THz Sensor System for Multilayer Coating Thickness Determination
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Solution Overview
Problem
Current methods for measuring paint film thickness using THz radiation are limited by their robustness and reliability, particularly for multilayer structures with small optical contrast and thick layers, as they often require contact and are unable to accurately determine individual layer thicknesses and paint identification.
Innovation Solution
A method utilizing the entire time trace of the THz radiation signal to fit a physical model, allowing for non-contact measurement of coating parameters, including thickness and paint type, by minimizing the error between predicted and measured responses, even with small interactions and low optical contrast between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If THz radiation methods are used for non-contact measurement, then contact mode limitations are overcome, but robustness and reliability for multilayer structures with small optical contrast deteriorate
Solution Approach 1:
The patent applies preliminary action by performing a comprehensive physical model fitting analysis on the entire time trace of the THz signal before final thickness determination. This involves minimizing the error between predicted and measured responses across all time points, which stabilizes the measurement process and improves reliability for multilayer structures with small optical contrast
Solution Approach 2:
The patent implements feedback through iterative optimization where the measured THz time trace is continuously compared with predictions from physical models, and the model parameters are adjusted to minimize the error between predicted and measured responses. This feedback loop enhances measurement robustness by continuously refining the thickness determination based on the entire signal rather than isolated features
2Ease of manufacture
If peak position subtraction method is used, then thickness calculation is simplified, but accuracy for multilayer structures with small optical contrast deteriorates
Solution Approach 1:
The patent replaces the simple peak position subtraction method with a comprehensive physical model fitting approach that minimizes error across the entire time trace. This substitution uses optimization algorithms and physical models to account for small optical contrasts in multilayer structures, significantly improving measurement accuracy while maintaining computational feasibility through systematic error minimization
3Ease of operation
If known group index of refraction is assumed, then thickness calculation becomes straightforward, but reliability for unknown paints deteriorates
Solution Approach 1:
The patent applies parameter changes by treating the group index of refraction as a variable parameter to be optimized rather than a fixed known value. The physical model fitting process simultaneously determines thickness and optical parameters by minimizing the error between predicted and measured responses, enabling accurate measurement of unknown paint types while maintaining calculation efficiency through parameter optimization
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate determination of individual layer thicknesses and paint identification in multilayer structures, improving the robustness and reliability of paint film measurement, especially for coatings with small optical contrast, and allowing for defect detection.
Implementation Method 1
an emitter system (10) for emitting THz radiation towards the coated body (2)
Implementation Method 2
a detector system (20) for detecting THz radiation coming from the coated body (2)
Implementation Method 3
The thickness is obtained by subtraction of peak positions of a time-domain signal
Implementation Method 4
The peak positions, together with a known group index of refraction of the paint, allow calculation of the thickness
Data Source
Figure 1~2b
Figure 3~4
Figure 5~6
AI summary
A method of characterizing a coated body by at least one coating parameter based on fitting to a physical model is provided. The coated body comprises a substrate coated by a polymeric coating such as a paint film, the polymeric coating having at least one layer. The method is carried out by a sensor system in a non-contact manner, the sensor system comprising an emitter system for emitting THz radiation, a detector system for detecting THz radiation, and a processing unit operationally coupled to the emitter system and the detector system. The method comprises : Emitting, by the emitter system, a THz radiation signal towards the coated body such that the THz radiation interacts with the polymeric coating; Detecting, by the detector system, a response signal being the detected THz radiation signal having interacted with the polymeric coating; Determining model parameters of the physical model by optimizing the model parameters such that a predicted response signal of the physical model is fitted to the detected response signal, the model parameters being indicative of optical properties of the polymeric coating describing the interaction of the THz radiation signal with the polymeric coating; Determining, from the determined model parameters, the at least one coating parameter, wherein the at least one coating parameter includes a thickness of the polymeric coating.