Fibre Optic Proximity Sensing for EMI-Resistant Aircraft Detection
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Solution Overview
Problem
Existing proximity sensors in aircraft applications face challenges with large numbers of electrical connections, susceptibility to contaminants, and inadequate shielding in composite materials, which can lead to reliability issues and increased complexity, especially when transitioning from metallic to organic matrix composite construction.
Innovation Solution
A fibre optic proximity sensor system utilizing a single optic fibre with a mass flexibly coupled to it, where the mass moves in response to a target, altering the strain on the fibre, and employing fibre Bragg gratings to detect changes in strain and temperature, allowing for non-contact detection with reduced electrical connections and improved resistance to contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductive proximity sensing with electrical connections is used, then reliable target detection is achieved, but the number of electrical connections and system complexity increases significantly
Solution Approach 1:
The patent replaces electrical inductive sensing with optical fibre-based sensing. The optical fibre sensor uses light transmission and detection instead of electrical fields and connections, eliminating the need for numerous electrical wires while maintaining reliable target detection capability. The optical fibre is mechanically coupled to the target object, and target movement is detected through optical property changes.
Solution Approach 2:
The patent introduces optical fibre as an intermediary element between the sensor system and the target. The optical fibre serves as a mediator that transmits light signals to detect target proximity and position without requiring direct electrical connections to the target or sensor head, thereby reducing electrical connection complexity.
2Reliability
If electrical proximity sensors are used in composite construction aircraft, then target detection is achieved, but shielding and lightning protection become inadequate
Solution Approach 1:
The patent replaces electrical sensing systems with optical fibre-based sensing. Optical fibres are inherently immune to electromagnetic interference and lightning strikes because they use dielectric materials (glass or plastic) to transmit light signals rather than electrical signals. This eliminates the shielding requirements and lightning protection issues associated with electrical sensors in composite aircraft structures.
Solution Approach 2:
The patent utilizes optical fibre composite materials that are inherently resistant to electromagnetic interference and lightning damage. The optical fibre sensor can be integrated into composite aircraft structures without requiring additional metallic shielding layers, making it suitable for modern composite construction where traditional metallic shielding is unavailable.
3Reliability
If fibre optic sensors with external reflection are used, then target detection is achieved, but the sensor becomes susceptible to contamination by dust and dirt
Solution Approach 1:
The patent inverts the traditional external reflection approach by using internal reflection within the optical fibre itself. Instead of emitting light outward and relying on external target reflection, the sensor detects changes in the optical properties of the fibre core when the target approaches and interacts with the evanescent field or physically contacts the fibre, causing internal total internal reflection changes that indicate target presence.
4Adaptability or versatility
If magnetic sensors with two fibres are used, then aircraft application suitability is improved, but the fibre quantity and electronics requirements increase
Solution Approach 1:
The patent makes a single optical fibre perform multiple functions: it serves as both the sensing element and the signal transmission medium. The optical fibre detects target proximity through its mechanical coupling and optical property changes, and simultaneously transmits the detection signal back to the interrogation system, eliminating the need for separate detection and transmission fibres required in magnetic 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 fibre optic system effectively detects target proximity with reduced electrical connections, enhanced resistance to contaminants, and improved shielding, making it suitable for aircraft applications with organic matrix composite construction, while minimizing the impact of temperature and vibration effects.
Implementation Method 1
The optic fibre strain sensor can have a period variation in the refractive index of the optic fibre, such as, for example, Bragg gratings
Implementation Method 2
The mass can be a magnet that moves in response to the target
Implementation Method 3
the optic fibre can include an optical delay, such as a length of optic fibre, in order to distinguish between the frequency response of the strain and temperature sensors
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
A proximity sensor for detecting non-contact detection of a target using a fibre optic strain sensor and a system for operating multiple such proximity sensors is disclosed. The proximity sensor includes an optic fibre that has an optic fibre strain sensor that is coupled to a mass that moves in response to the target. The mass can be a magnet that moves when a ferrous target is within the magnetic field of the magnet causing the magnet to move and apply strain to the optic fibre strain sensor. The optic strain sensor can include periodic variation in the refractive index of the optic fibre, such as a fibre Bragg grating. The proximity sensor can include a second fibre optic sensor that is sensitive to temperature or a second fibre optic strain sensor coupled to a second magnet that operates in opposition to the first magnet. A system coupling multiple proximity sensors can include an interrogator that has an optical power source and a detector, each coupled to a processor. The processor compares frequency information from the proximity sensor to a threshold to determine whether a target is in proximity to its corresponding proximity sensor.