Fibre Optic Sensing via Electromagnetic Force Induction
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Solution Overview
Problem
Fibre optic distributed acoustic sensing (DAS) systems struggle to accurately determine environmental characteristics, such as mechanical impedance and magnetic properties, due to dependencies on the surrounding environment and coupling of the optical fibre.
Innovation Solution
A method involving an optical fibre mechanically coupled to a first element responsive to electromagnetic fields, where a varying electric current is applied to induce a force on the fibre, allowing for the analysis of backscattered radiation to determine environmental characteristics, utilizing either ambient magnetic fields or additional magnetic fields generated by deployed elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fibre optic DAS is used to detect environmental characteristics, then acoustic activity along the fibre length can be monitored, but the detection accuracy is compromised due to dependency on surrounding environment and fibre coupling
Solution Approach 1:
A first element (such as a conductor or magnetic element) is introduced as an intermediary between the electromagnetic field source and the optical fibre. This intermediary converts electromagnetic fields into mechanical forces that directly stimulate the fibre, creating a controlled acoustic stimulus that is independent of the surrounding environmental coupling conditions.
Solution Approach 2:
The patent replaces the reliance on passive mechanical coupling with the environment by using active electromagnetic-to-mechanical conversion. Instead of depending on environmental acoustic waves to stimulate the fibre, an electromagnetic field is converted into a controlled mechanical force on the first element, which then stimulates the fibre in a predictable manner.
2Measurement precision
If a varying electric current is applied to induce force on the fibre, then environmental characteristics can be determined, but the system complexity increases due to additional electromagnetic field components
Solution Approach 1:
The first element serves multiple functions: it acts as an electromagnetic field sensor, a mechanical transducer, and an acoustic stimulus generator all in one component. This multi-functionality reduces the need for separate components for each function, thereby limiting the increase in system complexity.
Solution Approach 2:
The patent utilizes changes in electromagnetic field parameters (frequency, amplitude, phase) to control the mechanical stimulus applied to the optical fibre. By varying these parameters, different environmental characteristics can be probed without changing the physical structure of the sensing system.
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 the detection of environmental characteristics like mechanical impedance and magnetic properties, improving the accuracy and reliability of fibre optic sensing applications by generating a continuous acoustic stimulus through the interaction of electromagnetic fields and currents.
Implementation Method 1
applying a varying electric current so as to induce a varying force on said first element
Implementation Method 2
analysing optical radiation backscattered from within said optical fibre to determine a measurement signal indicative of any variation in the backscattered radiation
Data Source
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AI summary
This application relates to methods and apparatus for fibre optic sensing which can provide information about the environment in which the fibre optic is deployed. In particular the application relates to fibre optic based sensing of the mechanical impedance of the environment. The method comprises using an interrogator (201) to interrogate an optical fibre (104) which is coupled to a first element (202; 802) which is responsive to electromagnetic fields. In use a varying electric current (I), which may be an alternating current, is applied so as to induce a varying force (F) on said first element. The optical radiation backscattered from within the optical fibre is analysed to determine a measurement signal indicative of a variation in the backscattered radiation corresponding with said electric current applied. The first element may be a first conductor (202) and the varying current may be supplied to the first conductor, or to a second conductor (701). Alternatively the first element could be a magnetic element (802). By applying a variable force to the first element, and hence the optical fibre, the characteristics of the environment can be determined.