Sapphire Fabry-Perot Optical Sensor for High-Temperature Measurement
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Solution Overview
Problem
Existing optical sensors are unsuitable for harsh chemical environments and elevated temperatures, with silicon sensors failing above 450°C and sapphire sensors experiencing poor light reflectivity and limited temperature measurement capabilities.
Innovation Solution
A sapphire-based optical sensor with a hollow structure forming a Fabry-Perot cavity, allowing for improved light visibility and sensitivity to pressure and temperature changes, along with a reflective coating and passivation layers to maintain performance at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon sensor is used, then the sensor can be manufactured using conventional micromachining techniques, but the sensor becomes unsuitable for temperatures above 450°C and chemically harsh environments
Solution Approach 1:
The patent changes the material parameter from silicon to sapphire, which enables operation at temperatures up to 1600-1700°C and in chemically harsh environments while maintaining sensor functionality. This material substitution resolves the contradiction by prioritizing operational reliability over manufacturing ease, as sapphire can be fabricated using available techniques despite being more challenging than silicon.
Solution Approach 2:
The sensor employs a composite structure combining sapphire material with specific geometric features (hollow cylindrical shape with flat bottom) to achieve both high-temperature reliability and functional performance. The composite nature of the design integrates material selection with structural configuration to simultaneously address manufacturing feasibility and operational reliability.
2Temperature
If a sapphire fibre is used, then the sensor can operate at temperatures well above 450°C, but the reflectivity of the silica:sapphire and sapphire:air interfaces is only around 1% and 7% respectively, resulting in poor visibility of interference fringes
Solution Approach 1:
The patent modifies the geometric parameters of the sapphire structure by creating a hollow cylindrical shape with a flat bottom, which forms a Fabry-Perot cavity. This geometric parameter change enhances light reflection and interference fringe visibility while maintaining the high-temperature operational capability of sapphire material.
Solution Approach 2:
The sensor employs a cylindrical (curved) geometry rather than a flat structure. The curved outer surface of the hollow cylinder works in conjunction with the flat bottom to create the Fabry-Perot cavity, utilizing the curved geometry to improve light interaction and reflectivity characteristics while maintaining temperature resistance.
3Adaptability or versatility
If the end of the sapphire fibre is positioned adjacent a reflective surface, then indirect measurement of pressure, strain or temperature can be achieved, but the sensor is incapable of directly measuring the fluid pressure to which the sensor is exposed
Solution Approach 1:
The patent changes the structural parameter by creating a hollow cylindrical sapphire sensor that can be filled with fluid, enabling direct pressure measurement. The flat bottom surface of the hollow cylinder serves as one mirror of the Fabry-Perot cavity, while the fluid-filled interior allows direct interaction with the measured pressure, resolving the limitation of indirect measurement only.
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 sapphire-based sensor operates effectively in harsh environments, providing reliable measurements of pressure and temperature up to 1600-1700°C with enhanced sensitivity and accuracy, suitable for various industrial applications.
Implementation Method 1
A sapphire-based optical sensor with a hollow structure forming a Fabry-Perot cavity, allowing for improved light visibility and sensitivity to pressure and temperature changes
Implementation Method 2
The inner surface of the membrane and the end face of the optical fibre serve to define a Fabry-Perot cavity. Light incident along the optical fibre is reflected within the Fabry-Perot cavity
Implementation Method 3
Changes in temperature cause the sapphire fibre, and thus the length of the Fabry-Perot cavity, to expand or contract which is registered by changes in the interference fringes
Implementation Method 4
Changes in the external pressure cause the wall of the silicon slab directly opposite the fibre to deflect, causing a change in the length of the Fabry-Perot cavity
Data Source
AI summary
An optical sensor having a sapphire body is disclosed. A hollow in the sapphire body defines a surface which is used as a surface of a Fabry-Perot cavity. Interferometry is used to detect changes in the length of the Fabry-Perot cavity, and hence changes in, for example, the temperature or pressure of an environment in which the sensor is placed.