Microwave nondestructive testing device and method based on dielectric loading rectangular waveguide antenna and characterization method

Abstract

The invention provides a microwave nondestructive testing device and method based on a medium loading rectangular waveguide antenna and a characterization method. The device comprises the medium loading rectangular waveguide antenna, a computer, a microwave vector network instrument, a three-dimensional mobile station and a to-be-tested sample piece, the method and the device aim at realizing higher main lobe radiation intensity and lower radiation angle of the near-field probe by optimizing a waveguide feed structure and loading a specific low-loss dielectric material, so that the detection sensitivity and resolution are improved. The technology is widely applicable to internal defect detection of materials, layered recognition of multilayer structures and other complex detection scenes, and an efficient and accurate nondestructive detection solution is provided for modern industry.

Description

Technical Field

[0001] The present invention relates to the technical fields of electromagnetic science, detection, and signal processing, and particularly to a microwave non-destructive testing device, method, and characterization method based on a dielectric-loaded rectangular waveguide antenna. Specifically, it relates to a microwave / millimeter-wave characterization method and device for holes / debonding defects in aerospace insulation composite materials based on a dielectric-loaded rectangular waveguide antenna. The detection method and device are applicable to the field of precise quantitative evaluation of holes / debonding defects in aerospace insulation composite materials. Background Art

[0002] With the continuous development of industrial technologies, microwave non-destructive testing (NDT) technology has gradually become an important tool for the quality inspection of various industrial materials. With its non-contact, high-efficiency, and non-destructive characteristics, this technology has been widely used in the detection of surface and internal defects of metals, composite materials, and other engineering materials. In recent years, as an important implementation form of microwave non-destructive testing, the high-resolution near-field microwave imaging method has shown superiority in multiple fields, capable of detecting minute defects on the surface and subsurface of materials, and effectively identifying problems such as delamination, voids, inclusions, and microstructural changes within the materials.

[0003] Traditional non-destructive testing technologies, such as phased array ultrasonic testing, X-ray imaging, and infrared thermography, although having a relatively mature technical foundation in the field of industrial testing, still have limitations in terms of detection capabilities, resolution, sensitivity, and adaptability to certain specific materials and structures in complex environments. Near-field microwave imaging, with its characteristics of being able to deeply detect the internal properties of materials, high-resolution imaging, and strong adaptability to various materials, has gradually become a powerful supplement or even an alternative to traditional non-destructive testing technologies.

[0004] In existing research, Bao Xiaojun et al. from Guangdong Narui Radar Technology Co., Ltd. (Patent No. CN108075235B) disclosed a vertical slot waveguide antenna, which includes a slot leaky waveguide and a waveguide coaxial converter connected to each other. The slot leaky waveguide includes a waveguide and a plurality of vertical slots provided on the narrow side of the waveguide. A plurality of metal platforms are provided in the waveguide, and the metal platforms are respectively located on both sides of the vertical slots, and the side surfaces of the metal platforms and the side surfaces of the vertical slots are located in the same vertical plane; a plurality of vertical slots are opened on the waveguide, and metal platforms are provided beside the vertical slots. The waveguide coaxial converter introduces the energy of the feeder into the slot leaky waveguide, uses the waveguide coaxial converter to excite the electromagnetic field of the waveguide, and makes it propagate in the waveguide. During the propagation process, the electromagnetic field is distorted by the metal platforms, so that the electromagnetic energy can effectively leak out through the gaps between the metals, realizing the characteristics of low side lobe, low cross polarization, low loss and small size of the antenna. Huang Jianjun et al. from Shenzhen NIO RF Technology Co., Ltd. (Patent No. CN118073806B) disclosed a waveguide antenna and a probe, which relates to the technical field of waveguide antennas. Among them, the waveguide antenna includes a rectangular waveguide formed by electroplating a metal film on the surface of a dielectric. The rectangular waveguide includes an orthomode coupler. The orthomode coupler includes a common port and two transmission ports. The two transmission ports are used to respectively transmit the TE01 mode and the TE10 mode separated from the wave transmitted by the common port, and at the end of the common port, the dielectric protrudes from the metal film to form a dielectric lens. The purpose of the present invention is to propose a miniaturized and lightweight dual-polarization waveguide antenna. Zhao Yu et al. from Guizhou Aerospace Metrology and Test Technology Research Institute (Patent No. CN118758973A) disclosed a non-destructive testing device and method based on a transmissive array focusing antenna. The computer is respectively connected to a microwave signal generating and analyzing instrument and a three-dimensional motion stage. The microwave signal generating and analyzing instrument is connected to a transmitting antenna. The transmitting antenna feeds the transmissive array antenna. The transmitting antenna is fixed above the transmissive array antenna through a bracket, and the bracket is installed on the three-dimensional motion stage. The computer controls the microwave signal generating and analyzing instrument to feed the transmitting antenna, so that the transmitting antenna radiates an electromagnetic wave to the transmissive array antenna. The transmissive array antenna receives the electromagnetic wave and processes it through each element of the transmissive array antenna, and then radiates an electromagnetic wave focused at a specific position again; the object to be tested is placed at the initial focusing position of the transmissive array, and the computer controls the three-dimensional motion stage to move, changing the focusing focus of the transmissive array antenna, so as to realize a comprehensive scan of the object to be tested, and judge the defects of the object to be tested according to the imaging effect, improving the reliability of non-destructive testing. Xiao Xia et al. from Tianjin University (Patent No. CN117673736A) disclosed a flexible microstrip slot antenna suitable for non-destructive detection of human blood glucose concentration, and its structure includes a substrate of 28.5mm×30mm×0.4mm, a metal slotted layer and a feeder layer.The material selected for the antenna medium is the flexible material polyimide (PI), which has flexibility. The radiation metal layer is designed with slots, and two auxiliary arc-shaped small slots are partially connected to the main circular slot of the antenna ground. It is fed by a stub microstrip to achieve better impedance matching and dual-band characteristics within the working frequency band. The specific dimensions of the slot are obtained through simulation. The present invention can detect different body positions, has multiple operating frequencies, and the dual-band response makes it have higher robustness and accuracy. Zhou Hongwei et al. from Northeast Forestry University (Patent No. CN109696446B) invented a non-destructive detector for insect-induced defects inside trees. The detector includes: an external packaging module of the detector, a main chip processing module, an electromagnetic wave generation module, an electromagnetic wave reception module, a transceiver integrated antenna, a display module, a power management module, and a data analysis module. In addition, in order to improve the application range of the detector and prevent the occurrence of the breathing effect of electronic devices, a toothed rubber ring sealing and waterproof structure is adopted between the various integrated modules inside the detector. Under the control of the main chip processing module, through the combined action of other functional modules, the detector can complete the emission and reception of electromagnetic waves, and then through the analysis and processing of the data analysis module, the detection of defects inside the tree can be completed. Since this detector uses electromagnetic waves propagating in free space for detection, this process will not cause harm to trees, the surrounding environment, people, etc., and realizes non-destructive detection in the true sense.

[0005] Despite the significant progress made in the above technologies, there are still some problems with existing waveguide probes in practical applications. In near-field microwave imaging technology, the performance of the imaging probe directly determines the resolution and detection sensitivity of the system. Most existing near-field microwave imaging probes adopt various structural forms such as waveguide probes, coaxial probes, resonators, etc. However, these probes usually face problems such as low radiation intensity, limited lateral resolution, or complex structures in practical applications, which limit their practical utility in various industrial detection scenarios. Especially for waveguide probes, their resolution ability is often determined by the lateral size of the probe, and this limitation makes it difficult for existing technologies to meet the imaging requirements of high resolution and high sensitivity. Summary of the Invention

[0006] The object of the present invention is to solve the problems existing in the existing X-band rectangular waveguide antenna in the detection of aerospace insulation composite materials, such as beam divergence and insufficient lateral resolution, resulting in problems such as shape distortion and low detection sensitivity in defect imaging. A microwave non-destructive detection device, method, and characterization method based on a dielectric-loaded rectangular waveguide antenna are proposed.

[0007] The present invention is realized through the following technical solutions. The present invention proposes a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna. The device includes a dielectric-loaded rectangular waveguide antenna, a computer, a microwave vector network analyzer, a three-dimensional moving stage, and a specimen to be tested. Among them, the computer is respectively connected to the microwave vector network analyzer and the three-dimensional moving stage; the microwave vector network analyzer is connected to the dielectric-loaded rectangular waveguide antenna; the dielectric-loaded rectangular waveguide antenna is fixed above the three-dimensional moving stage through a bracket; the specimen to be tested is fixed on the three-dimensional moving stage.

[0008] Further, the dielectric-loaded rectangular waveguide antenna adopts a side-feed method with an SMA interface.

[0009] Further, the dielectric-loaded rectangular waveguide antenna includes an X-band open rectangular waveguide and a low-loss dielectric material processed into a special shape. The low-loss dielectric material is an FR-4 glass fiber composite material.

[0010] Further, the waveguide antenna consists of two parts. The front section is a rectangular waveguide, and the rear section is a dielectric structure. The dielectric structure includes a rectangular dielectric structure and a pyramidal dielectric structure. The cross-section of the rectangular waveguide is rectangular, with an external length of l1, a width of w1, and a height of h1, and an internal length of l2, a width of w2, and a height of h1, which is used for the transmission of electromagnetic waves. By ensuring a constant cross-sectional design, signal stability is ensured and transmission loss is reduced. The rectangular dielectric structure is closely attached to the inside of the rectangular waveguide. The length and width of the cross-section of the rectangular dielectric structure are the same as the length and width inside the waveguide, which are w2 and l2, and the height of the rectangular dielectric structure is h2. The height h3 of the pyramidal dielectric structure represents the vertical height between its upper and lower planes. The length and width of the top cross-section of the pyramidal dielectric structure are x1 and x2 respectively, and the length of the inclined connecting line is x3, which geometrically optimizes the signal transmission and energy radiation performance. The loaded dielectric material is FR-4.

[0011] The present invention also proposes a characterization method for the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna described above. The method includes the following steps:

[0012] Step 1: Identify the specimen to be tested and place the specimen to be tested on the moving stage.

[0013] Step 2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. This process includes turning on the computer, the microwave vector network analyzer, and the three-dimensional moving stage equipment.

[0014] Step 3: Adjust the position of the three-dimensional moving stage so that the specimen to be tested is in a suitable relative position with respect to the probe.

[0015] Step 4: After the computer sets the experimental parameters through the microwave non-destructive testing software, it issues an instruction. The microwave vector network analyzer generates a signal within the working frequency range of the antenna, transmits the signal to the sample to be tested through the antenna, and receives the reflected energy. The S parameter is calculated through the microwave vector network analyzer. At the same time, the computer issues an instruction to save the S parameter calculated by the microwave vector network analyzer to the hard disk of the computer. Then, the computer issues an instruction to control the mobile station to move to the next position and repeat the above steps; 11 The computer issues an instruction to save the S parameter calculated by the microwave vector network analyzer to the hard disk of the computer. Then, the computer issues an instruction to control the mobile station to move to the next position and repeat the above steps; 11 parameter to the hard disk of the computer. Then, the computer issues an instruction to control the mobile station to move to the next position and repeat the above steps;

[0016] Step 5: After the test data acquisition is completed, for the S 11 signal, a feature extraction algorithm is used to realize the imaging of the defects of the sample to be tested;

[0017] Step 6: After the test is completed, save the results obtained from the test. At the same time, the computer controls the microwave vector network analyzer to make its radiation energy become 0, and controls the two-axis driver to zero the three-dimensional mobile station;

[0018] Step 7: After the test is completed, turn off the computer, the microwave vector network analyzer and the three-dimensional mobile station in sequence, and place the antenna probe and the test piece to be tested in a specified storage container for proper storage.

[0019] Furthermore, the measurement parameters of the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna include: the amplitude and phase of the S 11 dB signal.

[0020] The present invention also proposes a non-destructive testing method according to the above-mentioned microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. The method includes: (1) Generation and radiation of signals: The microwave vector network analyzer is controlled by the computer to feed the antenna, so that the antenna radiates an electromagnetic wave signal to the sample to be tested; (2) Scanning of the sample to be tested: After the antenna is fixed, the sample to be tested is fixed on the three-dimensional mobile station, and the antenna is directly above the sample to be tested. The three-dimensional mobile station is controlled to scan the sample to be tested; (3) Reception and processing of the reflected signal: When the medium changes, it will cause impedance mismatch, and the signal will be reflected. The antenna receives the reflected electromagnetic wave, calculates the ratio of the intensity of the reflected signal to the incident signal and processes it to obtain the S 11 dB signal. Since the S 11 dB of different materials is different, the imaging effect after signal processing is also different, so as to obtain an image containing defects.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a microwave non-destructive testing device, method and characterization method based on a dielectric-loaded rectangular waveguide antenna. The method and device aim to achieve a higher main lobe radiation intensity and a lower radiation angle of the near-field probe by optimizing the waveguide feeding structure and loading a specific low-loss dielectric material, thereby improving the sensitivity and resolution of detection. This technology is widely applicable to the detection of internal defects in materials, the identification of delamination in multi-layer structures, and other complex detection scenarios, providing an efficient and accurate non-destructive testing solution for modern industry. Description of the Drawings

[0023] Figure 1 It is a structural diagram of the antenna.

[0024] Figure 2 It is a schematic diagram of a pyramidal dielectric structure.

[0025] Figure 3 It is a side view of the antenna structure.

[0026] Figure 4 It is the S 11 parameter diagram of the antenna.

[0027] Figure 5 It is a comparison diagram of the maximum gain of the main lobe of the antenna.

[0028] Figure 6 It is a comparison diagram of the 3dB beam width of the antenna at f = 11.846 GHz.

[0029] Figure 7 It is a schematic diagram of a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna.

[0030] Figure 8 It is a schematic diagram of a solid propellant simulated sample.

[0031] Figure 9 It is a detection result diagram of the original waveguide antenna.

[0032] Figure 10 It is a detection result diagram of the dielectric-loaded rectangular waveguide antenna.

[0033] Figure 11 It is a schematic diagram of a high-silica phenolic resin composite simulated sample.

[0034] Figure 12 It is a detection result diagram of the original waveguide antenna of the high-silica phenolic resin composite simulated sample.

[0035] Figure 13 It is a detection result diagram of the high-silica phenolic resin composite simulated sample based on the optimized dielectric-loaded rectangular waveguide antenna.

[0036] Figure 14It is the experimental result diagram of double - line scanning using a rectangular waveguide probe when SOD = 1mm. Among them, (a) amplitude response, (b) phase response.

[0037] Figure 15 It is the experimental result diagram of double - line scanning using the proposed probe when SOD = 1mm. Among them, (a) amplitude response, (b) phase response. Detailed implementation manner

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] Microwave vector network analyzer: Also known as a vector network analysis instrument, it is a test device for electromagnetic wave energy. It can measure both the amplitude values of various parameters of a single - port network or a two - port network and the phase. The vector network analyzer can display test data using a Smith chart.

[0040] S 11 dB: S 11 is the input - end reflection coefficient, which represents the degree of signal reflection at port 1 when the signal is input from port 1. When converting the S 11 parameter to a dB value, the formula: S 11 dB = 20×log 10 (S 11 ) can be used.

[0041] Impedance matching: It is mainly used on a transmission line to achieve the purpose that all high - frequency microwave signals can be transmitted to the load point, and almost no signal is reflected back to the source point, thereby improving energy efficiency. When the internal resistance of the signal source is equal to the characteristic impedance of the connected transmission line in magnitude and in phase, or when the characteristic impedance of the transmission line is equal to the load impedance connected thereto in magnitude and in phase, it is respectively called that the input end or the output end of the transmission line is in an impedance - matching state, simply referred to as impedance matching.

[0042] Main - lobe gain: It refers to the signal gain of the antenna in a certain direction when the antenna is pointed in that direction. Specifically, it is the ratio of the power density of the antenna radiation power in the selected main - lobe direction to the power density of the antenna under an omnidirectional radiation condition. The main - lobe gain is an important parameter for evaluating the directivity of the antenna and is one of the important indicators for describing the anti - interference ability of the antenna.

[0043] 3dB beamwidth: It refers to the angle between two directions in the antenna radiation pattern where the main - lobe gain drops by 3dB (the power is halved), which is used to reflect the strength of the antenna directivity. A narrow beam corresponds to strong directivity and high gain.

[0044] SMA interface: The full name is SubMiniature version A. There are two forms of SMA interfaces. The standard SMA has "outer thread + hole" at one end and "inner thread + pin" at the other end; the reverse polarity RP-SMA has "outer thread + pin" at one end and "inner thread + hole" at the other end.

[0045] Combined with Figures 1 - 15 , the present invention proposes a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna. The device includes a dielectric-loaded rectangular waveguide antenna, a computer, a microwave vector network analyzer, a three-dimensional moving stage, and a sample to be tested. Specifically, the computer is respectively connected to the microwave vector network analyzer and the three-dimensional moving stage; the microwave vector network analyzer is connected to the dielectric-loaded rectangular waveguide antenna; the dielectric-loaded rectangular waveguide antenna is fixed above the three-dimensional moving stage through a bracket; the sample to be tested is fixed on the three-dimensional moving stage. Specifically: The computer is respectively connected to the microwave vector network analyzer and the three-dimensional moving stage; the computer is mainly used to control the microwave vector network analyzer to generate signals, the movement of the three-dimensional moving stage, the signal recording and storage of the microwave vector network analyzer, etc.; the computer controls the microwave vector network analyzer to generate a suitable signal and radiate it outward through the antenna; the microwave vector network analyzer and the antenna are connected through a coaxial cable and an SMA interface. The transmitting antenna is a dielectric-loaded rectangular waveguide antenna, and the side-feed method is adopted, which is convenient for the installation of SMA; the dielectric material of the antenna is FR-4. After the antenna is fixed, through the movement of the three-dimensional moving stage, the antenna and the sample to be tested have relative movement, realizing the scanning of the sample to be tested.

[0046] The dielectric-loaded rectangular waveguide antenna adopts the side-feed method of the SMA interface.

[0047] The dielectric-loaded rectangular waveguide antenna includes an X-band open rectangular waveguide and a low-loss dielectric material processed into a special shape. The low-loss dielectric material is FR-4 glass fiber composite material.

[0048] The waveguide antenna consists of two parts. The front section is a rectangular waveguide, and the rear section is a dielectric structure. The dielectric structure includes a rectangular dielectric structure and a pyramidal dielectric structure. The cross-section of the rectangular waveguide is rectangular, with an external length of l1, a width of w1, and a height of h1, and an internal length of l2, a width of w2, and a height of h1, which is used for the transmission of electromagnetic waves. By ensuring a constant cross-sectional design, signal stability is ensured and transmission loss is reduced. The rectangular dielectric structure is closely attached to the inside of the rectangular waveguide. The length and width of the cross-section of the rectangular dielectric structure are the same as the length and width inside the waveguide, which are w2 and l2, and the height of the rectangular dielectric structure is h2. The height h3 of the pyramidal dielectric structure represents the vertical height between its upper and lower planes. The length and width of the top cross-section of the pyramidal dielectric structure are x1 and x2 respectively, and the length of the inclined connecting line is x3, which geometrically optimizes the signal transmission and energy radiation performance. The loaded dielectric material is FR-4, which has excellent mechanical and electromagnetic properties. The geometric parameters of the antenna are shown in Table 1.

[0049] Table 1 Geometric parameters of the antenna

[0050]

[0051]

[0052] Figure 4 is the S 11 (dB) parameter diagram of the antenna. The smaller the value of S 11 (dB), the less the reflected radiation power, and the better the matching of the antenna. The closer S 11 (dB) is to 0, the less energy the antenna radiates outward (in the state of impedance mismatch), and the worse the antenna performance. It can be visually seen from the figure that when the operating frequencies of the antenna are f = 8.56 GHz, 10.46 GHz, 11.14 GHz, and 11.85 GHz, the return loss is less than -10 dB, which indicates that the antenna has good matching characteristics and high energy transfer efficiency at the operating frequency points, meeting the actual needs.

[0053] Figure 5 is the comparison diagram of the maximum main lobe gain between the original waveguide antenna and the proposed dielectric-loaded waveguide antenna. The larger the maximum main lobe gain value, the stronger the radiation of the antenna and the better the antenna performance. It can be seen from the figure that at most operating frequencies, the maximum main lobe gain value of the antenna is greater than that of the X-band rectangular waveguide antenna, which indicates that the performance of the optimized antenna has been improved to a certain extent compared with the original antenna.

[0054] Figure 6It is a comparison diagram of the 3dB beam widths of the original waveguide antenna and the proposed dielectric-loaded waveguide antenna at the operating frequency. The smaller the radiation angle, the better the directivity of the antenna, and the more suitable the antenna is for high-precision non-destructive testing imaging. It can be seen from the figure that at the operating frequency, the 3dB beam width of the antenna is smaller than that of the X-band rectangular waveguide antenna, indicating that the directivity of the optimized antenna has been improved to a certain extent compared with the original antenna.

[0055] Through the dielectric loading technology, the present invention enables the probe to achieve better impedance matching within the frequency band of 8.2 - 12.4 GHz. The peak gain of the main lobe has been improved, the 3dB beam width has been narrowed, and the lateral resolution has been increased by 46%, reaching λ / 4.4. The improved probe can detect deeper defects and achieve a clearer imaging effect, and can realize sub-millimeter defect detection in the depth range of 1 - 8.5 mm.

[0056] The present invention also proposes a characterization method for a microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna as described above. The method includes the following steps:

[0057] Step 1: Identify the specimen to be tested and place the specimen to be tested on the moving table;

[0058] Step 2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna, which includes turning on the computer, microwave vector network analyzer, and three-dimensional moving table device;

[0059] Step 3: Adjust the position of the three-dimensional moving table so that the specimen to be tested is in a suitable relative position with respect to the probe;

[0060] Step 4: After the computer sets the experimental parameters through the microwave non-destructive testing software, it issues an instruction to generate a signal within the antenna operating frequency range through the microwave vector network analyzer, transmit the signal to the specimen to be tested through the antenna, and receive the reflected energy. The S 11 parameters are calculated through the microwave vector network analyzer. At the same time, the computer issues an instruction to save the S 11 parameters calculated by the microwave vector network analyzer to the hard disk of the computer. Then, the computer issues an instruction to control the moving table to move to the next position and repeat the above steps;

[0061] Step 5: After the test data acquisition is completed, for the S 11 signal, feature extraction algorithms such as maximum value, minimum value, and principal component analysis are used to realize the imaging of the defects of the specimen to be tested;

[0062] Step 6: At the end of the test, save the results obtained from the test. At the same time, the computer controls the microwave vector network analyzer to make its radiation energy become 0, and controls the two-axis driver to zero the three-dimensional moving table;

[0063] Step 7: After the test, turn off the computer, microwave vector network analyzer, and three-dimensional mobile stage in sequence, and place the antenna probe and the test specimen to be tested in the specified storage container for proper storage.

[0064] The measurement parameters of the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna include: S 11 The amplitude and phase of the dB signal.

[0065] The present invention also proposes a non-destructive testing method according to the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. The method includes: (1) Generation and radiation of signals: Feed the antenna through the computer-controlled microwave vector network analyzer, so that the antenna radiates an electromagnetic wave signal to the specimen to be tested; (2) Scanning of the specimen to be tested: After fixing the antenna, fix the specimen to be tested on the three-dimensional mobile stage. The antenna is directly above the specimen to be tested, and control the three-dimensional mobile stage to scan the specimen to be tested; (3) Reception and processing of the reflected signal: When the medium changes, it will cause impedance mismatch and the signal will be reflected. The antenna receives the reflected electromagnetic wave, and by calculating the ratio of the intensity of the reflected signal to the incident signal and processing it, the S 11 dB signal is obtained. Since the S 11 dB of different materials is different, the imaging effect after signal processing is also different, so as to obtain an image containing defects.

[0066] The present invention proposes a microwave non-destructive testing device and method based on a dielectric-loaded rectangular waveguide antenna. Compared with the original antenna, it innovatively adopts a pyramid-shaped dielectric loading structure, proposes a new mechanism of waveguide-dielectric coupling radiation, and by optimizing the dielectric material and geometric parameters, makes the antenna have stronger main lobe radiation intensity and smaller 3dB radiation angle. The main lobe peak gain of the proposed antenna at 39 frequency points is better than that of the rectangular waveguide, accounting for about 93% of the total frequency points. The 3dB beam width at the operating frequency f = 11.846 GHz is 51.1°, which is reduced by about 10.98%. In addition, the lateral resolution of the probe is improved. The proposed probe reaches a resolution of λ / 4.4 at f = 11.445 GHz, and the resolution is improved by 46.36% compared with the rectangular waveguide probe in the same frequency band. The above improvements can effectively make up for the distortion of the shape of the detected defect image and the problem of low resolution. At the same time, the device adopts a proposed modular loading mechanism design, and different dielectric structures can be replaced according to actual needs.

[0067] The present invention will be described in more detail below through preferred examples.

[0068] Example 1:

[0069] As Figure 7As shown in the figure, a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna mainly consists of 1. a microwave vector network analyzer; 2. a computer; 3. a three-dimensional mobile stage; 4. a dielectric-loaded rectangular waveguide antenna; 5. a sample to be tested (a solid propellant simulation sample), etc.

[0070] An experimental control software was developed based on C / C++ and installed in the computer, which is used for the control, data processing and imaging of the microwave vector network analyzer and the three-dimensional mobile stage.

[0071] As Figure 1 shown in the figure, the proposed dielectric-loaded rectangular waveguide antenna adopts a side-feed method with an SMA interface. The dielectric-loaded rectangular waveguide antenna includes an X-band open rectangular waveguide and a low-loss dielectric material processed into a special shape. Here, FR-4 glass fiber composite material is used. The waveguide antenna consists of two parts. The front section is a rectangular waveguide, and the rear section is a tapered transition structure (including a rectangular dielectric structure and a tapered dielectric structure). The cross-section of the rectangular waveguide is rectangular, with an external length of l1, a width of w1, and a height of h1, and an internal length of l2, a width of w2, and a height of h1. It is mainly used for the transmission of electromagnetic waves, and the signal stability is ensured and the transmission loss is reduced through a constant cross-section design. The rectangular dielectric structure is closely attached to the inside of the rectangular waveguide. The length and width of the cross-section of the rectangular dielectric structure are the same as the length and width inside the waveguide, which are w2 and l2, and the height of the rectangular dielectric structure is h2. The height h3 of the tapered dielectric structure represents the vertical height between its upper and lower planes. The length and width of the top cross-section of the tapered dielectric structure are x1 and x2 respectively, and the length of the inclined connecting line is x3, which geometrically optimizes the signal transmission and energy radiation performance. The internal filling material of the whole antenna is FR-4, and this material has excellent mechanical properties and electromagnetic properties.

[0072] The detection method is a point-scanning mode. In each scanning point scanning cycle, first, a signal is generated by the microwave vector network analyzer. The antenna is connected to the coaxial cable through an SMA interface, and the signal feeds the antenna through the coaxial cable. After the antenna obtains the feed, it generates an electromagnetic wave and radiates it outward. By installing the antenna on the three-dimensional mobile stage and controlling the movement of the three-dimensional mobile stage, the scanning of the solid propellant simulation sample is completed. When the microwave signal encounters a medium with different impedance, the signal will change. Therefore, there are obvious differences between the signals of the defective area and the intact area, and based on this, it can be determined whether there are defects. The information of the microwave signal includes amplitude and phase, and at the same time, the real part and the imaginary part signals can be calculated according to the amplitude and phase signals. To sum up, when the three-dimensional mobile stage drives the solid propellant simulation sample to move, the scanning of the solid propellant simulation sample can be realized, and the non-destructive detection of the internal defects of the solid propellant simulation sample can be realized by imaging the S 11 dB signal. As Figure 8 shown in the figure is the solid propellant simulation sample. Figure 9 shown in the figure is the detection result of the original waveguide antenna.Figure 10 The detection results of the dielectric-loaded rectangular waveguide antenna proposed based on the optimization of the waveguide antenna are shown. From Figure 9 and Figure 10 it can be seen that all 16 defects can be seen in both figures, but Figure 9 only #1 and #2 have high clarity in . Although the other defects can be detected, their clarity is low and the boundaries are not clear. And Figure 10 the defect morphology in is restored relatively well, with high clarity and clear boundaries. It shows that the designed dielectric-loaded rectangular waveguide antenna enhances the detection ability during imaging, reduces the distortion of the shape of the detected defect image, and increases the resolution of the detected defect image.

[0073] The microwave vector network analyzer mentioned refers to a device that can generate and record microwave signals, and the frequency coverage range of the microwave vector network analyzer should be adjustable within the range of 10 MHz to 43.5 GHz. The microwave vector network analyzer outputs the signal to the antenna through a cable and an SMA interface; the antenna is responsible for radiating the signal. The gain of the proposed antenna is determined during the design and cannot be changed once determined.

[0074] Example 2:

[0075] As Figure 7 shown, a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna mainly consists of 1. a microwave vector network analyzer; 2. a computer; 3. a three-dimensional moving stage; 4. a dielectric-loaded rectangular waveguide antenna; 5. a sample to be tested (high-silica phenolic resin composite material), etc.

[0076] In this embodiment, the sample to be tested is a high-silica phenolic resin glass fiber composite material. It mainly consists of glass fibers and a resin matrix and has low conductivity.

[0077] The microwave vector network analyzer is controlled by a computer to feed the antenna, so that the antenna radiates electromagnetic wave signals to the sample to be tested. The working frequency range of the microwave vector network analyzer is 10 MHz to 43.5 GHz. After the signal is generated, the electromagnetic wave is transmitted to the antenna through a coaxial cable and radiated to the sample to be tested through the antenna.

[0078] The sample to be tested is fixed above the three-dimensional moving stage, and the antenna is installed on the three-dimensional moving stage. The antenna scans the sample in a snake-like point pattern. The precise control of the three-dimensional moving stage enables the antenna to cover the entire surface of the sample to be tested and gradually collect data at different scanning positions.

[0079] The reflected signal is received by the antenna and transmitted to the microwave vector network analyzer. According to the intensity ratio of the reflected signal to the incident signal, S is calculated 11The amplitude and phase of the dB signal. When electromagnetic waves encounter the interface of different materials, reflection occurs, and the amplitude and phase will show corresponding changes, enabling the detection of defects inside the material.

[0080] Through the control software, the microwave vector network analyzer and the three-dimensional mobile stage can be controlled in real time to complete data acquisition and image processing. After image processing, the amplitude and phase changes of the signal are converted into defect images, which can display the defects inside the composite material. Nondestructive defect location and evaluation are achieved. As Figure 11 shown is a simulated sample of a high-silica phenolic resin composite material. Figure 12 shown is the detection result of the original waveguide antenna, Figure 13 shown is the detection result of the proposed dielectric-loaded rectangular waveguide antenna based on the optimization of the waveguide antenna. From Figure 12 and Figure 13 it can be seen that Figure 12 the boundary of the defect in [[ ]] is relatively blurred and has more noise, which cannot provide an accurate basis for subsequent quantitative defect detection. Figure 13 has a better detection effect. The boundary of the defect in the figure is clear, and it has a better contrast compared with the intact area. It shows that the designed dielectric-loaded rectangular waveguide antenna reduces the distortion of the shape of the detected defect image during imaging and increases the resolution of the detected defect image.

[0081] Example 3:

[0082] In this embodiment, the lateral resolution of the probe is evaluated by line scanning two metal wires. Two identical wires with a diameter of 0.6 mm are arranged in parallel along the y-axis, and the distance between the centers of the wires is defined as D. At a lift-off distance (Stand-off distance, SOD) of 1 mm, relative movement is carried out between the probe and the wires along the x-axis, and the total scanning distance of the experiment is 40 mm. A single probe is used to scan wires with different spacings. Figure 14 and 15 respectively show the experimental results of double-wire scanning using an X-band rectangular waveguide and the proposed probe at SOD = 1 mm. In Figure 14 when the wire spacing is reduced to 10 mm, the resolution of the rectangular waveguide is significantly limited. Specifically, when D = 8 mm, a single peak appears at the center of the image, and the two wires cannot be resolved. When the spacing is increased to D = 10 mm, although the intensity of the central peak gradually decreases, it still cannot be recognized. Two obvious peaks appear at D = 12 mm, indicating that the wires with a 12 mm spacing are successfully resolved. The experimental results show that the rectangular waveguide reaches a resolution of λ / 2.36 at f = 11.445 GHz. Figure 15It is shown that when the spacing between the wires is reduced to 4 mm, the resolution of the proposed probe is limited. At D = 4 mm, only one central peak is observed and the wires are not successfully distinguished. At D = 6 mm, two distinguishable peaks appear, confirming that the wires with a 6 mm spacing can be successfully distinguished. The experimental results show that the proposed probe achieves a resolution of λ / 4.4 at f = 11.445 GHz, which is a 46.36% improvement in resolution compared to the rectangular waveguide probe.

[0083] Although the present invention has been disclosed above in preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna, characterized in that, The device includes a dielectric-loaded rectangular waveguide antenna, a computer, a microwave vector network analyzer, a three-dimensional mobile stage, and a sample to be tested. Among them, the computer is respectively connected to the microwave vector network analyzer and the three-dimensional mobile stage. The microwave vector network analyzer is connected to the dielectric-loaded rectangular waveguide antenna. The dielectric-loaded rectangular waveguide antenna is fixed above the three-dimensional mobile stage through a bracket. The sample to be tested is fixed on the three-dimensional mobile stage.

2. The device according to claim 1, characterized in that, The dielectric-loaded rectangular waveguide antenna adopts a side-feed method with an SMA interface.

3. The device according to claim 1, characterized in that, The dielectric-loaded rectangular waveguide antenna includes an X-band open rectangular waveguide and a low-loss dielectric material processed into a special shape. The low-loss dielectric material is an FR-4 glass fiber composite material.

4. The device according to claim 1, characterized in that, The waveguide antenna consists of two parts. The front section is a rectangular waveguide, and the rear section is a dielectric structure. The dielectric structure includes a rectangular dielectric structure and a pyramidal dielectric structure. The cross-section of the rectangular waveguide is rectangular, with an external length of l1, a width of w1, and a height of h1, and an internal length of l2, a width of w2, and a height of h1, which is used for the transmission of electromagnetic waves. The signal stability is ensured and the transmission loss is reduced through a constant cross-section design. The rectangular dielectric structure is closely attached to the inside of the rectangular waveguide. The length and width of the cross-section of the rectangular dielectric structure are the same as the length and width inside the waveguide, which are w2 and l2, and the height of the rectangular dielectric structure is h2. The height h3 of the pyramidal dielectric structure represents the vertical height between its upper and lower planes. The length and width of the top cross-section of the pyramidal dielectric structure are x1 and x2 respectively, and the length of the inclined connection line is x3, which geometrically optimizes the signal transmission and energy radiation performance. The loaded dielectric material is FR-4.

5. A characterization method for a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 1, characterized in that, The method includes the following steps: Step 1: Identify the sample to be tested and place the sample to be tested on the mobile stage. Step 2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. This process includes turning on the computer, the microwave vector network analyzer, and the three-dimensional mobile stage device. Step 3: Adjust the position of the three-dimensional mobile stage so that the sample to be tested is in a suitable relative position with respect to the probe. Step 4: After the computer sets the experimental parameters through the microwave nondestructive testing software, it issues an instruction to generate a signal within the working frequency range of the antenna through the microwave vector network analyzer, transmit the signal to the sample to be measured through the antenna, and receive the reflected energy. The S 11 parameter is calculated through the microwave vector network analyzer. At the same time, the computer issues an instruction to save the S 11 parameter calculated by the microwave vector network analyzer to the hard disk of the computer. Then, the computer issues an instruction to control the mobile station to move to the next position and repeat the above steps; Step 5: After the test data acquisition is completed, for the S 11 signal, use the feature extraction algorithm to achieve the imaging of the defects of the sample to be tested; Step 6: At the end of the test, save the results obtained from the test. At the same time, the computer controls the microwave vector network analyzer to make its radiation energy become 0, and at the same time controls the two-axis driver to return the three-dimensional mobile stage to zero. Step 7: After the test is completed, turn off the computer, the microwave vector network analyzer, and the three-dimensional mobile stage in sequence, and place the antenna probe and the sample to be tested in a designated storage container for proper storage.

6. The method according to claim 5, wherein The measurement parameters of the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna include: the amplitude and phase of the S 11 dB signal.

7. A nondestructive testing method for a microwave nondestructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 1, characterized in that, The method includes: (1) Generation and radiation of signals: The antenna is fed by a computer-controlled microwave vector network analyzer so that the antenna radiates an electromagnetic wave signal to the sample to be measured; (2) Scanning of the sample to be measured: After the antenna is fixed, the sample to be measured is fixed on a three-dimensional moving stage. The antenna is directly above the sample to be measured, and the three-dimensional moving stage is controlled to scan the sample to be measured; (3) Reception and processing of reflected signals: When the medium changes, impedance mismatch will occur, and signals will be reflected. The antenna receives the reflected electromagnetic wave, and by calculating the ratio of the intensity of the reflected signal to the incident signal and performing processing, an S 11 dB signal is obtained. Since the S 11 dB of different materials is different, the imaging effect after signal processing is also different, thus obtaining an image containing defects.

Images