Multilayer Structure Measurement Using Tunable Interferometry
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Solution Overview
Problem
Current methods cannot non-destructively determine the number of layers and material composition of each layer in multilayer structures, nor accurately measure the thickness of each layer, which is crucial for non-destructive product verification testing in industries like automotive, aerospace, and glass manufacturing.
Innovation Solution
An interferometer apparatus with a low-coherence tunable light source is used to measure the optical thickness of each layer at multiple wavelengths, allowing for the identification of layer materials by comparing data to a reference database of group index of refraction dispersion curves, and determining the physical thickness of each layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-wavelength optical measurement methods are used, then the measurement process is simple, but the ability to identify material composition and determine layer thickness in multilayer structures is insufficient
Solution Approach 1:
The patent applies parameter changes by using a tunable light source that varies the wavelength parameter to measure optical thickness at multiple wavelengths. This enables the determination of group index of refraction dispersion curves, which are essential for identifying material composition and distinguishing between different materials in multilayer structures.
Solution Approach 2:
The patent transitions from single-wavelength to multi-wavelength measurements, adding the wavelength dimension to the measurement process. This dimensional expansion allows for the characterization of dispersion properties and provides additional information for material identification beyond what single-wavelength measurements can provide.
2Measurement precision
If destructive testing methods are used to identify material composition, then material identification can be achieved, but the sample is damaged and cannot be used for further testing
Solution Approach 1:
The patent replaces destructive mechanical or chemical analysis methods with non-destructive optical measurement techniques. By using low-coherence interferometry with tunable light sources, the system identifies material composition through optical property measurements that do not damage the sample, allowing continued use of the tested component.
Solution Approach 2:
The measurement system uses the optical properties of the material itself (refractive index, dispersion characteristics) to identify the material composition. The material's inherent optical characteristics serve as the identification signature without requiring external markers or destructive sampling.
3Measurement precision
If multiple separate measurements are performed to characterize each layer, then comprehensive characterization can be achieved, but the measurement time increases significantly
Solution Approach 1:
The patent implements continuous wavelength tuning across the measurement spectrum, allowing uninterrupted collection of optical thickness data at multiple wavelengths in a single continuous process. This eliminates the need for separate discrete measurements and reduces total measurement time while maintaining comprehensive layer characterization.
Solution Approach 2:
The patent combines multiple measurement functions into a single integrated low-coherence interferometry system. The system simultaneously measures optical thickness, determines dispersion curves, identifies materials, and calculates physical thicknesses in one unified measurement process, rather than requiring separate specialized measurements for each parameter.
4Measurement precision
If conventional optical measurement techniques are used, then the equipment is simple, but the ability to determine physical thickness from optical thickness measurements is limited
Solution Approach 1:
The patent uses wavelength as a variable parameter to measure optical thickness at multiple wavelengths. By analyzing how optical thickness changes with wavelength (dispersion relationship), the system can determine the group index of refraction and calculate physical thickness with high accuracy, overcoming the limitations of single-wavelength measurements.
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 non-destructive characterization of multilayer structures, accurately identifying material composition and thickness of each layer, enhancing product verification and reverse engineering capabilities.
Implementation Method 1
Low-coherence interferometry (LCI) has applications in many fields from medical imaging to glass manufacturing. Low-coherence interferometry is based on using a light source with a relatively short coherence length on the order of 1.0-40 micrometers (μm).
Implementation Method 2
The light is split between two arms of an interferometer and then recombined and directed onto a detector. Interference will occur when the path lengths of the two arms of the interferometer are equal to within a few coherence lengths of the light source.
Implementation Method 3
Optical dispersion in optical materials is the phenomenon in which the phase velocity of a wave depends on the wavelength of light λ traveling through the optical material. This results in a wavelength dependence of phase index of refraction which is different in different materials.
Data Source
AI summary
A method of identifying the material and determining the physical thickness of each layer in a multilayer structure is disclosed. The method includes measuring the optical thickness of each of the layers of the multilayer object as a function of wavelength of a light source and calculating a normalized group index of refraction dispersion curve for each layer in the multilayer structure. The measured normalized group index of refraction dispersion curves for each of the layers is then compared to a reference database of known materials and the material of each layer is identified. The physical thickness of each layer is then determined from the group index of refraction dispersion curve for the material in each layer and the measured optical thickness data. A method for determining the group index of refraction dispersion curve of a known material, and an apparatus for performing the methods are also disclosed.