A new technique for reducing extremely low frequency magnetic field emissions affecting large building structures

When large structures such as residentialcompounds or public buildings are under the influence ofextremely low frequency (ELF) magnetic fields, such asthe one generated by a system of railways fed by16.67 Hz, standard methods of designing shieldingstructures by numerical methods usually fail. The lattercan be explained by the difficulty posed in the computingprocess by the large aspect ratios involved due to thinlayers of metal (a few millimetres or centimetres) incontrast to the large dimensions of the affected structure(several tens of meters). In some cases one has to utilizespecial approximations such as surface conductivity,which are not easy to handle when the designed shieldingstructure is clearly three -dimensional. Other alternativessuch as experimentation in situ are very costly. Here, anew technique is presented of mitigating the field byusing three-dimensional propagation of induced currentsoptimizing the field reduction factors and minimizing thecost of shielding material. The particular designingmethod is a hybrid of numerical simulations combinedwith lab experimentation using scaled models of the largestructure. The method is rather cost-effective and flexible as various designs can be easily tested. Results are presented in the form of magnetic field values, at various locations in the buildings, before and after this mitigation technique is applied