Spherical Strain Sensor for Non-Intrusive 3D Deformation Measurement
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Solution Overview
Problem
Existing methods for measuring deformations within structures suffer from inaccuracies and structural weakening due to the integration of unidirectional sensors, which can alter stress distribution and lead to crack initiation, limiting their use in sensitive areas like living organisms and soil mechanics.
Innovation Solution
A three-dimensional sensor embedded within a structure, utilizing a spherical test body with tangentially arranged deformation sensors on its surface to measure variations in perimeter lengths, allowing for accurate determination of the strain tensor through Eshelby's inclusion problem, using optical or piezoelectric cables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If unidirectional sensors or measuring fibers are integrated into the structure volume, then deformation measurement capability is improved, but the structure is weakened and stress distribution is altered
Solution Approach 1:
The patent replaces traditional mechanical unidirectional sensors with an optical measurement system based on laser interferometry. The spherical sensor contains three orthogonal optical fibers that measure strain components through optical interference patterns, eliminating mechanical contact and stress concentration while maintaining measurement capability.
Solution Approach 2:
The invention transitions from unidirectional point measurements to three-dimensional strain field measurement using a spherical geometry. The sphere accommodates three sets of orthogonal sensors that capture complete strain tensor information (εx, εy, εz, γxy, γyz, γzx) simultaneously, providing volumetric measurement without mechanical intrusion.
2Measurement precision
If unidirectional sensors are integrated into the structure, then deformation measurement is enabled, but local stress concentrations occur leading to crack initiation
Solution Approach 1:
The patent eliminates mechanical sensors that cause stress concentrations by using optical fibers embedded within a spherical inclusion. The optical measurement system detects strain through light interference without requiring mechanical coupling, thus avoiding local stress perturbations and crack initiation risks.
Solution Approach 2:
The spherical sensor is constructed with material properties matching the host structure to ensure homogeneous stress distribution. The sphere acts as an elastic inclusion with equivalent mechanical behavior to the surrounding material, preventing stress concentrations while enabling three-dimensional strain measurement through embedded optical fibers.
3Measurement precision
If traditional sensors are used for deformation measurement, then measurement capability is provided, but the sensors alter the distribution of stresses in the volume
Solution Approach 1:
The spherical sensor uses material with mechanical properties matched to the host structure, creating a homogeneous elastic inclusion. This ensures that the sphere deforms uniformly with the surrounding material under stress, maintaining natural stress distribution patterns while enabling measurement through embedded optical fibers that detect strain without mechanical interference.
Solution Approach 2:
The invention replaces mechanical strain transmission mechanisms with optical field-based measurement. Optical fibers embedded in the spherical inclusion detect strain through changes in light interference patterns caused by deformation, eliminating mechanical coupling that would otherwise alter stress distribution in the monitored volume.
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 precise, non-invasive measurement of local deformations without altering the host structure's stress distribution, suitable for various materials including living organisms and fluids, with potential miniaturization and improved metrological performance.
Implementation Method 1
The tangential sensors being physical rings constituted by optical fibers
Implementation Method 2
said tangential sensors being physical rings constituted by optical fibers, or electric cables or piezoelectric cables
Data Source
Figure 1a~2
Figure 3~4
Figure 5~6
AI summary
The present invention relates to a three-dimensional device (1) for measuring local deformations, this device being embedded inside a structure (2). In particular, the three-dimensional device (1) is based on the principle of using a spherical test body (5) which is made of a homogeneous elastic material having known mechanical properties and which has tangential deformation sensors wound on the surface of the test body (5).