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Design of Frequency Selective Paper for Crack Detection of Concrete Building Structure

In this paper, a frequency selective paper with X-band reflection characteristics is designed for the crack detection of concrete building structures and the change of resonant frequency characteristics according to cracks are investigated. Based on the crossed dipole unit cell known to have narrow-band reflection characteristics, a frequency selective paper operating in the X-band was designed and the frequency characteristics of the frequency selective paper unit structure including cracks were observed. As the crack width increased by 0.2mm, the resonance frequency tended to move to the higher band by about 90MHz. It was confirmed through simulation that the existence and the width of the crack can be predicted. Designed frequency selective paper was fabricated and frequency reflection characteristics were measured for six types of cracks. From the measurement result, the existence of cracks and the shape of cracks can be predicted according to the polarization of the incident angle.