Device for generating a variable magnetic field

• US 6,535,092 B1
• Filed: 06/20/2002
• Issued: 03/18/2003
• Est. Priority Date: 09/21/1999
• Status: Expired due to Fees

• Current Assignee: Magnetic Solutions Limited (Tokyo Electron Limited)
• Original Assignee: Magnetic Solutions Limited (Tokyo Electron Limited)
• Inventors: Hurley, David Patrick, Coey, John Michael David
• Primary Examiner(s): Barrera, Ramon M.
• Application Number:
  US10/088,570
• Time in Patent Office: 271 Days
• Field of Search: 335/216, 335/296-306, 324/318, 324/319, 324/320, 117/917
• US Class Current: 335/306
• CPC Class Codes: C30B 15/305 Stirring of the melt
• CPC Class Codes: H01F 7/0278 for generating uniform fields, focusing, deflecting electrically charged particles for magnetic separation by Lorentz force B03C1/023; specially adapted for NMR applications G01R33/383
• CPC Class Codes: Y10S 117/917 Magnetic

Abstract

A device (1) for generating a variable composite magnetic field comprises top and bottom concentric ring members (3, 4) which define a main central axis (5) and a central area (4) within which the composite magnetic filed is formed. Rod-like permanent magnets are located thin respective annuli (15) of the respective ring members (2, 3), and are equi-spaced circumferentially along a pitched circle (21). The permanent magnets (18) are rotable about corresponding secondary axes (19) which extend parallel to each other and parallel to the main central axis (5). The permanent magnets (18) are magnetised with their respective direction of magnetisation extending transversely of their secondary axes (19) and are independently rotatable by corresponding stepper motors (22) in respective of annuli (16) of the ring members (2, 3) for orienting the permanent magnets (18) about their respective secondary axes (19) for in turn altering the composite magnetic field generated in the central area (4).

Claims

1. A device for generating a variable composite magnetic field, the device comprising a ring member (2,3) defining a main central axis (5) and a central area (4) around the central axis (5) within which the composite magnetic field is generated, a plurality of discrete magnetic field generating means (18) for generating respective magnetic fields mounted at spaced apart intervals around the ring member (2,3) for generating the composite magnetic field in the central area (4), characterised in that the respective magnetic field generating means (18) are orientably mounted on the ring member (2,3) for varying the orientations of the magnetic fields generated by the magnetic field generating means (18) for varying the composite magnetic field, and a means (22) is provided for varying the orientations of the magnetic field generating means (18) and for retaining the magnetic field generating means (18) in desired orientations.

2. A device as claimed in claim 1 characterised in that each magnetic field generating means (18) defines a corresponding secondary axis (19).

3. A device as claimed in claim 2 characterised in that the respective magnetic field generating means (18) are mounted on the ring member (2,3) with their respective secondary axes (19) extending parallel to each other and parallel to the main central axis (5).

4. A device as claimed in claim 2 or 3 characterised in that the respective magnetic field generating means (18) are mounted on the ring member (2,3) with their respective secondary axes (19) located on a common pitch circle (21), the centre of which coincides with the main central axis (5).

5. A device as claimed in any of claims 2 to 4 characterised in that the respective magnetic field generating means (18) are mounted with their secondary axes (19) equi-spaced apart circumferentially around the main central axis (5).

6. A device as claimed in any of claims 2 to 5 characterised in that each magnetic field generating means (18) generates a magnetic field extending transversely of its corresponding secondary axis (19).

7. A device as claimed in any of claims 2 to 5 characterised in that each magnetic field generating means (18) generates a magnetic field extending perpendicularly to its corresponding secondary axis (19).

8. A device as claimed in any of claims 2 to 7 characterised in that each magnetic field generating means (18) is magnetised such that its direction of magnetisation extends transversely of its secondary axis (19).

9. A device as claimed in claim 2 characterised in that each magnetic field generating means (18) is rotatably mounted in about its secondary axis (19) for varying the orientation of the magnetic filed generated by the magnetic field.

10. A device as claimed in claim 2 characterised in that the means (22) for orienting each magnetic field generating means (18) rotates the respective magnetic field generating means (18) about their respective secondary axes (19).

11. A device as claimed in claim 2 characterised in that a plurality of means (22) for orientating the magnetic field generating means (18) are provided, one orientating means (22) being provided for each magnetic field generating means (18).

12. A device as claimed in claim 11 characterised in that each orienting means (22) comprises an electrically powered motor (22).

13. A device as claimed in claim 12 characterised in that each electrically powered motor (22) is a stepper motor (22).

14. A device as claimed in claims 2 characterised in that a monitoring means (24) is provided for determining the angular position of each magnetic field generating means (18) about its secondary axis (19), and the orientating means (22) is responsive to the monitoring means (24) for orienting the magnetic field generating means (18).

15. A device as claimed in claim 14 characterised in that the monitoring means comprises a plurality of angular position determining encoders (24), one encoder (24) being provided for each magnetic field generating means (18).

16. A device as claimed in claim 1 characterised in that said retaining means (22) is provided for retaining each magnetic field generating means (18) in any one of a plurality of orientations.

17. A device as claimed in claim 16 characterised in that a plurality of retaining means (22) are provided, one retaining means (22) being provided associated with each magnetic field generating means (18).

18. A device as claimed in claim 16 characterised in that each retaining means (22) is provided by a stepper motor of the corresponding magnetic field generating means.

19. A device as claimed in claim 1 characterised in that each magnetic field generating means (18) is independently orientatable relative to the other magnetic field generating means (18).

20. A device as claimed in claim 1 characterised in that each magnetic field generating means (18) comprises a permanent magnet (18).

21. A device as claimed in claim 20 characterised in that each permanent magnet (18) is of a high coercivity grade material.

22. A device as claimed in claim 20 characterised in that each permanent magnet (18) is of a rare-earth material.

23. A device as claimed in claim 1 characterised in that each magnetic field generating means (18) is provided by a rod-shaped permanent magnet (18).

24. A device as claimed in claim 23 characterised in that the secondary axis (19) of each rod-shaped permanent magnet (18) is defined by the longitudinal geometrical central axis of the rod-shaped permanent magnet (18).

25. A device as claimed in claim 23 characterised in that each rod-shaped permanent magnet (18) is of circular cross-section.

26. A device as claimed in claim 1 characterised in that at least two ring members (2, 3) are provided, the ring members (2, 3) being co-axially arranged with their respective main central axis (5) coinciding with each other.

27. A device as claimed in claim 26 characterised in that the respective ring members (2,3) are arranged side by side axially along the main central axis (5).

28. A device as claimed in claim 26 characterised in that the respective ring members (2, 3) are of similar diameter.

29. A device a claimed in claim 26 characterised in that the respective ring members (2, 3) are arranged for axially abutting each other.

30. A device as claimed in claim 26 characterised in that the pitch circle (21) diameters of the respective ring members (2, 3) along which the corresponding magnetic field generating means (18) are located are of similar diameter.

31. A device as claimed in claim 26 characterised in that each ring member (2, 3) is of circular shape.

32. A device as claimed in claim 26 characterised in that each ring member (2, 3) comprises at least eight magnetic field generating means (18).

33. A method for generating a variable composite magnetic field using the device (1) as claimed in claim 1 characterised in that the method comprises orientating the respective magnetic field generating means (18) located on said each ring member (2, 3) to an orientation for generating the composite magnetic field of the desired type and direction.

34. A method for growing a semiconductor crystal using the device as claimed in claim 1 characterised in that the crystal being grown is grown in the composite magnetic field.