Structural design of iron–aluminum multilayer composite for geomagnetic field shielding

Two types of multilayer structure with high magnetic shield effectiveness are presented experimentally and theoretically. Aluminized coatings were deposited on the two sides of pure iron substrate by using hot dip aluminizing. After diffusion heat treatment, iron–aluminum multilayer composite was obtained with Fe–Al alloy/Fe/Fe–Al alloy structure, which could be seen as three permeable magnetic layers in macro scale. A spacer was inserted between a couple of iron–aluminum multilayer composite plates to form sandwich structure with permeable magnetic layer/non-magnetizer/permeable magnetic layer structure. The results indicate that good bonding exists between the pure iron substrate and the Fe–Al reaction layer with a clean and flat interface after heat treatment. Geomagnetic shielding factor (SF) of iron–aluminum multilayer composite arrives at 25.5, which is about 7.7 times of pure iron substrate. The value of SF for sandwich structure can reach 210, about 8.2 times as high as for the multilayer composite magnetizer. Mathematical equation of SF for multilayer composite and sandwich structure are derived according to magnetic reluctance and magnetic circuit method. The three permeable magnetic layers in multilayer composite shunt the magnetic field in parallel and the sandwich structure can shunt magnetic field twice to achieve excellent shielding effectiveness. The theoretical computational results of SF agree well with the experimental values.