Extrinsic Fabry-Perot Pressure Sensor for High Shock Stability
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Solution Overview
Problem
Existing Fabry-Perot interferometers using ball lenses are not rugged enough for high shock environments and are limited to low temperatures, preventing precise pressure measurements in harsh industrial applications.
Innovation Solution
An extrinsic Fabry-Perot pressure sensor with a hermetically sealed connector assembly, comprising an optical fiber, lens assembly, alignment socket, window assembly, and pressure diaphragm, aligned through degrees of freedom to maintain collimated light beam integrity under extreme conditions, using high-strength materials and bonding methods to ensure stability and temperature tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ball lenses are used in Fabry-Perot interferometers, then optical energy density and path length uniformity are improved, but the sensor becomes vulnerable to high shock environments
Solution Approach 1:
The ball lens is divided into two separate components: a ball lens holder that provides mechanical support and shock resistance, and a ball lens element that maintains optical precision. The holder is rigidly affixed to the optical fiber assembly while the lens element is positioned within it, separating the mechanical function from the optical function to resolve the contradiction between shock resistance and optical performance.
2Ease of manufacture
If adhesives are used to hold the lens in position, then alignment is simplified, but the sensor is limited to low temperature applications
Solution Approach 1:
The adhesive bonding method is replaced with a mechanical retention system where the ball lens holder provides physical support and positioning. The lens element is held in place through mechanical features of the holder rather than chemical bonding, eliminating the temperature limitation imposed by adhesive breakdown and enabling operation at temperatures exceeding 500°F.
3Speed
If integral micro-lenses are used on optical fibers, then collimated beam delivery is improved, but the assembly lacks ruggedness for harsh environments
Solution Approach 1:
The integral micro-lens is segmented into a separate ball lens element that can be independently optimized for both optical performance and mechanical robustness. The ball lens holder provides the rugged mechanical structure needed for harsh environments while the lens element maintains the collimated beam delivery capability for high sampling rates, resolving the contradiction between speed and reliability.
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
Enables precise, high-speed pressure measurements in severe shock and vibration environments up to 1200°F, suitable for industrial applications requiring high fidelity pressure measurements.
Implementation Method 1
An extrinsic Fabry-Perot interferometer is created by the second surface on said window assembly, the air space created by said shim, and the first surface on said diaphragm assembly. The air space between the two reflective surfaces comprises the Fabry-Perot interferometer cavity or gap which measured cavity or gap length is a function of the applied external pressure.
Implementation Method 2
The continuous collimated beam of light then reflects multiple times between the two plane, parallel, and partially reflective surfaces of the Fabry-Perot interferometer. Said Fabry-Perot interferometer reflects a portion of the light into the optical circuit from each reflective surface of the interferometer creating a continuous interferometrically-modulated light signal.
Implementation Method 3
Said continuous collimated beam of light is projected through the air space and onto a window where the light is refracted along a new path through said window and is refracted again upon exiting said window.
Implementation Method 4
said lens assembly having an optical axis and said lens assembly rigidly affixed to such optical fiber assembly positioning the lens a fixed distance from the end of the optical fiber to optimize the focus and transmission of a collimated beam of light
Implementation Method 5
said pressure diaphragm assembly capable of deflecting when subjected to applied external pressure
Data Source
AI summary
A temperature-tolerant, shock and vibration resistant absolute pressure sensor may be constructed by joining a ruggedized lens assembly and optical fiber assembly to create a stable beam of collimated light. The lens may be captured by brazing or welding to high-strength spherical metal components. The light delivery assembly may be comprised of a metal jacketed optical fiber, ceramic ferrule, and metal alignment sleeves that are mechanically and/or chemically joined to one another using high temperature sealing glass preforms or brazing materials. The optical fiber assembly may be joined to the lens assembly securing the end face of the optical fiber in the operative focal position relative to the lens. The joined assembly results in a structure where no parts are subject to movement even at extreme temperatures or when subjected to severe shock and vibration. All the air-to-glass interfaces may have anti-reflection coatings to reduce optical losses, back reflection, and false signals. This rugged collimated beam assembly may be joined to a sensor assembly comprised of a diaphragm and window which comprise a Fabry-Perot interferometer. The external wetted surfaces of the diaphragm may be coated to reflect the radiant energy or with passive conductive and convective arrangements to keep the sensor cool and to minimize the long-term change in sensitivity of the diaphragm due to oxidation. The resulting sensors can be further enhanced by attaching the sensor to an absolute, hermetically sealed connector comprised of a lens assembly which is aligned and welded to the sensor transducer body. The resulting sensors can be further enhanced with windows for collecting UV energy and may use wide spectral band optical fibers to multiplex UV, visible, and IR energy from the sensing environment. These enhancements can be used to detect the presence of a flame and to make temperature measurements resulting in safety-certified optical sensors for use in many harsh industrial applications.