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 principl e is described. The sensing element, which comprises a field-compensated re ceiving 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 t o collect data within a 400 X 400 mm(2) area in 18 min, using a scan step o f 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 disrup tion of the magnetic field as signals are acquired. The sensor is translate d within the frame using remotely placed stepper motors, and images are gen erated 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.