Phase shift-based passive microstrip antenna metal crack detector and detection method

Abstract

The invention provides a passive microstrip antenna metal crack detector based on phase deviation and a detection method. The detector comprises a high dielectric constant dielectric substrate (2) covering a to-be-detected metal surface (1), a spiral structure microstrip antenna (3) covering the surface of the high dielectric constant dielectric substrate (2), a comb structure microstrip antenna (4) covering the surface of the high dielectric constant dielectric substrate (2), and a one-to-four power divider (5) connecting the spiral structure microstrip antenna (3) and the comb structure microstrip antenna (4). And the impedance matching micro-strip structure (7) is connected with the one-to-four power divider (5) and the SMA connector (6) and is mainly applied to nondestructive crack detection in metal structure health monitoring. The detector detects the phase delay of a reflected signal and the phase angle change of input impedance, and combines a four-quadrant partition positioning algorithm to realize the multi-dimensional detection of the metal surface crack, including the position, length, width and depth of the crack. Experimental results show that the structure of the invention shows.

Description

Technical Field

[0001] This invention belongs to the field of antenna sensor technology, specifically relating to a passive microstrip antenna metal crack detector and detection method based on phase shift, which is applicable to metal crack detection in structural health monitoring systems. Background Technology

[0002] Metal structures, with their high fracture toughness and fatigue life, are widely used in modern machinery, civil engineering, marine engineering structures, and aerospace. However, under long-term loads, structural degradation is unavoidable, with fatigue crack initiation and propagation being the most common form of degradation. When such structural degradation defects accumulate to a certain extent, they can lead to a decrease in the structure's load-bearing capacity and fatigue resistance, resulting in serious consequences. Therefore, regular inspection and timely detection of cracks through non-destructive testing (NDT) methods are crucial for preventing structural failure.

[0003] Structural health monitoring (SHM) technology utilizes sensors and data processing to detect structural damage and cracks, improving the safety and reliability of metal structures, enabling more effective condition-based maintenance, extending structural lifespan, and reducing maintenance costs. However, since repair strategies are directly influenced by the geometric parameters of the detected cracks, SHM methods for metal structures, while achieving non-destructive testing, also need to provide quantitative information on crack characteristics, such as spatial extent, orientation, and depth. Currently, various crack detection methods have been developed for SHM of metal structures, including sensor technologies based on ultrasound, piezoelectric effect, and eddy currents. Among these methods, ultrasonic testing requires the use of a coupling agent, and the signal is susceptible to environmental noise, leading to complex signal processing. The need for specialized equipment and trained personnel also increases the cost. Piezoelectric sensors, which use piezoelectric transducers to drive Lamb waves to monitor fatigue cracks, are effective in laboratory environments but require complex signal processing and wiring for sensing equipment, making them unsuitable for field applications. Eddy current sensors generate magnetic field lines through alternating electromagnetic fields to reveal hidden defects. Due to their large penetration depth, they are very effective in identifying subsurface cracks; however, using these methods for long-term monitoring of crack patterns in large infrastructure is both time-consuming and expensive. In recent years, sensors based on passive microstrip antennas (PMAs) have seen significant development due to their passive wireless operation and low-cost transmission, and have been widely applied in various fields such as strain sensing, temperature sensing, crack sensing, and screw loosening detection. PMA sensors utilize microstrip antenna structures as sensing units and can operate without an external power supply. Their working principle is based on the interaction between the microstrip antenna and the surrounding environment or target. Changes in the target's physical quantities will affect the electromagnetic radiation characteristics of the PMA. These effects can be measured and quantified by observing changes in antenna parameters (such as frequency, gain, phase, impedance, etc.). Summary of the Invention

[0004] Technical Problem: The purpose of this invention is to provide a passive microstrip antenna metal crack detector and detection method based on phase shift, which is used for non-destructive detection and monitoring of surface cracks in metal structures. It enables accurate extraction of the region and size information (such as length, width, and depth) of surface cracks in metal structures, thereby improving the accuracy and efficiency of metal structure health monitoring.

[0005] Technical Solution: To solve the above-mentioned technical problems, this invention provides a passive microstrip antenna metal crack detector and detection method based on phase shift. The passive microstrip antenna metal crack detector based on phase shift includes:

[0006] The detector includes a high dielectric constant substrate covering the surface of the metal under test, a spiral microstrip antenna and a comb microstrip antenna covering the surface of the high dielectric constant substrate, a 1-to-4 power divider connecting the spiral microstrip antenna and the comb microstrip antenna, and an impedance matching microstrip structure connecting the 1-to-4 power divider and an SMA connector.

[0007] The spiral microstrip antenna and the comb microstrip antenna are symmetrically distributed on both sides of the center line of the high dielectric constant substrate, and are connected by a 1-to-4 power divider.

[0008] The high dielectric constant substrate has two identical spiral microstrip antennas on its surface, both made of copper, with a line width of 1 mm and a spacing of 1 mm between adjacent turns. The two spiral microstrip antennas are connected by a microstrip line.

[0009] There are two identical comb-shaped microstrip antennas coated on the surface of a high dielectric constant substrate. Each comb has four teeth, each tooth is 6 mm long, 1 mm wide, and 1 mm apart. The two comb-shaped microstrip antennas are connected by a microstrip line.

[0010] The spiral microstrip antenna and the comb-shaped microstrip antenna are symmetrically distributed on the surface of the high dielectric constant substrate, and the distance between them is 9 mm.

[0011] The detection method of the passive microstrip antenna metal crack detector based on phase shift of the present invention is as follows: the detector is covered on the surface of the metal to be tested. The crack in the surface of the metal to be tested will create a gap between it and the high dielectric constant dielectric substrate. This gap caused by the crack causes a change in the dielectric constant of the high dielectric constant dielectric substrate, which is converted into the effective dielectric constant of air and the high dielectric constant dielectric substrate. This causes a change in the impedance angle and the phase of the reflected signal of the spiral structure microstrip antenna and the comb structure microstrip antenna covered on the surface of the high dielectric constant dielectric substrate. The changes are used to determine the location of the crack.

[0012] The detection method of the passive microstrip antenna metal crack detector based on phase shift of the present invention is as follows: the phase change amount In the middle, the definition Phase angle, phase angle of a healthy metal structure As a reference, the phase angle of the damaged metal structure is denoted as... S s11 S represents the port 1 scattering parameter of the damaged metal structure. ref11 For the port 1 scattering parameter of the healthy metallic structure used as a reference, β ref β is the phase constant corresponding to the healthy metallic structure used as a reference. s Let α be the phase constant corresponding to the damaged metal structure. ref Let α be the attenuation constant corresponding to a healthy metallic structure. s Z is the attenuation constant corresponding to the damaged metal structure, Z0 is the characteristic impedance of the microwave transmission system, and Z s The equivalent input impedance of the damaged metal structure is given by j, where j is the imaginary unit. The reflection coefficient;

[0013] Phase change of metallic structures The definition is as follows:

[0014]

[0015] Where S 11 and The definition is as follows:

[0016]

[0017]

[0018] .

[0019] The impedance angle θ is defined as follows:

[0020] .

[0021] When the crack is located below the helical microstrip antenna, the phase change is... The phase change is positive when the crack is located below the comb-shaped microstrip antenna. The values ​​are negative; the sensitivity coefficient of the metal crack detector is 12.53° / mm for crack length, 594.8° / mm for crack width, and 24.9° / mm for crack depth.

[0022] As the location of the crack on the metal surface changes from left to right, the impedance angle gradually increases, exhibiting a linear relationship; the metal crack detector has a sensitivity coefficient of 9.036° / mm for changes in crack location.

[0023] Beneficial effects: The passive microstrip antenna metal crack detection sensor based on phase shift of the present invention has the following advantages:

[0024] 1. This invention discloses a passive microstrip antenna metal crack detector based on phase shift. The detector structure consists of two helical microstrip antennas, two comb-shaped microstrip antennas, a 1-to-4 power divider, and an impedance matching network. Using phase delay and impedance angle as detection parameters, it eliminates the need for traditional large-range frequency scanning to detect frequency shifts for crack detection. Detection can be completed using only a single 2.83GHz frequency signal, significantly reducing the hardware requirements of the detection equipment and lowering equipment purchase and maintenance costs. The metal sensor structure is simple, and the materials such as the radiating element and dielectric substrate are readily available, resulting in a significantly lower overall cost compared to detection schemes relying on complex wiring or broadband equipment.

[0025] 2. The area to be tested is divided into four quadrants. The location of the crack is located by the positive and negative values ​​of the phase delay and the impedance phase angle threshold. This makes up for the shortcomings of traditional methods in that they are difficult to locate accurately. It provides clear guidance for subsequent repair, reduces invalid detection and repetitive work caused by ambiguity in location, and indirectly reduces the cost of engineering maintenance.

[0026] 3. By directly using the metal structure under test as the ground plane, the design and fabrication of an independent ground plane are eliminated, simplifying the sensor structure, reducing material consumption and processing difficulty, while enhancing the electromagnetic coupling with the structure under test, making it easier to capture electromagnetic changes caused by cracks, thereby improving detection sensitivity and further controlling costs.

[0027] 4. The radiation element adopts a comb-shaped and spiral-shaped composite structure, which, together with a one-to-four power divider, enables multi-unit collaborative detection. This not only covers a wider detection area and effectively responds to cross-quadrant cracks, but also eliminates the need for multiple independent sensors. Through structural optimization, a wide range of detection coverage is achieved at low cost.

[0028] 5. It can achieve high-sensitivity detection without relying on high-precision and expensive materials, balancing detection performance and cost, making it suitable for large-scale engineering applications. Attached Figure Description

[0029] Figure 1 is a three-dimensional structural schematic diagram of a passive microstrip antenna metal crack detector based on phase shift, according to an example of the present invention.

[0030] Figure 2 is a top view of a passive microstrip antenna metal crack detector based on phase shift, according to an example of the present invention.

[0031] Figure 3 is a side view of a passive microstrip antenna metal crack detector based on phase shift, according to an example of the present invention.

[0032] Figure 4. Impedance angle θ of a passive microstrip antenna metal crack detector based on phase shift under healthy / unhealthy states of a metal structure.

[0033] Figure 5. Phase delay of the passive microstrip antenna metal crack detector based on phase shift under healthy / unhealthy states of the metal structure. ,

[0034] Figure 6 is a schematic diagram of the four-quadrant division of the test area in an example of the present invention.

[0035] Figure 7 shows the phase delay of the passive microstrip antenna metal crack detector based on phase shift when the crack is located in the upper half-quadrant (quadrants 1 and 2) and the lower half-quadrant (quadrants 3 and 4). Trend chart

[0036] Figure 8 shows the relationship between the impedance phase angle θ and the crack location of a passive microstrip antenna metal crack detector based on phase shift as the crack location moves from left to right.

[0037] Figure 9 shows the S11 curve of the passive microstrip antenna metal crack detector based on phase shift as the crack location moves from left to right.

[0038] Figure 10 shows the impedance phase angle θ and phase delay of the passive microstrip antenna metal crack detector based on phase shift for cross-quadrant cracks. Change curve graph

[0039] Figure 11 shows the phase delay of the passive microstrip antenna metal crack detector based on phase shift as the crack length increases. Change curve,

[0040] Figure 12 shows the S-value of the passive microstrip antenna metal crack detector based on phase shift as the crack length increases. 11 Curve graph

[0041] Figure 13 shows the phase delay of the passive microstrip antenna crack detection sensor as the crack width increases. Change curve,

[0042] Figure 14 shows the phase delay of the passive microstrip antenna crack detection sensor as the crack depth increases. Change curve.

[0043] The figure shows: 1. Metal surface under test; 2. High dielectric constant dielectric substrate; 3. Spiral microstrip antenna; 4. Comb microstrip antenna; 5. 1-to-4 power divider; 6. Impedance matching microstrip structure; 7. SMA connector. Detailed Implementation

[0044] To better understand the purpose, structure, and function of this invention, the following detailed description of a metal crack detection sensor based on a passive microstrip antenna is provided in conjunction with the accompanying drawings.

[0045] This invention includes a phase-shift-based passive microstrip antenna metal crack detector and a metal surface 1 to be tested; the metal crack detection sensor includes a high dielectric constant substrate 2, two helical microstrip antennas 3 and two comb-shaped microstrip antennas 4 located on the upper surface of the high dielectric constant substrate 2; a 1-to-4 power divider 5 is connected to the two helical microstrip antennas 3 and the two comb-shaped microstrip antennas 4; the lower surface of the high dielectric constant substrate 2 is bonded to the metal surface 1 to be tested, and an impedance matching microstrip structure 7 connects the 1-to-4 power divider 5 and the SMA connector 6; the metal surface 1 to be tested serves as the ground plane of the metal crack sensor.

[0046] The spiral microstrip antenna 3 and the comb-shaped microstrip antenna 4 are symmetrically distributed on both sides of the center line of the high dielectric constant substrate 2, and are connected by a 1-to-4 power divider 5. There are two identical spiral microstrip antennas 3 on the surface of the high dielectric constant substrate 2, both made of copper, with a linewidth of 1 mm and a spacing of 1 mm between adjacent turns. The two spiral microstrip antennas 3 are connected by a microstrip line. There are also two identical comb-shaped microstrip antennas 4 on the surface of the high dielectric constant substrate 2, each with four teeth, a tooth length of 6 mm, a tooth width of 1 mm, and a spacing of 1 mm between the teeth. The two comb-shaped microstrip antennas 4 are connected by a microstrip line. The spiral microstrip antennas 3 and the comb-shaped microstrip antennas 4 are symmetrically distributed on the surface of the high dielectric constant substrate 2, with a distance of 9 mm between them.

[0047] The four output ports of the 1-to-4 power divider are connected to a spiral microstrip antenna and a comb microstrip antenna, respectively, to achieve uniform distribution of signal power and collaborative operation of multiple units.

[0048] The 1-to-4 power divider integrates an impedance matching network to ensure impedance matching between each antenna element and the feed network, reducing signal transmission loss and enhancing the sensitivity to crack changes, enabling it to effectively detect cracks distributed across quadrants.

[0049] The dielectric substrate is made of Rogers 3010 material with a relative permittivity of approximately 11.2. Its lower surface is bonded to the metal surface to be tested, and the crack detection sensor structure is printed on the upper surface.

[0050] The surface of the metal under test serves as the grounding plane of the metal crack detection sensor. Cracks on its surface will form open gaps, changing the current distribution on the ground plane, which in turn causes changes in the input impedance angle and the phase of the reflected signal of the metal crack detection sensor.

[0051] The metal crack sensor uses a 2.83 GHz sine wave signal as excitation and measures the phase delay of the reflected signal using a vector network analyzer (VNA). ) and input impedance angle (θ); where phase delay is defined as the phase difference between the cracked state and the healthy state ( The impedance angle is calculated from the complex form of the input impedance (θ = arctan(Im(Z)). s ) / Re(Z s ))).

[0052] The metal crack sensor divides the measured area into four quadrants. The positive and negative values ​​of the phase delay are used to initially determine the upper and lower regions where the crack is located (positive values ​​in the first and second quadrants, and negative values ​​in the third and fourth quadrants). The specific quadrant position is further determined by combining the threshold range of the impedance angle. At the same time, based on the changes in phase delay and impedance angle, a correlation is established with the crack length, width, and depth to achieve quantitative characterization of crack size.

[0053] The detection method of the passive microstrip antenna metal crack detector based on phase shift of the present invention is as follows: the detector is covered on the surface of the metal surface 1 to be tested. The crack in the metal surface 1 will cause a gap between it and the high dielectric constant dielectric substrate 2. This gap caused by the crack causes a change in the dielectric constant of the high dielectric constant dielectric substrate 2, which is converted into the effective dielectric constant of air and the high dielectric constant dielectric substrate 2. This causes a change in the impedance angle and the phase of the reflected signal of the spiral structure microstrip antenna 3 and the comb structure microstrip antenna 4 covered on the surface of the high dielectric constant dielectric substrate 2. The changes are used to determine the location of the crack.

[0054] The phase change In the middle, the definition Phase angle, phase angle of a healthy metal structure As a reference, the phase angle of the damaged metal structure is denoted as... S s11 S represents the port 1 scattering parameter of the damaged metal structure. ref11 For the port 1 scattering parameter of the healthy metallic structure used as a reference, β refβ is the phase constant corresponding to the healthy metallic structure used as a reference. s Let α be the phase constant corresponding to the damaged metal structure. ref Let α be the attenuation constant corresponding to a healthy metallic structure. s Z is the attenuation constant corresponding to the damaged metal structure, Z0 is the characteristic impedance of the microwave transmission system, and Z s The equivalent input impedance of the damaged metal structure is given by j, where j is the imaginary unit. The reflection coefficient;

[0055] Phase change of metallic structures The definition is as follows:

[0056]

[0057] Where S 11 and The definition is as follows:

[0058]

[0059]

[0060] .

[0061] The impedance angle θ is defined as follows:

[0062] .

[0063] When the crack is located below the helical microstrip antenna 3, the phase change amount The phase change is positive when the crack is located below the comb-shaped microstrip antenna 4. The values ​​are negative; the sensitivity coefficient of the metal crack detector is 12.53° / mm for crack length, 594.8° / mm for crack width, and 24.9° / mm for crack depth.

[0064] Figure 1 is a schematic diagram of the three-dimensional structure of the sensor according to an embodiment of the present invention, including: a horizontally arranged test metal surface 1, a high dielectric constant dielectric substrate 2 covering the test metal surface 1, two spiral microstrip antennas 3 and two comb microstrip antennas 4 covering the surface of the high dielectric constant dielectric substrate 2, a 1-to-4 power divider 5 connecting the spiral microstrip antennas 3 and the comb microstrip antennas 4, and an impedance matching microstrip structure 7 connecting the 1-to-4 power divider 5 and an SMA connector 6; the spiral microstrip antennas 3 and the comb microstrip antennas 4 are symmetrically distributed on the surface of the high dielectric constant dielectric substrate 2, and the center of symmetry is on the same straight line as the center of the 1-to-4 power divider 5.

[0065] Figure 2 is a top view of the sensor according to an embodiment of the present invention, further illustrating the planar layout of the radiating unit: two spiral microstrip antennas 3 are located on both sides of the 1-to-4 power divider 5, with a line width of 1 mm and a spacing of 1 mm between adjacent turns; two comb-shaped microstrip antennas 4 are symmetrically distributed on the other side, with 4 comb teeth, each tooth having a length of 6 mm, a width of 1 mm, and a spacing of 1 mm between the comb teeth; an impedance matching microstrip structure 7 extends from the 1-to-4 power divider 4 to both sides, connecting the spiral microstrip antennas 3 and the comb-shaped microstrip antennas 4 respectively, to achieve impedance matching.

[0066] Figure 3 is a side view of the sensor according to an embodiment of the present invention, showing the stacking relationship of each layer: the lower surface of the high dielectric constant substrate 2 is tightly bonded to the metal surface 1 under test, and the bonding surface is free of bubbles and impurities. The upper surface is printed with a spiral microstrip antenna 3, a comb-shaped microstrip antenna 4, a 1-to-4 power divider 5, and an impedance matching microstrip structure 7; one end of the SMA connector 6 is connected to the 1-to-4 power divider 5, and the other end is used to connect an external vector network analyzer to realize the acquisition of signal input and reflected signals.

[0067] Unlike traditional crack detection sensors such as ultrasonic sensors which require coupling agents and piezoelectric sensors which require complex wiring, this invention employs a passive microstrip antenna structure. Using the metal surface under test (1) as the ground plane, it eliminates the need for a separate ground plane and detects the phase change of the reflected signal. Metal crack detection is achieved by combining the input impedance angle θ with the input impedance angle. This design not only simplifies the sensor structure and reduces costs, but also directly senses changes in the ground plane current distribution caused by the crack through electromagnetic coupling, thus improving detection sensitivity.

[0068] To improve the sensitivity response to cracks, this invention employs a comb-shaped and spiral-shaped composite radiation unit: the spiral-shaped microstrip antenna 3 enhances the electromagnetic field concentration effect through dense turns, while the comb-shaped microstrip antenna 4 expands the detection range through a multi-comb design. The combination of the two enables the sensitivity to changes in length, width, depth, and position to reach 12.53° / mm, 594.8° / mm, 24.9° / mm, and 9.036° / mm, respectively, which is far higher than that of traditional microstrip antenna sensors.

[0069] To achieve precise crack localization, this invention introduces a four-quadrant partitioning algorithm (Figure 5): Utilizing the signal distribution characteristics of the one-to-two power divider 5, the phase of the spiral antenna corresponding to the upper quadrant (quadrants 1 and 2) is made to lead (…). (Positive), the phase lag of the comb antenna in the lower half of the quadrant (quadrants 3 and 4) is ( (negative), combined with the threshold range of impedance phase angle θ (left half region θ < 150°, right half region θ > 150°), to achieve a positioning accuracy of ±5mm.

[0070] Figure 4 shows a comparison of the impedance angle θ of the metal structure under healthy and unhealthy states in an embodiment of the present invention. As can be seen from the figure, θ is stable at around 10.4° under healthy conditions, while θ increases significantly to 82.35° when cracks are present, with a difference of 71.95°, indicating that the impedance phase angle has a sensitive response to cracks.

[0071] Figure 5 shows the phase delay of the metal structure under healthy / unhealthy states according to an embodiment of the present invention. Comparison. Under healthy conditions. The angle is 80.18°, under cracked conditions. The phase shifted to -71.14°, with a phase difference of 151.32°, verifying the effectiveness of phase delay as a crack detection parameter.

[0072] Figure 6 shows a schematic diagram of the four-quadrant division of the test area in an example of the present invention. The upper right is the first quadrant, the upper left is the second quadrant, the lower left is the third quadrant, and the lower right is the fourth quadrant.

[0073] Figure 7 shows the phase delay when the crack is located in the upper half-quadrant (1 & 2) and the lower half-quadrant (3 & 4) according to an embodiment of the present invention. Trend of change. Upper quadrant. When the value is positive (e.g., 17.04°), it is in the lower quadrant. A negative value (such as -90.58°) can be used to directly distinguish the upper and lower regions of the splitting pattern.

[0074] Figure 8 shows the impedance phase angle θ change curve as the crack location moves from left to right according to an embodiment of the present invention. As the crack moves from the left half of the region (quadrants 2 & 3) to the right half of the region (quadrants 1 & 4), θ increases from -38.72° to 166.15°, showing a significant linear change trend, which can be used to determine the left and right positions.

[0075] Figure 9 shows the S11 curve of the embodiment of the present invention as the crack location moves from left to right. The resonant frequency of the curve is stable at around 2.83 GHz, with a change of <0.1 GHz, indicating that the frequency parameters are not sensitive to changes in location, further highlighting the advantages of phase and impedance phase angle.

[0076] Figure 10 shows the impedance phase angle θ and phase delay corresponding to the cross-quadrant crack in an embodiment of the present invention. Changes. When crossing quadrants 1 & 2, θ = 83.83°. =-151.32°, θ=63.58° when crossing quadrants 1 & 4. =-105.47°, the parameter difference between the two can effectively distinguish the cross-region type.

[0077] Figure 11 shows the phase delay as the crack length increases in an embodiment of the present invention. The variation curve. When the length increases from 5mm to 10.5mm, The linear range decreases from -78.57° to -99.99°, with a sensitivity of 12.53° / mm, enabling quantitative detection of length.

[0078] Figure 12 shows the S11 curve as the crack length increases according to an embodiment of the present invention. The resonant frequency of the curve remains stable at around 2.83 GHz, with a change of <0.1 GHz, indicating that the frequency parameters are not sensitive to changes in position, further highlighting the advantages of phase and impedance phase angle.

[0079] Figure 13 shows the phase delay when the crack width increases according to an embodiment of the present invention. The change curve. When the width increases from 0 to 1 mm, The sensitivity drops from -6.34° to -136.93°, reaching 594.8° / mm. Even a width change of 0.1mm can cause a phase shift of 59.48°, enabling the detection of minute cracks.

[0080] Figure 14 shows the phase delay as the crack depth increases in an embodiment of the present invention. Change curve. As the depth increases from 0.5mm to 2mm, The sensitivity is 24.9° / mm, which can reflect changes in crack depth, decreasing from -154.64° to -178.51°.

[0081] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0082] The terms “comprising,” “having,” “introducing,” and any variations thereof used in this application are intended to cover non-exclusive inclusion. For example, a structure, apparatus, product, or device that includes a series of components is not limited to the listed components, but may optionally include components not listed, or may optionally include other components inherent to such structure, apparatus, product, or device.

[0083] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A passive microstrip antenna-based metal crack detector based on phase shift, characterized in that, include: The detector includes a high dielectric constant substrate (2) covering the surface (1) of the metal to be tested, a spiral microstrip antenna (3) and a comb microstrip antenna (4) covering the surface of the high dielectric constant substrate (2), a 1-to-4 power divider (5) connecting the spiral microstrip antenna (3) and the comb microstrip antenna (4), and an impedance matching microstrip structure (7) connecting the 1-to-4 power divider (5) and the SMA connector (6).

2. The passive microstrip antenna metal crack detector based on phase shift according to claim 1, characterized in that, The spiral microstrip antenna (3) and the comb microstrip antenna (4) are symmetrically distributed on both sides of the center line of the high dielectric constant substrate (2), and the spiral microstrip antenna (3) and the comb microstrip antenna (4) are connected by a 1-to-4 power divider (5).

3. The passive microstrip antenna metal crack detector based on phase shift according to claim 2, characterized in that, There are two spiral microstrip antennas (3) on the surface of the high dielectric constant substrate (2) with the same structure. Both are made of copper, with a line width of 1 mm and a spacing of 1 mm between adjacent turns. The two spiral microstrip antennas (3) are connected by a microstrip line.

4. The passive microstrip antenna metal crack detector based on phase shift according to claim 3, characterized in that, There are two comb-shaped microstrip antennas (4) on the surface of a high dielectric constant substrate (2) with the same structure. The number of comb teeth is 4, the length of the comb teeth is 6 mm, the width of the comb teeth is 1 mm, and the spacing between the comb teeth is 1 mm. The two comb-shaped microstrip antennas (4) are connected by a microstrip line.

5. The passive microstrip antenna metal crack detector based on phase shift according to claim 4, characterized in that, The spiral microstrip antenna (3) and the comb-shaped microstrip antenna (4) are symmetrically distributed on the surface of the high dielectric constant substrate (2), and the distance between them is 9 mm.

6. A detection method for a phase-shift-based passive microstrip antenna metal crack detector as described in any one of claims 1-5, characterized in that, The detector is placed on the surface of the metal surface (1) to be tested. Cracks in the metal surface (1) will create a gap between it and the high dielectric constant substrate (2). This gap caused by the crack will cause a change in the dielectric constant of the high dielectric constant substrate (2), which will be converted into the effective dielectric constant of air and the high dielectric constant substrate (2). This will cause a change in the impedance angle and the phase of the reflected signal of the spiral structure microstrip antenna (3) and the comb structure microstrip antenna (4) placed on the surface of the high dielectric constant substrate (2). The changes are used to determine the location of the crack.

7. The detection method for a phase-shift-based passive microstrip antenna metal crack detector according to claim 6, characterized in that, The phase change In the middle, the definition Phase angle, phase angle of a healthy metal structure As a reference, the phase angle of the damaged metal structure is denoted as... S s11 S represents the port 1 scattering parameter of the damaged metal structure. ref11 For the port 1 scattering parameter of the healthy metallic structure used as a reference, β ref β is the phase constant corresponding to the healthy metallic structure used as a reference. s Let α be the phase constant corresponding to the damaged metal structure. ref Let α be the attenuation constant corresponding to a healthy metallic structure. s Z is the attenuation constant corresponding to the damaged metal structure, Z0 is the characteristic impedance of the microwave transmission system, and Z s The equivalent input impedance of the damaged metal structure is given by j, where j is the imaginary unit. The reflection coefficient; Phase change of metallic structures The definition is as follows: Where S 11 and The definition is as follows: 。 8. The detection method for a passive microstrip antenna metal crack detector based on phase shift according to claim 7, characterized in that, The impedance angle θ is defined as follows: 。 9. The detection method for a passive microstrip antenna metal crack detector based on phase shift according to claim 8, characterized in that, When the crack is located below the helical microstrip antenna (3), the phase change is The phase change is positive when the crack is located below the comb-shaped microstrip antenna (4). The values ​​are negative; the sensitivity coefficient of the metal crack detector is 12.53° / mm for crack length, 594.8° / mm for crack width, and 24.9° / mm for crack depth.

10. The detection method for a passive microstrip antenna metal crack detector based on phase shift according to claim 9, characterized in that, As the position of the crack on the metal surface (1) changes from left to right, the impedance angle gradually increases, showing a linear pattern; the sensitivity coefficient of the metal crack detector to the change of crack position is 9.036° / mm.

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