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Cracking of concrete structures is a phenomenon familiar to civil engineers but difficult to interpret and to quantify. While many remote sensing techniques have been proposed for quantifying surface crack properties (e.g., length, width, distribution) on concrete structures with an improved accuracy and efficiency, little has been known about the structural significance of concrete cracks without the knowledge about subsurface crack properties (e.g., depth, orientation, volume). Among several remote sensing techniques, radar (e.g., ground penetrating radar and synthetic aperture radar) imaging is chosen for its superior performance on subsurface sensing. This paper presents a numerical study on the near-field electromagnetic scattering pattern of surface cracks in plate-like structures for determining the optimal inspection angle using the finite difference time domain (FDTD) method. Three artificial cracks (1”-by-1”, 1”-by-0.5”, and 0.5”-by-1”) on a concrete plate (dielectric constant = 5, electrical conductivity = 0.05 S/m) were simulated to develop their near-field scattering response with a transverse electric (TE) wave at a carrier frequency from 8GHz to 18GHz. From the simulated result, a noise criterion (using the signal-to-noise ratio) and a robustness criterion (using standard deviation) are proposed for determining optimal inspection angle. Our simulation result reveals that, with the combined used of two criteria, an optimal inspection angle can be selected from the angular range of 41-deg. (12GHz) to 45-deg. (14GHz).
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