Patent ID: 7339373

Claim:
A magnetic shielding apparatus, comprising: (a) a first cylindrical shield provided with a circumferential part having first thickness and having a first angular range in a circumferential direction of the y-axis perpendicular to the z-axis, a first opening formed on the circumferential part, a portion parallel to the y-axis at both ends of the first angular range, two circular-arc parts parallel to a plane perpendicular to the y-axis and a first auxiliary cylinder where a cylindrical member is connected to the circumferential part in a state in which the central axis of the cylindrical member is coincident with the central axis of the first opening, and made of high-permeability material; (b) a second cylindrical shield provided with a circumferential part having second thickness and having a second angular range in the circumferential direction of the y-axis and two portions parallel to the y-axis at both ends of the second angular range, made of high-permeability material, and arranged inside the circumferential part of the first cylindrical shield; (c) a third cylindrical shield provided with a circumferential part having third thickness and having a third angular range in the circumferential direction of the y-axis and two portions parallel to the y-axis at both ends of the third angular range, made of high-permeability material, and arranged outside the circumferential part of the first cylindrical shield; (d) a base for fixing and supporting the first cylindrical shield in two locations in a direction of the y-axis; and (e) a revolving part for revolving the second and third cylindrical shields in the circumferential direction of the y-axis along the circumferential part of the first cylindrical shield, wherein: an opening in the circumferential direction of the y-axis is formed by the revolution in one direction; and a leakage magnetic field that invades closed internal space formed in the circumferential direction of the y-axis is screened by the revolution in the other direction.