to place the second pad 32 which contributes to delimiting the main air gap 29 in the central zone of the winding. The third pad 34 is not visible but it is comparable to that of FIG. 7A.

The yoke 30 connected to the studs 31, 32, 34 is also deposited on the face carrying the insulating layer 72. On the other face of the substrate 70, a sacrificial layer, for example made of silicon oxide, is deposited, it is etched at level of the magnetic connection pads 31, 34. A resin is deposited photolithographed through a mask and developed to create a box in which the moving magnetic part 22 and the flux recovery means 40 will be deposited. The sacrificial layer is then released under the movable magnetic part to give it freedom of movement. The sacrificial layer is not shown in FIG. 7D but its location is between the substrate 70 and the mobile magnetic part 22. The latter hides the flux recovery means. The mobile magnetic part 22 extends beyond the main air gap 29 to come opposite the two electrical contacts 75 carried by the substrate 70. When the actuator is closed, the two electrical contacts 75 are electrically connected via the free end of the mobile magnetic part 22. It is assumed that in this example, the mobile magnetic part or at least its free end is made of electrically conductive magnetic material. We will now describe another variant of a magnetic actuator according to the invention, the latter having great mechanical stability in torsion. Reference is made to FIGS. 8A to 8C.

We find the cylinder head 30 which is supported by a support 80 which can be glass, ceramic or silicon for example.

In FIG. 8B, it is provided with a first single stud 31 which provides both its magnetic connection with the mobile magnetic part 22 and with the flux recovery means 40 and with a second stud 32 which contributes to delimit the main air gap 29.

In FIG. 8C, it is provided with a pair of first studs 31.1, 31.2 which ensures both its magnetic connection with the movable magnetic part 22 and with the flux recovery means 40 and a second stud 32 which contributes to delimit the main air gap 29.

In FIG. 8D, the auxiliary air gap has a dimension in the direction of flow establishment which is minimal at the level of at least one zone of the portion contributing to delimit the main air gap.

The movable magnetic part 22 is always in the form of a substantially planar arm but instead of being massive the arm consists of two branches 22.1, 22.2 not parallel. On one side the branches 22.1, 22.2 are magnetically and mechanically connected either to the first single stud 31, or to one of the studs 31.1, 31.2 of the pair and on the other they come together to form the portion 28 which contributes to delimit the main air gap 29.

The flow recovery means 40, in this example, are in the form of a substantially planar arm which is housed between the two branches 22.1, 22.2 of the mobile magnetic part 22 substantially in the same plane.

The branches 22.1, 22.2 are substantially symmetrical with respect to a longitudinal axis of the arm of the flow recovery means 40. This arm is magnetically and mechanically connected on one side, either to the first single stud 31, or to the pair of first studs 31.1, 31.2, and on the other side is free. It approaches the portion 28. It defines with the mobile magnetic part 22 the auxiliary air gap 38. The means 27 for generating the flux take the form of one or more coils. In FIG. 8B, a single winding 27 has been shown around the first single stud 31 while in FIG. 8C a winding 27.1, 27.2 has been shown around each of the studs 31.1, 31.2 of the pair. We could have added a winding around the second pad 32.

The production of an actuator in microtechnology similar to that of FIG. 8A can be done as follows with reference to FIGS. 13A to 13F. On the substrate 80, the cylinder head 30 will be produced. A layer of resin is deposited, then a lithography step is carried out. An enclosure 130 is etched in the substrate 80 or in a layer deposited on the substrate. A conductive sub-layer 131 is deposited at the bottom of the enclosure 130 (FIG. 13A). The cylinder head 30 is deposited electrolytically. The deposit is then planarized so as to keep the cylinder head 30 only "in the box 130 (FIG. 13B).

A dielectric layer 81 is then deposited, for example made of silicon oxide, and at least one box 132 is etched therein to delimit the means 27 for generating the flux in the form of a coil with their electrical control pads. This engraving is preceded by a lithography step. It does not reach the cylinder head 30. The conductive tracks of the windings 27, for example made of copper, are deposited by electrolysis, this step is preceded by the deposition of a conductive sub-layer and is followed by a planarization step (figure 13C). We deposit a new dielectric layer

82. Boxes 133 intended to delimit the magnetic pads 31, 32 are etched in the two dielectric layers 81, 82. This etching is preceded by a lithography step. The caissons 133 reach the cylinder head 30. The magnetic pads 31, 32 are deposited by electrolysis, this step is preceded by the deposition of a conductive sub-layer and is followed by a planarization step (FIG. 13D).

Then a sacrificial layer 83 is deposited, for example made of silicon oxide, and it is etched to release the first magnetic pad 31 and ensure separation between the mobile magnetic part and the fixed magnetic part with the flux recovery means which will be deposited. (Figure 13E). A layer of magnetic material is then deposited to make the fixed magnetic part with the flux recovery means 40 and the mobile magnetic part 22 and by a lithography and etching step they are delimited. Finally, the sacrificial layer 83 is removed, for example by etching chemical, under the mobile magnetic part 22 to release it (Figure 13F).

The electrical control pads of the windings 27 are exposed (not shown). The actuator can be covered with a protective cover (not shown).

We will now see examples of electrical relays and switches, detailing their electrical contacts in more detail. In FIG. 9A, a top view is seen of an electrical relay comparable to that of FIG. 4A. The cylinder head 30 is supported by a substrate 90. The flow recovery means 40 are visible, they take the form of an arm with two branches. The movable magnetic part 22 projects beyond the second magnetic pad 32 and its end ends in a movable electrical contact 91 offset relative to the main air gap 29. The substrate 90 on which the yoke 30 rests comprises a discontinuous conductive track 92 . The discontinuity 93 is at the level of the movable electrical contact 91. When the actuator is in the closed state, the movable electrical contact 91 comes into contact with the conductive track 92 on each side of the discontinuity 93 so as to restore continuity. It is assumed that, on each side of the discontinuity 93, the track 92 has a contact zone 94 made of a material different from that of the track. This material can be gold for example, to improve the quality of the contact. The conductive track 92 can be a simple conductive line or a microstrip line for example. It is this latter configuration which is represented.

The portion 28 on which the force and the mobile electrical contact 91 are applied have been offset with respect to each other along the mobile magnetic part 22, but they remain in the same plan. They can be achieved by the same technological step. It is thus possible to keep the main air gap 29 as small as possible, compared to the case where the distance between the electrical contacts is included in the main air gap, when the actuator is in the open state and a distance between the movable electrical contact. 91 and runway 92 as large as possible. The movable electrical contact 91 can be placed anywhere on the movable magnetic part and is dimensioned independently of the dimensions of the latter. There is space to adjust the level of the track 91 on the substrate 90. This is an advantageous construction for increasing the closing force of the relay. We can consider making the electrical contact at the main air gap 29. This is the variant illustrated in FIGS. 10A, 10B, 10C.

A movable electrical contact 97 is fixed to the movable magnetic part 22 at the level of the seat portion 28 of the force generated by the magnetic flux. This mobile electrical contact 97 is electrically isolated from the mobile magnetic part 22 by an insulating layer 95. This insulating layer 95 can be removed if the mobile magnetic part 22 is electrically conductive and this property is used. In this case, the mobile magnetic part 22 can be electrically isolated from the rest of the magnetic actuator. It can thus serve itself for the transmission of an electrical signal, the movable electrical contact closing an electrical circuit integrating the movable magnetic part.

It is conceivable that the electrical contact is made by the magnetic material itself as illustrated in FIGS. 11. A discontinuous conductive track 96 is shown opposite the movable contact 97. It is found between the second magnetic pad 32 and the movable contact 97. In this configuration, contact areas have not been shown on the track to improve the quality of the contact. With such a configuration, the main air gap 29 is increased the more electrically conductive or insulating layers are added between the mobile magnetic part 22 and the second magnetic pad 32, while the spacing between the electrical contacts is substantially constant. Despite the increase in the air gap, the method for making the actuator can be simpler.

It can be envisaged so that the actuator can function as a switch, that the mobile magnetic part 22 is equipped with two mobile electrical contacts 97.1, 97.2. These contacts are placed substantially symmetrically with respect to a median plane of the movable magnetic part 22 substantially perpendicular to the direction of movement. They are each intended to close an electrical circuit, shown schematically by a contact area 96.1, 96.2, these circuits being arranged on either side of the movable magnetic part 22. By generating a magnetic flux in the main air gap 29 in one way or the other, the movable magnetic part 22 moves in one direction or in the opposite direction and one of the movable electrical contacts 97.1 or 97.2 closes one of the electrical circuits.

As in FIG. 10A, the fixed contact area 96.1 is located between the second magnetic pad 32 and the movable electrical contact 97.1. In this representation the insulating layer between the movable magnetic part 22 and the movable electrical contacts 97.1, 97.2 is omitted. To make a switch, it is also possible to place the anchor of the part moving magnetic 22 in its central part instead of placing it at one of its ends. Figures 11A and 11B illustrate this variant. Now the mobile magnetic part 22 is in a pendulum with two free ends 37.1, 37.2. It comprises two portions 28.1, 28.2 which each contribute to delimiting a main air gap 29.1, 29.2 and these portions are located on the side of its two free ends 37.1, 37.2. The cylinder head 30 is now provided with a first central magnetic anchoring stud 31 and with a pair of second studs 32.1, 32.2 which each contribute to delimit one of the main air gaps 29.1, 29.2. It is made of an electrically conductive magnetic material. It is assumed that in this example the first central magnetic pad 31 also serves to magnetically connect the flux recovery means 40 to the cylinder head 30. The flux recovery means 40 are comparable to those shown in Figures 6. The means for generating the magnetic flux 27 take the form of a pair of coils 27.1, 27.2, each of them surrounding one of the second pads. References 100.1 and 100.2 represent the electrical terminals for supplying the windings. The terminals 100.1 are electrically connected directly to one end of the conductor of a winding 27.1, 27.2 while the terminals 100.2 are connected via a conductor 100.3 and via one of the second magnetic pads 32.1, 32.2 to the other end of the conductor of a winding 27.1, 27.2.

The windings 27.1, 27.2 are electrically isolated from the yoke 30 by a dielectric layer 101 which also extends between the first magnetic pad 31 and the yoke. The mobile magnetic part 22 has at its free ends 37.1, 37.2 a zone 28.1, 28.2 on which the force is exerted upon actuation of the switch. This zone 28.1, 28.2 is located opposite each of the second studs 32.1,

32.2, it contributes to delimiting the main air gap 29.1, 29.2.

The two free ends 37.1, 37.2 end in an electrical contact area 102.1,

102.1 mobile. It is assumed that the mobile magnetic part 22 is electrically conductive as well as the first magnetic pad 31. The latter is connected to an input conductor E making it possible to route an electrical signal to the mobile magnetic part 22. Opposite screw of each of the electrical contact areas 102.1,

102.2 there is a fixed electrical contact 104.1, 104.2 electrically isolated from the second magnetic pad 32.1,

32.2 by a dielectric layer 101. This electrical contact is extended by an output conductor SI, S2. The mobile magnetic part comes into contact with one of the fixed electrical contacts 104.1, 104.2, the electrical signal can be collected on one or the other of the output conductors SI or S2. The windings 27.1, 27.2 are also electrically isolated from the output conductors S1, S2.

The passage of the electrical signals and the passage of the magnetic flux are shown diagrammatically on the right-hand side of FIG. 11B. In this example the electrical signal passes through the movable magnetic part but neither through the second magnetic pad nor through the yoke. One would have imagined that it passes through these parts of the magnetic circuit.

The windings can be independent or be electrically connected in series, for example opposite windings can be in series when using remanent magnetization materials or hysteresis materials. FIGS. 12A, 12B now illustrate an actuator according to the invention in a pump application and more particularly a micro-pump.

We find the mobile magnetic part 22 formed of several branches 22.1, 22.2, 22.3 in a star. The center 28 of the star contributes to delimiting the main air gap 29. It can take the form of a magnetic stud bearing the same reference 28. The ends of the branches 22.1, 22.2, 22.3 are support ends magnetically connected and mechanically to the single cylinder head 30. The cylinder head may for example be in the form of a disc. The cylinder head has a series of first studs 31.1, 31.2, 31.3 to connect it to the mobile magnetic part 22. It also has a second central stud 32 which contributes to delimiting the main air gap 29 and a series of third studs 34.1 , 34.2, 34.3 to connect it magnetically and mechanically to the flow recovery means 40.1, 40.2, 40.3. These flux recovery means contribute to delimiting an auxiliary air gap 38.1, 38.2, 38.3 with the mobile magnetic part 22. They occupy the space between two contiguous branches while remaining spaced from the branches.

In this pump configuration, it is assumed that the first pads and the third pads are joined in their upper part so as to form a peripheral ring to the cylinder head 30 on which a membrane 120 is fixed. This membrane 120 is also integral with the part mobile magnetic 22 and pad 28 but not flow recovery means 40. This membrane moves at the rate of movement of the mobile magnetic part 22. It is used to activate the circulation of a fluid. It can have a compression, suction or ejection effect on the fluid. It is carried out in a material compatible with the fluid to be pumped or is protected by a surface treatment.

In the example of FIGS. 12, the membrane 120 contributes to delimiting on one side with the cylinder head 30 a first cavity 121. The auxiliary air gaps 38.1, 38.2, 38.3 can serve as orifices contributing to the circulation of the fluid, for its ejection or from its suction in an actuating cavity 122 between the other side of the membrane 120 and the flow recovery means 40. At least one other orifice 44 also contributing to the circulation of the fluid could pass through the crown and lead into the actuating cavity 122. A valve system (not shown) would be used so that the fluid can circulate properly.

The means for generating the magnetic flux are represented in the form of coils 27 encircling the first magnetic pads 31.1, 31.2, 31.3 and the second magnetic pad 32. A sealing layer 123 coats the coils 27 between the yoke 30 and the magnetic pads 31.1, 31.2, 31.3, 32, 34.1, 34.2, 34.3 so as to isolate them from the cavity 121.

Other configurations are possible, in particular the fluid could be in a reservoir included in the pump and there would be at least one orifice to eject it.

By removing the membrane such a structure could be used as a relay.

Claims

1. Magnetic actuator having a closed magnetic circuit (26) capable of guiding a magnetic flux, this magnetic circuit (26) comprising a fixed magnetic part (30, 31, 32) with a yoke (30) and a mobile magnetic part (22 ) magnetically linked together and in addition at least one main air gap (29) delimited by at least one portion (28) of the mobile magnetic part (22) and by the yoke (30), in which the magnetic flux closes in s '' establishing substantially transversely to the mobile magnetic part (22), characterized in that the fixed magnetic part (30, 31, 32) comprises flux recovery means (40) which contribute to delimiting with the mobile magnetic part (22) an auxiliary air gap (38) in which the magnetic flux is established laterally to the mobile magnetic part

(22), the magnetic flux being contained on either side of the main air gap (29) on one side by the cylinder head (30) and on the other by the mobile magnetic part (22) and by the means flow recovery

(40) jointly via the portion (28) contributing to delimit the main air gap (29), the auxiliary air gap (38) has a dimension in the direction of establishment of the magnetic flux which is minimum at the level of at least one portion area (28) contributing to delimit the main air gap (29).

2. Magnetic actuator according to claim 1, characterized in that at least a first magnetic stud (31) makes it possible to mechanically and magnetically connect the yoke (30) to the mobile magnetic part (22).

3. Magnetic actuator according to one of claims 1 or 2, characterized in that at least one second magnetic pad (32) contributes to delimiting the main air gap (29), this magnetic pad (32) is made of a material at hysteresis.

4. Magnetic actuator according to one of claims 1 to 3, characterized in that at least one other magnetic pad (34) makes it possible to mechanically and magnetically connect the yoke (30) to the flow recovery means (40).

5. Magnetic actuator according to one of claims 1 to 4, characterized in that it comprises means (27) for generating the magnetic flux in the closed magnetic circuit (26), these means for generating the magnetic flux being produced by at least one winding.

6. Magnetic actuator according to one of claims 1 to 5, characterized in that the mobile magnetic part (22) generally takes the form of at least one arm with one or more non-parallel branches connected together at the portion helping to delimit the main air gap (29).

7. Magnetic actuator according to one of claims 1 to 6, characterized in that the movable magnetic part (22) takes the form of a star with several branches (22.1, 22.2, 22.3).

8. Magnetic actuator according to one of claims 1 to 7, characterized in that the flux recovery means (40) have, in the direction of movement of the movable magnetic part (22), a thickness (El) greater than (E2) presented by the mobile magnetic part (22) in the direction of movement so that the auxiliary air gap (38) is delimited by surfaces which remain opposite when the mobile magnetic part (22) is moving.

9. Magnetic actuator according to one of claims 1 to 8, characterized in that the main air gap (29) is defined by two surfaces (SI, S2) facing each other, the first (SI) belonging to the portion ( 28) of the movable magnetic part (22) and the second (S2) belonging to the cylinder head (30), the first surface (SI) being greater than the second surface (S2) and projecting around the second surface (S2).

10. Magnetic actuator according to any one of claims 1 to 9, characterized in that the dimension (D2) of the auxiliary air gap (38), in the direction of establishment of the magnetic flux, is almost maximum near the portion (28) contributing to delimit the main air gap (29) and decreases the further we go.

11. Magnetic actuator according to one of claims 1 to 10, characterized in that the mobile magnetic part (22) has at least one opening (42.2) through, in the direction of movement.

12. Magnetic actuator according to one of claims 1 to 11, characterized in that the cylinder head

(30) forms a first level of the actuator and the assembly formed by the flux recovery means (40) and by the mobile magnetic part (22) a second level, the two levels being stacked.

13. Magnetic actuator according to claim 12, characterized in that at least one of the levels has an oblong shape substantially rounded at its two ends.

14. Magnetic actuator according to one of claims 12 or 13, characterized in that the two levels overlap.

15. Magnetic actuator according to one of claims 12 to 14, characterized in that at least one of the levels comprises at least one central opening (43) through.

16. Magnetic actuator according to one of claims l to 15, characterized in that it is substantially symmetrical with respect to a median plane (P) passing through the mobile magnetic part (22) substantially perpendicular to the direction of movement.

17. Magnetic actuator according to one of claims 1 to 16, characterized in that the portion (28) contributing to delimit the main air gap (29) comprises at least one electrical contact (97), this electrical contact (97) being intended to contact at least one other electrical contact (96) when the actuator is closed.

18. Magnetic actuator according to one of claims 1 to 16, characterized in that the mobile magnetic part (22) ends with at least one electrical contact (91) offset with respect to the portion

(28) contributing to delimit the main air gap (29), intended to contact at least one other electrical contact when the actuator is closed.

19. Magnetic actuator according to one of claims 17 or 18, characterized in that the electrical contact (97) is electrically isolated from the movable magnetic part (22).

20. Magnetic actuator according to one of claims 17 to 19, characterized in that the mobile magnetic part (22) is made of electrically conductive magnetic material and serves as an electrical contact.

21. A method of producing a magnetic actuator according to one of claims 1 to 20, characterized in that it comprises the following steps: etching in a substrate (80) of a box (130) to be filled with magnetic material for producing a yoke (30) of a fixed magnetic part (30, 31, 32), - deposition of a first dielectric layer

(81) on the substrate (80) with the cylinder head (30),

- etching of at least one box (132) to define means for generating a magnetic flux (27), and depositing said means (27), - depositing a second dielectric layer

(82) on the first layer (81),

- etching of boxes (133) through the two layers (81, 82) reaching the yoke (30) to delimit at least a first magnetic pad (31) and at least a second magnetic pad (32), the second pad (32 ) helping to define at least one main air gap (29), depositing the first and second magnetic pads (31, 32) in the boxes (133),

- depositing a sacrificial layer (83) on the second dielectric layer (82) and etching the sacrificial layer (83) to release the first magnetic pad (31) and provide for separation between a mobile magnetic part (22) and flux recovery means (40) of the fixed magnetic part subsequently deposited, - deposition on the sacrificial layer (83) of magnetic material to produce the mobile magnetic part (22) and the flux recovery means (40), then etching magnetic material to delimit them, elimination of the sacrificial layer (83) under the mobile magnetic part (22) to release it and make the main air gap (26).

22. Relay characterized in that it comprises a magnetic actuator, according to one of claims 1 to 20.

23. Switch characterized in that it comprises at least one magnetic actuator, according to one of claims 1 to 20, so as to present several main air gaps (29.1, 29.2).

24. Pump characterized in that it comprises a magnetic actuator, according to one of claims 1 to 16, in which the mobile magnetic part (22) is integral with a membrane (120) contributing to delimit a cavity (122) to circulate a fluid.