A receiving flexible sensor for concrete fracture monitoring and its fabrication method

Abstract

This invention discloses a receiving flexible sensor for concrete fracture monitoring and its fabrication method, belonging to the field of solid-state electronic device technology, and relating to the preparation of flexible piezoelectric materials. The sensor size is flexibly customized according to the monitoring component. The fabrication method includes: preparing the piezoelectric functional phase of the flexible sensor using nano-scale lead zirconate titanate ceramic powder; preparing a SiO2 precursor solution; preparing a PZT / SiO2 spinning solution; preparing a flexible piezoelectric PZT / SiO2 nanofiber membrane using electrospinning; and encapsulating the flexible piezoelectric PZT / SiO2 nanofiber membrane as the sensitive layer of the sensor after drying and annealing. The fabrication process overcomes the limitations imposed by the substrate on flexibility, and the modified PZT surface activity effectively solves the problems of particle agglomeration and precipitation in the solution. This invention improves the sensor's compatibility with complex concrete, sensitively captures fracture elastic waves with a signal amplitude of up to 75 dB, and enables timely detection of concrete structural failure.

Description

Technical Field

[0001] This invention belongs to the field of solid-state electronic device technology, and relates to the preparation of flexible piezoelectric materials, specifically to a receiving flexible sensor for concrete fracture monitoring and its preparation method. Background Technology

[0002] With the rapid development of the construction industry, concrete structure health monitoring has become an important research field. In existing technologies, piezoelectric sensors acquire damage information from concrete by monitoring stress waves generated by tensile and compressive stresses. However, traditional piezoelectric sensors use rigid materials such as piezoelectric ceramics and piezoelectric single crystals as functional elements. Their rigidity prevents them from perfectly conforming to complex concrete surfaces, thus affecting signal acquisition efficiency and accuracy. Furthermore, they are easily damaged during installation and use, limiting the reliability and durability of the sensors in practical applications. Flexible piezoelectric sensors possess good mechanical flexibility, allowing for better matching with special spatial structures. Organic piezoelectric polymers, represented by PVDF polymers and their copolymers, are typically fabricated into soft, large-area piezoelectric thin-film sensors using electrospinning processes and are widely used. However, the piezoelectric properties of this material depend on the formation of the β phase. The β-phase PVDF thin film is thermodynamically metastable, making its state susceptible to changes caused by external environmental influences. This change, known as depolarization, affects its piezoelectric properties.

[0003] Lead zirconate titanate (PZT) possesses superior piezoelectric and dielectric properties, as well as a higher Curie temperature, compared to PVDF. Among these, the PZT-5H series piezoelectric ceramics, due to their large strain constant, are used as core components in receiver-type sensors. Utilizing their positive piezoelectric effect, the elastic wave signal from concrete fracture can be converted into a voltage signal, requiring no power source and thus constituting passive monitoring. However, because ceramics are polycrystalline, high annealing and polarization temperatures are required, significantly limiting the choice of substrate for PZT thin film growth. Therefore, achieving flexibility in piezoelectric composite thin film materials using PZT while maintaining good piezoelectric properties remains a major challenge in the fabrication of high-sensitivity sensors. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a receiving flexible sensor for monitoring concrete fracture and its fabrication method. PZT-5H ceramic powder is used as the functional component, and a piezoelectric thick-film material is prepared using a non-high-temperature annealing polarization process. This material combines the advantages of both bulk and thin films, is freed from the limitations of the substrate interface, and is no longer affected by surface shape or texture.

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

[0006] In a first aspect, the present invention provides a receiving flexible sensor for monitoring concrete fracture, the structure of which, from bottom to top, includes: an acoustic 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-sized Al2O3 powder, exhibiting viscoelasticity and flexibility, with a mass ratio of 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, with a thickness controlled between 500 and 800 μm.

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

[0009] Furthermore, the conductive layer employs silver or platinum electrodes sputtered onto a PI thin film substrate, or uses interdigitated electrodes designed via 3D printing. These interdigitated electrodes are 14 mm long, 600 μm wide, 1 mm apart, and 25–100 μm thick. The positive and negative electrodes are connected to coaxial shielded wires. Polyvinyl alcohol adhesive is applied to the surface of the interdigitated electrodes, which are then adhered to the sensitive layer.

[0010] Furthermore, the shielding layer consists of two layers: the lower layer is insulating and tightly bonded to the conductive layer, while the upper layer is a copper tape with an area larger than the sensitive layer but smaller than the sound-transmitting layer. The copper tape contacts the negative electrode of the interdigitated electrode, forming a Faraday cage-like shielding structure. Finally, PDMS encapsulation is used to form a protective layer.

[0011] Secondly, the present invention provides a method for fabricating a receiver-type flexible sensor for monitoring concrete fracture, comprising the following steps:

[0012] S1. Fabrication of the piezoelectric functional phase for flexible sensors;

[0013] S2. Prepare SiO2 precursor solution;

[0014] S3. Prepare PZT / SiO2 spinning solution;

[0015] S4. A flexible piezoelectric PZT / SiO2 nanofiber membrane was obtained by electrospinning the PZT / SiO2 spinning solution.

[0016] S5. Drying and annealing of flexible piezoelectric PZT / SiO2 nanofiber membrane.

[0017] Furthermore, in step S1, the piezoelectric functional phase PZT-5H is commercially available or obtained as an initial powder after drying with a 0.5 mol PZT solution. Based on the traditional solid-state method, it undergoes secondary crushing, grinding, and sieving to obtain a piezoelectric strain constant of 560 pC / N and a particle size of 200–600 nm.

[0018] Further, in step S2, the SiO2 precursor solution is obtained by dissolving 1.1g PVP in 10ml of ethanol to obtain a first solution; 5.5ml of tetraethyl orthosilicate is measured and slowly added to the first solution to obtain a second solution; finally, 1ml of DMF is added to the second solution and stirred for 24h to obtain the final solution.

[0019] 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 at a mass ratio of 10wt%. After ultrasonic dispersion, it is magnetically stirred for 2 hours to obtain the PZT / SiO2 spinning solution.

[0020] Furthermore, in step S4, the spinning solution obtained in S3 is subjected to electrospinning treatment to obtain the piezoelectric PZT / SiO2 nanofiber membrane. The electrospinning parameters are set, including a voltage of 25kV, a roller speed of 3000rpm, an injection rate of 2ml / h, a left and right movement range of 80mm, and a distance of 20cm between the collection device and the needle tip.

[0021] Furthermore, in step S5, the annealing includes drying the nanofiber membrane hot plate in S4 at 80°C for 1 hour, then raising the temperature to 135°C and annealing in air for 6-8 hours, thus completing the final preparation process.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention provides a method for fabricating a receiving flexible sensor for monitoring concrete fracture. Compared with traditional PVDF piezoelectric films, this invention utilizes nano-sized PZT-5H powder as a functional phase to enhance the piezoelectric properties of the flexible film. The modification technology effectively solves the problems of particle agglomeration and precipitation in solution. The electrospinning process eliminates the need for high-temperature polarization, overcoming the limitations imposed by the substrate on flexibility.

[0024] 2. This invention provides a receiving flexible sensor for concrete fracture monitoring. The shape can be customized 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 the timely detection of concrete structure failure, thus providing strong support for the health monitoring of concrete structures. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the structure of a receiving flexible sensor for monitoring concrete fracture according to the present invention.

[0026] The reference numerals in the above figures are as follows:

[0027] 1. Acoustic layer; 2. Sensitive layer; 3. Conductive layer; 4. Shielding layer; 5. Protective layer; 6. First conductor; 7. Second conductor;

[0028] Figure 2 This is a process flow diagram of the fabrication process of a receiving flexible sensor for concrete fracture monitoring according to the present invention.

[0029] Figure 3 SEM images of the modified PZT powder;

[0030] Figure 4 XRD pattern of modified PZT powder;

[0031] Figure 5 Electrical performance test diagram of a receiver-type flexible sensor for concrete fracture monitoring;

[0032] Figure 6 Acoustic performance test of a receiver-type flexible sensor for concrete fracture monitoring under lead breakage excitation. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. Unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, and / or combinations thereof;

[0034] Glossary: ​​PVDF film is polyvinylidene fluoride film; PZT piezoelectric ceramic is lead zirconate titanate piezoelectric ceramic; PDMS matrix is ​​polydimethylsiloxane; Al2O3 powder is alumina powder; PI film is polyimide film; SiO2 precursor solution is silica precursor solution; PZT / SiO2 nanofiber membrane is lead zirconate titanate / silica fiber membrane; PVP is polyvinylpyrrolidone; DMF is N,N-dimethylsiloxane; PEI aqueous solution is polyethyleneimine aqueous solution.

[0035] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0036] The present invention will now be described in detail with reference to the accompanying drawings, as follows:

[0037] like Figure 1 As shown, this embodiment of the present disclosure provides a receiving flexible sensor for monitoring concrete fracture, including an acoustically transparent 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;

[0038] The sound-transmitting layer 1, sensitive layer 2, conductive layer 3, shielding layer 4, and protective layer 5 are attached together from bottom to top, and the first wire 6 and the second wire 7 are connected to the conductive layer.

[0039] Specifically, the sound-transmitting layer 1 is a composite material formed by mixing PDMS matrix with nano-sized Al2O3 powder, which has viscoelasticity and flexibility. When the mass ratio is designed to be 20%, the sound velocity is 820.5 m / s and the acoustic impedance is 11.18 MNayl, at which point the sound wave transmittance is the highest. It is attached to the concrete surface, and its shape and size can be flexibly customized according to the needs of the monitoring object, with the thickness controlled between 500 and 800 μm.

[0040] The sensitive layer 2 is made of a PZT / SiO2 nanofiber membrane prepared by electrospinning. Its shape and size are flexibly customized according to the needs of the monitored object, but its area should be smaller than that of the sound-transmitting layer, and its thickness should be controlled within 200 μm. The two layers are tightly adhered before the sound-transmitting layer is cured.

[0041] The conductive layer 3 uses silver or platinum electrodes sputtered onto a PI thin film substrate, or employs 3D printing to design interdigitated electrodes. The electrodes are 14 mm long, 600 μm wide, 1 mm apart, and 25–100 μm thick. The first conductor 6 is the negative electrode and connects to the copper tape of the shielding layer. The second conductor 7 is the positive electrode, and both conductors are connected to the coaxial shielding conductor. Polyvinyl alcohol adhesive is applied to the surface of the interdigitated electrodes, which are then adhered to the sensitive layer.

[0042] The shielding layer 4 is tightly bonded to the conductive layer using copper tape. The area of ​​the copper tape should be larger than that of the sensitive layer but smaller than that of the sound-transmitting layer. The copper tape is in contact with the negative electrode of the interdigitated electrode, forming a Faraday cage-like shielding structure.

[0043] The protective layer 5 uses PDMS to encapsulate the entire device.

[0044] This disclosure provides a method for fabricating a receiver-type flexible sensor for monitoring concrete fracture, such as... Figure 2 As shown, it includes the following steps:

[0045] S1. Preparation of piezoelectric functional phase for flexible sensor: After the PZT-5H pretreatment step, it is crushed, ground and sieved again to prepare powder with a particle size of 200-600nm and a perovskite structure, which is the piezoelectric functional phase.

[0046] S2. Preparation of SiO2 precursor solution: Weigh 1.1g PVP and dissolve it in 10ml ethanol to obtain the first solution; measure 5.5ml tetraethyl orthosilicate and slowly add it to the first solution to obtain the second solution; finally, add 1ml DMF to the second solution and stir for 24h to obtain the SiO2 precursor solution.

[0047] S3. Preparation of 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 design the mass ratio to be 10wt%. After ultrasonic dispersion, stir magnetically for 2h to obtain PZT / SiO2 spinning solution.

[0048] S4. Preparation of flexible piezoelectric PZT / SiO2 nanofiber membrane: Set the electrospinning parameters, use a 10ml syringe to draw the spinning solution obtained in step S3, and spin at a relative humidity of 45% to 55% and a temperature controlled at 23 to 26℃ to obtain a piezoelectric PZT / SiO2 nanofiber membrane.

[0049] S5. Drying and annealing of flexible piezoelectric PZT / SiO2 nanofiber membrane: The piezoelectric PZT / SiO2 nanofiber membrane obtained in step S4 is placed flat in a forced-air drying oven at 60°C for 12 hours to evaporate the residual solvent, and finally a flexible piezoelectric PZT / SiO2 nanofiber membrane that does not require secondary high-temperature polarization is obtained.

[0050] In this embodiment, step S1 prepares the piezoelectric functional phase of the flexible sensor, using commercially available PZT-5H or drying it with a 0.5 mol PZT solution to obtain the initial morphological powder. The pretreatment steps include: pre-calcining the initial morphological powder in a muffle furnace at 600°C; ball milling for 24 hours, followed by drying and grinding; granulation and dry pressing; and calcination in a muffle furnace at a rate of 5°C / min to 1000–1300°C to promote grain growth. This is based on the traditional solid-state method, involving secondary crushing, grinding, and sieving. Figure 3 The image shows the SEM test results of the modified PZT powder. The PZT particle size ranges from 200 to 600 nm.

[0051] In this embodiment, step S3, the powder modification specifically includes: completely mixing the powder with 10 ml of PEI aqueous solution, with a mass ratio of 20 wt%, stirring at room temperature for 30 min, and then centrifuging at 3000 rpm for 10 min to separate the powder and PEI solution. Figure 4The image shows the XRD pattern of the modified PZT powder. It can be seen from the image that the modified PZT exhibits a single perovskite phase. The crystal phases (001), (101), (111), (002), (210), and (211) correspond one-to-one with the PDF card, which indicates that the modification does not affect its piezoelectric activity.

[0052] A flexible piezoelectric PZT / SiO2 nanofiber membrane was encapsulated to form a receiving flexible sensor for concrete fracture monitoring. Its electrical and acoustic performance were then tested. By directly connecting the sensor leads to an oscilloscope and tapping the sensor surface 10 times with a small rubber mallet, the average voltage output reached 15V. Figure 5 As shown. 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 from 10 lead-breaking tests are as follows. Figure 6 As shown, the average signal value is 75dB and the bottom noise is below 40dB, which far exceeds the performance of existing flexible acoustic signal receiving sensors.

[0053] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A receiving flexible sensor for monitoring concrete fracture, characterized in that, The sound-transmitting layer (1), sensitive layer (2), conductive layer (3), shielding layer (4) and protective layer (5) are attached together from bottom to top, and the first wire (6) and the second wire (7) are connected to the conductive layer (3); The sound-permeable layer (1) is a composite material formed by mixing PDMS matrix with nano-sized Al2O3 powder. 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. It is directly coated on the surface of concrete irregular components. The coating area is designed according to the size of the component, and the thickness is controlled at 500-800 μm using a custom scraper. The sensitive layer (2) is made of PZT / SiO2 nanofiber membrane prepared by electrospinning process, with a thickness controlled at 200μm. It is attached in the semi-cured state of the sound-permeable layer, and the adhesiveness of the sound-permeable layer is used to make the two tightly bonded. The area is smaller than that of the sound-permeable layer so as to fully encapsulate the subsequent functional layers. The conductive layer (3) is made by sputtering silver or platinum electrodes on a PI thin film substrate. The interdigitated electrodes are 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 to 100 μm. The first wire (6) is the negative electrode and is connected to the copper tape of the shielding layer. The second wire (7) is the positive electrode. The two wires are connected to the coaxial shielding wire. Polyvinyl alcohol adhesive is applied to the surface of the interdigitated electrode and pasted onto the sensitive layer (2). The shielding layer (4) is tightly bonded to the conductive layer using copper tape. The area of ​​the copper tape should be larger than that of the sensitive layer but smaller than that of the sound-transmitting layer (1). The copper tape is in contact with the negative electrode of the interdigitated electrode, forming a Faraday cage-like shielding structure. The protective layer (5) is encapsulated using PDMS. The PZT / SiO2 nanofiber membrane preparation steps include: S1. Fabrication of the piezoelectric functional phase for flexible sensors; S2. Prepare SiO2 precursor solution; S3. Prepare PZT / SiO2 spinning solution; S4. A flexible piezoelectric PZT / SiO2 nanofiber membrane was obtained by electrospinning the PZT / SiO2 spinning solution. S5, Drying and annealing of flexible piezoelectric PZT / SiO2 nanofiber membrane; In step S3, the modified PZT-5H powder is added to the prepared SiO2 precursor solution. The modification can prevent the particles from agglomerating or precipitating in the solution. The mass ratio is designed to be 10wt%. After ultrasonic dispersion, the mixture is magnetically stirred for 2 hours to obtain the PZT / SiO2 spinning solution.

2. The receiving flexible sensor for concrete fracture monitoring according to claim 1, characterized in that, In step S1, the piezoelectric functional phase, PZT-5H, is either commercially available or obtained by drying the initial form of powder with 0.5 mol of PZT solution. Based on the traditional solid-state method, it is subjected to secondary crushing, grinding, and sieving to obtain nanoscale powder particles with a piezoelectric strain constant of 560 pC / N and a particle size of 200-600 nm.

3. A receiving flexible sensor for monitoring concrete fracture according to claim 1, characterized in that, In step S2, the SiO2 precursor solution is prepared by dissolving 1.1g PVP in 10ml of ethanol to obtain a first solution; 5.5ml of tetraethyl orthosilicate is slowly added to the first solution to obtain a second solution; finally, 1ml of DMF is added to the second solution and stirred for 24h to obtain the final solution.

4. A receiving flexible sensor for monitoring concrete fracture according to claim 1, characterized in that, The modification method is as follows: the powder is completely mixed with 10 ml of surfactant PEI aqueous solution at a mass ratio of 20 wt%, stirred at room temperature for 30 min, and then centrifuged at 3000 rpm for 10 min to separate the powder and PEI solution. The modified PZT powder presents a single perovskite phase that corresponds one-to-one with the PDF card.

5. A receiving flexible sensor for monitoring concrete fracture according to claim 1, characterized in that, In step S4, the flexible piezoelectric PZT / SiO2 nanofiber membrane is obtained by electrospinning with PZT / SiO2 spinning solution. The electrospinning parameters are set as follows: voltage 25kV, roller speed 3000rpm, injection rate 2ml / h, left and right movement range 80mm, and distance between collection device and needle tip 20cm.

6. A receiving flexible sensor for monitoring concrete fracture according to claim 1, characterized in that, In step S5, the drying annealing conditions are to heat the oven from room temperature to 60°C, dry for 12 hours to evaporate the residual solvent, then cool to room temperature and remove the sensor. Electrical and acoustic performance tests are then performed on the sensor before and after packaging, using a lead-broken concrete fracture signal as the excitation signal.

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