Receiving type flexible sensor for concrete fracture monitoring and preparation method

Abstract

The invention discloses a receiving type flexible sensor for concrete fracture monitoring and a preparation method, belongs to the technical field of solid electronic devices, and relates to preparation of flexible piezoelectric materials. The size of the sensor is flexibly customized according to a monitoring component, and the preparation method comprises the following steps: preparing a piezoelectric functional phase of the flexible sensor by adopting nanoscale lead zirconate titanate ceramic powder; preparing a SiO2 precursor solution; preparing a PZT / SiO2 spinning solution; preparing a flexible piezoelectric PZT / SiO2 nanofiber membrane by using an electrostatic spinning process; and drying and annealing the flexible piezoelectric PZT / SiO2 nanofiber membrane, and packaging the flexible piezoelectric PZT / SiO2 nanofiber membrane as a sensitive layer of the sensor. The preparation process gets rid of the limitation of the substrate on the flexibility, and the modified PZT surface activity effectively solves the problems of agglomeration and precipitation of particles in a solution. According to the invention, the compatibility between the sensor and complex concrete is improved, fracture elastic waves are sensitively captured, the signal amplitude is up to 75dB, and timely sensing of concrete structure failure is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electronic devices and relates to the preparation of flexible piezoelectric materials, and in particular to a receiving-type flexible sensor for concrete fracture monitoring and a preparation method thereof. Background Art

[0002] With the rapid development of the construction industry, concrete structure health monitoring has become an important research field. In the prior art, piezoelectric sensors obtain concrete damage information by monitoring the stress waves generated by tensile and compressive stresses in concrete. However, traditional piezoelectric sensors use hard materials such as piezoelectric ceramics and piezoelectric single crystals as functional elements. Their rigidity makes it impossible for them to perfectly fit the complex concrete surface, thus affecting the signal acquisition efficiency and accuracy. In addition, they are easily damaged during installation and use, which limits the reliability and durability of the sensor in practical applications. Flexible piezoelectric sensors have good mechanical flexibility and can better match special spatial structures. Organic piezoelectric polymers represented by PVDF polymers and their copolymers are usually prepared into soft, large-area piezoelectric film sensors using electrospinning technology and are widely used. However, the piezoelectric properties of this material depend on the formation of the β phase in the material, and the β phase PVDF film belongs to the thermodynamic metastable state, which makes the state of the PVDF film easily affected by the external environment and changes. This change is called depolarization, which affects its piezoelectric properties.

[0003] Lead zirconate titanate PZT has superior piezoelectric and dielectric properties and a higher Curie temperature than PVDF. Among them, PZT-5H series piezoelectric ceramics are used as core components of receiving sensors due to their large strain constant. Using its positive piezoelectric effect, the elastic wave signal of concrete fracture can be converted into a voltage signal, which does not require power excitation and belongs to passive monitoring. However, since ceramics are polycrystalline, they require higher annealing and polarization temperatures, which greatly limits the choice of PZT film growth substrate. Therefore, using PZT to achieve the flexibility of piezoelectric composite film materials while maintaining good piezoelectric properties is a major challenge in the preparation of high-sensitivity sensors. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a receiving flexible sensor for concrete fracture monitoring and a preparation method thereof. PZT-5H ceramic powder is used as a functional body, and a non-high temperature annealing polarization process is adopted to prepare a piezoelectric thick film material, which takes into account the advantages of bulk materials and thin films, is free from the limitation of the matrix interface, and is no longer affected by the surface shape or texture.

[0005] To achieve the above object, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides a receiving-type flexible sensor for concrete fracture monitoring, the structure of which includes, from bottom to top, a sound-transmitting layer, a sensitive layer, a conductive layer, a shielding layer and a protective layer.

[0007] Furthermore, the sound-permeable layer is a composite material formed by mixing PDMS matrix with nano-scale Al2O3 powder, which has viscoelasticity and softness, and the mass ratio of the two is 5:1. It is attached to the concrete surface, and its shape and size can be flexibly customized according to the needs of the monitored object, and the thickness is controlled at 500~800 μm.

[0008] Furthermore, the sensitive layer is made of a PZT / SiO2 nanofiber membrane prepared by an electrospinning process. Its shape and size can be flexibly customized according to the needs of the monitored object, but the area should be smaller than the sound-transmitting layer, and the thickness is controlled at 200 μm. Before the sound-transmitting layer is solidified, the two are closely attached.

[0009] Furthermore, the conductive layer uses a silver electrode or a platinum electrode sputtered on a PI film as a substrate, or a forked electrode is designed by 3D printing, with a finger length of 14 mm, a finger width of 600 μm, a finger spacing of 1 mm, and a thickness of 25-100 μm. The positive and negative electrodes are connected to a coaxial shielded wire. A polyvinyl alcohol adhesive is applied to the surface of the forked electrode and attached to the sensitive layer.

[0010] Furthermore, the shielding layer is divided into two layers, the lower layer is insulated and tightly connected to the conductive layer, and the upper layer is a copper tape, the area of ​​which should be larger than the sensitive layer and smaller than the sound-transmitting layer. The copper tape contacts the negative electrode of the interdigital electrode, forming a Faraday cage-like shielding structure as a whole. Finally, PDMS is used for packaging to form a protective layer.

[0011] In a second aspect, the present invention provides a method for preparing a receiving flexible sensor for concrete fracture monitoring, comprising the following steps: S1. Prepare the piezoelectric functional phase of the flexible sensor; S2, preparing SiO2 precursor solution; S3, preparing PZT / SiO2 spinning solution; S4, preparation of flexible piezoelectric PZT / SiO2 nanofiber membrane; S5. Drying and annealing of flexible piezoelectric PZT / SiO2 nanofiber membrane.

[0012] Furthermore, in step S1, the piezoelectric functional phase is commercial PZT-5H or the initial powder obtained by drying 0.5 mol of PZT solution. Based on the traditional solid phase method, secondary crushing, grinding and sieving are performed to obtain a piezoelectric strain constant of 560 PC / N and a particle size of 200-600 nm.

[0013] Furthermore, in step S2, the SiO2 precursor solution is prepared by dissolving 1.1 g of PVP in 10 ml of ethanol to obtain a first solution; 5.5 ml of ethyl orthosilicate is measured and slowly added to the first solution to obtain a second solution; finally, 1 ml of DMF is added to the second solution and stirred for 24 h to obtain.

[0014] Furthermore, in step S3, the piezoelectric functional phase PZT-5H powder obtained in step S1 is modified and added to the SiO2 precursor solution prepared in step S2, with the mass fraction designed to be 10% wt. After ultrasonic dispersion, magnetic stirring is performed for 2 h to obtain the PZT / SiO2 spinning solution.

[0015] Furthermore, in step S4, the spinning solution obtained in S3 is subjected to electrospinning treatment to obtain the piezoelectric PZT / SiO2 nanofiber membrane, and the electrospinning parameters are set, including a voltage setting of 25 kV, a drum speed of 3000 rpm, an injection rate of 2 ml / h, a left and right moving range of 80 mm, and a distance of 20 cm between the collecting device and the needle tip.

[0016] Furthermore, in step S5, the annealing includes drying the nanofiber membrane in S4 on a hot plate at 80°C for 1 h, heating it to 135°C, and annealing it in air for 6-8 h, thus completing the final preparation process.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for preparing a receiving flexible sensor for concrete fracture monitoring. Compared with the traditional PVDF piezoelectric film, the present invention uses nano-scale PZT-5H powder as a functional phase to improve the piezoelectric properties of the flexible film. The modification technology effectively solves the problem of particle agglomeration and precipitation in the solution. The electrospinning preparation process is adopted, and high-temperature polarization is no longer required, and the limitation of the substrate on flexibility is eliminated; 2. The present invention provides a receiving-type flexible sensor for concrete fracture monitoring, which can be customized in shape according to the actual complex concrete structure. The manufacturing process is simple, the cycle is short, and the deployment is convenient. The self-powered, high-sensitivity piezoelectric thick film sensor can realize timely perception of concrete structure failure, thereby providing strong support for concrete structure health monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of a receiving type flexible sensor for concrete fracture monitoring of the present invention; Among them, the reference numerals in the above drawings are: 1. Sound-transmitting layer; 2. Sensitive layer; 3. Conductive layer; 4. Shielding layer; 5. Protective layer; 6. First conductor; 7. Second conductor; Figure 2This is a process flow chart of preparing a receiving-type flexible sensor for concrete fracture monitoring according to the present invention; Figure 3 This is the SEM test image of the modified PZT powder; Figure 4 This is the XRD test diagram of the modified PZT powder; Figure 5 Electrical performance test diagram of receiving flexible sensor for concrete fracture monitoring; Figure 6 Acoustic performance test of receiving flexible sensor for concrete fracture monitoring under lead breaking excitation. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present invention. It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by ordinary technicians in the technical field to which the present application belongs. Unless otherwise explicitly stated in the present invention, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices and / or combinations thereof; Glossary: ​​PVDF film is polyvinylidene fluoride film; PZT piezoelectric ceramic is lead zirconate titanate piezoelectric ceramic; PDMS matrix is ​​polydimethylsiloxane matrix; Al2O3 powder is aluminum oxide powder; PI film is polyimide film; SiO2 precursor solution is silicon dioxide precursor solution; PZT / SiO2 nanofiber membrane is lead zirconate titanate / silicon dioxide fiber membrane; PVP is polyvinyl polypyrrolidone; DMF is N,N-dimethylsiloxane; PEI aqueous solution is polyethyleneimine aqueous solution.

[0020] The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

[0021] The present invention is described in detail below in conjunction with the accompanying drawings, specifically as follows: like Figure 1 As shown, the embodiment of the present disclosure provides a receiving-type flexible sensor for concrete fracture monitoring, including a sound-transmitting layer 1, a sensitive layer 2, a conductive layer 3, a shielding layer 4, a protective layer 5, a first wire 6, and a second wire 7; The sound-transmitting layer 1, the sensitive layer 2, the conductive layer 3, the shielding layer 4 and the protective layer 5 are attached together from bottom to top, and the first conductive wire 6 and the second conductive wire 7 are connected to the conductive layer.

[0022] Specifically, the sound-permeable layer 1 is a composite material formed by mixing a PDMS matrix with nano-scale Al2O3 powder, which has viscoelasticity and softness. When the mass ratio is designed to be 20%, the sound velocity is 820.5 m / s and the acoustic impedance is 11.18 MRayl. At this time, the sound wave transmittance is the highest. It is attached to the concrete surface, and its shape and size are flexibly customized according to the needs of the monitored object, and the thickness is controlled at 500~800 μm; The sensitive layer 2 is made of a PZT / SiO2 nanofiber membrane prepared by an electrospinning process. Its shape and size can be flexibly customized according to the needs of the monitored object, but the area should be smaller than the sound-transmitting layer, and the thickness is controlled at 200 μm. Before the sound-transmitting layer is solidified, the two are closely attached; The conductive layer 3 uses a silver electrode or a platinum electrode sputtered on a PI film as a substrate, or uses a 3D printing method to design a forked electrode, with a finger length of 14 mm, a finger width of 600 μm, a finger spacing of 1 mm, and a thickness of 25-100 μm. The first wire 6 is a negative electrode connected to the copper tape of the shielding layer, and the second wire 7 is a positive electrode. The two wires are connected to the coaxial shielding wire. Polyvinyl alcohol adhesive is applied to the surface of the forked electrode and pasted to the sensitive layer; The shielding layer 4 is tightly connected to the conductive layer using copper tape, and the area of ​​the copper tape should be larger than the sensitive layer and smaller than the sound-transmitting layer. The copper tape contacts the negative electrode of the interdigital electrode, forming a Faraday cage-like shielding structure as a whole; The protective layer 5 uses PDMS to encapsulate the entire device.

[0023] The present disclosure provides a method for preparing a receiving flexible sensor for concrete fracture monitoring, such as Figure 2 As shown, the following steps are included: S1. Preparation of piezoelectric functional phase of flexible sensor: After the PZT-5H pretreatment step, it is crushed, ground and sieved again to prepare a powder with a particle size of 200-600 nm and a perovskite structure, i.e., a piezoelectric functional phase; S2. Prepare SiO2 precursor solution: weigh 1.1g PVP and dissolve it in 10ml ethanol to obtain a first solution; measure 5.5ml ethyl orthosilicate and slowly add it to the first solution to obtain a second solution; finally, add 1ml DMF to the second solution and stir for 24h to obtain a SiO2 precursor solution; S3, preparing PZT / SiO2 spinning solution: modify the piezoelectric functional phase PZT-5H powder obtained in step S1, add it to the SiO2 precursor solution prepared in step S2, and the mass fraction is designed to be 10% wt. After ultrasonic dispersion, magnetic stirring is performed for 2 h to obtain PZT / SiO2 spinning solution; S4, preparation of flexible piezoelectric PZT / SiO2 nanofiber membrane: setting electrospinning parameters, using a 10 ml syringe to absorb the spinning solution obtained in step S3, spinning at a relative humidity of 45% to 55% and a temperature controlled at 23 to 26°C to obtain a piezoelectric PZT / SiO2 nanofiber membrane; S5. Drying and annealing of the flexible piezoelectric PZT / SiO2 nanofiber membrane: Place the piezoelectric PZT / SiO2 nanofiber membrane obtained in step S4 flatly in a forced air drying oven at 60°C for 12 hours to evaporate the residual solvent, and finally obtain a flexible piezoelectric PZT / SiO2 nanofiber membrane that does not require secondary high-temperature polarization.

[0024] In this embodiment, step S1 prepares the piezoelectric functional phase of the flexible sensor, using commercial PZT-5H or drying 0.5 mol of PZT solution to obtain the initial powder. The pretreatment step includes: using the initial powder, pre-sintering it in a muffle furnace at 600 °C; ball milling for 24 hours, drying and grinding; granulation and dry pressing; calcining in a muffle furnace at a rate of 5 °C / min to promote grain growth. Secondary crushing, grinding and screening based on the traditional solid phase method, Figure 3 This is the SEM test picture of the modified PZT powder. It can be seen from the figure that the particle size of PZT is between 200 and 600 nm.

[0025] In this embodiment, in step S3, the powder modification specifically includes completely mixing the powder with 10 ml of PEI aqueous solution, the mass fraction of the two being 20% ​​wt, stirring at room temperature for 30 min, and then centrifuging at 3000 rpm for 10 min to separate the powder and the PEI solution. Figure 4 This is the XRD test diagram of the modified PZT powder. It can be seen from the figure that the modified PZT presents a single perovskite phase, and the crystal phases (001), (101), (111), (002), (210), and (211) correspond one to one with the PDF card, which shows that the modification will not affect its piezoelectric activity.

[0026] The flexible piezoelectric PZT / SiO2 nanofiber membrane was encapsulated into a receiving flexible sensor for concrete fracture monitoring, and its electrical and acoustic performance tests were performed. The sensor wire was directly connected to the oscilloscope, and the average voltage output of the sensor surface was 15 V when a small rubber hammer was used to knock on it 10 times. Figure 5 The sensor was attached to the concrete surface and a lead breaking experiment was conducted at a distance of 1 cm from the sensor. The acoustic signals of 10 lead breaking experiments were as follows: Figure 6 As shown, the average signal value is 75 dB and the bottom noise is below 40dB, which far exceeds the existing flexible acoustic signal receiving sensors.

[0027] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A receiving type flexible sensor for concrete fracture monitoring, characterized in that: It comprises a sound-transmitting layer (1), a sensitive layer (2), a conductive layer (3), a shielding layer (4) and a protective layer (5) attached together from bottom to top, and a first conductive wire (6) and a second conductive wire (7) connected to the conductive layer (3); The sound-transmitting layer (1) is a composite material formed by mixing a PDMS matrix with nano-sized Al2O3 powder, the mass ratio of which is designed to be 20% with a sound velocity of 820.5 m / s and an acoustic impedance of 11.18 MRayl. It is directly coated on the surface of a special-shaped concrete component, the coating area is designed according to the size of the component, and the thickness is controlled to be 500-800 μm using a customized scraper; The sensitive layer (2) is made of a PZT / SiO2 nanofiber membrane prepared by an electrospinning process, with a thickness controlled at 200 μm, and is attached to the sound-transmitting layer in a semi-cured state, using the viscosity of the sound-transmitting layer to make the two fit tightly together, with an area smaller than that of the sound-transmitting layer, so as to facilitate complete encapsulation of the subsequent functional layer; The conductive layer (3) uses a silver electrode or a platinum electrode sputtered on a PI film as a substrate, and a 3D printing method can be used to design the interdigitated electrodes, with a finger length of 14 mm, a finger width of 600 μm, a finger spacing of 1 mm, and a thickness of 25-100 μm; The first wire (6) is a negative electrode connected to the copper tape of the shielding layer, the second wire (7) is a positive electrode, the two wires are connected to the coaxial shielding wire, and the surface of the interdigitated electrode is coated with polyvinyl alcohol adhesive and adhered to the sensitive layer (2); The shielding layer (4) is tightly connected to the conductive layer using copper tape, the area of ​​the copper tape should be larger than the sensitive layer and smaller than the sound-transmitting layer (1), and the copper tape is in contact with the negative electrode of the interdigital electrode, forming a Faraday cage-like shielding structure as a whole; The protective layer (5) uses PDMS to encapsulate the entire device.

2. A method for preparing a receiving flexible sensor for concrete fracture monitoring, characterized in that: The following steps are involved: S1. Prepare the piezoelectric functional phase of the flexible sensor; S2, preparing SiO2 precursor solution; S3, preparing PZT / SiO2 spinning solution; S4, preparation of flexible piezoelectric PZT / SiO2 nanofiber membrane; S5. Drying and annealing of flexible piezoelectric PZT / SiO2 nanofiber membrane.

3. The method for preparing a receiving flexible sensor for concrete fracture monitoring according to claim 2, characterized in that: In step S1, the piezoelectric functional phase is commercial PZT-5H or an initial powder obtained by drying 0.5 mol of PZT solution, which is crushed, ground and sieved for the second time based on the traditional solid phase method to obtain nano-powder particles with a piezoelectric strain constant of 560 pC / N and a particle size of 200~600 nm.

4. The method for preparing a receiving flexible sensor for concrete fracture monitoring according to claim 2, characterized in that: In step S2, the SiO2 precursor solution is prepared by dissolving 1.1 g PVP in 10 ml ethanol to obtain a first solution; 5.5 ml ethyl orthosilicate is measured and slowly added to the first solution to obtain a second solution; finally, 1 ml DMF is added to the second solution and stirred for 24 h to obtain.

5. The method for preparing a receiving-type flexible sensor for concrete fracture monitoring according to claim 2, characterized in that: In step S3, the PZT / SiO2 spinning solution is prepared by using modified PZT-5H powder in a SiO2 precursor solution with a mass fraction of 10% wt. After ultrasonic dispersion, magnetic stirring is performed for 2 h to obtain the PZT / SiO2 spinning solution.

6. The method for preparing a receiving-type flexible sensor for concrete fracture monitoring according to claim 5, characterized in that: The modification method is: completely mix the powder with 10 ml of a surfactant PEI aqueous solution, the mass fraction of the two is 20% wt, stir at room temperature for 30 minutes, and then centrifuge at 3000 rpm for 10 minutes to separate the powder and the PEI solution. After modification, the PZT powder presents a single perovskite phase that corresponds one to one with the PDF card.

7. The method for preparing a receiving-type flexible sensor for concrete fracture monitoring according to claim 2, characterized in that: In step S4, the flexible piezoelectric PZT / SiO2 nanofiber membrane is obtained by treating the PZT / SiO2 spinning solution with an electrospinning process, and the electrospinning parameters are set, including a voltage setting of 25 kV, a drum speed of 3000 rpm, an injection rate of 2 ml / h, a left and right moving range of 80 mm, and a distance of 20 cm between the collecting device and the needle tip.

8. The method for preparing a receiving-type flexible sensor for concrete fracture monitoring according to claim 2, characterized in that: In step S5, the drying and annealing conditions are to heat the blast drying oven from room temperature to 60°C, dry for 12 hours to volatilize the residual solvent, then cool it down to room temperature and take it out, and perform electrical and acoustic performance tests on the sensor before and after packaging, using a broken lead simulated concrete fracture signal as an excitation signal.

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