| Terahertz passive detection imaging technology is an emerging imaging technology.The imaging technology uses a short wavelength of terahertz wave,so the resolution is high during imaging,and it does not actively emit electromagnetic waves,which is safe and radiation-free.The use of passive terahertz detection imaging technology for safety inspection has become a new trend in the development of human security inspection technology at home and abroad.In the terahertz passive detection imaging system,image data acquisition is an important function part of the system,which is the basis of the normal operation of the whole system.It mainly converts the analog signal from the frontend channel into a digital signal and sorts it into a digital image to achieve system imaging.Due to factors such as the level of manufacturing process and production cost,multichannel scanning imaging structures are often used in terahertz imaging systems,the inconsistent response function of each channel will have a serious impact on the imaging results,which will affect the subsequent detection and tracking algorithm processing.Based on the actual research project of the research group,this thesis completed the following research work in the image data acquisition and channel equalization method of passive terahertz imaging system:(1)The basic principle of terahertz passive detection imaging technology and the basic structure of imaging system are analyzed.The causes of strip noise and the characteristics of strip noise in multi-channel scanning imaging system are studied.Several evaluation methods of image striping effect are discussed.(2)According to the basic structure of the imaging system and the principle of scanning imaging,the data acquisition and control unit was analyzed and the design scheme was proposed.The index analysis and demonstration were carried out according to the project requirements.The main device selection and hardware circuit design and implementation were completed.At the same time,the hardware circuit is tested and the test results verify that the hardware circuit design meets the requirements.(3)Based on the development platform of Quartus software,the design of digital logic circuit of data acquisition and control unit is completed by using Verilog HDL language,which realizes the function requirements such as encoder angle acquisition,image data acquisition control,image arrangement storage,image data transmission.It was simulated and verified by ModelSim software.(4)Aiming at the problem of strip noise in the imaging results of multi-channel linear array scanning imaging system,the model of channel imbalance is studied.The advantages and disadvantages of the traditional two-point calibration method and the single-point calibration method are studied and analyzed.An improved equalization method that re-correction after single-point calibration is studied.And the improved method was verified by simulation experiments.(5)The common scene-based channel equalization method is studied,and its improvement effect on the image with banded noise is analyzed.Aiming at the problem that the traditional moment matching method changes the spectral structure of the original image and brings about new strip noise in the de-striping application of the near-field passive imaging system,a corresponding improved algorithm is studied,and the algorithm is verified by the image. |
PDF Full Text Request