Terahertz Nondestructive Inspection Of Heat Shield

Ceramic-fiber thermal-insulation tile, which has the advantages of light, high temperature resistance, low thermal conductivity, is the primary thermal protection material for the spacecraft. The defects between the insulation tiles and the aircraft will significantly affect their performance of thermal protection. Since THz radiation has the characteristics of high spectral resolution, transmissivity and low energy, it can be used to detect the internal defects of objects.The thesis focuses on the characterization of the adhesive quality of the insulation tiles through implementing THz nondestructive inspection technique, and consists of following parts:Focus on characterizing the adhesive quality of the insulation tiles, we analysis the limitations of traditional detection methods that used to characterize, such as supersonic waves and X-rays, as well as the advantages of THz nondestructive testing technology.The experimental system, i.e., SynViewScan300 THz frequency modulation continuous waves imaging system is introduced. Firstly, the THz source and detector used in this system and its mechanism is described. Then, we describe the principles of tomography and present the theoretical analysis to improve the ranging accuracy.Then we measured the optical properties of materials in THz regime, and the system performance of SynViewScan300. The reflection, transmission and absorption characteristics of different materials is analyzed. Then, we measure the spatial resolution of the system and analyze the factors that influenced it. Finally, the feasibility to screen the defects inside the objects with this system is analyzed.We designed a thermal-insulation tile consists of multi-bonding layers with multiple physical defects for simulating defects in actual samples, Then, according the measurement results, the ability of THz nondestructive technique to screen different defects is discussed.The thesis provides theoretical and experimental criterions for characterization of the adhesive quality of the thermal-insulation tiles using THz nondestructive techniques.