Optical Fiber Accelerometer with External Mass and Biasing
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Solution Overview
Problem
Existing accelerometer designs for oilfield services, such as those used in ocean bottom cables and towed streamers, face limitations in sensitivity and size due to the placement of a mass within a coil, leading to bulky devices with reduced longevity and limited sensitivity to acceleration in multiple dimensions.
Innovation Solution
An accelerometer device featuring an optical fiber wound around a former with a movable element that varies the fiber's length in response to acceleration, allowing for improved sensitivity and compactness, along with a biasing element and protective stops to manage force and prevent excessive deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mass is placed within a coil of optical fiber to detect acceleration, then the accelerometer can measure acceleration through fiber deformation, but the device becomes bulky and sensitivity is limited
Solution Approach 1:
The patent extracts the mass from the traditional coil configuration and positions it externally at one end of the former, while the optical fiber remains wound around the former. This separation allows the mass to be larger and more effective without increasing the overall device volume, as the fiber coil maintains its compact structure while the mass operates in the external space.
Solution Approach 2:
The patent arranges the optical fiber winding in a specific three-dimensional pattern around the former, with the fiber exiting at positions that allow the mass to move in one dimension while deforming the fiber in multiple dimensions. This dimensional arrangement maximizes the deformation effect for a given mass displacement, improving sensitivity without increasing size.
2Measurement precision
If the optical fiber is allowed to deform freely in response to acceleration, then sensitivity is improved, but the device lacks protection against excessive forces that could damage the fiber
Solution Approach 1:
The patent incorporates a biasing element that pre-loads the optical fiber in a compressed state, creating a protective mechanism before excessive forces can occur. During normal operation, the biasing element absorbs minor fluctuations, and during extreme events, it prevents the fiber from experiencing damaging tensile forces by maintaining compression, thus protecting the fiber while allowing sensitive detection of normal accelerations.
3Measurement precision
If a compliant material with low Young's modulus is used to allow fiber deformation, then acceleration sensitivity is improved, but the accelerometer lacks longevity due to material fatigue
Solution Approach 1:
The patent changes the mechanical parameter of the optical fiber from a compliant state to a pre-compressed state through the biasing element. This parameter change allows the fiber to remain in a compressed configuration where it can detect accelerations through controlled deformation while the compression preload prevents excessive stretching that would cause fatigue, thereby extending the device lifetime while maintaining sensitivity.
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 solution provides enhanced sensitivity to acceleration in multiple dimensions, reduces the likelihood of damage from excessive forces, and improves longevity, making it suitable for ocean bottom applications.
Implementation Method 1
an optical fiber arranged to be deformable in response to a component of an acceleration event in a direction of a desired sensitivity, deformation of the optical fiber varying the length thereof, which is indicative of an acceleration
Implementation Method 2
A biasing element is provided and arranged to apply a compressive force to the optical fiber
Implementation Method 3
Protective stops are provided which prevent excessive movement of the mass in either direction
Data Source
AI summary
An accelerometer device (100) comprises a former (118) and an optical fiber (120) wound around the former. The winding of optical fiber (120) has a sensing portion (126) that is free to move in relation to a direction of desired sensitivity (128). A movable element (106) is disposed opposite the sensing portion (126) of the optical fiber (120), the movable element (106) being translatable so as to urge against the sensing portion (126) of the optical fiber (120) from a position external to the winding of the optical fiber (120) in order to vary a length of the optical fiber (120). The variation in the length of the optical fiber (120) caused by the moveable element (106) is indicative of an acceleration in the direction of desired sensitivity (128).