Optical Sensor Thermal Management for High Temperature Operation
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Solution Overview
Problem
Existing optical sensors for measuring pressure and temperature are unsuitable for environments at elevated temperatures due to instability in silicon sensors and weakening of fusion bonds in sapphire sensors, leading to unreliable measurements and structural damage from thermal mismatch.
Innovation Solution
An optical sensor with a dielectric body and a waveguide where the waveguide is maintained at a lower temperature than the dielectric body, using a temperature reduction means such as a heat conductive metal tube to prevent damage and misalignment, and an optical alignment mechanism like a ball joint to ensure accurate beam alignment, allowing operation in higher temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon sensor is used for measuring pressure and temperature, then the sensor can be fabricated using conventional micromachining techniques, but the sensor becomes unsuitable for environments above 450°C due to instability in elastic properties
Solution Approach 1:
The sensor is divided into two distinct segments: a dielectric body (sapphire or silica) that withstands high temperatures and an optical fibre that remains at lower temperatures. This segmentation allows each component to operate within its optimal temperature range, resolving the contradiction between ease of manufacture and reliability at elevated temperatures.
Solution Approach 2:
A heat conductive tube acts as an intermediary element between the hot dielectric body and the cooler optical fibre. This intermediary manages thermal transfer, allowing the dielectric body to be exposed to high temperatures while maintaining the optical fibre at lower temperatures, thus preserving measurement reliability.
2Strength
If the waveguide is bonded directly to the optical sensor using fusion bonding, then strong bonding is achieved, but the bond weakens and may fail between 600°C and 1500°C
Solution Approach 1:
The bonding interface is extracted from the high-temperature environment. Instead of bonding the waveguide directly to the hot sensor, the waveguide is positioned remotely and coupled optically. This removes the bonding junction from the thermal stress zone, preventing bond failure at elevated temperatures while maintaining strong optical coupling.
Solution Approach 2:
Optical coupling acts as an intermediary mechanism between the waveguide and the optical sensor. This allows energy transfer without direct physical contact, eliminating the thermal degradation of bonded joints while maintaining functional connection.
3Reliability
If the waveguide is spaced from the optical sensor by a short distance, then thermal damage to the waveguide is reduced, but optical coupling efficiency decreases
Solution Approach 1:
A heat conductive tube serves as a thermal intermediary that bridges the gap between the hot dielectric body and the cooler waveguide. This tube conducts heat away from the waveguide while maintaining proper optical alignment, thus protecting the waveguide from thermal damage without sacrificing coupling efficiency.
Solution Approach 2:
The thermal parameters along the optical path are changed by introducing a temperature gradient through the heat conductive tube. This allows the dielectric body to be at high temperature while the waveguide remains at lower temperature, maintaining both protection and alignment.
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 optical sensor can operate in environments exceeding 700°C while maintaining accurate measurements, avoiding damage to the waveguide and ensuring reliable data collection, suitable for applications like gas turbines and jet engines.
Implementation Method 1
The waveguide is maintained at a lower temperature than that of the dielectric body in use so that the optical cavity may be responsive to environments at higher temperatures than would otherwise damage the waveguide
Implementation Method 2
an optical alignment mechanism like a ball joint to ensure accurate beam alignment
Implementation Method 3
Light incident along the silica fibre is reflected within the Fabry-Perot cavity and guided back along the silica fibre. The reflected light creates interference fringes whose characteristics are determined by the length of the Fabry-Perot cavity
Data Source
Figure 1~2
Figure 3~4
Figure 5~5a
AI summary
An optical sensor (10) comprises an optical cavity defined by a dielectric body and responsive to one or more physical environmental conditions, and a waveguide (70) having a terminal end spaced apart from the optical cavity such that light is optically coupled from the terminal end of the waveguide (70) to the optical cavity. The waveguide (70) is arranged such that, in use, it is maintained at a first temperature that would not damage the optical coupling to the optical cavity when the dielectric body is maintained at a second temperature sufficient to damage the optical coupling to the optical cavity.