Fiber Optic Fuel Sensor with Photonic Membrane
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Solution Overview
Problem
Existing liquid-level sensors in fuel tanks, particularly in aircraft, face challenges such as weight addition, electromagnetic interference, lightning issues, and maintenance requirements due to electrical wiring, and are prone to failures from fuel residue and temperature variations with fiber optic sensors.
Innovation Solution
A fiber optic fuel sensor system using a hermetically sealed package with a direct band gap semiconductor membrane and optical fiber, which operates as a Fabry-Perot interferometer, allowing for non-contact measurement of fuel temperature, density, and chemical composition without electrical wiring, reducing weight, size, and maintenance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrical fuel sensors are used in aircraft fuel tanks, then fuel level measurement can be achieved, but weight increases due to electrical wiring, cables, and support structures
Solution Approach 1:
The patent extracts the harmful electrical wiring, cables, and support structures from the fuel sensor system, replacing them with a fiber optic sensor that transmits light instead of electrical signals. This removes the source of weight while maintaining measurement capability through optical detection of fuel level changes.
Solution Approach 2:
The patent replaces the electrical measurement system with an optical system. Instead of using electrical circuits to detect fuel level, the invention uses light transmission through a lens assembly where the lens position changes with fuel level, converting electrical measurement into optical measurement to eliminate wiring weight.
2Measurement precision
If electrical wiring is installed in fuel tanks for sensor operation, then fuel level sensing is enabled, but electromagnetic interference and lightning protection become critical issues
Solution Approach 1:
The patent substitutes electrical signal transmission with optical signal transmission through fiber optic cables. Light signals are immune to electromagnetic interference and lightning effects, eliminating the harmful interactions between electrical wiring and electromagnetic environments in fuel tanks.
Solution Approach 2:
The patent introduces fiber optic cables as an intermediary medium to transmit sensor data from the fuel tank environment to the external processing system. This intermediary converts electrical measurements into optical signals that can traverse the electromagnetic environment without interference.
3Ease of operation
If fiber optic sensing elements are placed in fuel for level measurement, then contactless electrical measurement is achieved, but fuel temperature variation, icing, and fungus deposit block light transmission
Solution Approach 1:
The patent introduces a lens assembly as an intermediary that is positioned to change with fuel level but remains protected from direct fuel contact. The lens modifies light transmission based on its position relative to the fuel surface, allowing level measurement without exposing the optical path to fuel contaminants.
Solution Approach 2:
The patent creates an optical copy or representation of the fuel level condition through the lens position and light transmission pattern. Instead of directly measuring light blocked by fuel, the system uses the lens position (which copies the fuel level information) to modulate light transmission, indirectly sensing level while avoiding contamination issues.
4Measurement precision
If complex electrical wiring and shielding are used for fuel sensors, then measurement accuracy is maintained, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent extracts and removes the complex electrical wiring, shielding, bonding, and grounding infrastructure from the fuel sensor system. By using fiber optic technology, the system eliminates the need for electrical connections inside the fuel tank, dramatically simplifying the device while maintaining measurement accuracy through optical detection.
Solution Approach 2:
The patent replaces the complex electrical measurement system with a simpler optical system. The fiber optic sensor uses light transmission through a lens assembly to detect fuel level, eliminating the need for electrical shielding, bonding, and grounding complexities inherent in electrical sensor systems.
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 system provides accurate, multi-functional sensing of fuel properties without electrical interference, reducing weight and maintenance, and is resistant to contamination and environmental factors like icing and residue.
Implementation Method 1
The optical cavity formed by the bottom surface of the membrane and the surface of the distal end of the internal optical fiber is capable of behaving as a Fabry-Perot interferometer
Implementation Method 2
Any change in fuel density causes changes in the index of refraction of the fuel. This in turn causes a change in the intensity of the light transmitted from one fiber optic sensing element to the other.
Implementation Method 3
a photodetector array positioned at a distal end of the optical fiber opposite the membrane
Data Source
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AI summary
A fuel sensing system utilizes a fiber optic sensor comprising a membrane made of a direct band gap semiconductor material (such as gallium arsenide) that forms an optical cavity with an optical fiber inside a hermetically sealed sensor package located at the bottom of a fuel tank. The optical fiber inside the fuel tank is not exposed to the fuel. The optical cavity formed by the bottom surface of the membrane and the surface of the distal end of the internal optical fiber is capable of behaving as a Fabry-Pérot interferometer. Multiple light sources operating at different wavelengths and multiple spectrometers can be coupled to the confronting surface of the membrane via the optical fiber inside the fuel tank, a hermetically sealed fiber optic connector that passes through the wall of the fuel tank, and a fiber optic coupler located outside the fuel tank.