Visualization of Voids Between Tile and Concrete by Multi-Layered Scanning Method with Electromagnetic Waves

The tiles that are used to protect the exterior of a building may separate from the concrete substrate and fall off as they age. To prevent accidents, a tiled wall can be inspected using various methods. In this study, nondestructive inspection (NDI) with microwave electromagnetic waves (EMWs) is used for detecting tile separation, and the chance of detecting the separation by this method is discussed in this paper. Here, the inspection apparatus is used to detect voids in concrete, including voids that simulate tile separation. An antenna attached to the apparatus transmits and receives microwaves to obtain a reflected intensity from the concrete. In addition, the distribution of reflected intensity is obtained using a proposed scanning method, multi-layered scanning. This involves several scans along the concrete surface at different antenna-to-surface distances. Typically, EMWs have to be analyzed with an expensive network analyzer in the time or frequency domain. However, we demonstrate that voids are detected from the obtained distribution of the reflected intensity of EMWs measured by a simple device without a network analyzer. The proposed method of NDI with EMWs is cheaper and simpler than conventional inspection methods.