Millimeter wave-terahertz frequency band conductive wire surface conductivity testing device and method

Abstract

This invention provides a device and method for testing the surface conductivity of conductive wires in the millimeter-wave to terahertz frequency band, belonging to the field of surface conductivity testing technology. The testing device is designed based on a double-concave quasi-optical cavity and innovatively utilizes the differentiated multi-mode of the quasi-optical cavity to accurately extract key geometric and electrical parameters of the conductive wire: the electric field of the symmetric mode is concentrated on the cavity axis, and the radius of the conductive wire at this position directly affects the coupling volume with the electric field. Therefore, the frequency shift of the symmetric mode is used to calculate the precise radius of the conductive wire based on the principle of shape perturbation; the antisymmetric mode has a zero electric field at the axis and is more sensitive to surface loss. The quality factor variation value is determined using the antisymmetric mode. Finally, based on the cavity wall impedance perturbation theory, combined with the radius and quality factor, the surface conductivity of the conductive wire is measured, achieving accurate measurement of the surface conductivity of a single fine conductive wire in the millimeter-wave to terahertz frequency band.

Description

Technical Field

[0001] This invention belongs to the field of conductive material surface conductivity testing technology, specifically relating to a device and method for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz frequency band. Background Technology

[0002] In the millimeter-wave to terahertz frequency band, electronic systems and functional devices are rapidly developing towards miniaturization, integration, and high frequency. This trend places extremely high demands on the conductivity, structural dimensions, and high-frequency stability of high-frequency interconnect and signal transmission materials, making fine conductive filaments with excellent conductivity a key fundamental material in cutting-edge fields such as high-frequency transmission lines, micro-antennas, precision sensors, terahertz waveguides, and quantum interconnects. In these applications, the surface conductivity of the conductive filament directly affects signal transmission efficiency, energy loss, and overall device performance. Especially in the millimeter-wave to terahertz frequency band, due to the significant skin effect and the high concentration of electromagnetic fields in the very shallow surface of the conductor, surface conductivity becomes a core electromagnetic parameter determining device performance. Therefore, developing a testing device and method capable of directly, accurately, and reliably measuring the surface conductivity of a single fine conductive filament in the millimeter-wave to terahertz broadband band is an urgent technical need with significant application value.

[0003] Currently, the mainstream methods for measuring the surface conductivity of conductive wires mainly include the transmission line method and the resonant cavity method. Among them, the resonant cavity method, due to its high precision advantage, has been used to measure the surface resistivity of metal wires in the millimeter-wave band. For example, in the paper "Resonant microwave measurement of the electric conductivity of wires," Salski et al. used a cylindrical resonant cavity to achieve related measurements in the 20–40 GHz frequency band. However, traditional resonant cavity structures and methods face significant challenges when extending to higher frequency bands, especially the terahertz band: increasing frequency leads to a sharp reduction in resonant cavity size, increasing fabrication difficulty, increasing the difficulty of mode control and coupling, and imposing extremely stringent requirements on sample size and positioning accuracy, making it difficult for existing methods to achieve effective and accurate measurements in the terahertz band. In addition, the applicable frequency band of the testing equipment is too narrow.

[0004] The quasi-optical cavity method, based on perturbation theory, establishes a correlation between measurable physical quantities and the measured parameters by measuring the changes in resonant frequency and quality factor before and after sample loading. Currently, this method is mainly used for measuring the complex permittivity of dielectric materials and characterizing the dielectric properties of thin films and multilayer structures, employing a symmetrical mode of the quasi-optical cavity during testing. In the surface conductivity testing of conductive materials, the quasi-optical cavity method typically uses a resonant cavity composed of spherical and plane mirrors, with the sample under test replacing the original standard plane mirror as a reflecting end face of the resonant cavity. In this case, the surface conductivity of the sample directly affects the total cavity loss. By measuring the changes in the resonant frequency and Q-value of the cavity before and after loading the sample, the surface conductivity is deduced using a theoretical model. The limitations of this method lie in the requirement that the sample under test be directly integrated into the resonant structure, and that the sample must be sheet-like. The test area must be at least five times the beam waist radius to ensure that almost all electromagnetic energy is contained.

[0005] Therefore, how to achieve convenient, high-precision, and wide-bandwidth measurement of the surface conductivity of a single fine conductive filament based on the quasi-optical cavity method is an urgent problem to be solved. Summary of the Invention

[0006] To address the problems existing in the background technology, the present invention aims to provide a device and method for testing the surface conductivity of conductive wires in the millimeter-wave to terahertz frequency band. The testing device of this invention is designed based on a double-concave quasi-optical cavity, and innovatively utilizes the differentiated use of multiple modes of the quasi-optical cavity to accurately extract the key geometric and electrical parameters of the conductive wire: the electric field of the symmetric mode is concentrated on the cavity axis, and the radius of the conductive wire at this position directly affects the coupling volume with the electric field. Therefore, the frequency shift of the symmetric mode is used to calculate the accurate radius of the conductive wire based on the principle of shape perturbation; the antisymmetric mode has a zero electric field at the axis and is more sensitive to surface loss. The quality factor variation value is determined using the antisymmetric mode, and finally, based on the cavity wall impedance perturbation theory, the surface conductivity of the conductive wire is measured by combining the radius and the quality factor. Through the division of labor and cooperation between the two modes, the coupling influence of geometric parameters and electromagnetic parameters on the measurement results can be effectively separated, thus overcoming the limitation of traditional methods that are only applicable to sheet-like samples, and realizing the accurate measurement of the surface conductivity of a single fine conductive wire in the millimeter-wave to terahertz frequency band.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A device for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz band includes a quasi-optical cavity, a coupling unit, a fixing unit, a vector network analyzer, and a computing and processing unit.

[0009] The quasi-optical cavity is a double-concave quasi-optical cavity. A coupling hole is opened at the center of the short surface of the quasi-optical cavity for setting the coupling unit. The vector network analyzer is connected to the coupling device, and the calculation and processing unit is connected to the vector network analyzer to perform data processing. The fixing unit is used to fix and straighten the conductive wire under test so that the conductive wire under test passes through the center of the quasi-optical cavity. The magnetic field is strongest at this point under antisymmetric mode resonance and is perpendicular to the line connecting the center of the quasi-optical cavity.

[0010] The testing device employs TEM during testing. 00q The mode is symmetrical when q is even and antisymmetric when q is odd. The diameter of the conductive wire under test is measured in the symmetrical mode and the quality factor of the conductive wire under test is measured in the antisymmetric mode.

[0011] Furthermore, the dimensions of the conductive wire to be tested should meet the requirements for use of the perturbation method, preferably a conductive wire with a diameter of 0.1 mm to 2.0 mm.

[0012] Furthermore, the biconcave collimator is composed of two spherical mirrors.

[0013] The present invention also provides a testing method based on the above-described testing apparatus, comprising the following steps:

[0014] Step 1. Set up and debug the test setup. Set the frequency range and number of scan points of the vector network analyzer according to the test frequency and the required test time.

[0015] Step 2. Without placing the conductive wire under test, measure the resonant frequency of the quasi-optical cavity symmetrical mode in the cavity state. The resonant frequency of the antisymmetric mode And the quality factor of the antisymmetric model ;

[0016] Step 3. Place the conductive wire to be tested, and straighten it horizontally so that its axial direction is perpendicular to the central axis of the quasi-optical cavity. Measure the resonant frequency of the symmetrical mode at this point. And the quality factor of the antisymmetric model ;

[0017] Step 4. Based on the resonant frequency obtained from the two measurements. , The radius of the conductive wire under test is inverted using the shape perturbation method. The specific calculation method is as follows:

[0018]

[0019]

[0020] in, The permeability of free space, The vacuum permittivity, and These are the magnetic field vector and electric field vector of the symmetric mode inside the quasi-optical cavity, respectively. Let V be the volume of the conductive wire under test within the working area, and let V be the volume of the quasi-optical cavity containing the electromagnetic field. L is the radius of the conductive wire, and L is the length of the conductive wire within the working area, which is within 2.5 times the waist radius.

[0021] Based on the quality factor obtained from the two measurements , The surface conductivity of the conductive wire under test is calculated using the cavity wall impedance perturbation method. The specific calculation method is as follows:

[0022]

[0023] in, It is the ohmic loss of the conductive wire under test; It is the mirror loss of the dual-cavity mirror;

[0024] Surface conductivity The calculation formula is:

[0025]

[0026]

[0027]

[0028]

[0029] In the formula, W represents the energy stored at quasi-optical cavity resonance. To reduce power loss in the conductive wire, Surface resistivity, It is the resonant angular frequency. It is the resonant frequency of the cavity antisymmetric mode. The permeability of free space, It is the magnetic field vector of the antisymmetric mode inside the quasi-optical cavity. It is the tangential magnetic field vector of the antisymmetric mode on the surface of the conductive wire under test. Let be the surface area of ​​the conductive wire under test within the working area. Let ds be the tangential magnetic field vector of the antisymmetric mode inside the quasi-optical cavity, dv be the area element on the surface of the conductive wire to be measured, and dv be the volume element in the working region of the quasi-optical cavity.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] (1) This invention proposes a surface conductivity testing system based on an open double concave quasi-optical cavity. This structure has an extremely high quality factor and good mode purity in the millimeter-wave-terahertz frequency band, which can effectively suppress miscellaneous mode interference, improve the frequency applicability range, and overcome the limitations of traditional closed resonant cavities in high-frequency bands, such as difficulty in processing, mixed modes, and inconvenience in layout and positioning.

[0032] (2) This invention creatively utilizes the symmetric and antisymmetric modes in a double concave quasi-optical cavity to achieve synchronous measurement of the geometric and electrical parameters of the conductive wire: the radius of the conductive wire is inverted by the frequency shift of the symmetric mode, and the geometric dimensions are calibrated without damage; the surface conductivity is extracted by the change of the quality factor of the antisymmetric mode, giving full play to the high sensitivity of this mode to the surface loss of the conductor, and solving the problem that the traditional quasi-optical cavity method is difficult to directly and accurately measure the surface conductivity of a single fine conductive wire in the terahertz band.

[0033] (3) The present invention designs a special sampling and tension adjustment fixture that integrates V-groove, bearing and weight, which can keep the conductive wire in a uniform tension state during the measurement process, effectively avoid measurement errors caused by sample relaxation, bending or poor contact, and greatly improve the repeatability and accuracy of the test. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the conductive wire surface resistance testing system of the present invention.

[0035] Figure 2 This is a detailed assembly diagram of the conductive wire surface resistance testing system of the present invention.

[0036] Figure 3 This is an assembly diagram of the first conductive wire clamp of the present invention.

[0037] Figure 4 This is an assembly diagram of the second conductive wire clamp of the present invention.

[0038] Figure 5 This is a schematic diagram of the integration region involved in step 4 of the test method of the present invention.

[0039] Reference numerals in the attached figures: 1 is the quasi-optical cavity, 2 is the quasi-optical cavity fixing base, 3 is the coupling device, 4 is the weight, 5 is the X-displacement platform, 6 is the Z-displacement platform, 7 is the first positioning plate, 8 is the first conductive wire clamp, 9 is the second positioning plate, 10 is the second conductive wire clamp, 11 is the acrylic cover, 12 is the vector network analyzer, 13 is the V-groove, 14 is the wire rod, 15 is the conductive wire, 16 is the bearing fixing device, 17 is the bearing, 18 is the wire support rod, and 19 is the computer. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0041] A system for testing the surface conductivity of conductive wires in the millimeter-wave to terahertz frequency band, with overall schematic diagram and detailed schematic diagram, as follows: Figure 1 and Figure 2 As shown, it includes a quasi-optical cavity 1, a quasi-optical cavity fixing base 2, a coupling device 3, a weight 4, a horizontal displacement platform 5 (X displacement platform) along the cavity length direction, a height displacement platform 6 (Z displacement platform), a first positioning plate 7, a conductive wire clamp 1 8, a second positioning plate 9, a conductive wire clamp 2 10, an acrylic cover 11, a vector network analyzer 12, and a computer 19.

[0042] The collimated cavity 1 is a biconcave collimated cavity composed of two spherical mirrors; the collimated cavity fixing base 2 includes two identical "L"-shaped base plates, which are arranged opposite to each other. The two spherical mirrors of the collimated cavity are both horizontally arranged across the two base plates and kept parallel in the vertical direction; an acrylic cover 11 is placed outside the collimated cavity 1 to ensure the stability of the collimated cavity system and prevent disturbance; the first positioning plate 7 and the second positioning plate 9 are arranged opposite to each other and placed outside the collimated cavity 1. Both the first positioning plate 7 and the second positioning plate 9 have small circular holes with a diameter of 2.5 mm. The line connecting the centers of the holes is perpendicular to the line connecting the centers of the collimated cavity 1. The conductive wire to be tested can be initially positioned by passing through the small circular holes of the first positioning plate and the second positioning plate respectively.

[0043] The X-displacement platform 5, the Z-displacement platform 6, and the first conductive wire clamp 8 are fixed sequentially from top to bottom on the first positioning plate 7; the X-displacement platform 5, the Z-displacement platform 6, and the second conductive wire clamp 10 are fixed sequentially from bottom to top on the second positioning plate 9; one end of the conductive wire to be tested is fixed to the first conductive wire clamp 8, and the other end is connected to a weight and fixed to the second conductive wire clamp 10.

[0044] A coupling hole is opened at the center of the short surface of the quasi-optical cavity 1 to set up the coupling device 3. The vector network analyzer 12 is connected to the coupling device 3, and the computer 19 is connected to the vector network analyzer 12 for program control.

[0045] like Figure 3 The diagram shows the assembly schematic of the first conductive wire clamp 8. The first conductive wire clamp includes a support and a pull rod 14. The upper surface of the support is provided with a longitudinally extending groove. The cross-section of the groove is V-shaped 13 with an opening angle of 90° and a groove depth of 3mm. The pull rod is placed on the V-shaped groove. The front end of the pull rod has an opening for winding conductive wire 15. The pull rod is fixed to the support by screws, thereby fixing the conductive wire at one end.

[0046] like Figure 4The diagram shows the assembly of the second conductive wire clamp 10, which includes a bearing fixing device 16, a bearing 17, and a wire support rod 18. The bearing 17 is fixedly disposed at the center of the bearing fixing device 16, and the wire support rod 18 is fixedly disposed on the side of the bearing fixing device. The conductive wire 15 passes through the bearing 17 and the wire support rod 18, and the other end is connected to a weight 4. The weight should be selected to be of a suitable weight that can straighten the conductive wire without deformation. The bearing fixing device 16 includes a mounting base body, on which a first through hole extending horizontally is provided. The diameter of the first through hole is adapted to the outer ring diameter of the bearing for accommodating the bearing. The bearing has an overall disc-shaped structure, and an annular groove is provided on its outer peripheral wall in the circumferential direction, making the cross-section of the bearing "H" shaped. The central part of the bearing extends backward along the cavity length to form an extension, the outer ring diameter of which matches the first through hole of the bearing fixing device. The wire support rod is cylindrical, with an arc transition surface in the middle along the circumference. The conductive wire to be tested extends through an annular groove to the arc transition surface of the wire support rod. A weight is placed at the other end of the conductive wire to be tested, and the weight is vertically suspended.

[0047] Example 1

[0048] A method for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz band includes the following steps:

[0049] Step 1. Build and debug the test system. The radius of curvature of the spherical mirror of the quasi-optical cavity 1 is 120mm, the cavity length is 160mm, and the aperture of the spherical mirror is 151.67mm. A coupling hole with a diameter of 0.5mm is opened at the center of the short surface of the cavity. The quasi-optical cavity operates in the Ka band. Set the frequency range and number of scanning points of the vector network analyzer according to the test frequency and the test time required.

[0050] Step 2. Without placing the conductive wire under test, measure the resonant frequency of the quasi-optical cavity symmetrical mode in the cavity state. and the resonant frequency of the antisymmetric mode and quality factor ;

[0051] Step 3. Fix one end of the conductive wire using the first conductive wire clamp. Pass the conductive wire through the first positioning plate, the acrylic cover, and the second positioning plate, and place it on the second conductive wire clamp. Connect the other end of the conductive wire to a weight. Adjust the X-displacement platform and Z-displacement platform on the first and second positioning plates respectively to make the axial direction of the conductive wire to be measured perpendicular to the central axis of the quasi-optical cavity. After the conductive wire is horizontally stable, measure the resonant frequency of the symmetrical mode at this time. And the quality factor of the antisymmetric model ;

[0052] Step 4. Based on the resonant frequency obtained from the two measurements. , The radius of the conductive wire under test is inverted using the shape perturbation method. The specific calculation method is as follows:

[0053]

[0054]

[0055] in, The permeability of free space, The vacuum permittivity, and These are the magnetic field vector and electric field vector of the symmetric mode inside the quasi-optical cavity, respectively. Let V be the volume of the conductive wire under test within the working area, and let V be the volume of the quasi-optical cavity containing the electromagnetic field. L is the radius of the conductive wire, and L is the length of the conductive wire within the working area, which is within 2.5 times the waist radius.

[0056] Based on the quality factor obtained from the two measurements , The surface conductivity of the conductive wire under test is calculated using the cavity wall impedance perturbation method. The specific calculation method is as follows:

[0057]

[0058] in, It is the ohmic loss of the metal under test; It is the mirror loss of the dual-cavity mirror;

[0059] Surface conductivity The calculation formula is:

[0060]

[0061]

[0062]

[0063] In the formula, W represents the energy stored at quasi-optical cavity resonance. To reduce power loss in the conductive wire, It is the resonant angular frequency. It is the resonant frequency of the cavity antisymmetric mode. The permeability of free space, It is the magnetic field vector of the antisymmetric mode inside the quasi-optical cavity. It is the tangential magnetic field vector of the antisymmetric mode on the surface of the conductive wire under test, and V is the cavity space volume containing the electromagnetic field of the quasi-optical cavity. The surface area of ​​the conductive wire under test within the working area;

[0064] The schematic diagram of the integration region involved in step 4 is shown below. Figure 5 As shown in the figure, D is the quasi-optical cavity length, R is the radius of curvature, W0 is the beam waist radius, W(z) is the spot radius of the Gaussian beam at the mirror position, pink represents the integral cross-section of V, and gray represents the conductive filament. The length of the integration region.

[0065] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A device for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz frequency band, characterized in that, It includes a quasi-optical cavity, coupling unit, fixing unit, vector network analyzer, and computing processing unit; The quasi-optical cavity is a double-concave quasi-optical cavity. A coupling hole is opened at the center of the short surface of the quasi-optical cavity for setting the coupling unit. The vector network analyzer is connected to the coupling device, and the calculation and processing unit is connected to the vector network analyzer to perform data processing. The fixing unit is used to fix and straighten the conductive wire under test so that the conductive wire under test passes through the center of the quasi-optical cavity. The magnetic field is strongest at this point under antisymmetric mode resonance and is perpendicular to the line connecting the center of the quasi-optical cavity. The testing device employs TEM during testing. 00q The mode is symmetrical when q is even and antisymmetric when q is odd. The diameter of the conductive wire under test is measured in the symmetrical mode and the quality factor of the conductive wire under test is measured in the antisymmetric mode.

2. The device for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz band as described in claim 1, characterized in that, The dimensions of the conductive wire to be tested should meet the requirements for use of the perturbation method.

3. The device for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz band as described in claim 2, characterized in that, The diameter of the conductive wire to be tested is 0.1mm-2.0mm.

4. The device for testing the surface conductivity of conductive wires in the millimeter-wave-terahertz band as described in claim 1, characterized in that, The biconcave collimator consists of two spherical mirrors.

5. A test method based on the millimeter-wave-terahertz frequency band conductive wire surface conductivity testing device according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1. Set up and debug the test setup. Set the frequency range and number of scan points of the vector network analyzer according to the test frequency and the required test time. Step 2. Without placing the conductive wire under test, measure the resonant frequency of the quasi-optical cavity symmetrical mode in the cavity state. The resonant frequency of the antisymmetric mode And the quality factor of the antisymmetric model ; Step 3. Place the conductive wire to be tested, and straighten it horizontally so that its axial direction is perpendicular to the central axis of the quasi-optical cavity. Measure the resonant frequency of the symmetrical mode at this point. And the quality factor of the antisymmetric model ; Step 4. Based on the resonant frequency obtained from the two measurements. , The radius of the conductive wire under test is inverted using the shape perturbation method. The specific calculation method is as follows: ， ， in, The permeability of free space, The vacuum permittivity, and These are the magnetic field vector and electric field vector of the symmetric mode inside the quasi-optical cavity, respectively. Let V be the volume of the conductive wire under test within the working area, and let V be the volume of the quasi-optical cavity containing the electromagnetic field. L is the radius of the conductive wire, and L is the length of the conductive wire within the working area, which is within 2.5 times the waist radius. Based on the quality factor obtained from the two measurements , The surface conductivity of the conductive wire under test is calculated using the cavity wall impedance perturbation method. The specific calculation method is as follows: ， in, It is the ohmic loss of the conductive wire under test; It is the mirror loss of the dual-cavity mirror; Surface conductivity The calculation formula is: ， ， ， ， In the formula, W represents the energy stored at quasi-optical cavity resonance. To reduce power loss in the conductive wire, Surface resistivity, It is the resonant angular frequency. It is the resonant frequency of the cavity antisymmetric mode. The permeability of free space, It is the magnetic field vector of the antisymmetric mode inside the quasi-optical cavity. It is the tangential magnetic field vector of the antisymmetric mode on the surface of the conductive wire under test. Let be the surface area of ​​the conductive wire under test within the working area. Let ds be the tangential magnetic field vector of the antisymmetric mode inside the quasi-optical cavity, dv be the area element on the surface of the conductive wire to be measured, and dv be the volume element in the working region of the quasi-optical cavity.

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