A frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection

Abstract

The application provides a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection, comprising an electrode component and a piezoelectric fiber component, the electrode component comprises two electrode layers, the electrode layers are flexible printed circuit films, and the electrode layers are in the shape of a spiral, the piezoelectric fiber component comprises a piezoelectric fiber composite layer between the two electrode layers, the piezoelectric fiber composite layer comprises piezoelectric fibers and an epoxy resin matrix, the piezoelectric fibers are uniformly spaced and embedded in the epoxy resin matrix along the annular direction of the epoxy resin matrix; the transducer has strong directivity, can realize high-precision positioning of a signal source, can accurately determine the position of a signal in applications such as structural health monitoring and target tracking, and can accurately control the formation and direction of a beam, which can effectively reduce the influence of background noise in a complex environment.

Description

Technical Field

[0001] The present invention relates to the technical field of transducers, and in particular to a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection. Background Art

[0002] Ultrasonic guided wave technology plays a key role in structural health monitoring. Its basic principle is to use piezoelectric sensors as exciters and receivers to guide ultrasonic waves into the structure for propagation, and analyze the returned signals to assess the health of the structure. Through the appropriate arrangement of the excitation wave source and receiving units, the ultrasonic waves can propagate within the structure and produce reflections or scattering when contacting defects or damage, thereby achieving the purpose of real-time monitoring of structural defects or damage. For guided wave excitation and reception based on traditional piezoelectric sensors, existing technologies mainly focus on two aspects.

[0003] The first direction is the optimization of sensor layout and configuration: In this direction, researchers are committed to maximizing the efficiency and accuracy of structural health monitoring by optimizing the layout and configuration of sensors. Specifically, they considered the following aspects: Optimization of sensor position: Through numerical simulation and experimental research, the optimal sensor position is determined to ensure that the guided wave signal in the structure can be captured. This usually involves a comprehensive consideration of factors such as the geometry of the structure, material properties and expected damage types; Research on the number and arrangement of sensors: Researchers are also concerned with determining the appropriate number and arrangement of sensors to cover the entire structure and maximize the sensitivity of the monitoring system. They may consider parameters such as the distance, angle and direction between sensors to achieve the best monitoring effect; Integration of multi-sensor networks: In some complex structures or large systems, researchers have also studied how to achieve the goal of comprehensive structural monitoring by integrating multiple sensor networks, which includes data sharing and collaborative work between sensors, as well as comprehensive analysis and processing of multi-sensor data.

[0004] The second direction is the improvement of signal processing and analysis algorithms: In this direction, the focus is on developing more efficient and accurate signal processing and analysis algorithms to extract useful information contained in waveguide signals, such as damage location, type and severity. Specific work includes: Feature extraction and selection: By extracting and selecting features of the waveguide signals received by the sensor, the most representative features are determined for damage identification and location, which may involve the application of time domain, frequency domain or time-frequency domain analysis methods; Application of machine learning and pattern recognition technology: Researchers are also exploring the application of machine learning and pattern recognition technology to the analysis and identification of waveguide signals, which includes the application of supervised learning and unsupervised learning methods, as well as the processing and training of large-scale data sets; Noise and interference suppression: In order to improve the robustness and reliability of the monitoring system, researchers are also committed to suppressing noise and interference in waveguide signals, which may involve the research and application of technologies such as filtering, noise reduction and signal enhancement.

[0005] Problems or shortcomings of existing technologies: These methods often face the following challenges when monitoring fluctuations in structures: Challenges in sensor placement: Traditional methods require the placement of a large number of sensors on the surface or inside the structure to cover the entire monitoring area. However, placing sensors in complex structures often faces spatial limitations and wiring difficulties, resulting in insufficient monitoring coverage or unsatisfactory monitoring results; Multipath propagation and scattering effects: Fluctuations in structures often experience multipath propagation and scattering effects, resulting in complex and variable signals received by sensors. This complexity makes it difficult to accurately determine the source and propagation path of the fluctuations, affecting the accuracy and reliability of the monitoring results; Difficulty in directionality control: Traditional methods often have difficulty achieving precise directional control of fluctuations. The signals received by the sensors cannot accurately reflect the source and propagation direction of the fluctuations, resulting in a lack of directional information in the monitoring results, which limits the accurate assessment of the structural state; High cost and complexity: The placement of a large number of sensors and complex imaging algorithms make traditional fluctuation monitoring methods costly and complex, which not only increases the construction and maintenance costs of the monitoring system, but also reduces the practicality and scalability of the monitoring system. In general, traditional fluctuation excitation and detection methods face many challenges when monitoring fluctuations in structures, especially in achieving controllable directionality of the fluctuations. Summary of the Invention

[0006] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection, which is used to solve the many challenges faced by traditional fluctuation excitation and detection methods in the prior art when monitoring fluctuations in structures, especially the difficulty in achieving directional controllable fluctuations.

[0007] To achieve the above-mentioned and other related purposes, the present invention provides the following technical solutions:

[0008] A frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection includes an electrode component and a piezoelectric fiber component. The electrode component includes two electrode layers, the electrode layers are flexible printed circuit films, and the electrode layers are spirally shaped. The piezoelectric fiber component includes a piezoelectric fiber composite layer located between the two electrode layers. The piezoelectric fiber composite layer includes piezoelectric fibers and an epoxy resin matrix. The piezoelectric fibers are evenly embedded in the epoxy resin matrix along the annular direction of the epoxy resin matrix, so the piezoelectric fiber composite layer adopts a radially arranged piezoelectric fiber layout.

[0009] In one embodiment of the present invention, the spiral shape of the electrode layer is determined based on the frequency domain wave number, wherein the determination of the spiral shape of the electrode layer based on the frequency domain wave number includes: determining the shape of the transducer electrode layer according to the control equation of the propagation of guided waves in a transducer of any shape and the concept of frequency-based beam control, wherein the spiral-shaped electrode layer can effectively excite and receive guided waves in different directions.

[0010] In one embodiment of the present invention, determining the shape of the transducer electrode layer based on the governing equations of guided wave propagation in an arbitrarily shaped transducer and the concept of frequency-based beam steering includes:

[0011] Depend on Determine the analytical expression for the spatial distribution of piezoelectric materials. When designing continuous beam steering, select the desired maximum directivity position along a spiral trajectory in the wavenumber domain. The spiral shape makes the equal-frequency circles intersect the solitary directivity maximum, thus uniquely determining a single direction for a given wave vector.

[0012] In the formula Where a is the radius of the sensing electrode in the spatial domain, k n Indicates the corresponding angle θ n The wave vector of the spiral is k, N is the design parameter and is taken as 180; n =k n (θ n ) distribution design, the maximum directivity position is determined by Determine, where the minimum value k of the wave vector amplitude is used m and the maximum value k M To define, θ M and θ m Corresponding angle maximum and minimum values;

[0013] and The spatial distribution described can be discretized into continuous physical fields by setting the threshold. Among them, η is a set threshold value, and according to the above formula, not only the spiral shape of the electrode layer is determined, but also the frequency-angle correspondence curve of the transducer is determined.

[0014] In one embodiment of the present invention, the finite element simulation software COMSOL is used to test the directional performance of the piezoelectric fiber transducer, the excitation waveguide and the receiving waveguide. The tests of the directional excitation performance and the directional receiving performance of the corresponding transducer are respectively established on an aluminum plate with a size of 500mm×500mm and a thickness of 1mm, on which a piezoelectric fiber transducer model and a piezoelectric fiber transducer group model with a diameter of 50mm and a thickness of 0.2mm are placed. The design bandwidth is 80kHz~370kHz, corresponding to a transducer angle of 0°~180°.

[0015] In one embodiment of the present invention, when the directional excitation performance of the piezoelectric fiber transducer is tested using the finite element simulation software COMSOL: in the piezoelectric fiber transducer model, simple harmonic response analysis is used to perform a frequency sweep analysis to obtain the transducer directivity result, and the waveguide excitation effect of the transducer is verified based on the transducer directivity result. At the same time, it is confirmed based on the transducer directivity result whether the frequency-angle correspondence curve of the transducer conforms to the theoretical design.

[0016] In one embodiment of the present invention, when the directional receiving performance of the piezoelectric fiber transducer is tested using the finite element simulation software COMSOL: in the piezoelectric fiber transducer group model, transient dynamic analysis is used, and the occurrence of random impact events is set at the same time. The directional response characteristics of the two piezoelectric fiber transducers are used to evaluate the location of the damage. After the center frequency of the piezoelectric fiber transducer group sensor signal is extracted, the direction of the incident wave is determined by inverting the frequency-angle correspondence curve of the transducer. The point where the collision accident occurred is determined by the intersection of the test angles of the two piezoelectric fiber transducers, and the error between the actual impact position and the calculated position is judged.

[0017] In one embodiment of the present invention, the manufacturing process of the electrode layer is as follows: the spiral electrode shape analyzed based on MATLAB is imported into Altium Designer software, and the transducer electrode circuit design is completed using the PCB design module. The transducer electrode is printed on a flexible printed circuit to form the upper and lower electrode layers of the transducer sandwich; the manufacturing process of the piezoelectric fiber composite layer is as follows: silicon cutting technology is used to cut a thin layer of unpolarized piezoelectric ceramic into a radial pattern under a silicon wafer dicing machine, wherein the cut fiber width does not exceed 0.3 mm, and the fiber density is related to the radial capacity of the transducer; after the manufacturing is completed, the two electrode layers and the piezoelectric fiber composite layer are assembled.

[0018] As described above, the frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection of the present invention has the following beneficial effects: the present invention can achieve high-precision positioning: by adopting the frequency-wavenumber excitation technology, the transducer of the present invention has strong directionality and can achieve high-precision positioning of the signal source, which makes it possible to accurately determine the position of the signal in applications such as structural health monitoring and target tracking, thereby more effectively performing detection and analysis; the present invention can accurately control the beam: by adjusting the frequency and wavenumber of the excitation signal, the transducer of the present invention can accurately control the formation and direction of the beam, which effectively reduces the influence of background noise in complex environments, improves the signal-to-noise ratio, and thus significantly improves the clarity and reliability of the signal; the present invention is flexible and multifunctional: the transducer of the present invention not only has the ability to excite and detect fluctuations of different frequencies and wavenumbers, but also It can be flexibly configured and adjusted according to specific application requirements, which enables it to be flexibly adapted to different scenarios, with a wider range of applications and more diverse monitoring tasks; the present invention can improve the signal-to-noise ratio: the transducer of the present invention can minimize the interference of background noise, thereby significantly improving the clarity and accuracy of the signal, which enables more accurate extraction of effective signals in complex environments, and greatly reduces the false alarm rate, thereby improving the reliability and practicality of the monitoring system; the present invention can improve monitoring efficiency: because the transducer of the present invention has stronger directionality, precise beam control capability, more flexible versatility and improved signal-to-noise ratio, it can improve monitoring efficiency, which means that abnormal signals in the structure can be detected more quickly and the health status of the structure can be evaluated more accurately, thereby effectively guiding the maintenance and management of the structure and improving the overall performance of the monitoring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic diagram of the overall structure of the frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0020] Figure 2 Shown is a schematic diagram of a dual-channel display of an electrode layer in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0021] Figure 3 Shown is a schematic diagram of a piezoelectric fiber composite layer in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0022] Figure 4 Schematic diagram showing the design process of designing the spiral shape of the electrode layer based on the frequency domain wavenumber in the frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0023] Figure 5 A schematic diagram showing a frequency-angle correspondence curve of a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0024] Figure 6 Shown is a schematic diagram of a simulation model for verifying the directional excitation performance of a transducer in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0025] Figure 7 Schematic diagram showing the wave fields generated by the transducer at different frequencies in the frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection disclosed in an embodiment of the present invention;

[0026] Figure 8 Shown is a schematic diagram of a normalized beam simulated at different frequencies by a transducer in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0027] Figure 9 Shown is a schematic diagram of a simulation model for verifying the directional receiving performance of a transducer in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0028] Figure 10 A schematic diagram showing a signal spectrum collected by an impact monitoring transducer in a frequency-wavenumber piezoelectric fiber transducer for directivity fluctuation excitation and detection disclosed in an embodiment of the present invention;

[0029] Figure 11 Shown is a schematic diagram of a 3D image of a flexible printed circuit of an electrode layer in a frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection disclosed in an embodiment of the present invention;

[0030] Figure 12 Shown is a schematic diagram of a flexible printed circuit PCB design for an electrode layer in a frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection disclosed in an embodiment of the present invention;

[0031] Figure 13 Shown is a schematic diagram of a silicon wafer saw cutting a piezoelectric fiber in a frequency-wavenumber piezoelectric fiber transducer for directional fluctuation excitation and detection disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless there is a conflict.

[0033] See also Figures 1 to 3 The present invention provides a frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection, including an electrode component and a piezoelectric fiber component. The electrode component includes two electrode layers, the electrode layer is a flexible printed circuit film, and the shape of the electrode layer is a spiral shape. The electrode layer adopts a specific spatial distribution design, and through the coupling effect with the corresponding wavelength, it can effectively excite and receive waveguides in different directions. In practical applications, the waveguide can be directionally excited by wavenumber analysis, and the direction of the incident wave can be accurately evaluated by comparing and analyzing the frequency components captured by the sensor. The piezoelectric fiber component includes two electrode layers. The piezoelectric fiber composite layer between them includes piezoelectric fibers and an epoxy resin matrix. The piezoelectric fibers are evenly embedded in the epoxy resin matrix along the annular direction of the epoxy resin matrix. This structure not only gives the transducer excellent flexibility, but also makes its application on non-planar surfaces feasible. Therefore, the piezoelectric fiber composite layer adopts a radially arranged piezoelectric fiber layout. This design innovation not only improves the performance of the transducer, but also broadens its application scenarios, while ensuring that the flexible characteristics of the transducer are maintained, and by arranging the piezoelectric fibers in a radial pattern, the directional sensitivity can be enhanced.

[0034] Specifically, the present invention is divided into three parts: the first part is to determine the spiral shape of the electrode layer of the piezoelectric fiber transducer; the second part is to verify the properties of the transducer's waveguide excitation and receiving directions through the constructed three-dimensional numerical model; and the third part is to design the flexible printed electrode of the piezoelectric fiber transducer and make samples.

[0035] The first part is to determine the spiral shape of the piezoelectric fiber transducer electrode layer; the shape of the piezoelectric fiber transducer electrode layer is calculated based on frequency domain wave number analysis: the control equation of waveguide propagation in an arbitrary shape transducer is used to complete the design of the transducer electrode by introducing the concept of frequency-based beam steering. Determine the analytical expression for the spatial distribution of piezoelectric materials. When designing continuous beam steering, select the desired maximum directivity position along the spiral trajectory in the wavenumber domain. The spiral shape makes the equal frequency circles intersect the solitary directivity maximum, thus uniquely determining a single direction for a given wave vector. This method helps to accurately control the direction. In the formula Where a is the radius of the sensing electrode in the spatial domain, k n Indicates the corresponding angle θ n The wave vector of the spiral is k, N is the design parameter and is taken as 180; n =k n (θ n ) distribution design, the maximum directivity position is determined by Determine, where the minimum value k of the wave vector amplitude is used m and the maximum value kM To define, θ M and θ m Corresponding angle maximum and minimum; formula The spatial distribution described can be discretized into continuous physical fields by setting the threshold. Where η is the set threshold, please refer to Figure 4 ,exist Figure 4 In the figure, a is the wave number representation of the spiral FSAT, b is the corresponding continuous space shape, and c is the final spiral electrode shape (η=7%). According to the above formula, not only the spiral shape of the electrode layer is determined, but also the frequency-angle correspondence curve of the transducer is determined. For the determined frequency-angle correspondence curve of the transducer, please refer to Figure 5 .

[0036] The second part is to verify the directional properties of the transducer's guided wave excitation and reception through a constructed three-dimensional numerical model. Using the finite element simulation software COMSOL, the finite element model is combined with structural mechanics and statics to comprehensively evaluate the directional performance of the piezoelectric fiber transducer's guided wave excitation and reception. The specific experimental steps are as follows:

[0037] Research on directional excitation performance: A piezoelectric fiber transducer with a diameter of 50 mm and a thickness of 0.2 mm (its design bandwidth is 80kHz to 370kHz, corresponding to a transducer angle of 0° to 180°) is placed on an aluminum plate with a size of 500mm×500mm and a thickness of 1mm. Using simple harmonic response analysis, a frequency sweep analysis is performed on it to obtain the transducer directivity results. Figure 6 and Figure 7 The directivity of the transducer measured by the numerical model is explained. It can be observed that the ultrasonic guided waves excited by the transducer have very good directivity at different excitation frequencies. It also verifies that the frequency-angle correspondence curve of the transducer is consistent with the theoretical design, verifying the guided wave excitation effect of the transducer. You can also refer to Figure 8 , among which, in Figure 7 In the figure, the wave fields generated by the transducer at different frequencies (obtained by frequency domain simulation): a) 120KHZ; b) 160KHZ; c) 180kHz; d) 220KHZ; e) 280KHZ; f) 300KHZ. Figure 8 , normalized beam patterns of the transducer simulated at different frequencies (obtained from frequency domain simulation): a) 120 kHz; b) 160 kHz; c) 180 kHz; d) 220 kHz; e) 280 kHz; f) 300 kHz.

[0038] Discussion on directional receiving performance: The directional receiving capability of piezoelectric fiber transducers can realize the structural impact positioning effect with a small number of transducers. Therefore, two pairs of transducer groups are used in the research on receiving performance. Impact positioning is achieved based on their directional guided wave receiving capability. On an aluminum plate with a size of 500mm×500mm and a thickness of 1mm, a piezoelectric fiber transducer group with a diameter of 50mm and a thickness of 0.2mm is also placed (its design bandwidth is 80kHz~370kHz, corresponding to a transducer angle of 0°~180°). Using transient dynamic analysis, random impact events are set at the same time. The directional response characteristics of the two piezoelectric fiber transducers are used to evaluate the location of the damage. The experimental theoretical model is as follows: Figure 9 As shown, in Figure 9 Figure a is case 1, and figure b is case 2. In terms of arrangement, the second transducer is rotated 90 degrees counterclockwise to facilitate joint monitoring of the impact position with the first transducer. This design ensures that the sensitive scanning area of ​​the transducer is always facing the impact position, ensuring the accuracy of the center frequency after receiving the guided wave. The direction of the incident wave caused by the impact can be evaluated by analyzing the frequency components of the final signal. Figure 10 The frequency domain representation of the final signal is shown. Panel (a) corresponds to Case 1, and Panel (b) corresponds to Case 2. The vertical dashed line represents the center frequency of the signal, allowing for intuitive comparison of the prediction accuracy. The monitoring impact location results are derived based on the estimated center frequency of the piezoelectric fiber transducer sensor signal. After extracting the center frequency, the direction of the incident wave is determined by inverting the transducer's frequency-angle correspondence curve. The point of the collision accident is determined by the intersection of the two piezoelectric fiber transducer test angles. Table 1 shows the location results for both cases. The error between the actual impact location and the calculated location is within 1%, and the simulation results are very consistent with the assumptions, fully verifying the feasibility and effectiveness of the proposed scheme.

[0039] Table 1: Error analysis between monitoring position and actual impact position

[0040]

[0041] The third part is to design the flexible printed electrodes of the piezoelectric fiber transducer and make samples: Design the flexible printed electrodes of the transducer and make transducer samples: The transducer consists of a bottom electrode layer, a fiber layer and a top electrode layer.

[0042] Electrode layer production: After importing the spiral electrode shape analyzed based on MATLAB into Altium Designer software, the transducer electrode circuit design is completed using the PCB design module. Figure 11 and Figure 12 As shown, in Figure 11 and Figure 12In this embodiment, a is the top electrode layer, b is the bottom electrode layer, the transducer electrodes are printed on a flexible printed circuit, the upper and lower electrode layers that make up the transducer sandwich, further, the top and bottom electrode layers begin with a sheet of DuPont Kapton® LF7062 copper clad laminate, then chemically etch away unwanted copper material, leaving the desired electrode pattern (this is done by the PCB fabricator), upon receipt of the etched sheet, carefully separate the individual electrode layers using scissors and visually inspect the electrode fingers, any layer with broken, excessive or under etched electrodes should be discarded, as these defects can lead to potentially dangerous electrical faults in the final package, next apply solder to the tabs on the top and bottom electrode layers, this step will facilitate good electrical contact between the two electrode sheets in the final assembly, finally, clean the copper side of each electrode carefully using isopropyl alcohol and a lint free paper towel, then dry with inert pressurized nitrogen.

[0043] Piezoelectric fiber composite layer fabrication: using silicon dicing technology, thin layer of unpoled piezoelectric ceramic is cut into a radial pattern under the silicon wafer dicing machine, as shown in Figure 3 ; wherein the width of the cutting fiber does not exceed 0.3mm, the fiber density is related to the radial capability of the transducer, the specific number is determined by actual processing, not less than 20, further, the fiber layer of the transducer is initially a thin, monolithic unpoled piezoelectric ceramic block, PZT-5 material ceramic sheet purchased from Wuxi Huifeng Electronics Co., Ltd., then the wafer is adhered to a 0.003 inch (0.0762 mm) thick blue adhesive carrier film, then loaded into a computer-controlled wafer dicing saw, which uses a 0.055 mm thick, water-cooled, diamond-impregnated blade to cut back and forth along the length of the piezoelectric ceramic block at a speed of 5.08 mm per minute, as the ceramic sheet is still adhered to the carrier film during cutting, a layer of perfectly radial fibers is formed, with a cross-sectional width not exceeding 0.3mm, the cut fibers are attached to the blue carrier film between the clamping rings, after cutting, the blade is used to remove the fibers and film from the rings, at this time the adhesive film fixes the fibers in place, ensuring that they remain perfectly aligned and facilitate subsequent processing, please refer to Figure 13 .

[0044] Piezoelectric fiber transducer assembly: Assemble the two completed electrode layers and the piezoelectric fiber layer; Step 1 (preparation): Use an epoxy resin coating gun and an appropriate mixing nozzle to apply some mixed epoxy resin to one side of the bottom electrode containing the copper electrode pattern, and then spread the epoxy resin into a thin layer by gently dragging the blade parallel to the electrode fingers. The edge of the blade should be away from the direction of movement; Step 2 (laying the fiber layer to the bottom electrode): Apply epoxy resin to the fiber sheet and attach it to the blue carrier film. A reasonable amount of epoxy resin should be applied to one end of the fiber, and then use a blade to spread it along the fiber direction. Similarly, the sharp edge of the razor should be away from the direction of initial spreading. The goal is to press the epoxy resin completely between the fibers so that no bubbles remain. After spreading is completed, the blade should be pointed in the direction of fiber movement to remove excess epoxy resin from the top of the fiber; Step 3 (curing the bottom flexible printed circuit electrode and fiber layer): Partially cure by heating in a vacuum hot press, pump the vacuum to about 27 inches of mercury and maintain for 15 minutes , to eliminate the gaps between the fibers and the volatiles emitted from the epoxy resin. Next, while still under vacuum, the heated press plate is clamped and the temperature is raised to 46°C at a rate of 3°C per minute. Since only partial curing of the epoxy resin is required, the stack is kept at this temperature for only 15 minutes. The press plate is then restored to room temperature using a water cooling system, and the vacuum pressure is removed. The press plate is then disassembled and the semi-finished product is carefully taken out. Step 4 (assembling the semi-finished product with the top printed circuit electrode): Another layer of epoxy resin is applied to the exposed surfaces of the top electrode and the fiber using a blade in the same manner as above. The epoxy resin is diffused to the edges of the top and bottom electrodes to ensure that the layers are bonded together over their entire surface area. Step 5 (finished product curing and molding): The entire package is ready for the final curing process. It is placed in the hot press and returned to the vacuum hot press. Vacuum is applied to the vacuum hot press for another 15 minutes, and then the press plate is clamped and heated. The temperature is raised to 80°C at a rate of 15°C per minute and maintained for two hours. After the press plate is cooled to room temperature by water, the completed transducer is removed from the hot press plate, and the finished product is completed.

[0045] More specifically, for the above technical solution, the following alternatives may exist: Traditional piezoelectric sensor combined with directional antenna: Traditional piezoelectric sensors can be combined with directional antennas to achieve positioning of signal sources by controlling the directivity of the antenna. This solution can also improve the positioning accuracy of signals, but compared to the frequency-wavenumber piezoelectric fiber transducer, it may be limited by the trade-off between antenna directivity and sensor sensitivity; Sonar system: Using a sonar system can achieve excitation and detection of waves in the structure. Sonar systems use sound waves for detection and can achieve similar positioning accuracy to frequency-wavenumber piezoelectric fiber transducers to some extent, but need to consider environmental limitations and cost issues of sound wave propagation; Optical fiber sensing system: Optical fiber sensing systems use optical fibers to transmit signals and achieve detection and positioning of signals through optical principles. This system has high sensitivity and anti-interference ability, but in practical applications, the installation and maintenance costs of optical fibers and the complexity of optical systems need to be considered; Wireless sensor network: Using a wireless sensor network can achieve multi-point monitoring of structures. By deploying multiple sensor nodes in the structure, it can achieve all-around monitoring of the structure, but needs to consider the stability and power consumption of network communication.

[0046] The present application can achieve high-precision positioning: By adopting the frequency-wavenumber excitation technology, the transducer of the present application has strong directivity and can achieve high-precision positioning of signal sources. This enables accurate determination of the position of signals in applications such as structural health monitoring and target tracking, thereby enabling more effective detection and analysis; The present application can accurately control the beam: By adjusting the frequency and wavenumber of the excitation signal, the transducer of the present application can accurately control the formation and direction of the beam. This enables effective reduction of background noise in complex environments, improves the signal-to-noise ratio, and significantly improves the clarity and reliability of the signal; The present application is flexible and multifunctional: The transducer of the present application not only has the ability to excite and detect waves of different frequencies and wavenumbers, but also can be flexibly configured and adjusted according to specific application requirements. This enables it to be flexible and adaptable in different scenarios, with a wider range of applications and more diverse monitoring tasks; The present application can improve the signal-to-noise ratio: The transducer of the present application can minimize the interference of background noise, thereby significantly improving the clarity and accuracy of the signal. This enables more accurate extraction of effective signals in complex environments and significantly reduces the false alarm rate, improving the reliability and practicality of the monitoring system; The present application can improve monitoring efficiency: Due to the stronger directivity, accurate beam control capability, more flexible multifunctionality, and improved signal-to-noise ratio of the transducer of the present application, it can improve monitoring efficiency, which means that it can detect abnormal signals in the structure more quickly and more accurately assess the health status of the structure, thereby effectively guiding the maintenance and management of the structure and improving the overall performance of the monitoring system.

[0047] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any equivalent modifications or variations made by persons skilled in the art without departing from the spirit and technical concepts disclosed herein shall be encompassed by the claims of the present invention.

Claims

1. A frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection, characterized by: The device comprises an electrode component and a piezoelectric fiber component. The electrode component comprises two electrode layers, each of which is a flexible printed circuit film and has a spiral shape. The piezoelectric fiber component comprises a piezoelectric fiber composite layer located between the two electrode layers. The piezoelectric fiber composite layer comprises piezoelectric fibers and an epoxy resin matrix. The piezoelectric fibers are evenly embedded in the epoxy resin matrix along the annular direction of the epoxy resin matrix. The piezoelectric fiber composite layer adopts a radially arranged piezoelectric fiber layout. The spiral shape of the electrode layer is determined based on the frequency domain wave number, wherein determining the spiral shape of the electrode layer based on the frequency domain wave number includes: The shape of the transducer electrode layer is determined based on the governing equations for propagation of guided waves in an arbitrarily shaped transducer and the concept of frequency-based beam steering, wherein the spiral-shaped electrode layer can effectively excite and receive guided waves in different directions; The determining of the shape of the transducer electrode layer according to the governing equation of guided wave propagation in the arbitrarily shaped transducer and the concept of frequency-based beam control includes: Depend on Determine the analytical expression for the spatial distribution of piezoelectric materials. When designing continuous beam steering, select the desired directivity maximum position along a spiral trajectory in the wavenumber domain. The spiral shape makes the equal-frequency circles intersect the solitary directivity maximum, thus uniquely determining a single direction for a given wave vector. In the formula Where a is the radius of the sensing electrode in the spatial domain, k n Indicates the corresponding angle θ n The wave vector of the spiral is k, N is the design parameter and is taken as 180; n =k n (θ n ) distribution design, the maximum directivity position is determined by Determine, where the minimum value k of the wave vector amplitude is used m and the maximum value k M To define, θ M and θ m Corresponding angle maximum and minimum values; and The spatial distribution described can be discretized into continuous physical fields by setting the threshold. Among them, η is a set threshold value, and according to the above formula, not only the spiral shape of the electrode layer is determined, but also the frequency-angle correspondence curve of the transducer is determined.

2. The frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection according to claim 1, characterized in that: The finite element simulation software COMSOL was used to test the directional performance of the piezoelectric fiber transducer, the excitation waveguide and the receiving waveguide. The tests of the directional excitation performance and the directional receiving performance of the corresponding transducer were respectively established on an aluminum plate with a size of 500mm×500mm and a thickness of 1mm. A piezoelectric fiber transducer model and a piezoelectric fiber transducer group model with a diameter of 50mm and a thickness of 0.2mm were placed on the plate. The design bandwidth is 80kHz~370kHz, corresponding to a transducer angle of 0°~180°.

3. The frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection according to claim 2, characterized in that: When using the finite element simulation software COMSOL to test the directional excitation performance of the piezoelectric fiber transducer: in the piezoelectric fiber transducer model, simple harmonic response analysis is used to perform a frequency sweep analysis to obtain the transducer directivity result. The waveguide excitation effect of the transducer is verified based on the transducer directivity result. At the same time, the frequency-angle correspondence curve of the transducer is confirmed to be consistent with the theoretical design based on the transducer directivity result.

4. The frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection according to claim 2, characterized in that: When using the finite element simulation software COMSOL to test the directional receiving performance of the piezoelectric fiber transducer: in the piezoelectric fiber transducer group model, transient dynamic analysis is used, and random impact events are set at the same time. The directional response characteristics of the two piezoelectric fiber transducers are used to evaluate the location of the damage. After extracting the center frequency of the piezoelectric fiber transducer group sensing signal, the direction of the incident wave is determined by inverting the frequency-angle correspondence curve of the transducer. The point where the collision accident occurred is determined by the intersection of the test angles of the two piezoelectric fiber transducers, and the error between the actual impact position and the calculated position is judged.

5. The frequency-wavenumber piezoelectric fiber transducer for directional wave excitation and detection according to claim 1, characterized in that: The manufacturing process of the electrode layer is as follows: the spiral electrode shape analyzed based on MATLAB is imported into Altium Designer software, and the transducer electrode circuit design is completed using the PCB design module. The transducer electrodes are printed on a flexible printed circuit to form the upper and lower electrode layers of the transducer sandwich. The manufacturing process of the piezoelectric fiber composite layer is as follows: silicon cutting technology is used to cut a thin layer of unpolarized piezoelectric ceramic into a radial pattern under a silicon wafer dicing machine, wherein the cut fiber width does not exceed 0.3 mm, and the fiber density is related to the radial capacity of the transducer; after the production is completed, the two electrode layers and the piezoelectric fiber composite layer are assembled.

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