Filtering and fusion of THz images for defect detection in composite materials

Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. This was due to difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. THz waves can penetrate through diverse materials such that internal structures, invisible to other imaging modalities, can be visulaized. However, automated processing of THz images can be quite challenging. Low contrast and the presence of a widely unknown type of noise make the analysis of these images difficult. In this paper we attempt to detect defects in composite material using a Terahertz imaging system. According to our knowledge this is the first time that this type of materials are being tested under Terahertz cameras using filtering and information fusion. In this preliminary report, we employ stick filter and a simple fuzzy approach to detect defects by fusing information from both amplitude and phase images. The results show that using fuzzy techniques can easily incorporate domain knowledge and assist the defect detection.