Flexible bionic strain sensor for monitoring of underground structures and method of making the same

Abstract

The application discloses a flexible bionic strain sensor for underground structure monitoring and a preparation method thereof, and belongs to the technical field of flexible bionic strain sensors, and comprises an LIG layer, wherein an Ecoflex layer is arranged on the surface of the LIG layer, and the Ecoflex layer is combined with the LIG layer; a spider web structure is constructed on the Ecoflex layer through a fiber laser; the two sides of the Ecoflex layer are connected with conductive copper foils through silver glue; and a PDMS packaging layer is arranged outside the Ecoflex layer. The flexible bionic strain sensor can detect slight strain changes, such as slight deformation of a structure, crack propagation and the like, which is of great significance for early discovery of structure problems and prevention of safety accidents; and high sensitivity of the sensor makes monitoring data have high resolution, and can more accurately reflect the health condition of the structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flexible bionic strain sensors, and particularly relates to a flexible bionic strain sensor for monitoring underground structures and a preparation method thereof. BACKGROUND

[0002] It is well known that the health monitoring of underground structures is crucial for ensuring the safety and reliability of infrastructure. Underground structures such as bridges, tunnels, and subways are subjected to various environmental factors such as soil pressure, groundwater erosion, temperature changes, vibrations, etc. during long-term use, which may cause deformation, crack propagation, and stress concentration of the structure, thereby affecting the safety and service life of the structure.

[0003] Traditional rigid sensors such as metal strain gauges, optical fiber sensors, etc. are difficult to adapt to different structural shapes and curvatures in complex environments, and are prone to measurement errors. Rigid sensors are easily affected by environmental factors such as temperature changes, humidity, vibrations, etc. during long-term use, leading to a decline in sensor performance or even failure. Rigid sensors need to be accurately aligned and fixed during installation, which is difficult and time-consuming for complex underground structures. High-quality rigid sensors are expensive, and the maintenance and replacement costs are high. Optical fiber sensors have high manufacturing and installation costs, which are not suitable for large-scale applications. Optical fiber sensors are easily affected by electromagnetic interference in complex environments, affecting the accuracy of monitoring data. The installation of optical fiber sensors requires professional technology and equipment, and the installation process is complex and time-consuming. Nodes in wireless sensor networks usually need to be powered by batteries, which have high power consumption and need to be replaced frequently. In underground environments, wireless signal transmission is limited, and communication interruption and data loss problems are prone to occur. The number of nodes in wireless sensor networks is large, and maintenance and management are difficult. Therefore, it is of great practical significance to develop efficient, reliable, and adaptable monitoring technology. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned deficiencies in the prior art and provide a flexible bionic strain sensor for monitoring underground structures and a preparation method thereof, to solve the problems of traditional rigid sensors that are difficult to adapt to different structural shapes and curvatures in complex environments, prone to measurement errors, and high manufacturing and installation costs, which are not suitable for large-scale applications.

[0005] To achieve the above-mentioned purposes, the technical solution adopted by the present application is as follows:

[0006] In a first aspect, a flexible bionic strain sensor for monitoring underground structures comprises a LIG layer; the LIG layer is provided with an Ecoflex layer on the surface, and the Ecoflex layer is combined with the LIG layer; a spider web structure is constructed on the Ecoflex layer by a fiber laser; the two sides of the Ecoflex layer are connected with conductive copper foil through silver glue; and the Ecoflex layer is externally provided with a PDMS packaging layer.

[0007] Further, there is a gap between the strings in the spider web structure.

[0008] In a second aspect, a preparation method of a flexible bionic strain sensor for monitoring underground structures comprises the following steps:

[0009] S1, fixing a PI film on a glass slide;

[0010] S2, fixing the glass slide carrying the PI film on a laser processing platform, locally carbonizing the PI film by a CO2 laser, and then forming a LIG layer;

[0011] S3, uniformly dropping Ecoflex solution on the surface of the LIG layer, and obtaining an Ecoflex layer after drying at room temperature;

[0012] S4, peeling off the combined LIG layer and Ecoflex layer from the PI film, and fixing them on the laser processing platform, and constructing a spider web structure on the Ecoflex layer by a fiber laser;

[0013] S5, connecting the two sides of the Ecoflex layer electrode with copper foil by silver glue;

[0014] S6, coating a mixture of PDMS prepolymer and crosslinking agent on the outside of the Ecoflex layer, and forming a PDMS packaging layer after drying.

[0015] Further, S1 specifically comprises:

[0016] A PI film with a thickness of 100 μm is selected, and the PI film is pasted on a 10 cm x 10 cm glass slide by using water-soluble double-sided adhesive tape.

[0017] Further, in S2, the laser parameters of the CO2 laser are:

[0018] The laser power is 18.12%, the scanning speed is 180 mm / s, the scanning interval is 3.3 mm, and the focal length is 3.7 mm.

[0019] Further, S3 specifically comprises:

[0020] The Ecoflex solution is evenly dropped on the surface of the LIG layer, and dried at room temperature for 24 hours until the Ecoflex solution fully penetrates into the porous structure of the LIG layer, to obtain an Ecoflex layer.

[0021] Further, in S4, the laser parameters of the fiber laser are:

[0022] The laser power is 50%, the scanning speed is 100 mm / s, and the processing frequency is 20 kHz.

[0023] Further, S5 specifically includes:

[0024] The electrodes on both sides of the Ecoflex layer are connected with copper foils by using silver glue, and dried in a vacuum drying oven at 150 DEG C for 20 minutes until the silver glue solidifies, to complete the electrode connection.

[0025] Further, S6 specifically includes:

[0026] The PDMS prepolymer and the crosslinking agent are mixed in a ratio of 10:1, the air pressure is adjusted to-0.08 MPa at room temperature, after removing the bubbles, the PDMS prepolymer and the crosslinking agent mixture is coated on the sensor, and after drying in a vacuum drying oven at 80 DEG C for 2 hours, a PDMS packaging layer is formed.

[0027] In a third aspect, a method for using the flexible bionic strain sensor for underground structure monitoring, comprising the following steps:

[0028] T1: fixing the flexible bionic strain sensor on the surface of the underground structure to be monitored;

[0029] T2: connecting the copper foil electrodes of the sensor through an electrochemical workstation, and monitoring the strain change of the underground structure in real time;

[0030] T3: recording and analyzing the electrical signals output by the flexible bionic strain sensor, and evaluating the health condition of the underground structure.

[0031] The flexible bionic strain sensor for underground structure monitoring and the preparation method thereof provided by the application have the following beneficial effects:

[0032] 1、The sensor of the application can detect small strain changes, such as slight deformation of the structure and crack propagation, in actual application, which is of great significance for early detection of structural problems and prevention of safety accidents, and the high sensitivity of the sensor makes the monitoring data have high resolution, which can more accurately reflect the health condition of the structure.

[0033] 2. In dynamic environments such as bridges and tunnels, the sensor can monitor the dynamic changes of the structure such as vibration and impact in real time, and promptly detect potential safety hazards. In the event of natural disasters such as earthquakes and floods, the sensor can respond quickly and provide accurate data support for emergency response. In practical applications, the sensor can maintain stable performance over a monitoring period of several years, providing reliable data support for long-term health monitoring of the structure. The sensor has good flexibility and plasticity, and can adapt to different structural shapes and curvatures, which makes the sensor suitable for various complex underground structures, such as curved tunnel walls and irregular bridge beams and columns.

[0034] 3. The LIG used in this invention has good thermal and chemical stability, and can work stably for a long time in harsh environments such as high temperature and humidity; Ecoflex material has high elasticity and good weather resistance, and can maintain stable mechanical properties during long-term use; PDMS encapsulation layer has good waterproof, dustproof and moisture-proof performance, ensuring that the sensor works stably for a long time in complex environments. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the fabrication process of the flexible biomimetic strain sensor for underground structure monitoring according to the present invention.

[0036] Figure 2 This is a flowchart illustrating the use of the sensor in this invention.

[0037] Figure 3 This is a schematic diagram of the logarithmic spiral characteristic of the spider web structure in the sensor of the present invention;

[0038] Figure 4 This is a schematic diagram of the spider web structure combining the Ecoflex layer and LIG layer in laser scanning according to the present invention. Detailed Implementation

[0039] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0040] Example 1

[0041] This embodiment provides a flexible biomimetic strain sensor for monitoring underground structures, with reference to... Figure 1 Specifically, it includes:

[0042] LIG layer, Ecoflex layer, spider web structure and PDMS encapsulation layer;

[0043] The LIG layer surface is provided with an Ecoflex layer, the Ecoflex layer is combined with the LIG layer, the Ecoflex layer is provided with a spider web structure, the spider web structure is constructed on the Ecoflex layer by a fiber laser, and gaps exist between the strings in the spider web structure.

[0044] The Ecoflex layer is provided with conductive copper foil on both sides, the conductive copper foil is connected with the Ecoflex layer through silver glue, and the Ecoflex layer is externally provided with a PDMS packaging layer.

[0045] Reference Figure 2 and Figure 3 , the spider web structure constructed on the Ecoflex layer by the fiber laser has certain gaps between the strings, which can effectively amplify the strain signal and improve the sensitivity of the sensor. This design draws on the high sensitivity characteristics of the spider web, so that the sensor can detect small changes in strain. By optimizing the arrangement and spacing of the strings, the sensitivity of the sensor can be further improved to ensure accurate monitoring of strain changes in complex environments. The spider web structure has good mechanical properties and can maintain stability and durability in complex environments. By simulating the structure of the spider web, the sensor can maintain stable performance during long-term use and is suitable for long-term monitoring. By simulating the structure of the spider web, the sensor can better adapt to different environmental conditions to ensure stable operation in various situations. The strings in the spider web structure have high strength and elasticity and can quickly return to their original state when subjected to external forces. This feature allows the sensor to quickly respond and recover during dynamic monitoring, providing accurate monitoring data.

[0046] Embodiment 2

[0047] Based on Embodiment 1, the present embodiment provides a preparation method of a flexible bionic strain sensor for monitoring underground structures, referring to Figure 1 , which specifically comprises the following steps:

[0048] Step S1, fixing the PI film on a glass slide;

[0049] Specifically, the present embodiment selects a polyimide (PI) film with a thickness of 100 pm. The PI film has good high-temperature resistance, corrosion resistance, and mechanical properties, making it an ideal substrate for preparing LIG.

[0050] In the specific operation, the PI film is pasted on a 10 cm x 10 cm glass slide with water-soluble double-sided tape. The glass slide serves as a support platform, facilitating subsequent laser processing and handling.

[0051] Step S2, fix the glass carrying the PI film on the laser processing platform, use CO2 laser to locally carbonize the PI film, and then form the LIG layer;

[0052] Specifically, the CO2 laser (maximum power 60W, wavelength 10.6μm) is used to prepare the LIG layer in this embodiment. The CO2 laser has high energy density and good focusing performance, which is suitable for preparing the LIG layer on the PI film. According to the parameters predicted by machine learning, the laser power is set to 18.12%, the scanning speed is 180mm / s, the scanning interval is 3.3mm, and the focal length is 3.7mm. These parameters are optimized to ensure the high conductivity and uniformity of the LIG layer.

[0053] In the specific preparation, the PI film is placed on the laser processing platform and laser scanning is performed according to the set parameters. During the laser scanning process, the high energy density of the CO2 laser causes the PI film to be locally carbonized, forming a porous graphene structure (LIG layer).

[0054] Step S3, uniformly drop the Ecoflex solution on the surface of the LIG layer, and get the Ecoflex layer after drying at room temperature;

[0055] In this embodiment, the Ecoflex solution is uniformly dropped on the surface of the LIG layer to ensure uniform distribution of the solution. Ecoflex is a high-elasticity silicone material with good mechanical properties and biocompatibility. After drying for 24 hours at room temperature, the Ecoflex solution fully penetrates into the porous structure of the LIG. The combination of the Ecoflex layer and the LIG layer not only enhances the mechanical properties of the LIG, but also improves the flexibility and durability of the sensor.

[0056] Step S4, separate the combined LIG layer and Ecoflex layer from the PI film and fix it on the laser processing platform, and use a fiber laser to build a spider web structure on the Ecoflex layer;

[0057] Specifically, the combined LIG / Ecoflex film is separated from the PI film. The separated LIG / Ecoflex film has good flexibility and mechanical properties, which is suitable for subsequent processing and use. A fiber laser (maximum power 20W, wavelength 1064nm) is used to build a spider web structure on the LIG / Ecoflex film. The fiber laser has high precision and good controllability, which is suitable for fine structure processing. The laser power is set to 50%, the scanning speed is 100mm / s, and the processing frequency is 20kHz. These parameters are optimized to ensure the high sensitivity and stability of the spider web structure.

[0058] In the specific preparation, the LIG / Ecoflex film is placed on the laser processing platform, and laser scanning is performed according to the set parameters. During the laser scanning process, the high precision and controllability of the fiber laser enable the formation of a uniform spider web structure on the Ecoflex layer. The gaps between the strings in the spider web structure can effectively amplify the strain signal and improve the sensitivity of the sensor. At the same time, the spider web structure has good mechanical properties and can maintain stability and durability in complex environments.

[0059] Step S5, connect the copper foil to the electrodes on both sides of the Ecoflex layer with silver glue;

[0060] In this embodiment, copper foil with good electrical conductivity is selected as the electrode material. Copper foil has high electrical conductivity and good mechanical properties, making it suitable for electrode connection in sensors. Silver glue is used to connect the copper foil to the LIG / Ecoflex film. Silver glue has good electrical conductivity and adhesion, ensuring the stability and reliability of the electrode connection.

[0061] In the specific preparation, copper foil is connected to the electrodes on both sides of the LIG / Ecoflex film with silver glue, and dried in a vacuum drying oven at 150°C for 20 minutes to ensure the solidification of the silver glue. After the electrode connection is completed, the sensor can be connected to the electrochemical workstation to realize the transmission and monitoring of electrical signals.

[0062] Step S6, coat the mixture of PDMS prepolymer and crosslinking agent on the outside of the Ecoflex layer, and form a PDMS packaging layer after drying;

[0063] In this embodiment, PDMS is selected as the packaging material. PDMS has good waterproof, dustproof, and moisture-proof properties, which can protect the sensor from external environmental interference and prolong the service life of the sensor.

[0064] In the specific preparation, the PDMS prepolymer and the crosslinking agent are mixed in a ratio of 10:1, the air pressure is adjusted to -0.08 MPa at room temperature, and the bubbles are removed before coating on the sensor. The process of removing bubbles ensures the uniformity and density of the PDMS layer. Dry in a vacuum drying oven at 80°C for 2 hours to form a PDMS packaging layer. The drying process ensures the complete curing of the PDMS layer, forming a good protective layer.

[0065] Example 3

[0066] This embodiment is based on Example 1 and provides a use method of a flexible bionic strain sensor for monitoring underground structures. Referring to Figure 4 , the specific steps include:

[0067] Step T1: Fix the flexible bionic strain sensor on the surface of the underground structure to be monitored;

[0068] During sensor installation, key parts of the underground structure to be monitored are selected, such as the beam-column joint of the bridge, the arch top and side wall of the tunnel, and the support structure of the subway platform, which are usually the most concentrated and most prone to damage. The installation position should be able to represent the stress and strain state of the entire structure to fully reflect the health status of the structure.

[0069] Step T2: Connect the copper foil electrode of the sensor to the electrochemical workstation to monitor the strain change of the underground structure in real time.

[0070] Specifically, the copper foil electrode of the sensor is connected to the lead of the electrochemical workstation, ensuring firm connection and avoiding poor contact. A multimeter is used to check whether the sensor connection is normal, ensuring no short circuit or open circuit phenomenon. The electrochemical workstation is turned on for system initialization and calibration to ensure the accuracy and stability of the system. The electrochemical workstation is started to begin real-time monitoring of the strain change of the underground structure.

[0071] Step T3: Record and analyze the electrical signals output by the flexible bionic strain sensor to evaluate the health status of the underground structure.

[0072] Specifically, the electrical signals output by the sensor are recorded, including voltage, current and other parameters. The monitoring frequency is adjusted according to actual needs, and it is usually recommended to record data once a minute. For key parts or high-risk areas, the monitoring frequency can be appropriately increased. The monitored data is saved in the storage device of the workstation or sent to the remote server through the data transmission module. The data format can be CSV, Excel or other commonly used data file formats, which is convenient for subsequent analysis. Data analysis software such as MATLAB, Python, etc. is used to process and analyze the recorded data, calculate the strain value, analyze the deformation, crack propagation and stress distribution of the structure, and conduct short-term evaluation on the real-time monitoring data. If abnormal strain change is found, immediate measures are taken for inspection and repair to prevent potential risks from expanding.

[0073] Although the specific embodiments of the invention are described in detail with reference to the accompanying drawings, it should not be understood as limiting the scope of protection of the patent. Various modifications and variations made by those skilled in the art within the scope described in the claims are still within the scope of protection of the patent.

Claims

1. A method for fabricating a flexible biomimetic strain sensor for monitoring underground structures, characterized in that, Includes the following steps: S1. Fix the PI film onto the glass slide; S2. Fix the glass slide carrying the PI film onto the laser processing platform, and use a CO2 laser to locally carbonize the PI film to form a LIG layer. S3. The Ecoflex solution is evenly dropped onto the surface of the LIG layer and dried at room temperature to obtain the Ecoflex layer. S4. The combined LIG layer and Ecoflex layer are peeled off from the PI film and fixed on the laser processing platform. A spider web structure is constructed on the Ecoflex layer using a fiber laser. Spider webs exhibit characteristics of a logarithmic spiral, with a polar angle of 80°. S5. Use silver paste to connect the electrodes on both sides of the Ecoflex layer to the copper foil. S6. Coat the outside of the Ecoflex layer with a mixture of PDMS prepolymer and crosslinking agent, and after drying, form a PDMS encapsulation layer.

2. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, S1 specifically includes: Select a PI film with a thickness of 100 μm and use water-soluble double-sided tape to attach the PI film to a 10 cm × 10 cm glass slide.

3. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, In S2, the laser parameters of the CO2 laser are: The laser power is 18.12%, the scanning speed is 180 mm / s, the scanning spacing is 3.3 mm, and the focal length is 3.7 mm.

4. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, S3 specifically includes: Ecoflex solution was uniformly dropped onto the surface of the LIG layer and dried at room temperature for 24 hours until the Ecoflex solution fully penetrated into the porous structure of the LIG layer, thus obtaining the Ecoflex layer.

5. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, In step S4, the laser parameters of the fiber laser are: Laser power 50%, scanning speed 100 mm / s, processing frequency 20 kHz.

6. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, S5 specifically includes: The electrodes on both sides of the Ecoflex layer were connected to the copper foil using silver paste, and then dried in a vacuum drying oven at 150°C for 20 minutes until the silver paste solidified, thus completing the electrode connection.

7. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, S6 specifically includes: The PDMS prepolymer and crosslinking agent were mixed in a ratio of 10:

1. The gas pressure was adjusted to -0.08MPa at room temperature to remove air bubbles. The mixture of PDMS prepolymer and crosslinking agent was then coated onto the sensor and dried in a vacuum drying oven at 80°C for 2 hours to form a PDMS encapsulation layer.

8. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 1, characterized in that, A flexible biomimetic strain sensor includes a LIG layer; an Ecoflex layer is disposed on the surface of the LIG layer, and the Ecoflex layer is bonded to the LIG layer; a spider web structure is constructed on the Ecoflex layer using a fiber laser; The Ecoflex layer is connected to conductive copper foil on both sides by silver paste; the Ecoflex layer is provided with a PDMS encapsulation layer on the outside.

9. The method for fabricating a flexible biomimetic strain sensor for monitoring underground structures according to claim 8, characterized in that: There are gaps between the web strings in the spider web structure.

10. A method of using a flexible biomimetic strain sensor for underground structure monitoring, comprising a flexible biomimetic strain sensor prepared using the preparation method of the flexible biomimetic strain sensor for underground structure monitoring as described in claim 9, characterized in that... Includes the following steps: T1: Fix the flexible biomimetic strain sensor to the surface of the underground structure to be monitored; T2: The copper foil electrodes of the sensor are connected to the electrochemical workstation to monitor the strain changes of the underground structure in real time; T3: Record and analyze the electrical signals output by the flexible biomimetic strain sensor to assess the health status of underground structures.

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