Multi-Wavelength Fiber Bragg Grating Sensor for Strain Localization
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Solution Overview
Problem
Existing sensor systems, such as those described in GB 2485808A, are unable to localize 'hotspots' of environmental changes like leaks or cracks within a monitored region using optical fibers, as they lack the capability to determine the precise position of temperature or strain variations.
Innovation Solution
A sensor system employing a source of electromagnetic radiation emitting pulses at multiple wavelengths and an optical fiber with multiple fibre Bragg gratings, allowing for simultaneous interrogation of multiple gratings and spatially resolved intensity profiling to detect and localize changes in environmental conditions like temperature or strain, without requiring complex GHz optoelectronics or ADCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single long fibre Bragg grating is used to monitor temperature or strain over a long region, then the monitoring coverage is improved, but the ability to localize specific hotspots is lost
Solution Approach 1:
The system segments the monitoring region by placing multiple discrete fibre Bragg gratings at specific locations along the optical fibre. Each grating acts as an independent sensor that can be individually localized. The segmentation is achieved by writing multiple gratings with different Bragg wavelengths at different positions along the fibre, allowing spatial resolution of temperature or strain changes at specific locations rather than providing only an integrated average over the entire fibre length.
2Measurement precision
If multiple fibre Bragg gratings are used to enable localization, then the localization capability is improved, but the device complexity increases
Solution Approach 1:
The system uses periodic pulsed optical excitation at multiple wavelengths to interrogate the fibre Bragg gratings sequentially in time. By sending pulses at different wavelengths at different times and detecting the reflected signals in temporal sequence, the system achieves spectral-spatial resolution without requiring complex simultaneous multi-wavelength detection electronics. The pulse timing allows differentiation between gratings at different positions based on their reflection arrival times.
Solution Approach 2:
The system exploits changes in the Bragg wavelength of each grating in response to environmental conditions (temperature or strain). Each grating's reflected wavelength shifts according to the local environmental condition at its position. By monitoring these wavelength shifts and correlating them with the known positions of the gratings, the system achieves both measurement and localization without complex additional hardware.
3Productivity
If long pulse duration is used to simultaneously interrogate multiple gratings, then the interrogation efficiency is improved, but the spatial resolution deteriorates
Solution Approach 1:
The system performs preliminary action by sending optical pulses through the fibre in a controlled sequence at different wavelengths before detection. The pulse duration is deliberately made longer than the time required for light to travel between gratings, allowing each pulse to interact with multiple gratings simultaneously. The spatial resolution is maintained through temporal gating during detection, where signals arriving at different times (corresponding to different grating positions) are separated and assigned to their respective locations.
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 the detection and localization of temperature or strain changes with cm-scale precision on structures of 10s to 100s of meters, effectively identifying small events like leaks or cracks without the need for expensive high-frequency electronics, and can operate on larger structures with minimal spatial positioning requirements.
Implementation Method 1
A source of pulses of electromagnetic radiation is provided. The source is configured to emit electromagnetic radiation at a plurality of different wavelengths.
Implementation Method 2
The optical fibre includes one or more fibre Bragg gratings having a reflectance and/or transmittance which varies in dependence on the at least one environmental condition.
Implementation Method 3
The detection unit is configured for detecting electromagnetic radiation at the plurality of different wavelengths. In this way, a spectral response can be determined for different spatial regions along the optical fibre.
Data Source
AI summary
A sensor system for detection and localisation of changes in or values for at least one environmental condition includes a source of pulses of electromagnetic radiation, wherein the source is configured to emit electromagnetic radiation at a plurality of different wavelengths, an optical fibre in optical communication with the source of pulses, wherein the optical fibre includes a fibre Bragg grating having a reflectance and/or transmittance which varies in dependence on the at least one environmental condition, and a detection unit for detecting electromagnetic radiation which has been reflected or transmitted by the fibre Bragg gratings, wherein the detection unit is configured for detecting electromagnetic radiation at the plurality of wavelengths, such that a spectral response can be determined for different spatial regions along the optical fibre, wherein a change in or value for the environmental condition at a spatial region may be determined by monitoring the respective spectral response.