Optical Fiber Loop Extensometer for Specimen Deformation
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Solution Overview
Problem
Current extensometers are bulky, induce stress and bending in specimens, and struggle with precise measurements across cracks or on irregular surfaces, particularly in biological and soft materials, due to their size and requirement for high surface finish.
Innovation Solution
A single-mode optical fiber loop extensometer that can be attached to specimens at two points, allowing for direct measurement of displacement across cracks and on irregular surfaces without significant surface preparation, utilizing the principle of transmitted optical power changes to measure extension, compression, or bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional extensometers are used to measure specimen deformation, then measurement capability is provided, but the device induces stress and bending in the specimen due to its large size
Solution Approach 1:
The patent replaces traditional mechanical extensometer systems with an optical fiber-based measurement system. The optical fiber extensometer uses light transmission through the fiber to measure deformation, eliminating the need for mechanical contact elements that induce stress and bending in the specimen.
Solution Approach 2:
The optical fiber itself serves as a flexible, thin sensing element that can conform to the specimen surface without rigid mechanical structures. This flexible thin-film approach allows measurement without inducing harmful mechanical stresses or bending moments in the specimen.
2Measurement precision
If conventional extensometers are used, then deformation measurement is achieved, but knife-edge slip occurs leading to incorrect measurements
Solution Approach 1:
The patent eliminates mechanical knife-edge contact systems by using optical fiber-based measurement. The optical fiber measures deformation through light transmission changes caused by fiber elongation or bending, removing the sliding contact mechanism that causes knife-edge slip and measurement errors.
3Ease of operation
If extensometers are supported on the specimen itself, then measurement is enabled, but substantial bending of the specimen is produced
Solution Approach 1:
The patent replaces mechanical support structures with an optical measurement approach. The optical fiber can be attached to the specimen surface without requiring mechanical support legs or contact points that would create bending moments, thereby enabling measurement while minimizing specimen bending.
4Measurement precision
If FBG fiber-optic extensometers are used, then optical measurement capability is provided, but large size and low sensitivity are disadvantages
Solution Approach 1:
The patent optimizes the optical fiber parameters, specifically using a single-mode fiber with carefully selected diameter and refractive index parameters. This allows the fiber to be sufficiently thin and flexible for small-scale applications while maintaining high measurement sensitivity through optimized optical properties.
5Measurement precision
If strain gauges are used, then surface deformation measurement is achieved, but perfect bonding and high surface finish are required
Solution Approach 1:
The optical fiber acts as a flexible thin-film sensor that can adhere to irregular surfaces without requiring the perfect bonding conditions needed for traditional strain gauges. The fiber's flexibility and thin profile allow it to conform to rough or irregular surfaces while maintaining measurement accuracy.
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
Provides high sensitivity and dual measurement ranges, capable of precise displacement measurements with minimal stress on specimens, suitable for biological and irregularly shaped materials, and can be used in both tension and compression without the need for a high surface finish.
Implementation Method 1
utilizing the principle of transmitted optical power changes to measure extension, compression, or bending
Data Source
AI summary
A method for measuring the deformation of a specimen using an extensometer having a loop of a single-mode optical fiber. At least two points of the loop are attached to desired locations on a specimen. Light is transmitted through the loop and the transmitted optical power is measured by a photodetector. The deformation of the specimen causes the size and shape of the loop to change, which changes the transmitted optical power. The change in optical power is related to extension or compression using calibration curves. The sensor works on the principle of transmitted power modulation through the curved section.