Fiber-Optic Sensor CTE Mismatch Cryogenic Sensitivity
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Solution Overview
Problem
Fiber-optic sensors with Fiber Bragg Gratings (FBGs) face challenges in measuring temperature changes at cryogenic temperatures due to limited refractive index change, resulting in reduced sensitivity and accuracy.
Innovation Solution
The integration of a first element with a different coefficient of thermal expansion (CTE) than the optical fiber, bonded only on either side of the FBG, induces a uniform change in strain across the FBG in response to temperature changes, enhancing sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional FBG is used for temperature measurement at cryogenic temperatures, then the sensor structure remains simple, but the sensitivity to temperature changes is reduced due to limited refractive index change
Solution Approach 1:
The patent changes the physical parameters of the system by introducing a first element with different material properties (different CTE) than the optical fiber. This parameter change allows the first element to expand or contract at a different rate than the optical fiber in response to temperature changes, thereby inducing a larger strain change across the FBG that improves temperature measurement sensitivity at cryogenic temperatures
Solution Approach 2:
The patent employs a composite structure consisting of the optical fiber and the first element bonded together at two locations. This composite arrangement allows the differential thermal expansion between the two materials to generate enhanced strain on the FBG, improving measurement sensitivity while maintaining structural integrity
2Measurement precision
If the first element is bonded along the entire length of the first part, then structural stability is improved, but non-uniform strain distribution occurs across the FBG due to irregularities or defects in the element or bonding interface
Solution Approach 1:
The patent segments the bonding interface into three distinct regions: a first location, a first part (where no bonding occurs), and a second location. By placing the FBG within the first part and avoiding bonding in this region, the patent ensures that strain is uniformly distributed across the FBG while still maintaining structural stability through bonding at the end locations
Solution Approach 2:
The patent applies different bonding characteristics to different regions of the optical fiber. Specifically, the first element is bonded to the optical fiber at the first and second locations but deliberately left unbonded along the first part where the FBG is situated. This local differentiation in bonding quality ensures uniform strain distribution across the FBG while maintaining overall structural integrity
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 configuration significantly improves the sensitivity and accuracy of temperature measurements by increasing the strain across the FBG, particularly at cryogenic temperatures where traditional FBGs are less effective.
Implementation Method 1
The first element, in having a first CTE which is different to the CTE of the optical fiber, thereby expands or contracts in response to a given temperature change at a different rate to the optical fiber
Data Source
AI summary
A fiber-optic sensor including an optical fiber comprising a first Fiber Bragg Grating (FBG) arranged along a first part of the optical fiber; and a first element disposed on an outer surface of the optical fiber, the first element having a first coefficient of thermal expansion (CTE) different to a CTE of the optical fiber, and being configured to induce a change in strain across the FBG in response to a change in temperature of the fiber-optic sensor in the region of the first FBG, the first element bonded to the optical fiber at two first locations that are separated, along the optical fiber from one another by the first part and unbonded to the optical fiber along the first part.