Optical Extension Sensor Temperature Compensation
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Solution Overview
Problem
Existing optical strain sensors with Bragg gratings face challenges in achieving temperature-independent strain measurements, particularly when integrated into modern deformation bodies made of carbon fiber materials, due to mechanical decoupling and geometric/material manufacturing tolerances that affect temperature compensation.
Innovation Solution
The use of two thermo-mechanically coupled optical waveguides with different temperature coefficients of refractive indices allows for temperature-independent strain measurement through a simple calculation method, using only two Bragg grating wavelengths without requiring knowledge of the measuring point temperature, and can be easily integrated into deformation bodies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single Bragg grating is used for strain measurement, then the measurement is simple, but the measurement is temperature-dependent and cannot be compensated
Solution Approach 1:
The single Bragg grating is segmented into two separate Bragg gratings with different grating constants (Λ1 and Λ2). Each grating responds differently to strain and temperature changes, allowing the system to separate and compensate for temperature effects through mathematical evaluation of the two reflected wavelengths.
Solution Approach 2:
The invention changes the parameter of grating constant (Λ) between the two Bragg gratings. By selecting different grating constants, the gratings have different sensitivity characteristics to strain and temperature, enabling temperature compensation through comparative measurement and evaluation.
2Measurement precision
If a fourth Bragg grating is added for temperature compensation, then temperature compensation is achieved, but the sensor cannot be integrated into carbon fiber deformation bodies
Solution Approach 1:
The temperature compensation function is extracted from a separate mechanically decoupled Bragg grating and integrated into the strain measurement waveguide itself. The two Bragg gratings are now mechanically coupled and move together with the deformation body, enabling both strain measurement and temperature compensation while maintaining integration capability with carbon fiber structures.
Solution Approach 2:
The strain measurement waveguide is given multi-functionality by incorporating two Bragg gratings that simultaneously perform strain measurement and temperature compensation. This eliminates the need for separate compensation elements and allows integration with modern carbon fiber deformation bodies.
3Measurement precision
If compensation elements with different thermal expansion coefficients are used, then temperature compensation is achieved, but the compensation elements have complicated shapes and manufacturing tolerances
Solution Approach 1:
The mechanical compensation system with complicatedly shaped elements is replaced by an optical measurement system. Two Bragg gratings with different optical properties (refractive indices and grating constants) are used to achieve temperature compensation through optical wavelength measurements and mathematical evaluation, eliminating the need for complex mechanical compensation structures.
4Measurement precision
If material constants are predetermined for calculation, then temperature-independent strain measurement is achieved, but the system requires known material properties
Solution Approach 1:
The material constants (refractive indices n1 and n2, and grating constants Λ1 and Λ2) are predetermined and stored in the evaluation device before measurement. This preliminary preparation allows the system to quickly perform temperature-independent strain measurements without requiring real-time material characterization, reducing measurement complexity.
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 approach enables precise, high-accuracy strain measurements independent of temperature, with the ability to determine both strain and temperature changes using a straightforward evaluation method and known material constants, reducing production-related tolerances and enhancing measurement reliability.
Implementation Method 1
a periodic change in the refractive index is introduced as a so-called Bragg grating in the transmission direction of an optical waveguide. This Bragg grating acts like a frequency-selective filter, the grating constants of which are selected in such a way that a very narrow-band intensity maximum is reflected as a so-called peak when the light is radiated in a broad band.
Implementation Method 2
If an optical waveguide is stretched or compressed in the area of the periodic change in the refractive index, the position of the intensity maximum changes as a peak in its wavelength. This shift in the wavelength λ can be recorded and evaluated in terms of determining the extent of the elongation caused.
Implementation Method 3
the strain is always influenced by the temperature of the deformation body, so that this temperature must always be taken into account for a more precise strain measurement
Data Source
Figure 1~2
Figure 3
AI summary
An optical extension sensor (1) contains a level planar carrier layer (8) on or in which at least one optical waveguide (6, 7) is arranged in a force-fitting manner, said optical waveguide having at least one section with a Bragg grating (2, 3) for detecting the extension, wherein a first optical waveguide has an index of refraction and the Bragg grating (2, 3) has a particular grating constant. At least one further, second optical waveguide (7) or optical waveguide section (7) with a Bragg grating (3), which is arranged in a parallel manner, is also provided on or in the carrier layer (8). This second optical waveguide (7) is thermomechanically coupled to at least the first optical waveguide (6) or the first optical waveguide section and has a different temperature coefficient of the index of refraction to the first optical waveguide (6). The temperature-independent extension of the deformation body can be determined by measuring the two reflected wavelengths and by means of the refraction with a linear system of equations.