CN-122015666-A - Multilayer coating thickness measurement method based on terahertz time-domain spectroscopy

CN122015666ACN 122015666 ACN122015666 ACN 122015666ACN-122015666-A

Abstract

The invention discloses a multilayer coating thickness measurement method based on terahertz time-domain spectroscopy, which belongs to the technical field of coating thickness measurement and comprises the steps of respectively measuring signals with and without coatings on a metal plate by utilizing a reflection-type terahertz time-domain spectroscopy system, taking the signals as measurement signals and reference signals, establishing a coating thickness inversion model, fitting the multilayer coating signals, inputting the measurement signals and the reference signals into the coating thickness inversion model, solving the measurement signals and the reference signals through an evolutionary optimization algorithm to obtain optimal solutions of inversion parameters, and inverting the thickness of each layer of coating according to the optimal solutions. According to the method, based on terahertz time-domain spectroscopy, self-consistent and nondestructive measurement of the thickness of the multilayer coating is realized through a coating thickness inversion model and a hybrid optimization algorithm, and the error is small.

Inventors

DU YUHANG
ZHU HUANHUAN
LI SHUAI
PENG SHAOKUN
CHEN HAIYONG
LANG LIYING
CAO YANG
WANG MENG
ZHU ZIHONG
LIU HONGYAN

Assignees

河北工业大学
河北工业大学创新研究院(石家庄)
石家庄海山实业发展总公司

Dates

Publication Date: 20260512
Application Date: 20260126

Claims (9)

1. The method for measuring the thickness of the multilayer coating based on the terahertz time-domain spectroscopy is characterized by comprising the following steps of: S1, respectively measuring a signal with a coating and a signal without the coating on a metal plate by using a reflection type terahertz time-domain spectrum system, and taking the signals as a measurement signal and a reference signal; s2, a coating thickness inversion model is established, and fitting is carried out on the multilayer coating signals; S3, inputting the measurement signals and the reference signals into a coating thickness inversion model, and solving through an evolutionary optimization algorithm to obtain an inversion parameter optimal solution; s4, inverting the thickness of each layer of coating according to the optimal solution.
2. The method for measuring the thickness of the multilayer coating based on the terahertz time-domain spectroscopy of claim 1, wherein the step S2 of establishing a coating thickness inversion model comprises the following steps: s21, establishing a multi-element reflection signal regression sub-model, and calculating the flight time difference and the refractive index between each layer of reflection echo signals and the reference signals; s22, multiple reflection correction sub-models are built by considering multiple reflections of signals between layers; S23, a dispersion correction sub-model is established, and the dispersion effect of terahertz waves in the coating during propagation is corrected; S24, combining the three sub-models to obtain a total fitting signal; s25, defining fitting errors as objective functions of the coating thickness inversion model based on the total fitting signals and the measurement signals.
3. The method for measuring the thickness of the multilayer coating based on the terahertz time-domain spectroscopy of claim 2, wherein the multi-component reflection signal regression submodel in step S21 comprises: ; In the formula, Representation of Fitting signals of the individual reflected echo signals, Represent the first The echo signals are reflected by the plurality of transducers, Is the first Each reflected echo signal and reference signal The time of flight difference between the two, Indicating the number of reflected echoes, For the coefficients of the reflected pulses, the refractive index of each layer is calculated by Fresnel's law based on the coefficients of the reflected pulses 。
4. A method for measuring thickness of a multi-layered coating based on terahertz time-domain spectroscopy as set forth in claim 3, wherein the multiple reflection correction sub-model in step S22 includes: ; In the formula, Representing the time delay between multiple reflected signals, the multiple reflected signals having the same time delay, Representing the total signal of the multiple reflections, Is the multiple reflection amplitude attenuation coefficient, represents the loss of multiple reflection of terahertz waves in the coating, For the multiple reflection pulse coefficients, Representing the time delay between the reflected echo signal of the metal substrate and the reference signal, Represent the first The secondary multiple of the reflection is reflected, Representing the number of multiple reflected signals.
5. The method for measuring thickness of a multilayer coating based on terahertz time-domain spectroscopy as set forth in claim 4, wherein the dispersion correction submodel in step S23 includes: ; In the formula, Representing the parameters of the equivalent dispersion, Representing the dispersion transfer function of the terahertz wave in the coating, Indicating the angular frequency.
6. The method for measuring the thickness of the multilayer coating based on the terahertz time-domain spectroscopy of claim 5, wherein in step S23, three sub-models are combined to obtain a total fitting signal with a calculation formula: ; In the formula, The total fit signal is represented and, Representing the fourier transform.
7. The method for measuring thickness of a multilayer coating based on terahertz time-domain spectroscopy as set forth in claim 6, wherein the objective function in step S25 includes: ; In the formula, The value of the fitted signal is represented, The value of the measurement signal is represented, Representing the overall goal.
8. The method for measuring thickness of a multilayer coating based on terahertz time-domain spectroscopy of claim 7, wherein in step S3, a differential evolution algorithm DE and a covariance matrix adaptive evolution strategy CMA-ES are adopted for solving, and an inversion parameter optimal solution is obtained, wherein the inversion parameter comprises 、、、、。
9. The method for measuring thickness of a multi-layer coating based on terahertz time-domain spectroscopy as set forth in claim 6, wherein inverting the thickness of each layer of coating according to the optimal solution in step S4 includes: Obtaining the flight time difference between each layer of reflected echo signals and the reference signals according to the optimal solution And refractive index ; According to And Calculating the thickness of the coating of each layer The formula is: ; In the formula, Is the propagation velocity of light in air.

Description

Multilayer coating thickness measurement method based on terahertz time-domain spectroscopy Technical Field The invention relates to the technical field of coating thickness measurement, in particular to a multilayer coating thickness measurement method based on terahertz time-domain spectroscopy. Background The thickness measurement of the coating is a key procedure for ensuring the performance and service life of the coating, and directly influences the corrosion resistance, wear resistance, insulation and other performances of the product. Accurate thickness measurement can effectively avoid performance defects caused by insufficient protection or excessive thickness due to the fact that the coating is too thin, and is a necessary means for realizing quality control and guaranteeing product reliability. Currently, there are many methods for measuring the thickness of a coating in industry, such as an eddy current thickness measuring method, an ultrasonic thickness measuring method, a magnetic induction thickness measuring method, etc., but these thickness measuring methods are limited by some special application scenarios, such as contact damage to the surface of the coating, low measurement accuracy, sensitivity to a metal substrate, etc., and it is difficult to meet the requirements of accurate measurement and nondestructive detection. Disclosure of Invention The invention aims to provide a multilayer coating thickness measuring method based on terahertz time-domain spectroscopy, which aims to solve the problems in the background art. In order to achieve the above purpose, the invention provides a multi-layer coating thickness measuring method based on terahertz time-domain spectroscopy, comprising the following steps: S1, respectively measuring a signal with a coating and a signal without the coating on a metal plate by using a reflection type terahertz time-domain spectrum system, and taking the signals as a measurement signal and a reference signal; s2, a coating thickness inversion model is established, and fitting is carried out on the multilayer coating signals; S3, inputting the measurement signals and the reference signals into a coating thickness inversion model, and solving through an evolutionary optimization algorithm to obtain an inversion parameter optimal solution; s4, inverting the thickness of each layer of coating according to the optimal solution. Preferably, step S2 of establishing a coating thickness inversion model includes: s21, establishing a multi-element reflection signal regression sub-model, and calculating the flight time difference and the refractive index between each layer of reflection echo signals and the reference signals; s22, multiple reflection correction sub-models are built by considering multiple reflections of signals between layers; S23, a dispersion correction sub-model is established, and the dispersion effect of terahertz waves in the coating during propagation is corrected; S24, combining the three sub-models to obtain a total fitting signal; s25, defining fitting errors as objective functions of the coating thickness inversion model based on the total fitting signals and the measurement signals. Preferably, the multi-component reflection signal regression sub-model in step S21 includes: ; In the formula, Representation ofFitting signals of the individual reflected echo signals,Represent the firstThe echo signals are reflected by the plurality of transducers,Is the firstEach reflected echo signal and reference signalThe time of flight difference between the two,Indicating the number of reflected echoes,For the coefficients of the reflected pulses, the refractive index of each layer is calculated by Fresnel's law based on the coefficients of the reflected pulses。 Preferably, the multiple reflection correction submodel in step S22 includes: ; In the formula, Representing the time delay between multiple reflected signals, the multiple reflected signals having the same time delay,Representing the total signal of the multiple reflections,Is the multiple reflection amplitude attenuation coefficient, represents the loss of multiple reflection of terahertz waves in the coating,For the multiple reflection pulse coefficients,Representing the time delay between the reflected echo signal of the metal substrate and the reference signal,Represent the firstThe secondary multiple of the reflection is reflected,Representing the number of multiple reflected signals. Preferably, the dispersion correction submodel in step S23 includes: ; In the formula, Representing the parameters of the equivalent dispersion,Representing the dispersion transfer function of the terahertz wave in the coating,Indicating the angular frequency. Preferably, in step S23, three sub-models are combined to obtain a calculation formula of the total fitting signal as follows: ; In the formula, The total fit signal is represented and,Representing the fourier transform. Preferably, the objective function