Patent ID: 7379287

Claim:
A shielding apparatus that shields flux leakage from a magnetic circuit that has an exciting coil through which an excitation current passes and that generates alternating flux, the shielding apparatus comprising: a canceling exciting coil that generates canceling flux for canceling the flux leakage by applying a canceling current corresponding to said alternating flux; wherein said exciting coil and said canceling exciting coil are connected in series; wherein the canceling current is an alternating current of a phase opposite to a phase of said excitation current with respect to the same circulation direction of said exciting coil and said canceling exciting coil; and wherein said exciting coil and said canceling exciting coil satisfy the following relationship as to the frequency of at least the alternating current L 1 =k 1 ×k 1 ×LL; where k 1 is a coefficient of coupling between said exciting coil and said canceling exciting coil, LL is a self-inductance of said exciting coil, and L 1 is a self-inductance of said canceling exciting coil.