FBG Strain Sensor Bandwidth Discrimination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical fiber strain sensors face challenges in discriminating between temperature and strain responses due to wavelength shifts, requiring complex structures and expensive equipment for accurate measurements, especially in high-speed applications.
Innovation Solution
A method and sensor design utilizing an optical fiber with a uniform fiber Bragg grating (FBG) embedded in an asymmetric composite laminate structure, where strain induces compression in one portion and extension in another, allowing for strain measurement through changes in bandwidth, independent of temperature effects, using a simple photodiode for high-speed detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual wavelength technique with two superimposed FBGs is used to discriminate temperature and strain, then temperature compensation is achieved, but device complexity increases and requires two broadband sources
Solution Approach 1:
The FBG is segmented into two distinct portions with different grating periods written in the same fiber. The first portion has a first grating period and the second portion has a second grating period. When strain is applied, these portions experience different wavelength shifts, allowing temperature and strain discrimination through a single wavelength measurement, thereby avoiding the complexity of dual-wavelength systems.
Solution Approach 2:
The invention changes the grating period parameter within the same FBG structure to create portions with different periodicities. This parameter variation allows the sensor to respond differently to temperature and strain in each portion, enabling discrimination without requiring multiple separate gratings or complex optical systems.
2Measurement precision
If spectrum analyzers or tunable lasers are used to detect wavelength changes, then measurement precision is improved, but measurement speed is limited to maximum 1 kHz
Solution Approach 1:
The invention replaces the mechanical scanning system of spectrum analyzers and tunable lasers with a direct photodetector measurement system. By using the wavelength shift property of the FBG portions directly with photodetectors, the system achieves high-speed measurements without the bandwidth limitations of scanning equipment, enabling measurements well above 1 kHz.
3Measurement precision
If two FBGs mounted on opposite sides of bend surface are used for thermal compensation, then temperature response cancellation is achieved, but device complexity increases and requires fiber couplers and optical spectrum analyzers
Solution Approach 1:
The invention merges the temperature compensation function and strain measurement function into a single FBG structure. Instead of using separate FBGs mounted on opposite sides of a bend surface, the patent integrates two portions with different grating periods within one FBG, eliminating the need for fiber couplers, beam splitters, and optical spectrum analyzers while maintaining temperature compensation capability.
4Measurement precision
If commercially available Fabry-Perot filters or tunable lasers are used for wavelength detection, then measurement precision is maintained, but measurement speed is limited by scanning speed up to 1 kHz
Solution Approach 1:
The invention replaces the mechanical scanning mechanism of Fabry-Perot filters and tunable lasers with a direct optical detection approach using photodetectors. The wavelength shift is converted to a power ratio measurement between the two FBG portions, eliminating the scanning bottleneck and enabling high-speed strain monitoring suitable for blast-induced strain monitoring with frequency response in the MHz range.
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 approach enables accurate, high-speed strain measurement without the need for sophisticated equipment, as the bandwidth change directly correlates with strain, while maintaining temperature independence, allowing for efficient and cost-effective strain sensing.
Implementation Method 1
Fiber Bragg Grating (FBG) sensors have been used in temperature and strain sensor applications
Implementation Method 2
subjecting the optical fiber to a strain inducing force such that a grating period in a first portion of the FBG compresses and a grating period in a second portion of the FBG extends
Implementation Method 3
using a simple photodiode for high-speed detection
Data Source
AI summary
An optical fiber strain sensor, a method of fabricating the same, and a method of sensing strain. The method of strain sensing comprises providing an optical fiber having a fiber Bragg grating (FBG) formed therein; subjecting the optical fiber to a strain inducing force such that a grating period in a first portion of the FBG compresses and a grating period in a second portion of the FBG extends; and optically interrogating the FBG to determine a measure of a change in bandwidth of the FBG as a result of the compression and extension of the grating periods in the first and second portion respectively; whereby the measure of the change in the bandwidth is representative of the strain induced.