Electromagnetic sensor based on split-ring resonator array and crack detection method

Abstract

The invention relates to an electromagnetic sensor based on a split-ring resonator array and a crack detection method, the sensor comprises a first flexible dielectric substrate, a bonding layer, a second flexible dielectric substrate and a metal grounding layer which are bonded from top to bottom, and the top surface of the first flexible dielectric substrate is provided with a microstrip transmission line; one end of the first flexible dielectric substrate is provided with an SMA interface hole, and the bottom surface of the first flexible dielectric substrate is provided with a split-ring resonator array which is in electromagnetic coupling with the microstrip transmission line. The invention also provides a crack detection method of the sensor. The electromagnetic sensor is adjustable in detection area and uniform in field distribution.

Description

Technical Field

[0001] This invention relates to the field of structural health monitoring technology, specifically to an electromagnetic sensor based on an open resonant ring array and a crack detection method. Background Technology

[0002] Electromagnetic testing is a common method in the non-destructive testing of metal structures. To detect surface cracks, the sensor needs to be able to generate an effective response signal to minute changes in the metal surface.

[0003] A split-ring resonator is a circuit structure that resonates at a specific frequency. When it is brought close to a metal surface, its resonant characteristics change due to the electromagnetic properties of the metal. If a split-ring resonator is used as a sensor, this change can be used to sense the state of the metal surface. However, the effective operating area of ​​a single split-ring resonator is small, and its electromagnetic field distribution is concentrated, which is not conducive to uniform detection over a large area. To expand the detection range, a natural approach is to use multiple split-ring resonators in an array. However, a simple array arrangement may lead to uneven responses among the units, affecting the detection performance. Summary of the Invention

[0004] To address the problems of the existing technology, this invention provides an electromagnetic sensor based on an array of open resonant rings and a crack detection method. The electromagnetic sensor is fabricated on a flexible substrate, facilitating its application to surfaces of varying shapes. The open resonant rings in the array are arranged in multiple staggered rows to ensure a more uniform electromagnetic field distribution across the entire array. The detection method associated with this electromagnetic sensor primarily monitors changes in its resonant frequency. When a crack appears in the metal beneath the electromagnetic sensor, its resonant frequency shifts. By measuring this frequency shift, the crack can be identified and assessed. This electromagnetic sensor has a relatively simple structure and is suitable for applications requiring the detection of cracks on metal surfaces.

[0005] To achieve the above objectives, the specific solution of the present invention is as follows:

[0006] An electromagnetic sensor based on an open-ended resonant ring array includes a first flexible dielectric substrate, an adhesive layer, a second flexible dielectric substrate, and a metal grounding layer bonded together from top to bottom. The top surface of the first flexible dielectric substrate is provided with a microstrip transmission line, and one end of the first flexible dielectric substrate is provided with an SMA interface hole. The bottom surface of the first flexible dielectric substrate is provided with an open-ended resonant ring array that is electromagnetically coupled to the microstrip transmission line.

[0007] Furthermore, the open-loop resonant ring array is composed of multiple rows of double-open-loop resonant ring units arranged alternately along a direction perpendicular to the microstrip transmission line. The open regions of two adjacent rows of double-open-loop resonant ring units are arranged opposite each other, and the electromagnetic near-field coupling regions of one row of double-open-loop resonant ring units and another adjacent row of double-open-loop resonant ring units overlap in space.

[0008] Furthermore, the double-opening resonant ring unit consists of two concentric outer square metal rings and an inner square metal ring, with opening regions respectively provided at opposite positions of the outer square metal ring and the inner square metal ring.

[0009] Furthermore, the total thickness of the first flexible dielectric substrate, the adhesive layer, the second flexible dielectric substrate, and the metal ground layer after bonding is less than 0.5 mm. Furthermore, the number of open resonant ring units in the open resonant ring array is determined according to the required detection range.

[0010] A crack detection method includes the following steps:

[0011] Step S1: Attach the electromagnetic sensor to the surface of the metal structure to be tested and connect it to the vector network analyzer.

[0012] Step S2: Measure and obtain the initial transmission coefficient and initial resonant frequency f0 of the electromagnetic sensor under the defect-free state of the metal structure under test using a vector network analyzer; Step S3: Monitor and obtain the current transmission coefficient and real-time resonant frequency f0 in real time. 实时 The resonant frequency offset Δf is calculated. When the number of resonant peaks increases or the resonant frequency offset Δf exceeds the preset threshold, the size parameters of the crack in the detection area are quantitatively calculated according to the preset calibration relationship between crack size and resonant characteristic change.

[0013] Furthermore, the formula for calculating the resonant frequency offset is as follows:

[0014] Δf=|f 实时 -f0|,

[0015] In the formula, Δf represents the resonant frequency offset; f 实时 f0 represents the real-time resonant frequency; f0 represents the initial resonant frequency.

[0016] Advantages of the present invention

[0017] 1. The electromagnetic sensor and crack detection method based on the open resonant ring array of the present invention can effectively and uniformly distribute the electromagnetic field in the detection area by arranging multiple rows of double open resonant ring units in an interlaced array, thereby reducing the sensitivity to crack location and improving the consistency and reliability of detection.

[0018] 2. The electromagnetic sensor of the present invention has a thin structure and good flexibility, and can be closely attached to the surface of various curved metal structures.

[0019] Furthermore, the number of dual-opening resonant ring units in the open resonant ring array can be flexibly configured, enabling the detection range to be adjusted as needed.

[0020] 3. The electromagnetic sensor of this invention is based on printed circuit technology, which is easy to manufacture and has low cost. The electromagnetic sensor of this invention is suitable for long-term online health monitoring of large and complex metal structures in aerospace, shipbuilding, bridge construction, and other fields. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electromagnetic sensor based on an open resonant ring array according to the present invention.

[0022] Figure 2 for Figure 1 A schematic diagram of the staggered arrangement of the open resonant ring array.

[0023] Figure 3 for Figure 2 A schematic diagram of the structure of the double-opening resonant ring unit.

[0024] Figure 4 This is a graph showing the effect of the spacing between the near-field coupling regions of the open resonant ring array of the present invention.

[0025] Figure 5 The S21 curves are for detecting no cracks, 0.5mm cracks, 1mm cracks, and 1.5mm cracks on the surface of the metal structure under test by the electromagnetic sensor of the present invention.

[0026] Figure 6 This is a comparison chart of the standard deviation of the field strength of the double-row and single-row arrays of the present invention.

[0027] Figure 7 This is a calibration diagram of quantitative crack detection based on the S21 parameter curve of the present invention.

[0028] Figure 8 This is a flowchart of the crack detection method of the present invention.

[0029] In the picture:

[0030] 1. Microstrip transmission line; 2. First flexible dielectric substrate; 3. Adhesive layer; 4. Second flexible dielectric substrate; 5. SMA interface hole; 6. Open resonant ring array; 61. Double open resonant ring unit; 7. Metal ground layer. Detailed Implementation

[0031] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments are not intended to limit the scope of the present invention.

[0032] like Figures 1 to 8 As shown, this specific embodiment provides an electromagnetic sensor based on an open-loop resonant ring array, comprising a first flexible dielectric substrate 2, an adhesive layer 3, a second flexible dielectric substrate 4, and a metal ground layer 7 bonded together from top to bottom. The total thickness of the first flexible dielectric substrate 2, adhesive layer 3, second flexible dielectric substrate 4, and metal ground layer 7 after bonding is 0.355 mm, giving the sensor good flexibility. This total thickness can be controlled within the width of the microstrip transmission line 1, which is designed to be 1.04 mm, to achieve impedance matching. The first flexible dielectric substrate 2 and the second flexible dielectric substrate 4 are respectively made of Rogers RT 5880 high-performance flexible material.

[0033] The first flexible dielectric substrate 2 has a microstrip transmission line 1 printed on its top surface, and an SMA interface hole 5 is provided at one end of the first flexible dielectric substrate 2. The bottom surface of the first flexible dielectric substrate 2 has an open resonant ring array 6 that is electromagnetically coupled to the microstrip transmission line 1.

[0034] like Figure 3 As shown, the dual-slot resonant ring unit 61 consists of two concentric outer square metal rings and an inner square metal ring. Opening regions are located at relative positions on the outer and inner square metal rings, and the orientations of the two opening regions are opposite to each other. The key dimensions of the slot resonant ring unit—side length h, linewidth w, and opening gap d—are determined through simulation optimization. For example, h=5mm, w=1mm, and d=0.5mm are set to enable the flexible sensor to operate in the 6GHz frequency band.

[0035] like Figure 2 As shown, the open-loop resonant array 6 consists of two rows of double-open-loop resonant units 61, staggered along a direction perpendicular to the microstrip transmission line 1. The double-row double-open-loop resonant units 61 are arranged in an interleaved manner, meaning the units in the upper and lower arrays are not directly opposite each other, but rather offset by a certain amount. When arranged directly opposite each other, the field is uneven (large intensity deviation); however, with the interleaved arrangement, the open regions (high electric field regions) of the first row of double-open-loop resonant units 61 and the open regions (high magnetic field regions) of the second row of double-open-loop resonant units 61 overlap in projection, effectively smoothing the field strength gradient. The number of open-loop resonant units in the open-loop resonant array 6 is selected according to the actual monitoring length requirements, such as 5, 9, or 13 units.

[0036] like Figure 6As shown, a comparative test was conducted on the standard deviation of the field strength between the double-row array and the single-row array. The horizontal axis represents the array type, i.e., single-row array and double-row array, and the vertical axis represents the standard deviation of the field strength. Theoretical calculations show that the standard deviation of the field strength for the single-row array is approximately 16, while that for the double-row array is approximately 5. This comparative data directly verifies that by staggering the upper and lower rows of double-opening resonant ring units 61, the open areas (high electric field areas) of the first row of units and the open areas (high magnetic field areas) of the second row of units overlap in projection, significantly reducing the standard deviation of the field strength within the detection area. This structural feature achieves smoothing of the electromagnetic field distribution, effectively weakening the inherent edge effect of the single-row array, providing a more uniform electromagnetic field environment for quantitative crack detection, thereby improving the consistency and repeatability of the electromagnetic sensor's response to cracks at different locations.

[0037] The opening regions of the outer square metal rings of two adjacent rows of double-opening resonant ring units 61 are arranged opposite each other, and the near-field coupling regions of one row of double-opening resonant ring units 61 overlap with those of the other adjacent row of double-opening resonant ring units 61 to achieve a uniform distribution of the electromagnetic field within the detection area. Figure 4 As shown, the S21 curve parameters change for different array spacings within the 5.5GHz to 6.5GHz frequency band: three test curves for spacings of 0.6mm, 0.4mm, and 0.2mm. When the spacing is 0.2mm, the S21 curve parameters are ≤-20dB across the entire frequency band, reaching the optimal coupling state; as the spacing increases, the S21 curve parameters rise, and the coupling strength weakens.

[0038] This embodiment provides three typical configurations: such as Figure 5 As shown, within the frequency scanning range of 2GHz to 6GHz, the variations in the transmission coefficient S21 curves corresponding to three different resonant ring widths are as follows: the curve corresponding to a resonant ring width of 8mm exhibits resonant characteristics in the low-frequency band; the curve corresponding to a resonant ring width of 6mm exhibits resonant characteristics in the mid-frequency band; and the curve corresponding to a resonant ring width of 4mm exhibits resonant characteristics in the high-frequency band. Each curve shows a valley in the S21 parameter within its corresponding frequency band, reflecting different resonant frequency points.

[0039] like Figure 7 As shown, within the frequency scanning range of 5.0 GHz to 6.0 GHz, the transmission coefficient S21 curves corresponding to the four crack states are as follows: the crack-free state shows a single resonance peak; the curves of the 0.5 mm crack state, the 1 mm crack state, and the 1.5 mm crack state show resonance peak shift phenomena in turn, and the frequency shift Δf increases accordingly with the increase of crack width. Figure 7 The document describes the measured Δf values ​​corresponding to three crack sizes (e.g., 0.1 mm, 0.5 mm, and 1 mm), forming a pre-defined calibration relationship database between crack size and the change in resonance characteristics.

[0040] like Figure 8 As shown, the crack detection method using the above-mentioned electromagnetic sensor includes the following steps:

[0041] Step S1: Attach the electromagnetic sensor to the surface of the metal structure to be tested and connect it to the vector network analyzer;

[0042] Step S2: Measure the S21 curve of the initial transmission coefficient and the initial resonant frequency f0 of the electromagnetic sensor under a defect-free state in the metal structure under test using a vector network analyzer. These parameters serve as the reference parameters for crack detection. Step S3: Monitor and acquire the current transmission coefficient and real-time resonant frequency f0 in real time. 实时 Calculate the resonant frequency offset Δf = |f 实时 -f0|;When cracks appear on the surface of the metal structure under test, the cracks will disturb the electromagnetic field of the double-opening resonant ring unit 61, causing an increase in the number of resonance peaks in the initial transmission coefficient S21 curve or a resonance frequency shift Δf exceeding the preset threshold, according to Figure 7 The calibration relationship is used to quantitatively calculate the size parameters of the cracks within the detection area.

Claims

1. An electromagnetic sensor based on an open-loop resonant ring array, characterized in that, The first flexible dielectric substrate, the adhesive layer, the second flexible dielectric substrate, and the metal grounding layer are bonded together from top to bottom. The top surface of the first flexible dielectric substrate is provided with a microstrip transmission line, and one end of the first flexible dielectric substrate is provided with an SMA interface hole. The bottom surface of the first flexible dielectric substrate is provided with an open resonant ring array that is electromagnetically coupled to the microstrip transmission line.

2. The electromagnetic sensor according to claim 1, characterized in that, The open-loop resonant ring array is composed of multiple rows of double-open-loop resonant ring units arranged alternately along a direction perpendicular to the microstrip transmission line. The open regions of two adjacent rows of double-open-loop resonant ring units are arranged opposite each other, and the electromagnetic near-field coupling regions of one row of double-open-loop resonant ring units and another adjacent row of double-open-loop resonant ring units overlap in space.

3. The electromagnetic sensor according to claim 1, characterized in that, The double-opening resonant ring unit consists of two concentric outer square metal rings and an inner square metal ring, with opening regions respectively located at opposite positions on the outer and inner square metal rings.

4. The electromagnetic sensor according to claim 1, characterized in that, The total thickness of the first flexible dielectric substrate, the adhesive layer, the second flexible dielectric substrate, and the metal grounding layer after bonding is less than 0.5 mm.

5. The electromagnetic sensor according to claim 1, characterized in that, The number of open resonant ring units in the open resonant ring array is determined according to the required detection range.

6. A crack detection method, characterized in that, Includes the following steps: Step S1: Attach the electromagnetic sensor described in any one of claims 1 to 5 to the surface of the metal structure to be tested, and connect it to a vector network analyzer; Step S2: Measure and obtain the initial transmission coefficient and initial resonant frequency f0 of the electromagnetic sensor under the defect-free state of the metal structure under test using a vector network analyzer; Step S3: Monitor and obtain the current transmission coefficient and real-time resonant frequency f0 in real time. 实时 The resonant frequency offset Δf is calculated. When the number of resonant peaks increases or the resonant frequency offset Δf exceeds the preset threshold, the size parameters of the crack in the detection area are quantitatively calculated according to the preset calibration relationship between crack size and resonant characteristic change.

7. The method according to claim 6, characterized in that, The formula for calculating the resonant frequency offset is as follows: Δf=|f 实时 -f0|, In the formula, Δf represents the resonant frequency offset; f 实时 f0 represents the real-time resonant frequency; f0 represents the initial resonant frequency.

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