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

Abstract

The invention relates to a microwave nondestructive testing device and method based on a dielectric loading rectangular waveguide antenna, and belongs to the technical field of antenna nondestructive testing instruments. Comprising a microwave vector network instrument, a computer, a three-dimensional mobile station and an antenna, the three-dimensional mobile station is used for placing a sample piece, one end of the antenna is arranged above the three-dimensional mobile station, the computer is respectively connected with the microwave vector network instrument and the three-dimensional mobile station, and the microwave vector network instrument is connected with the antenna. According to the invention, the signal transmission and energy radiation performance is geometrically optimized; by optimizing a waveguide feed structure and loading a specific low-loss dielectric material, higher main lobe radiation intensity and a lower radiation angle of the near-field probe are realized, so that the detection sensitivity and resolution are improved.

Description

Technical Field

[0001] The present invention relates to an antenna-based microwave non-destructive testing device and method, belonging to the technical field of antenna non-destructive testing instruments. Background Art

[0002] With the continuous development of industrial technology, 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 many fields, capable of detecting tiny defects on the surface and subsurface of materials, and effectively identifying problems such as delamination, voids, inclusions, and microstructural changes inside materials.

[0003] Traditional non-destructive testing technologies, such as phased array ultrasonic testing, X-ray imaging, and infrared thermography, although having accumulated a relatively mature technical foundation in the field of industrial testing, still have limitations in terms of detection ability, resolution, sensitivity in complex environments, and adaptability to certain specific materials and structures. 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, the publication number is CN108075235B, and the invention title is 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. 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 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 lobes, low cross polarization, low loss and small size of the antenna. The publication number is CN118073806B, and the invention title is 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-polarized waveguide antenna. The publication number is CN118758973A, and the title is 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. The bracket is installed on the three-dimensional motion stage. By controlling the microwave signal generating and analyzing instrument by the computer to feed the transmitting antenna, 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 measured is placed at the initial focusing position of the transmissive array. The computer controls the three-dimensional motion stage to move, changing the focusing focus of the transmissive array antenna, so as to realize a full scan of the object to be measured, and judge the defects of the object to be measured according to the imaging effect, improving the reliability of non-destructive testing. The publication number is CN117673736A, and the invention title is a flexible microstrip slot antenna suitable for non-destructive detection of human blood glucose concentration. Its structure includes a substrate of 28.5mm×30mm×0.4mm, a metal slotted layer and a feeder layer.It is characterized in that the material selected for the antenna medium is the flexible material polyimide (PI), which has bendability. The radiation metal layer is of a slotted design. Two auxiliary arc-shaped small slots are partially connected to the main circular slot of the antenna ground and are fed by a stub microstrip, achieving better impedance matching and dual-band characteristics within the working frequency band. The specific dimensions of the slotted gap are obtained through simulation. The present invention can be used for detecting different body positions, has multiple operating frequencies, and the dual-band response makes it have higher robustness and accuracy. The publication number is CN109696446B, and the invention title is a non-destructive detector for insect-caused defects inside trees. The detector includes: an external encapsulation 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., realizing true non-destructive detection.

[0005] Although the above technologies have made remarkable progress, there are still some problems in the practical application of existing waveguide probes. 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 structure in practical applications, restricting 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 the existing technology to meet the imaging requirements of high resolution and high sensitivity.

[0006] Therefore, it is urgent to propose a microwave non-destructive detection device and method based on a dielectric-loaded rectangular waveguide antenna to solve the above technical problems. Summary of the Invention

[0007] 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 testing device and method based on a dielectric-loaded rectangular waveguide antenna are provided. A brief overview of the present invention is given below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify the key or important parts of the present invention, nor is it intended to limit the scope of the present invention.

[0008] Technical solution of the present invention:

[0009] A microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna includes a microwave vector network analyzer, a computer, a three-dimensional moving stage, and an antenna. The three-dimensional moving stage is used to place the sample, one end of the antenna is arranged above the three-dimensional moving stage, the computer is respectively connected to the microwave vector network analyzer and the three-dimensional moving stage, and the microwave vector network analyzer is connected to the antenna.

[0010] Preferably: The antenna includes a waveguide and a dielectric structure. The waveguide is a straight square tube, and a dielectric structure is arranged inside the lower part of the waveguide. The waveguide is connected to the microwave vector network analyzer.

[0011] Preferably: The dielectric structure includes a rectangular dielectric structure and a pyramidal dielectric structure. The outside of the rectangular dielectric structure is arranged in cooperation with the inside of the dielectric structure. The rectangular dielectric structure is arranged inside the waveguide, and the lower end of the rectangular dielectric structure is connected to the pyramidal dielectric structure.

[0012] Preferably: The waveguide is a rectangular waveguide. The outside length of the waveguide is l1, the width is w1, and the height is 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 waveguide. The length l2 and width w2 of the cross-section of the rectangular dielectric structure are the same as the length and width inside the waveguide. The height of the rectangular dielectric structure is h2, the height of the pyramidal dielectric structure is h3, 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.

[0013] Preferably: l1 is 24.5 - 25, w1 is 12 - 12.26, h1 is 148 - 160, l2 is 22.65 - 23.1, w2 is 10 - 10.26, x1 is 12 - 13, x2 is 12 - 13, x3 is 10.54 - 10.57.

[0014] Preferably: The antenna 4 adopts a side-feed method with an SMA interface.

[0015] Preferably: The antenna material is FR-4.

[0016] A microwave non-destructive testing method based on a dielectric-loaded rectangular waveguide antenna, using the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna, includes the following steps:

[0017] Step 1: Generation and radiation of signals: 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;

[0018] Step 2: Scanning of the sample to be tested: The three-dimensional moving stage is controlled to scan the sample to be tested;

[0019] Step 3: Reception and processing of the reflected signals.

[0020] Preferably: In Step 1, it includes the following steps:

[0021] Step 1.1: Place the test piece on the three-dimensional moving stage;

[0022] Step 1.2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna;

[0023] Step 1.3: Adjust the position of the three-dimensional moving stage to adjust the relative position between the test piece and the antenna;

[0024] Step 1.4: After the computer sets the experimental parameters through the microwave non-destructive testing software, it issues an instruction to generate a signal within the working frequency range of the antenna through the microwave vector network analyzer, transmit the signal to the sample to be tested 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 vector network analyzer to the hard disk of the computer;

[0025] In Step 2, the computer issues an instruction to control the three-dimensional moving stage to move to the next position and repeat the above Step 1.4;

[0026] In Step 3, it includes the following steps:

[0027] Step 3.1: After the test data acquisition is completed, for the S 11 signal, the maximum value, minimum value, and principal component analysis feature extraction algorithm are used to realize the imaging of the defects of the sample to be tested;

[0028] Step 3.2: 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.

[0029] The present invention has the following beneficial effects:

[0030] The antenna of the present invention has good matching characteristics at the working frequency point, high energy transfer efficiency, and meets the actual needs;

[0031] The structure of the present invention is ingenious and suitable for various industrial detection scenarios;

[0032] The present invention geometrically optimizes the signal transmission and energy radiation performance; by optimizing the waveguide feeding structure and loading specific low-loss dielectric materials, a higher main lobe radiation intensity and a lower radiation angle of the near-field probe are achieved, thereby improving the detection sensitivity and resolution;

[0033] 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 is increased, the 3dB beam width is narrowed, and the lateral resolution is improved by 46% to reach 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. Brief Description of the Drawings

[0034] Figure 1 is a schematic structural diagram of a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna.

[0035] Figure 2 is an exploded view of the antenna.

[0036] Figure 3 is a bottom view of the antenna.

[0037] Figure 4 is a sectional view of the antenna.

[0038] Figure 5 is an S11 parameter diagram of the antenna.

[0039] Figure 6 is a comparison diagram of the maximum gain of the main lobe of the antenna.

[0040] Figure 7 is a comparison diagram of the 3dB beam width of the antenna at f = 11.846 GHz.

[0041] Figure 8 is a solid propellant simulation sample.

[0042] Figure 9 is the detection result of the original waveguide antenna.

[0043] Figure 10 is the detection result of the dielectric-loaded rectangular waveguide antenna.

[0044] Figure 11 is a high-silica phenolic resin composite simulation sample.

[0045] Figure 12 is the detection result of the original waveguide antenna.

[0046] Figure 13 It is based on the detection results of the optimized dielectric-loaded rectangular waveguide antenna.

[0047] Figure 14 It is the experimental result of double-line scanning using a rectangular waveguide probe when SOD = 1 mm:

[0048] (a) Amplitude response; (b) Phase response.

[0049] Figure 15 It is the experimental result of double-line scanning using the proposed probe when SOD = 1 mm:

[0050] (a) Amplitude response; (b) Phase response.

[0051] In the figure: 1 - Microwave vector network analyzer, 2 - Computer, 3 - Three-dimensional moving stage, 4 - Antenna, 5 - Specimen, 6 - Waveguide, 7 - Dielectric structure, 8 - Rectangular dielectric structure, 9 - Pyramidal dielectric structure. Specific implementation manners

[0052] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are only exemplary and do not intend to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0053] Specific implementation manner 1: In combination with Figure 1-7 This implementation manner will be described. The microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna of this implementation manner includes a microwave vector network analyzer 1, a computer 2, a three-dimensional moving stage 3 and an antenna 4. The three-dimensional moving stage 3 is used to place the specimen 5. One end of the antenna 4 is fixedly arranged above the three-dimensional moving stage 3 through a bracket. The computer 2 is electrically connected to the microwave vector network analyzer 1 and the three-dimensional moving stage 3 respectively, and the microwave vector network analyzer 1 is electrically connected to the antenna 4; A microwave vector network analyzer, also known as a vector network analysis instrument, 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 the test data using a Smith chart.

[0054] The antenna 4 is a dielectric-loaded rectangular waveguide antenna, including a waveguide 6 and a dielectric structure 7. The waveguide 6 is a straight square tube. The dielectric structure 7 is arranged inside the lower part of the waveguide 6. The upper part of the waveguide 6 is electrically connected to the microwave vector network analyzer 1;

[0055] The solid dielectric structure 7 includes a rectangular dielectric structure 8 and a pyramidal dielectric structure 9. The external shape and size of the rectangular dielectric structure 8 are set to match the shape and size of the internal cavity of the dielectric structure 7. The rectangular dielectric structure 8 is disposed within the waveguide 6. The lower end of the rectangular dielectric structure 8 is integrally connected to the pyramidal dielectric structure 9, and the pyramidal dielectric structure 9 is located outside the lower part of the waveguide 6.

[0056] The waveguide 6 is a rectangular waveguide with a rectangular cross-section. The external length of the waveguide 6 is l1, the width is w1, and the height is h1. The internal length is l2, the width is w2, and the height is h1. It is mainly used for the transmission of electromagnetic waves. By means of a constant cross-sectional design, signal stability is ensured and transmission loss is reduced. The rectangular dielectric structure 8 fits tightly inside the waveguide 6. The length l2 and width w2 of the cross-section of the rectangular dielectric structure 8 are the same as the length and width inside the waveguide 6. The height of the rectangular dielectric structure 8 is h2, where h2 < h1. The height of the pyramidal dielectric structure 9 is h3, representing the vertical height between its upper and lower planes. The side surface of the pyramidal dielectric structure 9 is an isosceles trapezoid, and the lower and upper end faces are square. The length and width of the top cross-section of the pyramidal dielectric structure 9 are x1 and x2 respectively, and the length of the inclined connecting line is x3, where x2 > w2 and l2 > x1. Geometrically, the signal transmission and energy radiation performance are optimized. By optimizing the waveguide feeding structure and loading a specific low-loss dielectric material, a higher main lobe radiation intensity and a lower radiation angle of the near-field probe are achieved, thereby improving the detection sensitivity and resolution.

[0057] l1 ranges from 24.5 to 25, w1 ranges from 12 to 12.26, h1 ranges from 148 to 160, l2 ranges from 22.65 to 23.1, w2 ranges from 10 to 10.26, x1 ranges from 12 to 13, x2 ranges from 12 to 13, and x3 ranges from 10.54 to 10.57 (mm).

[0058] The optimal parameters adopted are shown in Table 1 below:

[0059] Table 1 Geometric parameters of the antenna

[0060]

[0061] As Figure 5 shown, the smaller the value of S 11 (dB), the less the reflected radiation power, and the better the antenna matching. The closer S 11 (dB) is to 0, the less energy the antenna radiates outward (in a state of impedance mismatch), and the worse the antenna performance. It can be visually seen from the figure that when the antenna operates at the working frequencies f = 8.56 GHz, 10.46 GHz, 11.14 GHz, and 11.85 GHz, the echo loss is less than -10 dB, indicating that the antenna has good matching characteristics at the working frequency points, high energy transfer efficiency, and meets the actual requirements.

[0062] As Figure 6 shown is the comparison chart 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, indicating that the performance of the optimized antenna has been improved compared to the original antenna.

[0063] Figure 7 Shown is the comparison chart of the 3dB beamwidth between 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 for high-precision non-destructive testing imaging. It can be seen from the figure that at the operating frequency, the 3dB beamwidth 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 compared to the original antenna. The 3dB beamwidth 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.

[0064] The present invention proposes a dielectric-loaded rectangular waveguide antenna for microwave non-destructive testing. By optimizing the waveguide feeding structure and loading a specific low-loss dielectric material, higher main lobe radiation intensity and lower radiation angle of the near-field probe are achieved, 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 on-line detection scenarios, providing an efficient and accurate non-destructive testing solution for modern industry and making up for the deficiencies in existing rectangular waveguides.

[0065] The dielectric material loaded on the antenna 4 is FR-4, which is creatively combined with the specially designed structure of the antenna 4, having more excellent mechanical properties and electromagnetic properties. The present invention enables the probe to achieve better impedance matching in the frequency band of 8.2 - 12.4GHz through the dielectric loading technology, improves the main lobe peak gain, narrows the 3dB beamwidth, and the lateral resolution is improved 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 - 8.5mm. Impedance matching is mainly used on the 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 the 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 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 the impedance matching state, simply referred to as impedance matching.

[0066] The antenna 4 adopts a side-feed method with an SMA interface; the full name of the SMA interface is SubMiniature version A, and there are two forms of the SMA interface. The standard SMA has "external thread + hole" at one end and "internal thread + pin" at the other end; the reverse-polarity RP-SMA has "external thread + pin" at one end and "internal thread + hole" at the other end.

[0067] Specific Embodiment 2: In combination with Figure 1-7 This embodiment is described. The microwave non-destructive testing method based on a dielectric-loaded rectangular waveguide antenna in this embodiment uses the microwave non-destructive testing device described in Specific Embodiment 1. The main measurement parameters of a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna include: S 11 The amplitude and phase of the dB signal. The computer 2 is respectively connected to the microwave vector network analyzer 1 and the three-dimensional moving stage 3; the computer 2 is mainly used to control the microwave vector network analyzer 1 to generate signals, the movement of the three-dimensional moving stage 3, the signal recording and storage of the microwave vector network analyzer 1, etc.; the computer 2 controls the microwave vector network analyzer 1 to generate a suitable signal and radiate it outward through the antenna; the microwave vector network analyzer 1 is connected to the antenna 4 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 the 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 measured have relative movement to realize the scanning of the sample to be measured.

[0068] The present invention is applicable to fields such as electromagnetic science and detection and signal processing. In particular, 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 system are applicable to the field of precise quantitative evaluation of holes / debonding defects in aerospace insulation composite materials;

[0069] The method includes the following steps:

[0070] Step 1: Generation and radiation of signals: The computer 2 controls the microwave vector network analyzer 1 to feed the antenna 4, so that the antenna 4 radiates an electromagnetic wave signal to the sample 5 to be measured.

[0071] In Step 1, the following steps are included:

[0072] Step 1.1: Identify the test piece to be measured and place the test piece 5 on the three-dimensional moving stage 3.

[0073] Step 1.2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. This process includes turning on devices such as the computer, microwave vector network analyzer, and three-dimensional moving stage.

[0074] Step 1.3: Adjust the position of the three-dimensional mobile stage 3, and adjust the relative position between the specimen 5 to be tested and the antenna 4 so that the specimen 5 to be tested is in a suitable initial position relative to the antenna 4 (probe).

[0075] Step 1.4: After the computer 2 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 4 through the microwave vector network analyzer 1. The signal is transmitted to the specimen 5 to be tested through the antenna 4, and the reflected energy is received. The S 11 parameter is calculated through the microwave vector network analyzer 1. At the same time, the computer issues an instruction to save the S 11 parameter calculated by the vector network analyzer to the hard disk of the computer 2.

[0076] Step 2: Scanning of the specimen to be tested: Control the three-dimensional mobile stage 3 to perform multi-position scanning on the specimen 5 to be tested.

[0077] In Step 2, the computer issues an instruction to control the three-dimensional mobile stage 3 to move to the next position and repeat the above Step 1.4.

[0078] Step 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. By calculating the ratio of the intensity of the reflected signal to the incident signal and performing processing, 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, thus obtaining an image containing defects; where S 11 dB: S 11 is the reflection coefficient at the input end, indicating the degree of reflection of the signal input from port 1 at 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.

[0079] Step 3 includes the following steps:

[0080] Step 3.1: 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; Step 3.2: After the test is completed, save the results obtained from the test. At the same time, the computer 2 controls the microwave vector network analyzer 1 to make its radiation energy become 0, and at the same time controls the two-axis driver to zero the three-dimensional mobile stage 3.

[0081] It also includes Step 4. 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 specimen to be tested in a designated storage container for proper storage.

[0082] The present invention is easy to operate and implement, with high detection efficiency and accuracy;

[0083] The main lobe gain refers to the signal gain of the antenna in a certain direction when it points to 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 one of the important indicators for describing the anti-interference ability of the antenna; 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, a pyramid-shaped dielectric loading structure is innovatively adopted, and a new waveguide-dielectric coupling radiation mechanism is proposed. By optimizing the dielectric material and geometric parameters, the antenna has a stronger main lobe radiation intensity and a 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 compensate 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 modular loading mechanism design and can replace different dielectric structures according to actual needs.

[0084] Example 1:

[0085] Combined with Figure 1 、 2 Examples 3, 4, 8, 9, and 10 adopt a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna. The sample to be measured is a solid propellant simulation sample. An experimental control software is developed based on C / C++ and installed in a computer for controlling the microwave vector network analyzer, three-dimensional mobile stage, data processing, and imaging; 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, an FR-4 glass fiber composite material waveguide antenna is used, which 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 structure is as Figure 2As shown in the figure; the cross-section of the rectangular waveguide is rectangular, with an external length of l1, a width of w1, and a height of h1. The internal length is l2, the width is w2, and the height is h1. It is mainly used for the transmission of electromagnetic waves. By maintaining a constant cross-sectional design, signal stability is ensured and transmission loss is reduced. The rectangular dielectric structure fits tightly inside the rectangular waveguide. The length and width of the cross-section of the rectangular dielectric structure are the same as those inside the waveguide, which are w2 and l2, and the height of the rectangular dielectric structure is h2. The height h3 of the conical dielectric structure represents the vertical height between its upper and lower planes. The length and width of the top cross-section of the conical 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 internal filling material of the entire antenna is FR-4, which has excellent mechanical and electromagnetic properties.

[0086] This detection method is in the point-scanning mode. During each scanning point's scanning cycle, first, a signal is generated by the microwave vector network analyzer 1. 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 receives the feed, it generates an electromagnetic wave and radiates it outward. By mounting the antenna on the fixed frame of the three-dimensional mobile stage 3 and controlling the movement of the three-dimensional mobile stage, the scanning of the solid propellant simulated sample is completed; when the microwave signal encounters media with different impedances, the signal will change. Therefore, there are obvious differences between the signals of the defective and intact regions, based on which it can be determined whether there are defects. The information of the microwave signal includes amplitude and phase, and the real and 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 simulated sample to move, the scanning of the solid propellant simulated sample can be realized, and imaging based on the obtained S11dB signal can achieve non-destructive detection of the internal defects of the solid propellant simulated sample. As Figure 8 shown is the solid propellant simulated sample. Figure 9 shown is the detection result of the original waveguide antenna, Figure 10 shown is the detection result of the dielectric-loaded rectangular waveguide antenna proposed after optimizing the waveguide antenna. 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 relatively high clarity. Although the other defects can be detected, their clarity is relatively low and the boundaries are not clear. While Figure 10 the defect morphology in it is restored relatively well, with relatively 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.

[0087] The microwave vector network analyzer refers to a device that can generate and record microwave signals. 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 signals to the antenna through a cable and an SMA interface; the antenna is responsible for radiating the signals. The gain of the proposed antenna is determined during design and cannot be changed once determined.

[0088] Embodiment 2:

[0089] Combined with Figure 1 、 2 、3, 4, 11, 12, 13 of this embodiment, as Figure 5 shown, a microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna. In this embodiment, the sample to be tested is a high-silica phenolic resin glass fiber composite material. It is mainly composed of glass fibers and a resin matrix and has low conductivity. 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 operating 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 by the antenna. 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 dot 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. 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, the amplitude and phase of the S 11 dB signal are calculated. When the electromagnetic wave encounters the interface of different materials, reflection occurs, and the amplitude and phase will show corresponding changes, so that defects inside the material can be detected. Through the control software, the microwave vector network analyzer and the three-dimensional moving 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. Realize non-destructive defect location and evaluation. As Figure 11 shown is a simulated sample of 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 optimized based on the waveguide antenna. From Figure 12 and Figure 13 it can be seen that Figure 12 the boundary of the defect in it 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 has a good contrast compared with the intact area. It shows that the designed dielectric-loaded rectangular waveguide antenna reduces the distortion of the shape of the measured defect image during imaging and increases the resolution of the measured defect image.

[0090] Example 3:

[0091] Combined with Figure 1 、 2 、Examples 3, 4, 14, and 15, in this example, 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 stand-off distance (SOD) of 1 mm, relative movement between the probe and the wires is carried out along the x-axis, and the total scanning distance of the experiment is 40 mm. A single probe is used to scan the 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 is still not recognizable. Two distinct 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 15 Shows that when the wire spacing is reduced to 4 mm, the resolution ability of the proposed probe is limited. When D = 4 mm, only a central peak is observed, and the wires are not successfully distinguished. Two resolvable peaks appear at D = 6 mm, confirming that the wires with a 6 mm spacing can be successfully distinguished. The experimental results show that 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.

[0092] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be arranged and combined. Those skilled in the art can exhaust all possibilities according to the mathematical knowledge of permutation and combination. Therefore, the present invention will not explain the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0093] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna, characterized in that: It includes a microwave vector network analyzer (1), a computer (2), a three-dimensional mobile stage (3) and an antenna (4). The three-dimensional mobile stage (3) is used to place the sample (5). One end of the antenna (4) is arranged above the three-dimensional mobile stage (3). The computer (2) is respectively connected to the microwave vector network analyzer (1) and the three-dimensional mobile stage (3), and the microwave vector network analyzer (1) is connected to the antenna (4).

2. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 1, characterized in that: The antenna (4) includes a waveguide (6) and a dielectric structure (7). The waveguide (6) is a straight rectangular tube. The dielectric structure (7) is arranged on the inner side of the lower part of the waveguide (6). The waveguide (6) is connected to the microwave vector network analyzer (1).

3. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 2, wherein: The dielectric structure (7) includes a rectangular dielectric structure (8) and a pyramidal dielectric structure (9). The outside of the rectangular dielectric structure (8) is arranged in cooperation with the inside of the dielectric structure (7). The rectangular dielectric structure (8) is arranged in the waveguide (6), and the lower end of the rectangular dielectric structure (8) is connected to the pyramidal dielectric structure (9).

4. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 3, characterized in that: The waveguide (6) is a rectangular waveguide. The outside length of the waveguide (6) is l1, the width is w1, and the height is 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 (8) is closely attached to the inside of the waveguide (6). The length l2 and width w2 of the cross-section of the rectangular dielectric structure (8) are the same as the length and width inside the waveguide (6). The height of the rectangular dielectric structure (8) is h2, the height of the pyramidal dielectric structure (9) is h3, the length and width of the top cross-section of the pyramidal dielectric structure (9) are x1 and x2 respectively, and the length of the inclined connecting line is x3. The signal transmission and energy radiation performance are geometrically optimized.

5. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 4, wherein: l1 is 24.5 - 25, w1 is 12 - 12.26, h1 is 148 - 160, l2 is 22.65 - 23.1, w2 is 10 - 10.26, x1 is 12 - 13, x2 is 12 - 13, x3 is 10.54 - 10.

57.

6. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to any one of claims 1-4, characterized in that: The material of the antenna (4) is FR-4.

7. The microwave non-destructive testing device based on a dielectric-loaded rectangular waveguide antenna according to claim 6, wherein: The antenna (4) adopts a side-feed method with an SMA interface.

8. A microwave non-destructive testing method based on a dielectric-loaded rectangular waveguide antenna, characterized in that: Adopt the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna described in any one of claims 1 - 7, including the following steps: Step 1: Generation and radiation of signals: Control the microwave vector network analyzer (1) by the computer (2) to feed the antenna (4), so that the antenna (4) radiates electromagnetic wave signals to the sample (5) to be measured. Step 2: Scanning of the sample to be measured: Control the three-dimensional mobile stage (3) to scan the sample (5) to be measured. Step 3: Reception and processing of the reflected signal.

9. The microwave non-destructive testing method based on a dielectric-loaded rectangular waveguide antenna according to claim 8, wherein: In Step 1, it includes the following steps: Step 1.1: Place the test piece (5) on the three-dimensional mobile stage (3). Step 1.2: Turn on the microwave non-destructive testing device based on the dielectric-loaded rectangular waveguide antenna. Step 1.3: Adjust the position of the three-dimensional mobile stage (3) to adjust the relative position between the test piece (5) to be measured and the antenna (4). Step 1.4: After setting the experimental parameters through the microwave non-destructive testing software, the computer (2) issues an instruction. The microwave vector network analyzer (1) generates a signal within the working frequency range of the antenna (4), transmits the signal to the sample to be measured (5) through the antenna (4), and receives the reflected energy. The S 11 parameter is calculated through the microwave vector network analyzer (1). At the same time, the computer issues an instruction to save the S 11 parameter calculated by the vector network analyzer to the hard disk of the computer (2); In Step 2, the computer issues an instruction to control the three-dimensional mobile stage (3) to move to the next position, and repeat the above Step 1.

4. In Step 3, it includes the following steps: Step 3.1: After the test data acquisition is completed, for the S 11 signal, use the maximum value, minimum value, and principal component analysis feature extraction algorithm to realize the imaging of the defects of the sample to be tested; Step 3.2: At the end of the test, save the results obtained from the test. Meanwhile, the computer (2) controls the microwave vector network analyzer (1) to make its radiation energy become 0.

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