Bragg Grating Fiber Sensor for Shock Front Detection
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Solution Overview
Problem
Current fiber optic sensors with Bragg gratings face challenges in precisely locating the position of a shock front within an optical fiber, are sensitive to electromagnetic interference, and have limited temporal resolution for measuring rapid physical phenomena, making them inadequate for detecting the passage and speed of high-speed events like detonation waves.
Innovation Solution
A device comprising a short, constant-pitch optical fiber with multiple Bragg gratings, a broad-spectrum laser source, and a photoelectric detector to measure the overall flux of reflected radiation, allowing for precise temporal analysis of the destruction of gratings and thus the passage of physical phenomena, with improved sensitivity to low stress pressures and reduced bulk size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional electrical sensors are used to detect pressure waves, then temporal information and wave speed can be measured, but the sensor is sensitive to stress pressure amplitude, requires electrical power, and is susceptible to electromagnetic interference
Solution Approach 1:
The patent replaces electrical sensors with an optical fiber-based sensing system. The optical fiber sensor uses light propagation and Bragg grating reflection principles to detect pressure waves, eliminating the need for electrical power and making the system immune to electromagnetic interference while maintaining temporal measurement precision
Solution Approach 2:
The patent changes the measurement parameter from electrical signals to optical parameters (wavelength shifts of reflected light). By monitoring the shift in Bragg wavelength caused by stress-induced fiber deformation, the system achieves precise temporal measurement without electrical components
2Object-affected harmful factors
If fiber optic sensors with Bragg gratings are used to measure shock front position, then electromagnetic interference is reduced, but the spatial location precision remains difficult to assess with uncertainty greater than 1 mm
Solution Approach 1:
The patent divides a single long Bragg grating into multiple short, discrete Bragg gratings along the optical fiber. Each short grating acts as an independent detection point, allowing precise localization of the shock front by identifying which specific grating is affected, thereby reducing spatial uncertainty from meter-scale to millimeter-scale precision
Solution Approach 2:
The patent transitions from measuring only wavelength shifts to also utilizing the spatial distribution dimension. By arranging multiple short gratings at known positions along the fiber and monitoring which grating experiences wavelength shift, the system adds spatial localization capability in the longitudinal dimension
3Length of stationary object
If long Bragg gratings are used to measure continuous phenomenon evolution, then the measurement coverage is improved, but the gratings are difficult to manufacture longer than one meter and require chirped designs
Solution Approach 1:
The patent replaces a single long grating with multiple short gratings distributed along the fiber. Each short grating is easier to manufacture with standard techniques, and their collective arrangement provides the desired long measurement coverage without requiring complex chirped designs or ultra-long single gratings
4Measurement precision
If optical fiber sensors are embedded in explosive material for concentric attack, then velocity measurement is improved, but the implementation is delicate and the fiber is too rigid and fragile
Solution Approach 1:
The patent uses the flexible and thin nature of optical fiber to create a sensor that can be embedded in explosive material. The fiber's flexibility allows it to conform to the material geometry, while its thin profile minimizes structural interference. The distributed short grating design provides multiple measurement points without requiring perfect concentric embedding
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 enhances the temporal resolution and sensitivity of fiber optic sensors, enabling precise location of shock fronts and measurement of high-speed events with reduced electromagnetic interference and improved mechanical strength, while being capable of operating under asymmetrical stress conditions.
Implementation Method 1
each Bragg grating being configured to reflect a narrow band of specific wavelengths associated therewith
Implementation Method 2
a photoelectric detector configured to measure at the output of the optical circulator, as a function of time, an overall flux of all the reflected radiation captured by the photoelectric detector
Implementation Method 3
an optical circulator configured to transmit the laser radiation from the at least one laser source to the first end of the optical fiber and capture the reflected radiation returned by the Bragg gratings
Implementation Method 4
a device for characterizing a physical phenomenon producing pressure on a fibre, which may lead, in certain cases, to its ablation
Data Source
Figure 1~3
Figure 4~5
AI summary
The present application relates to a device for characterizing a physical phenomenon comprising at least one optical fibre (4) with short Bragg gratings having constant spacing, at least one broad spectrum laser lighting source (1), an optical circulator (2) and a photoelectric detector (3) which is configured to measure a global flux of all the reflected radiation picked up at the output of the optical circulator (2), as a function of time. It also relates to a method of characterization in which the global flux of the signal is measured in such a way that a drop in the signal corresponds to the destruction of a Bragg grating.