High-Temperature Pressure Sensor Thermal Expansion Matching
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Solution Overview
Problem
Conventional fiber-optic pressure sensors face challenges in high-temperature environments due to packaging limitations, thermal expansion issues, and noise generation, which affect measurement accuracy and reliability, especially in harsh conditions like those found in gas turbines and internal combustion engines.
Innovation Solution
A Fabry-Perot interferometer design with a glass die and metal layers, bonded to a ferrule with a glass ceramic material to match thermal expansion, and an optical fiber aligned closely with the die, minimizing thermal stress and noise, and using a miniaturized structure for improved stability and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packaging materials are used in high-temperature environments, then the sensor can be manufactured with standard materials, but the packaging materials undergo oxidation and corrosion at temperatures exceeding 350°C, limiting reliable functioning
Solution Approach 1:
The patent employs a composite packaging structure consisting of a metal canister (invar or kovar) bonded to a ceramic disc (alumina or zirconia) with metal caps. This composite design combines the strength and thermal expansion properties of metal with the high-temperature stability and oxidation resistance of ceramic, enabling reliable operation at temperatures exceeding 350°C while preventing oxidation and corrosion of the internal components
Solution Approach 2:
The patent carefully selects materials with matched coefficients of thermal expansion: invar or kovar for the metal canister and alumina or zirconia for the ceramic disc. This thermal expansion matching prevents differential expansion stresses during temperature cycling, maintaining packaging integrity and preventing delamination or cracking in high-temperature environments
2Measurement precision
If conventional interferometer packaging is used, then the device can be manufactured with standard components, but variations in coefficient of thermal expansion cause stress state changes in optical cavities, leading to measurement uncertainty
Solution Approach 1:
The patent uses a composite structure of metal canister (invar/kovar) and ceramic disc (alumina/zirconia) with matched thermal expansion coefficients. This composite design maintains dimensional stability of the optical cavity under thermal stress, preventing stress-induced refractive index changes and cavity deformation that would otherwise cause measurement drift in high-temperature environments
Solution Approach 2:
The patent changes the material parameters (coefficient of thermal expansion, modulus of elasticity) of the packaging components to match each other. By selecting invar or kovar (low expansion metals) and alumina or zirconia (low expansion ceramics), the patent minimizes thermal stress on the optical cavity, maintaining measurement precision across wide temperature ranges
3Measurement precision
If fiber optic cable is positioned away from the die, then assembly is easier, but relative motion between fiber and cavity generates additional spectral signals and noise
Solution Approach 1:
The patent merges the fiber positioning function with the packaging structure by integrating the fiber into a recessed cavity in the ceramic disc, which is itself bonded to the metal canister. This integrated design mechanically constrains the fiber relative to the optical cavity, eliminating relative motion and noise-generating spectral signals while maintaining ease of assembly through the standardized packaging structure
Solution Approach 2:
The patent uses a thin metal layer (gold or other conductive material) deposited on the fiber and canister surface, which acts as a flexible yet stable interface. This thin metal layer allows for thermal expansion compatibility while maintaining precise fiber-to-cavity alignment, preventing relative motion that would generate noise without requiring rigid, difficult-to-assemble fixtures
4Reliability
If metal layers are used on the die and ferrule, then thermal expansion matching is achieved, but diffusion of metals at high temperatures creates brittle intermetallic compounds and failure
Solution Approach 1:
The patent introduces a diffusion barrier layer (such as nickel, palladium, or other refractory metal) between the metal canister and the ceramic disc, and between metal layers on the fiber and ferrule. This intermediary layer prevents direct contact between reactive metals at high temperatures, blocking diffusion and intermetallic compound formation while maintaining thermal expansion matching and mechanical bonding
Solution Approach 2:
The patent employs a multi-layer composite structure: metal canister (invar/kovar) + diffusion barrier layer + ceramic disc (alumina/zirconia) + metal cap. This composite design adds a thermal and chemical buffer zone that protects against metal diffusion and intermetallic formation during peak temperature exposure, while maintaining the overall structural integrity and thermal expansion compatibility of the packaging
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 enables reliable, high-sensitivity pressure measurements in harsh environments with high temperature stability, reduced noise, and passive data collection, allowing for accurate pressure monitoring in extreme conditions.
Implementation Method 1
One example of such optical devices is a Fabry-Perot interferometer, which is a fiber optic sensor sensitive to pressure or stress in a manner that causes a beam of light to be reflectively modulated in response to changes in pressure or stress on the sensor
Implementation Method 2
a ferrule having a second metal layer with a second orifice, the ferrule being bonded to the glass die with the first orifice aligned with the second orifice
Data Source
AI summary
A method for assembling a Fabry-Perot interferometer includes depositing a first metal layer on an end portion of a ferrule, depositing a second metal layer on a back portion of a die, placing the first metal layer and the second metal layer in contact with each other with respective first and second orifices aligned with respect to each other, and bonding the ferrule to the die by thermo compression. The resulting interferometer includes a glass die with a cavity, a silicon diaphragm disposed over the opening of the cavity and bonded to the glass die, a ferrule bonded to the glass die by thermo compression with the first and second orifices being aligned to each other, and an optical fiber inserted through the other end of the ferrule in direct contact to a back portion of the die and aligned with the first orifice.