Sapphire Fiber Bragg Grating Sensor for High-Temperature Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fiber Bragg grating sensors face limitations in measuring multiple parameters like temperature and strain at high temperatures due to erasure of index modulation, material deformation, and difficulty in distinguishing between temperature and stress effects, especially in silica optical fibers which become brittle and non-functional above 1200°C.
Innovation Solution
A high-temperature sensor system using sapphire optical fibers with femtosecond-pulse-written Bragg gratings that utilize blackbody radiation as an optical source, allowing for simultaneous measurement of temperature and strain by decoupling wavelength shifts through enhanced signal-to-noise ratios and evanescent coupling, eliminating the need for external optical sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If UV-induced fiber Bragg gratings are used in silica optical fibers, then the sensor can measure temperature and strain at room temperature, but the sensor becomes non-functional above 1200°C due to erasure of index modulation and material deformation
Solution Approach 1:
The patent changes the material parameter from silica glass to sapphire crystal, which has a fundamentally different thermal stability parameter. Sapphire maintains its structural integrity and optical properties at temperatures exceeding 1200°C where silica deforms and erases the grating index modulation, thus resolving the temperature limit contradiction.
Solution Approach 2:
The patent uses sapphire, a composite crystalline material (Al2O3), to replace silica glass. This material substitution provides both mechanical strength and optical transparency at high temperatures, enabling the Bragg grating to maintain its index modulation and sensing capability beyond 1200°C.
2Device complexity
If a single fiber Bragg grating is used to measure both temperature and strain, then the sensing configuration is simplified, but it becomes difficult to discriminate between temperature and stress effects
Solution Approach 1:
The patent introduces a spectral dimension by utilizing multiple reflection orders (first order, second order, third order) of the Bragg grating. Each reflection order provides an independent measurement channel with different sensitivities to temperature and strain, enabling mathematical decoupling of these two parameters while maintaining a single physical sensor element.
Solution Approach 2:
The single sapphire fiber Bragg grating performs multiple functions simultaneously: it acts as both a temperature sensor and a strain sensor through its multiple reflection orders. The first order provides one measurement channel while the second and third orders provide additional independent channels, allowing the same physical structure to deliver multi-parameter sensing capability.
3Measurement precision
If external optical sources are used to probe the fiber Bragg grating, then the spectral response can be measured, but the device complexity increases and the sensing system becomes less suitable for harsh environments
Solution Approach 1:
The sapphire fiber Bragg grating sensor system uses itself as the optical source. The high-temperature environment that would normally degrade the sensor instead generates blackbody radiation that serves as the probing light source. This self-service approach eliminates the need for separate external optical sources, reducing device complexity while enabling operation in harsh high-temperature environments.
Solution Approach 2:
The patent converts the harmful high-temperature environment into a beneficial resource. The blackbody radiation emitted by the hot environment, which would normally be considered thermal noise or interference, is instead utilized as the optical probe to measure the Bragg grating's spectral response. This transforms the adverse thermal condition into the measurement mechanism itself.
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 reliable, high-temperature measurement of multiple parameters with improved signal quality and sensitivity, maintaining functionality beyond the glass transition temperature of silica, and supporting distributed sensing arrays.
Implementation Method 1
utilize blackbody radiation as an optical source
Implementation Method 2
Fiber Bragg grating sensors have attracted considerable attention in sensing temperature and strain on an optical fiber due to the variation in the spectral response of the grating
Implementation Method 3
femtosecond-pulse-written Bragg gratings
Data Source
AI summary
A dual parameter sensor for sensing temperature and mechanical or chemical or related information is disclosed. The sensor is formed of an optical waveguide suitable for use in-situ in a high temperature environment having a Bragg grating written into a core region thereof with short-pulsed electromagnetic radiation. By noting the thermal Black Body radiation level above 650° C., wavelength shifts due to temperature can be decoupled from wavelength shifts due to the other parameter being sensed. Advantageously the thermal radiation can be used as an optical source to probe the Bragg grating, considerably simplifying the interrogating apparatus, removing the need for an extrinsic optical source to probe the sensor.