A microwave sensor suitable for non-destructive testing of metal mesh films

Abstract

A kind of microwave sensor suitable for metal mesh film nondestructive testing, belong to microwave sensor technology, by dielectric substrate, microstrip line, resonant structure, SMA joint pad, metallization via, depth control mounting hole, straight insertion type SMA joint, fixing screw, metal ground layer, radio frequency coaxial line and microwave transceiver equipment are constituted;Among them, resonant structure is a plurality of Archimedes spiral line etched on metal ground layer, is fed by microstrip line;Fixing screw is fixed with straight insertion type SMA joint and SMA joint pad;Fixing screw head is embedded in dielectric substrate, so that the bottom of sensor is flat without protrusion;Sensor realizes the detection of each direction width sub-millimeter level crack damage on metal mesh film and the identification of high square resistance sample respectively by the shift of resonant frequency and the change of resonant quality factor, detection sensitivity is high, and sensor structure is compact, small in size, fast in response speed, can be applied to nondestructive testing of large area metal mesh film.

Description

Technical Field

[0001] This invention belongs to the field of microwave sensors, and mainly relates to a microwave sensor suitable for non-destructive testing of metal mesh thin films. Background Technology

[0002] With the increasing intensity of electromagnetic waves in space and the continuous expansion of application bands, the electromagnetic environment is becoming increasingly complex, leading to the requirement for electromagnetic wave shielding in many fields. For optical instruments used in aerospace equipment for detection and observation, high light transmittance is required while ensuring strong electromagnetic shielding performance, rendering traditional electromagnetic shielding materials unsuitable. Metal mesh films, as a type of transparent conductive film, have low production costs and simple fabrication processes, and are currently being used in transparent window electromagnetic shielding in aerospace equipment and other fields.

[0003] Metal mesh optical windows are used in fields such as aerospace equipment. After prolonged use, cracks, damage, and even large-area detachment can occur, leading to a decrease in electromagnetic shielding efficiency or even complete failure. Simultaneously, oxidation and corrosion from exposure to air, as well as external abrasion, can cause a decrease in the conductivity and thickness of the metal mesh, resulting in increased sheet resistance and reduced shielding effectiveness. Therefore, there is an urgent need to develop corresponding non-destructive testing techniques for metal mesh to assess the phenomena of film damage and increased sheet resistance in metal mesh.

[0004] However, research on nondestructive testing technology for metal mesh thin films is currently very limited. Patent 201410131635.5, "A Method for Detecting and Identifying Defects in Metal Mesh Grids," describes a detection method based on optical imaging and image defect recognition algorithms. However, this method requires prior information about the mesh structure, and subsequent data processing is cumbersome, resulting in low overall detection efficiency and an inability to evaluate the sheet resistance of the mesh. Furthermore, the optical imaging-based method is highly dependent on background light, making it difficult to guarantee a high defect detection rate in complex environments. Therefore, a method for detecting metal mesh thin films capable of extracting the physical field characteristics of defects is needed.

[0005] Microwave sensors have advantages such as small size, high sensitivity, and non-contact detection, and have potential applications in areas such as crack detection on metal surfaces and measurement of dielectric constants of dielectrics. Some typical research works on this type of sensor are as follows:

[0006] 1. Patent 202011591212.3, "An Active Microwave Sensor Based on a Microstrip Complementary Open-Loop Resonator Structure," describes a microwave sensor for measuring the complex permittivity of a dielectric material. This sensor introduces an active amplification element, improving the quality factor and detection sensitivity. However, the sensor uses an SMA connector for power supply, resulting in limited detection space and making it unsuitable for detecting large-area metal mesh films.

[0007] 2. Patent 202122725602.1, "A Microstrip Metal Crack Detection Sensor Based on Resonance Shift," describes a contact-type microwave sensor that uses the metal under test as a compensation plane for the defect structure. When a crack is detected, the resonant frequency shifts. This sensor is a contact-type detection method and is not suitable for detecting easily scratched micro / nano metal structures such as metal mesh.

[0008] 3. In their paper “Microwave Subsurface Imaging of Composite Structures Using Complementary Split Ring Resonators”, Govind Greeshmaja et al. from Kanpur Institute of Technology in India proposed a microwave sensor with an etched circular complementary split ring structure for detecting subsurface defects inside a composite structure composed of dielectric and metal layers. It has high detection sensitivity; however, this structure does not have the ability to detect cracks at all angles.

[0009] 4. In his paper "A Simple High-Resolution Near-Field Probe for Microwave Non-Destructive Test and Imaging," Xie Zipeng of the University of Science and Technology of China proposed a single-port sensing structure for detecting and imaging micro-cracks on surfaces. This structure utilizes a microstrip ring connected to a short microstrip line to excite a complementary helical resonator, enabling the detection of crack defects in large-area metal samples. However, the resonant frequency of this sensing structure is relatively low, resulting in poor resonance performance when used for detecting metal mesh thin films. Currently, no microwave sensors suitable for detecting damage to metal mesh thin films have been reported. Summary of the Invention

[0010] To address the issues of low detection efficiency, difficulty in maintaining detection rates under complex backgrounds, and inability to identify high sheet resistance meshes using optical imaging methods, this invention designs a microwave sensor suitable for non-destructive testing of metal mesh thin films based on the cavity perturbation principle. This sensor can perform real-time localization and identification of sub-millimeter-width cracks and localized increases in sheet resistance on large-area metal mesh thin films.

[0011] The technical solution of the present invention is as follows:

[0012] A microwave sensor suitable for detecting damage to metal mesh thin films includes a dielectric substrate, a microstrip line, a resonant structure, SMA connector pads, metallized vias, depth-controlled mounting holes, a through-hole SMA connector, fixing screws, a metal ground plane, an RF coaxial cable, and a microwave transceiver. This sensor is a two-port sensor. The dielectric substrate, microstrip line, resonant structure, SMA connector pads, metallized vias, depth-controlled mounting holes, through-hole SMA connector, fixing screws, and metal ground plane together constitute the sensor's probe. Two annular SMA connector pads are printed on the front side of the dielectric substrate, and the outer pads of the connector pads penetrate the dielectric substrate. The metallized vias of the board maintain electrical connection with the underlying metal ground layer; fixing screws secure the through-hole SMA connector to the SMA connector pads through depth-controlled mounting holes, with the screw heads embedded in the dielectric substrate to ensure a flat, protrusion-free bottom for the sensor; the inner and outer conductors of the through-hole SMA connector contact the inner and outer pads of the SMA connector, respectively; the microstrip line is slotted through the outer conductor of the through-hole SMA connector, and the microstrip line width transitions uniformly from the diameter of the inner pad of the SMA connector to the microstrip width corresponding to a 50Ω characteristic impedance; the resonant structure is formed by etching M spiral lines on the metal ground layer on the back of the dielectric substrate, with the equation of a single spiral line being:

[0013]

[0014] Where s is the helix width, w is the distance between adjacent helices, and θ is the final angle of the helix; the resonant structure is obtained by rotating a single helix M times, with each rotation angle being (360 / M)°; the dielectric substrate is parallel to the surface of the grid under test, with a vertical distance of 0.1-1mm, to detect defects in the grid under test; the microwave transceiver is connected to the sensor probe via an RF coaxial line and records and displays the detection results.

[0015] As a preferred structure, the etching spiral equation has a spiral width s ranging from 0.1 to 0.2 mm, an adjacent spiral spacing w ranging from 0.1 to 0.2 mm, a spiral terminal angle θ ranging from 2π to 4π, and a spiral line number M ranging from 1 to 5.

[0016] As a preferred structure, the metal mesh film material that the sensor can detect includes copper, aluminum, gold, and silver; the substrate material includes ordinary glass, quartz glass, infrared materials, and transparent resin materials; the metal mesh linewidth ranges from 1 to 20 μm; the metal mesh period ranges from 50 to 400 μm; the metal mesh thickness ranges from 50 to 1000 nm; and the shape and arrangement of the metal mesh unit include square mesh, circular mesh, triangular distributed circular and sub-circular array mesh, metal mesh based on randomly distributed circular rings, and metal mesh based on multi-period nested array of metal circular rings.

[0017] As a preferred structure, the sensor probe is manufactured using standard PCB processes, and the dielectric substrate material is a high-frequency PCB substrate material.

[0018] This invention has the following advantages and outstanding effects:

[0019] 1. The microwave sensor proposed in this invention for non-destructive testing of metal mesh thin films employs a resonant structure obtained by etching multiple Archimedean spirals. This structure can generate a strong bound electric field in the near-field region and simultaneously form a uniform induced current on the metal surface, exhibiting high detection sensitivity for cracks and damage in all directions. Furthermore, compared to optical imaging methods, this microwave sensor has a faster response speed, can identify high sheet resistance meshes, requires no subsequent data processing, has high detection efficiency, and is versatile for detecting metal mesh thin films with different unit shapes and arrangements.

[0020] 2. The microwave sensor proposed in this invention, suitable for non-destructive testing of metal mesh thin films, adopts a through-hole SMA connector and has corresponding pads. The outer pad of the pad is electrically connected to the underlying metal ground layer through a metallized through-hole penetrating the dielectric substrate. The through-hole SMA connector is fixed to the SMA connector pad through a depth-controlled mounting hole by a fixing screw. The head of the fixing screw is embedded in the dielectric substrate, making the bottom of the sensor flat and without protrusions. This design avoids the use of traditional terminated SMA connectors, expands the detection space under the sensor, and is suitable for non-destructive testing of large-area samples. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the front structure of a microwave sensor suitable for detecting damage to metal mesh thin films according to the present invention.

[0023] Figure 2 This is a schematic diagram of the back structure of a microwave sensor suitable for detecting damage to metal mesh thin films according to the present invention.

[0024] Figure 3 This is a schematic diagram of the resonant structure of Example 1.

[0025] Figure 4 This is a schematic diagram of detecting damage to the metal mesh film in Example 1.

[0026] Figure 5 The transmission characteristic change curves of defect-free metal mesh, cracked and damaged metal mesh, and high sheet resistance metal mesh are shown in Example 1.

[0027] Part Number: In the figure, 1—dielectric substrate, 2—microstrip line, 3—resonant structure, 4—SMA connector pad, 5—metallized through-hole, 6—depth-controlled mounting hole, 7—through-hole SMA connector, 8—fixing screw, 9—metallic ground layer, 10—RF coaxial cable, 11—microwave transceiver. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments: The object of the present invention is achieved as follows: The present invention proposes a microwave sensor suitable for detecting damage to metal mesh thin films, comprising a dielectric substrate, a microstrip line, a resonant structure, SMA connector pads, metallized vias, depth-controlled mounting holes, a through-hole SMA connector, fixing screws, a metal ground layer, an RF coaxial cable, and a microwave transceiver; the sensor is a two-port sensor. Figure 1 This is a schematic diagram of the front structure of the sensor. Two circular SMA connector pads are printed on the front of the sensor. The outer pad of the SMA connector pad is electrically connected to the metal ground plane on the back side through a metallized via penetrating the dielectric substrate. A mounting screw secures the through-hole SMA connector to the SMA connector pad through a depth-controlled mounting hole. The screw head is embedded into the dielectric substrate, ensuring a flat, protrusion-free bottom for the sensor. The inner and outer conductors of the through-hole SMA connector are connected to the inner and outer pads of the SMA connector pad, respectively. A microstrip line is printed on the front side of the dielectric substrate, with each end connected to one of the two pads. A schematic diagram of the back structure of the sensor is shown below. Figure 2 As shown, the resonant structure is formed by etching M Archimedean spirals into the back metal substrate. The sensor detection principle is as follows: when a crack exists, electromagnetic energy penetrates into the high dielectric constant substrate, causing the overall dielectric constant of the resonant region to increase. According to the perturbation principle, the resonant frequency will shift downward. When the sheet resistance of the metal mesh increases, more electromagnetic energy is lost in the form of heat, resulting in a decrease in the quality factor of the resonance.

[0029] To facilitate understanding of the present invention, the invention will be described more clearly and completely below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Example 1:

[0031] Figure 3 The diagram below shows the sensor resonant structure in Example 1. In this example, the typical structural parameters of the resonant structure are: helix linewidth s = 0.12 mm, metal gap width w = 0.16 mm, helix terminal angle θ = 3π, and number of helix lines M = 5. The resonant structure has a resonant frequency of 7.05 GHz when detecting a defect-free metal mesh film under a lift-off distance of 0.3 mm. Figure 4This is a schematic diagram of the detection of metal mesh film damage in Example 1. A vector network analyzer was used as the microwave transceiver. The specific detection steps are as follows: First, the vector network analyzer was set to frequency sweep measurement, with a sweep range of 5-9 GHz, and the measurement parameter was S. 21 After performing open-circuit-short-circuit-matching-straight-through calibration on the two ports, the sensor's two ports are connected to the analyzer port via an RF cable. The sensor is fixed on the two-dimensional scanning mechanism, maintaining a vertical distance of 0.3 mm between the resonant structure and the metal mesh film under test. The motion trajectory of the scanning mechanism is set as follows. Figure 4 The dashed line traverses the trajectory to establish a communication connection between the network analyzer and the host computer, and collects the resonant frequency and amplitude at the resonant frequency of the analyzer in real time.

[0032] The effects of this invention can be achieved through Figure 5 Further explanation:

[0033] When the above embodiment detects a crack with a width of 0.6 mm and a length of 6 mm, the resonant frequency changes from 7.05 GHz to 6.58 GHz, a decrease of 470 MHz. When the sheet resistance of the grid under test is increased to twice its original value, the quality factor of the resonant curve decreases significantly, and the transmission amplitude at the resonant frequency increases from -17.2 dB to -8.6 dB. These results demonstrate that the above embodiment can achieve accurate detection of sub-millimeter-width grid cracks and identification of different grid sheet resistance values.

[0034] The above description is only one specific example of the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A microwave sensor suitable for metal mesh film non-destructive testing, comprising a dielectric substrate (1), a microstrip line (2), a resonant structure (3), an SMA connector pad (4), a metallized via (5), a depth control mounting hole (6), a straight-through SMA connector (7), a fixing screw (8), a metal ground layer (9), a radio frequency coaxial line (10) and a microwave transceiver device (11), wherein (1)-(9) collectively constitute a sensor probe, characterized in that, The front side of the dielectric substrate (1) is printed with an annular SMA connector pad (4) and a microstrip line (2). The outer pad of the SMA connector pad (4) is electrically connected to the metal ground layer (9) on the back side through a metallized through-hole (5) penetrating the dielectric substrate (1). The fixing screw (8) fixes the through-hole SMA connector (7) to the dielectric substrate (1) through the depth control mounting hole (6). The head of the fixing screw (8) is fully embedded in the dielectric substrate (1), making the bottom of the sensor flat and without protrusions. The inner and outer conductors of the through-hole SMA connector (7) are in contact with the inner and outer pads of the SMA connector pad (4), respectively. The microstrip line (2) is slotted through the outer conductor of the through-hole SMA connector (7). The width of the microstrip line (2) transitions evenly from the diameter of the inner pad of the SMA connector pad (4) to the microstrip width corresponding to the 50Ω transmission line impedance. The resonant structure (3) is formed by etching M spiral lines on the metal ground layer (9) on the back side of the dielectric substrate (1). The equation of a single spiral line is: Where s is the helix width, w is the distance between adjacent helices, and θ is the final angle of the helix; the resonant structure (3) is obtained by rotating a single helix M times, with each rotation angle being (360 / M)°; the dielectric substrate (1) is parallel to the surface of the grid to be tested, with a vertical distance of 0.1-1mm; the microwave transceiver (11) is connected to the sensor probe through the radio frequency coaxial line (10) and processes and displays the detection results.

2. A microwave sensor suitable for non-destructive testing of metal mesh thin films according to claim 1, characterized in that: The etching spiral equation has a spiral width s ranging from 0.1 to 0.2 mm, a spacing w between adjacent spirals ranging from 0.1 to 0.2 mm, a spiral terminal angle θ ranging from 2π to 4π, and a spiral line number M ranging from 1 to 5.

3. A microwave sensor suitable for non-destructive testing of metal mesh thin films as described in claim 1, characterized in that: The metal mesh film that the sensor can detect includes copper, aluminum, gold, and silver; the substrate material includes ordinary glass, quartz glass, infrared materials, and transparent resin materials; the metal mesh linewidth ranges from 1 to 20 μm, the metal mesh period ranges from 50 to 400 μm, the metal mesh thickness ranges from 50 to 1000 nm, and the shape and arrangement of the metal mesh unit include square mesh, circular mesh, triangular distributed circular and sub-circular array mesh, metal mesh based on randomly distributed circular rings, and metal mesh based on multi-period nested array of metal circular rings.

4. A microwave sensor suitable for non-destructive testing of metal mesh thin films as described in claim 1, characterized in that: The sensor probe is manufactured using standard PCB processes, and the dielectric substrate material is a high-frequency PCB substrate material.

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