Temperature Sensor with FBG and FPI for High Resolution
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Solution Overview
Problem
Existing sensors lack the necessary sensitivity and resolution for precise temperature measurement, particularly in medical and industrial applications where high resolution and wide temperature ranges are required.
Innovation Solution
A temperature sensor incorporating a fibre Bragg Grating (FBG) for coarse temperature measurement and a Fabry-Perot interferometer (FPI) with a fluid-filled chamber, utilizing thermal expansion of the fluid to induce pressure changes detectable by the FPI, offering high resolution and wide temperature range capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single temperature sensing mechanism is used, then the device complexity is reduced, but the measurement precision and temperature range are insufficient
Solution Approach 1:
The patent combines two different temperature sensing mechanisms (FBG and FPI) into a single integrated sensor system. The FBG provides coarse temperature measurement with wide range, while the FPI provides fine temperature measurement with high resolution. This merging allows the system to achieve both high measurement precision and wide temperature range without requiring separate sensing systems.
Solution Approach 2:
The temperature measurement function is segmented into two distinct sensing mechanisms with different capabilities. The FBG handles the coarse measurement aspect (lower resolution but wide range), while the FPI handles the fine measurement aspect (high resolution but limited range). This segmentation allows each component to be optimized for its specific function, resulting in overall superior performance.
2Volume of moving object
If the chamber volume is reduced for compact design, then the sensor size is reduced, but the sensitivity to temperature changes decreases
Solution Approach 1:
The patent replaces the traditional mechanical volume-based sensitivity approach with an optical interference-based detection system. The FPI uses optical path length changes caused by fluid thermal expansion to detect temperature, rather than relying solely on mechanical displacement. This substitution allows for enhanced sensitivity through optical amplification while maintaining a compact chamber volume.
Solution Approach 2:
The patent changes the detection parameter from direct mechanical displacement to optical path length variation. By using the FPI to detect changes in the optical path length caused by fluid expansion, the system achieves higher sensitivity to temperature changes within a compact volume, as optical measurements can detect sub-micrometer changes more precisely than mechanical measurements.
3Strength
If the diaphragm thickness is increased for structural strength, then the sensor reliability is improved, but the sensitivity to pressure and temperature changes is reduced
Solution Approach 1:
The patent employs a thin diaphragm made of flexible material that can undergo significant deformation in response to temperature-induced pressure changes. The thinness of the diaphragm (optimized balance between strength and sensitivity) allows it to flex more easily, translating small pressure changes into larger optical path length changes that can be detected by the FPI, thereby maintaining both structural integrity and measurement sensitivity.
Solution Approach 2:
The patent reduces dependence on large mechanical diaphragm deflections by substituting the detection mechanism with an optical FPI system. This allows the use of thinner, more sensitive diaphragms that would otherwise be too fragile, as the optical system can detect smaller deflections with high precision, thus achieving both strength and sensitivity requirements.
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 sensor achieves ultra-high temperature measurement resolution, rapid response, and compact design, capable of measuring temperature changes with sensitivity in the micro-Kelvin range, suitable for both medical and industrial applications, while being immune to electromagnetic interference.
Implementation Method 1
utilizing thermal expansion of the fluid to induce pressure changes detectable by the FPI
Implementation Method 2
a Fabry-Perot interferometer (FPI) with a fluid-filled chamber
Implementation Method 3
the FBG has a temperature resolution of 0.1°C or higher. In one embodiment, the Bragg Grating is in-fiber
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A temperature sensor (1) has a pressure sensor (10), the distal end of which is inserted in a sealed chamber (2) filled with a liquid. The pressure sensor has a light guide (4), a cavity (14) at a distal end of the light guide, a diaphragm (11) forming a wall of the cavity and being configured to deflect with applied pressure, and a detector to detect changes in light reflection due to deflection of the diaphragm. The liquid (3) which changes volume in response to temperature changes and this volume change is sufficient to change the pressure applied on the diaphragm (11), and the a interrogation system processes pressure data and/or light reflection data to generate an output indicating temperature of the fluid in the chamber.