Abstract

Smartphone-Mounted Handheld GPR are used to detect rebar, but quantitative detection of damage is difficult due to small reflectance. In this study, we propose an algorithm to quantitatively estimate damage thickness from received waveforms obtained from electromagnetic radar. A simple estimation method that separates peaks from above and below the crack from the time waveform is extremely difficult due to the presence of subtractive interference and side lobes. Therefore, we focus on the amplitude spectrum with the phase information dropped and estimate the damage thickness by pattern matching with a rigorous theoretical spectrum that takes multiple reflections into account. Rough damage thickness is determined by first combining multiple centroids of amplitude intensity and low-frequency components, and then spectral pattern matching is performed within the gating and bandwidth ranges set for each region, which also contributes to improving processing speed. As a result, damage thicknesses from 2 mm to 180 mm could be quantitatively estimated with a single algorithm in the 0.001 second range, confirming the practical feasibility of this algorithm.