WO2021226652A1 - Électroaimant - Google Patents

Électroaimant Download PDF

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Publication number
WO2021226652A1
WO2021226652A1 PCT/AU2020/050484 AU2020050484W WO2021226652A1 WO 2021226652 A1 WO2021226652 A1 WO 2021226652A1 AU 2020050484 W AU2020050484 W AU 2020050484W WO 2021226652 A1 WO2021226652 A1 WO 2021226652A1
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WO
WIPO (PCT)
Prior art keywords
electromagnetic
core
target space
elements
magnetic field
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PCT/AU2020/050484
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English (en)
Inventor
Colin James DEDMAN
Michael Samuel James BARSON
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Australian National University
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Application filed by Australian National University filed Critical Australian National University
Priority to PCT/AU2020/050484 priority Critical patent/WO2021226652A1/fr
Publication of WO2021226652A1 publication Critical patent/WO2021226652A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3808—Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/08—Electromagnets; Actuators including electromagnets with armatures
    • H01F7/121—Guiding or setting position of armatures, e.g. retaining armatures in their end position
    • H01F7/122—Guiding or setting position of armatures, e.g. retaining armatures in their end position by permanent magnets
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/28—Coils; Windings; Conductive connections
    • H01F27/30—Fastening or clamping coils, windings, or parts thereof together; Fastening or mounting coils or windings on core, casing, or other support
    • H01F27/306—Fastening or mounting coils or windings on core, casing or other support
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
    • H01F27/38—Auxiliary core members; Auxiliary coils or windings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/08—Electromagnets; Actuators including electromagnets with armatures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/08—Electromagnets; Actuators including electromagnets with armatures
    • H01F7/126—Supporting or mounting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/20—Electromagnets; Actuators including electromagnets without armatures
    • H01F7/202—Electromagnets for high magnetic field strength
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets

Definitions

  • Embodiments relate to an electromagnet and in particular, an electromagnetic apparatus which may be able to provide magnetic field components in three independent orthogonal directions (X, Y and Z directions).
  • Electromagnets which are able to provide magnetic field components in three independent orthogonal directions have applications in a number of fields such as quantum microscopy and nuclear magnetic resonance applications.
  • a permanent magnet that can be moved and rotated to any orientation can in principle provide the required arbitrary magnetic field vector.
  • mechanical complexity and physical constraints mean that practical permanent magnet systems are able to provide only a limited range of field strengths and directions.
  • the field homogeneity is usually poor, and the field strength varies significantly with temperature. Being a mechanical system, the field strength and direction can only be changed very slowly.
  • Helmholtz Coils are a well know coil structure, where pairs of air-cored coils in each axis provide magnetic field components in X, Y and Z directions.
  • the coils are relatively simple and cheap to build, and do not impede access to the region of interest provided the coils are made sufficiently large. Homogeneity of the field at the geometric centre of the coils is good. However, the attainable field strength is relatively low, limited by heating of the coils.
  • Iron-cored Quadrupole electromagnets are also known in similar applications.
  • a pair of coils is used for each axis, and the axis of each coil is in the direction of the field produced.
  • the coils are wired so that opposite poles oppose, but can equally well be connected in phase so as to produce a field in X or Y, as required for this application. While this geometry is efficient for producing fields in the X-Y plane, it does not provide a field in the Z-axis as required.
  • an attempt to provide similar coils and iron pole pieces in the Z-axis may limit the applicability of this equipment where direct access to a sample by other components such as optical microscopes or atomic force microscopes is required.
  • An embodiment provides an electromagnetic apparatus for applying a magnetic field at a target space, the apparatus comprising at least four electromagnetic elements distributed about the target space, each electromagnetic element having a corresponding coil wound about a core, wherein all of the cores have substantially the same orientation, and wherein all of the cores are attached to a common magnetic member, wherein a magnetic field produced by the electromagnetic apparatus at the target space is variable in strength and direction by controlling the four electromagnetic elements, and wherein the cores comprise respective extensions which delineate the target space.
  • the cores may be formed as an extension or extrusion of the common magnetic member.
  • the extensions of the cores may be provided as separate physical extensions or as extensions (e.g. extrusions) of the cores.
  • Each core may have an axis and all of the cores may be orientated so that their respective axes are substantially parallel.
  • the axis of a core may be an axis of symmetry.
  • the axis of a core may be an axis extending along a length of the core.
  • the electromagnetic apparatus may further comprise a fifth electromagnetic element.
  • the fifth electromagnetic element may comprise a core, wherein the core of the fifth electromagnetic element is attached to the common magnetic member.
  • the fifth electromagnetic element may comprise a core and a coil.
  • the core of the fifth electromagnetic element may have substantially the same orientation of the cores of the four electromagnetic elements.
  • the core of the fifth electromagnetic element may be attached to the common magnetic member, or may be an extension thereof. The considerations stipulated above with respect to the orientations of the cores of the four electromagnetic elements may apply equally to the orientation of the core of the fifth electromagnetic element.
  • the cores are ‘attached’ to the common magnetic member, but it is to be realised that an embodiment where the cores are formed from the common magnetic member are also possible and the term ‘attached’ is intended to cover such embodiments.
  • magnetic flux should be able to travel freely from the cores to the common magnetic member.
  • the five electromagnetic elements the cores include core portions supporting respective coils, may be arranged about the target space so that the core portions of the four electromagnetic elements are arranged substantially in a plane and the core portion of the fifth electromagnetic element is arranged spaced from the target space in a direction orthogonal to said plane.
  • the extensions of the cores of the four electromagnetic elements may have upper surfaces which define a horizontal plane so that the target space is located in said horizontal plane and said fifth electromagnetic core is spaced from the target space in a direction below said four electromagnetic elements.
  • the considerations regarding the orientations of the cores apply to the portion of the cores associated with the respective coils.
  • the core portions of the four electromagnetic elements may be arranged in a horizontal plane and the coil and core of the fifth electromagnetic element may be arranged below said target space.
  • the four electromagnetic elements may be arranged in two sets of pairs with the extensions of the cores of electromagnetic elements of the same set being arranged opposed to one another across the target space. ln embodiments, the location relative spacings of the core portions may be arbitrary, provided that the extensions of the cores are arranged opposed to one another across the target space. In an embodiment, the core portions of the four electromagnetic elements are arranged on a single straight line which may pass through the centre of the coil of the fifth electromagnetic element.
  • a distance between each of the coils of the four electromagnetic elements and the target space may be substantially equal.
  • the four coils may be spaced equally within the horizontal plane at angular intervals of 90°.
  • each coil may be located at a different distance from the target space, and with different angular separation between each core.
  • angular intervals need not be precisely 90° and that embodiments are possible with any angular interval.
  • the core of the fifth magnetic element may be hollow.
  • a hollow core may allow further apparatus to be located within the hollow core.
  • the hollow core is dimensioned to be able to receive at least one objective lens.
  • the core of the fifth magnetic element may be solid.
  • the extensions of one or more of the cores of the four electromagnetic elements may comprise a magnetic finger extending out in a direction towards the target space.
  • Each extension may comprise a finger.
  • a finger may extend out from, or be attached to, a portion of the corresponding core associated with a coil.
  • the portion of the core associated with the coil may be the portion of the coil around which the coil is wound.
  • All of the fingers may have the same size and shape.
  • at least one finger is cuboid with a rectangular cross-section.
  • at least one finger is shaped with a vertically stepped or sloping vertical cross-section. The vertical height of the top face of the finger may become lower at greater radial distance from the target space. This may, for example, provide mechanical clearance for components that resides above the apparatus.
  • Each core of the four electromagnetic elements may be a cylinder, each cylinder having an axis of symmetry, wherein each finger extends out from the corresponding core at a direction orthogonal to a corresponding axis of symmetry.
  • one or more of the cores may have a cross section which is square, round-edged square or octagonal.
  • the core cross sectional area is sufficiently large to prevent magnetic saturation
  • At least one finger may have a portion with a width substantially greater than a height.
  • the portion may be a terminal portion of each finger.
  • the portion may be a portion of the finger adjacent the target space. Fingers of opposed elements are arranged so that terminal portions oppose one another across the target space.
  • the width, height, and cross-sectional area may not be constant along a length of the finger.
  • the target space may lie substantially at or adjacent a top surface of terminal portions of the fingers.
  • the target space may lie substantially at or below a bottom surface of terminal portions of the fingers. There may be a space between the fingers and the tops of the coils to provide access to the target space from a side.
  • the fifth electromagnetic element may be spaced from the target space by an access distance.
  • the access distance may be between 5 and 20 mm. In an embodiment, the access distance is between 7 and 15 mm. In an embodiment, the access distance is about 10 mm. The access distance may be measured along the axis of symmetry of the coil of the fifth electromagnetic element.
  • the common magnetic member may be a base plate.
  • the base plate may be planar.
  • the base plate may be square, rectangular, circular or cross-shaped.
  • the base plate has a dome formed in a central zone.
  • the fifth electromagnetic element may be located on the dome.
  • the fingers may be angled to follow the dome.
  • a further embodiment provides an electromagnetic apparatus for applying a magnetic field at a target space, the apparatus comprising at least four electromagnetic elements distributed about the target space, each electromagnetic element having a corresponding coil wound about a core, each electromagnetic element adapted to produce a magnetic flux, the electromagnetic elements being orientated so that the magnetic flux from each electromagnetic element measured within the respective core has the same direction, wherein all of the cores are attached to a common magnetic member, a magnetic field produced by the electromagnetic apparatus at the target space is variable in strength and direction by controlling the four electromagnetic elements, and wherein the cores comprise respective extensions which delineate the target space.
  • a further embodiment provides a method of generating a magnetic field at a target space, the method comprising providing an electromagnetic apparatus comprising at least four electromagnetic elements distributed about the target space, each electromagnetic element having a corresponding coil wound about a core portion, wherein all of the core portions have substantially the same orientation; wherein all of the cores are attached to a common magnetic member; and wherein the cores comprise respective extensions which delineate the target space, the method further comprising: controlling the four electromagnetic elements to vary both a strength and direction of the magnetic field at the target space.
  • the method may further comprise arranging the four electromagnetic elements in two sets of two electromagnetic elements with the extensions of the cores of the electromagnetic elements of the same set being arranged opposed to one another across the target space.
  • the method may further comprise: controlling the first set of electromagnetic elements to vary the magnetic field in a first direction; controlling the second set of electromagnetic elements to vary the magnetic field in a second direction wherein the second direction is different from the first direction; and controlling both the first and second sets of electromagnetic elements to vary the magnetic field in a third direction, wherein the third direction is different from both the first and second directions.
  • the magnetic field may be varied in the first, second and third directions using only the first and second sets of electromagnetic elements.
  • the step of controlling the first set of electromagnetic elements to vary the magnetic field in a first direction may comprise driving the electromagnetic elements of the first set out-of-phase with each other; and the step of controlling the second set of electromagnetic elements to vary the magnetic field in a second direction may comprise driving the electromagnetic elements of the second set out-of-phase with each other; and the step of controlling both the first and second sets of electromagnetic elements to vary the magnetic field in a third direction may comprise driving the electromagnetic elements of the first and the second set in-phase with each other.
  • driving a set of electromagnetic elements out-of- phase to vary the magnetic field in a first, second or third direction comprises producing magnetic fields with each electromagnetic element of the set so that the fields reinforce each other in the target space in the corresponding direction.
  • Driving a set of electromagnetic elements in-phase to vary the magnetic field in a direction may comprise producing magnetic fields with each electromagnetic element of the set so that the fields reduce each other in the target space in the corresponding direction.
  • Driving an electromagnetic element with a polarity may refer to the magnetic polarity of the terminal portion of the corresponding core extension of that electromagnetic element when current is applied to the corresponding coil.
  • the first, second and third directions may be orthogonal to one another.
  • the electromagnetic apparatus may further comprise a fifth electromagnetic element.
  • the method may further comprise controlling the fifth electromagnetic element to vary the magnetic field in the third direction.
  • the electromagnetic apparatus may further comprise a fifth electromagnetic element, in which case the method may further comprise: controlling the first set of electromagnetic elements to vary the magnetic field in a first direction; controlling the second set of electromagnetic elements to vary the magnetic field in a second direction wherein the second direction is different from the first direction; and controlling the fifth electromagnetic element to vary the magnetic field in a third direction, wherein the third direction is different from both the first and second directions.
  • the first, second and third directions may be orthogonal to one another.
  • Controlling the first set of electromagnetic elements to vary the magnetic field in the first direction and controlling the second set of electromagnetic elements to vary the magnetic field in the second direction may comprise setting terminal portions of core extensions of all of the electromagnetic elements of both the first and the second set with the same polarity thereby setting a zero magnetic field, but non-zero magnetic field gradient, within the target space.
  • the method may further comprise altering a position of the zero magnetic field in the third direction by controlling the fifth electromagnetic element.
  • Figure 1 is a schematic illustration of a perspective view of an electromagnetic apparatus according to an embodiment
  • Figure 2 is a side view of the electromagnetic apparatus of Figure 1 ;
  • Figure 3 is a plan view of the electromagnetic apparatus of Figure 1 ;
  • Figure 4 is a schematic illustration of a perspective view of an electromagnetic apparatus according to an embodiment
  • Figure 5 is a side view of a portion of the electromagnetic apparatus of Figure
  • Figure 6 is a schematic illustration of a perspective view of an electromagnetic apparatus according to an embodiment
  • Figure 7 is a cross-sectional view of the electromagnetic apparatus of Figure
  • Figure 8 is a circuit diagram showing a circuit suitable for driving the electromagnetic elements of embodiments. Detailed Description of Specific Embodiment
  • FIG 1 is a schematic illustration of a perspective view of an electromagnetic apparatus 10 according to an embodiment.
  • Figure 2 is a side view of the electromagnetic apparatus 10 of Figure 1 and
  • Figure 3 is a plan view of the electromagnetic apparatus 10 of Figure 1.
  • the electromagnetic apparatus 10 comprises a target area 12 where a sample 14 is housed.
  • the apparatus 10 delivers a magnetic field to the sample 14 situated at the target area 12 in the manner described below.
  • the apparatus 10 comprises four electromagnetic elements 16, 18, 20 and 22. Each of these four electromagnetic elements comprises a coil 16A, 18A, 20A and 22A.
  • the coils are schematically represented as cylinders. In this embodiment the coils are cylindrical coils wrapped around a corresponding core portion16B, 18B, 20B and 22B (as illustrated in Figure 2).
  • each of the core portions 18B, 20B and 22B are mechanically and magnetically connected to base plate 24 by connectors 18F-1 , 20F-1 and22 F-1.
  • Core portion 16B is provided with a corresponding connector to the base plate 24, but this is not shown in Figure 2. . It is to be realised that the connectors are optional.
  • the core portions supporting the coils may be directly attached to the base plate and the fingers.
  • each electromagnetic element has a corresponding finger 16C 18C, 20C and 22C.
  • Each finger is attached to the corresponding core portion with a corresponding connector so, for example, finger 16A is attached to corresponding core 16C (not shown in the Figures).
  • Core portions 18B, 20B and 22B are mechanically and magnetically connected to corresponding fingers 18C, 20C and 22C by connectors 18F-2, 20F-2 and 22F-2.
  • each electromagnetic element comprises the core portion around which the corresponding coil is wrapped as well as the finger.
  • the finger and the core portion are comprised of a magnetic material, the finger is functionally an extension of the core, even where (as is the case in the illustrated embodiments) the finger is provided as a distinct element to the element forming the core portion.
  • the entire core comprises the core portions supporting the winding, the fingers as well as the parts joining the core portions to the base plate and the fingers.
  • core portions are illustrated with dashed lines to illustrate the relationship between the cores, core portions and coil.
  • Each finger has a terminal portion 16C-1 , 18C-1 , 20C-1 and 22C-1 (see Figure 3) being the portion of the finger adjacent the target space 12.
  • the fingers have a constant cross-section and therefore the terminal portions are not physically distinguished from the remainder of the finger.
  • the terminal portions may have a different cross-section to the reminder of the finger.
  • the terminal portions of the fingers are the portions which interact most directly with the magnetic field at the target space 12. Therefore, the shape and position of the terminal portions may have a significant effect on the magnetic field at the target space 12.
  • the base plate 24, core portions 16B, 18B, 20B and 22B (including the connectors connecting the core portions to the base plate and the fingers) and fingers 16C 18C, 20C and 22C are provided as separate elements, all comprised of soft iron. In a further embodiment these elements may be formed from an integrated single block of soft iron.
  • soft iron is a preferred material for the core portions, connectors, base plate and fingers in certain embodiments, it is to be realised that these elements may be constructed of any suitable magnetic material. In certain embodiments it is preferable that the material have a high permeability, and be magnetically “soft” with low magnetic remanence.
  • 18B, 20B and 22B are cylindrical and have a corresponding central axis of symmetry 16D, 18D, 20D, and 22D.
  • the base plate 24 is planar and the core portions 16B, 18B, 20B and 22B are attached to the base plate 24 so that their corresponding axes of symmetry 16D, 18D, 20D, and 22D are orthogonal to the base plates 24.
  • the core portions 16B, 18B, 20B and 22B are orientated so that their corresponding axes of symmetry 16D, 18D, 20D, and 22D are parallel to one another.
  • embodiments may deviate from a similar orientation by an amount of up to 35° before the apparatus becomes ineffective. In an embodiment, a deviation of 5° or less may be desirable. In further embodiments, deviations of less than 10°, 15°, 20°, 25° or 30° may be desirable, depending on design parameters.
  • the fingers 16C, 18C, 20C and 22C are orientated so that they lie orthogonal to the axes of symmetry of the core portions. Flowever, in further embodiments it may be necessary to deviate from the orthogonal relationship between the fingers, core portions and the base plate, e.g., to accommodate other apparatus such as microscope objective lenses.
  • terminal portion 16C-1 lies opposite terminal portion 20C-1 and terminal portion 18C-1 lies opposite terminal portion 22C-1.
  • elements 16 and 20 form a first set and elements 18 and 22 form a second set.
  • electromagnetic elements of the same set are used to vary the magnetic field generated at the target space in a specific spatial dimension. Therefore, for example, electromagnetic elements 16 and 20 are used to vary the magnetic field in a direction denoted by dashed line 30 (here designated the Y-axis or Y direction).
  • Electromagnetic elements 18 and 22 are used to vary the magnetic field in the direction denoted by dashed line 32 (here designated the X-axis or X direction). As explained in greater detail below, these electromagnetic elements may be used for other changes to the field too.
  • electromagnetic elements 18 and 22 are arranged so that an imaginary line drawn through the middle of these two electromagnetic elements (dashed line 32 in Figure 3) lies orthogonal to an imaginary line drawn between the centres of the other set of electronic elements 16 and 20 (dashed line 30).
  • the angle Q ( Figure 3) between line 30 and line 32 is 90° in the embodiment illustrated. Flowever, it is to be realised that this angle may be chosen to suit design constraints and that any angular interval between the core portions and corresponding coils is possible. In a further embodiment all four X-Y cores and coils are on the same line, passing through a central axis of the fifth, central core.
  • a fifth electromagnetic element 34 comprising a coil 34A and core34B is situated directly below the target space 12 with the core 34B directly connected to the base plate 24.
  • the core 34B of the fifth electromagnetic element comprises a core portion around which the coil 34A is wound and a connector connecting this core portion to the base plate 24 as well as a further portion standing proud of the top of the coil 34, the entire core is here referred to and designated as 34B).
  • the fifth element 34 is used to control the magnetic field at the target space 12 in the direction orthogonal to the X-axis and Y-axis (i.e. in the Z- axis or Z direction).
  • the core 34B is comprised of soft iron too, but any other magnetic material having sufficiently high permeability and low remanence for the particular application could be used instead.
  • Embodiment illustrated in Figures 1 , 2 and 3 is intended for magnetic field strengths in the region of the target area 12 of the order of 100 Gauss with low heating and temperature rise of the coils and assembly, though higher fields are attainable with a higher temperature rise. It has been found at these modest field strengths, the core 34B of the electromagnetic element 34 may be provided as a hollow member having a void 40 formed in the centre, as shown in Figures 1 and 2.
  • the core 34B is located directly below the sample 14 in the target space 12, there may be advantages to providing a hollow core.
  • apparatus such as a microscope objective may be housed in the core with direct access to the sample.
  • the terminal portions 16C-1 , 18C-1 , 20C-1 and 22C-1 may reduce the field strength in the Z-direction at the target space 12., by shielding the magnetic flux originating from the Z-axis core. Therefore, in this embodiment, the terminal portions are formed with their width substantially greater than their height.
  • the terminal portions of the fingers illustrated have a rectangular cross-section, it is to be realised that other cross-section complying with the height/width stipulation are possible e.g. oval.
  • the end face of the terminal portions need not be planar, but can be curved or profiled to tailor the exact shape and strength of desired field.
  • the fingers 16C, 18C, 20C and 22C have a constant cross-section so that the terminal portions of each finger are indistinguishable from the remainder of the finger, but it is to be realised that terminal portions may be formed differently to the portions of the fingers extending back towards their connection with the respective core portions. In certain embodiments, the terminal portions of the portions of the fingers lie adjacent the target space 12.
  • the fingers have an upper surface (upper surfaces 22E and 18E are designated in Figure 2).
  • upper surfaces 22E and 18E are designated in Figure 2.
  • the sample 14 lies in the horizontal plane defined by these upper surfaces. Although it is not necessary for the sample to lie directly in such a horizontal plane, it has been found that certain advantages such as mechanical clearance and access to the sample may accrue to situating the sample, and therefore the corresponding target space where the magnetic field is concentrated, adjacent to this horizontal plane.
  • the apparatus may weigh less than 1.5 kg.
  • the apparatus is supported by a nano-positioner stage and, in this case, a greater weight may not be within the nano-positioner ratings.
  • the apparatus 10 may be provided with a fifth electromagnetic element having a solid core instead of the hollow core as illustrated.
  • An arrangement with a solid core may help to make the generation of flux in the vertical direction more efficient, and may also allow the fingers to be optimized further towards generating flux in the X and Y directions.
  • higher field strengths may be obtained in all axes compared to the apparatus having a hollow core. Flowever, such an arrangement will lose the access below the target space provided by the hollow core 34B.
  • Such an arrangement, with a solid core may be suited for integration into microscopes where access to only one side of the sample is sufficient or for optical microscopes where placing the objective inside the Z-pole piece isn’t suitable, for example, those with a rotating objective lens turret.
  • FIGS. 4 and 5 depict an electromagnetic apparatus 100 according to a second embodiment. Like reference numbers are used to denote like parts.
  • the apparatus 100 also comprises four electromagnetic elements 116, 118, 120 and 122 with each electromagnetic element including a corresponding core 116A, 118A,
  • the core portions 116B, 118B, 120B and 122B are attached to the base plate 24 by connectors 116F-1 , 118F-1 , 120F-1 and 122F-1.
  • the core portions 116B, 118B, 120B and 122B are attached to the fingers by connectors 116F-2, 118F-2, 120F-2 and 122F-2 which extend significantly above the tops of the coils 116A, 118A, 120A and 122A, as shown in Figure 5.
  • the electromagnetic elements 116 and 120 have been omitted from Figure 5).
  • the fingers 116C, 118C, 120C and 122C are attached to the tops of the connectors 116F-2, 118F-2, 120F-2 and 122F-2 and extend out, orthogonal to a central axis of symmetry of the cores, towards a target space 14. Terminal portions of pairs of fingers oppose one another.
  • the fingers 118C and 122C are formed with respective terminal portions 118C-1 and 122C-1 which oppose one another across the target space 12.
  • the fingers 116C and 120C are formed with terminal portions which oppose one another across the target space 14.
  • the terminal portions of the fingers have the same profile as the terminal portions of the fingers of the electromagnetic apparatus 10 illustrated in Figures 1 , 2 and 3.
  • the embodiment of Figures 4 and 5 may be operated to produce magnetic fields in the order of 1 ,000 G and for these operating parameters, fingers with terminal portions different from those illustrated are possible.
  • the terminal portions of the fingers may be thicker relative to their width, compared to the lower-field embodiment shown in Figures 1 to 3.
  • the terminal portions of the fingers may be curved or profiled to accommodate an objective lens mounted above the magnetic structure, where it may be necessary for the bottom of the lens to be in close vertical proximity to the sample at the target space.
  • the apparatus 100 is also provided with a fifth electromagnetic element 134 having a coil 134A and core 134B.
  • the fifth electromagnetic element 134 is similar to the fifth electromagnetic element 34 of the embodiment of Figures 1 , 2 and 3, but the core 134B is solid.
  • the cores of the five electromagnetic elements of the apparatus 100 have the same orientation and the apparatus 100 is operated in the same manner as the apparatus 10, and as described in further detail below.
  • the fingers may be provided spaced from the tops of the coils of the four X-Y electromagnetic elements, and the core of the Z electromagnetic element.
  • the tops of the X-Y coils, and the top of the fifth core are now a distance FI below the bottom face of the terminal portions of the fingers. In an embodiment, this distance FI is 10 mm.
  • FI may be between 5 and 20 mm. In further embodiments, FI may be between 7 and 15 mm.
  • FI is measured from the bottom of the terminal portions of the fingers to the top of the core of the fifth element.
  • inventions 4 and 5 has a number of applications and may, for example, find application in nanoscale NMR (Nuclear Magnetic Resonance) or ESR (electron spin resonance).
  • FIGS 6 and 7 illustrated a further embodiment of an electromagnetic apparatus 200.
  • the apparatus 200 comprises electromagnetic elements 216, 218, 220 and 222 having core portions 216B, 218B, 220B and 222B around which respective coils 216A, 218A, 220A and 222B are would.
  • Connectors 216F-1 , 218F- 1 , 220F-1 and 222F-1 connect the core portions to a base plate 224.
  • Connectors 216F-2, 218F-2, 220F-2 and 222F-2 connect the core portions to fingers 216C,
  • FIG. 6 and 7 differs from that of Figures 4 and 5 in that the base plate 224 is formed with a raised dome section in the middle and the fifth electromagnetic element 234 is located on the raised dome section.
  • the fingers 216C, 218C, 220C and 222C have a sloped portion which generally follows the slope of the raised dome section 250, allowing the terminal portions of the fingers to define a target space in proximity to the top of the core 234B of the fifth electromagnetic element 234.
  • Figures 6 and 7 may be used for systems that have limited free space on the same horizontal plane as the sample. For example where electronics or sample mounts may be needed near the sample..
  • the target space this is the area where the variable magnetic field of interest is situated and the area where the sample is most conveniently located. It is to be realised that since the field produced by the apparatus is variable, there is some freedom of where the sample is to be placed.
  • the space delimited by the terminal portions of the fingers may be considered the target space.
  • the point of interest where the variable magnetic field is focused may be significantly smaller than the target space and may, by driving the X, Y and Z electromagnetic elements appropriately, be locatable within the target space.
  • weight is less than 6 kg, so the apparatus may be supported on a typical optical bench. Furthermore, in an embodiment, the apparatus fits within a cube of 230 x 230 x 140 mm. The weight and size may vary significantly, depending on a number of factors.
  • a feature that all of the illustrated embodiments have in common is that an entire hemisphere above the apparatus is kept free. This may have advantages since this may provide direct access from a multitude of directions to the sample located in the target space.
  • an atomic force microscope may be located within this free hemisphere.
  • the space above the sample and/or target space may be occupied by an oil immersion microscope objective lens.
  • the cores are equally spaced from the target space, but this is not essential.
  • the cores have different radial distances from the target space and/or different angular spacings.
  • the fingers will have different lengths.
  • Figure 8 is a circuit diagram illustrating a circuit for a current driver of one of the coils. It is to be realised that variations to the circuit may be made to allow for different field strengths and other operating parameters and arrangements.
  • the coils of the four electromagnetic elements (16, 18, 20 and 22 in the illustrated embodiments) are driven out-of-phase to generate variations in the magnetic field at the target space in the X and Y directions.
  • the terminal portions of opposing fingers are driven with opposite polarities so that the respective magnetic fields reinforce one another in the respective X or Y direction.
  • the X direction is taken along dashed line 32 and the Y direction is taken along line 30.
  • the Z direction is then the direction orthogonal to the paper of Figure 3 (the vertical direction in Figure 2).
  • the electromagnetic elements are arranged in pairs so that, with reference to the embodiment of Figures 1 , 2 and 3, the magnetic field is controlled in the X direction by electromagnetic elements 18 and 22, the terminal portions of their fingers being driven to opposite magnetic polarity, for example one terminal portion being North and the other South.
  • the magnetic field is controlled in the Y direction by electromagnetic elements 16 and 20, the terminal portions of their fingers similarly being driven to opposite magnetic polarity, for example one terminal portion being North and the other South.
  • the pair of coils in the X-direction may be wired in series or parallel, so that only a single current driver power supply is required to drive both coils, and likewise in the Y-direction. Therefore, a total of three current drivers may be required, one for each axis.
  • the field is controlled in the Z direction by the fifth electromagnetic element 34 or 134.
  • the return path for the magnetic flux for the field in the Z-direction is provided by the four electromagnetic elements,, and the common member to which the four electromagnetic elements are attached, which may be the planar base plate.
  • the fifth electromagnetic element is not actively driven.
  • the magnetic field is controlled by the four electromagnetic elements spaced about the horizontal plane of the target space.
  • the field in the Z-direction is varied by driving the four electromagnetic elements in- phase (i.e. the terminal portions of opposing fingers are driven with the same polarity so that the respective magnetic fields cancel one another in the respective X or Y direction, but drive magnetic flux in the Z-direction). Then by adjusting the magnitude of the in-phase and out-of-phase currents, with the aid of a suitable computer algorithm, it is possible to independently vary the X, Y and Z components of the field at the target space. This mode of operation may require a separate current driver power supply for each of the four coils.
  • the fifth electromagnetic element need not be provided with a coil and may, for example, comprise an extension of the base plate in proximity to the target space in the vertical direction.
  • a core connected to the base plate may be provided without a corresponding coil, to drive magnetic flux in the vertical direction.
  • providing a coil and current driver for the vertical direction may provide more efficient generation of the field in the Z-direction. .
  • a third mode of operation five current drivers and five coils are provided, but the field in the Z-direction may be boosted over what would be possible with the Z-coil alone, by simultaneously operating the four electromagnetic elements in phase.
  • a suitable computer algorithm may be used to determine the appropriate current to each of the five coils, so as to produce the desired field component in X, Y and Z. . Therefore, this mode is effectively a combination of the first and second modes.
  • a fourth mode of operation five current drivers are provided, but the terminal portions of the four electromagnetic elements are driven at the same polarity. This will produce a magnetic field with zero strength (a zero magnetic field) between the terminal portions of the fingers. The height of this zero magnetic field (position in the Z-direction) can then be varied by driving the fifth electromagnetic element.
  • the X-Y elements By operating the four electromagnetic elements (the X-Y elements) in phase, and simultaneously operating the fifth electromagnetic element (the Z-element) so that it's upper pole tip has the same magnetic polarity as the terminal portions of the fingers, for example all North or all South and adjusting magnitude of the Z-element drive relative to the drive applied to the X- and Y-elements, it will be possible to shift the point of zero magnetic field vertically relative to the horizontal faces of the terminal portions of the fingers.
  • Embodiments therefore may provide for a homogeneous, fully orientable vector magnetic field which can be varied in three dimensions in both direction and magnitude, using less power and thus potentially producing less temperature rise than currently available technologies. It should also be mentioned that the materials required to build embodiments may be relatively cheap. Alternate systems may require larger power supplies and cooling systems or even cryogenic superconducting systems. Additionally, for many systems designed for nano-NMR or other applications, embodiments are compatible and could be retrofitted with no or minor alterations.

Abstract

L'invention concerne un appareil électromagnétique destiné à appliquer un champ magnétique au niveau d'un espace cible, l'appareil comprenant au moins quatre éléments électromagnétiques répartis autour de l'espace cible, chaque élément électromagnétique ayant une bobine correspondante enroulée autour d'un noyau, toutes les bobines ayant sensiblement la même orientation, tous les noyaux étant fixés à un élément magnétique commun, un champ magnétique produit par l'appareil électromagnétique au niveau de l'espace cible étant de puissance et de direction variables en commandant les quatre éléments électromagnétiques, et les noyaux comprenant des extensions respectives qui délimitent l'espace cible. Dans un mode de réalisation, les quatre éléments électromagnétiques commandent le champ magnétique dans les directions X et Y, et un cinquième élément électromagnétique est prévu pour commander le champ magnétique dans la direction Z.
PCT/AU2020/050484 2020-05-15 2020-05-15 Électroaimant WO2021226652A1 (fr)

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WO2023104733A1 (fr) * 2021-12-07 2023-06-15 Hprobe Système de génération de champ magnétique

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