Miniature Fiber Optic Pressure Sensor with Pre-Stressed Diaphragm
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Solution Overview
Problem
Miniaturized Fabry-Perot and capacitance-based pressure sensors suffer from reduced sensitivity and accuracy due to diaphragm thinning, leading to limited sensitivity at higher pressures and increased internal stress, which can result in diaphragm failure, especially at bias pressures like atmospheric pressure.
Innovation Solution
A miniature fiber optic pressure sensor design is introduced, where a diaphragm with internally pre-stressed layers, such as a dot or ring, is used to increase sensitivity by relaxing internal stresses and altering the diaphragm shape, enhancing sensitivity at biased pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diaphragm size is reduced to miniaturize the sensor, then the sensor size decreases, but the sensitivity and measurement accuracy deteriorate
Solution Approach 1:
The patent changes the physical parameters of the diaphragm by introducing pre-stress and creating non-linear geometric profiles (such as domed or curved surfaces). These parameter changes enable miniaturized sensors to maintain high sensitivity by amplifying deflection responses without increasing overall sensor size, thus resolving the contradiction between small size and measurement accuracy.
Solution Approach 2:
The patent applies local quality by creating non-uniform thickness distributions or adding localized structural features (such as raised regions or varying curvature) to specific areas of the diaphragm. This allows different regions to contribute differently to the overall sensitivity, enabling high measurement accuracy in miniaturized sensors by concentrating stress and deflection in optimal locations.
2Measurement precision
If the diaphragm thickness is reduced to increase sensitivity, then the sensitivity increases, but the internal stress increases and reliability deteriorates
Solution Approach 1:
The patent introduces pre-stress as a controlling parameter and designs non-linear geometric profiles that distribute stress more effectively throughout the diaphragm structure. This allows the use of thinner diaphragms for high sensitivity while the pre-stress and geometry prevent stress concentration that would lead to failure, thus maintaining reliability.
Solution Approach 2:
The patent applies pre-stress to the diaphragm during manufacturing to establish an initial stress state that optimizes both sensitivity and reliability. This preliminary action of pre-stressing the structure before operation allows the thin diaphragm to respond more strongly to pressure changes while the pre-established stress distribution prevents failure under operating conditions.
3Measurement precision
If the diaphragm thickness is reduced to improve sensitivity at low pressure, then the sensitivity at vacuum increases, but the sensitivity saturation occurs at higher pressure
Solution Approach 1:
The patent introduces pre-stress and non-linear geometric profiles as additional parameters that modify the pressure-deflection relationship. These changes enable the diaphragm to maintain a more linear and extended response across a broader pressure range, preventing early saturation and allowing the sensor to adapt to both low and high pressure measurements with a single thin diaphragm design.
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 pre-stressed diaphragm design significantly increases pressure sensitivity, particularly at higher pressures like atmospheric pressure, while reducing the risk of diaphragm failure, and improves accuracy and reliability of the sensor.
Implementation Method 1
The second material comprises internal pre-stresses to cause the center of the diaphragm to camber away from the substrate upon relaxing the internal pre-stresses
Implementation Method 2
Fabry-Perot sensor can be made of a small diameter and can be made at a low cost as they can be produced using micromachining techniques (Microelectromechanical Systems = MEMS)
Implementation Method 3
A diaphragm with internally pre-stressed layers, such as a dot or ring, is used to increase sensitivity by relaxing internal stresses and altering the diaphragm shape
Data Source
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AI summary
There is described a miniature fiber optic pressure sensor design where sensitivity around specific biased pressure is optimized. In an embodiment, the pressure sensor is a Fabry-Perot (FP) sensor which comprises a substrate; and a diaphragm mounted on the substrate. The diaphragm has a center and comprises: a first layer comprising a first material; and a second layer comprising a second material. The second layer forms a dot or a ring. The dot or ring is mounted on the first layer and is centered about the center of the diaphragm. The second material comprises internal pre-stresses to cause the center of the diaphragm (in the case of a dot) or the peripheral area about the center of the diaphragm (in the case of a ring) to camber away from the substrate upon relaxing the internal pre-stresses.