A device and method for measuring strain sensitivity of fiber grating in a wide temperature range

Abstract

The application discloses a kind of measuring device and method of fiber grating strain sensitivity in wide temperature range, including test piece, first / second optical fiber, first / second fiber grating;First fiber grating is engraved on first optical fiber, and second fiber grating is engraved on second optical fiber, and first protection device, second protection device are used to protect first fiber grating, second fiber grating, so that it is not subjected to the fixed stress of first / second connecting device;Different tensile strain is applied to first fiber grating and second fiber grating at room temperature, and first measuring device and second measuring device are installed on test piece by first connecting device and second connecting device.The difference of wavelength change of fiber grating at different temperatures is used to measure the strain sensitivity of fiber grating at different temperatures, which overcomes the influence of structural size change, inaccurate material mechanics / thermal parameters and other factors on the measurement of fiber grating strain sensitivity in wide temperature range in traditional test device.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a device and method for measuring the strain sensitivity of a fiber optic grating over a wide temperature range. Background Technology

[0002] Fiber Bragg grating strain sensors have been successfully applied to structural health monitoring of spacecraft, aircraft and other devices due to their advantages such as small size, light weight and resistance to electromagnetic interference. However, they are currently mainly used in the room temperature range. Fiber Bragg grating strain testing technology with a wide temperature range is still in the research stage.

[0003] Monitoring of rocket engines, aircraft engines, and spacecraft thermal insulation structures requires fiber Bragg grating strain sensors to operate over a wide temperature range. However, existing measurement devices for measuring the strain sensitivity coefficient of fiber Bragg gratings over a wide temperature range are costly, and their accuracy is limited by factors such as changes in structural dimensions and inaccuracies in material mechanical / thermal parameters under high and low temperature environments. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a device and method for measuring the strain sensitivity of fiber optic gratings over a wide temperature range, thus overcoming the problems of high cost and low measurement accuracy of existing fiber optic grating strain sensitivity measuring devices over a wide temperature range.

[0005] The technical solution of this invention is:

[0006] A measuring device for fiber optic grating strain sensitivity over a wide temperature range includes a specimen, a first measuring device, a second measuring device, a first connecting device for fixing the first measuring device to the specimen, and a second connecting device for fixing the second measuring device to the specimen.

[0007] The first measuring device includes a first optical fiber, a first fiber grating, and a first protection device; the second measuring device includes a second optical fiber, a second fiber grating, and a second protection device.

[0008] The first fiber grating is etched on the first fiber, and the second fiber grating is etched on the second fiber. The first fiber grating and the second fiber grating are fiber gratings of the same state and batch. The first protection device is used to protect the first fiber grating so that the first fiber grating is not subjected to the fixing stress of the first connecting device. The second protection device is used to protect the second fiber grating so that the second fiber grating is not subjected to the fixing stress of the second connecting device.

[0009] At room temperature, tensile strains of different magnitudes are applied to the first fiber grating and the second fiber grating, and the first measuring device and the second measuring device are mounted on the specimen through the first connecting device and the second connecting device.

[0010] The first protection device includes a first capillary sleeved on the outside of the first optical fiber, the length of which covers the length of the first fiber grating; the second protection device includes a second capillary sleeved on the outside of the second optical fiber, the length of which covers the length of the second fiber grating.

[0011] The space between the inner surface of the first capillary and the outer surface of the first fiber grating is filled with air; the space between the inner surface of the second capillary and the outer surface of the second fiber grating is filled with air.

[0012] The inner diameter of the first capillary is greater than the outer diameter of the first fiber grating and less than or equal to 1.5 times the outer diameter of the first fiber grating; the inner diameter of the second capillary is greater than the outer diameter of the second fiber grating and less than or equal to 1.5 times the outer diameter of the second fiber grating.

[0013] The first connecting device includes a first adhesive, and the second connecting device includes a second adhesive.

[0014] The first fiber grating and the second fiber grating are bonded and installed on the specimen in parallel.

[0015] The first and second fiber gratings experience different tensile strains at room temperature.

[0016] A method for measuring the strain sensitivity of a fiber Bragg grating over a wide temperature range, using any of the measuring devices described above, includes the following steps:

[0017] S1: Strain measurements are performed on the first and second fiber gratings at room temperature T0 to obtain the strain sensitivity coefficients K of the first and second fiber gratings at room temperature T0. ε,T0 ;

[0018] S2: At room temperature T0, apply tensile strain ε1 to the first fiber grating and tensile strain ε2 to the second fiber grating. Then, fix the optical fibers at both ends of the first and second fiber gratings, as well as the first and second protective devices, onto the specimen using the first and second connecting devices to obtain the device under test. Record the center wavelength λ of the first fiber grating after fixing. 1,T0 The center wavelength λ of the second fiber grating 2,T0 ;

[0019] S3: Place the device under test at temperature T, and after the temperature stabilizes, record the center wavelength λ of the first fiber grating. 1,T and the center wavelength λ of the second fiber optic grating 2,T ;

[0020] Based on the center wavelength λ of the first fiber grating at room temperature T0 1,T0 The center wavelength λ of the second fiber grating 2,T0The tensile strain ε1 of the first fiber grating, the tensile strain ε2 of the second fiber grating, and the center wavelength λ of the first fiber grating at temperature T. 1,T The center wavelength λ of the second fiber grating 2,T Determine the strain sensitivity K of the fiber grating at temperature T. ε,T .

[0021] The strain sensitivity K of the first fiber grating and the second fiber grating at temperature T ε,T Represented as

[0022]

[0023] In summary, this application includes at least the following beneficial technical effects:

[0024] (1) The present invention provides a device and method for measuring the strain sensitivity of fiber gratings over a wide temperature range. It proposes to measure the strain sensitivity of fiber gratings by preloading them with different tensile strains. This overcomes the influence of factors such as changes in the structural dimensions of the test device under high and low temperature environments and inaccurate material mechanical / thermal parameters on the measurement of the strain sensitivity of fiber gratings over a wide temperature range in traditional measurement methods.

[0025] (2) The present invention provides a device and method for measuring the strain sensitivity of fiber optic gratings over a wide temperature range. It proposes to use fiber optic gratings of the same state and batch for differential measurement, thereby compensating for the influence of temperature on fiber optic gratings and realizing accurate measurement of the strain sensitivity of fiber optic gratings over a wide temperature range. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the device structure of a specific embodiment of the fiber optic grating strain sensitivity measurement device and method over a wide temperature range according to the present invention.

[0027] Figure 2 for Figure 1 Sectional view at point AA.

[0028] Explanation of reference numerals in the attached drawings: 1-1, First optical fiber; 1-2, Second optical fiber; 2-1, First fiber grating; 2-2, Second fiber grating; 3-1, First capillary; 3-2, Second capillary; 4, Specimen; 5-1, First adhesive; 5-2, Second adhesive. Detailed Implementation

[0029] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0030] The following will provide a more detailed description of the device and method for measuring the strain sensitivity of a fiber optic grating over a wide temperature range, in conjunction with the accompanying drawings and specific embodiments.

[0031] like Figure 1 As shown, the present invention discloses a measuring device and method for measuring the strain sensitivity of fiber Bragg gratings over a wide temperature range. The measuring device includes a first optical fiber 1-1, a second optical fiber 1-2, a first fiber Bragg grating 2-1 and a second fiber Bragg grating 2-2 of the same state and batch, a first capillary tube 3-1, a second capillary tube 3-2, a specimen 4, a first adhesive 5-1, and a second adhesive 5-2.

[0032] like Figure 1 and Figure 2 As shown, a first fiber grating 2-1 is etched on the upper part of the first optical fiber 1-1, and a second fiber grating 2-2 is etched on the upper part of the second optical fiber 1-2. The first fiber grating 2-1 is placed inside the first capillary tube 3-1, and the second fiber grating 2-2 is placed inside the second capillary tube 3-2. The length of the first capillary tube 3-1 covers the length of the first fiber grating 2-1, and the length of the second capillary tube 3-2 covers the length of the second fiber grating 2-2. The inner diameter of the first capillary tube 3-1 is larger than that of the first fiber grating. The outer diameter of the first fiber grating 2-1 is less than or equal to 1.5 times the outer diameter of the first fiber grating 2-1. The inner diameter of the second capillary 3-2 is greater than the outer diameter of the second fiber grating 2-2 but less than or equal to 1.5 times the outer diameter of the second fiber grating 2-2. There is air between the inner surface of the first capillary 3-1 and the outer surface of the first fiber grating 2-1, and there is air between the inner surface of the second capillary 3-2 and the outer surface of the second fiber grating 2-2. The first capillary 3-1 and the second capillary 3-2 are made of polyimide or quartz.

[0033] like Figure 1 and Figure 2 As shown, different preload tensile strains were applied to the first fiber Bragg grating 2-1 and the second fiber Bragg grating 2-2 under room temperature conditions. The optical fibers at both ends of the first fiber Bragg grating 2-1 and the second fiber Bragg grating 2-2, the first capillary tube 3-1, and the second capillary tube 3-2 were then bonded to the specimen 4 using the first adhesive 5-1 and the second adhesive 5-2. The lengths of the first capillary tube 3-1 and the second capillary tube 3-2 were within the bonding length range of the first adhesive 5-1 and the second adhesive 5-2. The first adhesive 5-1 completely covered the circumference of the first capillary tube 3-1 and the first optical fiber 1-1, and the second adhesive 5-2 completely covered the circumference of the second capillary tube 3-2 and the second optical fiber 1-2. Furthermore, the width of the first adhesive 5-1 and the second adhesive 5-2 increased along the direction closer to the surface of the specimen 4, ensuring the stability of the bonding. The bonding length, width, and position of the first adhesive 5-1 and the second adhesive 5-2 were consistent.

[0034] After the first adhesive 5-1 and the second adhesive 5-2 are bonded, air remains between the inner surface of the first capillary 3-1 and the outer surface of the first fiber grating 2-1, and between the inner surface of the second capillary 3-2 and the outer surface of the second fiber grating 2-2. The first adhesive 5-1 and the second adhesive 5-2 can be used to fix the first optical fiber 1-1 and the second optical fiber 1-2 without causing direct contact stress on the first fiber grating 2-1 and the second fiber grating 2-2. Furthermore, the first fiber grating 2-1 and the second fiber grating 2-2 are bonded and installed parallel to each other on the specimen 4. With this relative position setting, the structural dimensional changes of the first fiber grating 2-1 and the second fiber grating 2-2 under the influence of the same specimen 4 are basically consistent under high and low temperature environments, thus essentially eliminating the error caused by structural dimensional changes under high and low temperature environments.

[0035] Strain measurements were performed on the first fiber grating 2-1 and the second fiber grating 2-2 at room temperature T0 to obtain the strain sensitivity coefficient K. ε,T0 The measurement method refers to "GB13992-2010-T Metal-bonded Resistance Strain Gauge".

[0036] Measurement methods include:

[0037] A tensile strain ε1 was applied to the first fiber grating 2-1 and a tensile strain ε2 was applied to the second fiber grating 2-2 at room temperature T0. Then, the optical fibers at both ends of the first fiber grating 2-1 and the second fiber grating 2-2, as well as the first capillary and the second capillary, were bonded to the specimen using the first adhesive and the second adhesive, respectively. The first fiber grating 2-1 was parallel to the second fiber grating 2-2. The center wavelength λ of the first fiber grating 2-1 after bonding was recorded. 1,T0 The center wavelength λ of the second fiber grating 2-2 2,T0 .

[0038] Place the measuring device at temperature T, and after the temperature stabilizes, record the center wavelength λ of the first fiber grating 2-1. 1,T The center wavelength λ of the second fiber grating 2-2 2,T .

[0039] Based on the center wavelength λ of the first fiber grating 2-1 at room temperature T0 1,T0 The center wavelength λ of the second fiber grating 2-2 2,T0 The tensile strain ε1 on the first fiber grating 2-1, the tensile strain ε2 on the second fiber grating 2-2, and the center wavelength λ of the first fiber grating 2-1 at temperature T. 1,T The center wavelength λ of the second fiber grating 2-2 2,T The strain sensitivity K of the fiber grating at temperature T was calculated. ε,T .

[0040]

[0041] The parts of this invention not disclosed in detail are common knowledge to those skilled in the art.

[0042] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A device for measuring the strain sensitivity of a fiber optic grating over a wide temperature range, characterized in that: Includes a test piece (4), a first measuring device, a second measuring device, a first connecting device for fixing the first measuring device to the test piece (4), and a second connecting device for fixing the second measuring device to the test piece (4); The first measuring device includes a first optical fiber (1-1), a first fiber optic grating (2-1), and a first protection device; the second measuring device includes a second optical fiber (1-2), a second fiber optic grating (2-2), and a second protection device. A first fiber grating (2-1) is inscribed on a first optical fiber (1-1), and a second fiber grating (2-2) is inscribed on a second optical fiber (1-2). The first fiber grating (2-1) and the second fiber grating (2-2) are fiber gratings of the same state and batch. A first protective device is used to protect the first fiber grating (2-1) so that the first fiber grating (2-1) is not subjected to the fixing stress of the first connecting device. A second protective device is used to protect the second fiber grating (2-2) so that the second fiber grating (2-2) is not subjected to the fixing stress of the second connecting device. At room temperature, tensile strains of different magnitudes are applied to the first fiber grating (2-1) and the second fiber grating (2-2), and the first measuring device and the second measuring device are mounted on the specimen (4) through the first connecting device and the second connecting device. The first protection device includes a first capillary tube (3-1) sleeved on the outside of the first optical fiber (1-1), the length of the first capillary tube (3-1) covering the length of the first fiber grating (2-1); the second protection device includes a second capillary tube (3-2) sleeved on the outside of the second optical fiber (1-2), the length of the second capillary tube (3-2) covering the length of the second fiber grating (2-2). Air is present between the inner surface of the first capillary (3-1) and the outer surface of the first fiber grating (2-1); air is present between the inner surface of the second capillary (3-2) and the outer surface of the second fiber grating (2-2). The inner diameter of the first capillary (3-1) is greater than the outer diameter of the first fiber grating (2-1) and less than or equal to 1.5 times the outer diameter of the first fiber grating (2-1); the inner diameter of the second capillary (3-2) is greater than the outer diameter of the second fiber grating (2-2) and less than or equal to 1.5 times the outer diameter of the second fiber grating (2-2); The first connecting device includes a first adhesive (5-1), and the second connecting device includes a second adhesive (5-2); The first fiber grating (2-1) and the second fiber grating (2-2) are bonded and installed in parallel on the specimen (4); The tensile strains experienced by the first fiber grating (2-1) and the second fiber grating (2-2) at room temperature are different.

2. A method for measuring the strain sensitivity of a fiber optic grating over a wide temperature range, characterized in that... Using the measuring device according to claim 1 includes the following steps: S1: Strain measurements were performed on the first fiber grating (2-1) and the second fiber grating (2-2) at room temperature T0 to obtain the strain sensitivity coefficient K of the first fiber grating (2-1) and the second fiber grating (2-2) at room temperature T0. ε,T0 ; S2: At room temperature T0, apply tensile strain ε1 to the first fiber grating (2-1) and tensile strain ε2 to the second fiber grating (2-2). Then, fix the optical fibers at both ends of the first fiber grating (2-1) and the second fiber grating (2-2), as well as the first and second protective devices, to the specimen through the first and second connecting devices to obtain the device under test. Record the center wavelength λ of the fixed first fiber grating (2-1). 1,T0 The center wavelength λ of the second fiber grating (2-2) 2,T0 ; S3: Place the device under test at temperature T, and after the temperature stabilizes, record the center wavelength λ of the first fiber grating (2-1). 1,T The center wavelength λ of the second fiber grating 2,T ; Based on the center wavelength λ of the first fiber grating (2-1) at room temperature T0 1,T0 The center wavelength λ of the second fiber grating (2-2) 2,T0 The tensile strain ε1 on the first fiber grating (2-1) and the tensile strain ε2 on the second fiber grating (2-2), and the center wavelength λ of the first fiber grating (2-1) at temperature T. 1,T The center wavelength λ of the second fiber grating (2-2) 2,T Determine the strain sensitivity K of the fiber grating at temperature T. ε,T ; The strain sensitivity K of the first fiber grating (2-1) and the second fiber grating (2-2) at the temperature T. ε,T Represented as 。

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