Thanks for the replies. I'll post the following quote (taken from a Wikipedia entry on "electromagnetic shielding") as an FYI:
"Equipment sometimes requires isolation from external magnetic fields. . .In these cases shields made of high
magnetic permeability metal
alloys can be used, such as sheets of
permalloy and
mu-metal or with nanocrystalline grain structure ferromagnetic metal coatings. These materials do not block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the
magnetic field lines around the shielded volume. The best shape for magnetic shields is thus a closed container surrounding the shielded volume. The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and high field strengths where the material becomes
saturated. Therefore, to achieve low residual fields, magnetic shields often consist of several enclosures, one inside the other, each of which successively reduces the field inside it. Entry holes within shielding surfaces may degrade their performance significantly.
"Because of the above limitations of passive shielding, an alternative used with static or low-frequency fields is active shielding, in which a field created by
electromagnets cancels the ambient field within a volume.
Solenoids and
Helmholtz coils are types of coils that can be used for this purpose, as well as more complex wire patterns designed using methods adapted from those used in coil design for
magnetic resonance imaging. Active shields may also be designed accounting for the electromagnetic coupling with passive shields, referred to as
hybrid shielding, so that there is broadband shielding from the passive shield and additional cancellation of specific components using the active system.
"Additionally,
superconducting materials can expel magnetic fields via the
Meissner effect."
Would any of these types of magnetic shielding--active, passive, or hybrid--be feasible in protecting the items listed above (including the Walkman) in the face of a 3-Tesla magnetic field? For our purposes, let's assume that money is no object.