Defect monitoring method for composite gas cylinder and flexible ultrasonic monitor

Abstract

The invention relates to the technical field of nondestructive testing and structural health monitoring, in particular to a defect monitoring method for a composite gas cylinder and a flexible ultrasonic monitor. The defect monitoring method of the composite material gas cylinder comprises the following steps: collecting echo signals generated by reflecting plane waves emitted into the composite material gas cylinder at different incident angles; and obtaining plane wave imaging data of each angle through convolution operation and a delay summation algorithm in sequence. And fusing the plane wave imaging data of the multiple angles to obtain a multi-angle plane wave composite image, and obtaining a plurality of differential images. And positioning the position of the defect in the monitoring area according to the local gray abnormal position in the multi-angle plane wave composite image and in combination with a space coordinate mapping technology. And a plurality of difference images are compared according to a time sequence to obtain the change rule of each defect in the monitoring area, so that the future change trend of each defect in the monitoring area is deduced, and long-term continuous monitoring and state evaluation can be carried out on the detected structure.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing and structural health monitoring technology, specifically to a defect monitoring method for composite material gas cylinders and a flexible ultrasonic monitoring instrument. Background Technology

[0002] As the service life of pressure-bearing equipment such as composite gas cylinders and storage tanks extends, problems such as material fatigue, corrosion thinning, and crack propagation become increasingly serious. Structural health monitoring has become an important technical means to ensure the safety of high-pressure gas storage and transportation (such as hydrogen and natural gas storage and transportation) and the integrity of industrial facilities. Although traditional ultrasonic monitoring has high sensitivity and good quantitative capabilities, it mostly relies on manual handheld probes for intermittent testing, and most probes are single probes. They are not only large and expensive, but also have problems such as low detection efficiency, poor signal consistency, and great susceptibility to human factors, making it difficult to meet the needs of long-term, automated, in-situ monitoring in complex environments.

[0003] In the energy and chemical industries, composite gas cylinders are often subjected to harsh environments with high pressure (up to 70 MPa), fluctuating temperatures (-40℃ to 85℃), and potential corrosive media (such as hydrogen embrittlement and corrosion from fuel gas impurities). Existing manual inspection methods not only require periodically removing the outer protective layer of the cylinder (such as the epoxy resin protective layer outside the carbon fiber winding layer), damaging the original structural integrity, but also face problems such as high operational hazards, high cost of repeated inspections, and unstable signals, especially in critical areas such as the curved surface of the end caps and the circumferential welds of the cylinder body. Traditional transducers are difficult to fit stably, and signal coupling fluctuations lead to a decrease in the accuracy of thickness or defect identification. Therefore, the application of existing ultrasonic testing equipment in the long-term continuous monitoring of curved pressure-bearing structures is limited. In recent years, ultrasonic array and phased array imaging technologies have developed rapidly. Beam focusing and scanning can be achieved through inter-element delay control, thereby improving imaging resolution. However, traditional full-focusing imaging requires element-by-element excitation and full-channel reception, resulting in a complex system structure and high power consumption, which is not conducive to long-term online monitoring. Summary of the Invention

[0004] To address the technical problem that existing methods for monitoring defects in composite gas cylinders are insufficient for long-term continuous monitoring and condition assessment, this invention provides a method for monitoring defects in composite gas cylinders and a flexible ultrasonic monitoring instrument.

[0005] This invention employs the following technical solution: a defect monitoring method for composite material gas cylinders, comprising the following steps: acquiring echo signals generated by reflections of plane waves emitted at different incident angles into the composite material gas cylinder; constructing actual defect echo signal templates at different incident angles; performing convolution operations between the acquired echo signals at each angle and the corresponding actual defect echo signal templates to enhance the defect main wave present in the echo signal, and obtaining the convolutional echo signal; then using a delay summation algorithm to focus and reconstruct each pixel in the convolutional echo signal, thereby generating plane wave imaging data for that angle; fusing the plane wave imaging data from multiple angles to obtain a multi-angle plane wave composite image; acquiring multi-angle plane wave composite images of the same monitoring area at different times according to a certain time interval, and performing a difference operation between each imaging and the multi-angle plane wave composite image at the previous time to obtain multiple difference images. The location of defects within the monitoring area is determined by the local gray-level anomalies in the multi-angle plane wave composite image and by combining spatial coordinate mapping technology. Furthermore, multiple differential images are compared in chronological order to obtain the variation pattern of each defect within the monitoring area, thereby inferring the future variation trend of each defect within the monitoring area.

[0006] As a further improvement of this invention, the specific steps for focusing and reconstructing any single pixel are as follows: A plane wave full matrix dataset is constructed by synchronously sampling the echo signals received by each array element using a multi-channel sampling module. Then, based on the constructed plane wave full matrix dataset and the speed of sound of the plane wave propagating in the composite gas cylinder, the propagation time of the plane wave from the array element to the imaging point and back to the array element is calculated. The echo signals acquired by each channel and subjected to convolution operations are then compensated for the propagation time delay corresponding to that pixel and superimposed to achieve focusing and reconstruction of that pixel.

[0007] As a further improvement of the present invention, the construction process of the differential image is as follows: the amplitude difference is obtained by calculating the pixel-by-pixel amplitude difference between the multi-angle plane wave composite image obtained at the current moment and the multi-angle plane wave composite image obtained at the previous moment; the amplitude difference is converted into a logarithmic scale and the obtained amplitude difference is mapped to image coordinates to obtain the differential image.

[0008] This invention also provides a flexible ultrasonic monitoring instrument, which uses the aforementioned method for monitoring defects in composite material gas cylinders. The flexible ultrasonic monitoring instrument includes a host computer, a controller, and a flexible ultrasonic transducer. The flexible ultrasonic transducer includes multiple array elements respectively attached to the outer surface of the composite material gas cylinder. After acquiring an excitation signal, the flexible ultrasonic transducer emits plane waves with different incident angles into the composite material gas cylinder through each array element. Each array element is also used to synchronously receive echo signals generated by the reflection of plane waves with different incident angles. The controller drives each array element to emit ultrasonic signals by generating an excitation signal, and collects the echo signals received by all array elements and sends them to the host computer. The host computer converts the acquired echo signals into a multi-angle plane wave composite image using an ultrasonic imaging algorithm, and locates the position of defects on the monitoring area of ​​the composite material gas cylinder based on the local gray-level anomaly positions in the multi-angle plane wave composite image and combined with spatial coordinate mapping technology. The host computer is also used to acquire multi-angle plane wave composite images of the same area on the composite gas cylinder at different times, and to obtain multiple differential images by subtracting the multi-angle plane wave composite image at the previous time after each imaging. The host computer also compares multiple differential images in chronological order to obtain the change pattern of each defect in the monitoring area, and then infers the future change trend of each defect in the monitoring area.

[0009] As a further improvement of the present invention, the array element is made of piezoelectric ceramic material; the array element is used as a transmitting unit and a receiving unit.

[0010] As a further improvement of the present invention, the flexible ultrasonic transducer also includes a flexible circuit, on which multiple array elements are distributed at intervals; electrodes are provided on the flexible circuit, which are used to send the excitation signal generated by the controller to the piezoelectric ceramic material or to send the echo signal received by the piezoelectric ceramic material to the controller through the flexible circuit.

[0011] As a further improvement of the present invention, the host computer is also used to send the scanning parameter configuration for defect monitoring of composite gas cylinders to the controller.

[0012] As a further improvement of the present invention, the number of array elements is 11 to 22, and the multiple array elements are distributed at equal intervals on the flexible circuit; the width of each array element is 0.6 mm to 1.2 mm; and the interval between two adjacent array elements is 1.0 mm to 2.0 mm.

[0013] As a further improvement of the present invention, the electrode adopts an independent small-lobe electrode structure.

[0014] As a further improvement of the present invention, the flexible ultrasonic monitoring instrument also includes a display for displaying the location of defects on the monitoring area of ​​the composite gas cylinder and the variation pattern of each defect.

[0015] As a further improvement of the present invention, the excitation signal is a 5-cycle Gaussian envelope sine signal with a center frequency of 5MHz.

[0016] The technical solution provided by this invention has the following beneficial effects: (1) The defect monitoring method for composite gas cylinders provided by this invention locates the defect within the monitoring area by combining the local gray-level anomaly location in a multi-angle plane wave composite image with spatial coordinate mapping technology. By comparing multiple differential images in chronological order, the variation pattern within the monitoring area can be obtained, and its future trend can be inferred based on this variation pattern. The defect monitoring method for composite gas cylinders provided in this solution can not only perform long-term continuous monitoring of the tested structure (such as composite gas cylinders), but also evaluate the state of the tested structure based on the monitoring results. At the same time, it can also take corresponding measures in a timely manner according to the variation pattern to solve the defect problem of composite gas cylinders and avoid safety problems caused by defects in composite gas cylinders.

[0017] (2) The defect monitoring method for composite gas cylinders provided by this invention uses plane wave imaging technology to control the array to emit plane waves at different angles, thereby achieving multi-angle sound field coverage of the detection area with a small amount of excitation. This enables large-area focused imaging with a small amount of emission, resulting in fast detection speed and high signal-to-noise ratio, which has good engineering application prospects. Compared with full-focus imaging technology, it has a faster scanning rate and faster data processing speed, which can meet the real-time requirements of long-term continuous monitoring. Furthermore, by obtaining multi-angle plane wave composite images, it can enhance the defect echo in the image and suppress artifacts. Combined with signal optimization methods such as convolution operation and automatic gain control, it can improve the signal-to-noise ratio of the image and the resolution of shallow defects, so that the imaging signal-to-noise ratio is stable at 30-43dB and the defect positioning error is <0.3mm. It can clearly identify shallow and deep defects, solving the problems of blurred shallow defect imaging and insufficient positioning accuracy of existing arrays.

[0018] (3) The flexible ultrasonic monitoring instrument provided by this invention is used to monitor defects in composite material gas cylinders. The flexible ultrasonic monitoring instrument uses flexible circuitry as the substrate material and employs an independent small-lobe electrode structure, resulting in a thin, lightweight, and low-cost flexible ultrasonic transducer structure that can be permanently installed between the composite material gas cylinder and the anti-corrosion layer, achieving high-resolution and automated monitoring of the structural health of the composite material gas cylinder. Furthermore, the flexible ultrasonic transducer in this solution, through reasonable array element design and signal optimization processing, can effectively suppress interference signals and improve imaging quality, possessing good application and promotion value. Attached Figure Description

[0019] Figure 1 This is a flowchart of the defect monitoring method for composite material gas cylinders provided in Embodiment 1 of the present invention.

[0020] Figure 2 This is a schematic diagram showing the connections between the various components of the flexible ultrasonic monitoring instrument in Embodiment 2 of the present invention.

[0021] Figure 3 This is a schematic diagram of the flexible ultrasonic transducer attached to the object to be tested in Embodiment 2 of the present invention.

[0022] Figure 4 This is a simplified structural diagram of the flexible ultrasonic transducer in Embodiment 2 of the present invention.

[0023] Figure 5 This is a comparison of the simulation imaging results of three sets of flexible ultrasonic transducers with different geometric parameters constructed in Embodiment 2 of the present invention under the full-focus imaging method and the plane wave imaging method.

[0024] Figure 6 This is a schematic diagram of the monitoring block of the flexible ultrasonic monitoring instrument in Embodiment 2 of the present invention.

[0025] Figure 7 This is a comparison diagram of the signals before and after the received echo signals are convolved after monitoring the test block of the flexible ultrasonic monitoring instrument in Embodiment 2 of the present invention.

[0026] Figure 8 This is the final image obtained after the flexible ultrasonic monitoring instrument monitors the test block in Embodiment 2 of the present invention. Detailed Implementation

[0027] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0028] In the description of this invention, it should be noted that directional terms such as "center," "lateral," "longitudinal," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific scope of protection of this invention. The terms "first," "second," etc., in the specification and claims of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "comprising" and "having," and any variations thereof, in the specification and claims of this invention, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0029] Example 1 This embodiment provides a defect monitoring method for composite material gas cylinders. Please refer to... Figure 1 It includes the following steps: (a) Acquiring echo signals In this embodiment, a flexible ultrasonic transducer is selected and plane wave imaging technology is used to acquire echo signals. Plane wave imaging technology enables large-area focused imaging with a small number of emitted plane waves, thereby improving the speed of echo signal acquisition. Specifically, a 5-cycle Gaussian envelope sinusoidal pulse with a center frequency of 5MHz can be used as the excitation signal. A controller (such as an FPGA ultrasonic transmitter-receiver acquisition board) is configured to output a preset delay sequence to drive multiple array elements on the flexible ultrasonic transducer to emit sequentially or synchronously, thus forming plane wave sound fields with different incident angles. When the emitted plane waves propagate within the composite gas cylinder and encounter defects (such as cracks, pores, or corrosion discontinuities), they are reflected, generating echo signals. All array elements synchronously receive the echo signals after each emission. By constructing a set of echo signals received by all array elements, a full plane wave matrix dataset is obtained. The constructed full plane wave matrix dataset can serve as the raw information basis for subsequent data analysis, signal processing, and imaging reconstruction. The plane wave imaging technology in this scheme controls the array to emit plane waves at different angles, achieving multi-angle sound field coverage of the detection area with a small amount of excitation. This enables large-area focused imaging with a small number of emissions, resulting in fast detection speed and high signal-to-noise ratio. It has good prospects for engineering applications. Compared with total focusing imaging technology, it has a faster scanning rate and faster data processing speed, which can meet the real-time requirements of long-term continuous monitoring.

[0030] (ii) Obtaining multi-angle plane wave composite images The specific steps are as follows: 2.1 Construct actual defect echo signal templates at different incident angles. Perform convolution operations between the echo signals acquired at each angle and the corresponding actual defect echo signal templates to obtain the convolutional echo signals. Then, analyze the convolution results (such as peak value, correlation, energy distribution, etc.) to determine whether there are defect echoes in the acquired echo signals that match the template. In addition, convolution operations can enhance the main echoes of defects with waveforms similar to the constructed actual defect echo signal templates at each angle, while suppressing the first and last wave vibrations with large waveform feature differences. This achieves signal enhancement and artifact suppression in a suitable manner, significantly improving the signal-to-noise ratio and positioning accuracy of the acquired shallow defects.

[0031] An echo signal template is a pre-constructed signal model representing the typical characteristics of defect echoes. It can be a standard waveform obtained from a real defect echo signal collected in the laboratory after processing (e.g., normalization, alignment); it can also be an ideal defect echo simulated based on a theoretical model (e.g., an acoustic wave reflection model); or it can be a waveform representation after feature extraction and parameterization. The purpose of constructing a real defect echo template is to characterize the echo characteristics corresponding to a certain type or size / location of defect, so as to compare or match it with the actual detection signal later.

[0032] 2.2 A delay-sum algorithm is used to focus and reconstruct each pixel within the monitoring area, thereby generating plane wave imaging data at that angle. The specific steps for focusing and reconstructing any single pixel are as follows: The echo signals received by each flexible array unit are sampled using a multi-channel sampling module to obtain a full plane wave matrix dataset. Then, based on the constructed full plane wave matrix dataset and the sound speed of the plane wave propagating in the composite gas cylinder, the propagation time of the plane wave from the array element to the imaging point and back to the array element for each pixel is calculated. Finally, the echo signals acquired by each channel and subjected to convolution operations are compensated for the propagation time delay corresponding to that pixel, and then superimposed to achieve focused reconstruction of that pixel. Through the above operations, each pixel within the monitoring area is reconstructed, thereby generating plane wave imaging data for that angle. In this embodiment, by performing focused reconstruction on each pixel, the imaging clarity of the subsequently obtained multi-angle plane wave composite image is improved.

[0033] 2.3 Multi-angle plane wave imaging data are fused to obtain a multi-angle plane wave composite image. In this embodiment, the fusion method can be any of the following common existing fusion methods: linear superposition, maximum / minimum value fusion, etc. For linear superposition, the plane wave imaging data from multiple angles are generally added or averaged directly to improve the signal-to-noise ratio, thus obtaining a multi-angle plane wave composite image. For maximum / minimum value fusion, the maximum / minimum value of each pixel in each angle image is taken; this fusion method can retain the strongest reflection or clearest features. In this scheme, using multi-angle plane wave imaging data ensures that defects located in different directions (e.g., horizontal, vertical, oblique) within the monitoring area can be detected by plane waves at a certain angle, thereby improving the detection rate of defects inside composite gas cylinders. Simultaneously, by fusing plane wave imaging data from multiple angles, a detection image with higher contrast and richer details can be obtained.

[0034] (III) Obtaining the difference image Multi-angle plane wave composite images of the same monitoring area at different times are acquired at regular time intervals. After each image is captured, a difference operation is performed between the composite image acquired at the current time and the composite image acquired at the previous time: the amplitude difference is obtained by calculating the pixel-by-pixel amplitude difference between the composite image acquired at the current time and the composite image acquired at the previous time; the amplitude difference is converted to a logarithmic scale and mapped back to image coordinates to obtain the difference image. Repeating the above operation yields multiple difference images at different times.

[0035] (iv) Obtaining monitoring results for composite material gas cylinders The location of defects within the monitoring area of ​​composite gas cylinders is determined by combining local gray-level anomalies in multi-angle plane wave composite images with spatial coordinate mapping technology. Multiple differential images are compared chronologically to obtain the variation patterns of each defect within the monitoring area, thereby inferring its future trend. For example, the presence of local high-amplitude regions in the differential images (i.e., significantly enhanced or weakened echo intensity) may indicate the appearance of new defects (such as cracks or pores) inside the composite gas cylinder. The appearance of continuously expanding regions in the differential images (i.e., spatially contiguous differences that gradually increase over time) suggests that the defect is slowly expanding, such as fatigue crack growth or corrosion propagation. Therefore, this method uses chronological comparison of multiple differential images to obtain the variation patterns within the monitoring area and infers its future trend based on these patterns. The defect monitoring method for composite material gas cylinders provided in this solution can not only perform long-term continuous monitoring of the tested structure (such as composite material gas cylinders), but also assess the condition of the tested structure based on the monitoring results. Furthermore, it can take timely measures to address defects in composite material gas cylinders based on the changing patterns, thus preventing safety issues caused by defects. In summary, the monitoring method provided in this application can not only accurately locate the defects on composite material gas cylinders, but also obtain the changing patterns of internal defects, providing a detailed and robust data foundation for material aging analysis and the inspection of composite material gas cylinders and pressure vessels.

[0036] Example 2 The purpose of this embodiment is to provide a flexible ultrasonic monitoring instrument with a specific structure for monitoring composite material gas cylinders, which can monitor defects in composite material gas cylinders in the manner described in Embodiment 1. Please refer to... Figure 2 The flexible ultrasonic monitoring instrument includes a flexible ultrasonic transducer, a controller, and a host computer.

[0037] The flexible ultrasonic monitoring device may also include a display ( Figure 2 (Not shown in the image), the display is used to show the location of defects on the monitoring area of ​​the composite gas cylinder and the variation pattern of each defect.

[0038] The flexible ultrasonic transducer includes flexible circuitry and multiple array elements. Please refer to... Figure 3 and Figure 4The flexible circuit serves as the substrate for the flexible ultrasonic transducer, which can be connected to the controller via the flexible circuit. Multiple array elements are evenly distributed on the flexible circuit. The array elements are primarily made of piezoelectric ceramic material. Electrodes are provided on the flexible circuit; these electrodes are used to guide the excitation signal generated by the controller into the piezoelectric ceramic material or to transmit the echo signal received by the piezoelectric ceramic material to the controller via the flexible circuit. In this scheme, the array elements can be used as both transmitting and receiving units. When used as transmitting units, the array elements can convert the excitation signal into plane waves with different incident angles and transmit them into the composite material gas cylinder. When used as receiving units, the array elements receive the generated echo signals and transmit them to the controller. It is understood that by setting multiple array elements and a flexible circuit in this scheme, the constructed flexible ultrasonic transducer can undergo adaptive bending during use, thereby allowing the flexible ultrasonic transducer to stably conform to the surface of the area to be monitored, such as... Figure 4As shown, this is especially true for curved structures (such as bends and welded areas). The flexible ultrasonic transducer provided by this solution can achieve stable signal coupling with the monitored area, thereby improving the accuracy of monitoring. When monitoring curved structures, the flexible ultrasonic transducer of this solution can bend according to the specific shape of the measured structure, allowing its array elements to stably conform to the surface of the measured structure. Furthermore, the flexible ultrasonic transducer provided by this solution only needs to be fixed to the measured structure (such as a composite gas cylinder) during the first monitoring. It is understood that the flexible ultrasonic transducer and the composite gas cylinder can be fixed using common methods in existing technology, such as wrapping a rope around the surface of the flexible ultrasonic transducer to securely fix it to the composite gas cylinder, or using a clamp method, such as first placing the flexible ultrasonic transducer on the area to be monitored on the composite gas cylinder and then fixing it to the composite gas cylinder with a clamp; other existing methods can also be used for fixation. By fixing a flexible ultrasonic transducer to a composite gas cylinder, long-term and continuous monitoring of a specific area of ​​the structure under test can be achieved. The electrodes can employ an independent small-lobe electrode structure, which reduces interference and mechanical stress caused by bending of the flexible ultrasonic transducer. It also offers high bending freedom and good surface fit, resulting in a thin, lightweight, and low-cost design suitable for permanent installation. In practical use, the side of the array element furthest from the flexible circuit can be tightly fitted to the area to be monitored on the composite gas cylinder. A coupling agent can be applied at the contact point between the array element and the composite gas cylinder. The combination of the array element and the coupling agent ensures stable acoustic contact with the composite gas cylinder, guaranteeing efficient transmission of sound energy into the cylinder. It is understood that this solution uses a flexible circuit as the substrate material and an independent small-lobe electrode structure, resulting in a thin, lightweight, and low-cost flexible ultrasonic transducer structure that can be permanently installed between the composite gas cylinder and the anti-corrosion layer, enabling high-resolution, automated monitoring of the structural health of the composite gas cylinder. Furthermore, the flexible ultrasonic transducer in this solution, through reasonable array element design and signal optimization processing, can effectively suppress interference signals and improve imaging quality, and has good application and promotion value.

[0039] In this scheme, multiple array substrates can also be provided on the flexible circuit, and each array element can be mounted on the flexible circuit through the array substrate.

[0040] Furthermore, this application also investigates the geometric parameters of the array element distribution on the flexible circuit. The purpose of studying these geometric parameters is to establish the width of the array element and the center-to-center spacing between adjacent elements as key design parameters. These parameters directly affect the formation of the ultrasonic wave velocity and the directionality of the array element, and also directly determine the imaging resolution, the sensitivity during monitoring, and whether imaging artifacts such as grating lobes will occur. Firstly, according to the traditional Nyquist rule, the center-to-center spacing of the array elements is generally set to half the wavelength of the ultrasonic wave in the detected medium to ensure that there are no grating lobes in the obtained image. However, this setting is generally only suitable for constructing an infinitely large array element array and under ideal conditions where the emitted signal is of a single frequency. In practical applications, the number of array elements is limited, and the signal is generally a broadband pulse; therefore, artifacts such as grating lobes inevitably appear in the images obtained during actual monitoring. Generally, if some degree of imaging artifacts occurs outside the region of interest in the structure, such artifacts are acceptable. Research has found that the larger the aperture formed by the array elements, the fewer grating lobes appear in the image during monitoring. A larger aperture also produces a smaller point spread function, resulting in a more efficient flexible ultrasonic transducer with better imaging resolution. This improves the sensitivity of the entire flexible ultrasonic composite gas cylinder monitor, enabling the detection of even small defects. The aperture refers to the linear length in the width direction of multiple array elements arranged sequentially on the flexible circuit. The aperture is calculated as follows: Aperture = (Number of array elements - 1) × Center-to-center distance between adjacent array elements. Therefore, in practical design, if the number and width of array elements remain constant, a flexible ultrasonic transducer with a larger aperture can be constructed by appropriately increasing the center-to-center distance between the array elements.

[0041] In this study, the applicant constructed three sets of flexible ultrasonic transducers with different geometric parameters to investigate their impact on imaging performance. The first set consists of 22 elements, each 0.6 mm wide, with a center-to-center spacing of 1.0 mm, and an aperture size of approximately 24.0 mm. The second set consists of 16 elements, each 1.0 mm wide, with a center-to-center spacing of 1.5 mm, and an aperture size of approximately 23.5 mm. The third set consists of 11 elements, each 1.2 mm wide, with a center-to-center spacing of 2.0 mm. These three flexible ultrasonic transducers, along with a controller and a host computer, form three sets of flexible ultrasonic monitoring instruments for composite material gas cylinders. The controller and host computer are of the same type and specifications. These three sets of flexible ultrasonic monitoring instruments are used to monitor the same area of ​​the same composite material gas cylinder, employing both total focusing and plane wave imaging methods for imaging. The simulation process can be as follows: Three sets of flexible ultrasonic monitoring instruments are constructed. Each set of flexible ultrasonic monitoring instruments uses both the full-focusing method and the plane wave imaging method to monitor the same area of ​​the same composite gas cylinder and obtain imaging results. A two-dimensional acoustic simulation model is then established using the k-Wave toolbox, and the obtained imaging results are processed and compared to obtain the following results: Figure 5 The results are shown. Through the analysis of... Figure 5 Analysis reveals that, while maintaining both a limited number of array elements and high imaging performance, a geometric arrangement of 16 array elements with an element width of 1.0 mm and a center-to-center spacing of 1.5 mm is suitable. In this scheme, the overall thickness of the constructed flexible ultrasonic transducer is less than 1 mm, enabling tight bonding to the surfaces of composite material gas cylinders, storage tanks, and other structures. This improves bonding stability and signal repeatability during monitoring, allowing for stable and long-term monitoring of such structures and enabling effective and accurate assessment of the monitored object's condition based on the monitoring results.

[0042] The controller drives each array element to emit ultrasonic signals by generating excitation signals, and collects the echo signals received by all array elements and sends them to the host computer. In this scheme, the controller can use an FPGA ultrasonic transmitter-receiver acquisition board to drive each array element to emit ultrasonic signals. The excitation signal can be a 5-cycle Gaussian envelope sine pulse with a center frequency of 5MHz. The specific operation is as follows: using a 5-cycle Gaussian envelope sine pulse with a center frequency of 5MHz as the excitation signal, and configuring the FPGA ultrasonic transmitter-receiver acquisition board to output a preset delay sequence, thereby driving the array elements to sequentially or synchronously generate plane waves with different incident angles into the structure under test (such as composite gas cylinders). The controller can also collect the echo signals received by the flexible array through its internal multi-channel acquisition module and send them to the host computer.

[0043] The host computer uses an ultrasonic imaging algorithm to convert the acquired echo signals into multi-angle plane wave composite images. Based on the local grayscale anomalies in these images and combined with spatial coordinate mapping technology, the location of defects on the monitoring area of ​​the composite gas cylinder is determined, thus achieving precise location of defects within the cylinder. The host computer also acquires multi-angle plane wave composite images of the same area on the composite gas cylinder at different times and performs differential analysis with the previous image after each imaging step to obtain multiple differential images. Furthermore, the host computer compares these differential images chronologically to obtain the variation patterns of each defect within the monitoring area, thereby inferring the future trends of each defect within the monitoring area.

[0044] In this scheme, the host computer can connect to the controller via USB or Ethernet. Furthermore, the number of transducers and the placement of array elements within the transducers in the flexible ultrasonic monitoring instrument constructed in this scheme can be modularly designed according to the actual monitoring locations, thereby improving the flexibility of the flexible ultrasonic monitoring instrument and enabling it to effectively monitor composite material gas cylinders.

[0045] The plane wave imaging technology in this scheme achieves multi-angle sound field coverage of the detection area with a small amount of excitation by controlling the array to emit plane waves at different angles. This enables large-area focused imaging with a small number of emissions, resulting in fast detection speed and high signal-to-noise ratio, showing promising engineering application prospects. Compared with total focusing imaging technology, it has a faster scanning rate and data processing speed, meeting the real-time requirements of long-term continuous monitoring. Furthermore, by obtaining multi-angle plane wave composite images, it can enhance the defect echo in the image while suppressing artifacts. Combined with signal optimization methods such as convolution operation and automatic gain control, it can improve the imaging signal-to-noise ratio and the resolution of shallow defects, making the imaging signal-to-noise ratio stable at 30-43dB, with defect positioning errors all <0.3mm. It can clearly identify shallow and deep defects, solving the problems of blurry shallow defect imaging and insufficient positioning accuracy of existing arrays.

[0046] Performance testing In this proposal, the applicant also verified the performance of the constructed flexible ultrasonic monitoring instrument as follows. The constructed flexible ultrasonic monitoring instrument includes 16 array elements, each array element has a width of 1.0 mm, and the center-to-center distance between two adjacent array elements is 1.5 mm.

[0047] The monitored object is an 80mm thick test block with multiple through-hole defects of varying depths (10mm, 25mm, 40mm, 55mm, 70mm) machined inside to simulate typical corrosion or porosity damage. Please refer to... Figure 6As shown, a 5-cycle Gaussian envelope sinusoidal pulse with a center frequency of 5MHz is used as the excitation signal. A preset output sequence is configured by the controller to drive the array elements to generate ultrasonic signals towards the test block, and the echo signal is synchronously received after each transmission. The received echo signal is convolved to obtain the following... Figure 7 The results are shown. Through the analysis of... Figure 7 Analysis reveals that this scheme, by performing convolution on the received echo signal, enhances the main echo of the defect, which is similar in waveform to the constructed actual defect echo template, while suppressing the initial wave tailing vibration and noise with significant waveform differences. This achieves signal enhancement and artifact suppression in the time domain, significantly improving the signal-to-noise ratio and positioning accuracy of shallow defects, and effectively solving the problems of initial wave tailing vibration interference and signal-to-noise ratio degradation. Furthermore, after convolution processing (such as matched filtering), the amplitude of the main peak of the shallow signal is significantly increased, and background noise is significantly reduced, thereby enabling effective acquisition of shallow defect signals and improving the accuracy of shallow defect imaging.

[0048] After convolving the acquired echo signals from each angle with the actual defect echo template, a delayed summation algorithm is used to focus and reconstruct each pixel within the monitoring area based on the convolved echo signals, thereby generating plane wave imaging data for that angle. Finally, the plane wave imaging data from multiple angles are fused to obtain a multi-angle plane wave composite image, as shown below. Figure 8 As shown. By observation Figure 8 It can be seen that after the convolution operation, Figure 8 The imaging of shallow defects with a depth of about 10 mm can achieve clear focused imaging, improve the signal-to-noise ratio, significantly reduce artifacts, and the positioning deviation of each defect is less than 0.3 mm. Furthermore, the measurement deviation is less than 0.1 mm in each monitoring session, indicating that the imaging results have good repeatability and reliability.

[0049] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. A method for defect monitoring of composite material gas cylinders, characterized in that, It includes: Echo signals generated by reflections of plane waves emitted at different incident angles into the monitoring area of ​​composite gas cylinders were collected. Echo signal templates of actual defects at different incident angles are constructed. The echo signal acquired at each angle is convolved with the corresponding actual defect echo signal template to enhance the defect main wave in the echo signal and obtain the echo signal after convolution. Then, a delay summation algorithm is used to focus and reconstruct each pixel in the monitoring area based on the echo signal after convolution, thereby generating plane wave imaging data at that angle. The plane wave imaging data from multiple angles are fused to obtain a multi-angle plane wave composite image. Multiple plane wave composite images of the same monitoring area at different times are acquired at certain time intervals, and the images are compared with the previous multi-angle plane wave composite image after each imaging to obtain multiple differential images. The location of defects within the monitoring area is determined by the local gray-level anomalies in the multi-angle plane wave composite image and by combining spatial coordinate mapping technology. Furthermore, multiple differential images are compared in chronological order to obtain the variation pattern of each defect within the monitoring area, thereby inferring the future variation trend of each defect within the monitoring area.

2. The defect monitoring method for composite material gas cylinders as described in claim 1, characterized in that, The specific steps for focusing and reconstructing any single pixel are as follows: A plane wave full matrix dataset is constructed by synchronously sampling the echo signals received by each array element through a multi-channel sampling module. Then, based on the constructed plane wave full matrix dataset and the sound speed of plane waves propagating in the composite material gas cylinder, the propagation time of the plane wave from the array element to the imaging point and back to the array element is calculated for the pixel. The echo signals acquired by each channel and after convolution operation are compensated for the propagation time delay corresponding to the pixel and then superimposed to achieve focused reconstruction of the pixel.

3. The defect monitoring method for composite material gas cylinders as described in claim 1, characterized in that, The process of constructing the difference image is as follows: The amplitude difference is obtained by calculating the pixel-by-pixel amplitude difference between the multi-angle plane wave composite image obtained at the current moment and the multi-angle plane wave composite image obtained at the previous moment; the amplitude difference is converted into a logarithmic scale and mapped back to image coordinates to obtain the difference image.

4. A flexible ultrasonic monitoring instrument, characterized in that, It uses the defect monitoring method for composite material gas cylinders as described in any one of claims 1-3 to monitor composite material gas cylinders; the flexible ultrasonic monitoring instrument includes a host computer, a controller, and a flexible ultrasonic transducer; The flexible ultrasonic transducer includes multiple array elements that are respectively attached to the outer surface of the composite material gas cylinder; after acquiring the excitation signal, the flexible ultrasonic transducer emits plane waves with different incident angles into the composite material gas cylinder through each array element; each array element is also used to synchronously receive the echo signals generated by the reflection of plane waves with different incident angles. The controller generates excitation signals to drive each array element to emit ultrasonic signals, and collects the echo signals received by all array elements and sends them to the host computer. The host computer uses an ultrasonic imaging algorithm to convert the acquired echo signal into a multi-angle plane wave composite image. Based on the local gray-scale anomaly location in the multi-angle plane wave composite image and combined with spatial coordinate mapping technology, it locates the defect on the monitoring area of ​​the composite gas cylinder. The host computer is also used to acquire multi-angle plane wave composite images of the same area on the composite gas cylinder at different times and perform differential analysis with the multi-angle plane wave composite image at the previous time after each imaging to obtain multiple differential images. The host computer also compares the multiple differential images in chronological order to obtain the change pattern of each defect in the monitoring area, and then infers the future change trend of each defect in the monitoring area.

5. The flexible ultrasonic monitoring instrument as described in claim 4, characterized in that, The array element is made of piezoelectric ceramic material; the array element is used as a transmitting unit and a receiving unit.

6. The flexible ultrasonic monitoring instrument as described in claim 5, characterized in that, The flexible ultrasonic transducer further includes a flexible circuit, on which multiple array elements are spaced apart; the flexible circuit is provided with electrodes, which are used to send the excitation signal generated by the controller to the piezoelectric ceramic material or to send the echo signal received by the piezoelectric ceramic material to the controller through the flexible circuit.

7. The flexible ultrasonic monitoring instrument as described in claim 4, characterized in that, The host computer is also used to send the scanning parameter configuration for defect monitoring of composite gas cylinders to the controller.

8. The flexible ultrasonic monitoring instrument as described in claim 6, characterized in that, The number of array elements is 11 to 22, and the array elements are distributed at equal intervals on the flexible circuit; the width of each array element is 0.6 mm to 1.2 mm; the interval between two adjacent array elements is 1.0 mm to 2.0 mm. And / or, the electrode adopts an independent small-lobe electrode structure.

9. The flexible ultrasonic monitoring instrument as described in claim 4, characterized in that, The flexible ultrasonic monitoring instrument also includes a display screen, which is used to display the location of defects on the monitoring area of ​​the composite gas cylinder and the variation pattern of each defect.

10. The flexible ultrasonic monitoring instrument as described in claim 4, characterized in that, The excitation signal is a 5-cycle Gaussian envelope sine signal with a center frequency of 5MHz.

Images