Fiber grating sensor with strain sensitivity capable of being tuned in real time and preparation method

Abstract

The invention belongs to the technical field of optical sensing, and particularly relates to a preparation method of a fiber grating sensor with strain sensitivity capable of being tuned in real time, and the preparation method comprises the following steps: S1, selecting an optical fiber, and fixing the optical fiber; s2, preparing a structure modulation type LPFG by using a laser, wherein the prepared structure modulation type LPFG is of a double-sided asymmetric D-shaped groove structure; s3, combining the magnetic nanoparticles with a curing agent to prepare a mixed solution; s4, putting the structure modulation type LPFG structure prepared in the S2 and the mixed solution in the S3 into a mold, and heating and curing to obtain a cylindrical sensor; and S5, taking out the cylindrical sensor, and checking the cylindrical sensor. According to the invention, the magneto-rheological elastomer is combined with the structure modulation type LPFG, so that the sensitivity can be effectively improved, and the dynamic adjustment of the strain sensitivity of the fiber grating sensor can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical sensing, and in particular relates to a fiber grating sensor with real-time tunable strain sensitivity and a preparation method thereof. Background Art

[0002] Fiber optic sensors can be widely used in structural health monitoring, oil exploration, aerospace, medical diagnosis and other fields due to their high sensitivity, anti-electromagnetic interference, corrosion resistance, small size and suitability for harsh environments. Long-period fiber grating (LPFG) is a fiber structure with axial periodic modulation of the refractive index. Its period is usually above 1 micron. It can be used as a transmission-type band-stop filter and can respond to physical quantities such as temperature, strain, and refractive index in the environment. Compared with traditional fiber Bragg gratings, LPFG has a wider spectral response range and higher sensitivity, so it has certain potential in sensing applications. The phase matching condition of LPFG is Where λ is the design wavelength, and are the effective refractive index of the core and the effective refractive index of the cladding, m is the cladding mode order, and Λ is the period. The characteristic of the structural modulation LPFG is that it modulates the cladding significantly. When the two ends of the structural modulation LPFG are subjected to a certain tension, its period will change significantly, which will affect the phase matching conditions and cause its resonance peak to drift significantly. Therefore, the strain sensitivity of its structure is relatively high.

[0003] Magnetorheological elastomer (MRE) is a smart material with adjustable mechanical properties under the action of a magnetic field. It is made of magnetic particles (such as iron powder or magnetic oxide particles) dispersed in an elastomer matrix (such as silicone rubber or polyurethane). Under the action of an external magnetic field, these magnetic particles interact through magnetic forces to form a chain structure or a local network, which significantly changes the mechanical properties of the elastomer, such as stiffness, Young's modulus, and damping characteristics. When there is no magnetic field, the mechanical properties of the magnetorheological elastomer are similar to those of ordinary elastomer materials, showing soft and compressible characteristics. However, once a magnetic field is applied, the magnetic particles will respond quickly, and the stiffness and hardness of the material will increase, showing a significant stiffening effect. This change in mechanical properties caused by the magnetic field is reversible. After the magnetic field is removed, the magnetorheological elastomer will return to its original state.

[0004] The strain sensitivity of existing long-period fiber grating sensors is usually fixed and cannot be adjusted in real time according to different application requirements. This limitation makes fiber optic sensors less adaptable in complex environments. For example, in some application scenarios, sensors need to detect subtle strains with high sensitivity, while in other cases the sensitivity needs to be reduced to avoid over-response or noise interference. Summary of the invention

[0005] The purpose of the present invention is to provide a fiber Bragg grating sensor with real-time tunable strain sensitivity and a preparation method, which can effectively improve the sensitivity and realize dynamic adjustment of the strain sensitivity of the fiber Bragg grating sensor by combining a magnetorheological elastomer with a structure-modulated LPFG.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for preparing a fiber grating sensor with real-time tunable strain sensitivity, the method comprising the following steps:

[0008] S1: Select the optical fiber and fix it;

[0009] In S1, 3-5 cm of the optical fiber coating is removed, and after being wiped with alcohol, the portion where the coating is removed is placed under the carbon dioxide laser and fixed with an optical fiber clamp; the stress applied to the optical fiber is controlled by a high-precision translation stage, so that the optical fiber is in a taut state.

[0010] S2: Using laser to prepare a structure-modulated LPFG, the prepared structure-modulated LPFG is a double-sided asymmetric D-shaped groove structure;

[0011] In S2, the specific steps of preparing the structure-modulated LPFG structure are as follows:

[0012] S21: setting a laser scanning path on a computer, and then controlling the laser to periodically etch the optical fiber to form a periodic D-shaped groove structure on the optical fiber;

[0013] S22: Then the optical fiber clamp is rotated to etch a D-shaped groove on the back of the D-shaped groove structure using the same parameters as in S21. The D-shaped groove etched on the back and the D-shaped groove on the front are offset by 300 μm. The width of the D-shaped groove is 200 μm, the period is 500 μm, and the number of periods is 10 μm.

[0014] S23: Connect the obtained optical fiber to a light source and a spectrometer. If a clear resonance peak appears in the spectral range, the structure-modulated LPFG is successfully prepared.

[0015] S3: combining the magnetic nanoparticles with the curing agent to prepare a mixed solution;

[0016] In S3, the specific steps of preparing the mixed solution are as follows:

[0017] S31: Mix polydimethylsiloxane and a curing agent according to a mass ratio, add magnetic Fe3O4 particles with a particle size of 10 nm, and stir evenly; the curing agent is made of resin material, and the mass ratio of polydimethylsiloxane to resin is 10:1.

[0018] S32: The solution is then placed in an ultrasonic oscillator and oscillated for 5 minutes to obtain a Fe3O4-PDMS nanoparticle mixed solution.

[0019] S4: placing the structure-modulated LPFG structure prepared in S2 and the mixed solution in S3 into a mold, heating and curing, and obtaining a cylindrical sensor;

[0020] In S4, the specific steps of preparing the cylindrical sensor are as follows:

[0021] S41: placing the structure-modulated LPFG into a polytetrafluoroethylene template, wherein the template has a semicircular groove and a fiber optic slot;

[0022] S42: pouring the mixed solution into the template, then fastening the two templates together, and placing them in a drying oven for curing;

[0023] S43: The PDMS solution containing Fe3O4 in the template is solidified at a temperature of 110°C for 1.5 h; a magnetorheological elastomer coating layer is formed on the periphery of the structure-modulated LPFG, and a cylindrical sensor is obtained after cooling.

[0024] S5: Take out the cylindrical sensor and inspect it.

[0025] In S5, the cylindrical sensor is taken out, and the two ends of the optical fiber sensing structure are connected to a light source and a spectrometer respectively to check the position and loss of the transmission spectrum of the structure.

[0026] A fiber grating sensor with real-time tunable strain sensitivity is prepared by adopting the preparation method of the fiber grating sensor with real-time tunable strain sensitivity.

[0027] The technical effects achieved by the present invention are:

[0028] The fiber grating sensor with real-time tunable strain sensitivity and the preparation method of the present invention improve the applicability of the LPFG strain sensor, and a magnetorheological elastomer is covered on its surface to improve its mechanical strength. When the external magnetic field intensity increases, the Young's modulus of the magnetorheological elastomer increases, thereby limiting the period of the structure-modulated LPFG so that it cannot be changed, so that the sensor has a smaller axial strain response. When the external magnetic field intensity is small, the Young's modulus of the magnetorheological elastomer is small, which has little effect on the sensitivity of the structure-modulated LPFG, so that the sensor maintains the original strain response. According to the characteristics of the real-time regulation of the sensor response by the magnetic field, an optical fiber strain sensor with real-time adjustable sensitivity is realized; it can be used in the field of optical fiber sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of the structure of a sensor according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the preparation process of the structure-modulated LPFG according to an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the structure and response mechanism of the structure-modulated LPFG according to an embodiment of the present invention.

[0032] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0033] 1. Structural modulation LPFG; 2. Magnetorheological elastomer coating; 3. Computer; 4. D-shaped groove; 5. High-precision translation stage; 6. Laser; 7. Optical fiber; 8. Optical fiber clamp; 9. Optical fiber end face; 10. Optical fiber axis. DETAILED DESCRIPTION

[0034] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0035] The optical fiber sensor is composed of a structure-modulated LPFG1 and a magnetorheological elastomer coating layer 2. The specific manufacturing method is to use a laser 6 to prepare the structure-modulated LPFG1, and then coat the magnetorheological elastomer coating layer 2 thereon.

[0036] like Figure 1-Figure 3 As shown, a method for preparing a fiber grating sensor with real-time tunable strain sensitivity comprises the following steps:

[0037] S1: Select the optical fiber 7 and fix the optical fiber 7;

[0038] In S1, 3-5 cm of the coating of the optical fiber 7 is removed, and after being wiped with alcohol, the portion without the coating is placed under the carbon dioxide laser 6 and fixed with a fiber clamp 8; the stress applied to the optical fiber 7 is controlled by the high-precision displacement stage 5, so that the optical fiber 7 is in a taut state.

[0039] S2: using a laser 6 to prepare a structure-modulated LPFG1, wherein the prepared structure-modulated LPFG1 is a double-sided asymmetric D-shaped groove 4 structure;

[0040] In S2, the specific steps of preparing the structure-modulated LPFG1 structure are as follows:

[0041] S21: setting a scanning path of the laser 6 on the computer 3, and then controlling the laser 6 to periodically etch the optical fiber 7, so as to form a periodic D-shaped groove 4 structure on the optical fiber 7;

[0042] S22: Then, the optical fiber clamp 8 is rotated to etch a D-shaped groove 4 on the back of the D-shaped groove 4 structure using the same parameters as in S21. The D-shaped groove 4 etched on the back is offset by 300 μm from the D-shaped groove 4 on the front side. The width of the D-shaped groove 4 is 200 μm, the period is 500 μm, and the number of periods is 10 μm.

[0043] S23: Connect the obtained optical fiber 7 to a light source and a spectrometer. If a clear resonance peak appears in the spectral range, the structure-modulated LPFG1 is successfully prepared.

[0044] like Figure 3 As shown in FIG. 1 , when the two ends of the structure-modulated LPFG1 are subjected to tension, its period will change significantly, thereby affecting the phase matching condition and causing its resonance peak to drift significantly.

[0045] S3: combining the magnetic nanoparticles with the curing agent to prepare a mixed solution;

[0046] In S3, the specific steps of preparing the mixed solution are as follows:

[0047] S31: polydimethylsiloxane and curing agent are mixed according to a mass ratio, and magnetic Fe3O4 particles with a particle size of 10 nm are added and stirred evenly; the curing agent is a resin material, and the mass ratio of polydimethylsiloxane to resin is 10:1.

[0048] S32: The solution is then placed in an ultrasonic oscillator and oscillated for 5 minutes to obtain a Fe3O4-PDMS nanoparticle mixed solution.

[0049] S4: placing the structure-modulated LPFG1 structure prepared in S2 and the mixed solution in S3 into a mold, heating and curing, and obtaining a cylindrical sensor;

[0050] In S4, the specific steps of preparing the cylindrical sensor are as follows:

[0051] S41: placing the structure-modulated LPFG1 into a polytetrafluoroethylene template, wherein the template has a semicircular groove and a slot for optical fiber 7;

[0052] S42: pouring the mixed solution into the template, then fastening the two templates together, and placing them in a drying oven for curing;

[0053] S43: The PDMS solution containing Fe3O4 in the template is solidified at a temperature of 110°C for 1.5 hours; a magnetorheological elastomer coating layer 2 is formed on the periphery of the structure-modulated LPFG1, and a cylindrical sensor is obtained after cooling.

[0054] S5: Take out the cylindrical sensor and inspect it.

[0055] In S5, the cylindrical sensor is taken out, and the two ends of the optical fiber sensing structure are connected to the light source and the spectrometer respectively to check the position and loss of the transmission spectrum of the structure.

[0056] A fiber Bragg grating sensor with real-time tunable strain sensitivity is prepared by using the above-mentioned preparation method of a fiber Bragg grating sensor with real-time tunable strain sensitivity. This preparation method is also applicable to other types of structure-modulated LPFG1 or doped with other types of magnetic particles. For example, the fiber D-shaped groove 4 can be replaced with a fiber bevel groove, and the Fe3O4 particles in this article can be replaced with cobalt particles.

[0057] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity, characterized in that: The preparation method comprises the following steps: S1: Select the optical fiber and fix it; S2: Using laser to prepare a structure-modulated LPFG, the prepared structure-modulated LPFG is a double-sided asymmetric D-shaped groove structure; S3: combining the magnetic nanoparticles with the curing agent to prepare a mixed solution; S4: placing the structure-modulated LPFG structure prepared in S2 and the mixed solution in S3 into a mold, heating and curing, and obtaining a cylindrical sensor; S5: Take out the cylindrical sensor and inspect it.

2. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 1, characterized in that: In S1, 3-5 cm of the optical fiber coating is removed, and after being wiped with alcohol, the portion where the coating is removed is placed under the carbon dioxide laser and fixed with an optical fiber clamp; the stress applied to the optical fiber is controlled by a high-precision translation stage, so that the optical fiber is in a taut state.

3. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 1, characterized in that: In S2, the specific steps of preparing the structure-modulated LPFG structure are as follows: S21: setting a laser scanning path on a computer, and then controlling the laser to periodically etch the optical fiber to form a periodic D-shaped groove structure on the optical fiber; S22: Then the optical fiber clamp is rotated to etch a D-shaped groove on the back of the D-shaped groove structure using the same parameters as in S21. The D-shaped groove etched on the back is offset by 300 μm from the D-shaped groove on the front side. S23: Connect the obtained optical fiber to a light source and a spectrometer. If a clear resonance peak appears in the spectral range, the structure-modulated LPFG is successfully prepared.

4. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 3, characterized in that: The width of the D-groove is 200 μm, the period is 500 μm, and the number of periods is 10 μm.

5. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 1, characterized in that: In S3, the specific steps of preparing the mixed solution are as follows: S31: polydimethylsiloxane and curing agent are mixed according to a mass ratio, and magnetic Fe3O4 particles with a particle size of 10 nm are added and stirred evenly; S32: The solution is then placed in an ultrasonic oscillator and oscillated for 5 minutes to obtain a Fe3O4-PDMS nanoparticle mixed solution.

6. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 5, characterized in that: The curing agent is a resin material, and the mass ratio of polydimethylsiloxane to the resin is 10:

1.

7. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 1, characterized in that: In S4, the specific steps of preparing the cylindrical sensor are as follows: S41: placing the structure-modulated LPFG into a polytetrafluoroethylene template, wherein the template has a semicircular groove and a fiber optic slot; S42: pouring the mixed solution into the template, then fastening the two templates together, and placing them in a drying oven for curing; S43: The PDMS solution containing Fe3O4 in the template is solidified to form a magnetorheological elastomer coating layer on the periphery of the structure-modulated LPFG, and a cylindrical sensor is obtained after cooling.

8. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 7, characterized in that: The curing temperature is 110°C and the curing time is 1.5h.

9. The method for preparing a fiber Bragg grating sensor with real-time tunable strain sensitivity according to claim 1, characterized in that: In S5, the cylindrical sensor is taken out, and the two ends of the optical fiber sensing structure are connected to a light source and a spectrometer respectively to check the position and loss of the transmission spectrum of the structure.

10. A fiber Bragg grating sensor with real-time tunable strain sensitivity, characterized in that: The fiber Bragg grating sensor is manufactured by adopting the method for manufacturing a fiber Bragg grating sensor with real-time tunable strain sensitivity as described in any one of claims 1 to 9.

Images