Selective passive shielding and the Faraday bracelet

We describe a general approach for the design of passive conducting structures that preferentially shield the ac magnetic field produced by a specific coil geometry. We demonstrate the utility of selective passive shielding with the Faraday bracelet, an open-access shield for saddle-shaped rf coils. Our data also corroborate the poorly known fact that effective shielding can occur when the ratio of shield thickness to skin depth is much less than unity.