Laser speckle photometry: an advanced method for defect detection in ceramics

Due to the special structural and functional properties, the advanced ceramic technology plays an important role in many areas of the industry. Fraunhofer IKTS develops novel ceramic materials for industrial applications, e.g. Na-β-alumina. These materials are used to produce high-temperature, low-cost ceramic batteries. In Na-β-alumina the defects occurs in production by extrude process. Therefore, defect detection is of great importance for quality assurance of ceramics for industrial applications, and advanced non-destructive diagnostic procedures are required. Laser Speckle Photometry (LSP) is an innovative optical non-destructive and monitoring technique based on the detection and analysis of thermally or mechanically activated characteristic speckle dynamics in the non-stationary optical field. Unlike other techniques based on speckle phenomenona, which concentrate on the distortion of whole speckle pattern or fringes, LSP is based on measuring spatial-temporal dynamics of laser speckles in near field, which focuses on the intensity change of each single pixel of camera sensor. The advantages of the new NDT method are, for instance, contactless, noninvasive, full field, fast, real time, high precision and sensitivity. The basic LSP setup has a simple but robust design to reduce the cost compared with other conventional NDT methods, and depending on its working principle, it can be integrated into in-line manufacturing process. The results of measurements will be presented by an imaging LSP method. At current research stage, the detectability of LSP for defects in ceramics is 300 μm in terms of length for crack and 200 μm in terms of diameter for pore.