US3454838A

US3454838A - Magnetic system

Info

Publication number: US3454838A
Application number: US613498A
Authority: US
Inventors: Raymond Defain
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1966-02-18
Filing date: 1967-02-02
Publication date: 1969-07-08
Anticipated expiration: 1986-07-08
Also published as: FR1475013A; GB1178733A; DE1589570A1

Description

July 8, 1969 R. DEFAIN MAGNETIC SYSTEM y Filed Feb. a, 1967 xNveNToR:

R DEFA/N @y QA. 34.79.

ATTORNEY K A United States Patent 3,454,838 MAGNETIC SYSTEM Raymond Defaiu, Paris, France, assignor to CSF-Compagnie Generale de Telegraphie Sans Fil, a corporation of France I Filed Feb. 2, 1967, Ser. No. 613,498 Claims priority, application France, Feb. 18, 1966,

50, Int. Cl. H01h 47/ 00,' Htllf 1/00, 7/20 U.S. Cl. 317--123 14 vClaims ABSTRACT OF THE DISCLOSURE the pole pieces of the main magnet, preferably in the form of sheets of nonmagnetic material.

Background of the invention This invention relates to magnetic structures of the type which includes one or more permanent magnets and two pole pieces, for example, of soft iron, secured one to each of two free ends of the magnet or magnets. More particularly, the invention is concerned with means for controlling the intensity of the magnetic field in the air gap formed by the space separating the two pole pieces.

Structures of this type are known in which the magnetic field in the air gap can be controlled by means of magnetic shunt comprising a mild-steel piece, displaceable with the aid of an adjustment screw in the region of the air gap. To permit field variations within wide limits, the magnetic shunt piece must be placed as near as possible to the air gap and, under these conditions, any variation of the magnetic field in the air gap also brings about a modification of the field pattern or configuration. Moreover, such systems have the disadvantage that they do not permit fast variations of the field.

In certain applications it is important that the configuration of the lines of force of the magnetic field should remain unchanged while the field intensity is being adjusted. For example, a substantially xed niagnetic field configuration is required in travelling wave tubes which make use of this field either for focusing an electron beam (tubes of the so-called O-type) or for propagating au electron beam by the magnetic field associated with a perpendicular electric field (tubes of the so-called M-type).

Summary of the invention It is an object of the present invention to provide an improved magnetic structure in which the above disadvantages are eliminated or at least effectively reduced.

The present invention consists in a device for controlling the magnetic field intensity in an air gap defined between two pole pieces of a permanent magnet structure, which device4 comprises an electromagnet disposed with its extremities adjacent the pole pieces with sheets of nonmagnetic material interposed between the electromagnet and the pole pieces, the electromagnet being energized by a controllable current source, so that the magnetic field intensity in the air gap can be controlled by the control of the current supplied to the electromagnet.

In the accompanying drawings:

FIGURE l shows one embodiment of a magnetic system in accordance with the invention; and

FIGURE 2 shows another embodiment of the invention.

In carrying the invention into effect according to one convenient mode by way of example, FIGURE l shows a magnetic system which includes a U-shaped permanent magnet 1 with two mild-

steel pole pieces

2 and 3, fastened respectively to each of the two extremities of magnet 1 an-d forming therewith an air gap 4.

The

assembly

1, 2, 3 is provided with a control device comprising a U-shaped electromagnet 5, carrying a wind ing 6 energized by a current source 7 in series with a variable resistor (rheostat) 8. A suitable polarity reversal device of conventional construction, such as a manual or electronic device, may be connected also between the current source 7 and its load 6.

Interposed between the outer surfaces of the pole pieces 2 and the electromagnet 5 are sheets 9 of nonmagnetic material (for example, duralumin), intended to limit the flux portion of magnet 1 derived in electromagnet 5.

With this disposition, by controlling the direction and the intensity of the electric current in the winding 6, it is possible to supply a magnetic flux of a desired intensity and direction passing through the air gap 4, wherein it is added to or subtracted from the ux of the permanent magnet 1.

It has been vertified experimentally that this system enables the magnetic field intensity in the air gap 4 to be varied within wide limits while the field configuration in the gap remains substantially unchanged even for large field variations.

Moreover, the electrical energy required for the control as supplied by the source 7 is relatively small because slight current variations in the winding 6 cause significant variations in the reluctance of the magnetic circuit of electromagnet 5, which in turn lead to variations of the ux portion of magnet 1 derived in electromagnet 5.

In an embodiment in which the permanent magnet had a length of 11.5 cm. and a cross-section of 20 cm2, and the electromagnet had a length of l5 cm. and a cross-section of 7 cm?, it was possible to vary the magnetic field in the air gap of the permanent magnet between 0 and 3600 gauss with an energy of only 40 watts in the electrical circuit of the electromagnet.

FIGURE 2 shows an embodiment with two air gaps in which the field intensity is controllable in one gap and fixed in the other. The right-hand portion of the structure is here effectively the same as in FIGURE l, but the U-shaped permanent magnet is replaced here by two straight bar

permanent magnets

11 and 12 arranged in special parallel relationship and two

pole pieces

13 and 14 between which there is defined an air gap 15. Thus, the field intensity is fixed in gap 15 and controllable in gap 4.

While I have shown and described only two embodiments according to the present invention, it is obvious that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to the details described and illustrated herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A device for controlling the magnetic field intensity in an air gap between two pole pieces of a magnet structure substantially ywithout affecting the field configuration thereof, comprising magnet means having two pole pieces defining therebetween an air gap, and means for controlling the magnetic field intensity in said air gap substantially without affecting the field configuration thereof including electromagnet means having two end portions placed near and operatively associated with said pole pieces.

2. A device according to claim 1, wherein said control means includes means for varying the energization of said electromagnet means. l

3. A device according to rclairn 2, further comprising a nonmagnetic material interposed between said end portions and adjacent surfaces of said pole pieces.

4. A device according to claim 3, wherein said firstmentioned magnet means is a permanent magnet.

5. A device according to claim 4, wherein said magnet means has only a single air gap which is defined between said two pole pieces.

6. A device according to claim 4, wherein said magnet means has at least two air gaps, one of said air `gaps being defined between said two pole pieces and the other air gap being defined by a further break in the structure of said magnet means.

7. A device according to claim 1, wherein said control means includes means for selectively Ivarying or reversing the polarity of the energization of said electromagnet means.

8. A device according to claim 1, further comprising a nonmagnetic material interposed between said end portions and adjacent surfaces of said pole pieces.

9. A device according to claim 1, wherein said firstmentioned magnet means is a permanent magnet.

10. A device according to claim 9, wherein said magnet means has only a single air gap which is defined between said two pole pieces.

11. A device according to claim 9, wherein said magnet means has at least two air gaps, one of said air gaps being defined between said two pole pieces and the other air gap being defined by a further break in theA structure of said magnet means.

12. A device according to claim 1, wherein said magnet means has only a single air gap which is defined between said two pole pieces.

13. A device according to claim 1, wherein said magnet means has at least two air gaps, one of said air gaps being defined between said two pole pieces and the other air gap being defined by a further break in the structure of said magnet means.

14. A magnet assembly in which the magnetic field intensity in an air gap defined between two pole pieces of a permanent magnet structure is adapted to be controlled, wherein the improvement icomprises an elecromagnet disposed with its extremities adjacent the pole pieces with sheets of non-magnetic material interposed between the electromagnet and the pole pieces, the electromagnet -bein'g energized by a controllable current source.

References Cited UNITED STATES PATENTS 2,718,606 9/1955 Zuerker 335-210 3,069,602 12/1962 Stout 335-236 3,146,381 8/1964 Moreau 335-237 LEE T. HIX, Primary Examiner.

DENNIS HARNISH, Assistant Examiner.

U.S. Cl. X.R. 335-209, 210