Fiber Optic Level Sensor with Strain Layer for Cryogenic Tanks
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Solution Overview
Problem
Existing technologies face challenges in accurately measuring liquid levels, particularly in cryogenic environments and under mechanical stresses, such as those encountered in launch vehicles, due to limitations in temperature tolerance and mechanical integrity.
Innovation Solution
A fiber optic level sensor system utilizing Bragg gratings with strain layers, which induce strain based on temperature changes, allowing for accurate liquid level detection by shifting reflection spectra, and is immune to electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitive, diode-based, or differential pressure sensors are used to measure liquid levels, then the measurement can be performed under normal conditions, but the sensors fail to operate reliably in cryogenic temperatures and under significant mechanical stresses
Solution Approach 1:
The patent replaces traditional mechanical/electrical sensors (capacitive, diode-based, differential pressure sensors) with an optical fiber sensor system that uses Bragg gratings. This substitution eliminates the need for electrical components that are sensitive to temperature and mechanical stress, allowing the sensor to operate reliably in cryogenic conditions and under launch vehicle mechanical loads.
Solution Approach 2:
The patent utilizes changes in the physical parameters of the optical fiber (specifically the Bragg wavelength) in response to temperature and strain. The Bragg grating's reflection wavelength shifts according to the strain applied to the fiber, which is caused by differential thermal contraction between the strain layer and fiber core. This parameter change provides a measurable signal that is immune to electromagnetic interference and suitable for harsh environments.
2Measurement precision
If electrical sensors are used in cryogenic environments, then liquid level measurement is possible, but the sensors are affected by extreme temperatures and electromagnetic interference
Solution Approach 1:
The patent replaces electrical sensing mechanisms with an optical-based sensing system using fiber optic Bragg gratings. This substitution eliminates susceptibility to electromagnetic interference entirely, as optical fibers are dielectric materials that do not conduct electricity. The measurement precision is maintained through the wavelength-shift encoding of the sensing signal.
Solution Approach 2:
The patent introduces a strain layer as an intermediary element between the optical fiber and the environment. This strain layer has a coefficient of thermal expansion matched to the fiber core material, creating differential strain when temperature changes occur. This intermediary mechanism converts temperature changes into measurable strain-induced wavelength shifts while isolating the fiber from direct thermal and electromagnetic environmental effects.
3Adaptability or versatility
If conventional sensors are subjected to significant mechanical stresses during launch, then they can be used in launch vehicles, but their mechanical integrity and measurement accuracy deteriorate
Solution Approach 1:
The patent replaces mechanical/electrical sensing components with an optical fiber sensor that has no moving parts and is inherently resistant to mechanical stress. The fiber optic sensor can withstand the high-g forces and vibrations of launch vehicle operation without the mechanical failure modes that plague traditional sensors. The Bragg grating structure is embedded within the fiber, providing structural integrity during mechanical loading.
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 liquid level measurement in cryogenic conditions and harsh environments, including launch vehicles, with improved mechanical resilience and reduced risk of electrical interference.
Implementation Method 1
Each strain layer is configured to induce a strain on the fiber at a respective Bragg grating based on a temperature of the strain layer
Implementation Method 2
Each sensing region of the plurality of sensing regions includes a Bragg grating configured to generate a reflection spectrum responsive to incident light
Data Source
AI summary
A level sensor assembly includes a fiber that is configured to be at least partially disposed in a tank and to be coupled to a light source and to a light detector. The fiber includes a plurality of sensing regions spaced apart along a length of the fiber. Each sensing region of the plurality of sensing regions includes a Bragg grating configured to generate a reflection spectrum responsive to incident light and a strain layer around the Bragg grating. Each strain layer is configured to induce a strain on the fiber at a respective Bragg grating based on a temperature of the strain layer such that shifts in the reflection spectra of the Bragg gratings indicate which of the sensing regions are submerged in a liquid.