By means of a permanent magnet ized ferromagnetic core with a controllable bias magnetisation

摘要

708,134. Electron lenses. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Aug. 27, 1951 [April 23, 1951], No. 20139/51. Addition to 708,132. Class 39(1) [Also in Group XXXV] An electron lens made in accordance with the invention of the parent Specification comprises a coil 19 surrounded by a highly permeable core 14, 15, 18 in which, lying in the plane of the core limb is a permanent magnet insert 4. This is of material having a non-cubic crystal structure, and a coercivity of at least 750 Oersted, e.g. the material forming the subject of Specification 708,127, [Group XXXV], and is magnetized across its thickness. To effect a fine adjustment of the lens the current through coil 19 is varied and to effect a coarse adjustment part 18 of the core is moved relative to the permanent magnet and the rest of the core. The application of the invention to inductors is described (see Group XXXV). Specifications 708,132, 708,133 and 708,135 also are referred to.