Chipless rfid metal crack sensing tag integrated with frequency band encoding and identification method
By integrating frequency band coding into a chipless RFID metal crack sensing tag, and utilizing a concentric arc patch grouping design and a hollowed-out structure in the center of the metal base plate, the problems of increased tag area and high detection cost are solved. This achieves high-sensitivity crack monitoring and coding flexibility, and supports remote real-time detection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA RAILWAY TENTH BUREAU GRP ELECTRIC ENG CO LTD
- Filing Date
- 2026-02-12
- Publication Date
- 2026-07-10
AI Technical Summary
Existing chipless RFID metal crack sensing tags require increased tag area when integrating identification codes, which limits their application and large-scale deployment. Furthermore, traditional crack detection technologies are costly, complex to operate, and difficult to monitor remotely in real time.
The chipless RFID metal crack sensing tag with integrated frequency band coding uses a concentric arc patch grouping design. The first group is used for frequency band coding, and the second group is used for polarization direction identification. Combined with the coaxial cutout design in the center of the metal base plate, it realizes tag identification coding and crack monitoring.
It achieves highly sensitive crack detection, combines coding flexibility without increasing tag size, supports remote real-time monitoring, and reduces cost and complexity.
Smart Images
Figure CN122366492A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of contactless identification technology, and specifically relates to a chipless RFID metal crack sensing tag with integrated frequency band coding and an identification method. Background Technology
[0002] Structural health monitoring is a key technology for ensuring the safety of infrastructure such as buildings, bridges, and aircraft. If cracks in metal structures caused by fatigue or external forces are not detected in time, they may lead to safety hazards.
[0003] Traditional crack detection technologies (ultrasonic, magnetic leakage, eddy current, etc.) suffer from drawbacks such as high cost, complex operation, large manpower requirements, and difficulty in remote real-time monitoring. Chipless RFID sensors, as an important branch of microwave sensing, have emerged as a novel solution due to their low cost and wireless transmission advantages. However, existing inventions have limitations such as the need to increase tag size for integrated identification coding schemes, restricting tag application and large-scale deployment.
[0004] Therefore, there is an urgent need to develop a chipless RFID crack sensing tag that combines high sensitivity with integrated identification coding function without increasing tag size, in order to meet the actual needs of the structural health monitoring field. Summary of the Invention
[0005] In view of this, the present invention provides a chipless RFID metal crack sensing tag with integrated frequency band coding, including a dielectric substrate, a tag patch unit and a metal base plate, wherein the tag patch unit is disposed on the upper surface of the dielectric substrate and the metal base plate is disposed on the lower surface of the dielectric substrate. The tag patch unit includes a disc patch antenna and six arc patches.
[0006] Preferably, the disk patch antenna is disposed at the center of the dielectric substrate; the six arc patches are all concentrically distributed in an arc shape with the center of the disk patch antenna as the common center, and are divided into two groups: The first group consists of four arc-shaped patches, evenly distributed around the common center in four directions: above, below, left, and right, with equal distances from the common center. The second group consists of two arc-shaped patches distributed circumferentially above and below the common center. They are equidistant from the common center and closer to it than the arc-shaped patches in the first group, and do not contact the arc-shaped patches in the first group.
[0007] Preferably, the metal base plate has a circular cutout in the central area, the circular cutout is coaxially arranged with the disc patch antenna, and the radius of the circular cutout is equal to the radius of the disc patch antenna.
[0008] Preferably, the disk patch antenna is used to realize the sensing function of cracks on the metal surface.
[0009] Preferably, the arc patch in the first group is used to realize the identification encoding of chipless RFID tags. It adopts frequency band encoding technology and changes the position of the resonant point in the RCS spectrum of the tag by adjusting the arc length, thereby realizing the configuration of the tag identification encoding.
[0010] Preferably, the arc patch of the second group is used to identify the polarization direction of the excitation signal emitted by the reader. The polarization direction of the incident wave is determined by detecting whether a resonant point appears in a specific frequency band of the tag's RCS spectrum, thereby helping to determine the crack direction.
[0011] To achieve the above objectives, the present invention also provides a method for identifying chipless RFID metal crack sensing tags with integrated frequency band coding, comprising the following steps: S10, when the electromagnetic waves emitted by the reader irradiate the label surface, the disc patch antenna receives the electromagnetic waves and is excited to generate surface current. S20, with six arc patches serving as encoding and polarization identification units, works in conjunction with the disk patch antenna to generate specific scattered electromagnetic wave signals; S30, by receiving and parsing the scattered signal, the reader can simultaneously obtain the tag's identification code information and the polarization direction of the incident electromagnetic wave; S40, when a crack is generated and propagates in the metal structure under test, the crack changes the electromagnetic environment around the tag, causing changes in the amplitude and phase characteristic parameters of the scattered electromagnetic wave. The S50 can monitor and identify metal cracks by analyzing the variation of scattered signals.
[0012] The present invention provides a chipless RFID metal crack sensing tag with integrated frequency band coding. Compared with the existing chipless RFID metal crack sensing tags that use "multi-resonant unit binary coding" (which requires increasing the coding capacity by adding resonant units, resulting in an increase in tag size), the present invention uses frequency band coding technology to change the resonant frequency by adjusting the length of the arc patch to achieve identification coding. It has the advantages of flexible coding and no need to increase the tag size.
[0013] This solution has the following significant differences compared to conventional RFID sensors: 1. Functionalization of concentric arc patches: The six concentric arc patches are divided into two groups, one of which is dedicated to "frequency band coding" (increasing coding capacity without increasing size), and the other is dedicated to "identifying polarization direction".
[0014] 2. Automatic polarization direction identification mechanism: By determining whether the reader signal is horizontally or vertically polarized by whether the first set of arc patches has a resonant point in a specific frequency band (such as around 5GHz), a reference assistance is provided for the subsequent determination of crack direction (0°, 45°, 90°, etc.).
[0015] 3. Coaxial, equal-radius cutout base plate design: The metal base plate has a cutout at its center that is coaxial with and has the same radius as the front-facing circular antenna. This design is not simply for weight reduction, but to enhance the electromagnetic coupling between the crack and the antenna, thereby improving sensing sensitivity. Attached Figure Description
[0016] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 Figure (a) is a front view and Figure (b) is a back view. Figure 2 This is a test schematic diagram of a chipless RFID metal crack sensing tag with integrated frequency band coding according to the present invention. Figure 3 This is an RCS curve of a chipless RFID metal crack sensing tag with integrated frequency band coding under crack-free conditions according to the present invention. Figure 4 The present invention relates to a chipless RFID metal crack sensing tag with integrated frequency band coding. Figure (a) shows the surface current distribution at each resonant point under horizontally polarized electromagnetic wave excitation, and Figure (b) shows the surface current distribution at each resonant point under vertically polarized electromagnetic wave excitation. Figure 5 This is a schematic diagram of the identification encoding of a chipless RFID metal crack sensing tag with integrated frequency band encoding according to the present invention. Figure (a) shows the excitation of vertical polarized waves under each encoding, and Figure (b) shows the excitation of horizontal polarized waves under each encoding. Figure 6 Figure (a) shows the response curves of a chipless RFID metal crack sensing tag with integrated frequency band coding, which is placed on cracks in different directions according to the present invention. Figure (b) shows the response curve of the vertically polarized electromagnetic wave and the response curve of the horizontally polarized electromagnetic wave. Figure 7 The simulation results of a chipless RFID metal crack sensing tag with integrated frequency band coding of the present invention are placed on metal crack samples with different widths in the vertical direction. Figure (a) is the response curve under horizontal polarization wave excitation and Figure (b) is the response curve under vertical polarization wave excitation. Figure 8This is a response curve of a chipless RFID metal crack sensing tag with integrated frequency band coding according to the present invention, which detects cracks of different widths in the horizontal direction using vertical polarization waves. Detailed Implementation
[0017] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0018] See Figure 1 This is a schematic diagram of the structure of a chipless RFID metal crack sensing tag with integrated frequency band coding according to the present invention. It includes a dielectric substrate 20, a tag patch unit and a metal base plate 30. The tag patch unit is disposed on the upper surface of the dielectric substrate 20 and the metal base plate 30 is disposed on the lower surface of the dielectric substrate 20. The tag patch unit includes a disc patch antenna 11 and six arc-shaped patches. The disc patch antenna 11 is located at the center of the dielectric substrate 20; the six arc-shaped patches are all concentrically distributed in an arc shape with the center of the disc patch antenna 11 as the common center, and are divided into two groups: The first group of 12 consists of four arc-shaped patches, evenly distributed around the circumference at the top, bottom, left, and right of the common center, with equal distances from the common center. The second group 13 consists of two arc-shaped patches distributed circumferentially above and below the common center. They are equidistant from the common center and closer to it than the arc-shaped patches in the first group 12. They do not contact the arc-shaped patches in the first group 12.
[0019] The metal base plate 30 has a circular cutout 31 in the center area. The circular cutout 31 is coaxially arranged with the disc patch antenna 11, and the radius of the circular cutout 31 is equal to the radius of the disc patch antenna 11.
[0020] The disc patch antenna 11 is used to sense cracks on the metal surface. The first group 12 consists of arc-shaped patches used for identification encoding of chipless RFID tags. Frequency band coding technology is employed; by adjusting the arc length, the position of the resonant point in the tag's RCS spectrum is changed, thus configuring the tag's identification encoding. The second group 13 consists of arc-shaped patches used to identify the polarization direction of the excitation signal emitted by the reader. By detecting whether a resonant point appears in a specific frequency band of the tag's RCS spectrum, the polarization direction of the incident wave is determined, thereby assisting in determining the crack direction.
[0021] To achieve the above objectives, the present invention also provides a method for identifying chipless RFID metal crack sensing tags with integrated frequency band coding, comprising the following steps: S10, when the electromagnetic waves emitted by the reader irradiate the label surface, the disc patch antenna receives the electromagnetic waves and is excited to generate surface current. S20, with six arc patches serving as encoding and polarization identification units, works in conjunction with the disk patch antenna to generate specific scattered electromagnetic wave signals; S30, by receiving and parsing the scattered signal, the reader can simultaneously obtain the tag's identification code information and the polarization direction of the incident electromagnetic wave; S40, when a crack is generated and propagates in the metal structure under test, the crack changes the electromagnetic environment around the tag, causing changes in the amplitude and phase characteristic parameters of the scattered electromagnetic wave. The S50 can monitor and identify metal cracks by analyzing the variation of scattered signals.
[0022] To facilitate a detailed description of the embodiments, Table 1 lists the specific dimensional parameters of the designed tag structure. The dielectric substrate material is Rogers RO4350B (dielectric constant of 3.66 and loss tangent of 0.004), which is suitable for high-frequency sensing scenarios.
[0023] Table 1. Size parameters of metal crack sensor tags
[0024] The specific test block diagram of the chipless RFID tag of this invention is as follows: Figure 2 As shown, the test system includes a reader, the sensing tag of this invention, and a metal plate under test. A simulation test system was constructed using CST electromagnetic simulation software. A crack-free metal plate was placed on the back of the tag. The reader excited the tag using horizontally polarized and vertically polarized electromagnetic wave signals, respectively. The simulated RCS (radar cross section) spectrum data is shown below. Figure 3 As shown. Analysis Figure 3 The spectrum curves show that when the tag emits horizontally polarized electromagnetic waves, it forms three resonant frequencies in the spectrum, located at 5.05 GHz, 6.49 GHz, and 6.81 GHz, respectively; when it emits vertically polarized electromagnetic waves, the tag exhibits two resonant frequencies in the spectrum, located at 6.42 GHz and 6.84 GHz, respectively.
[0025] To clarify the mechanism by which the above resonant frequencies are generated, Figure 4Simulations demonstrate the current distribution on the tag surface at various resonant frequencies. The current distribution results show that under horizontally polarized electromagnetic wave excitation, the second group of 13 arc-shaped patches used for polarization identification, the disk patch antenna used for crack sensing, and the first group of 12 upper and lower arc-shaped patches used for identification coding generate strong surface currents at 5.05 GHz, 6.49 GHz, and 6.81 GHz, respectively. Under vertically polarized electromagnetic wave excitation, only the disk patch antenna used for crack sensing and the first group of upper and lower arc-shaped patches used for identification coding generate strong surface currents at 6.42 GHz and 6.84 GHz, respectively. This phenomenon indicates that the polarization direction of the excitation electromagnetic wave can be identified by determining whether a resonant point exists near the 5 GHz band, providing auxiliary information for subsequent crack direction determination.
[0026] Implementation of label encoding scheme To meet the needs of large-scale metal crack monitoring scenarios, each sensor tag needs to be uniquely identified to determine its placement within the monitoring environment. This invention employs a frequency band coding method. By adjusting the arc length of the four arc patches in the first group of 12, their resonant positions in the RCS spectrum are changed. Different resonant frequency bands correspond to different coding information, thus achieving tag identification.
[0027] Figure 5 Simulations demonstrate the RCS resonance characteristics of the tags corresponding to the first group of 12 circular arc patches with different arc lengths. As shown in the figures, adjusting the arc length of the circular arc patch significantly alters the frequency position of the resonant point. Furthermore, this encoding method does not require increasing the overall tag size, offering a high degree of coding flexibility compared to existing chipless RFID metal crack tag encoding schemes. Table 2 lists the specific dimensions of the circular arc patches and their corresponding tag encoding information in this embodiment, realizing frequency band-based binary identity encoding.
[0028] Table 2 Label Encoding Information
[0029] Implementation of crack direction sensing by tags Figure 6 The RCS spectrum characteristics of the tag are shown when horizontally polarized and vertically polarized electromagnetic waves are used to excite the metal plate under test with cracks in different directions. Figure 7 This reflects the influence of cracks of different widths on the tag's resonance characteristics. To facilitate rapid identification of crack direction through spectral resonance characteristics, Table 3 summarizes the tag resonance characteristics under different combinations of crack direction and electromagnetic wave polarization direction.
[0030] Table 3. Tag resonance characteristics corresponding to different crack directions
[0031] Based on the above simulation analysis, the present invention adopts a dual-polarization detection mode to identify the crack direction. The specific process is as follows: the reader emits horizontally polarized and vertically polarized electromagnetic waves to excite the tag in turn, records and analyzes the RCS spectrum resonance characteristics under the two excitations, and obtains the crack direction information by judging whether there is a polarization identification resonance point and the frequency shift law of the disk patch antenna resonance point and referring to the resonance characteristic correspondence in Table 3.
[0032] Implementation of a tag-based crack width sensing scheme Figure 8 The RCS spectrum characteristics of the tag corresponding to different crack widths are shown when a metal plate with a horizontal crack is excited by a vertically polarized electromagnetic wave. As can be seen from the figure, the resonant frequency corresponding to the disk patch antenna shows a regular and significant shift trend as the crack width increases. To achieve quantitative detection of crack width, this invention can establish a fitting formula (1) to construct the correspondence between crack width and resonant frequency shift. Based on this fitting relationship, the width information of the crack under test can be calculated.
[0033] (1) in This represents the offset of the resonant point of the disk patch antenna compared to its state without cracks. This indicates the crack width.
[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A chipless RFID metal crack sensing tag with integrated frequency band coding, characterized in that, It includes a dielectric substrate, a label attaching unit, and a metal base plate. The label attaching unit is disposed on the upper surface of the dielectric substrate, and the metal base plate is disposed on the lower surface of the dielectric substrate. The tag patch unit includes a disc patch antenna and six arc patches.
2. The chipless RFID metal crack sensing tag with integrated frequency band coding according to claim 1, characterized in that, The disk patch antenna is positioned at the center of the dielectric substrate; the six arc patches are all concentrically distributed in an arc shape with the center of the disk patch antenna as the common center, and are divided into two groups: The first group consists of four arc-shaped patches, evenly distributed around the common center in four directions: above, below, left, and right, with equal distances from the common center. The second group consists of two arc-shaped patches distributed circumferentially above and below the common center. They are equidistant from the common center and closer to it than the arc-shaped patches in the first group, and do not contact the arc-shaped patches in the first group.
3. The chipless RFID metal crack sensing tag with integrated frequency band coding according to claim 2, characterized in that, The metal base plate has a circular cutout in the center area. The circular cutout is coaxially arranged with the disc patch antenna, and the radius of the circular cutout is equal to the radius of the disc patch antenna.
4. The chipless RFID metal crack sensing tag with integrated frequency band coding according to claim 2, characterized in that, The disk patch antenna is used to detect cracks on the metal surface.
5. The chipless RFID metal crack sensing tag with integrated frequency band coding according to claim 2, characterized in that, The first set of arc patches is used to realize the identification encoding of chipless RFID tags. It adopts frequency band encoding technology and changes the position of the resonant point in the RCS spectrum of the tag by adjusting the arc length, thereby realizing the configuration of the tag identification encoding.
6. The chipless RFID metal crack sensing tag with integrated frequency band coding according to claim 2, characterized in that, The second set of arc patches is used to identify the polarization direction of the excitation signal emitted by the reader. By detecting whether a resonant point appears in a specific frequency band of the tag's RCS spectrum, the polarization direction of the incident wave is determined, thereby helping to determine the crack direction.
7. A method for identifying a chipless RFID metal crack sensing tag with integrated frequency band coding, comprising the chipless RFID metal crack sensing tag with integrated frequency band coding as described in any one of claims 1-6, characterized in that, Includes the following steps: S10, when the electromagnetic waves emitted by the reader irradiate the label surface, the disc patch antenna receives the electromagnetic waves and is excited to generate surface current. S20, with six arc patches serving as encoding and polarization identification units, works in conjunction with the disk patch antenna to generate specific scattered electromagnetic wave signals; S30, by receiving and parsing the scattered signal, the reader can simultaneously obtain the tag's identification code information and the polarization direction of the incident electromagnetic wave; S40, when a crack is generated and propagates in the metal structure under test, the crack changes the electromagnetic environment around the tag, causing changes in the amplitude and phase characteristic parameters of the scattered electromagnetic wave. The S50 can monitor and identify metal cracks by analyzing the variation of scattered signals.