Overlapped Chirped Fiber Bragg Grating Strain Sensor
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Solution Overview
Problem
Optical fiber strain sensing technologies face challenges with Rayleigh scatter's weak signal and delta-correlated broadband response, and FBG sensors' narrow frequency response and manufacturing difficulties, which affect accuracy and robustness in strain measurements.
Innovation Solution
An optical sensor with overlapping chirped frequency fiber Bragg gratings that scatter light at multiple frequencies, allowing for a broadband response and direct measurement of delay, enabling robust strain sensing with improved signal strength and manufacturing ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Rayleigh scatter is used for strain sensing, then the sensor is inexpensive and easy to manufacture, but the signal strength is weak and the signal to noise level is low
Solution Approach 1:
The patent combines Rayleigh scatter with Fiber Bragg Gratings (FBG) to create a composite sensing mechanism. The FBG provides strong reflection signals while Rayleigh scatter provides distributed sensing capability, achieving both ease of manufacture and high signal strength through the composite approach
2Reliability
If Fiber Bragg Gratings are used for strain sensing, then the signal strength is high, but the frequency response is narrow and manufacturing is difficult
Solution Approach 1:
The patent segments the FBG structure into multiple overlapping chirped gratings with different center frequencies. This segmentation allows the system to maintain high signal strength from FBG while expanding the frequency response and simplifying manufacturing by using standard FBG writing processes
3Measurement precision
If Rayleigh scatter is used, then the broadband response allows direct measure of delay, but the delta correlated response requires extensive processing
Solution Approach 1:
The patent extracts the broadband delay measurement capability from Rayleigh scatter and combines it with the periodic structure of FBG. This extraction allows the system to maintain direct delay measurement while the periodic FBG structure simplifies the correlation processing by providing reference frequencies
4Reliability
If overlapping chirped FBG are used, then the broadband response improves robustness, but the manufacturing precision requirements increase
Solution Approach 1:
The patent changes the grating parameters (chirp rate, center frequency, overlap distance) to optimize the balance between broadband response and manufacturing precision. By carefully selecting these parameters, the system achieves robust broadband sensing while maintaining compatibility with standard FBG manufacturing tolerances
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
The solution provides a robust and accurate strain measurement system that simplifies data processing, maintains signal strength, and avoids manufacturing defects, making it suitable for aggressive sensing environments.
Implementation Method 1
an optical fiber inscribed with a repeated refraction pattern including overlapping chirped frequency fiber Bragg gratings such that light scattered from a location on the optical fiber is scattered at multiple frequencies in a range of frequencies
Data Source
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Figure 3~4A
Figure 4B
AI summary
An optical sensor includes an optical fiber inscribed with a repeated refraction pattern such that light scattered from a location on the optical fiber is scattered at multiple frequencies in a range of frequencies. The inscribed patterns overlap at every measurement point along at least a portion of the length of the sensor. An optical sensing system including control circuitry coupled to the optical fiber detects measurement scatter data from the optical fiber over the range of frequencies, determines a change in the detected measurement scatter data over the range of frequencies, and extracts a parameter describing a state of the optical fiber from the determined change in the detected measurement scatter data. The sensor may be made by inscribing a first light refracting pattern on the optical fiber at every measurement point along at least a portion of the length of the sensor and inscribing a second light refracting pattern on the optical fiber that overlaps the first inscribed light refracting pattern at every measurement point along at least that portion of the length of the sensor.