Crossed PTFE Diffuser for NIR Coating Thickness Measurement
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Solution Overview
Problem
Existing methods for measuring coating thickness on substrates with directionally oriented components, such as fiber-reinforced polymer composites, face challenges due to variations in spectral data caused by sensor orientation, especially for thin coatings and opaque coatings, leading to inconsistent and unreliable results.
Innovation Solution
A diffuser assembly composed of two crossed layers of PTFE thin film is used between the NIR light source and the substrate to minimize specular reflectance and scatter NIR light, ensuring accurate and reproducible measurements by converting the light source into a diffuse nature, thereby eliminating orientation-dependent variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single diffuser element is used, then some reduction in orientation variation is achieved, but orientation-dependent variations are not completely eliminated
Solution Approach 1:
The patent uses a composite diffuser assembly consisting of two crossed PTFE diffuser elements arranged perpendicular to each other. This composite structure combines the light-diffusing properties of both elements to create a more effective orientation-independent measurement system, where the crossed configuration ensures that light scattering occurs in multiple directions regardless of substrate orientation.
Solution Approach 2:
The patent transitions from a single-plane diffuser to a two-dimensional crossed diffuser configuration. By adding the second diffuser element perpendicular to the first, the system introduces an additional dimension of light scattering, which effectively eliminates orientation-dependent variations in spectral data by ensuring uniform light distribution in all directions.
2Measurement precision
If measurements are taken at multiple orientations and averaged, then orientation effects are compensated, but measurement time and complexity increase
Solution Approach 1:
The patent replaces the mechanical approach of physically rotating the sensor to multiple orientations with an optical solution using crossed diffuser elements. This substitution eliminates the need for time-consuming manual repositioning and averaging of multiple measurements, as the diffuser assembly optically achieves orientation independence in a single measurement position.
3Reliability
If the same sensor and substrate alignment is maintained for all measurements, then consistency is achieved, but small variations in orientation negatively impact reproducibility
Solution Approach 1:
The patent changes the optical parameters of the measurement system by introducing crossed diffuser elements that fundamentally alter how light interacts with the substrate. This parameter change transforms the system from one sensitive to orientation parameters to one that is orientation-independent, allowing measurements to be taken without strict alignment requirements while maintaining high reproducibility.
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
This solution enables precise and reproducible measurement of coating thicknesses, particularly for coatings less than 2 mils and those with shiny finishes, by improving the measurement of diffuse reflected NIR light and reducing specular reflectance from substrate irregularities, resulting in reliable thickness measurements independent of sensor orientation.
Implementation Method 1
A diffuser assembly composed of two crossed layers of PTFE thin film is used between the NIR light source and the substrate to minimize specular reflectance and scatter NIR light
Implementation Method 2
transmitting NIR radiation through the stacked and crossed diffuser elements of the diffuser assembly towards a sample
Data Source
AI summary
A system and method for measuring coating thickness upon a substrate containing directionally oriented elements is disclosed. A near infrared light is directed upon the coating and reflected near infrared light is collected to determine the coating thickness. A pair of stacked and crossed diffuser elements is placed between the light source and the sample, and between the sample and the reflected near infrared light collector to improve the accuracy of the measurement, especially for coating thickness of less than about 2 mils and for coatings on substrates containing directionally oriented components. Each diffuser element is formed of a polytetrafluoroethylene fluoropolymer (PTFE) film.