High-sensitivity strain sensor based on vernier effect air microbubble

Abstract

This invention belongs to the field of fiber optic sensing application technology, specifically relating to a high-sensitivity air microbubble strain sensor based on the vernier effect and its fabrication method. The sensor consists of a parallel microbubble sensing cavity Fabry-Perot interferometer and an air reference cavity Fabry-Perot interferometer. The microbubble sensing cavity Fabry-Perot interferometer is made by fusion splicing two single-mode optical fibers, with an ellipsoidal microbubble embedded at the center of its conical region. The air reference cavity Fabry-Perot interferometer is made by fusion splicing two single-mode optical fibers through a hollow capillary tube, with the two single-mode fiber segments forming an air cavity within the capillary tube. When the microbubble sensing cavity and the air reference cavity are connected in parallel, their signals overlap, resulting in an envelope modulation effect. Compared to using the microbubble sensing cavity alone, this significantly amplifies the sensitivity, improves the sensor's sensing performance, and achieves high-sensitivity air microbubble strain sensing.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing application technology, specifically relating to a high-sensitivity strain sensor for air microbubbles based on the vernier effect and its fabrication method. Background Technology

[0002] Strain is a crucial parameter in medical monitoring, civil engineering, aerospace, structural engineering, the automotive industry, and the military. Fiber optic sensors offer unique advantages such as small size, remote monitoring capability, high flexibility, low propagation loss, low manufacturing cost, and resistance to electromagnetic interference, making them widely studied. Fiber optic sensors based on different principles have been demonstrated and researched, including fiber Bragg gratings (FBGs), Sagnac interferometers, Mach-Zehnder interferometers (MZIs), and Fabry-Perot interferometers (FPIs). Compared to other sensor structures, fiber optic sensors based on the Fabry-Perot interferometry principle offer advantages such as high sensitivity, linear response, low-temperature cross-sensitivity, and miniaturization.

[0003] In strain measurement, fiber optic sensors based on the Fabry-Perot interferometry principle offer advantages such as high sensitivity, linear response, low temperature cross-sensitivity, and small size compared to other sensor structures. Among them, bubble strain sensors exhibit even higher sensitivity than traditional strain sensors. Furthermore, because air has minimal thermal expansion and contains no moisture-sensitive materials, the effects of ambient temperature and humidity on strain measurements are negligible when the Fabry-Perot interferometer composed of bubbles operates in an atmospheric environment. Therefore, the bubble strain sensor has very low cross-sensitivity to temperature and humidity. Summary of the Invention

[0004] Based on existing technologies in the background section, this invention provides a high-sensitivity strain sensor based on the vernier effect using air microbubbles, and a method for fabricating the same. This strain sensor significantly improves the sensitivity of stress measurement and is cost-effective.

[0005] The technical solution adopted in this invention is: a high-sensitivity strain sensor for air microbubbles based on the vernier effect, wherein the strain sensor is composed of a parallel microbubble sensing cavity Fabry-Perot interferometer and an air reference cavity Fabry-Perot interferometer.

[0006] The microbubble sensing cavity Fabry-Perot interferometer is made by fusion splicing two single-mode optical fibers. An ellipsoidal microbubble is embedded in the center of the conical region of the microbubble sensing cavity Fabry-Perot interferometer. The air reference cavity Fabry-Perot interferometer is made by fusion splicing two single-mode optical fibers through a hollow capillary tube. The two single-mode optical fibers form an air cavity inside the hollow capillary tube.

[0007] Furthermore, the axial diameter of the ellipsoidal microbubble is 51.15 μm - 53.15 μm, and its longitudinal diameter is 65.15 μm - 67.15 μm; the length of the air cavity is 62.32 μm - 64.32 μm.

[0008] Furthermore, the axial diameter of the ellipsoidal microbubble is 51.15 μm, its longitudinal diameter is 65.15 μm, and the length of the air cavity is 62.32 μm.

[0009] Furthermore, the axial diameter of the ellipsoidal microbubble is 52.15 μm, its longitudinal diameter is 66.15 μm, and the length of the air cavity is 63.32 μm.

[0010] Furthermore, the axial diameter of the ellipsoidal microbubble is 53.15 μm, its longitudinal diameter is 67.15 μm, and the length of the air cavity is 64.32 μm.

[0011] Furthermore, the fabrication method of the microbubble sensing cavity Fabry-Perot interferometer includes the following steps:

[0012] Step 1: Wipe the stripped single-mode fiber with alcohol and cut it smoothly with a fiber optic cleaver; then put the single-mode fiber into the fiber optic fusion splicer (Fujikura 80 s), and precisely control the left and right motors of the fiber optic fusion splicer to place the single-mode fiber near the discharge electrode.

[0013] Step 2: Adjust the discharge time and discharge power parameters of the fiber optic fusion splicer, and shape the flat end face of the single-mode fiber into a smooth spherical surface through multiple discharges; manually remove the two single-mode fiber sections from the fiber optic fusion splicer, and immerse a small amount of refractive index matching liquid (Nd: 1.47) on the surface of the smooth spherical surface of the two single-mode fibers.

[0014] Step 3: Place the single-mode fiber processed in Step 2 back into the fiber fusion splicer. Adjust the drive motor on the fiber fusion splicer to align the cores of the two single-mode fiber segments, that is, align the centers of the two cores (align the centers of the two cores in the X and Y planes). After alignment, the two single-mode fiber segments are in a slightly compressed state ready for fusion. By precisely controlling the discharge time and discharge power of the fiber fusion splicer, microbubbles are formed in the middle of the two smooth spherical surfaces.

[0015] Step 4: Perform several discharges on the microbubbles generated in Step 3. Apply axial tension to the single-mode fiber by precisely controlling the motor of the fiber optic fusion splicer. Use arc discharge technology to precisely control and adjust the discharge time and discharge power. Use arc discharge technology to form thin-walled ellipsoidal microbubbles. The resulting optical fiber with ellipsoidal microbubbles is a microbubble sensing cavity Fabry-Perot interferometer.

[0016] Furthermore, the fabrication method of the air reference cavity Fabry-Perot interferometer includes the following steps:

[0017] Step 1: Insert the flattened end of the single-mode fiber into the hollow capillary tube. Then, place the hollow capillary tube with the single-mode fiber inserted into the fiber fusion splicer. Use the fiber fusion splicer to discharge the end of the hollow capillary tube with a discharge power of +5 and a discharge time of 600ms to fuse the hollow capillary tube and the single-mode fiber together.

[0018] Step 2: Take another single-mode fiber and insert the flattened end of the single-mode fiber into the hollow capillary. Adjust the distance between the end faces of the two single-mode fibers inside the hollow capillary using the drive motor of the fiber fusion splicer until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble. Then, use the fiber fusion splicer to discharge the end of the hollow capillary with a discharge power of +5 and a discharge time of 600ms, fusing the hollow capillary and the other single-mode fiber together. The two single-mode fibers connected to the hollow capillary form an air cavity in the hollow capillary. The resulting fiber with an air cavity is an air reference cavity Fabry-Perot interferometer.

[0019] Furthermore, applying the optical simulation of the vernier effect to fiber optic interferometers is an effective means to improve the sensitivity and resolution of optical sensors. The vernier effect is achieved by acquiring two slightly detuned interference signals and superimposing them to generate a vernier envelope. Compared to a single interferometer constituting the structure, the vernier envelope exhibits amplified sensitivity. Structurally, a parallel fiber Fabry-Perot interferometer is fabricated using the optical vernier effect. An elliptical microbubble formed by two single-mode fibers prepared by arc discharge in a fusion splicer is used to fabricate the microbubble sensing cavity, while the air reference cavity consists of two end-face-cut flattened single-mode fibers inserted into a quartz capillary.

[0020] Furthermore, the parallel microbubble sensing cavity Fabry-Perot interferometer and the air reference cavity Fabry-Perot interferometer are connected via a two-to-two coupler.

[0021] Furthermore, the elliptical microbubble and air cavity of the high-sensitivity strain sensor are used as the sensing cavity and reference cavity, respectively, and the parallel sensing cavity and reference cavity constitute a strain sensor with high sensitivity.

[0022] The beneficial effects of this invention are as follows: It provides a high-sensitivity strain sensor based on the vernier effect for air microbubbles and its fabrication method. The parallel structure strain sensor significantly improves the sensitivity of stress measurement, achieving an ultra-high strain sensitivity of -42.04 pm / με, which is 4.76 times higher in lateral strain sensitivity compared to existing single microbubble sensing cavities. Within a temperature range of 30-60°C, the sensor's temperature sensitivity and lateral temperature sensitivity are 3.64 pm / °C and 0.087 µε / °C, respectively, thereby reducing measurement errors caused by temperature changes. This makes strain measurements less affected by temperature in complex environments, resulting in more accurate data. Furthermore, the fabrication process is simple and the manufacturing cost is low. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 1;

[0024] Figure 2 This is a schematic diagram of the microbubble sensing cavity Fabry-Perot interferometer in Example 1;

[0025] Figure 3 This is a schematic diagram of the air reference cavity Fabry-Perot interferometer in Embodiment 1;

[0026] Figure 4 This is a schematic diagram of step one of the high-sensitivity strain sensor fabrication method in Example 5;

[0027] Figure 5 This is a schematic diagram of step two in the fabrication method of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 5;

[0028] Figure 6 This is a schematic diagram of step three in the fabrication method of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 5;

[0029] Figure 7 This is a schematic diagram of step four in the fabrication method of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 5;

[0030] Figure 8 This is a schematic diagram of step 1 in the fabrication method of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 6;

[0031] Figure 9 This is a schematic diagram of step 2 in the fabrication method of the high-sensitivity strain sensor for air microbubbles based on the vernier effect in Example 6;

[0032] Figure 10This is the interference spectrum of a high-sensitivity air microbubble strain sensor based on the vernier effect after applying axial stress of 0-1000 με to the sensor in 200 με steps.

[0033] Figure 11 This is the interference spectrum of an air microbubble high-sensitivity strain sensor based on the vernier effect, where the temperature is increased from 30℃ to 60℃ in 5℃ increments.

[0034] Figure labels: 1. Microbubble sensing cavity Fabry-Perot interferometer; 2. Air reference cavity Fabry-Perot interferometer; 3. Ellipsoidal microbubble; 4. Hollow capillary; 5. Air cavity; 6. Fiber optic fusion splicer; 7. Smooth spherical surface; 8. Refractive index matching fluid; 9. Fiber core; 10. Microbubble. Detailed Implementation

[0035] Example

[0036] like Figure 1 As shown, the high-sensitivity strain sensor based on the vernier effect for air microbubbles consists of a parallel microbubble sensing cavity Fabry-Perot interferometer 1 and an air reference cavity Fabry-Perot interferometer 2.

[0037] like Figure 2 and Figure 3 As shown, the microbubble sensing cavity Fabry-Perot interferometer 1 is made by fusion splicing two single-mode optical fibers. An ellipsoidal microbubble 3 is embedded in the center of the conical region of the microbubble sensing cavity Fabry-Perot interferometer 1. The air reference cavity Fabry-Perot interferometer 2 is made by fusion splicing two single-mode optical fibers through a hollow capillary tube 4. The two single-mode optical fibers inside the hollow capillary tube 4 form an air cavity 5. The axial diameter of the ellipsoidal microbubble 3 is 51.15 μm, and its longitudinal diameter is 65.15 μm; the length of the air cavity 5 is 62.32 μm.

[0038] Example

[0039] Based on the technical solution of Example 1, the parameters of the microbubble and the air cavity are changed. The axial diameter of the ellipsoidal microbubble 3 is 52.15 μm, and its longitudinal diameter is 66.15 μm; the length of the air cavity 5 is 63.32 μm.

[0040] Example

[0041] Based on the technical solution of Example 1, the parameters of the microbubble and the air cavity are changed. The axial diameter of the ellipsoidal microbubble 3 is 53.15 μm, and its longitudinal diameter is 67.15 μm; the length of the air cavity 5 is 64.32 μm.

[0042] Example

[0043] The high-sensitivity air microbubble strain sensors based on the vernier effect in the above three embodiments are applied to the field of strain measurement technology.

[0044] Example

[0045] like Figures 4-7 As shown, the fabrication method of the microbubble sensing cavity Fabry-Perot interferometer includes the following steps:

[0046] Step 1: Wipe the single-mode fiber with alcohol to remove the coating, and then use a fiber optic cleaver to smoothly cut the single-mode fiber. Then, put the single-mode fiber into the fiber optic fusion splicer 6, and precisely control the left and right motors of the fiber optic fusion splicer to place the single-mode fiber near the discharge electrode.

[0047] Step 2: Adjust the discharge time and discharge power parameters of the fiber optic fusion splicer 6, and shape the flat end face of the single-mode fiber into a smooth spherical surface 7 through multiple discharges; manually remove the two single-mode fiber segments from the fiber optic fusion splicer 6, and immerse a small amount of refractive index matching liquid 8 on the surface of the smooth spherical surface 7 of the two single-mode fibers.

[0048] Step 3: Place the single-mode fiber processed in Step 2 back into the fiber fusion splicer 6. Align the cores 9 of the two single-mode fibers by adjusting the drive motor on the fiber fusion splicer 6, that is, align the centers of the two cores. The two single-mode fibers are then in a slightly compressed state ready for fusion. By precisely controlling the discharge time and discharge power of the fiber fusion splicer 6, microbubbles 10 are formed in the middle of the two smooth spherical surfaces 7.

[0049] Step 4: Perform several discharges on the microbubbles 10 generated in Step 3. Apply axial tension to the single-mode fiber by precisely controlling the motor of the fiber optic fusion splicer 6. Use arc discharge technology to precisely control and adjust the discharge time and discharge power. Form thin-walled ellipsoidal microbubbles 3 through arc discharge technology. The resulting optical fiber with ellipsoidal microbubbles 3 is a microbubble sensing cavity Fabry-Perot interferometer.

[0050] Example

[0051] like Figure 8 and Figure 9 As shown, the fabrication method of the air reference cavity Fabry-Perot interferometer includes the following steps:

[0052] Step 1: Insert the flattened end of the single-mode fiber into the hollow capillary tube 4, then place the hollow capillary tube 4 with the single-mode fiber inserted into the fiber optic fusion splicer 6. Use the fiber optic fusion splicer to discharge the end of the hollow capillary tube 4 with a discharge power of +5 and a discharge time of 600ms to fuse the hollow capillary tube 4 and the single-mode fiber together.

[0053] Step 2: Take another single-mode fiber and insert the flattened end of the single-mode fiber into the hollow capillary tube 4. Adjust the distance between the end faces of the two single-mode fibers in the hollow capillary tube 4 using the drive motor of the fiber optic fusion splicer 6 until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble 3. Then, use the fiber optic fusion splicer 6 to discharge the end of the hollow capillary tube 4 with a discharge power of +5 and a discharge time of 600ms to fuse the hollow capillary tube 4 and the other single-mode fiber together. The two single-mode fibers mated with the hollow capillary tube 4 form an air cavity 5 in the hollow capillary tube 4. The resulting fiber with the air cavity 5 is an air reference cavity Fabry-Perot interferometer.

[0054] A microbubble sensing cavity Fabry-Perot interferometer is used as the sensing cavity, and an air reference cavity Fabry-Perot interferometer is used as the reference cavity. Because the lengths of the sensing and reference cavities are close, the interference frequencies generated by the two interferometers are slightly offset. When the microbubble sensing cavity and the air reference cavity are connected in parallel, their signals overlap, resulting in an envelope modulation effect. Compared to using the microbubble sensing cavity alone, this structure can significantly amplify the sensitivity and improve the sensor's sensing performance. Therefore, by using a parallel configuration of the sensing and reference cavities, based on the vernier effect design, high-sensitivity air microbubble strain sensing can be achieved. This sensor combines the optical vernier effect; the sensing cavity of the fiber optic sensor is composed of an ellipsoidal microbubble formed by arc discharge of single-mode fiber through a fusion splicer, and the reference cavity is formed by inserting two single-mode fibers with flattened end faces into a hollow capillary tube.

[0055] like Figure 10 As shown, the change in interference spectrum of a high-sensitivity air microbubble strain sensor based on the vernier effect is illustrated by applying axial stress ranging from 0 to 1000 με in steps of 200 με. Through the linear relationship between different stress levels and wavelengths, and by fitting the wavelength drift to the stress, the strain sensitivity of the fabricated sensor is obtained as -42.04 pm / με.

[0056] like Figure 11 As shown, the temperature was increased from 30℃ to 60℃ in 5℃ increments, and the interference spectrum was collected at each temperature. The temperature sensitivity of the vernier effect-based air microbubble high-sensitivity strain sensor is 3.64 pm / ℃, and the temperature cross-sensitivity is 0.087 με / ℃. It has low temperature sensitivity, which reduces the measurement error caused by temperature changes, making the strain measurement less affected by temperature in complex environments and resulting in more accurate data.

[0057] The high-sensitivity strain sensor based on the vernier effect, combined with the optical vernier effect, significantly improves the sensitivity of stress measurement. Compared with existing technologies, this sensor can be fabricated using only single-mode optical fiber, hollow capillary tube, and a commercial fusion splicer, making it simple to manufacture, easy to operate, and low in cost.

Claims

1. A high-sensitivity strain sensor for air microbubbles based on the vernier effect, characterized in that: The strain sensor consists of a parallel microbubble sensing cavity Fabry-Perot interferometer (1) and an air reference cavity Fabry-Perot interferometer (2); The microbubble sensing cavity Fabry-Perot interferometer (1) is made by splicing two single-mode optical fibers. An ellipsoidal microbubble (3) is embedded in the center of the conical region of the microbubble sensing cavity Fabry-Perot interferometer (1). The air reference cavity Fabry-Perot interferometer (2) is made by splicing two single-mode optical fibers through a hollow capillary tube (4). The two single-mode optical fibers in the hollow capillary tube (4) form an air cavity (5). The axial diameter of the ellipsoidal microbubble (3) is 53.15 μm, and its longitudinal diameter is 67.15 μm; the length of the air cavity (5) is 64.32 μm.

2. The application of the high-sensitivity air microbubble strain sensor based on the vernier effect as described in claim 1 in strain measurement.

3. A method for fabricating a microbubble sensing cavity Fabry-Perot interferometer, characterized in that: The preparation method includes the following steps: Step 1: Wipe the single-mode fiber with alcohol to remove the coating, and cut the single-mode fiber smoothly with a fiber optic cleaver; then put the single-mode fiber into the fiber optic fusion splicer (6), and control the left and right motors of the fiber optic fusion splicer to place the single-mode fiber near the discharge electrode. Step 2: Adjust the discharge time and discharge power parameters of the fiber optic fusion splicer (6) and shape the flat end face of the single-mode fiber into a smooth spherical surface (7) through multiple discharges; manually remove the two single-mode fibers from the fiber optic fusion splicer (6) and immerse the surface of the smooth spherical surface (7) of the two single-mode fibers in a refractive index matching liquid (8). Step 3: Put the single-mode fiber processed in Step 2 back into the fiber fusion splicer (6). Align the fiber cores (9) of the two single-mode fibers by adjusting the drive motor on the fiber fusion splicer (6). The two single-mode fibers are then in a state of waiting to be fused. By precisely controlling the discharge time and discharge power of the fiber fusion splicer (6), microbubbles (10) are formed in the middle of the two smooth spherical surfaces (7). Step 4: Discharge the microbubbles (10) generated in Step 3 several times. Apply axial tension to the single-mode fiber by precisely controlling the motor of the fiber fusion splicer (6). Use arc discharge technology to precisely control and adjust the discharge time and discharge power. Form thin-walled ellipsoidal microbubbles (3) through arc discharge technology. The resulting fiber with ellipsoidal microbubbles (3) is a microbubble sensing cavity Fabry-Perot interferometer (1).

4. A method for fabricating an air reference cavity Fabry-Perot interferometer, characterized in that: The preparation method includes the following steps: Step 1: Insert the flattened end of the single-mode fiber into the hollow capillary tube (4), and then put the hollow capillary tube (4) with the single-mode fiber inserted into the fiber fusion splicer (6). Use the fiber fusion splicer (6) to discharge the end of the hollow capillary tube (4) with a discharge power of +5 and a discharge time of 600ms. Then, fuse the hollow capillary tube (4) and the single-mode fiber together. Step 2: Take another single-mode fiber and insert the flattened end of the single-mode fiber into the hollow capillary tube (4). Adjust the distance between the end faces of the two single-mode fibers in the hollow capillary tube (4) by the drive motor of the fiber fusion splicer (6) until the distance between the two end faces is close to the cavity length of the ellipsoidal microbubble (3). Then use the fiber fusion splicer (6) to discharge the end of the hollow capillary tube (4) with a discharge power of +5 and a discharge time of 600ms. The hollow capillary tube (4) and another single-mode fiber are fused together. The two single-mode fibers that are connected to the hollow capillary tube (4) form an air cavity (5) in the hollow capillary tube (4). The fiber with the air cavity (5) is the air reference cavity Fabry-Perot interferometer.

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