Study Of Testing Application Of Continuous Wave Terahertz Imaging

Terahertz (THz) can be used as imaging light source, just like X radiation and visible light. Because its' special characteristics, THz imaging technology has huge application potentiality in biological medicine, security inspection, testing of aerospace materials aspects and so on. Solely depending on the type of THz, THz imaging technology can be divided into pulsed and continuous-wave (CW) THz imaging. Based on the distinguished characteristics of many biologic and chemical media in THz range, and special imaging advantages of pulsed imaging, pulsed imaging has become an important choice in many applied fields. But with the development of semiconductor technologies, a compact, relative fast, easily operated and portable CW imaging system has been realized, showing its' practicability increasingly in many applied fields, and become another important choice apart from pulsed imaging, promoting development of THz imaging technologies together.This thesis mainly focuses on the CW THz imaging technology, analyzing a few critical questions from theoretical and experiment aspects, more concerned with the applications of CW THz imaging technology, which are very essential to further research and exploration. The main research works are listed as follows:(1) Debug the CW THz imaging system; discuss the imaging principle of CW, data acquisition and so on, to prove the easily operated, compact, relative fast and etc. of this technology. Because the speed of data acquisition and scanning are not disagreed, the displacement is introduced in image. By changing the value of speed, acceleration of stage and position lag, the extent of displace is reduced, the system is also optimized.(2) The testing applications of CW THz imaging technology are described in detail, successfully testing mobile phone, bag of a mobile phone, hidden letters, burned glass fiber reinforced plastics, man-made defects of space shuttle insulating foam, cracks, voids and debonds in space shuttle insulating foam. Associative with the property of samples in THz range, the theoretical analyses of results are included, which proved the ability of CW THz imaging technology. Improve the image contrast of cracks detect by inserting alcohol, and discuss the influence of area, depth and edge of flaws.(3) The 0.2THz and 0.38THz system are introduced and discussed. Compare the setups and imaging characteristics theoretically and experimentally. 0.38THz system provides a higher spatial resolution; on the other hand 0.2THz system has a better signal to noise ratio. As for polyurethane foam, the absorption index of foam increases with frequency in the THz frequency range, so 0.38THz system has higher contrast in image, and 0.2THz system has less loss in propagation. Meanwhile, based on eight imaging processed algorithms, imaging results are optimized, and so more information characteristics are extracted, targets are also easily identified. At last, taking fiber glass reinforced plastics for an example, better analysis can be obtained from processed images, to avoid impossibly of analyze the original image, which improves the ability of testing of CW imaging technology.