Fiber Bragg Grating Sensor for Tunnel Convergence Measurement
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Solution Overview
Problem
Conventional methods for measuring tunnel convergence in subway tunnels, such as electric resistance gauges, are prone to low precision and interference from electromagnetic waves, making real-time measurements during subway operation challenging.
Innovation Solution
An apparatus and method utilizing a fiber Bragg grating sensor installed on a tunnel, featuring a main body, rotator, optical fiber, and bob, which measures angular and gravitational acceleration displacement through wavelength displacement detection, allowing for precise measurements unaffected by electromagnetic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electric resistance gauge is used for tunnel convergence measurement, then the measurement can be performed, but the precision is low and electromagnetic wave interference occurs
Solution Approach 1:
The patent replaces the electrical measurement system (electric resistance gauge) with an optical measurement system (fiber Bragg grating sensor). The FBG sensor uses optical fiber to detect wavelength changes caused by mechanical deformation, eliminating susceptibility to electromagnetic wave interference while maintaining high measurement precision for tunnel convergence
Solution Approach 2:
The patent introduces optical fiber as an intermediary medium between the measurement target and the detection system. The optical fiber transmits light signals that are modulated by the mechanical deformation of the tunnel, providing an indirect measurement method that is immune to electromagnetic interference
2Productivity
If electric resistance gauge is used for tunnel convergence measurement, then the measurement can be performed, but real-time measurement during subway operation is difficult
Solution Approach 1:
The optical-based FBG sensor system enables real-time measurement during subway operation by replacing the electrical system. The optical sensors can operate in the harsh electromagnetic environment created by subway operations, providing continuous monitoring of tunnel convergence without interruption
Solution Approach 2:
The patent utilizes the change in Bragg wavelength of the fiber grating as a direct measure of strain. This parameter change approach allows for continuous, real-time detection of tunnel deformation as the subway operates, with the wavelength shift providing immediate feedback on convergence conditions
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 precise, real-time measurement of tunnel convergence regardless of subway operation, with improved accuracy and reduced space requirements due to the fiber Bragg grating sensor's resistance to electromagnetic interference and ability to connect multiple sensors in series.
Implementation Method 1
a fiber Bragg grating sensor that is installed on the optical fiber between the fixture and the rotator
Data Source
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AI summary
Disclosed is an apparatus for measuring convergence using a fiber Bragg grating sensor measuring slight deformation, capable of measuring the convergence such as the inclination or the gravitational acceleration of a measurement target including a bridge or a tunnel by measuring the deformation of the fiber Bragg grating sensor when the measurement target is inclined or vibrated, as well as a measurement method using the apparatus. The apparatus includes a main body that is installed on a measurement target; a fixture that is fixedly installed at the front of the main body; a rotator that is horizontally installed apart from the fixture at a predetermined distance and is rotatably installed in the main body using a bearing; an optical fiber that is adhered to upper outer surfaces of the fixture and the rotator so as to maintain a horizontally tensioned state and has optical terminals installed on opposite ends thereof; a fiber Bragg grating sensor that is installed on the optical fiber between the fixture and the rotator; and a bob that is vertically connected with a lower portion of the rotator by a support having a predetermined length. The apparatus is installed on the measurement target after setting a reference value and then calculates a quantity of displacement caused by variation of the ground, so that values of angular displacement and gravitational acceleration displacement are measured.