EP4445395A1

EP4445395A1 - Magnetic field generation system

Info

Publication number: EP4445395A1
Application number: EP22823599.0A
Authority: EP
Inventors: Gilles Zahnd; Antoine CHAVENT; Siamak Salimy
Original assignee: Hprobe SA
Current assignee: Hprobe SA
Priority date: 2021-12-07
Filing date: 2022-12-05
Publication date: 2024-10-16
Also published as: CN118613885A; FR3130067B1; WO2023104733A1; FR3130067A1

Abstract

The present invention relates to a magnetic field generation system (200) comprising: - a central pole (220) positioned above a plane (XY), the axis of said central pole extending in a direction orthogonal to the plane; - at least two planar poles (216A, 216B, 216C, 216D) positioned symmetrically on the plane with respect to the axis of the central pole; and - at least two coils (230A, 230B, 230C, 230D), at least one of which is associated with each planar pole; two coils associated with two different planar poles being suitable for being connected to two separate supply circuits; each supply circuit being suitable for causing a current of a determined intensity and direction to flow in at least one coil to which it is connected on the basis of a desired magnetic field and the orientation in the plane of the planar pole associated with said coil.

Description

DESCRIPTION

Magnetic field generation system

The present application is based on, and claims the priority of, the French patent application 2113055 filed on December 7, 2021 with the title "Système de generatement de champmagnetic", which is considered to form an integral part of the present description within the limits provided for by law.

Technical area

This application relates to the field of magnetic field generators, and in particular a system adapted to generate a high amplitude magnetic field.

Prior technique

[0002] In certain technical fields, for example for the electrical test of an integrated circuit wafer component under a magnetic field, in particular of a memory point of a wafer, the application of a magnetic field is desired. at the component level.

[0003] In certain cases, for the electrical test of a particular wafer component, for example a spintronics component or a cell of a magnetic random-access memory (MRAM, Magnetic Random-Access Memory), it can be sought the application of a magnetic field of high amplitude, typically greater than or equal to 0.5 T, and this, in several directions. A magnetic field generator capable of generating a magnetic field of high amplitude in several directions is therefore sought.

Summary of the invention

[0004] There is a need to improve magnetic field generation techniques. [0005] In particular, there is a need to improve magnetic field generation techniques for electrical testing of an integrated circuit wafer component.

[0006] One embodiment overcomes all or part of the drawbacks of known magnetic field generators.

[0007] One embodiment provides a magnetic field generation system comprising a magnetic circuit comprising:

- a central pole disposed above a plane, the axis of said central pole extending in an orthogonal direction substantially corresponding to the direction orthogonal to the plane;

- At least two planar poles arranged symmetrically on the plane with respect to the axis of the central pole, each planar pole being carried by a portion of the magnetic circuit; And

- At least two coils, including at least one coil associated with each planar pole, each coil associated with a planar pole surrounding the magnetic circuit portion carrying said planar pole; two coils associated with two different planar poles being adapted to be connected to two separate supply circuits; each supply circuit being adapted to circulate in at least one coil to which it is connected a current of intensity and direction determined according to a desired magnetic field and the orientation in the plane of the planar pole associated with said coil.

[0008]According to one embodiment, the system further comprises a processing unit suitable for determining the current to be circulated in each coil.

According to one embodiment, the processing unit is adapted to determine an equivalent current, for example represented in the form of an equivalent current vector, for the desired magnetic field, and in determining the current to be circulated in each coil as a function of the determined equivalent current and of the orientation in the plane of the planar pole associated with said coil. In other words, the intensity and the direction of the current in each coil are determined according to the geometry of the magnetic circuit, and according to the determined equivalent current. For example, the desired magnetic field is in the form of a magnetic field vector.

[0010] According to one embodiment, the system comprises three coils and three planar poles arranged symmetrically on the plane with respect to the axis of the central pole and being oriented at a first angle of approximately 120° with respect to each other. to the other.

According to a particular embodiment, the currents to circulate in the three coils are respectively: I ₁ = leq _X + Ieq _Z for a first coil associated with a first planar pole oriented towards the axis of the central pole in the positive direction of a first direction of the plane; for a second coil associated with a second planar pole oriented at the first angle in the plane relative to the first planar pole; And for a third coil associated with a third planar pole oriented at the first angle in the plane relative to the second planar pole; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current leq respectively according to the first direction, the second perpendicular direction to the first direction in the plane, and the orthogonal direction.

According to one embodiment, the system comprises four coils and four planar poles symmetrical with respect to two orthogonal planes containing the axis of the central pole, two adjacent planar poles being oriented at a second angle of approximately 90° l one relative to the other.

According to a particular embodiment, the currents to be circulated in the four coils are respectively: for a first coil associated with a first planar pole oriented towards the axis of the central pole at approximately 45° between first and second orthogonal directions in the plane, in the positive directions of said first and second directions;

I ₂ = —leq _X + Ieq _Y + Ieq _Z for a second coil associated with a second planar pole oriented at the second angle in the plane relative to the first planar pole;

I ₃ =—leq _X —leq _Y +Ieq _Z for a third coil associated with a third planar pole oriented at the second angle in the plane with respect to the second planar pole; And

I ₄ = leq _X — Ieq _Y + Ieq _Z for a fourth coil associated with a fourth planar pole oriented at the second angle in the plane with respect to the third planar pole; where I _X , l _Y , I _Z are the components of the vector representing the equivalent current leq respectively according to the first direction, the second direction and the orthogonal direction.

[0014]According to one embodiment, the central pole is surrounded by a fifth coil adapted to be connected to a supply circuit distinct from the coils associated with the planar poles and adapted to circulate in said fifth coil a current of intensity and direction determined according to the desired magnetic field and the orientation of the central pole, for example a current: I ₅ = Ieq _Z where Ieq _Z is the component of the vector representing the equivalent current along the orthogonal direction.

According to one embodiment, each pole corresponds to a first end of an arm, the arms being connected to a frame.

According to one embodiment, each arm associated with a planar pole extends substantially in a direction parallel to the plane, a second end of said arm being assembled to a bar passing inside the at least one coil associated with said planar pole, each bar extending substantially in the orthogonal direction.

According to one embodiment, the arm associated with the central pole is assembled to a horizontal rod connected to two opposite sides of the frame.

According to one embodiment, the coils have outer diameters greater than 70 mm, or even greater than 80 mm, for example greater than or equal to 90 mm.

One embodiment provides a magnetic field generation method implementing a system comprising a magnetic circuit comprising:

- At least two planar poles arranged symmetrically on the plane with respect to the axis of the central pole, each planar pole being carried by a portion of the magnetic circuit; And - At least two coils, including at least one coil associated with each planar pole, each coil associated with a planar pole surrounding the magnetic circuit portion carrying said planar pole; two coils associated with two different planar poles being connected to two separate power supply circuits; the method comprising:

- circulate in at least one coil connected to each power supply circuit, a current of intensity and direction determined according to a desired magnetic field and the orientation in the plane of the planar pole associated with said coil.

According to one embodiment, the method comprises:

- determining an equivalent current, for example in the form of an equivalent current vector, as a function of the desired magnetic field; And

- Determine the current to circulate in each coil according to the determined equivalent current and the orientation in the plane of the planar pole associated with said coil.

According to one embodiment, the method further comprises:

- measure the magnetic field obtained when the determined current flows in each coil;

- compare the measured magnetic field with the desired magnetic field; and, if the difference is greater than a defined threshold,

- determining a second equivalent current as a function of the difference between the measured magnetic field and the desired magnetic field;

- determining the current to circulate in each coil according to the second determined equivalent current and the orientation in the plane of the planar pole associated with said reel ; And

- repeating at least the steps of measuring the magnetic field and of comparison, and, for example, also repeating the steps of determining the second equivalent current and the current to be circulated.

According to a particular embodiment, in which the system comprises three coils and three planar poles arranged symmetrically on the plane with respect to the axis of the central pole and being oriented at a first angle of approximately 120° l' one relative to the other; the method comprising: circulating in a first coil associated with a first planar pole oriented towards the axis of the central pole in the positive direction of a first direction of the plane a current of intensity:

I ₁ = leq _X + Ieq _Z ; circulate in a second coil associated with a second planar pole oriented at the first angle in the plane with respect to the first planar pole a current of intensity:

- circulating in a third coil associated with a third planar pole oriented at the first angle in the plane with respect to the second planar pole a current of intensity: where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current leq respectively according to the first direction, the second direction perpendicular to the first direction in the plane and the orthogonal direction.

According to a particular embodiment, in which the system comprises four coils and four planar poles symmetrical with respect to two orthogonal planes containing the axis of the central pole, two adjacent planar poles being oriented substantially at a second angle of approximately 90° relative to each other; the method comprising: circulating in a first coil associated with a first planar pole oriented towards the axis of the central pole at approximately 45° between first and second orthogonal directions in the plane, in the positive directions of said first and second directions, a intensity current: circulating in a second coil associated with a second planar pole oriented at the second angle in the plane with respect to the first planar pole a current of intensity: / ₂ = —leq _X + Ieq _Y + Ieq _Z ;

- circulating in a third coil associated with a third planar pole oriented at the second angle in the plane with respect to the second planar pole a current of intensity:

/ ₃ = —leq _X — Ieq _Y + leq _Z ;

- circulating in a fourth coil associated with a fourth planar pole oriented at the second angle in the plane with respect to the third planar pole a current of intensity:

I ₄ = leq _X — leq _Y + Ieq _Z ; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current leq according to the first direction, the second direction and the orthogonal direction respectively.

According to one embodiment, the determined equivalent current vector and the desired magnetic field are dynamic.

Brief description of the drawings

[0025] These and other features and advantages will be discussed in detail in the following mode description. specific embodiments made on a non-limiting basis in relation to the attached figures including:

Figure 1A is a first perspective view of an example of a magnetic field generator;

Figure 1B is a second perspective view of the magnetic field generator of Figure 1A;

Figure 2A is a perspective view of a magnetic field generation system according to one embodiment;

[0029] Figure 2B is a simplified cross-section of the system of Figure 2A;

Figure 3A is a simplified perspective view of a magnetic field generation system according to another embodiment;

[0031] Figure 3B is a simplified cross-section of the system of Figure 3A; And

[0032] Figure 4 is a simplified cross-section of a magnetic field generation system according to another embodiment.

Description of embodiments

The same elements have been designated by the same references in the various figures. In particular, the structural and/or functional elements common to the various embodiments may have the same references and may have identical structural, dimensional and material properties.

[0034] For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed. In particular, the supply circuits of the coils are not represented, being able to be conductors connected on the one hand to the coil to power, and on the other hand to a current generator provided with or connected to a current regulator.

[0035] Unless otherwise specified, when reference is made to two elements connected together, this means directly connected without intermediate elements other than conductors, and when reference is made to two connected elements (in English "coupled") between them, this means that these two elements can be connected or be linked via one or more other elements.

[0036] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "rear", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc. ., unless otherwise specified, reference is made to the orientation of the figures.

[0037] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably within 5%.

[0038] Unless specified otherwise, the angle values are given counterclockwise. For example, an angle value of 45°, 90° or 120° must be understood as being respectively +45°, +90° or +120° in the trigonometric direction.

An example of magnetic field generator 100 is shown in Figure 1A. It comprises a magnetic circuit comprising a substantially square frame 102 whose axis (central axis) extends in a vertical direction Z, and vertical bars 104 extending downwards from each corner of the frame. Each vertical bar is extended towards the central axis by a radial arm 106 ending in a pole end 108 (planar pole). Each vertical bar is surrounded by two coils 110, 112 (represented in transparency in FIG. 1A in order to be able to visualize the vertical bars). Two other coils 118A, 118B are arranged around a horizontal rod 114 on either side of a connecting block 116 located in the middle of the rod 114. The horizontal rod 114 is attached to two opposite sides of the frame 102. The connecting block 116 is extended by a vertical arm 120 having a pole end 122 (central pole) in the shape of a cone. The central pole can be surrounded by a coil 124.

[0040] The coils are connected to supply circuits, not shown.

There is shown in Figure 1B more precisely all the coils around the vertical bars: a first upper coil 110A and a first lower coil 112A around a first vertical bar 104A, a second upper coil 110B and a second lower coil 112B around a second vertical bar 104B, a third upper coil 110C and a third lower coil 112C around a third vertical bar 104C, a fourth upper coil 110D and a fourth lower coil 112D around a fourth vertical bar 104D.

The coils 118A, 118B arranged around the horizontal rod 114 can be supplied within the same power supply network (field supply in Z) so as to produce respective magnetic induction fluxes which, either away from the Z axis, resulting in an upward magnetic flux in the vertical arm 120, or are directed towards the Z axis, resulting in a downward directed flux in the vertical arm 120 In both cases, this aims to get the most magnetic flux in the Z direction. When the aim is to obtain the most magnetic induction flux in the X direction, it is possible to act on the power supplies of the upper coils 110A, 110B, 110C, 110D within the same power supply network (power supply field in X). For example, the coils 110C, 110D can be supplied in phase opposition relative to the coils 110A, 110B. According to an example, one can feed the coils 110A, 110B to produce a magnetic flux directed upwards and the coils 110C, 110D to produce a magnetic flux directed downwards, the two fluxes being able to combine in the direction X.

When the aim is to obtain the most magnetic induction flux in the Y direction, it is possible to act on the power supplies of the lower coils 112A, 112B, 112C, 112D within the same power supply network (power supply Y field). For example, the coils 112A, 112D can be supplied in phase opposition relative to the coils 112B, 112C. For example, coils 112A, 112D can be energized to produce magnetic flux directed downwards and coils 112B, 112C can be powered to produce magnetic flux directed upwards, the two fluxes possibly combining in the Y direction.

[0045] A drawback of this technique is that the power of all the coils cannot be allocated in a single direction, and therefore the magnetic field which could be generated by all the coils cannot be maximized. If we take the problem in reverse, this technique requires having a lot of coils to generate a high magnetic field in several directions at the same time.

Another technique, aimed at increasing the magnetic flux in one direction, consists in using a system of relays connected to the coils to reallocate one or more coils of a power supply network to another direction. For example, one can reallocate all or part of the coils 110A, 110B, 110C, 110D to a direction other than the X direction or all or part of the coils 112A, 112B, 112C, 112D to a direction other than the Y direction.

A disadvantage of this other technique is on the one hand that obtaining a high magnetic flux in one direction is done to the detriment of other directions, and that it therefore does not make it possible to maximize the magnetic flux in several directions. In addition, the change from one configuration to another, by activating the relays concerned, can be a long operation, which can last a few hundred milliseconds, for example between approximately 500 and approximately 1000 milliseconds, and can induce wear on the system. field generation, in particular relays.

[0048] In certain applications of the present description, the generated magnetic field is for example applied for the test of integrated circuit wafers, where test tips are brought into electrical contact with a component of the wafer, generally via pads of electric contact. The electrical measurements carried out on the test tips, for example variations in electrical resistance between the test tips, as a function of the intensity and/or of the direction of the applied magnetic field make it possible to characterize the component of the wafer.

For these applications, in particular when the application to the component of a high amplitude magnetic field in several directions is sought, it may be necessary to carry out several tests by changing the configuration at each test, for example a first high magnetic field test pattern in a first direction, then a second high magnetic field test pattern in a second direction. The multiplication of tests can also result in premature wear of the test tips and/or the test studs. electrical contact of the wafer by repeated contact with the tips.

[0050] The inventors propose a system making it possible to meet the needs for improving magnetic field generation techniques, making it possible to generate a magnetic field of high amplitude simultaneously in several directions, without this requiring excessively long operations, without it is necessary to multiply the coils and/or to use relays, and without risking premature wear of the system.

[0051] Embodiments of systems will be described below. The embodiments described are non-limiting and various variants will appear to those skilled in the art from the indications of this description.

Figures 2A and 2B are respectively perspective and cross-sectional views of a magnetic field generation system 200 according to one embodiment.

The magnetic field generation system 200 represented comprises a magnetic circuit comprising a frame 210 of substantially square section with rounded corners. Other frame shapes are possible. The axis of the frame (central axis) extends in the vertical direction Z (orthogonal direction) and each side of the frame extends either in a first horizontal direction X or in a second horizontal direction Y perpendicular to the direction X. Vertical cylindrical bars 212A, 212B, 212C, 212D extend downward from each corner of the frame, each bar extending towards the central axis by a radial arm 214A, 214B, 214C, 214D extending substantially in a horizontal plane, even slightly inclined with respect to a horizontal plane, and ending in a pole end 216A, 216B, 216C, 216D (planar pole). Planar poles have lower faces located in the same substantially horizontal XY plane.

[0054] The radial arms 214A, 214B, 214C, 214D and the planar poles 216A, 216B, 216C, 216D are oriented in the horizontal plane at approximately 45° with respect to the X direction and the Y direction, as can be seen see in Figure 2B. Therefore, two adjacent planar poles are oriented by an angle α equal to approximately 90° with respect to each other.

Furthermore, a vertical arm 218 (central arm) having an elongated parallelepiped shape with a pole end 220 (central pole) in the shape of a truncated inverted pyramid extends vertically from the middle of the frame 210 downwards. The central pole ends in a substantially horizontal face (truncation of the truncated inverted pyramid).

The magnetic circuit (frame, bars, arms, poles) is made of a soft ferromagnetic material, for example soft iron.

Each vertical bar is surrounded by a coil 230A, 230B, 230C, 230D. The coils can be identical.

The coils can be sized according to the magnetic field values that it is desired to generate.

Preferably, the coils have outer diameters greater than 30 mm, for example between 70 and 95 mm. Each coil can be formed by winding a conductive wire, for example copper, the number of turns of conductive wire depending in particular on the diameter of the wire. Each coil can comprise several hundred turns of conducting wire, for example between 100 and 5000 turns. For example, the coils have diameters of about 90 mm, and are made with copper wires of diameter 3.5 and a number of turns of about 900. Each coil is connected to its own power supply circuit, not shown. Each power supply circuit makes it possible to circulate a current of determined direction and intensity as a function of a desired magnetic field H and of the orientation in the plane of the planar pole associated with said coil.

According to one embodiment, an equivalent current leq is defined, for example in the form of a vector for the desired magnetic field B, for example also in the form of a vector and the current to be circulated in each coil is determined according to the equivalent current defined to help orient the magnetic field, projected in a plane parallel to that of the planar poles, according to the desired direction (s) . For example, the current to be circulated in each coil is determined from the equivalent current defined so as to maximize the magnetic field in one or more directions. The equivalent current leq can be determined using an optimization or search algorithm, and /or an iterative algorithm. Preferably, the algorithm is adapted to determine an equivalent current leq for a desired magnetic field in the three directions.

For example, the algorithm is suitable for determining a dynamic equivalent current vector, that is to say as a function of time, as a function of a dynamic magnetic field vector

According to one example, the algorithm is adapted to compensate for the delay between the circulation of the different currents in the different coils and the magnetic field generated by these different currents, for example the algorithm comprises one or more iterations. An example of an iterative algorithm is as follows: determination of a first equivalent current vector leq1 (t) as a function of the desired magnetic field vector B(t), for example by using a usual optimization or search algorithm for a person skilled in the art;

- determination of the currents to be circulated in each of the coils as a function of the first equivalent current vector leq1 (t), for example using the equations described later;

- measurement of the magnetic field vector B1(t) obtained by circulating the determined currents in the coils;

- comparison of the magnetic field vector B1(t) obtained with the desired magnetic field B(t); then, if the measured magnetic field vector B1(t) is different from the desired magnetic field B(t), or is outside a range defined around the desired magnetic field B(t), determination of a second (new) equivalent current vector Ieq2 (t) as a function of the difference between the measured magnetic field vector B1(t) and the desired magnetic field vector B (t).

The steps of determining the currents to be circulated, of measuring the magnetic field vector obtained, and of determining a new equivalent current vector are then repeated.

This succession of steps can be repeated until the measured magnetic field vector is equal to the desired magnetic field B(t) or included in the range defined around the desired magnetic field B(t).

It should be noted that the equivalent current leq is to be considered as an intermediate parameter entity, and not as a current to be circulated as such in a circuit. According to one example, the current to be circulated in each of the four coils can be determined using the four equations described below.

A current of intensity I ₁ is circulated in a first coil 230A associated with a first planar pole 216A, with:

/ ₁ = leq _X + Ieq _Y + Ieq _Z ; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current leq respectively along the first horizontal direction X, the second horizontal direction Y and the vertical direction Z.

The first planar pole 216A is oriented towards the Z axis of the central pole in the positive senses of the X and Y directions, which explains the "+" signs in front of the X and Y components of the intensity I. Moreover, as each planar pole is oriented at approximately 45° with respect to these directions in the plane, the fact of positively adding all the components of the equivalent current vector leq makes it possible to maximize the magnetic flux generated by this first coil in each of the X and Y directions, but also in the Z direction as explained later.

According to the same principle, and simultaneously, circulating in a second coil 230B associated with a second planar pole 216B oriented at approximately 90° in the plane with respect to the first planar pole 216A, a current of intensity I ₂ , with :

/ ₂ = —leq _X + Ieq _Y + Ieq _Z

The sign in front of the X component of the intensity I is explained by the fact that the second planar pole 216B is oriented towards the Z axis of the central pole in the negative direction of the X direction, whereas it is oriented in the positive direction of the Y direction, hence the "+" sign in front of the Y component of the intensity I. According to the same principle, and simultaneously, a current of intensity I ₃ is circulated in a third coil 230C associated with a third planar pole 216C oriented at approximately 90° in the plane with respect to the second planar pole, with: I ₃ = — leq _X — leq _Y + Ieq _Z

The signs in front of the X and Y components of the intensity I are explained by the fact that the third planar pole 216C is oriented towards the Z axis of the central pole in the negative directions of the X and Y directions.

According to the same principle, and simultaneously, a current of intensity I ₄ is circulated in a fourth coil 230D associated with a fourth planar pole 216D oriented at approximately 90° in the plane with respect to the third planar pole, with: I ₄ = leq _X — leq _Y + Ieq _Z

The sign in front of the Y component of the intensity I is explained by the fact that the fourth planar pole 216D is oriented towards the Z axis of the central pole in the negative direction of the Y direction, whereas it is oriented in the positive direction of the X direction, hence the "+" sign in front of the X component of the equivalent current leq.

The magnetic flux generated by each coil is directed towards the central pole 220. It rises in the Z direction upwards (positive direction of the Z direction) via the vertical arm 218, which makes it possible to have a maximized component of the magnetic field also in this direction, without it being necessary to arrange a coil around the central pole. In other words, the magnetic flux along the Z direction comes from the field lines attracted in the central arm 218, the material of which has greater permeability than air. Keeping the same sign ("+ " sign in the given example) for the term I _Z in the equations of each of the coils aims to promote this transfer of flux, which makes it possible to maximize the magnetic flux generated along the direction Z. Alternatively, one could put the same sign for the term I _Z in the equations of each of the coils.

This example makes it possible to maximize the current generated by each of the four coils, simultaneously in each of the directions X, Y, Z. The equations giving the intensities of the coils, and in particular the signs in front of the components of the equivalent current, are chosen from so that each coil contributes to the same intensity, for example to prevent certain components of said intensity canceling out between them, and that on the contrary they combine. Thus, all the power of the four coils can be allocated at the same time in the three directions, without having to increase the number of coils and without the need to switch from one configuration to another, for example without it whether it is necessary to use relays.

A processing unit 240 can be connected to the supply circuit of each coil, and in some cases to a magnetic field sensor (not shown), and be suitable for determining the components of the equivalent current vector leq as a function of the desired magnetic field H using an optimization and/or iterative algorithm such as that described further on, and determining the intensities to be circulated in each coil, for example according to the equations described above.

Figures 3A and 3B are respectively perspective and cross-sectional views of a magnetic field generation system 300 according to another embodiment, which differs from the embodiment of Figures 2A and 2B mainly in that that there are three planar poles 316A, 316B, 316C and three coils 320A, 320B, 320C, a coil associated with a planar pole, instead of four planar poles and four coils.

Similarly to the system of Figures 2A and 2B, the planar poles 316A, 316B, 316C are ends of radial arms 314A, 314B, 314C extending substantially in a horizontal plane, or even slightly inclined relative to a plane horizontal, the radial arms being assembled with vertical cylindrical bars 312A, 312B, 312C. The planar poles have lower faces located in the same XY plane, said plane being substantially horizontal.

A first radial arm 314A and a first planar pole 316A are oriented in a first direction X of the plane. A second radial arm 314B and a second planar pole 316B are oriented at an angle θ in the plane relative to the first planar pole. A third radial arm 314C and a third planar pole 316C are oriented at the same angle θ in the plane relative to the second planar pole. The angle θ is equal to approximately 120°.

In addition, a vertical arm 318 (in the Z direction), or central arm, having the shape of an elongated parallelepiped with a pole end 320 (central pole) in the shape of a truncated inverted pyramid extends downwards. The central pole ends in a substantially horizontal face (truncated inverted pyramid truncation).

The vertical bars and the vertical arm can be assembled to a frame, not shown, but which can be similar to the frame of Figures 2A and 2B, or have another shape, for example triangular, hexagonal, circular, or any other suitable form.

The planar poles are arranged symmetrically on the XY plane with respect to the axis of the central pole. The magnetic circuit (frame, bars, arms, poles) is made of a soft ferromagnetic material, for example soft iron.

Each vertical bar is surrounded by a coil 330A, 330B, 330C. The coils can be identical. The coil sizing examples given in relation to FIGS. 2A and 2B can be applied.

Similar to the system of Figures 2A and 2B, each coil is connected to its own power supply circuit, not shown. Each circuit makes it possible to circulate a current of determined direction and intensity as a function of a desired magnetic field H and of the orientation in the plane of the planar pole associated with said coil.

According to an embodiment similar to that described in relation to FIGS. 2A and 2B, an equivalent current leq is defined, for example in the form of a vector /, for the desired magnetic field, and the current to be made flow in each coil is determined based on the equivalent current set to help orient the magnetic field, projected in a plane parallel to that of the planar poles, the desired direction(s). For example, the current to be circulated in each coil is determined so as to maximize the magnetic field in one or more directions.

According to one example, the current to be circulated in each of the three coils can be determined using the three equations described below. The principle is similar to the example described in relation to FIGS. 2A and 2B, but the equations are adapted to three coils instead of four.

Is circulated in a first coil 330A associated with the first planar pole 316A a current of intensity I ₁ , with: where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current Ieq respectively according to the first direction X, the second direction Y perpendicular to the first direction in the plane and the orthogonal direction Z. The first pole planar 316A is oriented towards the Z axis of the central pole in the positive direction of the X direction, hence the "+" sign in front of the X component of the intensity I. On the other hand, the first planar pole is perpendicular to the Y direction, which explains why the Y component of the intensity I does not appear in the equation. According to the same principle, and simultaneously, a current of intensity I ₂ is circulated in a second coil 330B associated with the second planar pole 316B, with: The "-" sign in front of the X component of the intensity I is explained by the fact that the second planar pole 316B is oriented towards the Z axis of the central pole in the negative direction of the X direction, then that it is oriented in the positive direction of the Y direction, hence the "+" sign in front of the Y component of the intensity I. The coefficients and are calculated as a function of the orientation of the second planar pole with respect to the X and Y directions. According to the same principle, and simultaneously, a current of intensity I ₃ is circulated in a third coil 330C associated with the third planar pole 316C, with: The signs in front of the X and Y components of the intensity I are explained by the fact that the third planar pole 316C is oriented towards the Z axis of the central pole in the negative directions of the X and Y directions.

[0098] The coefficients and are calculated as a function of the orientation of the third planar pole with respect to the X and Y directions.

The magnetic flux generated by each coil is directed towards the central pole. It rises in the Z direction upwards (positive direction of the Z direction), which allows to have a maximized component of the magnetic field also in this direction, without the need to have a coil around the central pole .

[0100] A processing unit (not shown) can be connected to the supply circuit of each coil, and in some cases to a magnetic field sensor (not shown), and be adapted to determine the components of the equivalent current vector as a function of the magnetic field H desired by an optimization and/or iterative algorithm such as that described further on, and in determining the intensities to be circulated in each coil, for example according to the equations described above.

This example makes it possible to maximize the current generated by each of the three coils, simultaneously in each of the directions X, Y, Z. Indeed, the equations giving the intensities of the coils, and in particular the signs and coefficients in front of the components of the equivalent, are chosen so that each coil contributes to the same intensity, for example to prevent certain components of said intensity from canceling each other out, and on the contrary from combining. Thus, all the power of the three coils can be allocated at the same time in the three directions, without having to increase the number of coils and without the need to switch from one configuration to another, for example without the need to use relays.

The two embodiments described implement three or four planar poles. We see that with at least three planar poles, it is possible to adjust the three components X, Y, Z of the magnetic field. In addition, the embodiments make it possible to adjust them precisely.

Two examples and equations have been given with three and four coils, but other examples and equations are possible, for example depending on the number of coils, the orientations of the planar poles associated with the coils with respect to the reference frame chosen to define the components of the equivalent current, of the desired magnetic field, and/or of the directions in which one wishes to maximize the magnetic field.

In general, the embodiments make it possible, by determining currents of intensity and of direction specific to each coil, to maximize the components of the magnetic field in several directions at the same time. The intensities and directions of the currents to circulate in each coil can be determined so as to maximize the magnetic field in directions other than the directions X, Y, Z of the chosen frame of reference.

According to other embodiments, there may be more planar poles, or even two planar poles. In the case of two planar poles, it is possible to adjust two components of the magnetic field, a vertical component (Z) and a horizontal component (X or Y).

[0106] Although coils arranged around elements of the magnetic circuit have been described in a particular configuration in the two embodiments, other configurations are possible. Alternatively, the coils can be replaced with coils located around the sides of the frame.

[0107] In addition, no coil has been shown around the central arm in the two embodiments above. Indeed, in general, the embodiments can be implemented without it being necessary to associate a coil with the central pole to generate the component of the magnetic field in Z, the latter being obtained by the magnetic fluxes generated in the X, Y directions of the plane and then ascending (or descending) in the Z direction, in particular in the central pole. It is however possible to add at least one coil around the central arm if one wishes to maximize the magnetic flux in the Z direction, as shown in figure 4.

FIG. 4 is a simplified cross-section of a magnetic field generation system 400 according to another embodiment, which differs from the embodiment of FIGS. 2A and 2B mainly in that the central arm 412E has a cylindrical shape and is surrounded by a fifth coil 430E.

Similar to the system of Figures 2A and 2B, each coil is connected to a power supply circuit which is specific to it, not shown. Each circuit makes it possible to circulate a current of determined direction and intensity as a function of a desired magnetic field H and of the orientation in the plane of the planar pole associated with said coil.

According to an embodiment similar to that described in relation to FIGS. 2A and 2B, an equivalent current leq defined, for example in the form of a vector leq, for the desired magnetic field, and the current to be circulated in each coil is determined based on the equivalent current set to contribute a magnetic field wish. For example, the current to be circulated in each coil is determined so as to maximize the magnetic field in one or more directions.

According to one example, the current to be circulated in each of the five coils can be determined using the five equations described below. The principle is similar to the example described in relation to FIGS. 2A and 2B, but the equations are adapted to the presence of a central coil, in addition to the four coils.

Similar to FIGS. 2A and 2B, the following are circulated simultaneously:

- in a first coil 430A associated with a first planar pole 416A a current of intensity I ₁ , with:

- in a second coil 430B associated with a second planar pole 416B oriented at approximately 90° in the plane with respect to the first planar pole 416A, a current of intensity I2, with:

I ₂ = — leq _X + Ieq _Y + Ieq _Z ;

- in a third coil 430C associated with a third planar pole 416C oriented at approximately 90° in the plane with respect to the second planar pole, a current of intensity I ₃ , with:

I ₃ = —leq _X — Ieq _Y + leq _Z ;

- in a fourth coil 430D associated with a fourth planar pole 416D oriented at approximately 90° in the plane with respect to the third planar pole, a current of intensity I ₄ , with: I ₄ = leq _X — leq _Y + leq _Z

In addition, a current of intensity is circulated in the fifth coil 430E: I ₅ =Ieq _Z

Various embodiments and variants have been described. Those skilled in the art will appreciate that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, a vertical bar can have a shape other than cylindrical and/or can be surrounded by more than one coil. In addition, a vertical arm may have a shape other than parallelepiped with one end in the shape of a truncated pyramid, for example a cylindrical shape with one end in the shape of a truncated cone.

Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art based on the functional indications given above.

Claims

1. System (200; 300; 400) for generating a magnetic field comprising a magnetic circuit comprising: - a central pole (220; 320; 412E) disposed above a plane (XY), the axis of said pole central extending in an orthogonal direction (Z) substantially corresponding to the direction orthogonal to the plane; - at least two planar poles (216A, 216B, 216C, 216D; 316A, 316B, 316C) arranged symmetrically on the plane with respect to the axis of the central pole, each planar pole being carried by a portion of the magnetic circuit; and - at least two coils (230A, 230B, 230C, 230D; 330A, 330B, 330C), including at least one coil associated with each planar pole, each coil associated with a planar pole surrounding the magnetic circuit portion carrying said planar pole ; two coils associated with two different planar poles being adapted to be connected to two separate power supply circuits; each supply circuit being adapted to circulate in at least one coil to which it is connected a current of intensity and direction determined according to a desired magnetic field and the orientation in the plane of the planar pole associated with said coil.

2. System (200; 300; 400) according to claim 1, further comprising a processing unit (240) adapted to determine the current to be circulated in each coil.

3. System (200; 300; 400) according to claim 2, in which the processing unit (240) is adapted to determine an equivalent current (Ieq), for example represented in the form of an equivalent current vector, for the desired magnetic field, and to determine the current to be circulated in each coil as a function of the current determined equivalent and of the orientation in the plane of the planar pole associated with said coil.

4. System (300) according to any one of claims 1 to 3, comprising three coils (330A, 330B, 330C) and three planar poles (316A, 316B, 316C) arranged symmetrically on the plane with respect to the axis of the central pole (320) and being oriented at a first angle (θ) of approximately 120° with respect to each other.

5. System (300) according to claim 4 in its dependence on claim 3, in which the currents to be circulated in the three coils (330A, 330B, 330C) are respectively: for a first coil (330A) associated with a first planar pole (316A) oriented towards the axis of the central pole (320) in the positive direction of a first direction (X) of the plane; for a second coil (330B) associated with a second planar pole (316B) oriented at the first angle (θ) in the plane with respect to the first planar pole; And for a third coil (330C) associated with a third planar pole (316C) oriented at the first angle (θ) in the plane with respect to the second planar pole; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current Ieq respectively according to the first direction (X), the second direction (Y) perpendicular to the first direction in the plane, and the orthogonal direction (Z) .

6. System (200; 400) according to any one of claims 1 to 5, comprising four coils (230A, 230B, 230C, 230D) and four planar poles (216A, 216B, 216C, 216D) symmetrical with respect to two orthogonal planes containing the axis of the central pole (220), two adjacent planar poles being oriented by a second angle (α) d 90° to each other.

7. System (200) according to claim 6 in its dependence on claim 3, in which the currents to be circulated in the four coils (230A, 230B, 230C, 230D) are respectively: for a first coil (230A) associated with a first planar pole (216A) oriented towards the axis of the central pole (220) at approximately 45° between first (X) and second (Y) orthogonal directions in the plane, in the positive directions of said first and second directions; for a second coil (230B) associated with a second planar pole (216B) oriented at the second angle (α) in the plane with respect to the first planar pole; for a third coil (230C) associated with a third planar pole (216C) oriented at the second angle (α) in the plane with respect to the second planar pole; And for a fourth coil (230D) associated with a fourth planar pole (216D) oriented at the second angle (α) in the plane with respect to the third planar pole; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current Ieq respectively according to the first direction (X), the second direction (Y) and the orthogonal direction (Z).

8. A system (600) according to any one of claims 1 to 7 when dependent on claim 3, wherein which the central pole (412E) is surrounded by a fifth coil adapted (430E) to be connected to a supply circuit distinct from the coils associated with the planar poles and adapted to cause a current of intensity and directions determined according to the desired magnetic field and the orientation of the central pole, for example a current: where Ieq _Z is the component of the vector representing the equivalent current Ieq along the orthogonal direction (Z).

9. System (200; 300; 400) according to any one of claims 1 to 8, in which each pole corresponds to a first end of an arm (214A, 214B, 214C, 214D, 218; 314A, 314B, 314C , 318), the arms being connected to a frame (210).

10. System (200; 300; 400) according to claim 9, in which each arm (214A, 214B, 214C, 214D; 314A, 314B, 314C) associated with a planar pole (216A, 216B, 216C, 216D; 316A, 316B, 316C) extends substantially in a direction parallel to the plane, a second end of said arm being assembled to a bar (212A, 212B, 212C, 212D; 312A, 312B, 312C) passing inside the at least one coil associated with said planar pole, each bar extending substantially in the orthogonal direction (Z).

11. System according to claim 9 or 10, in which the arm associated with the central pole is assembled to a horizontal rod connected to two opposite sides of the frame.

12. System according to any one of claims 1 to 11, in which the coils have external diameters greater than 70 mm, or even greater than 80 mm, for example greater than or equal to 90 mm.

13. Magnetic field generation method implementing a system (200; 300; 400) comprising a magnetic circuit comprising: - a central pole (220; 320; 412E) disposed above a plane (XY), the the axis of said central pole extending in an orthogonal direction (Z) substantially corresponding to the direction orthogonal to the plane; - at least two planar poles (216A, 216B, 216C, 216D; 316A, 316B, 316C) arranged symmetrically on the plane with respect to the axis of the central pole, each planar pole being carried by a portion of the magnetic circuit; and - at least two coils (230A, 230B, 230C, 230D; 330A, 330B, 330C), including at least one coil associated with each planar pole, each coil associated with a planar pole surrounding the magnetic circuit portion carrying said planar pole ; two coils associated with two different planar poles being connected to two separate power supply circuits; the method comprising: - circulating in at least one coil connected to each power supply circuit, a current of intensity and direction determined according to a desired magnetic field and the orientation in the plane of the planar pole associated with said coil.

14. Method according to claim 13 comprising: - determining an equivalent current, for example in the form of an equivalent current vector, as a function of the desired magnetic field; and - determining the current to be circulated in each coil as a function of the determined equivalent current and of the orientation in the plane of the planar pole associated with said coil.

15. Method according to claim 14, further comprising: - measuring the magnetic field obtained when the determined current flows in each coil; - compare the measured magnetic field with the desired magnetic field; and, if the difference is greater than a defined threshold, - determining a second equivalent current according to the difference between the measured magnetic field and the desired magnetic field; - determining the current to circulate in each coil according to the second determined equivalent current and the orientation in the plane of the planar pole associated with said coil; and - repeating at least the steps of measuring the magnetic field and of comparison, and, for example, also repeating the steps of determining the second equivalent current and the current to be circulated.

16. Method according to claim 14 or 15, in which the system comprises three coils (330A, 330B, 330C) and three planar poles (316A, 316B, 316C) arranged symmetrically on the plane with respect to the axis of the central pole ( 320) and being oriented at a first angle (θ) of approximately 120° relative to each other; the method comprising: - circulating in a first coil (330A) associated with a first planar pole (316A) oriented towards the axis of the central pole (Z) in the positive direction of a first direction (X) of the plane a current of intensity: - circulating in a second coil (330B) associated with a second planar pole (316B) oriented at the first angle (θ) in the plane with respect to the first planar pole a intensity current: ; And - circulating in a third coil (330C) associated with a third planar pole (316C) oriented at the first angle (θ) in the plane with respect to the second planar pole a current of intensity:; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current Ieq respectively according to the first direction (X), the second direction (Y) perpendicular to the first direction in the plane (XY) and the orthogonal direction ( Z).

17. Method according to claim 16, comprising four coils (230A, 230B, 230C, 230D) and four planar poles (216A, 216B, 216C, 216D) symmetrical with respect to two orthogonal planes containing the axis of the central pole (220) , two adjacent planar poles being oriented substantially at a second angle (α) of approximately 90° relative to each other; the method comprising: - circulating in a first coil (230A) associated with a first planar pole (216A) oriented towards the axis of the central pole (220) at approximately 45° between first (X) and second (Y) directions orthogonal in the plane, in the positive directions of said first and second directions, a current of intensity:; - circulating in a second coil (230B) associated with a second planar pole (216B) oriented at the second angle (α) in the plane with respect to the first planar pole a current of intensity:; - circulating in a third coil (230C) associated with a third planar pole (216C) oriented at the second angle (α) in the plane with respect to the second planar pole a current of intensity:; - circulating in a fourth coil (230D) associated with a fourth planar pole (216D) oriented at the second angle (α) in the plane with respect to the third planar pole a current of intensity:; where Ieq _X , Ieq _Y , Ieq _Z are the components of the vector representing the equivalent current Ieq respectively according to the first direction (X), the second direction (Y) and the orthogonal direction (Z).

18. System (300) according to any one of claims 1 to 12 in combination with claim 3, or method according to any one of claims 13 to 17 in combination with claim 14, in which the determined equivalent current vector and the desired magnetic field are dynamic.