A millimeter-wave band conductivity testing cavity

Abstract

A millimeter-wave conductivity testing cavity includes a dielectric resonator, a support structure, and a metal shielded cavity. The dielectric resonator is placed within the metal shielded cavity via a support, and the dielectric resonator uses an anisotropic dielectric. The dielectric resonator, support structure, and metal shielded cavity work together to achieve a TE01n operating mode, where the electric field rotates in the X-Y plane, with no electric field component along the Z-axis. The Z-axis direction is the direction in which the support structure supports the dielectric resonator. Using this testing cavity, the conductivity of a sample can be calculated. Conductivity testing of metallic materials has promising applications in aerospace technology.

Description

Technical Field

[0001] This invention relates to a conductivity testing cavity in the millimeter-wave band, belonging to the field of terrestrial and satellite communications. Background Technology

[0002] 3D printing-based spaceborne microwave component manufacturing technology can minimize material usage and reduce the manufacturing cost of complex microwave devices. Furthermore, the integrated molding technology advantage of 3D printing is also an important means to achieve lightweight, integrated, and short-cycle design of payloads. Taking the development of next-generation high-throughput flexible payload technologies as an example, whether it's multi-beam feed arrays, traveling wave tube amplifiers, MPA, or Butler matrices, there is an urgent need to adopt 3D printing to achieve high integration and lightweight design.

[0003] When microwave current propagates within a microwave cavity, the surface roughness introduced by 3D printing inevitably increases the surface impedance of the microwaves. Surface resistance represents the conductivity of the outermost surface of a conductor, and microwave conductivity is typically related to the operating frequency of the material being measured. The detection depth of surface resistance is related to the skin depth δs of the material. For typical good conductors, such as copper, silver, and gold, the detection depth is ~1 μm at 10 GHz.

[0004] Compared to traditional manufacturing processes, 3D printing methods can result in particularly poor surface finishes (the surface roughness Ra of directly printed samples is around 10 μm), and may also lead to additional ohmic losses depending on the printing orientation. For example, the vertical surfaces of samples appear to exhibit higher average microwave losses than equivalent horizontally constructed samples. This can be explained by current flowing across layer boundaries, and when evaluating RS, it is best to assess this by forcing current to flow laterally towards these boundaries.

[0005] Considering that electroplating and other methods are often used to improve the high-loss characteristics of printed parts with high surface roughness, we also need to pay attention to the improvement of conductivity by surface thin film coatings. A team led by Yukta P. Timalsina at Rensselaer Polytechnic Institute in the United States studied the effect of nanoscale surface roughness on the resistivity of ultrathin epitaxial copper films. Their research demonstrated that the temperature-dependent component of resistivity can be described by the Bloch-Grunnersen equation, which has a thickness-dependent el-ph coupling constant and a thickness-dependent Debye temperature. Furthermore, as the film thickness decreases, the el-ph coupling constant increases, leading to an enhancement of the temperature-dependent component of resistivity.

[0006] For 3D-printed amorphous alloy space microwave devices, both Zr-based and Fe-based amorphous alloys typically exhibit lower electrical conductivity compared to traditional Al-Si-Mg alloys (Al-Si-Mg alloys have a static conductivity of 15–20 MS / m, while amorphous alloys are typically <5 MS / m, and the conductivity decreases with increasing microwave frequency). Therefore, accurately obtaining the surface conductivity is crucial for the design and optimization of the electrical performance of 3D-printed devices for space microwave applications. Summary of the Invention

[0007] The problem solved by this invention is that it designs a millimeter-wave conductivity testing cavity based on an anisotropic dielectric resonator, which can accurately obtain the surface conductivity.

[0008] The technical solution of this invention is: a millimeter-wave frequency band conductivity testing cavity, comprising a dielectric resonator, a support structure, and a metal shielding cavity; the dielectric resonator is placed in the metal shielding cavity through the support structure, and the dielectric resonator uses an anisotropic dielectric; the dielectric resonator, support structure, and metal shielding cavity work together to make the cavity operate in TE01n mode, where the electric field rotates in the XY plane and there is no electric field component in the Z direction; the Z direction is the axis between the support structure and the dielectric resonator.

[0009] Preferably, the dielectric resonator is a hollow cylinder made of high-purity aluminum oxide with a purity of not less than 99.9%.

[0010] Preferably, the dielectric resonator has a dielectric constant of 8.5-10.5 in the XY plane and a dielectric constant greater than 11.5 in the Z-axis direction.

[0011] Preferably, the support structure is a hollow cylinder made of quartz material with a dielectric constant of less than 5; the ratio of the outer diameter of the quartz support to the outer diameter of the ring resonator is 1:2 to 1:2.5.

[0012] Preferably, the metal shielding cavity is made of silver-plated aluminum; the ratio of the inner diameter of the metal shielding cavity to the outer diameter of the dielectric resonator is 1:0.4-1:0.5.

[0013] A method for determining surface conductivity using the millimeter-wave band conductivity testing cavity includes: A millimeter-wave conductivity testing chamber was built according to the testing requirements, and the working mode of the chamber was TE01n, in which the electric field rotates in the XY plane and there is no electric field component in the Z direction. Adjust the dimensions of the dielectric resonator and its supporting structure, as well as the dimensions of the metal shielding cavity, so that the resonant frequency of the dielectric resonator is at the frequency point used for testing. The calibration sample is installed above the dielectric resonator in the millimeter-wave conductivity test cavity. The test cavity is fed with current, and the Q value of the dielectric resonator is measured and recorded as Q0. The sample to be tested is installed above the dielectric resonator in the millimeter-wave conductivity testing cavity. The testing cavity is fed with current, and the Q value of the dielectric resonator cavity is measured again and recorded as Q1. The ratio of the conductivity of the test sample to that of the calibration sample can be determined by the Q value obtained from the two measurements. If the conductivity value of the calibration sample is known, the conductivity value of the test sample can be calculated.

[0014] Preferably, the conductivity value of the sample to be tested is calculated using the Q values ​​from the two measurements through the following formula.

[0015] Where G is a geometric factor determined by the cavity size, sample position, and electromagnetic field distribution. To calibrate the conductivity of the sample, Q0 is the quality factor of the resonant cavity when measuring the calibration sample, and Q1 is the quality factor of the resonant cavity when measuring the sample to be tested.

[0016] Preferably, the surface roughness Ra of the calibration sample is controlled within 0.6.

[0017] Preferably, the network analyzer is connected to the test cavity and connected to the coupling loop inside the test cavity. The plane of the coupling loop is parallel to the cross section of the dielectric resonator, and the Q value of the cavity is measured using the network analyzer.

[0018] Preferably, a constant pressure is applied above the sample to maintain good contact between the sample and the cavity during both measurements.

[0019] The advantages of this invention compared to the prior art are: (1) The present invention uses an anisotropic medium to enable the high-purity aluminum oxide resonator to work in the TE01n mode. The electric field rotates in the XY plane and there is no electric field component in the Z axis. The dielectric constant used in the working mode of the resonator is 8.5-10.5, which makes the resonator in the millimeter wave band easy to process.

[0020] (2) The present invention uses an aluminum oxide dielectric resonator, which has a very small loss tangent and a Q value of over 10,000. Even a slight change in the conductivity of the material under test will cause a significant change in the Q value of the resonator, resulting in high conductivity testing accuracy. Attached Figure Description

[0021] Figure 1 Schematic diagram of the test cavity structure Figure 2 This is a schematic diagram of the electric field in the working mode of a dielectric resonant cavity; Figure 3This is a simulation diagram of the S-parameters of the test chamber; Detailed Implementation The following is in conjunction with the appendix Figure 1-3 The specific embodiments of the present invention will be described in further detail below. The coordinate axes involved in the present invention are in a Cartesian coordinate system, with the Z-direction being the axial direction of the support structure and the dielectric resonator.

[0022] A millimeter-wave conductivity testing cavity includes a dielectric resonator, a support structure, and a metal shielding cavity. The dielectric resonator is placed inside the metal shielding cavity via a support, and the dielectric resonator uses an anisotropic dielectric. The dielectric resonator, support structure, and metal shielding cavity work together to enable the cavity to operate in a TE01n mode, where the electric field rotates in the XY plane and has no electric field component in the Z direction. The Z direction is the axis between the support structure and the dielectric resonator.

[0023] In a preferred embodiment of this invention, the dielectric resonator is a toroidal alumina; the dielectric resonator is 99.99% high-purity alumina; the dielectric constant of the high-purity alumina dielectric resonator in the XY plane is 9.4; the dielectric constant of the high-purity alumina dielectric resonator in the Z-axis direction is 11.5; the high-purity alumina dielectric resonator has a loss tangent < 0.0001, and the electric field of the dielectric resonance mode is far from the cavity wall, and the Q value can reach over 10,000.

[0024] The support structure of the dielectric resonator is made of low-loss quartz material; the dielectric constant of the quartz support is 3.8; the ratio of the toroidal quartz support to the aluminum oxide resonator is 1:2. The metal shielding cavity is made of silver-plated aluminum; the ratio of the cavity size to the dielectric resonator size is 1:0.4.

[0025] The present invention also provides a method for determining surface conductivity using the millimeter-wave frequency band conductivity testing cavity, comprising the following steps: Establish a simulation model of a dielectric resonator-shielded metal cavity, such as Figure 2 As shown, an anisotropic medium is used to operate a high-purity alumina resonator in TE01n mode, where the electric field rotates in the XY plane and has no electric field component in the Z direction. The dielectric constant used in the resonator's operating mode is 9.4, while the dielectric constant in the Z-axis direction is 11.5.

[0026] Adjust the dimensions of the resonator and support, as well as the shielding metal cavity, so that the resonant frequency of the resonator is at the intended frequency point. In this example, the resonant frequency is 20 GHz. Figure 3 As shown.

[0027] The calibration sample is mounted above the dielectric resonator inside the millimeter-wave conductivity testing cavity. The shape of the calibration sample is not limited, as long as it covers the testing area of ​​the cavity. To minimize the influence of the sample surface morphology on the surface resistivity test results, the surface roughness Ra of the calibration sample should be controlled below 0.6. like Figure 1 As shown, the coaxial cable of the network analyzer is connected to the test cavity, and the coupling ring inside the test cavity is connected. The plane of the coupling ring is kept parallel to the cross section of the dielectric resonator. When the network analyzer signal is fed into the resonant cavity in the above manner, the resonant cavity is made to work in TE01n mode. A pressurization device is used to ensure that the pressure is constant during the measurement process to reduce the influence of air gap and sample unevenness. The measured Q value of the resonant cavity is recorded as Q0. The sample to be tested is installed above the dielectric resonator in the millimeter-wave conductivity testing cavity. The testing cavity is then fed with current, and the Q value of the dielectric resonator is measured again and recorded as Q1. The conductivity of the sample under test can be calculated using the Q values ​​obtained from two measurements and the following formula.

[0028] Where G is a geometric factor determined by the cavity size, sample position, and electromagnetic field distribution. To calibrate the conductivity of the sample, Q0 is the quality factor of the resonant cavity when measuring the calibration sample, and Q1 is the quality factor of the resonant cavity when measuring the sample to be tested.

[0029] 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 features or steps in the disclosed methods or processes may be combined in any way, except for mutually exclusive features and / or steps.

[0030] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A conductivity testing cavity in the millimeter-wave band, characterized in that: Includes dielectric resonator, support structure, and metal shielding cavity; The dielectric resonator is placed in a metal-shielded cavity by a support structure, and the dielectric resonator uses an anisotropic dielectric. The cavity operates in TE01n mode through the cooperation of a dielectric resonator, a support structure, and a metal shielding cavity. The electric field rotates in the XY plane, with no electric field component in the Z direction. The Z direction is the axis between the support structure and the dielectric resonator. The dielectric resonator is a hollow cylinder made of high-purity aluminum oxide with a purity of not less than 99.9%. The dielectric constant of the dielectric resonator in the XY plane is 8.5-10.5, and the dielectric constant in the Z-axis direction is greater than 11.

5. The support structure is a hollow cylinder made of quartz with a dielectric constant less than 5. The ratio of the outer diameter of the quartz support to the outer diameter of the dielectric resonator is 1:2 to 1:2.

5. The metal shielding cavity is made of silver-plated aluminum. The ratio of the inner diameter of the metal shielding cavity to the outer diameter of the dielectric resonator is 1:0.4 to 1:0.

5.

2. A method for determining surface conductivity using the millimeter-wave frequency band conductivity testing cavity described in claim 1, characterized in that... include: A millimeter-wave conductivity testing chamber was built according to the testing requirements, and the working mode of the chamber was TE01n, in which the electric field rotates in the XY plane and there is no electric field component in the Z direction. Adjust the dimensions of the dielectric resonator and its supporting structure, as well as the dimensions of the metal shielding cavity, so that the resonant frequency of the dielectric resonator is at the frequency point used for testing. The calibration sample is installed above the dielectric resonator in the millimeter-wave conductivity test cavity. The test cavity is fed with current, and the Q value of the dielectric resonator is measured and recorded as Q0. The sample to be tested is installed above the dielectric resonator in the millimeter-wave conductivity testing cavity. The testing cavity is fed with current, and the Q value of the dielectric resonator cavity is measured again and recorded as Q1. The ratio of the conductivity of the test sample to that of the calibration sample can be determined by the Q value obtained from the two measurements. If the conductivity value of the calibration sample is known, the conductivity value of the test sample can be calculated.

3. The method according to claim 2, characterized in that: The conductivity of the sample under test can be calculated using the Q values ​​obtained from two measurements and the following formula. Where G is a geometric factor determined by the cavity size, sample position, and electromagnetic field distribution. To calibrate the conductivity of the sample, Q0 is the quality factor of the resonant cavity when measuring the calibration sample, and Q1 is the quality factor of the resonant cavity when measuring the sample to be tested.

4. The method according to claim 2, characterized in that: The surface roughness Ra of the calibration sample is controlled within 0.

6.

5. The method according to claim 2, characterized in that: The network analyzer is connected to the test chamber and connected to the coupling loop inside the test chamber. The plane of the coupling loop is parallel to the cross-section of the dielectric resonator. The Q value of the chamber is measured using the network analyzer.

6. The method according to claim 2, characterized in that: To maintain good contact between the sample and the cavity during both measurements, a constant pressure was applied above the sample.

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