Fibre Optic Accelerometer with Seismic Mass Cylinder
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Solution Overview
Problem
Existing fibre optic accelerometers face limitations in sensitivity without increasing component size or complexity, particularly in monitoring low vibrations, as they tend to be sensitive to orthogonal accelerations and require larger sizes to enhance sensitivity.
Innovation Solution
A fibre optic accelerometer design featuring a seismic mass coaxially constrained within a compliant cylinder wound with optical fibre, utilizing a tension member and a rigid support ring to allow relative movement, which increases strain in the fibre and reduces buckling, while minimizing size and cost, by using a compliant material with low Young's modulus and a Poisson's ratio close to 0.5, and optionally using two cylinders for enhanced sensitivity and orthogonal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the seismic mass and cylinder height are increased to enhance sensitivity, then the sensitivity is improved, but the accelerometer size increases and sensitivity to orthogonal acceleration worsens
Solution Approach 1:
The patent changes the material parameters of the cylinder by selecting a compliant material with specific properties (low Young's modulus, high Poisson's ratio close to 0.5). This allows the cylinder to be more flexible and responsive to axial acceleration while maintaining structural integrity, thereby increasing sensitivity without increasing the physical dimensions of the accelerometer.
Solution Approach 2:
The patent employs a composite structure consisting of a compliant material cylinder with circumferentially wound optical fibre. This composite design allows the cylinder to deform more readily under axial acceleration (increasing sensitivity) while the optical fibre provides measurement capability. The combination enables enhanced performance within the same volume constraints.
2Measurement precision
If the cylinder wall thickness is reduced to increase sensitivity, then the sensitivity is improved, but the structural strength and resistance to buckling worsen
Solution Approach 1:
The patent selects a compliant material with a Poisson's ratio close to 0.5, which fundamentally changes the mechanical behavior of the cylinder. This material property allows thin-walled cylinders to maintain structural integrity while exhibiting high flexibility, enabling reduced wall thickness without compromising strength or buckling resistance.
Solution Approach 2:
The patent explicitly employs a thin-walled compliant cylinder as the core sensing element. The cylinder acts as a flexible shell that can deform readily under axial acceleration, converting mechanical stress into measurable optical signal variations. This approach maximizes sensitivity while maintaining adequate structural strength through the careful selection of compliant material properties.
3Measurement precision
If the cylinder is made more compliant to increase strain in the fibre, then the sensitivity is improved, but the resistance to orthogonal acceleration and buckling worsens
Solution Approach 1:
The patent changes the mechanical parameters of the cylinder by selecting a material with low Young's modulus and high Poisson's ratio. This creates a cylinder that is highly compliant in the axial direction (improving sensitivity) while the high Poisson's ratio provides lateral constraint that resists buckling and orthogonal acceleration effects.
Solution Approach 2:
The cylindrical geometry with circumferential optical fibre winding provides inherent resistance to orthogonal disturbances. The curved geometry and circumferential reinforcement from the fibre winding create structural stability that prevents buckling while allowing axial compliance, thus maintaining reliability while improving 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
This design enhances sensitivity in a single axis while maintaining a compact size, reducing the risk of buckling and orthogonal acceleration sensitivity, thus improving performance in miniaturized applications.
Implementation Method 1
axial displacement of the seismic mass deforming the cylinder so as to vary the stress induced in the optical fibre
Implementation Method 2
vary the stress induced in the optical fibre
Implementation Method 3
a Poisson's ratio close to 0.5, such that the stiffness of the accelerometer arises more from the circumferential winding than the cylinder itself
Implementation Method 4
fibre-optic accelerometers based on interferometric techniques
Data Source
AI summary
A fibre optic accelerometer particularly intended for use with an interferometer using the compliant cylinder approach but further providing a seismic mass at the core of the cylinder resulting in improved sensitivity and rejection of out-of-axis inputs.