A carbon nanosensor with gradient gradient pore structure and its preparation method and application

Abstract

The application discloses a carbon nano sensor with a gradient gradient pore structure and a preparation method and application thereof, and belongs to the field of structural health monitoring. The carbon nano sensor comprises a sensing base layer, a sensing layer and a flexible electrode; the sensing layer is located between the sensing base layer and the flexible electrode; the sensing layer is made by mixing at least two of zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials and three-dimensional conductive nanomaterials and a surfactant; the sensing base layer is made of a high molecular polymer, and the pore structure of the sensing base layer gradually increases in the direction away from the sensing layer to form a gradient pore structure. The application can solve the defects of traditional sensor signal response lag, large measurement error and long-term performance attenuation, realize high-sensitivity, high-precision and high-stability collaborative perception of material structure states under complex working conditions, and provides a breakthrough technical scheme for the field of structural health monitoring.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and more specifically, to a carbon nanotube sensor with a gradient pore structure, its preparation method, and its application. Background Technology

[0002] In modern industrial fields such as aerospace, deep-sea exploration, and energy and chemical engineering, equipment and structures are subjected to extreme conditions involving multiple physical fields coupled together, including high temperature, high pressure, strong stress, and corrosion. This places stringent demands on the accuracy and reliability of structural health monitoring (SHM). Traditional monitoring technologies struggle to meet these requirements, while carbon nanomaterials (such as carbon nanotubes and graphene) have become ideal materials for constructing high-performance sensors due to their excellent mechanical, electrical, and thermal properties. Carbon nanomaterial-based sensors, with their advantages of high sensitivity, rapid response, and miniaturization, can efficiently convert minute strains in the material structure into electrical signals, providing a new direction for achieving high-precision, early-warning structural health monitoring.

[0003] However, traditional carbon nanotube sensors face significant technical bottlenecks under complex multi-physics coupled conditions involving forces, heat, and humidity. First, mechanical property mismatch leads to interface failure. Traditional carbon nanotube sensors often employ a single-structure design, with significant differences in mechanical properties (such as elastic modulus and coefficient of thermal expansion) between the sensor and the monitored material. Under high-temperature thermal expansion or strong stress impact, the deformation of the sensor and substrate materials becomes incompatible, causing stress concentration at the interface and ultimately leading to sensor-structure separation. Second, interface failure exacerbates performance degradation. Interface separation makes sensors more susceptible to corrosion from external factors in complex environments. For example, in deep-sea exploration and aerospace, high-pressure airflow accelerates the damage to the sensor-substrate interface, resulting in a continuous decrease in sensor sensitivity and an increase in signal error, making it difficult to achieve long-term stable monitoring with high sensitivity and accuracy. Furthermore, traditional carbon nanotube sensors cannot achieve simultaneous optimization of mechanical and sensing performance through structural design, failing to meet the differentiated requirements for sensor strength, sensitivity, and stability under various extreme conditions, thus limiting their application range in complex multi-physics environments.

[0004] Therefore, developing a carbon nanotube sensor for structural health monitoring that can adapt to complex multi-physics coupling conditions and possesses high sensitivity, high precision, and strong environmental adaptability is of great theoretical significance and engineering application value for breaking through existing technological bottlenecks and ensuring the safe operation of major projects and key equipment. Summary of the Invention

[0005] To address the technical bottlenecks of low sensitivity, insufficient accuracy, and poor service stability of sensors in multi-physics coupled fields, this invention provides a carbon nanotube sensor with a gradient-varying pore structure, its preparation method, and its application. This invention solves the defects of traditional sensors, such as lag in signal response, large measurement error, and long-term performance degradation, and achieves high-sensitivity, high-precision, and high-stability collaborative sensing of the material structure state under complex working conditions, providing a breakthrough technical solution for the field of structural health monitoring.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A carbon nanotube sensor with a gradient pore structure, comprising a sensing substrate, a sensing layer, and a flexible electrode; the sensing layer is located between the sensing substrate and the flexible electrode; the sensing layer is made of at least two of zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials, and three-dimensional conductive nanomaterials mixed with a surfactant; the sensing substrate is made of a polymer, and the pore structure of the sensing substrate gradually increases in size away from the sensing layer to form a gradient pore structure, such as... Figure 1 As shown.

[0008] Optionally, the zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials and three-dimensional conductive nanomaterials in the sensing layer are in a weight ratio of 1~5:1~10:1~5:1~5.

[0009] Optionally, the zero-dimensional conductive nanomaterial is carbon black and / or fullerene; the one-dimensional conductive nanomaterial is carbon nanofiber and / or carbon nanotube; the two-dimensional conductive nanomaterial is MXene and / or graphene; and the three-dimensional conductive nanomaterial is biochar and / or porous carbon.

[0010] Optionally, the pore size of the sensing layer is 5~500nm, and the pore size of the sensing substrate is 100nm~10μm.

[0011] Optionally, the gradient pore structure is a pore structure in which the pore diameter increases sequentially along the direction away from the sensing layer.

[0012] Optionally, the sensing substrate includes a top layer and a bottom layer; the top layer is in contact with the sensing layer; the pore size of the top layer is 100~1000nm; and the pore size of the bottom layer is 1~10μm.

[0013] Optionally, the aperture size ratio of the top layer to the bottom layer is 1:1 to 100.

[0014] Optionally, the sensing substrate further includes at least one intermediate layer, with each intermediate layer located between the top layer and the bottom layer; the pore size of the intermediate layer is 500nm~10μm.

[0015] Optionally, the polymer may include at least one of polyimide, polysulfone, polyurethane, cellulose, and sodium alginate.

[0016] Optionally, the surfactant may include polyvinylpyrrolidone and / or Triton.

[0017] Optionally, the flexible electrode is made of metal wires or flexible circuits (FPC).

[0018] This invention also discloses a method for fabricating a carbon nanotube sensor with a gradient pore structure as described above, comprising the following steps:

[0019] (1) Multidimensional carbon nanomaterials and surfactants are added to a solvent and then ground, stirred, dispersed and centrifuged in sequence to obtain multidimensional conductive nano-ink; wherein, the multidimensional carbon nanomaterials include at least two of zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials and three-dimensional conductive nanomaterials.

[0020] (2) The polymer is uniformly dispersed in a solvent and a homogeneous polymer solution with gradient concentration is formed by full miscibility treatment. Then, a sensing substrate with a gradient pore structure is constructed by film forming process.

[0021] (3) By means of directional assembly technology, multidimensional carbon nanomaterials in the multidimensional nano-conductive ink are embedded and integrated into the sensing substrate to form a sensing layer on the sensing substrate. After drying, a carbon nano-sensing film is obtained. The carbon nano-sensing film includes the sensing layer and the sensing substrate. The pore structure of the sensing substrate increases in size along the direction away from the sensing layer to form a gradient pore structure.

[0022] (4) After cutting the carbon nanofilm sensing film, a flexible electrode is prepared on the sensing layer to obtain the carbon nanosensor.

[0023] Optionally, in step (1), the mass ratio of the multidimensional carbon nanomaterial to the surfactant is 1 to 10:1.

[0024] Optionally, in step (1), the dispersion concentration of the multidimensional carbon nanomaterials in the multidimensional conductive ink is 0.1~1 mg / ml.

[0025] Optionally, in step (1), the solvent is water.

[0026] Optionally, in step (1), the stability of the multidimensional nano-conductive ink is that the change rate of UV absorbance is <5% over 3 months.

[0027] Optionally, in step (2), the film-forming process includes electrospinning, phase separation technology or 3D printing technology.

[0028] Optionally, in step (2), the type and concentration ratio of the adaptable solvent system need to be designed and controlled specifically based on the solubility characteristics of the polymer, the rheological properties of the solution, and the expected pore gradient distribution characteristics of the film.

[0029] Optionally, in step (3), the thickness a of the sensing substrate is 40~150μm, the thickness b of the sensing layer is 10~30μm, and the thickness c of the carbon nanofilm sensing film is 40~180μm, where a+b>c.

[0030] Optionally, in step (3), the directional assembly technology includes one of vacuum filtration, direct writing with dispensing, spin coating, and spray coating.

[0031] Optionally, in step (4), the preparation of the flexible electrode includes: fixing a metal wire to the surface of the carbon nanotube sensing film using conductive silver paste to form the flexible electrode.

[0032] Optionally, in step (4), the size and shape of the carbon nanofilm sensing film are determined based on the structure, size and specific requirements of the monitoring material.

[0033] The present invention also discloses the application of a carbon nanotube sensor with a gradient pore structure as described above in structural health monitoring.

[0034] Optionally, the applications include: utilizing the gradient porosity structure of carbon nanotube sensors, and through the penetration of adhesives, integrating the carbon nanotube sensors with composite materials or externally attaching them to the surface of composite materials, metals, ceramics, or plastics to achieve a high-strength, tight bond between the sensor and the monitoring structure. A digital source meter is used to monitor changes in the sensor's resistance, thereby achieving the purpose of monitoring the health of the material structure.

[0035] Specifically, when a composite material component undergoes microstructural changes due to external factors, the internal sensing network subsequently alters, such as... Figure 2 As shown, this triggers an electron tunneling mechanism, leading to a change in the sensor's resistance value. Based on the correlation between the resistance signal and the material's structural state, this sensor can effectively monitor the health of composite material structures.

[0036] Implementing the embodiments of the present invention will have the following beneficial effects:

[0037] (1) High sensitivity, high precision and stability: The synergistic network formed by the multidimensional carbon nanomaterials in the sensing layer endows the sensor with excellent signal capture capability, enabling it to accurately perceive minute signal changes in complex environments and achieve high sensitivity and high precision material structure health monitoring. At the same time, the pore structure of the sensing substrate gradually increases in size along the direction away from the sensing layer to form a gradient pore structure. The small pore structure near the sensing layer enhances the spatial confinement effect of the conductive filler (multidimensional carbon nanomaterials), which enhances the stability of the conductive pathway between nanomaterials and limits the slip range between nanomaterials, ensuring the sensitivity and stability of the sensor during long-term service.

[0038] (2) Enhanced intrinsic mechanical properties and interfacial bonding: The large pore design of the sensing substrate, which is far from the sensing layer, provides a channel for the penetration of resin / adhesive. While ensuring the mechanical properties of the sensor itself, it can enhance the interfacial bonding between the sensor and the monitored sample or make the sensor and the composite material integrally molded, avoiding sensor detachment or performance degradation caused by interfacial failure, and significantly improving the service stability and reliability of the sensor in multi-physics coupling environment.

[0039] (3) Performance regulation flexibility and application value: By precisely adjusting the microstructure parameters of the sensing substrate and sensing layer (such as pore size, gradient distribution, type of nanomaterials and entanglement mode, etc.), the mechanical properties and sensing performance of the sensor can be customized.

[0040] In summary, the carbon nanotube sensor prepared by this invention, with its high sensitivity, high precision, and strong environmental adaptability, meets the long-term stable health monitoring requirements of material structures under various complex working conditions such as aerospace and deep-sea exploration. It provides reliable technical support for ensuring the safe operation of major projects and key equipment, and has significant economic value and social benefits. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the sensing substrate structure with gradient porosity according to the present invention.

[0042] Figure 2 This is a schematic diagram showing the structural changes of the sensor network of the present invention under the action of external force. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0044] Example 1

[0045] The carbon nanotube sensor with a gradient pore structure in this embodiment includes a sensing substrate, a sensing layer, and a flexible electrode. The sensing layer is located between the sensing substrate and the flexible electrode. The sensing layer is made of a mixture of multi-walled carbon nanotubes, graphene, and surfactant. The sensing substrate is made of a polymer, and the pore structure of the sensing substrate increases gradually in the direction away from the sensing layer to form a gradient pore structure.

[0046] The pore size of the sensing layer is 5~500nm; the sensing substrate includes a top layer and a bottom layer; the top layer is in contact with the sensing layer; the middle layer is located between the top layer and the bottom layer; the pore size of the top layer is ~430nm; the pore size of the bottom layer is ~2μm; the pore size range of the two middle layers is ~800nm~1.5μm.

[0047] The method for fabricating a carbon nanotube sensor with a gradient pore structure in this embodiment includes the following steps:

[0048] (1) A mixture of 80 mg of multi-walled carbon nanotubes, 80 mg of graphene, and 40 mg of polyvinylpyrrolidone was added to 400 ml of deionized water, and a combined physical synergistic processing technology was used to prepare multidimensional conductive nano-ink. The combined physical synergistic processing technology included tower mechanical grinding (400 r / min, 1 h), low-speed stirring (200 r / min, 30 min), ultrasonic dispersion (120 W, 1 h), and gradient centrifugation (1000 r / min-10 min, 2000 r / min-10 min) to obtain multidimensional conductive nano-ink.

[0049] (2) Sodium alginate powder was dissolved in deionized water and stirred evenly to obtain sodium alginate spinning solutions of 1.5, 2, 2.5 and 3 wt%. The different spinning solutions were extruded onto tin foil in sequence by electrospinning technology. After drying at 60°C for 3 hours, a sensing substrate with a gradient pore structure and a thickness of ~50 μm was obtained.

[0050] (3) The multidimensional nano-conductive ink from step (1) is embedded into the pore structure of the sensing substrate in step (2) by inkjet printing technology to form a sensing layer with a thickness of ~20μm composed of a three-dimensional sensing network. It is dried in an oven at 50℃ for 1h to obtain a carbon nano-sensing film with a gradient pore structure and a thickness of ~60μm.

[0051] (4) Cut the carbon nanotube sensing film prepared in step (3) into 0.5 x 1 cm pieces. 2 A rectangular shape was obtained by fixing copper wires to the surface of the sensing film using conductive silver paste, resulting in a gradient-porous carbon nanotube sensor.

[0052] (5) Utilizing the large pore structure of the bottom layer of the gradient-porous carbon nanotube sensor in step (4), the carbon nanotube sensor and the composite material are integrated through resin permeation. The resistance signal of the sensor is monitored in real time using a digital source meter. When the microstructure of the composite material component changes due to external factors, the sensing network constructed inside it changes accordingly. Figure 2 This triggers an electron tunneling mechanism, causing a change in the sensor's resistance. Based on the correlation between the resistance signal and the material's structural state, this sensor can effectively monitor the health of composite material structures.

[0053] Example 2

[0054] The carbon nanotube sensor with a gradient pore structure in this embodiment includes a sensing substrate, a sensing layer, and a flexible electrode. The sensing layer is located between the sensing substrate and the flexible electrode. The sensing layer is made of a mixture of multi-walled carbon nanotubes, graphene, biochar, and surfactant. The sensing substrate is made of a polymer, and the pore structure of the sensing substrate increases gradually in the direction away from the sensing layer to form a gradient pore structure.

[0055] The pore size of the sensing layer is 5~500nm; the sensing substrate includes a top layer and a bottom layer; the top layer is in contact with the sensing layer; the middle layer is located between the top layer and the bottom layer; the pore size of the top layer is ~300nm; the pore size of the bottom layer is ~1μm; the pore size range of the two middle layers is ~500~800nm.

[0056] The method for fabricating a carbon nanotube sensor with a gradient pore structure in this embodiment includes the following steps:

[0057] (1) A mixture of 80 mg of multi-walled carbon nanotubes, 40 mg of graphene, 40 mg of biochar, and 40 mg of Triton was added to 400 ml of deionized water, and a combined physical synergistic processing technology was used to prepare multidimensional conductive nano-ink. The combined physical synergistic processing technology included tower mechanical grinding (500 r / min, 30 min), low-speed stirring (150 r / min, 30 min), ultrasonic dispersion (100 W, 1 h), and gradient centrifugation (500 r / min-10 min, 1000 r / min-10 min) to obtain multidimensional conductive nano-ink.

[0058] (2) Polyimide (PI) was dissolved in N-dimethylacetamide (DMAc) solvent and stirred evenly to obtain PI spinning solutions of 25, 26, 27 and 28 wt%. The different spinning solutions were extruded onto tin foil in sequence by electrospinning technology. After drying at 50°C for 4 hours, a sensing substrate with a gradient pore structure and a thickness of ~70 μm was obtained.

[0059] (3) The multidimensional nano-conductive ink from step (1) is embedded into the pore structure of the sensing substrate in step (2) by inkjet printing technology to form a sensing layer with a thickness of ~15μm composed of a three-dimensional sensing network. It is dried in an oven at 60℃ for 1h to obtain a carbon nano-sensing film with a gradient pore structure and a thickness of ~80μm.

[0060] (4) and (5) are the same as in Example 1.

[0061] Example 3

[0062] The carbon nanotube sensor with a gradient pore structure in this embodiment includes a sensing substrate, a sensing layer, and a flexible electrode. The sensing layer is located between the sensing substrate and the flexible electrode. The sensing layer is made of a mixture of single-walled carbon nanotubes, graphene, biochar, and surfactant. The sensing substrate is made of a polymer, and the pore structure of the sensing substrate increases gradually in the direction away from the sensing layer to form a gradient pore structure.

[0063] The pore size of the sensing layer is 5~500nm; the sensing substrate includes a top layer and a bottom layer; the top layer is in contact with the sensing layer; the middle layer is located between the top layer and the bottom layer; the pore size of the top layer is ~300nm; the pore size of the bottom layer is ~3μm; the pore size of the middle five layers is ~0.5~2.5μm.

[0064] The method for fabricating a carbon nanotube sensor with a gradient pore structure in this embodiment includes the following steps:

[0065] (1) A mixture of 40 mg of single-walled carbon nanotubes, 90 mg of graphene, 70 mg of biochar, and 50 mg of Triton was added to 400 ml of deionized water, and a combined physical synergistic processing technology was used to prepare multidimensional conductive nano-ink. The combined physical synergistic processing technology included tower mechanical grinding (400 r / min, 1 h), low-speed stirring (150 r / min, 30 min), ultrasonic dispersion (120 W, 1 h), and gradient centrifugation (10000 r / min-10 min, 3000 r / min-10 min) to obtain multidimensional conductive nano-ink.

[0066] (2) PI is dissolved in DMAc solvent and stirred evenly to obtain PI spinning solutions of 22, 23, 24, 25, 26, 27, and 28 wt%. The above spinning solutions are extruded onto tin foil in sequence by electrospinning technology. After drying at 50°C for 6 hours, a sensing substrate with a gradient pore structure and a thickness of ~50 μm is obtained.

[0067] (3) The multidimensional nano-conductive ink from step (1) is embedded into the pore structure of the sensing substrate in step (2) by inkjet printing technology to form a sensing layer with a thickness of ~15μm composed of a three-dimensional sensing network. It is dried in an oven at 50℃ for 1h to obtain a carbon nano-sensing film with a gradient pore structure and a thickness of ~60μm.

[0068] (4) Cut the carbon nanotube sensing film prepared in step (3) into a circle with a diameter of 1 cm, and use conductive silver paste to fix silver wires at both ends of the diameter of the circular sensing film to obtain a gradient-varying pore carbon nanotube sensor.

[0069] (5) Utilizing the large pore structure of the bottom layer of the gradient-porous carbon nanotube sensor in step (4), the carbon nanotube sensor is externally attached to the surface of the metal structure through the penetration of the adhesive, achieving a high-strength and tight fit between the sensor and the monitoring structure. The resistance signal of the sensor is monitored in real time using a digital source meter. When the microstructure of the metal component changes due to external factors, its surface sensing network changes accordingly. Figure 2 This triggers an electron tunneling mechanism, causing a change in the sensor's resistance. Based on the correlation between the resistance signal and the material's structural state, this sensor can effectively monitor the health of metallic material structures.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A carbon nanotube sensor with a gradient pore structure, characterized in that, The carbon nanotube sensor includes a sensing substrate, a sensing layer, and a flexible electrode; the sensing layer is located between the sensing substrate and the flexible electrode. The sensing layer is made of a mixture of zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials, and three-dimensional conductive nanomaterials and a surfactant; the zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials, and three-dimensional conductive nanomaterials in the sensing layer are in a weight ratio of 1~5:1~10:1~5:1~5; the three-dimensional conductive nanomaterials are biochar and / or porous carbon; The sensing substrate is made of a polymer, and the pore structure of the sensing substrate gradually increases in size along the direction away from the sensing layer to form a gradient pore structure. The pore size of the sensing layer is 5~500nm, and the pore size of the sensing substrate is 100nm~10μm; The gradient pore structure is characterized by pore diameters that increase sequentially away from the sensing layer. The sensing base layer includes a top layer and a bottom layer; the top layer is in contact with the sensing layer. The top layer has a pore size of 100~1000nm; the bottom layer has a pore size of 1~10μm. The aperture ratio of the top layer to the bottom layer is 1:1~100; When a composite material component undergoes microstructural changes due to external factors, the internal sensing network changes accordingly, prompting an electron tunneling mechanism to respond, which in turn leads to a change in the sensor resistance value. Based on the correlation between the resistance signal and the material structural state, the sensor can effectively monitor the health of the composite material structure.

2. The carbon nanotube sensor with a gradient pore structure according to claim 1, characterized in that, The zero-dimensional conductive nanomaterial is carbon black and / or fullerene; the one-dimensional conductive nanomaterial is carbon nanofiber and / or carbon nanotube; and the two-dimensional conductive nanomaterial is MXene and / or graphene.

3. The carbon nanotube sensor with a gradient pore structure according to claim 1, characterized in that, The sensing base layer further includes an intermediate layer, which is located between the top layer and the bottom layer; The pore size of the intermediate layer is 500nm~10μm.

4. The carbon nanotube sensor with a gradient pore structure according to claim 1, characterized in that, The polymer includes at least one of polyimide, polysulfone, polyurethane, cellulose, and sodium alginate; The surfactant includes polyvinylpyrrolidone and / or Triton; The flexible electrode is made of metal wires or flexible circuit FPC.

5. A method for fabricating a carbon nanotube sensor with a gradient pore structure as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Multidimensional carbon nanomaterials and surfactants are added to a solvent and then ground, stirred, dispersed and centrifuged in sequence to obtain multidimensional conductive nano-ink; wherein, the multidimensional carbon nanomaterials include at least two of zero-dimensional conductive nanomaterials, one-dimensional conductive nanomaterials, two-dimensional conductive nanomaterials and three-dimensional conductive nanomaterials. (2) The polymer is uniformly dispersed in a solvent and a homogeneous polymer solution with gradient concentration is formed by full miscibility treatment. Then, a sensing substrate with a gradient pore structure is constructed by film forming process. (3) By means of directional assembly technology, multidimensional carbon nanomaterials in the multidimensional nano-conductive ink are embedded and integrated into the sensing substrate to form a sensing layer on the sensing substrate. After drying, a carbon nano-sensing film is obtained. The carbon nano-sensing film includes the sensing layer and the sensing substrate. The pore structure of the sensing substrate increases in size along the direction away from the sensing layer to form a gradient pore structure. (4) After cutting the carbon nanofilm sensing film, a flexible electrode is prepared on the sensing layer to obtain the carbon nanosensor.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of the multidimensional carbon nanomaterial to the surfactant is 1~10:1; In step (1), the dispersion concentration of the multidimensional carbon nanomaterials in the multidimensional conductive ink is 0.1~1 mg / ml; In step (1), the solvent is water; In step (2), the film-forming process includes electrospinning, phase separation technology or 3D printing technology; In step (3), the thickness a of the sensing substrate is 40~150μm, the thickness b of the sensing layer is 10~30μm, and the thickness c of the carbon nanofiber sensing film is 40~180μm, where a+b>c; In step (3), the directional assembly technology includes one of vacuum filtration, direct writing with dispensing, spin coating, and spray coating; In step (4), the preparation of the flexible electrode includes: fixing the metal wires to the surface of the carbon nanotube sensing film using conductive silver paste to form the flexible electrode.

7. The application of a carbon nanotube sensor with a gradient pore structure as described in any one of claims 1-4 in structural health monitoring.

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