Optical Fiber Pressure Sensor with Internal Cavity and Grating
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Solution Overview
Problem
Conventional optical fibers with Bragg gratings have low sensitivity to external pressure, making them inadequate for applications requiring precise pressure measurement without additional mechanical amplification devices, such as those needed in aerodynamic testing where drilling numerous holes is costly and disruptive.
Innovation Solution
An optical fiber design featuring a core with at least one Bragg grating associated with an internal closed cavity, allowing pressure differences to influence the grating's physical form and wavelength shift, enabling high-precision pressure measurement without external mechanical devices, and potentially including multiple cavities and gratings for enhanced reliability and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical fiber with Bragg grating is used for pressure measurement, then the device complexity is low, but the measurement precision is insufficient due to low sensitivity to external pressure
Solution Approach 1:
The optical fiber core is segmented into multiple regions with different refractive indices, creating distinct functional zones: a central core region for light propagation, an intermediate region with modified refractive index for enhanced pressure sensitivity, and an outer cladding region. This segmentation allows the fiber to simultaneously maintain low device complexity while achieving high pressure measurement precision through the specialized intermediate region that amplifies pressure-induced refractive index changes.
Solution Approach 2:
The intermediate region is designed with specific local properties: a refractive index that falls between the core and cladding refractive indices, and a thickness optimized for pressure sensitivity. This local quality enhancement in the intermediate region creates a gradient structure that amplifies the effect of external pressure on the Bragg grating, thereby improving measurement precision without requiring complex external devices.
2Measurement precision
If additional external components such as polymer coatings, pressure spacers, or diaphragms are added to increase pressure sensitivity, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The pressure-sensing functionality is merged directly into the optical fiber structure by creating an intermediate region within the fiber itself. This eliminates the need for separate external components such as polymer coatings, pressure spacers, or diaphragms. The merged structure maintains simplicity while achieving high pressure sensitivity through the refractive index gradient in the intermediate region that enhances the Bragg grating's response to pressure changes.
Solution Approach 2:
The optical fiber structure serves its own pressure-sensing function through the intermediate region's inherent properties. The refractive index gradient in the intermediate region automatically amplifies pressure effects on the Bragg grating without requiring external mechanical amplification devices. This self-service capability reduces device complexity while maintaining high measurement precision.
3Measurement precision
If multiple holes are drilled in the surface for pressure measurement, then the measurement precision improves, but the object-generated harmful factors increase due to airflow interference
Solution Approach 1:
The mechanical drilling and hose connection system is replaced with an optical sensing system. Instead of drilling multiple holes and connecting pressure gauges with hoses, the invention uses an optical fiber with a Bragg grating in an intermediate region that directly senses pressure through optical wavelength shifts. This substitution eliminates airflow interference caused by physical holes while maintaining high measurement precision for pressure distribution.
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
This design allows for precise measurement of small pressure differences with high accuracy and reliability, reducing costs and minimizing airflow interference, suitable for applications like wind tunnel models and aircraft testing.
Implementation Method 1
The principle is based on light with a known wavelength spectrum being sent through an optical fiber and reflected by one or more Bragg gratings. The known methods most commonly make use of the physical changes that occur in gratings upon changes in physical parameters such as temperature or strain. The physical changes of a grating give rise to changes in the reflection of light by the grating.
Implementation Method 2
The core comprises at least one Bragg grating and at least one internal closed cavity, wherein the at least one Bragg grating is associated with said cavity. The internal cavity will allow the grating to change its physical form by means of the pressure difference between the pressure inside the cavity and the pressure surrounding the fiber when the pressure surrounding the fiber changes.
Data Source
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AI summary
An optical fiber capable of measuring pressure or pressure difference with high sensitivity is disclosed. The optical fiber (1) comprises a core (2) having a Bragg grating (4) and an internal closed cavity (5), wherein the Bragg grating is associated with the internal closed cavity. By means of the optical fiber, there is no need for external components for mechanically imparting the optical fiber to enable measurement of pressure by means of the optical fiber.