GB1528151A - Permanent magnets - Google Patents

Abstract

1528151 Permanent magnets ENGLISH ELECTRIC VALVE CO Ltd 31 Oct 1975 [7 Jan 1975] 523/75 Heading H1P A permanent magnet 1 (Figs. 1, 2), e.g. for a magnetron is composed of magnetic alloy with soft iron polepieces and has U-shape with rectangular cross-section; arms 2, 3 having polar extensions 4, 5 secured thereto mechanically or by magnetic attraction. Conical polepieces carried at right angles to the polar extensions 6, 7 terminate in opposed flat faces 8, 9 separated by gap 10, and the end faces of the extensions 4, 5 carry thin permanently magnetized pads 13, 14 of samarium cobalt alloy poled to oppose the fluxes at the end faces 11, 12 of the U-shaped magnet, so as to increase the flux across the gap. A soft iron bar 15 connecting the outer faces of the pads provides a flux return path and further magnetized pads 16, 17, 18, 19 overlying the polar extensions may reduce flux leakage. A magnetron is located in the gap 10 with its cathode in the peak magnetic field, and may have a tubular envelope sealed at its end to polar extensions 4, 5. The magnet may be horn shaped, E-shaped, or bowl shaped, and in Fig. 3 (not shown) two horns are mounted on a soft iron base with soft iron polepieces thereon shaped to produce a peak magnetic field therebetween, with magnetized pads of samarium cobalt alloy superimposed on the surfaces of the polepieces to reduce flux leakage. An E-shaped magnet (Fig. 4, not shown) or a bowl shaped magnet enclosing a pair of polepieces may incorporate similar magnetized pads. In other modifications (Figs. 5, 6, not shown) rectangular permanent magnet slabs are joined by yokes and opposed polepieces of soft iron, on which magnetized pads of samarium cobalt alloy are superimposed to reduce flux leakage.