28 June 2002 Microwave sub-surface imaging of damage in concrete structures
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It has been well demonstrated that the structural performance of reinforced concrete (RC) columns can be enhanced by retrofitting using fiber reinforced polymer (FRP) composite jackets. Therefore, an increasingly large number of bridges and building columns have been retrofitted with such jackets. The authors developed a microwave imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column. The authors developed surface imaging technology using focused microwave in previous works. In this paper, extending the earlier analytical and experimental works, a microwave sub-surface imaging system using antenna array was developed and verified for its capabilities to assess the damage of concrete structures. The proposed imaging system uses an arrangement consisting of several cylindrical or planar arrayed antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. This paper describes a numerical focusing procedure and numerical simulations demonstrated that the sub-surface image can be successfully reconstructed by using the proposed sub-surface imaging technology. For the experimental verification, the prototype of planar antenna array was fabricated and tested on the concrete block, in which the artificial voids were inserted.
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Yoo Jin Kim, Yoo Jin Kim, Luis Jofre, Luis Jofre, Franco De Flaviis, Franco De Flaviis, Maria Qing Feng, Maria Qing Feng, } "Microwave sub-surface imaging of damage in concrete structures", Proc. SPIE 4696, Smart Structures and Materials 2002: Smart Systems for Bridges, Structures, and Highways, (28 June 2002); doi: 10.1117/12.472569; https://doi.org/10.1117/12.472569

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