A Novel Microwave Camera for Nde of Concrete Structures

Nondestructive assessment of concrete structures heavily relies on visual inspections, which apparently have limitations to detect such invisible damage as voids and cracks inside concrete caused by aging, deterioration, and seismic loading. The authors have developed a novel microwave camera for detecting and quantitatively assessing such internal damage in concrete structures. The camera consists of several cylindricalor planar-arrayed antennas for transmitting and receiving signals, and a numerical bi-focusing operator is applied to the external signals both in transmitting and in receiving fields. An imaging algorithm using the numerical focusing operator was developed for reconstructing a 2-dimensional image from the scattered field. Numerical simulation demonstrated that a sub-surface image can be successfully reconstructed by using the antenna array and the imaging algorithm. For the experimental verification, a prototype planar microwave camera was fabricated and tested on a concrete block. Internal and invisible voids in the block were successfully detected. The microwave camera is being further developed for condition assessment of concrete structures strengthened with fiber reinforced polymer jackets. 1 Professor, Department of Civil and Environmental Engineering, University of California, Irvine, CA 92697-2175 2 Post-Doctoral Researcher, Department of Civil and Environmental Engineering, University of California, Irvine, CA 92697-2175 3 Assistant Professor, Department of Electrical and Computer Engineering, University of California, Irvine, CA 92697-2175 4 Professor, Department of Signal Theory and Communications, Technical University of Catalonia, Barcelona, Spain