Fresnel matrix THz wave propagation model based high-precision thickness detection method for coatings

Abstract

The invention discloses a Fresnel matrix THz wave propagation model based high-precision thickness detection method for coatings. Based on a electromagnetic field theory model, a reflecting propagation one-dimensional electric field model of normal incidence THz wave in a multi-layer medium structure is established according to a reflecting type THz time domain spectrum system used in coating thickness detection. On this basis, a Fresnel coefficient matrix and a phase matrix are introduced and a Fresnel matrix THz wave propagation model is proposed and validated. Quantitative detection of coating thickness is realized by utilizing the Fresnel matrix THz wave propagation model based LS (Least Squares) thickness optimization method and the coating thickness is solved through iterative optimization so as to minimize the minimal residual sum of squares of a simulation result and a measurement result and to realize the high precision optimization of thickness parameters. A distance parameter DTS between a THz emitter and a to-be-measured piece is introduced and visible treatment is performed on distance errors between the THz emitter and the to-be-measured piece, so that the accuracy ofcoating thickness detection is improved further.

Description

technical field [0001] The invention belongs to the field of non-destructive testing, and in particular relates to a high-precision coating thickness testing method based on a Fresnel matrix THz wave propagation model. Background technique [0002] With the continuous development of science and technology and the continuous improvement of mechanical structure processing technology, engineering has put forward higher requirements for the performance of modern components. Since the performance improvement of modern components usually depends on the special properties of materials, in order to ensure the reliability of components It is necessary to use corresponding technical means to protect and strengthen materials, and coatings are usually used to improve product performance such as durability and reliability of components. Considering the complex environment that components may encounter in actual engineering applications, only one layer of coating may not be able to meet t...

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Problems solved by technology

[0005] Since the THz wave thickness measurement method measures the thickness of the coating through the time-of-flight difference of the reflected echoes of the THz wave at the interface of different media, when the coating is a thin layer (in fact, the coating is usually even Thin layer), usually because the time-of-flight difference is too small, it is difficult to distinguish the upper and lower surface echoes of the coating in a timely and effective manner, which will lead to low detection accuracy, poor efficiency or even undetectable coating thickness. The phenomenon

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