| 摘要 |
PROBLEM TO BE SOLVED: To attain high accuracy machining and to ensure high magnetic uniformity by combining a large number of magnetic plates parallel to the direction of the magnetic lines of force, to form almost axially symmetric structure. SOLUTION: Insulating coating or insulating material is applied to the side face of each sector magnetic thin plate 1, formed of an iron-cobalt alloy, pure iron or Permalloy(R). Each magnetic thin plate 1 is attached and overlapped to form axially symmetric cylindrical shape, and a polygonal center hole 3 is formed at the tip part of each magnetic thin plate 1. If the center hole 3 has six angles or more, third or lower order aberrations do not occur on an optical axis. The directionality of the magnetic thin plates 1 is arranged so that a material magnetization facilitating axis points toward the center hole 3. Each magnetic thin plate 1 is screw fixed with screw at a fixing hole 4 to be integrated with upper and lower boards. Insulating material 2 of about 10μm is inserted between the respective magnetic thin plates 1 to provide the insulating material 2 in the direction of a magnetic line of force. Magnetic resistance can therefore be kept small, and the generation of eddy current is prevented to improve frequency response property.
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