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Title:
DEVICES AND METHODS FOR INFLUENCING MAGNETIC FIELDS
Document Type and Number:
WIPO Patent Application WO/2021/028620
Kind Code:
A1
Abstract:
There is provided a device for creating and controlling magnetic fields in miniature atomic devices, the device comprising one or several coil assemblies (210, 220) each comprising coils, wherein each coil or combination of coils within or across coil assemblies (210, 220) create separate field profiles.

Inventors:
ZETTER RASMUS (FI)
IIVANAINEN JOONAS (FI)
PARKKONEN LAURI (FI)
LIUS ELIAS (FI)
Application Number:
FI2020/050526
Publication Date:
February 18, 2021
Filing Date:
August 12, 2020
Export Citation:
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Assignee:
AALTO UNIV FOUNDATION SR (FI)
International Classes:
H01F5/00; G01C19/60; G01R33/00; G01R33/025; G01R33/26; G04F5/14; G05F7/00; H01F7/06; H01F7/20
Foreign References:
US20090079531A12009-03-26
CN104730476A2015-06-24
US8853613B12014-10-07
Other References:
HOLMES, N. ET AL.: "A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography", NEUROLMAGE, vol. 181, 19 July 2018 (2018-07-19), pages 760 - 774, XP085472136, ISSN: 1053-8119, DOI: 10.1016/ j.neuroimage. 2018.07.02 8
Attorney, Agent or Firm:
LAINE IP OY (FI)
Download PDF:
Claims:
CLAIMS

1. A device for creating and controlling magnetic fields in miniature atomic devices, the device comprising one or several coil assemblies each comprising coils, wherein each coil or combination of coils within or across coil assemblies create separate field profiles.

2. The device of claim 1, wherein the one or several coil assemblies comprise coils for all three orthogonal axes.

3. The device of claim 1 or 2, wherein the coil assemblies are manufactured on printed circuit boards.

4. The device of claim 3, wherein the printed circuit boards are multi-layer printed circuit boards with several coils.

5. The device of claim 3 or 4, wherein the printed circuit board is flexible.

6. The device of claim 4 or 5, wherein the several coils are arranged as pairs of coils contributing to different field profiles.

7. The device of any preceding claim, wherein at least one of the coil assemblies comprises a hole for optical path and/or for attachment purposes.

8. The device of any preceding claim, arranged to create a well-defined and well-controlled field profile in one or several target regions and minimal field in regions other than the one or several target regions.

9. The device of any preceding claim, wherein geometry of coil windings and field profile are designed using stream-function design methods.

10. The device of any preceding claim, wherein the one or several coil assemblies are curved coil assemblies.

11. The device of any preceding claim, wherein the one or several coil assemblies are planar coil assemblies.

12. The device of any preceding claim, wherein the device comprises two or more coil assemblies.

13. An optically-pumped magnetometer, or an atomic spin gyroscope, or an atomic clock comprising the device of any preceding claim for creating and controlling magnetic fields.

Description:
DEVICES AND METHODS FOR INFLUENCING MAGNETIC FIELDS

FIELD OF THE INVENTION

The invention is related to devices and methods for influencing magnetic fields.

BACKGROUND OF THE INVENTION

Optical atomic devices are a broad category of sensors and instruments that utilize light-atom interactions to measure some physical quantity. Examples of these devices include atomic clocks, optically-pumped magnetometers and atomic spin gyroscopes.

Atomic clocks are utilized in demanding time-keeping applications such as telecommunications and global navigation satellite systems.

Optically-pumped magnetometers (OPMs) are at this point utilized mainly in geophysics and prospecting as well as in certain military applications (e.g. submarine detection). Due to recent advances, new applications requiring very high sensitivity are opening up. These applications include biomagnetic measurements for clinical and research purposes (the authors' research field).

Atomic spin gyroscopes can be utilized in demanding control and inertial navigation systems, e.g. in self-driving cars, missiles, or spacecrafts.

The aforementioned atomic devices have existed for decades but have only recently been miniaturized into "chip-scale" size, enabling new applications. The surrounding magnetic field affects the operation of all these devices and thus it is essential to control it for them to function properly.

Atomic clocks measure the passage of time but are also sensitive to changes in magnetic field. They thus need to be magnetically shielded. Field coils can be used for active shielding in addition to the metallic passive shields that are typically used.

Spin-exchange relaxation free (SERF) OPMs require a very low background magnetic field for high sensitivity. In addition, the background field must be kept as stable as possible to avoid changing or drifting calibration. Finally, some OPM variants require a high-frequency magnetic field modulation created using a set of coils.

Atomic spin gyroscopes fall in between clocks and magnetometers: they require precise control of the magnetic field, but they do not generally require a low field: these gyroscopes typically employ an integrated "co-magnetometer", whose output is used to drive field coils in a negative feedback loop.

Some applications (e.g. measurement of biomagnetic signals with OPMs in MEG or MCG) require dense arrays of sensors. The required sensor-wise coils will produce a stray magnetic field in the neighborhood of each sensor/device, resulting in crosstalk that diminishes the performance of the array if the sensors are placed too densely or if the sensors move in relation to each other. In different applications, other sensitive instruments may be placed close to the atomic device, leading to the same issue.

In miniature atomic devices, such as OPMs, magnetic field control is typically achieved using relatively simple coil designs and manufacturing processes requiring manual labor. For example, the coils may be manufactured on flexible kapton foil, which is then hand-wrapped around a holder geometry. Alternatively, thin copper wire may be hand-wound into simple patterns on similar holders. These coils typically have non-optimal field homogeneity, low manufacturing precision and high stray field (leading to the above crosstalk issues).

Thus, there is a need for a solution i) that provides a precise field profile (e.g. good homogeneity) within the target volume and a low stray field, ii) that can be easily mass-produced, and iii) is applicable to miniature atomic devices.

SUMMARY OF THE INVENTION

In different embodiments, the invention can provide optimized, manufacturable devices and methods for influencing magnetic fields. In preferred embodiments, the invention may comprise magnetic field coils for miniature atomic devices.

Embodiments of the invention may comprise a set of coils producing an accurately controlled magnetic field in one or several directions, such as along the orthogonal X-, Y- and Z-axes of the 3D cartesian coordinate system. The coils can advantageously be manufactured as assemblies such as single- or multi-layer Printed Circuit Boards (PCBs) placed in the vicinity of one or several target regions within which they create the desired field profile. Each assembly may include several components, each producing its own controlled field profile. The use of such assemblies reduces the component count and minimizes alignment issues during manufacturing. The field created by the coils in other than the target volume can be minimized, thus reducing crosstalk and interference in adjacent sensors or other sensitive components.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an exemplary embodiment of the invention.

Figure 2 shows an exemplary embodiment of the invention comprising two planar coil assemblies with six coils each. The coil assemblies can produce independent homogeneous field in X- Y- and Z- directions within a target region.

Figure 3 shows an example of how the device may be manufactured as a multi-layer PCB, with pairs of coils contributing to the different field profiles.

Figure 4 shows an exemplary embodiment of the device with curved coil assemblies.

Figure 5 shows an exemplary embodiment of the device, including multiple target regions and two planar coil assemblies.

Figure 6 shows an example of how the invention may be used as a part of a closed-loop OPM.

Figure 7 shows, by way of an example, a geometry, coil fields and coils implemented on a pair of printed circuit boards (PCBs).

DETAILED DESCRIPTION OF EMBODIMENTS

As shown in Figs. 1 & 2, an embodiment of the device may comprise e.g. two coil assemblies 110, 120 placed on either side or otherwise around a target region 130. Each coil assembly in this embodiment consists of e.g. multi-layer PCBs in which each layer or groups of layers comprise a separate coil as shown in Fig. 3. In this exemplary embodiment, a pair 310, 320, 330 of coils in either coil assembly 210, 220 produces an orthogonal homogeneous field along the X- Y- and Z- directions 240, 242, 244 in the target region 230 while producing a minimal field elsewhere, as shown in Fig. 2. The assemblies may include coils for all three orthogonal axes. Each coil assembly has electrical connectors through which a sensor/coil control system or other current source can feed current into the coils. Coils which produce separate field profiles may have separate electrical connectors.

In another embodiment of the invention, curved coil assemblies 410, 420 may be used as shown in an exemplary embodiment in Fig. 4. In this embodiment, multi-layer or stacked flex PCBs are laminated or otherwise fastened to a pre-formed geometry. Alternatively, lithography may be used to directly manufacture the coils onto a curved surface.

In a third embodiment of the invention, microelectromechanical systems (MEMS) processes are used to manufacture the coil assemblies onto a substrate made of e.g. glass or silicon. In this embodiment, multi-layer structures may be used e.g. with thin insulator layers between conductor layers.

Due to the use of coil assemblies, only a small number of components need to be aligned with respect to each other and other device components during manufacturing. As the coils produce minimal stray field outside the target region(s), other sensitive devices can be placed in close proximity to a device using the invention without adverse effects. For an embodiment of the invention with multiple target regions 531, 532, 533, 534, see Fig. 5.

To optimize the field profile of the coils, a stream-function design method may be used. The coil optimization criteria, given the geometry of the coil surfaces, may be e.g. minimum-energy or minimum-power while creating the desired field profile in the target region(s). To adjust the field strength per input current unit, the number of discrete conductor windings can be adjusted without affecting the field profile significantly.

The geometry of the coil assemblies can be adjusted to fit the specific application. For example, in a magnetometer, the coil assemblies and target region(s) can be placed so that the standoff distance between the sensitive volume and any measured object is minimized. The invention can be used for any type of magnetic field control, including but not limited to, e.g. nulling of the ambient field, magnetic modulation, and negative feedback applications (see Fig. 6).

An embodiment of the invention is a device for the creation and control of magnetic fields in miniature atomic devices, made using easily mass-manufacturable materials and processes, such as fiberglass or flex PCBs. The device comprises a number of coil assemblies, each of which may contain several coils. Each or combination of coils (within or across coil assemblies) may create separate field profiles.

The coil assemblies are placed in the vicinity of one or several target regions, in which the device creates a well-defined and -controlled field profile. The geometry of the coil windings within the assemblies may be determined using stream-function design methods, e.g. with minimum-energy or minimum-power optimization criteria. Outside of the target region(s) the device creates minimal field, thus avoiding crosstalk issues. The magnetic field produced by the device per each input current unit can be adjusted without affecting the magnetic field profile.

Further embodiments of the invention include the following as a numbered list.

The different embodiments and aspects of the invention can be combined.

1. A device for the creation and control of magneticfields

2. A device of any other embodiment where the device comprises one or several coil assemblies each comprising one or several coils

3. A device of any other embodiment where each coil or combination of coils (within or across coil assemblies) may create separate field profiles.

4. A device of any other embodiment made using easily mass-manufacturablematerials and processes, such as fiberglass or flex PCBs. 5. A device of any other embodiment arranged to influence the magnetic field in miniature atomic devices.

6. A device of any other embodiment configured to provide a desired field within the target area, such as a homogenous field or any other field as required by the application

7. A device of any other embodiment where coil assemblies have been arranged to minimize the number of separate components required for magnetic field control and to reduce alignment issues during manufacturing

8. A device of any other embodiment where each coil assembly includes electrical contacts

9. A device of any other embodiment where current from a control system is fed into the coils through the contacts

10. A device of any other embodiment where the contacts may comprise soldered-on components or metal-coated parts of on the edge of the coil assembly

11. A device of any other embodiment where the device creates a well-defined and -controlled field profile in one or several target regions

12. A device of any other embodiment where the coil assemblies are placed in vicinity of one or several target regions

13. A device of any other embodiment where the device creates minimal field ("stray field") in regions other than the target region(s)

14. A device of any other embodiment where the device minimizes crosstalk issues

15. A device of any other embodiment where the field-per-current may be adjusted by altering the number of windings in the coils without affecting the field profile

16. A device of any other embodiment where the device is configured to control the magnetic field in miniature atomic devices, for example optically-pumped magnetometers

17. A device of any other embodiment where coil windings and field profile may be designed using e.g. stream-function design methods

Figure 7 shows, by ways of examples, a geometry 700, coil fields 710, 712, 714 in the X-, Y-, and Z- directions, respectively, and coils implemented on a printed circuit board 720, e.g. a glass-fiber substrate. Top 730 and bottom 735 coils may be manufactured as two assemblies, or may be printed on a single sheet. If implemented as a single flex PCB, it may have copper traces on both front and back sides. If printed on a single sheet, the top 730 and bottom 735 coils may be separated from the sheet, while leaving a flexible ribbon connection to carry current between the coils. The assembly or assemblies, either a single sheet or a multi-layer PCB, may comprise one or more holes 740, 741,

742, 743, 744. The holes may be for attachment purposes, and/or for providing an optical path. The optical path may be needed e.g. in applications where a light beam is to be directed to a target region. The holes may be of different sizes. The radius of the hole may be set suitable for the application. The hole 742 is an example of a larger hole, holes 740, 741, 743, 744 are examples of smaller holes. Corresponding holes may be seen in the geometry 700. The holes have also been taken into account in the coil design, which is based on stream-function design method. For example, the holes 743 and 703 are corresponding holes; the holes 744 and 704 are corresponding holes, and the holes 741 and 701 are corresponding holes. It may be seen in the coil design (see reference number 752) how, for example, the big hole 702 has been taken into account.

Referring back to Fig. 3, the coil system 300 is manufactured as a multi-layer PCB. In Fig. 3, the multilayer PCT comprises 6 layers. The coil pairs may be stacked on printed circuit board for easy sensor assembly. As shown in Fig. 3, the inner-outer coil spacing 340 is larger than typical distance between PCB layers. Spacing 340 may be adjusted. The spacing 340 affects the shielding. The spacing 340 may be e.g. approximately 0.75-1.25 mm, e.g. 1 mm. The entire coil stack may have a thickness of 1.75- 2.25 mm, e.g. 2 mm. Each coil pair 310, 320, 330 creates field in one orthogonal direction (X, Y, Z). For each field axis, an inner coil pair produces most of the field within the target volume, while an outer coil pair connected in series with the inner pair limits the stray field. Biplanar coil system, e.g. the coil system 300, provides good self-shielding enabling minimizing the stray field and crosstalk.

Alternatively, the coil system 300 may comprise e.g. two multi-layer PCBs, both multi-layer PCBs comprising 3 layers. Two PCBs may be used in situations, where the structure of one multi-layer PCB is too thick. However, number of components may be reduced using one multi-layer PCB, and possible difficulties relating to accurate positioning of the PCBs on top of each other may be avoided.