Estimation of the position of a steel bar by a planer typed first order micro SQUID gradiometer

Abstract

We investigated the new nondestructive evaluation techniques for construction based on measuring the magnetic field. For one of the applications of these techniques, we estimated the position of a steel bar in concrete by using a SQUID sensor. We obtained the way to abstract a component of the magnetic field from a magnetic model of a steel bar with regard to the symmetry. This made it possible to estimate the position of a steel bar without necessity of magnetizing it artificially. A planer typed first order SQUID gradiometer was used, since it is a well balanced thin film gradiometer, and it is not readily affected by environmental magnetic noises.
We tested this procedure by running an experiment using specimens. The results showed that the horizontal position is able to be estimated within 1 millimeter. On the other hand, the estimation of depth may be realized by using the regression equation.