Metal wire conductivity testing device and method based on coaxial resonant cavity structure

Abstract

The invention provides a metal wire conductivity testing device and method based on a coaxial resonant cavity, and belongs to the technical field of conductivity testing. According to the device, a sample clamping mode is innovatively set, and pressure is applied to the two ends of a metal wire, so that the sample in the cavity is subjected to obliquely downward pulling force, the sample to be tested is always kept in a straight state in the testing process, the flatness of the sample is ensured, and the problem that the middle part is bent due to light weight of the sample to be tested in a conventional lofting test is solved. The field distribution between the inner conductor and the outer conductor is destroyed, so that the working mode is not a strict TEM mode any more, and the test accuracy is improved; in addition, the coaxial cavity short-circuit surface cavity and the cover in the device are separated, so that the samples with different sizes can be tested only by replacing the end cover when facing the samples with different sizes, and the operation is simple, convenient and easy to implement.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductivity testing, and particularly relates to a device and method for testing the conductivity of a metal wire based on a coaxial resonant cavity structure. Background Art

[0002] Due to the skin effect of electromagnetic waves, the surface resistivity of a conductor changes at different frequencies; and the conductivity of a material affects the performance of a device such as insertion loss, power capacity, impedance matching, etc. Therefore, accurately obtaining the conductivity of a material at different frequencies is of great significance for the design and performance evaluation of microwave and millimeter-wave devices. Among them, in practical applications, for example, many cable-like devices need to use small-sized metal wires, such as coaxial cables, etc. Therefore, the demand for testing the conductivity of small-sized metal wires is also increasing day by day.

[0003] The main methods for measuring the conductivity of metal materials can be divided into the transmission line method and the resonant cavity method. The transmission line method mainly makes the material into the form of a microwave transmission line, and calculates the conductivity of the material by directly measuring the attenuation coefficient of a section of the transmission line. The applicable frequency of this method depends on the type of transmission line selected, and at the same time its accuracy is also lacking. The resonant cavity method is more widely used in high-frequency, high-precision surface resistance measurement. The resonant cavity method mainly utilizes the change in the quality factor before and after the sample is placed in the cavity to estimate the surface resistivity value of the material. The resonant cavity method mainly includes the waveguide resonant cavity method, the coaxial resonant cavity method, etc. Ming Ye et al. (Ye M, Wang L, He Y, et al. In situ test of thickness and sheet resistance of conductive nanomaterial using microwave cavity[J]. IEEE Microwave and Wireless Components Letters, 2017, 27(10): 942-944.) completed the measurement of the surface resistivity of a metal thin film at two resonant frequencies of 10.8 GHz and 17.7 GHz using a cylindrical resonant cavity in the TE 011 mode. If the coaxial resonant cavity method is used for testing, there are requirements for the size and flatness of the sample to be tested. If the diameter of the sample to be tested is too small, such as a metal wire, the surface of the sample to be tested will be uneven due to its own weight inside the cavity, and the edge effect error is relatively large, resulting in low accuracy of the test result.

[0004] Therefore, how to test the surface resistivity of small-sized metal samples has become an urgent problem to be solved. Summary of the Invention

[0005] Aiming at the problems existing in the background technology, the purpose of the present invention is to provide a device and method for testing the conductivity of a metal wire based on a coaxial resonator. The device innovatively sets the sample clamping method, applying pressure to both ends of the metal wire, so that the sample in the cavity will be subjected to a downward oblique pulling force, thereby straightening the measured part of the sample and ensuring the flatness of the sample. In addition, the short-circuit surface cavity and the cover of the coaxial cavity in the device are separated, so that when facing samples of different sizes, the test of samples of different sizes can be completed only by replacing the end cover, and the operation is simple and easy.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A device for testing the conductivity of a metal wire based on a coaxial resonator structure, including a fixture, a lower cavity body, a lower cavity cover, an upper cavity body and an upper cavity cover; both the upper cavity body and the lower cavity body are semi-circular cavities, which are stacked up and down to form a complete cylindrical cavity; the upper cavity cover is rectangular, arranged at both ends of the upper cavity body, and a semi-circular hole is arranged at the center of one edge side of the upper cavity cover; the lower cavity cover is L-shaped, its vertical surface is arranged at both ends of the lower cavity body, and a semi-circular hole is arranged at the center of one edge side of the lower cavity cover. The semi-circular hole on the upper cavity cover and the semi-circular hole on the lower cavity cover form a complete circular hole for the sample to be measured to pass through; the sample to be measured and the cylindrical cavity together form a coaxial resonator.

[0008] The fixture includes two fixture units, which are respectively fixed and symmetrically arranged on the horizontal plane of the lower cavity cover, so that the horizontal height of the central axis of the coaxial cavity is higher than the height of the fixture's fixed point for the sample to be measured, and is used to apply a downward oblique pulling force to the sample to be measured; the sample to be measured is arranged on the central axis of the cylindrical cavity, and is fixed and straightened by the two fixture units through the circular hole of the cavity cover; the sample to be measured is a metal wire.

[0009] Further, the upper cavity cover is connected to the upper cavity body by bolts.

[0010] Further, the fixture unit includes a base, a support part, a pressing plate, a clamping arm and a pressing head; the base is fixedly arranged on the end surface of the lower half cavity, and a support part with a "V" cross-section is fixedly arranged on the base. One end of the clamping arm is fixedly connected to the support part, and this end is hinged to one end of the pressing plate; the other end of the clamping arm passes through a fixing bolt, and the bolt is the pressing head, and the central axis of the pressing head is perpendicular to the end surface of the lower half cavity; by lifting and pressing the pressing plate, the lifting and falling of the pressing head are driven, so as to loosen and fix the sample to be measured.

[0011] Further, the size of the circular hole on the upper cavity cover is determined according to the diameter of the sample to be measured.

[0012] Further, the test device of the present invention is applicable to samples to be measured of different sizes, especially suitable for metal wires with a diameter of 0.05-1 mm.

[0013] Further, the surfaces of the upper cavity cover and the lower cavity cover facing the cavity are polished.

[0014] The present invention also provides a testing method based on the above testing device, comprising the following steps:

[0015] Step 1. Remove the upper half cavity, press one end of the sample to be tested under the fixture unit, then straighten the sample to be tested through the upper half cavity and the upper cavity cover, and then press it down through the other end fixture unit to ensure that the metal wire is straightened;

[0016] Step 2. Use a vector network analyzer to measure the cavity resonance frequency f and the quality factor Q after placing the sample to be tested;

[0017] Step 3. Based on the resonance frequency f and the quality factor Q measured in Step 2, inversely calculate the resistivity R of the sample to be tested by using the coaxial cavity quality factor calculation formula s1 , and finally obtain the corresponding conductivity σ.

[0018] Further, the specific process of inversion is as follows:

[0019] The field inside the cavity is,

[0020]

[0021] where E r is the radial electric field, is the magnetic field in the Φ direction, E m is the magnitude of the electric field amplitude, a is the radius of the sample to be tested, p is the mode number, p = 1, 2, 3..., z is the axial coordinate, L is the cavity length, r is the radial coordinate, η is the wave impedance;

[0022] The calculation process of the Q value is as follows,

[0023]

[0024] where W h is the total energy stored in the resonant cavity, P w1 is the power loss of the outer conductor, P w2 is the power loss of the inner conductor, P end is the power loss of the short-circuit surface, ω is the angular frequency of the cavity resonance, η is the wave impedance, b is the radius of the outer conductor, μ0 is the magnetic permeability of air, R s1 、R s2 、R s3 are the surface resistivities of the outer conductor, the sample to be tested, and the short-circuit surface respectively, and σ is the conductivity of the sample to be tested.

[0025] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0026] 1. The device of the present invention designs the outer conductor into upper and lower half-cavities, which facilitates the laying of samples. At the same time, the discontinuity of such cavity walls does not affect the continuity of the main-mode current and helps to suppress the spurious modes, improving the accuracy of the test results.

[0027] 2. The test device of the present invention innovatively applies an obliquely downward force to the sample to be tested through a fixture arranged outside the cavity, enabling the sample to be tested to always remain taut during the test, ensuring the flatness of the sample, and avoiding the situation where the middle part of the sample to be tested bends due to its relatively light self-weight during conventional sample-laying tests, which would damage the field distribution between the inner and outer conductors and cause its working mode to no longer be a strictly TEM mode. The device of the present invention improves the test accuracy.

[0028] 3. Through the separated design of the cavity cover and the cavity body, when testing samples to be tested with different sizes, only the cavity cover needs to be replaced, greatly reducing the actual test usage cost. Brief Description of the Drawings

[0029] Figure 1 It is a three-dimensional structural schematic diagram of the metal wire conductivity test device based on the coaxial resonant cavity structure of the present invention.

[0030] Figure 2 It is a three-dimensional structural schematic diagram of the separated state of the upper and lower cavities of the test device based on the coaxial resonant cavity of the present invention.

[0031] Figure 3 It is a two-dimensional structural schematic diagram of the test device of the present invention.

[0032] Figure 4 It is a two-dimensional structural schematic diagram of the sample loading of the metal wire to be tested in the test device of the present invention.

[0033] Figure 5 It is a three-dimensional structural schematic diagram of the fixture unit in the test device of the present invention.

[0034] Figure 6 It is a two-dimensional structural schematic diagram of the upper and lower cavity covers in the test device of the present invention.

[0035] Figure 7 It is a test result diagram of the silver wire sample by the test device of the present invention.

[0036] Reference Numerals: 1 is the upper cavity cover, 2 is the fixture unit, 3 is the sample to be tested, 4 is the pressing head, 5 is the lower cavity cover, 6 is the upper cavity body, and 7 is the lower cavity body. Detailed Embodiments

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0038] A metal wire conductivity test device based on a coaxial resonant cavity structure, the overall three-dimensional structure schematic diagram is shown in Figure 1 The schematic diagram of the separated three-dimensional structure is shown in Figure 2 As shown, the two-dimensional structure diagram is as follows Figure 3 As shown, it includes a fixture, a lower cavity 7, a lower cavity cover 5, an upper cavity 6 and an upper cavity cover 1;

[0039] The upper cavity 6 and the lower cavity 7 are both semicircular cavities, which are stacked up and down to form a complete cylindrical cavity. Such a separation structure will not destroy the continuity of the main mode current, but also has the effect of suppressing the mixed mode; the upper cavity cover 1 is rectangular, arranged at the two ends of the upper cavity, and a semicircular hole is arranged at the center of one edge side of the upper cavity cover; the lower cavity cover 5 is L-shaped, and its vertical surface is arranged at the two ends of the lower cavity, and a semicircular hole is arranged at the center of one edge side of the lower cavity cover. The semicircular hole of the upper cavity cover 1 and the semicircular hole on the lower cavity cover 5 form a complete circular hole for the sample 3 to be tested to pass through; the sample 3 to be tested and the cylindrical cavity together constitute a coaxial resonant cavity;

[0040] The fixture includes two fixture units 2, which are fixed and symmetrically arranged on the horizontal plane of the lower chamber cover, so that the horizontal height of the central axis of the coaxial cavity is higher than the height of the fixture fixing point of the sample to be tested, and are used to apply an oblique downward pulling force to the sample to be tested, such as Figure 4 As shown; the sample to be tested is set on the central axis of the cylindrical cavity, and is fixed and straightened by two clamp units through the circular hole of the cavity cover; the sample to be tested is a metal wire.

[0041] Figure 5 It is a schematic diagram of the three-dimensional structure of the clamp unit in the test device of the present invention, the clamp unit 2 includes a base, a support part, a pressing plate, a clamping arm and a pressing head 4; the base is fixedly arranged on the end face of the lower cavity, and a support part with a "V"-shaped cross-section is fixedly arranged on the base, one end of the clamping arm is fixedly connected to the support part, and the end is hinged to one end of the pressing plate; the other end of the clamping arm is fixed by a bolt, the bolt is the pressing head, and the central axis of the pressing head is perpendicular to the end face of the lower cavity; the pressing head is driven to rise and fall by lifting and pressing the pressing plate, so that the sample to be tested is loosened and fixed.

[0042] Figure 6 The schematic diagram of the upper and lower cavity covers is as shown in the figure. The cavity cover and the cavity body are separated and fixed by bolts. When testing samples of different sizes, it is only necessary to replace the upper and lower cavity covers with different semicircular diameters, which greatly reduces the actual test cost.

[0043] Example 1

[0044] The testing method based on the above testing device comprises the following steps:

[0045] Step 1. Remove the upper cavity. Press one end of the sample to be measured under the fixture unit, then straighten the sample to be measured through the upper cavity and the upper cavity cover, and then press it down through the other end fixture unit to ensure that the wire is straightened.

[0046] Step 2. Use a vector network analyzer to measure the cavity resonance frequency f and quality factor Q after placing the sample to be measured.

[0047] Step 3. Based on the resonance frequency f and quality factor Q measured in Step 2, use the coaxial cavity quality factor calculation formula to inversely calculate the resistivity R of the sample to be measured s1 , and finally obtain the corresponding conductivity σ; the specific inversion process is as follows:

[0048] The internal field of the cavity is

[0049]

[0050] where E r is the radial electric field (the radial direction is from the inner conductor to the outer conductor), is the magnetic field in the Φ direction, E m is the magnitude of the electric field amplitude, a is the radius of the sample to be measured, p is the mode number, p = 1, 2, 3..., z is the axial coordinate (the axial direction is the central axis direction, and the line connecting the center of the bottom surface and the center of the top surface is the central axis), L is the cavity length, r is the radial coordinate, and η is the wave impedance;

[0051] The calculation process of the Q value is as follows

[0052]

[0053] where W h is the total energy stored in the resonant cavity, P w1 is the power loss of the outer conductor, P w2 is the power loss of the inner conductor, P end is the power loss of the short-circuit surface, ω is the angular frequency of the cavity resonance, η is the wave impedance, b is the radius of the outer conductor, μ0 is the magnetic permeability of air, R s1 、R s2 、R s3 are the surface resistivities of the outer conductor, the sample to be measured, and the short-circuit surface respectively, and σ is the conductivity of the sample to be measured.

[0054] Figure 7 This is the test result diagram of the silver wire sample by the test device of the present invention. The diameter of silver wire 1 is 0.281 mm, and the diameter of silver wire 2 is 0.284 mm. The test frequency points are 0.5 GHz, 1.0 GHz, 1.5 GHz, 2.0 GHz, 2.5 GHz, 3.0 GHz, 3.5 GHz respectively; the standard conductivity of pure silver is 6.17×10 7 S / m. Observe Figure 7It can be found that the measurement results have a small difference from the standard values, proving that this method has good accuracy. Moreover, by observing the two groups of data, it can be found that this device has good stability when measuring samples with different diameters.

[0055] As described above, the above are only specific embodiments of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all features disclosed, or all steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A test device for the conductivity of a metal wire based on a coaxial resonator structure, characterized in that It includes a fixture, a lower cavity, a lower cavity cover, an upper cavity, and an upper cavity cover. The upper cavity and the lower cavity are both semi-cylindrical cavities, which are stacked vertically to form a complete cylindrical cavity. The upper cavity cover is rectangular and is arranged at both ends of the upper cavity. A semi-circular hole is provided at the center of one edge of the upper cavity cover. The lower cavity cover is L-shaped, and its vertical surface is arranged at both ends of the lower cavity. A semi-circular hole is provided at the center of one edge of the lower cavity cover. The semi-circular hole on the upper cavity cover and the semi-circular hole on the lower cavity cover form a complete circular hole for the sample to be measured to pass through. The sample to be measured and the cylindrical cavity together form a coaxial resonant cavity. The fixture includes two fixture units, which are respectively fixed and symmetrically arranged on the horizontal surface of the lower cavity cover, so that the horizontal height of the central axis of the coaxial cavity is higher than the height of the fixture's fixed point for the sample to be measured, and is used to apply an obliquely downward pulling force to the sample to be measured. The sample to be measured is arranged on the central axis of the cylindrical cavity, and is fixed and straightened by the two fixture units through the circular hole of the cavity cover. The sample to be measured is a metal wire.

2. The wire conductivity testing device according to claim 1, wherein The upper cavity cover and the upper cavity are connected by bolts.

3. The wire conductivity testing device according to claim 1, wherein, The fixture unit includes a base, a support part, a pressing plate, a clamping arm, and a pressing head. The base is fixedly arranged on the end surface of the lower half cavity. A support part with a "V" - shaped cross - section is fixedly arranged on the base. One end of the clamping arm is fixedly connected to the support part, and this end is hinged to one end of the pressing plate. The other end of the clamping arm is a fixed bolt, and the bolt is the pressing head, and the central axis of the pressing head is perpendicular to the end surface of the lower half cavity. By lifting and pressing the pressing plate, the lifting and falling of the pressing head are driven, so as to loosen and fix the sample to be measured.

4. The wire conductivity testing device according to claim 1, wherein The size of the circular hole on the upper cavity cover is determined according to the diameter of the sample to be measured.

5. The wire conductivity testing device according to claim 1, wherein The testing device of the present invention is applicable to samples to be measured with different sizes.

6. The wire conductivity testing device according to claim 5, wherein, The sample to be measured is a metal wire with a diameter of 0.05 - 1 mm.

7. The wire conductivity testing device according to claim 1, characterized in that, The surfaces of the upper cavity cover and the lower cavity cover facing the cavity are polished.

8. A testing method based on the wire conductivity testing device according to any one of claims 1-7, characterized in that, It includes the following steps: Step 1. Remove the upper half cavity, press one end of the sample to be measured under the fixture unit, then straighten the sample to be measured through the upper half cavity and the upper cavity cover, and then press it down through the other fixture unit to ensure that the metal wire is straightened. Step 2. Use a vector network analyzer to measure the resonant frequency f and quality factor Q of the cavity after placing the sample to be measured. Step 3. Based on the resonant frequency f and quality factor Q measured in Step 2, the resistivity R of the sample to be measured is inversely obtained by using the coaxial cavity quality factor calculation formula, s1 and finally the corresponding conductivity σ is obtained.

9. The test method according to claim 8, wherein The specific process of inversion is: The field inside the cavity is, Among them, E r is the radial electric field, is the magnetic field in the Φ direction, E m is the magnitude of the electric field amplitude, a is the radius of the sample to be measured, p is the mode number, p = 1, 2, 3..., z is the axial coordinate, L is the cavity length, r is the radial coordinate, and η is the wave impedance; The calculation process of the Q value is as follows, Among them, W h is the total energy storage of the resonant cavity, P w1 is the loss power of the outer conductor, P w2 is the loss power of the inner conductor, P end is the loss power of the short-circuit surface, ω is the cavity resonance angular frequency, η is the wave impedance, b is the outer conductor radius, μ0 is the air permeability, R s1 , R s2 , R s3 are the surface resistivities of the outer conductor, the sample under test, and the short-circuit surface respectively, and σ is the conductivity of the sample under test.

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