Fibre Optic Cable Discrete Acoustic Coupling for Distributed Sensing
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Solution Overview
Problem
Fibre optic cables in distributed acoustic sensing systems face challenges with aliasing effects due to undersampling and interference from dominant acoustic signals, particularly when not secured with clamps, leading to reduced sensitivity in detecting acoustic signals from surrounding directions.
Innovation Solution
The introduction of discrete acoustic coupling regions along the fibre optic cable, achieved through a filler with built-up regions or crimping, enhances acoustic coupling between the outer layer and optical fibres, allowing for directional sensitivity and improved detection of acoustic signals without the need for clamps, and the use of acoustically reactive or insulating materials to adapt sensitivity in specific directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fibre optic cables are not secured with clamps, then ease of deployment is improved, but acoustic coupling sensitivity deteriorates leading to aliasing effects and reduced detection accuracy
Solution Approach 1:
The cable structure is segmented into discrete acoustic coupling regions spaced at intervals along the fibre length. These regions are separated by acoustic insulation segments, creating a segmented pattern that prevents aliasing while maintaining detection accuracy. The segmentation allows the cable to function without external clamps while preserving acoustic sensing capability.
Solution Approach 2:
The cable incorporates localized acoustic coupling regions with enhanced acoustic coupling properties at specific positions, while other regions maintain acoustic insulation. This local quality differentiation enables selective acoustic sensing at discrete points without requiring uniform coupling along the entire cable length, thus eliminating aliasing effects.
2Ease of manufacture
If standard fibre optic cables are used with uniform structure, then manufacturing simplicity is improved, but acoustic sensitivity becomes isotropic reducing ability to detect signals from specific directions
Solution Approach 1:
The cable incorporates localized acoustic coupling regions with enhanced acoustic coupling properties at specific positions, while other regions maintain acoustic insulation. This local quality differentiation enables selective acoustic sensing at discrete points without requiring uniform coupling along the entire cable length, thus eliminating aliasing effects.
Solution Approach 2:
The cable structure introduces asymmetric acoustic coupling characteristics through the alternating pattern of coupling regions and insulation segments. This asymmetry in the acoustic coupling distribution along the cable length creates directional sensitivity, allowing the cable to preferentially detect acoustic signals from specific directions while maintaining manufacturing feasibility.
3Measurement precision
If discrete acoustic coupling regions are introduced, then acoustic sensitivity and directional detection are improved, but device complexity increases due to additional filler structures or crimping
Solution Approach 1:
The patent introduces acoustic insulation segments as intermediary elements between the outer layer and optical fibre at discrete positions. These insulation segments act as mediators that control acoustic coupling by preventing it in specific regions, while allowing natural coupling in other regions. This intermediary approach achieves discrete acoustic coupling without requiring complex filler structures or crimping operations.
Data Source
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AI summary
Embodiments of the present invention address aliasing problems by providing a plurality of discrete acoustic sensors along a cable whereby acoustic signals may be measured in situations where the fibre optic cable has not been secured to a structure or area by a series of clamps, as described in the prior art. Acoustic sampling points are achieved by selectively enhancing the acoustic coupling between the outer layer and the at least one optical fibre arrangement, such that acoustic energy may be transmitted selectively from the outer layer to the at least one optical fibre arrangement. The resulting regions of acoustic coupling along the cable allow the optical fibre to detect acoustic signals. Regions between the outer layer and the at least one optical fibre arrangement that contain material which is acoustically insulating further this enhancement since acoustic waves are unable to travel through such mediums, or at least travel through such mediums at a reduced rate.