Optical Interferometric Sensor Thermal Stability
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Solution Overview
Problem
Fabry-Perot-style optical sensors face issues due to thermal expansion and contraction mismatches between materials with different coefficients of thermal expansion (CTE), leading to thermal stress, deformation, and measurement errors.
Innovation Solution
A thermally stable optical interferometric sensor assembly is designed with a diaphragm and support structure made from materials with matched CTE, using low-CTE glass and CTE-matched metallic components, and incorporating a reference optical interferometer to compensate for temperature effects, along with a retaining ring to apply preload and adjust the interferometric gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallic supporting structures with high CTE are used to support optical diaphragms, then mechanical strength and structural stability are improved, but thermal stress and strain increase due to CTE mismatch, causing deformation and measurement errors
Solution Approach 1:
The patent changes the material parameter (CTE) of the supporting structure by using Invar alloy instead of traditional stainless steel. Invar has a CTE of approximately 1.2×10^-6/°C, which closely matches the CTE of optical glass (0.5-1.0×10^-6/°C), thereby reducing thermal stress and maintaining measurement accuracy across temperature variations.
Solution Approach 2:
The patent employs composite material construction where Invar alloy components are combined with optical glass elements. This composite approach allows the structural components to provide mechanical strength while the matched CTE properties minimize thermal deformation, resolving the contradiction between strength and measurement precision.
2Ease of manufacture
If adhesive joints are used to connect optical glass and metallic structures, then assembly ease is improved, but the adhesive joints become high strain regions that fracture under thermal stress
Solution Approach 1:
The patent eliminates the adhesive joint by using interference fits and mechanical connection methods. The Invar supporting structures are designed with precise dimensional tolerances that create interference fits with optical components, removing the weak adhesive interface that would otherwise concentrate thermal stress and fail.
Solution Approach 2:
The patent introduces precision-machined mechanical interfaces as intermediaries between optical glass and metallic structures. These interfaces use controlled interference fits and mechanical retention methods that distribute thermal stress evenly, replacing the problematic adhesive mediator with a more reliable mechanical connection.
3Ease of manufacture
If traditional stainless steel supporting structures are used, then manufacturing cost is reduced, but thermal expansion causes cracking and fracturing at material interfaces
Solution Approach 1:
The patent changes the material selection parameter from conventional stainless steel to Invar alloy. This material substitution addresses the fundamental CTE mismatch problem, preventing thermal stress-induced cracking and fracturing at material interfaces while maintaining structural integrity under thermal cycling conditions.
4Measurement precision
If CTE-matched materials are used to minimize thermal stress, then measurement accuracy is improved, but material selection and manufacturing complexity increase
Solution Approach 1:
The patent changes the material parameter to Invar alloy, which has well-established manufacturing processes and available commercial stock. While the material is more specialized than stainless steel, its predictable properties and availability actually simplify the overall design and manufacturing process by eliminating the need for complex thermal compensation mechanisms.
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
The solution minimizes thermal stress and strain, enhances measurement accuracy by reducing false readings, and maintains dimensional stability under varying temperatures, effectively addressing the limitations of existing sensors.
Implementation Method 1
a sensing optical interferometer having a first optical cavity in communication with at least a portion of the diaphragm and the diaphragm support structure. The sensing optical interferometer is configured to interact with received first light to produce a measurement light signal corresponding to the applied stimulus.
Implementation Method 2
a reference optical interferometer having a second optical cavity in communication with the diaphragm support structure, the reference optical interferometer is configured to interact with received second light to produce a reference light signal.
Implementation Method 3
The sensor assembly includes a housing in communication with the diaphragm and the diaphragm support structure, and configured to reduce a thermal expansion mismatch in the sensor assembly.
Data Source
AI summary
Certain example implementations of the disclosed technology include an optical-interferometer sensor assembly for measuring pressure or acceleration. The sensor assembly includes a diaphragm configured to deflect responsive to an applied stimulus, a diaphragm support structure in communication with the diaphragm, a sensing optical interferometer having a first optical cavity in communication with at least a portion of the diaphragm and the diaphragm support structure, and a reference optical interferometer having a second optical cavity in communication with the diaphragm support structure. The sensor assembly can include a sensing optical fiber in communication with the sensing optical interferometer and a reference optical fiber in communication with the reference optical interferometer. The sensor assembly can include a housing in communication with the diaphragm and the diaphragm support structure, and configured to reduce a thermal expansion mismatch in the sensor assembly.