For basic considerations and formulas about shielding at low intensity field levels can be studied at: EMF Fundamentals Copyright (c)1995 VitaTech Engineering, Inc. Written by Lou Vitale, President & Chief Engineer. Lou has an interesting statement:
After assembling a prototype, the design engineer measures the shielding factor (SF) and modifies the design (adds materials, additional layers, anneals bends, etc.) to achieve the maximum shielding requirements. This is a very iterative design process, from concept to final product. Shielding is more of an art than a science, especially when shielding very large areas and rooms from multiple, high-level, magnetic field sources. At this time there are no reliable design formulas or EMF simulation programs that offer design engineers practical guidelines for shielding large exposed areas from multiple, high-level, magnetic field sources.
Offered by Mike.