One-dimensional current imaging based on an analytical solution of magnetic field distribution: Applications to non-destructive testing of reinforcing bars in concrete

The condition of steel components embedded within reinforced and pre-stressed concrete is one of the most important factors in determining the useful life of structures built from this material. Civil engineers often use magnetic methods to determine the approximate depth and diameter of steel bars and tendons. However, due to the magnetic field distribution around conductors, direct two-dimensional imaging by such methods is subject to severe blurring. A precise deconvolution expression has been developed that eliminates blurring in the one-dimensional case. By taking the Fourier transform of the magnetic field distribution, an analytical expression has been obtained for the spatial frequency response. The deconvolution algorithm was applied in its discrete form to the measurement profile of a magnetic field, in which several wire loops, representing reinforcement bars, were excited with an AC voltage. The deconvolution yielded a highly accurate reconstruction. Further work suggests that this method could be extended to the two-dimensional case. The problem of measurement misalignment in relation to the discrete-space Fourier transform is also addressed.