Distributed Fiber Optic Sensor for Deformation
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Solution Overview
Problem
Conventional deformation sensing methods, particularly using Brillouin scattering in optical fibers, face challenges in distinguishing between strain and temperature changes due to their shared frequency shift effect, leading to inaccurate measurements and the need for multiple sensors, which is impractical for large-scale engineering projects.
Innovation Solution
A distributed optical fiber sensing apparatus with multiple strands of fibers mechanically attached to a thermal conducting tape, allowing for the subtraction of temperature and axial strain effects, enabling independent deformation measurement and conversion of strain data into curvature or displacement information over long lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single optical fiber sensor is used to measure deformation, then the device complexity is reduced, but the measurement precision deteriorates because temperature and strain effects cannot be distinguished
Solution Approach 1:
The single optical fiber is segmented into two separate sensing regions: one embedded in the structural element to measure both strain and temperature, and another placed on the surface to measure temperature only. This segmentation allows independent measurement of temperature and combined strain-temperature effects, enabling accurate deformation measurement through differential analysis.
Solution Approach 2:
The patent introduces temperature as an intermediary measurement parameter. By measuring temperature separately and using it to compensate for thermal effects in the strain measurement, the system resolves the ambiguity between temperature-induced and deformation-induced frequency shifts in Brillouin scattering measurements.
2Measurement precision
If multiple point sensors are placed across a large range to measure deformation, then the measurement precision is improved, but the device complexity and cost increase significantly
Solution Approach 1:
The optical fiber sensor system performs multiple functions simultaneously: it measures both temperature and strain distributions along the entire length of the structural element, provides spatially distributed measurements rather than discrete point measurements, and enables both qualitative and quantitative analysis of deformation patterns through a single integrated system.
Solution Approach 2:
The patent transitions from discrete point measurements in one dimension to continuous distributed measurements along the length of the structural element. The optical fiber acts as a continuous sensing line, providing measurement data at every point along its length rather than at discrete intervals, effectively adding a spatial dimension to the measurement capability.
3Reliability
If optical fiber sensors are used in harsh industrial environments, then the reliability is improved due to immunity to electrical interference, but the measurement precision deteriorates due to thermal effects
Solution Approach 1:
The patent extracts the temperature measurement function from the strain measurement process by placing a dedicated temperature-sensing fiber section in thermal contact with the structural element. This separate temperature measurement is then used to remove thermal effects from the strain measurement, isolating the deformation signal from temperature interference.
Solution Approach 2:
The system monitors changes in Brillouin frequency as a function of both strain and temperature, then uses the separately measured temperature parameter to compensate for thermal frequency shifts. By changing the measurement approach from direct strain measurement to differential measurement that accounts for temperature variations, the system maintains precision in harsh thermal environments.
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 solution allows for accurate, single-sensor monitoring of deformation across kilometers, providing clear displacement data and minimizing temperature and thermal expansion-induced errors, making it suitable for industrial applications like avalanche predictions.
Implementation Method 1
The sensors that are based on measurement of Brillouin scattered light include BOTDA (Brillouin Optical Time Domain_analysis), BOTDR (Brillouin Optical Time Domain Reflectometry), BOFDA (Brillouin Optical Frequency Domain_analysis) and correlation-based Brillouin distributed sensors.
Implementation Method 2
A distributed optical fiber sensing apparatus with multiple strands of fibers mechanically attached to a thermal conducting tape
Data Source
AI summary
A cable for distributed fiber optic sensing comprising a flexible tape, an optical fiber suitable for Brillouin scattering measurement forming at least two lengths, and at least one free end of at least one length being connectable to a reading unit, wherein at least a section of the longitudinal length of the flexible tape is situated between at least a section of the two lengths such that the two lengths are in close proximity such that a temperature gradient between the two lengths is minimized, and wherein the section of the tape and the section of lengths can flex together.