"Modern aircraft structures have to comply with severe requirements: they have to be light as well as safe. These requirements lead to an increased use of composite materials in the aircraft industry. However, new materials also require new techniques in order to inspect aircraft components during production in a non-destructive way.The primary goal of the DOTNAC project is to develop a safe, contact-free, high resolution, and potentially on-site NDT tool based on terahertz (THz) waves, which will be easy to integrate in industrial facilities, and allowing the detection of surface, subsurface and in-depth defects in a variety of composite materials used in aeronautics. The developed NDT tool will fill in the performance gaps that are still present amongst the established NDT techniques and will therefore be an extremely useful tool in NDT in terms of sensor fusion.The THz spectrum covers a frequency spectrum from the far-IR region to the mid-IR region (centre frequency between 100 GHz and 10 THz). Over the past several years, there has been a significant interest in the potential of THz detection for imaging. There are two major factors contributing to this interest: (1) Terahertz radiation is readily transmitted through most non-metallic and non-polarized media, thus enabling THz systems to ‘see-through’ materials, (2) THz radiation is non-ionizing and poses no health risk to the system’s operator. Nowadays very little research is being performed using THz radiation for air transport NDT, and little is known on how typical composite material defects such as delamination, porosities and inclusions can be detected by THz waves.Because of the rapidly increasing use of composites, especially in critical parts, nearly any industry (civilian and military) that fabricates and/or maintains composite structures can benefit both in terms of cost savings and part integrity."