A Stress Detection Method Integrating Graphene Composite Piezoelectric Material and Fiber Optic Sensing

Abstract

The present invention discloses a stress detection method for integrated optical fiber sensing of graphene composite piezoelectric materials, which relates to the field of multi-mode sensor integration and includes: generating a signal by using a signal generator and transmitting it to the composite flexible piezoelectric material through a power amplifier; generating ultrasonic waves by using the composite flexible piezoelectric material and conducting them in the material to be measured; demodulating the ultrasonic waves conducted in the material to be measured by using an optical fiber grating sensing and demodulation module and transmitting them to the upper computer; and displaying, storing, and processing the demodulated ultrasonic wave signals by using the upper computer to obtain the stress suffered by the material to be measured, thereby completing the stress detection of integrated optical fiber sensing of graphene composite piezoelectric materials. The present invention solves the problems that the existing methods cannot perform real-time detection on the tiny stress changes in complex structures and are limited in application environments.

Description

Technical Field

[0001] The present invention relates to the field of multi-mode sensor integration, and particularly to a stress detection method for integrating graphene composite piezoelectric materials and optical fiber sensing. Background Art

[0002] Flexible transducers and fiber optic sensors each have a series of unique advantages in pressure measurement, making them widely applicable in different application scenarios. First of all, flexible transducers have high sensitivity and can quickly and accurately respond to tiny pressure changes, which makes them particularly suitable for occasions where low pressure needs to be measured and can maintain high stability and reliability. In addition, flexible transducers use corrosion-resistant materials and sealing technologies and can resist the erosion of various corrosive media. Moreover, flexible transducers have a simple structure, small size, and light weight, and can be easily installed in various narrow and limited spaces, being suitable for some application occasions with restrictions on weight and volume.

[0003] Fiber optic sensors exhibit many advantages in pressure measurement, making them a popular measurement technology. First of all, fiber optic sensors are based on optical principles and have a highly sensitive response to tiny pressure changes and minute strains. This enables fiber optic sensors to provide high-precision pressure measurement, especially suitable for application scenarios with high requirements for measurement accuracy. The flexibility and delicate design of fiber optic sensors are another advantage, which can adapt to measurement objects of various sizes and shapes, minimize interference with the measurement target, and can simultaneously monitor pressure changes at different positions, thereby improving the comprehensiveness and flexibility of the system. This is very beneficial for application scenarios that require synchronous monitoring at multiple positions.

[0004] However, existing stress detection methods cannot perform real-time detection of tiny stress changes in complex structures, and the application environment is limited. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, a stress detection method for integrating graphene composite piezoelectric materials and optical fiber sensing provided by the present invention solves the problems that existing methods cannot perform real-time detection of tiny stress changes in complex structures and the application environment is limited.

[0006] To achieve the above invention objective, the technical solution adopted by the present invention is: A stress detection method for integrating graphene composite piezoelectric materials and optical fiber sensing, comprising the following steps:

[0007] S1: Use a signal generator to generate a signal, which is transmitted to the composite flexible piezoelectric material through a power amplifier;

[0008] S2: Use the composite flexible piezoelectric material to generate ultrasonic waves and conduct them in the material to be measured;

[0009] S3: Demodulate the ultrasonic waves propagating in the material under test using the fiber Bragg grating sensing and demodulation module, and transmit them to the host computer;

[0010] S4: Use the host computer to display, store, and process the demodulated ultrasonic wave signals to obtain the stress applied to the material under test, and complete the stress detection of the integrated fiber sensing of the graphene composite piezoelectric material.

[0011] Further, the preparation of the composite flexible piezoelectric material in S1 includes the following sub-steps:

[0012] S11: Prepare graphene on a single-crystal silicon substrate using metal-free and atmospheric pressure chemical vapor deposition technology;

[0013] S12: Prepare zirconium titanate using the sol-gel method;

[0014] S13: Composite the prepared graphene and zirconium titanate to obtain a composite flexible piezoelectric material.

[0015] Further, S13 includes the following sub-steps:

[0016] S131: Grind zirconium titanate, add an ethanol solution as a dispersant to graphene and the ground zirconium titanate, and mix them evenly;

[0017] S132: Heat-treat the evenly mixed graphene and zirconium titanate, and characterize them using a scanning electron microscope to obtain a composite flexible piezoelectric material.

[0018] Further, the fiber Bragg grating sensing and demodulation module in S3 includes a free enhanced laser bandwidth light source, an optical circulator, a reference grating, a sensing grating, a photodetector, and a data acquisition card.

[0019] Further, S3 includes the following sub-steps:

[0020] S31: Transmit the ultrasonic waves propagating in the material under test to the sensing grating located on the material under test through a single-mode fiber, and use the sensing grating to identify the ultrasonic signals;

[0021] S32: Guide the broadband light emitted by the free enhanced laser bandwidth light source to the sensing grating located on the material under test through the circulator. Based on the ultrasonic signal identification result, if the broadband light meets the wavelength condition, the broadband light is reflected back to the circulator and enters the reference grating;

[0022] S33: Use the photodetector to capture the optical signal transmitted by the reference grating and convert the optical signal into a voltage signal;

[0023] S34: Collect the voltage signal using a data acquisition card and transmit the collected voltage signal to the host computer.

[0024] Further, the reference grating is pasted on the surface of the composite flexible piezoelectric material.

[0025] Further, under the action of ultrasonic waves in S31, the strain field model along the axial direction of the sensing grating is:

[0026]

[0027] where ε AE (·) is the strain field model, A AE is the ultrasonic amplitude, λ AE is the wavelength of ultrasonic waves in the material to be measured, z is the coordinate point along the axial direction of the sensing grating, ω AE is the angular frequency of ultrasonic waves, and t is the time.

[0028] Further, the central wavelength λ B (t) of the sensing grating is:

[0029] λ B (t) = λ B0 +Δλ0cos(ω s t)

[0030]

[0031] where λ B0 is the reference wavelength of the sensing grating, Δλ0 is the change in the central wavelength of the sensing grating after interacting with ultrasonic waves, ω s is the period of the sensing grating, ε AE (·) is the strain field model, n eff0 is the effective refractive index of the core axis of the sensing grating when not affected by external forces, p 11 is the first Poisson's ratio of the material to be measured, p 12 is the second Poisson's ratio of the material to be measured, and v is the propagation speed of ultrasonic waves in the material.

[0032] The beneficial effects of the present invention are:

[0033] (1) In the present invention, graphene has extremely high strength and toughness due to its two-dimensional carbon atom plane structure. Introducing it into zirconium titanate can significantly improve the mechanical strength of the composite material. At the same time, the flexibility of graphene makes the composite material have better bending and deformation capabilities, which is an important property for piezoelectric materials used in monitoring equipment for force-induced deformation.

[0034] (2) In the present invention, graphene has extremely high chemical stability and can maintain its structure and properties unchanged in various environments. After combining with zirconium titanate, this stability can help the composite material maintain its piezoelectric properties in harsh environments (such as high temperatures, corrosive gases or liquids).

[0035] (3) In the present invention, zirconium titanate itself has good piezoelectric properties. The composite with graphene not only maintains this property, but also, due to the high conductivity of graphene, provides a good electron transport channel for the composite material. The high specific surface area and conductivity of graphene may also enhance its piezoelectric effect to a certain extent.

[0036] (4) In the present invention, the comprehensive characteristics of this composite material provide a new way for the design of novel flexible piezoelectric materials, which has certain reference significance for further research and development of applications such as flexible electronic devices, sensors, and actuators, and is also expected to have broad application prospects in the fields of energy conversion, sensor technology, and intelligent materials.

[0037] (5) In the present invention, by integrating the flexible transducer and the fiber optic sensor in a structural design, multimodal sensing can be achieved, that is, different types of sensing information can be obtained simultaneously. After the flexible transducer generates sound waves, they are transmitted through the measured material to the FBG, and the degree of pressure received is reflected by the change in the central wavelength of the FBG.

[0038] (6) In the present invention, fiber optic sensors usually have high sensitivity and accuracy and can provide real-time monitoring and feedback. The flexible transducer also has a relatively fast response speed to mechanical changes. Combined with the flexible transducer, real-time sensing and feedback can be achieved, and high-sensitivity sensing can be realized in the application scenario of structural health monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flowchart of a stress detection method for integrating fiber optic sensing with a graphene composite piezoelectric material.

[0040] Figure 2 It is a schematic diagram of a metal-free APCVD device

[0041] Figure 3 It is the composition of an integrated detection system of a fiber Bragg grating and a flexible transducer.

[0042] Figure 4 It is a reference grating structure diagram.

[0043] Figure 5 It is a schematic diagram of a FBG detecting the acoustic wave signal of the measured material. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0045] As Figure 1 shown, a stress detection method for integrating graphene composite piezoelectric materials with optical fiber sensing includes the following steps:

[0046] S1: Use a signal generator to generate a signal, which is transmitted to the composite flexible piezoelectric material through a power amplifier;

[0047] In the present invention, the power amplifier is also connected to a digital oscilloscope. The digital oscilloscope can monitor the output signal from the power amplifier in real time and display information such as the waveform of the signal, including amplitude, frequency, phase, etc. In addition, the digital oscilloscope has a data recording and storage function, and can save the monitored signal data for subsequent comparison and analysis of the center frequency offset with the demodulated ultrasonic waveform;

[0048] S2: Use the composite flexible piezoelectric material to generate ultrasonic waves and conduct them in the material to be measured;

[0049] S3: Use the fiber grating sensing and demodulation module to demodulate the ultrasonic waves conducted in the material to be measured and transmit them to the upper computer;

[0050] S4: Use the upper computer to display, store and process the demodulated ultrasonic signal to obtain the stress on the material to be measured, and complete the stress detection of integrating graphene composite piezoelectric materials with optical fiber sensing.

[0051] The preparation of the composite flexible piezoelectric material in S1 includes the following sub-steps:

[0052] S11: Prepare graphene on a single crystal silicon substrate using metal-free and atmospheric pressure chemical vapor deposition technology;

[0053] In this embodiment, when preparing graphene, methods such as chemical vapor deposition (CVD), chemical oxidation-reduction method and mechanical exfoliation method were compared. Among them, the chemical reduction method has a lower cost, but the prepared graphene has problems such as difficult control of quality and structure, and inability to achieve large-area and continuous production; although the mechanical exfoliation method can prepare high-quality graphene from natural graphite or other materials with high graphite content, it is a manual or semi-automated process with low production efficiency, and can also only prepare graphene on a small scale;

[0054] The chemical vapor deposition method (CVD) has high controllability and scalability, and can achieve precise control of parameters such as temperature, gas composition and pressure during the graphene growth process, and is suitable for large-scale production. Therefore, the chemical vapor deposition method is selected for preparation;

[0055] Low-temperature CVD can effectively catalyze the growth of graphene at a relatively low temperature using metal catalysts such as copper or nickel. However, considering that metal impurities will remain in the graphene and affect the performance of the finished product, in this invention, metal-free, atmospheric pressure chemical vapor deposition technology is used to grow graphene on a single-crystal silicon substrate, avoiding the introduction of metal impurities and making the quality of graphene purer;

[0056] Select a single-crystal silicon (500 μm thick, (100), (111), (110) planes, N-type, P-type, intrinsic silicon, R a <0.5 nm) produced by Suzhou Jingui Electronic Technology Co., Ltd. as an example for the substrate;

[0057] The growth of graphene uses a customized portable chamber with a ceramic wafer as the heating platform. The temperature control is precisely calibrated with an error of less than ±0.1 °C;

[0058] Before placing the single-crystal silicon substrate (inverted) in front of the heating platform, first soak it in 15% HF for 15 min for pretreatment, then wash it with deionized water and dry it with N2 flow, Figure 2 It is a schematic diagram of a metal-free APCVD device.

[0059] The gas deposition chamber is evacuated and backfilled with argon (Ar) three times to form an inert environment;

[0060] Heat the single-crystal silicon surface to the required temperature (900 - 930 °C) and stabilize it for 10 minutes under 100 sccm H2 (1 sccm = 1 ml / min under standard atmospheric pressure) and 200 sccm Ar to remove any organic residues and activate the growth sites;

[0061] Grow graphene for 1 hour in a gas mixture of 180 sccm CH4 and 10 sccm H2, and then cool it to room temperature within 1 hour using 180 sccm CH4 and 10 sccm H2.

[0062] S12: Prepare zirconium titanate using the sol-gel method;

[0063] The precursors of zirconium and titanium are selected as zirconium chloride (ZrCl4) and tetrabutyl titanate (Ti(OC4H9)4), and dissolve them separately in ethanol.

[0064] The suitable pH range for generating zirconium titanate (ZrTiO3) is between acidic and neutral. Use acidic substances such as acetic acid to adjust the pH value of the solution to be kept between 1 and 5, and then stir the two solutions evenly to form a sol.

[0065] Gelify the sol by stirring or heating (gradually increasing the temperature) to form a gel, and then calcine the gel at a high temperature (1000 °C) to form the precursor of zirconium titanate.

[0066] The formed zirconium titanium oxide particles are separated by centrifugation, washed with ethanol to remove unreacted precursors and solvent residues, and then dried to remove moisture and ethanol.

[0067] A scanning electron microscope (SEM) is used to verify the existence of a special structure with piezoelectric properties in the obtained material, such as the particle arrangement in the polarization direction, to exclude interference factors for subsequent composite material characterization.

[0068] S13: Graphene and zirconium titanium oxide prepared are compounded to obtain a composite flexible piezoelectric material.

[0069] The S13 includes the following sub-steps:

[0070] S131: Zirconium titanium oxide is ground, and an ethanol solution is added as a dispersant to graphene and the ground zirconium titanium oxide, and they are uniformly mixed;

[0071] S132: The uniformly mixed graphene and zirconium titanium oxide are heat-treated in the range of 500 - 800 °C, and characterized using a scanning electron microscope to obtain a composite flexible piezoelectric material.

[0072] Through heat treatment, the structure of the material can be deeply changed, promoting the chemical and physical interactions between the two, which helps to improve its stability. After compounding, the morphology of the material is characterized using a scanning electron microscope (SEM) to determine the distribution of graphene in the zirconium titanium oxide matrix.

[0073] The present invention combines the prepared graphene with zirconium titanium oxide with excellent piezoelectric properties to form a new type of flexible piezoelectric material, which is used to replace traditional materials in transducers. This material not only has high flexibility and conductivity, but also is suitable for monitoring stress deformation and can fit well with the measured material.

[0074] In the S3, the fiber Bragg grating sensing and demodulation module includes a free enhanced laser bandwidth light source, an optical circulator, a reference grating, a sensing grating, a photodetector, and a data acquisition card, as Figure 3 shown.

[0075] The S3 includes the following sub-steps:

[0076] S31: The ultrasonic wave conducted in the measured material is transmitted to the sensing grating located on the measured material through a single-mode optical fiber, and the ultrasonic signal is identified using the sensing grating;

[0077] S32: Guide the broadband light emitted by the free-enhanced laser bandwidth light source to the sensing grating located on the material under test through an optical circulator. Based on the ultrasonic signal recognition result, if the broadband light meets the wavelength condition, the broadband light is reflected back to the optical circulator and enters the reference grating;

[0078] S33: Use a photodetector to capture the optical signal transmitted by the reference grating and convert the optical signal into a voltage signal;

[0079] S34: Use a data acquisition card to collect the voltage signal and transmit the collected voltage signal to the host computer.

[0080] The reference grating is pasted on the surface of the composite flexible piezoelectric material.

[0081] The present invention uses double Bragg gratings and piezoelectric materials for detection, combining a flexible transducer with an optical fiber sensor. A fiber Bragg grating (FBG) is used instead of a traditional piezoelectric sensor to detect ultrasonic signals. When the system is working, the acoustic wave signal is transmitted into the FBG through a single-mode optical fiber, and the FBG is used as a sensing element to identify the ultrasonic signal.

[0082] An FBG is an optical sensor, usually made of optical fiber, and its internal refractive index is periodically modulated to form a grating structure. This structure can reflect light of a specific wavelength, while other wavelengths pass through. By introducing such a structure into the optical fiber, the optical fiber can be made sensitive to light of a specific wavelength, and this sensitivity can be changed according to environmental conditions or factors such as strain.

[0083] When the sensing grating is embedded in the material under test and affected by ultrasonic waves, it will cause a change in the central wavelength in the grating reflection spectrum. This is because the presence of ultrasonic waves causes a slight deformation of the grating, thereby changing the optical properties of the grating. Through an optical fiber demodulation system, the grating reflection spectrum can be demodulated, and the offset of the central wavelength can be measured. By analyzing this offset, the defect position can be obtained, and at the same time, the characteristics of the acoustic wave signal propagating in the material under test, such as frequency, amplitude, etc., can be determined. This technology can be used to non-contact detect and monitor the acoustic wave signal in the material under test, providing an efficient and accurate method for acoustic detection and material evaluation.

[0084] The system structure of the present invention includes two FBGs: one is the reference FBG: which is pasted on the surface of the piezoelectric material and serves as the reference grating, as Figure 4 shown. The spectral characteristics of this FBG are used as a benchmark under normal conditions. The other is the elastic wave sensor FBG: The other FBG is designed as an elastic wave sensor, and a change in its position or shape will cause a change in the spectral characteristics of the FBG.

[0085] With such a design, when elastic waves act on the grating, stress is generated on the fiber Bragg grating (FBG), and parameters such as its effective refractive index will change. This causes a change in the grating pitch, resulting in a shift in its reflection wavelength, achieving the sensing of acoustic waves, and thus intuitively reflecting the applied stress as a change in the central wavelength of the FBG. The ultrasonic signal is demodulated by the grating demodulation system, and information such as the time-domain signal and frequency-domain signal of the ultrasonic wave is analyzed by the host computer to obtain information such as the size and location of internal defects in the measured material.

[0086] As Figure 5 shown, the ultrasonic signal passes through the measured material and is then transmitted into the FBG through a single-mode fiber. During this process, the peak wavelength λ B of the FBG reflection spectrum satisfies:

[0087]

[0088] where is the initial refractive index of the FBG without the action of stress waves, and Λ is the period of the FBG;

[0089] When there is no external force, the effective refractive index in the core axis direction of the FBG is:

[0090]

[0091] where Λ0 is the initial period of the FBG and n is the maximum change in refractive index.

[0092] In step S31, under the action of ultrasonic waves, the strain field model along the sensing grating axis is:

[0093]

[0094] where ε AE (·) is the strain field model, A AE is the ultrasonic amplitude, λ AE is the wavelength of the ultrasonic wave in the measured material, z is the coordinate point along the sensing grating axis, ω AE is the angular frequency of the ultrasonic wave, and t is the time.

[0095] By deriving the change in refractive index under elastic wave energy, the central wavelength λ B (t) of the sensing grating is obtained as:

[0096] λ B (t) = λ B0 + Δλ0cos(ω s t)

[0097]

[0098] where λ B0$\lambda_0$ is the reference wavelength of the sensing grating, which is the central wavelength corresponding to the reflection or transmission of the grating without any stress or environmental changes. $\Delta\lambda_0$ is the change in the central wavelength of the sensing grating after interacting with ultrasonic waves, $\omega$ s is the period of the sensing grating, which defines the distance between adjacent reflection regions in the grating, represents the repeating distance of the microstructure for reflection or transmission in the grating, and affects the selective reflection or transmission of light of different wavelengths by the grating, $\varepsilon$ AE $\varepsilon(\cdot)$ is the strain field model, $n$ eff0 is the effective refractive index of the core axis of the sensing grating when not affected by external forces, $p$ 11 is the first Poisson's ratio of the material to be measured, which reflects the ratio of the strain in the perpendicular direction to the strain in the direction when the material is stressed in one direction. For fiber Bragg gratings, this parameter is related to the mechanical properties of the material and directly affects the response of the grating under external stress, $p$ 12 is the second Poisson's ratio of the material to be measured, which describes the strain caused in other directions when stress is applied in one direction. This parameter is also related to the elastic characteristics of the grating and affects the sensitivity of the grating to external pressure or stress. $v$ is the propagation speed of ultrasonic waves in the material. The change in the sound speed can affect the reflection wavelength of the grating because the propagation of ultrasonic waves will cause dynamic strain in the material, which in turn affects the structure and optical characteristics of the grating.

[0099] Those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the invention.

Claims

1. A stress detection method for graphene composite piezoelectric material integrated optical fiber sensing, characterized in that It includes the following steps: S1: Generate a signal using a signal generator and transmit it to the composite flexible piezoelectric material through a power amplifier; The preparation of the composite flexible piezoelectric material in S1 includes the following sub-steps: S11: Prepare graphene on a single-crystalline silicon substrate using metal-free and atmospheric pressure chemical vapor deposition technology; S12: Prepare zirconium titanate using the sol-gel method; S13: Composite the prepared graphene and zirconium titanate to obtain a composite flexible piezoelectric material; S2: Use the composite flexible piezoelectric material to generate ultrasonic waves and conduct them in the material to be measured; S3: Use a fiber Bragg grating sensing and demodulation module to demodulate the ultrasonic waves conducted in the material to be measured and transmit them to the upper computer; The fiber Bragg grating sensing and demodulation module in S3 includes a free enhanced laser bandwidth light source, an optical circulator, a reference grating, a sensing grating, a photodetector, and a data acquisition card; The following sub-steps are included in S3: S31: Transmit the ultrasonic waves conducted in the material to be measured to the sensing grating located on the material to be measured through a single-mode optical fiber, and use the sensing grating to identify the ultrasonic signal; S32: Guide the broadband light emitted by the free enhanced laser bandwidth light source to the sensing grating located on the material to be measured through the circulator. Based on the ultrasonic signal identification result, if the broadband light meets the wavelength condition, the broadband light is reflected back to the circulator and enters the reference grating; S33: Use a photodetector to capture the optical signal transmitted by the reference grating and convert the optical signal into a voltage signal; S34: Use a data acquisition card to collect the voltage signal and transmit the collected voltage signal to the upper computer; The central wavelength λ B (t) of the sensing grating is as follows: λ B (t) = λ B0 + Δλ0cos(ω s t) where λ B0 is the reference wavelength of the sensing grating, Δλ0 is the change in the central wavelength of the sensing grating after interacting with ultrasonic waves, ω s is the period of the sensing grating, ε AE (·) is the strain field model, n eff0 is the effective refractive index of the core axis of the sensing grating when not affected by external forces, p 11 is the first Poisson's ratio of the material to be measured, p 12 is the second Poisson's ratio of the material to be measured, v is the propagation speed of ultrasonic waves in the material, and t is time; S4: Use the upper computer to display, store, and process the demodulated ultrasonic wave signal to obtain the stress received by the material to be measured, and complete the stress detection of the graphene composite piezoelectric material integrated fiber sensing.

2. The stress detection method of graphene composite piezoelectric material integrated optical fiber sensing according to claim 1, characterized in that, The following sub-steps are included in S13: S131: Grind zirconium titanate, add an ethanol solution as a dispersant to graphene and the ground zirconium titanate, and mix them evenly; S132: Heat-treat the evenly mixed graphene and zirconium titanate and characterize them using a scanning electron microscope to obtain a composite flexible piezoelectric material.

3. The stress detection method of graphene composite piezoelectric material integrated optical fiber sensing according to claim 1, wherein The reference grating is pasted on the surface of the composite flexible piezoelectric material.

4. The stress detection method of graphene composite piezoelectric material integrated optical fiber sensing according to claim 1, characterized in that, Under the action of ultrasonic waves in S31, the strain field model along the axial direction of the sensing grating is: Among them, ε AE (·) is the strain field model, A AE is the ultrasonic amplitude, λ AE is the wavelength of the ultrasonic wave in the material to be measured, z is the coordinate point along the axial direction of the sensing grating, ω AE is the angular frequency of the ultrasonic wave, and t is the time.

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