Fibre Optic Cable Moveable Mass Seismic Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional distributed acoustic fibre optic sensors lack sufficient sensitivity and directional sensitivity, particularly in seismic applications, where they struggle to effectively monitor seismic p-waves and S-waves, and require complex designs with inertial masses that strain the fibre.
Innovation Solution
A fibre optic cable design featuring a core structure with a moveable mass that changes the length of the wound optical fibre, enhancing sensitivity by directing force transfer through the fibre, and a deformable structure that varies guide portion separation to prioritize sensitivity in a preferred direction, such as vertical orientation for seismic monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fibre optic cable is used for distributed acoustic sensing, then the sensor is simple and cost-effective, but the sensitivity is insufficient for seismic applications
Solution Approach 1:
The cable is segmented into distinct functional zones: a rigid core structure for mechanical stability, a compliant layer for controlled deformation, and an optical fibre winding path. This segmentation allows each zone to perform its specific function optimally while maintaining overall system simplicity
Solution Approach 2:
The cable employs composite construction combining rigid core material (for structural integrity), compliant material (for controlled mechanical response), and optical fibre. This composite approach enables the cable to achieve enhanced sensitivity through material property optimization without requiring complex active sensing components
2Measurement precision
If conventional fibre optic cable is used, then manufacturing is simple, but directional sensitivity cannot be achieved
Solution Approach 1:
The optical fibre is wound asymmetrically around the core structure with non-uniform spacing, creating preferential sensitivity directions. The asymmetric winding pattern ensures that mechanical deformations in specific directions produce larger fibre length changes, enabling directional sensitivity while maintaining a relatively simple manufacturing process
Solution Approach 2:
Different regions of the cable cross-section are designed with different mechanical properties: the core provides rigid structural support, while the compliant layer allows controlled deformation. This local differentiation of mechanical properties enables directional sensitivity without requiring complex active components throughout the entire cable
3Measurement precision
If inertial mass is attached to enhance directional sensitivity, then directional sensitivity is improved, but the fibre is strained and the design becomes complex
Solution Approach 1:
The cable structure incorporates dynamic mechanical properties through the compliant layer, allowing the cable to respond differently to vibrations in different directions. This dynamic response is achieved through the mechanical design of the layered structure rather than adding inertial masses, avoiding fibre strain and design complexity
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 design improves sensitivity and directional sensitivity of distributed acoustic fibre optic sensors, allowing for more effective monitoring of seismic activities by maximizing signal response in the preferred direction while maintaining stability in orthogonal directions, thus overcoming the limitations of conventional sensors.
Implementation Method 1
The Rayleigh backscattering of light from intrinsic reflection sites within the fibre is sampled and demodulated
Implementation Method 2
movement of said mass in said preferred direction causes a change in length of the fibre wound around the periphery of the core
Data Source
Figure 1~3
Figure 4~5b
AI summary
This application relates to fibre optic cable structures that are suitable for distributed acoustic sensing, and which may usefully be used for seismic monitoring/detection. The cable structures provide good sensitivity may further exhibit a directional sensitivity and thus can be used to discriminate between stimuli acting on the cable in different directions. One such fibre optic cable comprises a core structure (202, 203, 204) with an optical fibre wound around the periphery of the core structure. The core comprises a mass(203)which is moveable in a preferred direction within the cable such that movement of said mass in said preferred direction causes a change in length of the fibre wound around the periphery of the core.