Natural ferromagnetic resonance in cast microwires and its application to the safety control of infrastructures

Abstract

The natural ferromagnetic resonance (NFMR) in cast glass-coated amorphous magnetic microwires has been studied theoretically and experimentally. The NFMR reveals large residual stresses appearing in the microwire core in the course of casting. These stresses, together with the magnetostriction, deteRmine the magnetoelastic anisotropy. Beside the residual internal stresses, the NFMR frequency is influenced by external stresses applied to the microwire or to the composite containing the latter (the so-called stress effect).

The dependence of the NFMR frequency on the deformation of the microwires is proposed to be used in the distant diagnostics of dangerous deformations of critical infrastructure objects such as bridges, dams, wind turbine towers, skyscrapers, stack-furnaces, embankments, etc. To this end, fragments of magnetic microwires will be embedded in the bulk of concrete structures or fixed on their surface during construction or after it by means of coating with a special concrete-adhesive plaster. Further, these structures are periodically irradiated with microwaves from a radar at frequencies close to the original NFMR, and the presence of latent dangerous deformations of the concrete structure is judged by the NFMR frequency shift.