Optical Fiber Sensor Expansion Reserve Case
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Solution Overview
Problem
Existing optical fiber sensors with Fabry-Perot cavities face challenges in harsh environments like nuclear reactors due to thermal expansion and radiation-induced compaction of the stainless steel sheath and silica fiber, leading to length differential issues that affect measurement accuracy and signal transmission.
Innovation Solution
An optical fiber sensor with a Fabry-Perot cavity and an expansion reserve case designed to minimize friction and snagging, featuring a 'gendarme hat' shape with a convex central part and symmetrical concave ends, allowing the fiber to form a single arch and maintain tangency with the case surfaces, made from stainless steel and silica with an aluminum coating, to absorb differential variations in length without creating mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical fiber and stainless steel sheath are used in harsh environments, then the sensor can operate in nuclear reactors, but thermal expansion and radiation-induced compaction cause length differential issues affecting measurement accuracy
Solution Approach 1:
The optical transport is divided into two segments: a first part in a stainless steel sheath for mechanical protection and thermal expansion accommodation, and a second part in a low-friction tube for signal transmission. This segmentation isolates the fiber from direct mechanical stress while maintaining measurement capability.
Solution Approach 2:
A low-friction tube filled with polyethylene glycol acts as an intermediary between the fiber and the external environment. This intermediary reduces friction and snagging forces on the fiber during thermal cycles and radiation exposure, preventing measurement errors.
2Strength
If the optical fiber is protected by a stainless steel sheath, then mechanical strength is improved, but friction and snagging increase causing signal loss and reduced lifespan
Solution Approach 1:
The protective structure is segmented into a stainless steel sheath for mechanical strength and a separate low-friction tube for signal transmission. The fiber transitions from the sheath to the tube, gaining protection without the friction and snagging problems of the sheath material.
Solution Approach 2:
The low-friction tube filled with polyethylene glycol serves as an intermediary that reduces friction between the fiber and surrounding structures. This intermediary prevents snagging forces that would otherwise cause signal loss and reduce component lifespan.
3Stability of the object's composition
If the fiber is fixed at multiple points along the transport, then mechanical stability is improved, but friction and mechanical stress increase affecting measurement precision
Solution Approach 1:
The fiber is extracted from the stainless steel sheath and placed in a separate low-friction tube. This extraction removes the source of friction and mechanical stress, allowing the fiber to move freely during thermal expansion and contraction without affecting measurement precision.
Solution Approach 2:
The low-friction tube acts as an intermediary that allows the fiber to move independently of external mechanical constraints. This intermediary enables thermal expansion and contraction without creating friction or snagging forces that would compromise measurement accuracy.
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 solution enables precise elongation measurements with minimal signal disruption and increased lifespan by accommodating thermal cycles and radiation effects, maintaining precision and reliability in extreme conditions.
Implementation Method 1
These two signals overlap and form an interference system. The two reflected signals having undergone different paths are out of phase. This phase shift depends on the wavelength λ of the signal and the distance Lc.
Implementation Method 2
The end of the fiber and the rod are made integral with a sample E to be measured by point connections which do not produce excessive stresses in the material. The end of the optical fiber and the end 6 of the rod 5 facing each other constitute a Fabry-Pérot cavity of length Lc.
Implementation Method 3
Existing optical fiber sensors with Fabry-Perot cavities face challenges in harsh environments like nuclear reactors due to thermal expansion and radiation-induced compaction of the stainless steel sheath and silica fiber
Implementation Method 4
Existing optical fiber sensors with Fabry-Perot cavities face challenges in harsh environments like nuclear reactors due to thermal expansion and radiation-induced compaction of the stainless steel sheath and silica fiber
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The general field of the invention is that of optical fibre sensors for measuring deformation, said sensors being intended to operate in a harsh environment. The sensor according to the invention comprises an optical measuring head with a Fabry-Pérot cavity, an optical transport fibre and an expansion reserve case (20), the case comprising a segment of the optical transport fibre. The internal thickness of the case is between one and several millimetres, the case being flat and of so-called policeman's cap-like form, the form comprising a central convex portion (21) and two concave symmetrical ends (22), the optical fibre forming a single arch inside the cap, the segment of the optical fibre being at most tangential to the internal surfaces of the reserve case, whatever the temperature conditions.