| Terahertz wave has a wide range of applications in the field of terahertz imaging,such as nondestructive testing,biomedical imaging and so on.Because of its low photon energy and no ionizing radiation to human body or organisms,terahertz transmission tomography has its unique application scenario compared with X-ray tomography.Based on X-ray transmission tomography,the transmission tomography of terahertz wave is studied in this thesis.The main contents are as follows:The first chapter introduces the research progress of terahertz wave transmission tomography by relevant research groups at home and abroad in recent years,and introduces the overall structure of this thesis;In Chapter 2,the fundamental wave equation of terahertz wave transmission tomography is derived from Maxwell's equations.Because terahertz wave transmission tomography is no longer linear propagation,two approximate methods are proposed:Born approximation and Rytov approximation.When the approximate conditions are met,it is considered that the propagation of terahertz wave is still linear propagation.The third chapter adopts two image reconstruction algorithms commonly used in Xray,filtered back projection algorithm(FBP)and joint algebraic iteration algorithm(SART).The two reconstruction algorithms are compiled and simulated by MATLAB.The simulation results restore the original image well.In Chapter 4,a terahertz transmission tomography system based on 100 GHz Hz solid-state source and detector is built.The light spot of the system is measured.The transverse light spot is 11.01 mm and the longitudinal light spot is 12.38 mm.The light spot size meets the size requirements of the imaging object.The data acquisition program based on Lab VIEW is introduced.Several groups of samples were selected,the transmission tomography data of the samples were scanned,and the image was reconstructed with FBP algorithm and SART algorithm.The reconstruction results better restored the morphology and size of the samples,and one of the samples was visually reconstructed in three-dimensional direction.The diffraction free Bessel beam generated based on the axicon is simulated.The axicon with bottom angles of 5 °,10 °,15 ° and 20 °are simulated and processed respectively,and the terahertz transmission tomography system based on the Bessel beam is built.The data of the sample to be tested is collected and the image is reconstructed.The effect of the reconstructed image is relatively better when the bottom angle is 10 ° and 15 °.Finally,the high refractive index samples are simulated.The propagation of terahertz through the samples in the case of single layer and double layer are simulated respectively,and the simulated data are recorded.The image is reconstructed by using the simulated projection data,and the reconstructed image accurately restores the sample size in the two cases. |
PDF Full Text Request