A method for testing the magnetic permeability of materials at high frequencies

Abstract

The present invention discloses a method for testing the magnetic permeability of materials at high frequencies. Using a TE mode resonant cavity as a testing tool, the method includes: a resonant cavity, a pressurizing device, a network analyzer, and a sample to be tested. By simply testing the material's skin depth and its corresponding surface resistivity, the material's magnetic permeability can be calculated. The method also tests the effect of magnetic films of varying thickness on the resonant frequency f and quality factor Q, calculates a magnetic film thickness-surface resistivity curve, analyzes the skin depth, and then calculates the magnetic properties of the magnetic material. This method significantly improves the accuracy and efficiency of material permeability measurements.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic permeability parameter measurement applications of materials, and in particular to a method for testing the magnetic permeability of magnetic materials at high frequencies. Background Art

[0002] Magnetic materials are widely used in microwave devices such as circulators, isolators, microwave switches, and phase shifters. In the design and simulation of microwave devices using magnetic materials, the material's magnetic properties (magnetic permeability and magnetic loss) are typically measured using the lumped parameter method to obtain RF test results. However, the magnetic properties of magnetic materials are highly dependent on frequency, resulting in significant errors in the simulation results.

[0003] Traditional microwave permeability testing methods, such as the rectangular waveguide method, coaxial transmission / reflection method, and free-space method, utilize advanced microwave network analyzers (MWNAs) to rapidly and accurately measure the scattering parameters of a sample-carrying test fixture at microwave frequencies, thereby calculating the material's complex permeability. However, these methods suffer from cumbersome calculations, large test errors, and limited ability to reflect the changing trends of material properties. Summary of the Invention

[0004] In view of the above difficulties in testing the magnetic permeability of magnetic materials in the microwave frequency band, the present invention specifically relates to a method for testing the magnetic permeability of materials at high frequencies.

[0005] In order to achieve high-precision testing of the magnetic properties of magnetic materials, the present invention adopts the following technical solutions:

[0006] (1) This test method uses a designed TE mode resonant cavity to test non-magnetic metal films of different thicknesses. Based on the "film thickness-surface resistivity" curve, combined with simulation and theoretical research on the electromagnetic performance test scheme of magnetic materials based on the TE mode resonant cavity, the skin depth of the non-magnetic metal film is obtained. The "skin depth-surface resistivity" relationship is used to calculate the magnetic permeability of the non-magnetic metal film, and relevant model corrections are made based on the test results. This is a test method that indirectly obtains the material's magnetic permeability performance by testing the surface resistivity of the magnetic film and performing data analysis;

[0007] (2) Using a material with a high-smoothness surface as a substrate, and preparing a multi-component magnetic thin film material with different thicknesses by coating the substrate surface to form a sample to be tested;

[0008] (3) In order to reduce the influence of sample surface morphology on the surface resistivity test results, a profilometer was used to collect sample surface morphology data to control the arithmetic mean roughness of the sample surface to be tested within 0.01 μm;

[0009] (4) The test samples include: coated samples with different thicknesses of magnetic films coated on the surfaces of substrates of the same material and size, and the sample size should completely cover the upper end surface of the resonant cavity;

[0010] (5) Connect the coaxial connecting line of the network analyzer to the annular coupler of the resonant cavity, and keep the plane where the coupling ring is located parallel to the circular cross-section of the resonant cavity. When the network analyzer signal is fed into the resonant cavity in the above manner, the resonant cavity operates in TE mode, and the electric field at its upper end face is parallel to the cross-section of the resonant cavity. When using the end face replacement method for measurement, the influence of the air gap between the upper end plate and the top of the side wall on the measurement results can be reduced. The electrical parameter test device composed of the resonant cavity and the network analyzer is used in conjunction with a pressurizing device, and the pressure sensor value is kept unchanged for multiple measurements to improve the consistency of the external environment during the test;

[0011] (6) Covering the calibration and test samples with the coating surface facing downward on the upper end surface of the resonant cavity in turn, recording the resonant frequency f and quality factor Q, and calculating the surface resistivity of the sample;

[0012] (7) The calculation formula for the surface resistivity of the resonant cavity test is:

[0013]

[0014] In formula (I), ρ s1 : surface resistivity of the sample to be tested; ρ s0 : Surface resistivity of the inner wall material; Q0: Intrinsic quality factor of the original cavity; Q1: Loaded quality factor of the cavity after loading the sample to be tested; M: Cavity geometry factor, determined by the cavity size.

[0015] (8) The geometric factor M of the surface resistivity calculation formula is calculated by using the inherent quality factor Q0 and the loaded quality factor Q1 of the measured data of the calibration piece (pure copper and pure silver);

[0016] (9) Calculate the surface resistivity of the sample using the calibrated formula based on the measured resonant frequency f and quality factor Q. Plot and fit the "surface resistivity-coating thickness" curve to obtain the skin depth. Substitute this data into the calculated permeability of the magnetic material at high frequencies.

[0017] According to the testing method of the present invention, in step (8), for the magnetic material sample, its surface resistivity is:

[0018]

[0019] Where, ρ s : surface resistivity; μ: magnetic permeability; f: test frequency; σ: electrical conductivity.

[0020] Theoretically, there is a skin depth for the coating sample to be tested:

[0021]

[0022] The above calculation formula is theoretically derived. In actual testing, instrument system errors and human errors are inevitable. Therefore, it is necessary to establish a correction factor for the material's skin depth by testing a reference material (with recognized permeability data, such as gold, silver, and copper).

[0023] The corrected material skin depth calculation formula is established as:

[0024]

[0025] Where, K: correction factor.

[0026] Through formula (II) and formula (IV), we can get:

[0027]

[0028] From equation (V), we can see that there is a correlation between the skin depth and surface resistivity of a material. The only unknown parameter is the established correction factor, which will be calculated through testing of reference materials (copper and silver).

[0029] By analyzing the test data of the coating samples and fitting the relationship curve, the relationship curve between the coating thickness and the surface resistance is obtained.

[0030] Through the above method, the skin depth and corresponding surface resistivity of the material to be tested at a specific frequency are obtained.

[0031] Substituting the skin depth and surface resistivity data obtained in (9) into formula (V) can finally obtain the magnetic permeability of the material.

[0032] By comparing with known test data of magnetic films, the calculation model is further modified (correction factor K) to obtain a high-precision test method for the magnetic properties of magnetic materials in the microwave frequency band.

[0033] Based on a modified calculation model, this method utilizes the characteristics of the TE mode resonant cavity to test electrical conductivity, magnetic permeability, and dielectric properties. This allows testing of metals, ferrites, and dielectric materials widely used in microwave devices, thus achieving a universally applicable method for testing the electrical properties of materials in the microwave frequency band. The successful implementation of this method provides a high-precision, nondestructive testing solution for the performance of precise magnetic materials, significantly improving the accuracy and efficiency of material magnetic permeability measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1The theoretical change curve of the relationship between the coating thickness and surface resistivity of the material obtained by testing the coating sample of the present invention;

[0035] Figure 2 Schematic diagram of the structure of the TE mode dielectric resonant cavity and its supporting device used for testing in the present invention (including the test sample or calibration sample used for testing);

[0036] Figure 3 A graph showing the relationship between coating thickness and surface resistivity for gold at 3 GHz. Calibration sample data with known permeability is used to derive correction factors.

[0037] Figure 4 A graph showing the relationship between film thickness and surface resistivity for silver at 3 GHz. Calibration sample data with known permeability is used to derive correction factors.

[0038] Figure 5 A graph showing the relationship between nickel coating thickness and surface resistivity at 3 GHz, with samples of unknown magnetic permeability used to verify the feasibility of the magnetic permeability testing method of the present invention.

[0039] Among them, 1 is a pressure regulating device, 2 is a pressure sensor, 3 is a test sample, 4 is a coaxial cable, 5 is a TE mode resonant cavity, 6 is a pressurizing device, and 7 is a test device support frame. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific embodiments.

[0041] First, the term "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "embodiment" used throughout this specification does not necessarily refer to the same embodiment, nor does it refer to separate or selective embodiments that are mutually exclusive with other embodiments.

[0042] The present invention designs a method for measuring the magnetic permeability of magnetic materials at a specific frequency. First, based on the characteristics of the TE mode resonant cavity and utilizing the principle of the end face substitution method, a resonant cavity for measuring the surface resistivity of the material is designed; the coaxial waveguide cable of the network analyzer is connected to the annular coupler of the resonant cavity, and the plane where the coupling ring is located is kept parallel to the circular cross-section of the resonant cavity. When the network analyzer signal is fed into the cavity in the above manner, the cavity operates in the TE mode, and the electric field at its upper end face is parallel to the cavity cross-section. When using the end face substitution method for measurement, the influence of the air gap between the upper end plate and the top of the side wall on the measurement results can be reduced. Figure 2As shown, an electrical parameter test device consisting of a resonant cavity and a network analyzer is used in conjunction with a pressurizing device. Multiple measurements are performed to keep the pressure sensor data unchanged, thereby improving the consistency of the external environment during testing and reducing test errors.

[0043] The surface resistivity of the sample to be tested is calculated from the data obtained from the test sample.

[0044]

[0045] The resistivity test data of the calibration sample and the sample to be tested are plotted and fitted as follows: Figure 1 Based on the "coating thickness-surface resistivity" curve shown in the figure, the skin depth and corresponding surface resistivity of the reference material at a specific frequency are first obtained. Substituting the obtained skin depth and surface resistivity data of the reference material into equation (II) can determine the value of the correction factor K.

[0046]

[0047] Substituting the skin depth and surface resistivity data of the nickel and ferrite coating samples to be tested into the calculation formula after obtaining the correction factor K value, the magnetic permeability value of the material to be tested can be obtained.

[0048] For ease of description, the following are typical but non-limiting examples of the present invention, which should not limit the scope of protection of the present invention.

[0049] Example 1

[0050] In this example, a high-quality 304 stainless steel substrate was used as the substrate. A magnetic film of varying thickness was deposited on the substrate surface via electroplating to form the test samples. The film thickness was 0.2 nm (n = 5, 6, 7, ..., 10). Three samples with identical parameters were prepared, and each sample was tested twice. To minimize measurement error, each set of data is the average of six test results.

[0051] In order to reduce the influence of sample surface morphology on the surface resistivity test results, a profilometer was used to collect sample surface morphology data to control the arithmetic mean roughness of the sample surface to be tested within 0.01 μm.

[0052] The test samples include: 304 stainless steel surfaces with the same material and size are electroplated with gold, silver, and nickel coating samples with a thickness of 0.2 nm (n = 5, 6, 7...10), and the present invention selects a 50 mm × 50 mm × 1 mm substrate for coating;

[0053] According to the measured curves of the calibration samples (gold and silver), the calibration factor K is calculated by formula (II) in the specific embodiment to be 1.14;

[0054] Analysis of the nickel coating thickness-surface conductivity trend curve shows a significant downward shift in the data points at a coating thickness of 1.6 μm, with a rapid decrease in conductivity. This indicates that the skin depth is reached around this thickness, affecting the resistivity of the sample being tested. 1.6 μm can be considered the skin depth at 3 GHz. Using this data, equation (IV) calculates that the relative magnetic permeability of nickel at 3 GHz is 4.616.

[0055] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for testing the magnetic permeability of a material at high frequency, characterized in that: Methods include: 1) Using 304 stainless steel with a high-finish surface as a substrate, a film was deposited on the substrate surface to prepare a calibration sample of the resonant cavity composed of a conductor material with a thickness of 0.2 nm, and n = 5, 6, 7, 8, 9, and 10; 2) Using 304 stainless steel with a high-finish surface as a substrate, a magnetic thin film material with a thickness of 0.2 nm and n = 5, 6, 7, 8, 9, and 10 was prepared on the substrate surface to form the test sample; 3) In order to reduce the influence of sample surface morphology on the surface resistivity test results, the surface profile roughness of the sample to be tested should be controlled within 0.01μm; 4) The test samples include: calibration coating samples with known magnetic permeability for obtaining correction factors and coating samples to be tested with unknown magnetic permeability; 5) Connect the coaxial cable of the network analyzer to the annular coupler of the resonant cavity, keeping the plane of the coupling ring parallel to the circular cross-section of the resonant cavity. When the network analyzer signal is fed into the resonant cavity in the above manner, the resonant cavity operates in TE mode, and the electric field at its upper end surface is parallel to the cross-section of the resonant cavity. The electrical parameter test device consisting of the resonant cavity and the network analyzer is used in conjunction with a pressurizing device, and the pressure sensor data is kept unchanged during multiple measurements; 6) Place the calibration and test samples with the coating surface facing downward on the upper end surface of the resonant cavity, and record the resonant frequency and quality factor; 7) Based on the test data, the surface resistivity of the calibration sample and the sample to be tested is obtained using the calculation formula of the surface resistivity of the resonant cavity test; 8) Using the resistivity data of the measured calibration sample and the sample to be tested, plot and fit the "surface resistivity-coating thickness" Curve to obtain the skin depth of conductor materials and magnetic materials at the test frequency; 9) Obtaining correction factors for the formula for calculating material permeability parameters based on the resistivity test data of the calibration sample; In actual testing, the calculation formula for material skin depth after adding the correction factor K is: Where, K is the correction factor; 10) Based on the measured skin depth and resistivity data of the sample to be tested, the corrected calculation formula is substituted to obtain the magnetic permeability of the magnetic material at high frequency.

2. The method according to claim 1, characterized in that: The conductor material is copper, silver or gold.

3. The method according to claim 1, characterized in that: In step (1) and step (2), the material and size of the coating substrate are the same.

4. The method according to claim 1, wherein: In step (3), the surface roughness of the sample is obtained by profilometer testing to complete the sample screening.

5. The method according to claim 1, wherein: In step (5), the resonant cavity is a brass metal workpiece with a silver-plated inner wall.

6. The method according to claim 1, characterized in that: In step (7), the calculation formula for the surface resistivity of the resonant cavity test is: In formula (I), ρ s1 : surface resistivity of the sample to be tested; ρ s0 : surface resistivity of the inner wall material of the resonant cavity; Q0: intrinsic quality factor of the original cavity; Q1: loaded quality factor of the resonant cavity after loading the sample to be tested; M: Cavity geometry factor, determined by the cavity size.

7. The method according to claim 1, characterized in that: In step (8), for the magnetic material sample, the surface resistivity is calculated as follows: Where, ρ s : surface resistivity; μ: magnetic permeability; f: test frequency; σ: electrical conductivity, Theoretically, there is a skin depth for the coating sample to be tested:

8. The method according to claim 1, characterized in that: Through formula (II) and formula (IV), we can get: By plotting the surface resistivity test data of the calibration sample and the sample to be tested and fitting the relationship curve, the relationship curve between the coating thickness on the substrate surface and the surface resistivity is calculated to obtain the skin depth of the material to be tested at the test frequency. The data is substituted into formula (V) to calculate the magnetic permeability of the magnetic material.

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