Stretchable electromagnetic ultrasonic guided wave sensor and preparation method thereof

Abstract

The invention belongs to the technical field of pipeline sensors, and discloses a stretchable electromagnetic ultrasonic guided wave sensor and a preparation method thereof.The sensor comprises a flexible substrate, a cavity is formed in the flexible substrate, the cavity is filled with a liquid metal coil formed by liquid metal, and the two ends of the liquid metal coil are both connected with metal electrodes; the two metal electrodes are fixed to the two ends of the flexible substrate respectively. The sensor can be used for ultrasonic guided wave detection of thin pipelines with different pipe diameters, and defect positioning is achieved. According to the sensor coil, the flexible substrate is filled with the liquid metal, and the sensor coil can be stretched or shrunk along with the flexible stretching substrate.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline sensors, and in particular relates to a stretchable electromagnetic ultrasonic guided wave sensor and a preparation method thereof. Background Art

[0002] Pipelines are one of the economic means of transporting oil, natural gas and other media, and they play an important role in the national economy and production. However, pipelines can also fail due to corrosion and other reasons. In some areas, a large number of medium and small diameter oil and gas pipelines are distributed in densely populated areas. Once a corrosion leakage accident occurs, the consequences will be more serious. Therefore, the detection of oil and gas pipelines is particularly important.

[0003] In the petrochemical industry, narrow diameter pipes are used in various aspects of petrochemical piping systems. Applications include:

[0004] 1. Pipeline transportation: Pipelines with small diameters can connect different equipment and process units to achieve fluid transportation and distribution.

[0005] 2. Measurement and instrumentation: By installing flow meters, pressure sensors, temperature sensors and other measuring instruments on small-diameter pipelines, process parameters can be monitored and controlled in real time to ensure the safety and quality of the production process.

[0006] 3. Process control: Small diameter pipes are used in process control systems in petrochemical plants by connecting to control valves, regulating valves and other control elements.

[0007] 4. Equipment connection and installation: Small diameter pipes are used as connecting elements to connect various equipment and machinery in petrochemical plants, such as pumps, compressors, heat exchangers, etc.

[0008] Although thin-diameter pipelines are generally made of corrosion-resistant and high-temperature-resistant high-strength materials, due to the harsh working environment (humid, corrosive gas or water and vibration load), pipeline systems in long-term operation will inevitably produce some defects such as oxidation, corrosion, metal fatigue and cracks. Common pipeline non-destructive testing methods include: magnetic flux leakage detection, eddy current detection, ultrasonic detection and ultrasonic guided wave detection. Among them, eddy current detection can be used for various metal pipelines to detect cracks and corrosion defects, but eddy current detection has weak penetration ability for ferromagnetic metals and can only detect surface or near-surface defects. When the surface corrosion products contain magnetic scale, the signal-to-noise ratio of the detection signal will be greatly reduced, resulting in detection errors. Ultrasonic testing is generally used to detect whether there are cracks in the thickness direction of the pipeline. It can also be used through a phased array to focus the ultrasonic wave to achieve the purpose of fixed-point detection, but the disadvantage is that it cannot perform rapid detection of a large area. Ultrasonic phased arrays require the use of special timing circuit design, the amount of data obtained is huge, and data processing takes a long time, so the detection efficiency is relatively low. Magnetic flux leakage testing is a commonly used detection method in China. It has more intuitive results than other detection methods, but it can only detect surface defects of pipelines and is highly subjective. Ultrasonic guided wave testing detects defects through the transmission and reflection characteristics of guided waves. It is efficient and fast and is suitable for pipeline detection.

[0009] Ultrasonic guided wave detection for small diameter pipelines is different from conventional pipeline detection and has the following difficulties:

[0010] 1. Coupling is difficult. Since the curvature radius of a thin-diameter pipe is small, the contact area between the probe and the pipe is small, and the coupling is poor, resulting in low transducer excitation and reception efficiency.

[0011] 2. It is difficult to locate and quantify defects. For thin-diameter pipes, the short length and thin thickness of the pipes make the waveguide sound path short, which affects the positioning and quantification of defects during detection in the near field area.

[0012] 3. Interference from false signals. The thickness of thin-walled welds is slightly different from that of the parent material. During inspection, the thickness of the welds on the inner and outer surfaces will produce more signal interference, making it difficult to identify real defects.

[0013] 4. Influence of the joint form. Pipes with small diameters are mostly branches. The complex waveguide propagation makes the received signal complex, which affects the defect judgment.

[0014] In view of this, it is necessary to design a thin-diameter sensor that can be used with different diameters to realize ultrasonic guided wave detection of thin-diameter pipes. Summary of the invention

[0015] In view of the above problems, the present invention provides a stretchable electromagnetic ultrasonic guided wave sensor and a preparation method thereof, which adopts the following technical solutions:

[0016] A stretchable electromagnetic ultrasonic guided wave sensor comprises a flexible substrate, wherein the flexible substrate has a cavity inside, the cavity is filled with a liquid metal coil formed by liquid metal, both ends of the liquid metal coil are connected to metal electrodes, and the two metal electrodes are respectively fixed at the two ends of the flexible substrate.

[0017] Furthermore, the metal electrode is made of copper, aluminum or silver.

[0018] Furthermore, the liquid metal coil is a zigzag coil.

[0019] Furthermore, the flexible substrate is in a strip shape, and the metal electrode is in a square plate shape.

[0020] The present invention also provides a method for using the stretchable electromagnetic ultrasonic guided wave sensor, comprising the following steps:

[0021] A stretchable electromagnetic ultrasonic guided wave sensor is wrapped around the outer wall of the pipeline along the circumference of the pipeline, and a magnet is installed on the outer wall of the pipeline to provide a bias static magnetic field for the liquid metal coil;

[0022] The stretchable electromagnetic ultrasonic guided wave sensor is used as an excitation end to pass an AC excitation signal, and the stretchable electromagnetic ultrasonic guided wave sensor is used as a receiving end to receive a reflected wave;

[0023] The propagation velocity of the guided wave is determined according to the pipeline dispersion curve, and the distance between the pipeline defect and the stretchable electromagnetic ultrasonic guided wave sensor is determined according to the time when the AC excitation signal is introduced, the time when the reflected wave is received, and the propagation velocity of the guided wave.

[0024] Furthermore, the stretchable electromagnetic ultrasonic guided wave sensor is used as an excitation end to pass an AC excitation signal, and the stretchable electromagnetic ultrasonic guided wave sensor is used as a receiving end to receive a reflected wave, including:

[0025] When the stretchable electromagnetic ultrasonic guided wave sensor is used as the excitation end, the AC excitation signal is introduced into the metal electrode through a wire and transmitted to the liquid metal coil, generating induced eddy currents on the inner wall of the pipeline. Under the action of the biased static magnetic field formed by the magnet on the outer wall of the pipeline, the induced eddy currents generate a force perpendicular to the radial direction of the pipeline, and the vibration generates ultrasonic guided waves, which propagate along the axial direction of the pipeline. When the ultrasonic guided wave encounters a defect, the reflected wave will propagate in the opposite direction from the defect and be transmitted back along the propagation path of the incident wave to the stretchable electromagnetic ultrasonic guided wave sensor as the receiving end.

[0026] Furthermore, according to the time when the AC excitation signal is input, the time when the reflected wave is received, and the propagation speed of the guided wave, the distance between the pipeline defect and the stretchable electromagnetic ultrasonic guided wave sensor is determined, including:

[0027] L=(t2-t1) / (2*v)

[0028] Among them, v represents the propagation speed of the guided wave, t1 represents the excitation time, and t2 represents the time when the reflected wave is received.

[0029] The present invention also provides a method for preparing the stretchable electromagnetic ultrasonic guided wave sensor, comprising the following steps:

[0030] Making a solid coil with the same shape as the liquid metal coil;

[0031] The manufactured solid coil is placed in a mold, and a liquid flexible stretchable material is poured in, and a fluid inlet and a fluid outlet are reserved, and after the liquid flexible stretchable material solidifies, a flexible substrate is obtained;

[0032] Pour a corrosive agent into the fluid inlet of the flexible substrate to corrode the solid coil, pour it out from the corrosive fluid outlet, and rinse it with clean water until no corrosive liquid remains, forming a cavity in the flexible substrate that matches the shape of the liquid metal coil;

[0033] Liquid metal is poured into the fluid inlet of the flexible substrate, and the fluid inlet and fluid outlet are sealed with conductive solid materials, and metal electrodes are attached to the fluid inlet and fluid outlet. After the liquid metal solidifies, a liquid metal coil is formed to obtain a stretchable electromagnetic ultrasonic guided wave sensor.

[0034] Furthermore, the method further comprises the following steps:

[0035] The size of the flexible substrate is determined according to the volume of the liquid metal coil, and the size of the mold is determined according to the size of the flexible substrate.

[0036] Furthermore, the solid coil is an iron wire or an aluminum wire, and the corrosion agent is a nitric acid solution.

[0037] Beneficial effects of the present invention: The sensor of the present invention can be used for ultrasonic guided wave detection of thin pipes of different diameters to locate defects. The sensor coil of the present invention is filled with liquid metal in a flexible substrate and can be stretched or contracted along with the flexible stretchable substrate.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A schematic structural diagram of a stretchable electromagnetic ultrasonic guided wave sensor according to an embodiment of the present invention is shown;

[0041] Figure 2 A schematic diagram showing the installation of a stretchable electromagnetic ultrasonic guided wave sensor and a pipeline according to an embodiment of the present invention is shown;

[0042] Figure 3 A schematic diagram showing the principle of pipeline defect positioning using a stretchable electromagnetic ultrasonic guided wave sensor according to an embodiment of the present invention.

[0043] In the figure: 1. Flexible substrate; 2. Liquid metal coil; 3. Metal electrode; 4. Magnet; 5. Pipeline. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be noted that the terms "first", "second", etc. in this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so as to describe the embodiments of the present application described here.

[0046] Small diameter pipelines are widely used in the petrochemical industry. Although the pipe body is generally made of high-strength materials that are resistant to high temperatures and corrosion, long-term operation in harsh environments will inevitably produce defects such as oxidation, corrosion, metal fatigue, and cracks. The existence of such defects will eventually lead to leakage and explosion accidents, causing huge losses to people's lives and property. Ultrasonic guided wave testing is fast and efficient, and is suitable for the detection of petrochemical pipelines.

[0047] Ultrasonic guided wave detection can be divided into electromagnetic ultrasonic guided wave and piezoelectric ultrasonic guided wave. Piezoelectric ultrasonic guided wave uses polarized piezoelectric material attached to the surface of the material to be detected, and passes the excitation signal into the high-impedance polarized piezoelectric material, so that the piezoelectric material produces vibration in the polarization direction, that is, converts the electrical signal into a mechanical vibration signal, and transmits the vibration signal to the material to be detected to generate ultrasonic guided waves. Nowadays, piezoelectric sensors are relatively mature, and companies produce them from large to small, from hard to soft, and the frequency bandwidth and amplitude response are very good. However, piezoelectric sensors also have obvious and inevitable disadvantages. First, the use of this type of sensor requires the surface of the material to be detected to be cleaned to reduce the impact of dirt on the surface of the material to be detected on the detection signal. Secondly, the use of piezoelectric sensors has to be used with coupling agents. The type of coupling agent and the application operation will affect the detection effect, and it is difficult to apply coupling agents in some environments, such as high temperature. Electromagnetic ultrasonic guided wave sensors can be divided into sensors based on the magnetostrictive principle and sensors based on the Lorentz force. Among them, sensors based on the magnetostrictive principle are composed of materials with large magnetostrictive strain (nickel strip) and coils. The material is pre-magnetized and attached to the surface of the material to be tested, and then an excitation signal is passed through the coil to generate an induced magnetic field. The nickel strip vibrates due to magnetostriction caused by the magnetic field, and the vibration is transmitted to the material to be tested. Its shortcomings are similar to those of piezoelectric sensors. Electromagnetic ultrasonic sensors based on the Lorentz force are non-contact sensors that do not need to contact the surface of the material to be tested or clean the surface. Therefore, they are very suitable for non-destructive testing of pipelines in the petrochemical industry.

[0048] Currently, there are few electromagnetic ultrasonic guided wave sensors for narrow-diameter pipe inspection. The diameters and types of narrow-diameter pipes are various, and traditionally, a single designed sensor can only detect one diameter of pipe.

[0049] Based on the above theory, the present invention provides a stretchable electromagnetic ultrasonic guided wave sensor and a preparation method thereof, which can be used for ultrasonic guided wave detection of thin pipes with different diameters, and utilizes the static magnetic field and eddy current effect of the coil to generate ultrasonic guided waves in the pipe.

[0050] like Figure 1 As shown, a stretchable electromagnetic ultrasonic guided wave sensor includes a flexible substrate 1. For example, the flexible substrate 1 is made of flexible and stretchable materials such as silica gel and PDMS (polydimethylsiloxane).

[0051] Polydimethylsiloxane is a high molecular polymer, odorless, highly transparent, heat-resistant, cold-resistant, with little viscosity change with temperature, waterproof, low surface tension, thermal conductivity, thermal conductivity of 0.134-0.159W / (m·K), light transmittance of 100%, dimethyl silicone oil is non-toxic and odorless, physiologically inert, and has good chemical stability. It has good electrical insulation, weather resistance, hydrophobicity, high shear resistance and stretchability, can be used for a long time at -50℃~200℃, and has excellent physical properties.

[0052] Among them, the flexible substrate 1 has a cavity inside, and the cavity is filled with a liquid metal coil 2. Both ends of the liquid metal coil 2 are connected to the metal electrodes 3. The two metal electrodes 3 are respectively fixed at the two ends of the flexible substrate 1. The two ends of the liquid metal coil 2 are led out by the metal electrodes 3 and can be connected to wires to conduct excitation signals or receive signals.

[0053] For example, the metal electrode 3 and the liquid metal coil 2 can be made of copper, aluminum or silver. The liquid metal coil 2 is a combination of one or more of a zigzag coil, a spiral coil, a racetrack coil, a spiral coil, a zigzag coil and a racetrack coil. For example, the shape of the liquid metal coil 2 is a single zigzag coil. The liquid metal coil 2 is not limited to a single coil, but can also be a spiral coil, a racetrack coil, a plurality of spiral coils, or a combination of a zigzag coil and a racetrack coil.

[0054] For example, the flexible substrate 1 is in the shape of a strip, the metal electrode 3 is in the shape of a square plate, the cavity is in the shape of a zigzag line, and the cavity is filled with liquid metal to form a zigzag coil. The reason why the liquid metal coil 2 of the present invention does not directly use copper wire is that although the copper wire is soft and can be bent to adapt to the curved surface of the pipe 5, the copper wire has poor stretchability and cannot be stretched and contracted with the flexible substrate 1 according to the change in the pipe diameter. Therefore, the liquid metal coil 2 of the present invention is designed to use liquid metal filled in the flexible substrate 1, which can be stretched or contracted with the flexible stretchable substrate.

[0055] The present invention also provides a method for using the stretchable electromagnetic ultrasonic guided wave sensor, comprising the following steps:

[0056] S11, wrap the stretchable electromagnetic ultrasonic guided wave sensor around the outer wall of the pipeline 5 along the circumference of the pipeline 5, and install a magnet 4 on the outer wall of the pipeline 5 to provide a bias static magnetic field for the liquid metal coil 2.

[0057] For example, the magnet 4 is a high coercive force hard magnet. When the outer diameter of the pipe 5 is less than 10 cm, a stretchable electromagnetic ultrasonic waveguide sensor is wrapped around the outer wall of the pipe 5, and a magnet 4 is used to provide a bias static magnetic field for the liquid metal coil 2.

[0058] When the outer diameter of the pipe 5 is greater than 10 cm, a plurality of metal electrodes 3 of stretchable electromagnetic ultrasonic waveguide sensors are connected end to end and wrapped around the outer wall of the pipe 5 , and a plurality of magnets 4 are used to provide a biased static magnetic field for the liquid metal coil 2 .

[0059] For example, Figure 2 As shown, two metal electrodes 3 of stretchable electromagnetic ultrasonic waveguide sensors are arranged end to end and surround the outer wall of the pipe 5 according to the outer diameter of the pipe 5, and the first magnet 4 and the second magnet 4 are respectively arranged at the upper and lower ends of the outer wall of the pipe 5, and the N pole of the first magnet 4 and the S pole of the second magnet 4 are arranged opposite to each other.

[0060] In the present invention, since the stretchable electromagnetic ultrasonic guided wave sensor adopts a flexible substrate 1, it can be fitted with the outer wall of the pipe 5 as it is stretched. Since the liquid metal coil 2 is a zigzag coil, the liquid metal coil 2 can be stretched along with the flexible substrate 1. Metal electrodes 3 are provided at both ends of the flexible substrate 1. When the outer diameter of the pipe 5 is large, the metal electrodes 3 of multiple stretchable electromagnetic ultrasonic guided wave sensors can be connected end to end and wrapped around the outer wall of the pipe 5, thereby achieving matching settings of thin pipes 5 with different diameters.

[0061] S12, using the stretchable electromagnetic ultrasonic guided wave sensor as an excitation end to pass an AC excitation signal, and using the stretchable electromagnetic ultrasonic guided wave sensor as a receiving end to receive reflected waves, as follows:

[0062] When the stretchable electromagnetic ultrasonic guided wave sensor is used as the excitation end, the AC excitation signal is introduced into the metal electrode 3 through the wire and transmitted to the liquid metal coil 2, generating induced eddy currents on the inner wall of the pipe 5. Under the action of the biased static magnetic field formed by the magnet 4 on the outer wall of the pipe 5, the induced eddy currents generate a force perpendicular to the radial direction of the pipe 5, and the vibration generates ultrasonic guided waves, such as Figure 3 As shown, the guided wave propagates axially along the pipe 5. When the ultrasonic guided wave encounters a defect, reflection and transmission will occur. The reflected wave will propagate in the opposite direction from the defect and return to the stretchable electromagnetic ultrasonic guided wave sensor along the propagation path of the incident wave. At this time, the stretchable electromagnetic ultrasonic guided wave sensor serves as the receiving end.

[0063] In this step, since an AC signal is introduced into the liquid metal, an induced eddy current will be generated from the surface of the pipe 5 to the skin depth according to the principle of electromagnetic induction. The magnets 4 placed at both ends of the coil will generate a static bias magnetic field along the circumference of the pipe 5 in the pipe 5. According to the formula: L =B 0 ×J e , the Lorentz force is generated due to the interaction between the eddy current and the bias magnetic field. Among them, f L is the Lorentz force, B 0 is the bias magnetic field, J eis the eddy current density. For the receiving end, when the ultrasonic guided wave is transmitted to the sensor, the charged particles moving in the material under test in the area below the sensor generate an induced current under the action of the external bias magnetic field. This current is a dynamic current and will generate a dynamic magnetic field in and around the material under test. The receiving coil part of the electromagnetic ultrasonic sensor in this magnetic field will generate an induced electromotive force, that is, convert the vibration mechanical signal into an electrical signal.

[0064] S13, determining the propagation velocity of the guided wave according to the dispersion curve of the pipeline 5, and determining the distance between the defect of the pipeline 5 and the stretchable electromagnetic ultrasonic guided wave sensor according to the time when the AC excitation signal is input, the time when the reflected wave is received, and the propagation velocity of the guided wave, thereby completing the defect detection of the pipeline 5, as follows:

[0065] L=(t2-t1) / (2*v)

[0066] Where v represents the propagation velocity of the guided wave, t1 represents the excitation moment, and t2 represents the moment when the reflected wave is received.

[0067] The present invention also provides a method for preparing the above-mentioned stretchable electromagnetic ultrasonic guided wave sensor, comprising the following steps:

[0068] S21 . Determine the size of the flexible substrate 1 according to the volume of the liquid metal coil 2 , and determine the size of the mold according to the size of the flexible substrate 1 .

[0069] S22, a solid coil having the same shape as the liquid metal coil 2 is wound by solid material, and the solid coil is easily corroded.

[0070] In this step, a suitable solid material is selected to make a solid coil. The material is easily corroded by a reagent, but the corrosive reagent will not corrode or damage the stretchable flexible material, and the solid material has good plasticity. For example, the solid coil can be iron wire, aluminum wire, etc., and the corrosive reagent can be a nitric acid solution.

[0071] In this step, the solid material is used to wind a coil to form a coil of the desired shape. The shape is not limited to a zigzag coil or a single coil, but can also be a spiral coil, a racetrack coil, or a combination of multiple spiral coils or a zigzag coil and a racetrack coil.

[0072] S23, placing the manufactured solid coil into a mold, pouring in a liquid flexible stretchable material, and reserving a fluid inlet and a fluid outlet, and after the liquid flexible stretchable material solidifies, obtaining a flexible substrate 1.

[0073] S24, pouring a corrosive agent into the fluid inlet of the flexible substrate 1 to corrode the solid coil, pouring it out from the corrosive fluid outlet, and rinsing it with clean water until no corrosive liquid remains, forming a cavity in the flexible substrate 1 that matches the shape of the liquid metal coil 2.

[0074] S26. Pour liquid metal into the fluid inlet of the flexible substrate 1, seal the fluid inlet and fluid outlet with conductive solid material, and attach metal electrodes 3 to the fluid inlet and fluid outlet. After the liquid metal solidifies, a liquid metal coil 2 is formed to obtain a stretchable electromagnetic ultrasonic guided wave sensor.

[0075] The stretchable electromagnetic ultrasonic guided wave sensor of the present invention adopts a stretchable flexible substrate 1, which can be tightly coupled with pipes 5 of different sizes. During the measurement process, a magnet 4 can be installed on the outer wall of the pipe 5 to provide a biased static magnetic field for the liquid metal coil 2. After identifying the approximate location of the defect, the distance between the defect in the pipe 5 and the stretchable electromagnetic ultrasonic guided wave sensor can be determined, thereby locating the defect.

[0076] The present invention determines the distance between the stretchable electromagnetic ultrasonic guided wave sensor and the defect of the pipeline 5, thereby realizing defect positioning. The stretchable flexible substrate 1 is adopted, and a biased static magnetic field is provided by the magnet 4, so that the stretchable electromagnetic ultrasonic guided wave sensor of the present invention can be installed at any position on the pipeline 5. During the measurement process, induced eddy currents are generated on the inner wall surface of the pipeline 5. Under the action of the biased static magnetic field formed by the magnet 4 on the outer wall of the pipeline 5, the induced eddy currents generate a force perpendicular to the radial direction of the pipeline 5, and vibrate to generate ultrasonic guided waves, which can avoid the interference of false signals and the influence of the joint form, thereby making the defect positioning more accurate.

[0077] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A stretchable electromagnetic ultrasonic guided wave sensor, characterized in that: It comprises a flexible substrate, wherein the flexible substrate has a cavity inside, the cavity is filled with a liquid metal coil formed by liquid metal, both ends of the liquid metal coil are connected to metal electrodes, and the two metal electrodes are respectively fixed at the two ends of the flexible substrate.

2. The stretchable electromagnetic ultrasonic guided wave sensor according to claim 1, characterized in that: The metal electrodes are made of copper, aluminum or silver.

3. The stretchable electromagnetic ultrasonic guided wave sensor according to claim 1, characterized in that: The liquid metal coil is a zigzag coil.

4. The stretchable electromagnetic ultrasonic guided wave sensor according to claim 1, characterized in that: The flexible substrate is in the shape of a strip, and the metal electrode is in the shape of a square plate.

5. A method for using the stretchable electromagnetic ultrasonic guided wave sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: A stretchable electromagnetic ultrasonic guided wave sensor is wrapped around the outer wall of the pipeline along the circumference of the pipeline, and a magnet is installed on the outer wall of the pipeline to provide a bias static magnetic field for the liquid metal coil; The stretchable electromagnetic ultrasonic guided wave sensor is used as an excitation end to pass an AC excitation signal, and the stretchable electromagnetic ultrasonic guided wave sensor is used as a receiving end to receive a reflected wave; The propagation velocity of the guided wave is determined according to the pipeline dispersion curve, and the distance between the pipeline defect and the stretchable electromagnetic ultrasonic guided wave sensor is determined according to the time when the AC excitation signal is introduced, the time when the reflected wave is received, and the propagation velocity of the guided wave.

6. The method for using the stretchable electromagnetic ultrasonic guided wave sensor according to claim 5, characterized in that: The stretchable electromagnetic ultrasonic guided wave sensor is used as an excitation end to pass an AC excitation signal, and the stretchable electromagnetic ultrasonic guided wave sensor is used as a receiving end to receive a reflected wave, including: When the stretchable electromagnetic ultrasonic guided wave sensor is used as the excitation end, the AC excitation signal is introduced into the metal electrode through a wire and transmitted to the liquid metal coil, generating induced eddy currents on the inner wall of the pipeline. Under the action of the biased static magnetic field formed by the magnet on the outer wall of the pipeline, the induced eddy currents generate a force perpendicular to the radial direction of the pipeline, and the vibration generates ultrasonic guided waves, which propagate along the axial direction of the pipeline. When the ultrasonic guided wave encounters a defect, the reflected wave will propagate in the opposite direction from the defect and be transmitted back along the propagation path of the incident wave to the stretchable electromagnetic ultrasonic guided wave sensor as the receiving end.

7. The method for using the stretchable electromagnetic ultrasonic guided wave sensor according to claim 5, characterized in that: According to the time when the AC excitation signal is input, the time when the reflected wave is received and the propagation speed of the guided wave, the distance between the pipeline defect and the stretchable electromagnetic ultrasonic guided wave sensor is determined, including: L=(t2-t1) / (2*v) Among them, v represents the propagation speed of the guided wave, t1 represents the excitation time, and t2 represents the time when the reflected wave is received.

8. A method for preparing a stretchable electromagnetic ultrasonic guided wave sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: Making a solid coil with the same shape as the liquid metal coil; The manufactured solid coil is placed in a mold, and a liquid flexible stretchable material is poured in, and a fluid inlet and a fluid outlet are reserved, and after the liquid flexible stretchable material solidifies, a flexible substrate is obtained; Pour a corrosive agent into the fluid inlet of the flexible substrate to corrode the solid coil, pour it out from the corrosive fluid outlet, and rinse it with clean water until no corrosive liquid remains, forming a cavity in the flexible substrate that matches the shape of the liquid metal coil; Liquid metal is poured into the fluid inlet of the flexible substrate, and the fluid inlet and fluid outlet are sealed with conductive solid materials, and metal electrodes are attached to the fluid inlet and fluid outlet. After the liquid metal solidifies, a liquid metal coil is formed to obtain a stretchable electromagnetic ultrasonic guided wave sensor.

9. The method for preparing a stretchable electromagnetic ultrasonic guided wave sensor according to claim 8, characterized in that: The following steps are also included: The size of the flexible substrate is determined according to the volume of the liquid metal coil, and the size of the mold is determined according to the size of the flexible substrate.

10. The method for preparing a stretchable electromagnetic ultrasonic guided wave sensor according to claim 8, characterized in that: The solid coil is an iron wire or an aluminum wire, and the corrosion agent is a nitric acid solution.

Images