US2849636A - Magnetic electron lens - Google Patents

Magnetic electron lens Download PDF

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Publication number
US2849636A
US2849636A US322962A US32296252A US2849636A US 2849636 A US2849636 A US 2849636A US 322962 A US322962 A US 322962A US 32296252 A US32296252 A US 32296252A US 2849636 A US2849636 A US 2849636A
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United States
Prior art keywords
magnets
magnetic
magnet
focusing
electron
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Expired - Lifetime
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US322962A
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English (en)
Inventor
Verhoef Johan Anton
Amesz Wilhelm Godfried
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/58—Arrangements for focusing or reflecting ray or beam
    • H01J29/64—Magnetic lenses
    • H01J29/68—Magnetic lenses using permanent magnets only

Definitions

  • This invention relates to magnetic electron lenses with adjustable focal length such as are used, for example, for focusing the electron beam in cathode-ray tubes, for example of television receivers.
  • Such electron lenses suffer from the disadvantage that the stray or leakage field produced outside the permanent magnet is unduly large. Notably in cathode-ray tubes for television receivers, said leakage field has been found to extend to the deflection coil or to the ion trap, which involves undue distortion of the deflection of the beam and causes the ion trap to cease to function properly.
  • the present invention has for its object a magnetic electron lens of variable focal length with which said stray field is avoided in a simple manner. It is characterized by the use of two, co-axial, disc-shaped, permanent magnets which are movable with respect to each other and the fields of which substantially neutralize each other on the axis outside the magnets. According to a further aspect of the invention, said neutralization is achieved in a simple manner by opposite directions of magnetisation of both magnets.
  • Fig. 1 illustrates the principle of a magnetic electron lens in which the permanent magnets are magnetized radially
  • Fig. 2 shows the principle of a magnetic electron lens in which the permanent magnets are magnetized axially
  • Fig. 3 is a cross-sectional view of the neck area of a cathode-ray tube in a television receiver and containing a focusing, magnetic lens of the invention.
  • the magnetic electron lens shown in Fig. 1 comprises two, annular, disc-shaped, co-axial, permanent magnets 1 and 2, Whose directions of magnetisation NS extend radially i. e. for the magnet 1 from the inside to the outside, and for the magnet 2 from the outside to the inside.
  • a radially symmetric electron-focusing magnetic field is produced about the axis of symmetry 3 of the magnets 1 and 2, the value H, of said active magnetic field between the magnets being fairly high.
  • the stray field H outside the magnets is feeble, since the outside fields produced by each individual magnet 1 and 2 substantially neutralize each other in situ.
  • a ferromagnetic, for example soft iron, shielding box 4 may be provided.
  • the space between the magnets 1 and 2 is free of other ferromagnetic members.
  • the focal length of the electron lens is adjustable by 2,849,636 Patented Aug. 26, 1958 making, for example, the magnet 2 stationary and by shifting the other magnet 1 in an axial direction by means of a driving mechanism 5, the co-axial position of the magnets 1 and 2 being maintained by means of a guide (not shown). In this instance compression springs are unnecessary, since the magnets 1 and 2 attract each other continuously.
  • Fig. 2 shows a similar electron lens, but in this instance the annular permanent magnets 1 and 2 are magnetized axially with opposite directions of magnetisation NS.
  • Such a lens has the advantage over that shown in Fig. 1 that the active field H along the axis at the magnet 1 is as large and oppositely directed compared with that at the magnet 2 resulting in avoidance of image rotation. Further, since the magnets repel one another, the focuschanging mechanism 5 is now required to engage that side of the magnet 1 which faces away from the stationary magnet 2, thus simplifying the construction.
  • a plate 6 movable in a radial direction may be provided in the proximity of the side of the magnet 1 facing the source of electrons, said plate causing dissymmetry of the magnet field with consequent image displacement.
  • the permanent magnetic material preferably has a remanent induction B which, measured in gauss, is smaller than four times the coercive field strength H measured in oersteds, since in spite of the demagnetizing fields the magnets retain their magnetic properties to a sufiicient degree.
  • Materials satisfying this condition and suitable for application in the invention are the permanent magnet materials which are fully described in United States Patent No. 2,762,777. These materials are characterized by a composition substantially consisting of non-cubic crystals consisting principally of a composite oxide of iron and of at least one of the metals barium,
  • strontium and lead and, alternatively, a small amount of calcium as a partial substituent for one of the latter metals.
  • Fig. 3 shows the lens of Fig. 2 mounted in position on the neck of a cathode-ray tube 10 adapted for use in a television receiver. Only the neck portion of the cathoderay tube 10 is shown, the electron-receiving, phosphor screen (not shown) being located at the right.
  • the tube contains the usual bent, electron gun 11 for producing an electron beam free of ions along the axis 3 of the tube and the lens. This end is attained in cooperation with an ion trap 12 mounted on the neck and producing within the tube a magnetic field. Closer to the phosphor screen are the usual deflection coils 13, which establish within the tube a magnetic field causing the beam to scan a raster on the phosphor screen.
  • the focusing unit for the beam which is magnetic in this case, is mounted between the ion trap and deflection coils. Due to the nearness of the latter, as explained above, the stray or leakage field of the focusing unit should be a minimum, especially along the axis 3, to avoid interference with the ion trap and deflection fields. This elfect is obtained with the lens of the invention, as the opposed magnetization of the two magnets tends to neutralize the axial, external, stray fields. To vary the lens power or its focal length, the axial spacing between the magnets may be varied. As shown, this is obtained by making the magnet 2 stationary, and providing means 5 for axially displacing the magnet 1 relative thereto.
  • said focusing means comprising a pair of substantially annular, permanent magnets mounted substantially coaxially with and adjacent one another and surrounding the beam-path and cooperating to produce an active magnetic field substantially at their axes and substantially in the area within the magnets, said magnets being magnetized' in opposite directions whereby the stray magnetic fields. produced'by said pair of magnets attheir axes on the side of each magnet remote from the other magnet are substantially neutralized, and means for varying the axial. spacing between the magnets thereby to vary the strength of the activemagnetic field and the focusing etiect on the beam.
  • a variable magnetic electron lens adapted for focusing' an electron beam passing therethrough, comprising two, flat, ring-shaped, permanent magnets mounted adjacent and coaxial with one another, said permanent magnets definingtherebetween an area free of other ferromagnetic. material and defining along the axes of and within the coaxialmagnets an empty area to be traversed by the electron beam and within which an active magnetic field is. established by said cooperating magnets to focus said beam, said magnets being magnetized in opposite directions whereby the stray magnetic fields produced on the axes but outside the magnets are reduced to a minimum, and means for varying the axial spacing of the magnets thereby to vary the strength of the active magnetic field and the focusing effect on an electron beam.
  • variable magnetic electron lens as set forth in claim 3. wherein the ferromagnetic material consists prin- .cipally of a'composite oxide of iron and a metal selected from the group consisting of barium, strontium and lead.
  • a variable permanent magnet focusing device comprising a pair of coaxially-mounted, adjacent, disc-shaped, annular, permanent magnets, said magnets being magnetizedin a direction parallel to their axes but in opposite directions, thereby producing poles of the same polarity '4 on facing surfaces of said magnets, and means for varying axially the spacing between the magnets thereby to vary the strength of a magnetic field produced by said device.
  • said focusing means comprising a pair of coaxiallymounted, adjacent, disc-shaped, permanent magnets, surrounding the beam path, said magnets being magnetized in a direction at right angles to their axes but in opposite directions, thereby producing poles of opposite polarity on the outer peripheral surfaces of said magnets, and means for varying axially the spacing between the magnets thereby to vary the strength of the magnetic field produced by said focusing means at the beam path and thus vary the focusing effect on the beam.
  • said focusing means comprising a pair of coaxially-mounted, adjacent, disc-shaped, permanent magnets surrounding the electron beam path, said permanent magnets being magnetized in opposite directions and establishing a strong, active, magnetic field at the beam path within the magnets but a weak stray field at the beam path outside of the magnets, thereby to limit the active magnetic field of the focusing means to their immediate vicinity, said focusing means including means for varying the spacing between the magnets by moving the magnets relative to one another thereby tovary the focusing of the electron beam.
US322962A 1952-01-04 1952-11-28 Magnetic electron lens Expired - Lifetime US2849636A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL310959X 1952-01-04

Publications (1)

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US2849636A true US2849636A (en) 1958-08-26

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US322962A Expired - Lifetime US2849636A (en) 1952-01-04 1952-11-28 Magnetic electron lens

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US (1) US2849636A (xx)
BE (1) BE516722A (xx)
CH (1) CH310959A (xx)
DE (1) DE976927C (xx)
FR (1) FR1069392A (xx)
GB (1) GB729840A (xx)
NL (2) NL166477B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3324433A (en) * 1963-12-27 1967-06-06 Hitachi Ltd Electron lens system excited by at least one permanent magnet
US3387158A (en) * 1965-04-14 1968-06-04 Sony Corp Focus magnet assembly for cathode ray tubes
CN103890442A (zh) * 2011-09-10 2014-06-25 本田技研工业株式会社 变阻尼力阻尼器
US11483919B2 (en) * 2019-03-27 2022-10-25 Huazhong University Of Science And Technology System of electron irradiation

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3354336A (en) * 1965-06-30 1967-11-21 Zenith Radio Corp Ring magnetized across thickness with two diametrically opposed and oppositely oriented groups of magnetic pole pairs
NL7812540A (nl) * 1978-12-27 1980-07-01 Philips Nv Kathodestraalbuis.
NL8700528A (nl) * 1987-03-05 1988-10-03 Philips Nv Magnetische focusseerlens voor een kathodestraalbuis.

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2582788A (en) * 1949-02-01 1952-01-15 Gen Electric Magnetic suspension for horizontal shafts
US2615738A (en) * 1950-03-18 1952-10-28 Bailey Meter Co Linkage connector
US2678729A (en) * 1950-12-12 1954-05-18 Spodig Heinrich Automatically operative magnetic separator
US2714678A (en) * 1950-09-03 1955-08-02 Siemens Ag Electron microscopes
US2722617A (en) * 1951-11-28 1955-11-01 Hartford Nat Bank & Trust Comp Magnetic circuits and devices
US2799813A (en) * 1954-03-05 1957-07-16 Philips Corp Magnetic electron lens

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2102421A (en) * 1934-07-12 1937-12-14 Gen Electric Cathode ray oscillograph
FR796502A (fr) * 1934-10-19 1936-04-09 Fernseh Ag Aimant maintenant le rayon rectiligne dans les tubes de braun
DE682031C (de) * 1936-09-11 1939-10-06 Aeg Rotationssymmetrische magnetische Elektronenlinse aus Dauermagneten
DE720927C (de) * 1937-02-25 1942-05-19 Telefunken Gmbh Magnetische Elektronenlinse
DE688644C (de) * 1937-05-29 1940-02-27 Aeg r koaxialen Teillinsen besteht
GB522377A (en) * 1938-12-07 1940-06-17 Ferranti Ltd Improvements in or relating to focusing systems for electron beams
DE758548C (de) * 1939-02-10 1953-05-26 Telefunken Gmbh Magnetische Elektronenlinse ohne Bilddrehung
NL147275B (nl) * 1948-07-01 Plessey Uk Limited Elektrische momentschakelaar voor drukknopbediening.
US2564737A (en) * 1949-12-23 1951-08-21 Rauland Corp Cathode-ray tube
US2565533A (en) * 1950-05-19 1951-08-28 Rauland Corp Cathode-ray tube

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2582788A (en) * 1949-02-01 1952-01-15 Gen Electric Magnetic suspension for horizontal shafts
US2615738A (en) * 1950-03-18 1952-10-28 Bailey Meter Co Linkage connector
US2714678A (en) * 1950-09-03 1955-08-02 Siemens Ag Electron microscopes
US2678729A (en) * 1950-12-12 1954-05-18 Spodig Heinrich Automatically operative magnetic separator
US2722617A (en) * 1951-11-28 1955-11-01 Hartford Nat Bank & Trust Comp Magnetic circuits and devices
US2799813A (en) * 1954-03-05 1957-07-16 Philips Corp Magnetic electron lens

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3324433A (en) * 1963-12-27 1967-06-06 Hitachi Ltd Electron lens system excited by at least one permanent magnet
US3387158A (en) * 1965-04-14 1968-06-04 Sony Corp Focus magnet assembly for cathode ray tubes
CN103890442A (zh) * 2011-09-10 2014-06-25 本田技研工业株式会社 变阻尼力阻尼器
CN103890442B (zh) * 2011-09-10 2015-12-02 本田技研工业株式会社 变阻尼力阻尼器
US11483919B2 (en) * 2019-03-27 2022-10-25 Huazhong University Of Science And Technology System of electron irradiation

Also Published As

Publication number Publication date
FR1069392A (fr) 1954-07-07
BE516722A (xx)
GB729840A (en) 1955-05-11
DE976927C (de) 1964-08-06
NL87342C (xx)
NL166477B (nl)
CH310959A (de) 1955-11-15

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