Analysis of Crack Detection in Metallic and Non-metallic Surfaces Using FDTD Method

摘要

The use of microwave techniques for crack detection in metallic and nonmetallic surfaces is a forerunner method. In this method, the reflection of incident wave to a cracked surface has been considered and from the characteristics of the reflected wave the crack can be detected. In our research, the interaction between crack and an ultra wide band pulse as an incident wave is simulated by FDTD (Finite Difference Time Domain) method and the reflected wave is stored and analyzed in time domain. FDTD is a space-grid time domain technique that directly solves the Maxwell's curl equations. This method is based upon volumetric sampling of the unknown electric and magnetic field within and surrounding the structure of interest and over a period of time. Where the modelled region extends to infinity, Absorbing Boundary Conditions (ABCs) are employed at the outer lattice truncation planes which ideally permit all outgoing wave to exit the region with negligible reflection. With FDTD method the cracks of arbitrary shape in metallic and non-metallic surfaces can be simulated. Even if the crack is coated with a thin layer of dust or paint, it can be distinguished with this method. The crack dimensions can be determined from the characteristic of reflected wave. The method was used for the simulation of some cases. The accuracy of the presented model is checked by some analytically solvable cases.