Research On Terahertz Time-domain Spectroscopy Detection Technology Of Plate Structure

Terahertz Time-Domain Spectroscopy(THz-TDS)technology,as an emerging non-destructive testing method,the propagation characteristics of terahertz waves in the tested samples are studied,to achieve rapid and accurate measurement of physical and chemical information.Terahertz time-domain spectroscopy technology has unique advantages such as high frequency components,high spatio-temporal resolution,and rich spectral information.It is especially suitable for non-contact,fast,and comprehensive nondestructive testing of plate structures.This subject studies terahertz time-domain spectroscopy technology systematically and deeply from theoretical analysis,system construction,experimental research,signal analysis and imaging technology,etc.,which is used to achieve plate structure thickness measurement and quantitative defect detection.The main research contents are given as follows:(1)Theoretical study of THz detection.The terahertz wave spectral characteristics and excitation detection mechanism is introduced,the time-frequency propagation characteristics of the pulsed terahertz signal is studied,the interaction process of the terahertz wave and the medium is discussed,the multi-parameter characterization of the measured object in the terahertz band is formed,and influence of multi-layer material parameter differences(such as refractive index,absorption coefficient and thickness)on the propagation characteristics of terahertz waves are determined,the detection mechanism of terahertz time-domain spectroscopy technology is revealed,and theoretical guidance for the study of terahertz time-domain spectroscopy technology of plate structures is provided.(2)Development of terahertz time-domain spectroscopy detection system.A set of terahertz time-domain spectroscopy detection experiment system for board structure is built,terahertz time-domain spectroscopy automatic detection software is developed,based on the overall design of hardware drive and communication,waveform acquisition and transmission,signal processing and analysis.It independently implements functions such as fast scanning of the delay line mechanism,accurate acquisition of terahertz wave signals,automatic extraction of eigenvalues and thickness measurement of micrometer samples,etc.,in order to carry out experimental research on the thickness measurement of the plate-shaped sample and the quantitative detection of defects.(3)Research on terahertz time-domain spectral thickness measurement technology.First,the mechanism of the interaction between the pulsed terahertz wave and the sample is explored,and a method for measuring the refractive index of the composite material in reflection mode is proposed.Subsequently,according to the developed terahertz time-domain spectroscopy detection system,for single-layer composite materials and multi-layer composite materials,the experimental study of the thickness measurement of each layer of material was carried out,and the detection accuracy of the experimental results was evaluated.Finally,based on terahertz time-domain spectroscopy technology,the refractive index calculation of composite materials and the thickness measurement of micrometer materials are realized.(4)Research on quantitative defect detection based on terahertz time-domain spectral imaging technology.First,the propagation characteristics of different defects in the terahertz band are combined,the defect response of plate-like materials is analyzed,and varieties of time-frequency characteristic parameter imaging methods are developed.Subsequently,an experimental study on imaging detection of two types of holes in metal plates with different sizes and positions was conducted,and the defect detection effects of time-frequency imaging methods were compared and analyzed.Finally,defect imaging recognition and quantitative detection is achieved,based on the terahertz time-domain spectral imaging technology reconstruct the internal media information of the material.