Ultrasound excitation fiber node and method of manufacturing the same

Abstract

The application discloses an ultrasonic excitation optical fiber node, which comprises two bare optical fiber segments and two spherical bare optical fiber intersection segments, one bare optical fiber segment is integrally connected with the spherical surface of one side of the two spherical bare optical fiber intersection segments, and the other bare optical fiber segment is integrally connected with the spherical surface of the other side of the two spherical bare optical fiber intersection segments, the two spherical radii of the two spherical bare optical fiber intersection segments are equal, and the common chord d of the two spherical bare optical fiber intersection segments is determined by the spherical radius r of the two spherical bare optical fiber intersection segments and the difference l between the spherical radius r of the two spherical bare optical fiber intersection segments and the chord distance. The application can solve the problems that the piezoelectric ultrasonic transducer is susceptible to electromagnetic interference, has a relatively large volume and is difficult to detect a non-planar structure, and effectively widens the detection range of the optical fiber ultrasonic transducer.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic exciter technology, specifically to an ultrasonic excitation fiber optic node and its manufacturing method. Background Technology

[0002] As a key component in the field of ultrasonic nondestructive testing, the performance of ultrasonic transducers is an important indicator for evaluating nondestructive testing capabilities. Traditional ultrasonic transducers are mainly piezoelectric ultrasonic transducers, which have advantages such as high sensitivity and low cost, but also have problems such as susceptibility to electromagnetic interference, large size, and difficulty in testing non-planar structures.

[0003] Fiber optic ultrasonic transducers have been studied in recent years due to their small size, flexible deployment, and resistance to electromagnetic interference. A fiber optic ultrasonic transducer refers to a photoacoustic conversion device fabricated on or on an optical fiber. Existing fiber optic ultrasonic transducers are mainly single-point ultrasonic transducers fabricated on the fiber end face, primarily used in medical imaging and structural health monitoring. However, these transducers are difficult to use for distributed ultrasonic excitation. Distributed ultrasonic excitation refers to a multi-point, large-area ultrasonic excitation method. Distributed ultrasonic excitation can effectively broaden the detection range of an ultrasonic testing system, compensating for the shortcomings of fiber optic ultrasonic transducers. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrasonically excited fiber optic node and its manufacturing method. The ultrasonically excited fiber optic node of this invention can solve the problems of piezoelectric ultrasonic transducers being susceptible to electromagnetic interference, having a large size, and being difficult to detect non-planar structures, thus effectively expanding the detection range of fiber optic ultrasonic transducers.

[0005] To achieve this objective, the ultrasonic excitation fiber optic node designed in this invention is characterized by comprising two bare fiber segments and two intersecting spherical bare fiber segments. One bare fiber segment is integrally connected to one side of the spherical surface of the intersecting spherical bare fiber segment, and the other bare fiber segment is integrally connected to the other side of the intersecting spherical bare fiber segment. The two spheres in the intersecting spherical bare fiber segment have equal radii. The common chord d of the two spheres in the intersecting spherical bare fiber segment is determined by the spherical radius r in the intersecting spherical bare fiber segment and the difference l between the spherical radius r and the chord center distance in the intersecting spherical bare fiber segment.

[0006] A method for manufacturing an ultrasonically excited fiber optic node, characterized by comprising the following steps:

[0007] Step 1: Cut the end faces of the two bare optical fibers flat, with the core diameter of the bare optical fibers being 200-1000 μm;

[0008] Step 2: Grind and polish the end faces of the two bare optical fibers;

[0009] Step 3: Clean the two bare optical fibers after grinding and polishing;

[0010] Step 4: Discharge the cleaned bare fiber end face with an electric arc to melt the two bare fiber end faces for 9-10 seconds. After cooling, the two bare fiber end faces form a spherical end face. The radius of the sphere in the spherical end face is 1-1.5 times the radius of the bare fiber core.

[0011] Step 5: Align the two opposite spherical end faces of the two bare optical fibers, ensuring they are in contact and aligned on the same straight line. Use an electric arc to discharge the two opposite spherical end faces, bringing them into a pre-fusion state for 4–6 seconds. Then, continue to discharge and fuse the two opposite spherical end faces with the electric arc for 1–3 seconds. Simultaneously, advance both bare optical fibers the same distance in the fusion direction. The advancing distance of each bare optical fiber is equal to the difference l between the spherical radius r and the chord center distance in the intersection segment of the two spherical bare optical fibers. After cooling, the first ultrasonically excited fiber node is obtained.

[0012] The beneficial effects of this invention are:

[0013] The ultrasonic excitation fiber node provided by this invention solves the problems of piezoelectric ultrasonic transducers, such as susceptibility to electromagnetic interference, large size, and inability to detect non-planar structures, compared with piezoelectric ultrasonic transducers. The fiber has good bendability and can detect non-planar structures.

[0014] This invention uses large-core optical fiber (core radius range of 100-500um) as excitation fiber, which has a larger cross-sectional area and less energy carried per unit area, so it has the characteristics of a higher damage threshold and can excite stronger ultrasonic signals than existing fiber ultrasonic transducers.

[0015] Compared with existing fiber optic ultrasonic transducers, this invention achieves multi-point distributed excitation and balanced excitation (by changing r, l, and d to control the intensity of ultrasonic excitation), resulting in ultrasonic signals with high consistency and a larger ultrasonic coverage range. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the ultrasonic excitation fiber optic node of the present invention;

[0017] Figure 2 This is a geometric diagram of the intersection of two spherical bare optical fibers in this invention;

[0018] Figure 3 This is a schematic diagram of the fabrication process of the ultrasonically excited fiber optic node of the present invention;

[0019] Figure 4This is a schematic diagram showing the installation state of the ultrasonic excitation fiber optic node of the present invention.

[0020] Figure 5 This is a schematic diagram of a multi-ultrasonic excitation fiber optic node structure.

[0021] Figure 6 This is a diagram of the ultrasonic signal generated by the ultrasonic excitation fiber node of the present invention.

[0022] Among them, 1.1—bare fiber segment, 1.2—intersection of two spherical bare fibers. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] like Figure 1 and 2 The diagram illustrates an ultrasonically excited fiber optic node comprising two bare fiber segments 1.1 and an intersecting segment 1.2 of two spherical bare fibers. One bare fiber segment 1.1 is integrally connected to one side of the spherical surface of the intersecting segment 1.2, and the other bare fiber segment 1.1 is integrally connected to the other side of the spherical surface of the intersecting segment 1.2. The two spheres in the intersecting segment 1.2 have equal radii. The common chord d of the two spheres in the intersecting segment 1.2 is determined by the spherical radius r in the intersecting segment 1.2 and the difference l between the spherical radius r and the chord center distance in the intersecting segment 1.2. The above design allows the fiber core radius to vary from large to small and then back to large. When the core diameter varies from large to small, some light will leak into the cladding or coupling agent and generate ultrasound due to the thermoelastic effect, while the other part of the light continues to propagate. When the core diameter varies from small to large, it ensures that the propagating light will not leak and can be used at the next node.

[0025] In the intersection segment 1.2 of the two spherical bare optical fibers, the common chord d of the two spherical fibers satisfies the following formula:

[0026]

[0027] Where r is the radius of the sphere in the intersection segment 1.2 of the two bare spherical optical fibers, and l is the difference between the radius r and the chord center distance in the intersection segment 1.2 of the two bare spherical optical fibers. In this embodiment, r is 600 μm and l is 30 μm. In the actual fabrication process, different values ​​of d can be obtained by changing l and r, thereby obtaining different ultrasonic intensities.

[0028] In the above technical solution, the radius r of the sphere in the intersecting segment 1.2 of the two spherical bare optical fibers is 1 to 1.5 times the core radius of the bare optical fiber segment 1.1.

[0029] In the above technical solution, the core radius of each bare fiber segment 1.1 ranges from 100 to 500 μm. This design can carry higher energy, increase the damage threshold, and ensure that the node will not be damaged during operation.

[0030] A method for manufacturing an ultrasonically excited fiber optic node, such as Figure 3 As shown, it includes the following steps:

[0031] Step 1: Cut the end faces of the two bare optical fibers flat, with the core diameter of the bare optical fibers being 200-1000 μm;

[0032] Step 2: Grind and polish the end faces of the two bare optical fibers;

[0033] Step 3: Clean the two bare optical fibers after grinding and polishing;

[0034] Step 4: Use an electric arc of 400-1000 watts to discharge the cleaned bare fiber end face, so that the two bare fiber end faces melt for 9-10 seconds. After cooling, the two bare fiber end faces form a spherical end face, and the radius of the sphere in the spherical end face is 1-1.5 times the radius of the bare fiber core.

[0035] Step 5: Align the two opposing spherical end faces of the two bare optical fibers, ensuring they are in contact and aligned on the same straight line. Use a 400-1000 watt electric arc to discharge the two opposing spherical end faces, bringing them into a pre-fusion state for 4-6 seconds. Then, continue discharging and fusing the two opposing spherical end faces with a 400-1000 watt electric arc for 1-3 seconds. Simultaneously, use a motor to advance both bare optical fibers the same distance in the fusion direction. The advancing distance of each bare optical fiber is equal to the difference l between the spherical radius r and the chord center distance in the intersection segment 1.2 of the two spherical bare optical fibers (the total advancing distance of the two bare optical fibers is equal to 2l). After cooling, the first ultrasonically excited fiber node is obtained. At the node, some light leaks into the cladding or coupling agent, generating ultrasound due to the thermoelastic effect, while the other part of the light continues to propagate along the fiber core.

[0036] In step 5 of the above technical solution, the distance that each bare optical fiber segment is advanced in the splicing direction is 10 to 150 μm.

[0037] In step 2 of the above technical solution, the specific method for grinding and polishing the end faces of the two bare optical fibers is as follows: the end faces of the two bare optical fibers are ground sequentially using 600-grit, 1200-grit, 3000-grit, and 10000-grit sandpaper, and the ground end faces are polished with a silica polishing pad. The sandpaper grinding makes the optical fiber end faces smoother, and the polishing pad fills the optical fiber end faces to make them flatter.

[0038] In step 3, the specific method for cleaning the two bare optical fibers after grinding and polishing is as follows: the two bare optical fibers after grinding and polishing are ultrasonically cleaned in sequence with acetone, anhydrous ethanol, and deionized water to clean their surfaces. In the above design, acetone cleans the organic matter on the surface, anhydrous ethanol cleans the acetone, and deionized water cleans the anhydrous ethanol.

[0039] When multiple ultrasonically excited fiber nodes need to be manufactured, step 6 is added after step 5 above: discharge melting is performed on the non-spherical end face of the bare fiber of the first ultrasonically excited fiber node and the end face of a section of new bare fiber after grinding, polishing and cleaning for 9-10 seconds. After cooling, the non-spherical end face of the first ultrasonically excited fiber node and the end face of a section of new bare fiber are both formed into spherical end faces.

[0040] Step 7: Align the two spherical end faces formed in Step 6, ensuring they are flush. The bare fiber in the first ultrasonically excited fiber node and the new bare fiber should be aligned in a straight line. Discharge the two spherical end faces with a 400-1000 watt arc to induce a pre-fusion state for 4-6 seconds. Then, continue discharging and fusing the two spherical end faces with a 400-1000 watt arc for 1-3 seconds. Simultaneously, use a motor to advance both the bare fiber in the first ultrasonically excited fiber node and the new bare fiber in the fusion direction by the same distance. The advancing distance of both the bare fiber and the new bare fiber in the first ultrasonically excited fiber node is equal to 4 / 5 of the advancing distance of each bare fiber segment in step 5 (under the condition that other factors remain unchanged, since the light energy propagating to the second node is less than that of the first node (at the first node, a portion of the light energy is converted into ultrasound), reducing the advancing distance can increase light leakage, that is, increase the proportion of light converted into ultrasound, making the ultrasound intensity of the two nodes more balanced). The two fiber segments are advanced a shorter distance than the first node in the splicing direction to improve the consistency of the ultrasound signals excited by the two nodes. After cooling, the second ultrasonically excited fiber node is obtained, as shown below. Figure 5 As shown, repeating the above operation can yield multiple photo-induced ultrasonic transducer nodes. Multiple nodes allow for a wider ultrasonic coverage area. At the first node, some light leaks into the cladding or coupling agent, generating ultrasound due to a thermoelastic effect. The remaining light continues to propagate along the fiber core to the second node. Since the light energy propagating to the second node is less than that at the first node (where some light energy is converted into ultrasound), reducing the propagation distance can increase light leakage, i.e., increase the proportion of light converted into ultrasound, making the ultrasonic intensity more balanced between the two nodes.

[0041] In the above technical solution, the high-voltage arc discharge is carried out in an environment where the atmospheric pressure is less than 3.5 kPa.

[0042] A method for installing the above-mentioned ultrasonically excited fiber optic node includes the following steps:

[0043] Step A: Place the ultrasonic excitation fiber node flat on the object to be tested;

[0044] Step B: Apply a drop of the epoxy resin and graphite adhesive mixture to the ultrasonically excited fiber optic node, ensuring it completely covers the node. Allow the adhesive mixture to cure for at least 8 hours before completing the installation. Figure 4 As shown, connecting one end of the ultrasonic excitation fiber node to a pulsed laser can generate an ultrasonic signal with a peak-to-peak value greater than 20mV. The pulsed laser used has the following specifications: wavelength 1064nm, repetition rate 10Hz, pulse width 10ns, pulse energy 20mJ, and bandwidth range of 30kHz-2MHz. Figure 6 The peak-to-peak values ​​of the three node signals shown are relatively balanced, and the ultrasound signals are clear with a high signal-to-noise ratio.

[0045] In the above technical solution, epoxy resin has good heat resistance and graphite has good light absorption. After the adhesive is cured, it can withstand a large amount of energy without being damaged. In addition, the light absorbed by graphite can promote the thermoelastic effect and reduce the light leaked into the air, thus protecting the operators.

[0046] In the above technical solution, the preparation method of the epoxy resin and graphite mixed adhesive is as follows: epoxy resin and 200-1000 mesh micro-powder graphite are stirred and mixed at a mass ratio of 1000:2.5. During the stirring process, graphite is continuously added until no obvious powdery graphite is precipitated. Then, a curing agent (polyamide curing agent) with a volume ratio of 1:1 with epoxy resin is added and stirred evenly to obtain the epoxy resin and graphite mixed adhesive.

[0047] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for manufacturing an ultrasonically excited fiber optic node, characterized in that: The ultrasonic excitation fiber optic node has two sections, each consisting of two bare fiber segments and an intersecting section of two spherical bare fibers. One bare fiber segment is integrally connected to one side of the spherical surface of the intersecting section, and the other bare fiber segment is integrally connected to the other side of the intersecting section. The two spheres in the intersecting section have equal radii, and the common chord of the two spheres in the intersecting section is... d The radius of the sphere in the intersection segment of two bare spherical optical fibers r The radius of the sphere in the intersection segment of the two bare spherical optical fibers r Difference from the center of the string l It is confirmed that when the core diameter changes from large to small, some light will leak into the cladding or coupling agent and generate ultrasound due to the thermoelastic effect, while the other part of the light continues to propagate; when the core diameter changes from small to large, it is ensured that the propagated light will not leak, and the bare fiber segment between the two nodes is the same segment; The manufacturing method includes the following steps: Step 1: Cut the end faces of the two bare optical fibers flat. The core diameter of the bare optical fibers is 200~1000μm. Step 2: Grind and polish the end faces of the two bare optical fibers; Step 3: Clean the two bare optical fibers after grinding and polishing; Step 4: Discharge the cleaned bare fiber end face with an electric arc to melt the two bare fiber end faces. After cooling, the two bare fiber end faces form a spherical end face. The radius of the sphere in the spherical end face is 1 to 1.5 times the radius of the bare fiber core. Step 5: Align the two opposite spherical end faces of the two bare optical fibers, ensuring they are flush and aligned. Apply an electric arc to the two opposite spherical end faces to initiate a pre-fusion process. Continue applying the electric arc to fuse the two opposite spherical end faces. Simultaneously, advance both bare optical fibers the same distance in the fusion direction. The advancing distance for each fiber is equal to the difference between the radius of the sphere and the distance from the center of the chord in the intersecting segment of the two bare optical fibers. ， The first ultrasonically excited fiber node was obtained after cooling. Step 6: Perform discharge melting on the non-spherical end face of the bare fiber in the first ultrasonically excited fiber node and the end face of the new bare fiber section after grinding, polishing and cleaning. After cooling, the non-spherical end face in the first ultrasonically excited fiber node and the end face of the new bare fiber section both form spherical end faces. Step 7: Align the two spherical end faces formed in Step 6 and fit them together. The bare fiber in the first ultrasonically excited fiber node and the new bare fiber are on the same straight line. Use an electric arc to discharge the two spherical end faces, so that the two spherical end faces enter the pre-fusion state. Continue to discharge and fuse the two spherical end faces using an electric arc. While discharging and fusing the two spherical end faces, simultaneously advance the bare fiber in the first ultrasonically excited fiber node and the new bare fiber in the fusion direction by the same distance. The advancing distance of the bare fiber in the first ultrasonically excited fiber node and the new bare fiber is equal to 4 / 5 of the advancing distance of each bare fiber segment in Step 5. The light energy propagating to the second node is less than that of the first node. At the first node, part of the light energy is converted into ultrasound. Reducing the advancing distance increases the light leakage, making the ultrasound intensity of the two nodes more balanced. After cooling, the second ultrasonically excited fiber node is obtained. At the first node, some light leaks into the cladding or coupling agent, causing a thermoelastic effect that generates ultrasound. The other part of the light continues to propagate along the fiber core to the second node. Since the light energy propagating to the second node is less than that at the first node, reducing the propagation distance can increase the light leakage.

2. The method for manufacturing an ultrasonically excited fiber optic node according to claim 1, characterized in that: The common chord of the two spherical bare optical fibers in the intersecting segment d Satisfy the following formula: in, r Let be the radius of the sphere in the intersection segment of the two bare spherical optical fibers. l The radius of the sphere in the intersection segment of two bare spherical optical fibers r The difference between the distance from the center of the string and the distance from the center of the string.

3. The method for manufacturing an ultrasonically excited fiber optic node according to claim 1, characterized in that: The radius of the sphere in the intersection segment of two bare spherical optical fibers r It is 1 to 1.5 times the core radius of the bare fiber segment.

4. The method for manufacturing an ultrasonically excited fiber optic node according to claim 1, characterized in that: The core radius of each bare fiber segment (1.1) ranges from 100 to 500 μm.

5. The method for manufacturing an ultrasonically excited fiber optic node according to claim 1, characterized in that: In step 5, the distance each bare fiber segment is advanced in the splicing direction is 10~150μm.

6. The method for manufacturing an ultrasonically excited fiber optic node according to claim 1, characterized in that: In step 2, the specific method for grinding and polishing the end faces of the two bare optical fibers is as follows: the end faces of the two bare optical fibers are ground sequentially using 600-grit, 1200-grit, 3000-grit, and 10000-grit sandpaper, and the ground end faces are polished with a silicon dioxide polishing pad. In step 3, the specific method for cleaning the two bare optical fibers after grinding and polishing is as follows: the two bare optical fibers after grinding and polishing are ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water.

7. A method for installing the ultrasonically excited fiber optic node as described in claim 1, characterized in that, It includes the following steps: Step A: Place the ultrasonic excitation fiber node flat on the object to be tested; Step B: Apply a drop of epoxy resin and graphite mixed adhesive to the ultrasonic excitation fiber node, ensuring it completely covers the node. Once the epoxy resin and graphite mixed adhesive has cured, the installation is complete.

8. The method for installing an ultrasonically excited fiber optic node according to claim 7, characterized in that: The preparation method of the epoxy resin and graphite mixed adhesive is as follows: epoxy resin and 200~1000 mesh micro-graphite are stirred and mixed at a mass ratio of 1000:2.

5. During the stirring process, graphite is continuously added until there is no obvious powdery graphite. Then, a curing agent with a volume ratio of 1:1 with epoxy resin is added and stirred evenly to obtain the epoxy resin and graphite mixed adhesive.

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