A portable inductive scanning system for imaging steel-reinforcing bars embedded within concrete

A novel portable scanning system and inductive sensor that produces images of steel-reinforcing bars embedded within concrete by an inductive principle is described. The sensing element, which comprises a field-compensated receiving coil, detects the magnetic field generated by the steel bars due to eddy currents induced on their surfaces by an excitation coil. The sensor is mounted within a purpose-designed computer-controlled x-y scanner used to collect data within a 400 X 400 mm(2) area in 18 min, using a scan step of 1 mm along the x-axis and 2 mm along the y-axis. This scanner assembly is fabricated from a unique combination of plastic components to avoid disruption of the magnetic field as signals are acquired. The sensor is translated within the frame using remotely placed stepper motors, and images are generated with a grey-scale resolution of 16 bits/pixel. These images are then enhanced using application-specific image processing techniques developed by the authors. The complete system incorporates fully integrated control, acquisition and processing software, which makes it convenient for on-site use. (C) 2000 Elsevier Science S.A. All rights reserved.