A resonant loop multilayer dielectric probe and method for detecting defects in a radar absorbing material on a metallic outer surface

Abstract

A resonant ring multilayer dielectric probe and method for detecting defects in absorbing materials on the outer surface of metals, belonging to the field of microwave detection technology. To address the current lack of resonant multilayer dielectric structure probes capable of detecting defects in non-metallic absorbing materials on the surface of metal layers, this invention presents a multilayer planar printed structure probe, consisting of, from bottom to top, a feed line, a lower dielectric substrate, a ground plane, an upper dielectric substrate, and a radiating metal patch. The radiating metal patch, ground plane, and feed line are metal layers. A rectangular slit is provided in the center of the ground plane. A microstrip line is printed on the underside of the lower dielectric substrate for feeding. The radiating metal patch consists of multiple rectangular resonant rings arranged symmetrically in a matrix structure. Each rectangular resonant ring comprises an outer ring and an inner ring, with a gap between them. Both the outer and inner rings have openings. The resonant rings are printed on the upper dielectric substrate. During detection, the S11 curve corresponding to the probe is used to detect damage to the absorbing coating on the outer surface of the metal.

Description

Technical Field

[0001] This invention belongs to the field of microwave detection technology, specifically relating to a detection probe and method for detecting defects in microwave absorbing coatings on the outer surface of metals. Background Technology

[0002] Microwave nondestructive testing is a non-contact testing method that uses the dielectric properties of materials and the electromagnetic properties of microwaves to detect hidden defects such as cracks, holes, inclusions, and lack of fusion in the tested materials. It has advantages such as not requiring the addition of coupling agents, not requiring treatment of the metal surface, and not requiring bonding.

[0003] Currently, most existing resonant structure probes detect defects in metals. There is no resonant multilayer dielectric structure probe that can detect defects in non-metallic absorbing materials on the surface of a metal layer. Summary of the Invention

[0004] This invention aims to address the current lack of resonant multilayer dielectric structure probes capable of detecting defects in non-metallic absorbing materials on the surface of metallic layers.

[0005] A resonant ring multilayer dielectric probe for detecting defects in absorbing materials on the outer surface of metals is disclosed. The probe has a multilayer planar structure, consisting of a feed line, a lower dielectric substrate, a ground plane, an upper dielectric substrate, and a radiating metal patch from bottom to top. The radiating metal patch, the ground plane, and the feed line are metal layers. A rectangular slit is provided in the center of the ground plane. A microstrip line is printed on the underside of the lower dielectric substrate for feeding. The radiating metal patch consists of multiple rectangular resonant rings arranged symmetrically in a matrix structure. Each rectangular resonant ring is composed of an outer ring and an inner ring, with a gap between them. Both the outer and inner rings have openings. The resonant rings are printed on the upper dielectric substrate.

[0006] Furthermore, the outer ring opening points towards the geometric center of the upper dielectric substrate plane, while the inner ring opening is away from the geometric center of the upper dielectric substrate plane.

[0007] Furthermore, the radiating metal patch consists of six rectangular resonant rings arranged in a 3*2 matrix structure. Three rectangular resonant rings in one row are arranged side by side to form a group, and the other three rectangular units form another group and are symmetrically arranged with the first group.

[0008] Furthermore, the outer ring opening of the rectangular resonant ring is 0.21 mm, the inner ring opening is 0.25 mm, the outer ring diameter is 1.4 mm, the inner ring diameter is 1.04 mm, the gap between the outer and inner rings is 0.08 mm, and the width of both the outer and inner rings is 0.1 mm.

[0009] Furthermore, the two sets of rectangular resonant rings are spaced 1.9 mm apart.

[0010] Furthermore, the upper dielectric substrate is smaller than the ground plane, and the three edges of the upper dielectric substrate coincide with the three edges of the ground plane.

[0011] Furthermore, the material of the lower dielectric substrate has a relative permittivity of 9.8 and an electrical loss tangent of 0.0020; the material of the upper dielectric substrate has a relative permittivity of 3.2 and an electrical loss tangent of 0.0018.

[0012] Furthermore, the thickness of the radiating metal patch, ground plane, and feeder cable is 0.035 mm.

[0013] Furthermore, the upper dielectric substrate has the following dimensions: The dimensions of the upper and lower dielectric substrates are The dimensions of the grounding plate are: There is an 8mm*2mm rectangular gap located 7.35cm from the top edge of the floor, 10.65cm from the bottom edge, 6mm from the left edge, and 6mm from the right edge.

[0014] A method for detecting defects in microwave absorbing materials on the outer surface of metals involves using the probe to detect the microwave absorbing coating on the outer surface of the metal and obtaining the corresponding S11 curve. The method is based on the changes in the S11 curve to detect damage to the microwave absorbing coating on the outer surface of the metal.

[0015] Beneficial effects: This invention can not only detect defects in non-metallic absorbing materials on the surface of a metal layer, but also has advantages such as no need to add coupling agent, no need to treat the metal surface, and no need to bond. Moreover, it can achieve high-resolution and high-sensitivity defect detection. Attached Figure Description

[0016] Figure 1 This is a front view of the probe structure.

[0017] Figure 2 This is a schematic diagram of the ground plane of the probe structure.

[0018] Figure 3 This is a side view of the probe structure.

[0019] Figure 4 This is a schematic diagram of the back of the probe structure.

[0020] Figure 5 This is a schematic diagram of the multi-layer structure (side view) of the probe during application.

[0021] Figure 6 This is a structural diagram of an SMA connector.

[0022] Figure 7 This is a schematic diagram and equivalent circuit diagram of a square open-loop resonant ring.

[0023] Figure 8 The simulation results show the electric field energy distribution of the square resonant ring.

[0024] Figure 9 Simulation results of electric field energy distribution for some square resonant rings.

[0025] Figure 10 The simulation results show the energy distribution of the bottom feed layer in the coupled feeding method.

[0026] Figure 11 The simulation results show the energy distribution of the rectangular slit.

[0027] Figure 12 Simulation results of energy distribution settings for the resonant ring.

[0028] Figure 13 This is an energy curve diagram when three resonant rings on the same side are close to each other.

[0029] Figure 14 The curve of S11 changes when the probe structure detects defects of different depths in the absorbing coating outside the metal. Detailed Implementation Summary of the Invention: Most existing resonant probes detect defects in metals. The purpose of this invention is to provide a resonant multilayer dielectric structure for detecting defects in non-metallic absorbing materials on the surface of a metal layer in the X-band.

[0031] Specific implementation method one: Combining Figures 1 to 12 This implementation method is described below. This embodiment describes a resonant ring multilayer dielectric probe for detecting defects in the absorbing material on the outer surface of a metal layer. It has a multilayer planar printed structure, consisting of, from bottom to top, a feed line, a lower dielectric substrate, a ground plane, an upper dielectric substrate, and a radiating metal patch. The radiating metal patch, ground plane, and feed line are metal layers. A microstrip line is printed on the underside of the lower dielectric substrate for feeding. The radiating metal patch consists of six rectangular resonant rings arranged in a 3*2 configuration. The resonant rings are printed on the upper dielectric substrate. This 3*2 arrangement can clearly detect defects in the absorbing coating on the outer surface of the metal layer. The S11 curve changes with the depth of the defects in the coating.

[0032] The radiating metal patch consists of a 3*2 arrangement of six rectangular resonant rings. Each rectangular resonant ring is composed of an outer ring and an inner ring, with a gap between them. Both the outer and inner rings have openings. Three rectangular resonant rings in a row are arranged side by side to form a group of secondary units. Another three rectangular units form another group of secondary units and are arranged symmetrically with it. The opening of the outer ring points towards the geometric center of the upper dielectric substrate plane, while the opening of the inner ring faces away from the geometric center of the upper dielectric substrate plane.

[0033] A rectangular gap is provided in the center of the grounding plate; the lower medium board is the same size as the grounding plate.

[0034] In some embodiments, the resonant ring multilayer dielectric probe comprises two dielectric substrates, each with double-sided copper plating and laser-cut grooves according to the designed shape of the metal layers. Preferably, the feed layer, ground plane, and radiating metal patch are all made of copper.

[0035] In some embodiments, the thickness of the radiating metal patch, the ground plane, and the feed line is all 0.035 mm, and the resonant ring is printed on... On the upper dielectric substrate, The lower dielectric substrate has microstrip lines printed on its underside, measuring 11.9 mm in length and 0.5 mm in width, for power feeding. Figure 1 This is a schematic diagram of the probe's front structure. The orange part is the upper dielectric substrate, the gray part above the upper dielectric substrate represents the radiating metal patch, and the gray part to the west represents the ground plane. Figure 1 In reality, the upper dielectric substrate is smaller than the ground plane when viewed from the top to the bottom. The material type of the upper dielectric substrate is Rogers RO4232(tm), with a relative permittivity of 3.2 and an electrical loss tangent of 0.0018.

[0036] The outer ring of the rectangular resonant ring has an opening of 0.21 mm, and the inner ring has an opening of 0.25 mm. The outer ring diameter (distance from the outer edges of the two sides of the rectangle) is 1.4 mm, and the inner ring diameter (distance from the outer edges of the two sides of the rectangle) is 1.04 mm. The gap between the outer and inner rings is 0.08 mm, and the width of both the outer and inner rings is 0.1 mm. In the 3*2 arrangement of the six rectangular resonant rings, three rectangular resonant rings are arranged side by side in a straight line to form a group of secondary units. The other three rectangular units form another group of secondary units and are placed symmetrically with them, 1.9 mm apart. The top edge of the upper row of secondary units is 6.21 mm from the upper boundary of the probe, and the bottom edge of the lower row of secondary units is 5.09 mm from the lower boundary of the probe.

[0037] More specifically, the probe's geometric parameters are L1=20mm, L2=16mm, L3=1.4mm, W1=20mm, W2=0.1mm, W3=4.2mm, D1=6.21mm, D2=1.9mm, D3=5.09mm, G1=0.21mm, G2=0.25mm, s1=0.08mm, and s2=0.2mm.

[0038] Figure 2This is a schematic diagram of the probe's ground plane structure. The gray part is metal, and the white part is a rectangular slit. In some embodiments, there is an 8mm*2mm rectangular slit located at a distance of 7.35cm from the top edge of the ground plane, 10.65cm from the bottom edge, 6mm from the left edge, and 6mm from the right edge, i.e., L4=2mm, W4=8mm, and D4=10.65mm.

[0039] Figure 3 This is a schematic diagram of the back structure of a probe. The gray part is metal (feed wire), and the blue part is the lower dielectric substrate. More specifically, L5=11.9mm, W5=0.5mm; the material type of the lower dielectric substrate is RogersTMM 10i(tm), with a relative permittivity of 9.8 and an electrical loss tangent of 0.0020.

[0040] Figure 4 This is a schematic diagram of the side structure of the probe. The gray part is metal, the orange part is the upper dielectric substrate, and the blue part is the lower dielectric substrate. More specifically, h1=0.5mm, h2=0.3mm, and t=0.035mm.

[0041] In the probe's multi-layer structure, non-adjacent layers are not connected during actual fabrication. However, it should be noted that this only applies to the probe portion. In actual fabrication, the resulting board will be soldered using SMA connectors, with the grounding pin connected to the ground plane and the inner conductor pin of the coaxial cable connected to the feed layer. A schematic diagram is shown below. Figure 5 As shown, the SMA connector is as follows Figure 6 As shown.

[0042] It should also be noted that the above structure was determined through research and analysis during the probe development process. To obtain a high-performance probe, the resonant characteristics of the square-aperture resonant ring were analyzed and studied during the development process. Figure 7 The diagram shows the structure and equivalent circuit of a square open-circuit resonator. When an electromagnetic wave is incident on the open-circuit resonator, the metal ring will induce a current due to the changing electromagnetic field. Figure 7 (a) is the structural diagram, where the gray parts are highly conductive metals and the white parts are the hollow gaps. The SRR consists of two concentric metal rings. The radius of the larger metal ring is r (the distance from the geometric center to the outer side of one side of the rectangle), the width of the two metal rings is w, and the distance between the larger and smaller rings is g. The entire open-circuit resonant ring can be approximately equivalent to an LC resonant circuit, such as... Figure 7As shown in (b), the metal portion can be equivalent to the total inductance L, and the empty portion, especially the gap between the two rings, combined with the metal rings, forms a capacitor. Since the capacitance at the openings of the two resonant rings is much smaller than the capacitance between the two rings, it is ignored in the analysis to simplify circuit calculations. The inter-ring capacitance of the open resonant ring is divided into upper and lower parts at its opening, both with a capacitance value of C0 / 2, and they are in series. Therefore, the total capacitance C of this resonant ring is C0 / 4. The energy distribution of the square resonant ring is mainly at the opening capacitance, with a higher energy density at the opening of the outer ring. Figures 8-9 As shown. Analysis based on simulation results shows that by using appropriate resonant ring size and arrangement, the radiated electric field energy can be more concentrated, resulting in higher probe sensitivity and resolution. Furthermore, research has revealed that in coupled feeding methods, the energy distribution of the bottom feed layer is concentrated at the microstrip line ends, such as... Figure 10 As shown. The energy distribution characteristics of the rectangular gap are: the energy is more concentrated on the longer side of the rectangle than on the shorter side, and the energy is more concentrated at the center of the longer side than at the ends of the longer side, as shown. Figure 11 As shown. Because the energy is more concentrated at the top of the microstrip line and radiates from the top, the energy is more concentrated on the upper long side of the rectangular slit than on the lower long side.

[0043] Based on the energy distribution characteristics of each layer, the opening of the resonant ring is chosen near the long side of the rectangular slot and the top of the microstrip line. Therefore, the resonant rings are arranged in a straight line along both long sides. The upper resonant ring is used to concentrate the energy along the upper long side of the rectangular slot, and the lower resonant ring is used to concentrate the energy along the lower long side of the rectangular slot. The outer ring opens towards the inside of the rectangular slot, and the inner ring opens towards the outside of the rectangular slot. This concentrates the energy and prevents it from dissipating too much outward. Figure 12 As shown.

[0044] Research and extensive simulation experiments have revealed that the energy is most concentrated when the three resonant rings on the same side are close to each other. For example... Figure 13 As shown, when the spacing between the three resonant rings is 0 (i.e., RING_x = 1.4, and the spacing between rings on the same side = RING_x - 1.4, unit: mm), S11 is minimized, indicating the best probe matching and more energy is radiated. Because energy is most concentrated at the center of the long side of the rectangle, when the position of the middle ring remains unchanged, the coupled energy decreases as the two outer rings are pulled apart. Although the tighter fit between the rings increases the metal width (reducing inductance) and also eliminates some inter-ring capacitance, its impact on matching is less significant than the change in coupled energy.

[0045] Regarding the Y-axis distribution of the secondary units (three rings on the same side constitute one secondary unit), it is necessary to select a position where the opening of the resonant ring is close to the edge of the rectangular slot or the top edge of the microstrip line. The precise optimal position is determined by software simulation and parameter scanning. Based on the above research and analysis, the arrangement and structure of the open resonant rings were finally determined. A probe with the above structure was ultimately developed.

[0046] This invention employs a multi-layer dielectric stepped structure. The lower dielectric plate has a metal feed wire on its lower surface, and the upper surface is covered with a 0.035mm metal ground plane. The ground plane has a rectangular gap for coupling the feed. Above the ground plane is an upper dielectric plate with a smaller area. The upper surface of the upper dielectric plate is a resonant ring structure. The resonant ring alters the current distribution, resulting in a converging effect that concentrates electromagnetic wave energy and improves sensitivity. Exposing a 4mm wide ground plane facilitates the soldering of SMA connectors. A single-layer side-feed structure, being coplanar with the resonant ring, would affect test results. The multi-layer structure makes the feed end and the resonant ring structure non-planar and increases the distance between the feed point and the test surface. It should be noted that, due to the need to expose part of the ground plane for easier physical fabrication (i.e., connecting the SMA connector), although the upper dielectric plate is designed to be smaller than the ground plane, its three edges must coincide with the ground plane. An upper dielectric plate that is too small or smaller than the ground plane will affect electromagnetic field propagation; however, an area that is too large will involve cost issues and inconvenience in practical applications. The ground plane reflects electromagnetic waves, and only through the gaps can electromagnetic waves reach the upper dielectric substrate. Misalignment will affect performance. The electromagnetic field energy distribution on the feeder line is regular. We only want the electromagnetic field radiated from the top of the feeder line to propagate to the upper dielectric substrate. Therefore, the lower dielectric substrate and the ground plane are the same size to prevent unwanted energy from radiating up.

[0047] Aperture-coupled feeding, compared to waveguide feeding, does not increase the cross-sectional area of ​​the unit (the cross-sectional area of ​​this unit is 20mm*20mm, while the rectangular waveguide in the X-band is 22.86mm*10.16mm, and the outer diameter of the circular waveguide also exceeds 20mm). Compared to traditional microstrip line feeding, aperture-coupled feeding has more adjustable parameters, such as the shape and length / width of the feed line, as well as the shape and length / width of the opening slot. This means that aperture-coupled feeding is easier to achieve impedance matching. Furthermore, it should be noted that the rectangular slot in the center of the ground plane is also part of the aperture-coupled feeding method. Electromagnetic waves from the SMA connector radiate at the top of the feed line. If the ground plane is intact, electromagnetic waves propagating from the lower dielectric substrate will be reflected and attenuated. This slot allows electromagnetic waves to pass through the ground plane and radiate to the upper dielectric substrate. Specific Implementation Method Two: This embodiment is a method for detecting defects in the microwave absorbing material on the outer surface of a metal. The probe of the first embodiment is used to detect the microwave absorbing coating on the outer surface of the metal and obtain the corresponding S11 curve. The damage detection of the microwave absorbing coating on the outer surface of the metal is realized based on the changes in the S11 curve.

[0049] Figure 14 To demonstrate the S11 curve variation when the probe structure detects defects at different depths in the metal outer absorbing coating, CST modeling and simulation were used. The absorbing material has a relative permittivity of 8.0, a relative permeability of 1.2, an electrical loss tangent of 0.5, a magnetic loss tangent of 0.9, and a thickness of 2.4 mm. The thickness of the metal behind the absorbing coating is 1 mm. Both the absorbing coating and the metal behind it are 100 mm * 100 mm in size. The test distance is 10 mm, and the defect is 10 mm long and 10 mm wide. The S11 curve of this probe changes with different depths of defects in the coating. Therefore, the probe of this invention can be used to detect defects in the absorbing material on the outer surface of metal. By mounting a robotic arm and connecting it to a vector network analyzer, the change of S11 at any scanning position can be obtained. Image data can be obtained through an inversion algorithm and then imaged.

[0050] The detection principle of this invention is near-field detection in microwave non-destructive testing. Therefore, this invention has many advantages of microwave non-destructive testing, especially near-field detection. Electromagnetic waves are transmitted from the feed end to the gap in the ground plane and radiated, where they are concentrated and emitted into free space by the resonant ring structure. When facing a complete absorbing material, the electromagnetic waves are absorbed, and the S11 parameter (i.e., reflection coefficient, in dB) is very small. However, when the absorbing material is damaged, its absorption capacity decreases, and some electromagnetic waves are reflected back and absorbed by the probe, thus increasing S11. Simulation results show... Figure 14 It can be seen that the deeper the defect, the larger S11 is.

[0051] Microwave nondestructive testing (NDT) is a non-contact testing method that utilizes the dielectric properties of materials and the electromagnetic properties of microwaves to detect hidden defects such as cracks, pores, inclusions, and lack of fusion in the tested material. It offers advantages such as requiring no coupling agent, no surface treatment of the metal, and no bonding. Microwave NDT is divided into two categories: far-field defect detection and near-field defect detection.

[0052] Near-field defect detection methods are a class of detection techniques based on the near-field effect. They utilize changes in the electromagnetic field, acoustic field, or other physical fields within the near-field region to detect minute defects in materials or devices. The basic principle is to leverage the localization and enhancement effect of the near-field field to overcome the diffraction limit of traditional far-field detection methods, achieving high-resolution and high-sensitivity defect detection. The importance of near-field defect detection methods lies in their ability to detect minute defects that are difficult to detect using traditional far-field methods, such as nanoscale cracks, micropores, and interface defects. These minute defects often have a significant impact on the performance and reliability of materials or devices; therefore, timely detection and identification of these defects are crucial for improving product quality and extending service life. Because near-field defect detection is closer to the object being detected, there is less external interference, making it more accurate than far-field defect detection.

[0053] The above examples of the present invention are merely illustrative of the computational model and process of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A resonant ring multilayer dielectric probe for detecting defects of a non-metallic wave-absorbing material on a metallic outer surface, characterized in that, The probe has a multi-layer planar structure, consisting of a feed line, a lower dielectric substrate, a ground plane, an upper dielectric substrate, and a radiating metal patch from bottom to top. The radiating metal patch, the ground plane, and the feed line are metal layers. A rectangular slot is provided in the center of the ground plane. Microstrip lines are printed on the underside of the lower dielectric substrate for power feeding. The radiating metal patch consists of multiple rectangular resonant rings arranged symmetrically in a matrix structure. Each rectangular resonant ring is composed of an outer ring and an inner ring, with a gap between them. Both the outer and inner rings have openings. The resonant rings are printed on the upper dielectric substrate. The outer ring opening points towards the geometric center of the upper dielectric substrate plane, while the inner ring opening faces away from the geometric center of the upper dielectric substrate plane. The size of the upper dielectric substrate is smaller than that of the ground plane, and the three edges of the upper dielectric substrate coincide with the three edges of the ground plane.

2. The resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in claim 1, is characterized in that... The radiating metal patch consists of six rectangular resonant rings arranged in a 3*2 matrix structure. The three rectangular resonant rings in one row are arranged side by side to form a group, and the other three rectangular units form another group and are symmetrically arranged with the first group.

3. A resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in any one of claims 1 to 2, characterized in that, The rectangular resonant ring has an outer ring opening of 0.21 mm, an inner ring opening of 0.25 mm, an outer ring diameter of 1.4 mm, an inner ring diameter of 1.04 mm, a gap distance of 0.08 mm between the outer and inner rings, and a width of 0.1 mm for both the outer and inner rings.

4. A resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in claim 3, is characterized in that... The two sets of rectangular resonant rings are 1.9 mm apart.

5. A resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in claim 1, is characterized in that... The material of the lower dielectric substrate has a relative permittivity of 9.8 and an electrical loss tangent of 0.0020; the material of the upper dielectric substrate has a relative permittivity of 3.2 and an electrical loss tangent of 0.0018.

6. A resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in claim 1, is characterized in that... The thickness of the radiating metal patch, ground plane, and feeder cable is 0.035mm.

7. A resonant ring multilayer dielectric probe for detecting defects in non-metallic absorbing materials on the outer surface of a metal, as described in claim 1, is characterized in that... The upper dielectric substrate size is The dimensions of the lower dielectric substrate are The dimensions of the grounding plate are: There is an 8mm*2mm rectangular gap located 7.35cm from the top edge of the floor, 10.65cm from the bottom edge, 6mm from the left edge, and 6mm from the right edge.

8. A method for detecting defects in microwave absorbing materials on the outer surface of metals, characterized in that, The probe described in any one of claims 1 to 7 is used to detect the non-metallic absorbing coating on the outer surface of a metal and obtain the corresponding S11 curve. Based on the changes in the S11 curve, the damage detection of the absorbing coating on the outer surface of the metal is realized.

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