Temperature-compensated Fiber Optic Strain Gauge
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Solution Overview
Problem
Existing fiber optic strain gauges face challenges in accurately measuring strain while accounting for temperature influences and ensuring reliability, particularly in environments where conventional electrical gauges are unsuitable due to electromagnetic interference, moisture exposure, and vibration.
Innovation Solution
A temperature-compensated fiber optic strain gauge design featuring a mount with a void separating sections, pre-strained first FBG for strain measurement and a second FBG for temperature compensation, along with removable bridging portions and waterproof glue to prevent moisture and oscillation, providing a failure-proof feature by detecting wavelength shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single FBG is used to measure strain, then the strain measurement is simple, but temperature influences cannot be eliminated
Solution Approach 1:
The single strain measurement function is segmented into two specialized FBGs: one dedicated to strain sensing and another to temperature sensing. This segmentation allows each sensor to optimize its function while eliminating cross-interference, resolving the contradiction between simple structure and accurate measurement.
Solution Approach 2:
The dual-FBG configuration provides multi-functionality by simultaneously measuring both strain and temperature using two separate sensors within a single gauge assembly. This universal approach enables independent measurement of both parameters, eliminating temperature influence on strain measurements.
2Reliability
If the FBG is pre-strained beyond operational range, then failure detection capability is improved, but the FBG may break under normal conditions
Solution Approach 1:
Instead of designing the FBG to withstand maximum operational strain directly, the invention inverts the approach by pre-straining the FBG beyond the operational range during installation. This creates a safety margin where normal operational strains cannot cause failure, while any return to the original un-prestrained wavelength state indicates abnormal failure conditions.
Solution Approach 2:
The FBG is pre-strained during the installation phase before actual operational use. This preliminary action establishes a known reference state and creates a safety buffer, allowing the system to detect failures through wavelength shifts while protecting the FBG from breaking under normal operational conditions.
3Adaptability or versatility
If bridging portions are removed after mounting, then the mount adapts to the host structure, but the installation process becomes more complex
Solution Approach 1:
The bridging portions are pre-installed during manufacturing to provide temporary structural support and maintain alignment. This preliminary action simplifies the initial assembly process, while the removal step afterward enables the mount to adapt to the host structure's contours, achieving both ease of assembly and adaptability.
Solution Approach 2:
The bridging portions serve as temporary sacrificial elements during installation that are discarded after serving their purpose. This allows the mount to achieve proper adaptation to the host structure while the discarded bridges having facilitated the installation process, effectively trading temporary complexity for long-term adaptability.
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 design enhances accuracy by eliminating temperature influences on strain measurements, ensures reliability through failure detection, and offers immunity to electromagnetic interference and vibration, making it suitable for safety-critical applications like railways.
Implementation Method 1
FBGs are structures recorded within a core of an optical fiber. The structure of an FBG causes light of a specific wavelength, known as the Bragg wavelength, to be reflected within the fiber.
Implementation Method 2
Both the pitch (A) and effective refractive index (neff) of the structure and consequently, the Bragg wavelength (given by 2neffA), are sensitive to strain and temperature in a highly repetitive manner.
Implementation Method 3
the first FBG is covered by a waterproof resilient glue such as silicone glue to protect the first FBG from moisture and to dampen the first FBG to avoid sideways oscillations
Data Source
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AI summary
A temperature-compensated fibre optic strain gauge (10) for measuring strain of a host structure, the strain gauge (10) comprising: a mount (20) to be operatively attached to the host structure, the mount (20) having a void (19) separating a first section (17) of the mount (20) from a second section (18) of the mount (20); a first fiber Bragg grating (FBG) (30) recorded within a core of an optical fiber (11) to measure strain and temperature, the first FBG (30) being located transverse to the void (19) and a first end portion of the first FBG (30) is operatively attached to the first section (17) of the mount (20) and a second end portion of the first FBG (30) is operatively attached to the second section (18) of the mount (20), the end portions of the first FBG (30) being pre-strained by an amount larger than a predetermined operational range of the first FBG (30); a second fiber Bragg grating (FBG) (40) recorded within the core of the optical fiber (11) to measure temperature, the temperature measurement of the second FBG (40) being used to eliminate temperature as an influence on the strain measurement of the first FBG (30), a first end portion of the second FBG (40) is operatively attached to the first FBG (30) and a second end portion of the second FBG (40) is operatively attached to the mount (20) so that the second FBG (40) is free from strain; and removable bridging portions (24) adjacent to the void (19) to connect the first section (17) to the second section (18) of the mount (20), the bridging portions (24) being removed after the mount (20) is operatively attached to the host structure; wherein a right-side failure proof feature is provided by detecting whether a reflection wavelength reverts to an original Bragg wavelength of the first FBG (40) to indicate whether the first FBG (40) has broken.