A method for measuring the ferromagnetic resonance linewidth with high precision

Abstract

The present invention belongs to the field of measuring parameters of magnetic materials in the microwave and millimeter-wave bands, and specifically provides a method for measuring the ferromagnetic resonance linewidth with high precision to solve the problem that the measurement error of the ferromagnetic resonance linewidth of existing microwave ferrite materials increases due to the large measurement magnetic field accuracy. The present invention uses a vector network analyzer as the signal source and receiver, adopts a measurement process of coarse scanning with the swept field decreasing step by step, the first fine scanning, and the second fine scanning, and interpolates the test data of the second fine scanning based on the fitting parameters of the first fine scanning as precision compensation, making the measurement data more convergent and significantly improving the precision of the measurement result; at the same time, the interpolation to achieve precision compensation can effectively solve the problem of insufficient magnetic field accuracy, reduce the error caused by measurement, make the measurement data obtain a better fitting effect, and further improve the precision of the ferromagnetic resonance linewidth measurement; in addition, the measurement method of the present invention is applicable to common resonance cavity methods and coplanar waveguide methods, etc.

Description

Technical Field

[0001] The present invention belongs to the field of measuring parameters of magnetic materials in the microwave and millimeter-wave bands, and relates to the measurement of the ferromagnetic resonance linewidth of microwave ferrite materials. Specifically, a method for measuring the ferromagnetic resonance linewidth with high precision is provided. Background Art

[0002] Nowadays, microwave communication is developing rapidly. Many traditional devices are moving towards miniaturization, low power consumption, high stability, and high precision. Microwave integrated devices have become indispensable devices in communication systems and electronic equipment and are widely used in various aspects such as artificial satellites, radars, and communication base stations. Therefore, microwave ferrite devices have good application prospects. Microwave ferrite devices have relatively high requirements for microwave ferrite materials, such as small ferromagnetic resonance linewidth, small dielectric loss, etc. Ferrite materials with good performance can be made into filters, phase shifters, circulators, isolators, etc. A common characteristic of microwave ferrites is the ferromagnetic resonance phenomenon. Briefly speaking, the microwave ferrite material will resonate at a certain frequency under a steady bias magnetic field and an alternating magnetic field that are perpendicular to each other. Therefore, measuring the ferromagnetic resonance linewidth of microwave ferrite materials is a common way to characterize microwave ferrite materials and is used to measure the magnetic loss of ferrite materials. A small ferromagnetic resonance linewidth indicates small magnetic loss, and a large ferromagnetic resonance linewidth indicates larger magnetic loss. As the operating frequency increases, the magnetic loss of microwave ferrite devices gradually increases. When evaluating microwave ferrite devices, the ferromagnetic resonance linewidth is one of the important basic parameters and has a great impact on whether the device can work normally in the system in which it is applied. Therefore, accurately measuring the ferromagnetic resonance linewidth of microwave ferrite materials is of great significance for the research of microwave ferrite devices.

[0003] Currently, the methods for measuring the ferromagnetic resonance linewidth of microwave ferrite materials mostly use the resonant cavity method or the transmission line method. The spherical ferrite materials usually use the resonant cavity method, but the resonant cavity method can only measure specific resonant frequency points; ferrite thin films usually use the coplanar waveguide method, which is convenient for placing and measuring samples, but the accuracy is not as high as that of the resonant cavity method. However, whether measuring spherical ferrite materials or ferrite thin films, at higher frequencies, due to the increase in coaxial cable loss, the measurement error will increase; in addition, when the frequency increases, the steady magnetic field required for measurement will become larger, and the distance between the electromagnets should be as small as possible to ensure the magnetic field strength, while the minimum accuracy of the current source is limited; when measuring with the minimum accuracy of the current source, the accuracy of the magnetic field may still be large, that is, the magnetic field change caused by the change in unit current is large. With limited current accuracy, the data point set for measurement becomes smaller, ultimately resulting in a larger error in the ferromagnetic resonance linewidth and inaccurate fitting parameters for the fitting curve, which in turn increases the error of other parameters when substituting into the calculation; therefore, there is still much room for improvement in improving the accuracy of the ferromagnetic resonance linewidth. Summary of the Invention

[0004] The object of the present invention is to propose a high-precision measurement method for the ferromagnetic resonance linewidth in view of the problem that the measurement error of the ferromagnetic resonance linewidth of the existing microwave ferrite material increases due to the large measurement magnetic field accuracy. The present invention uses a vector network analyzer as the signal source and receiver, adopts a measurement process of rough sweep, first fine sweep and second fine sweep, and the sweep field step decreases in turn. At the same time, based on the fitting parameters of the first fine sweep, an effective precision compensation is carried out on the second fine sweep, significantly reducing the error during measurement and improving the measurement precision of the ferromagnetic resonance linewidth.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A high-precision measurement method for the ferromagnetic resonance linewidth, comprising the following steps:

[0007] Step 1: Set the test frequency and the rough sweep step ε1, and perform a sweep field within the maximum range at the test frequency to obtain the absorption peak of the sample to be measured;

[0008] Step 2: Set the first fine sweep step ε2, ε2 < ε1, perform a sweep field on the absorption peak to obtain the sampling point set Q1 of the sample to be measured = [(x1, y1), (x2, y2),..., (x M , y M )], (x m , y m ) represents the data of the m-th sampling point of the first fine sweep, where x is the magnetic field strength and y is the S 21 parameter;

[0009] Step 3: Perform Lorentz fitting on the sampling data set Q1 to obtain the resonance curve y of the sample to be measured, and take the derivative of the resonance curve to obtain:

[0010]

[0011] where x is the magnetic field strength, y is the S 21 parameter, A, y0, x c are fitting parameters, and w is the fitting parameter of the ferromagnetic resonance linewidth;

[0012] Step 4: Set the second fine sweep step ε3, ε3 < ε2, perform a sweep field on the absorption peak again to obtain the sampling point set Q2 of the sample to be measured = [(x1′, y1′), (x2′, y2′),..., (x′ N , y′ N )], (x n ′, y n ′) represents the data of the n-th sampling point of the second fine sweep;

[0013] Step 5: Set the interpolation accuracy ε, and interpolate the sampling point set Q2 to obtain the interpolation point set Q3 = [(x1″, y1″), (x2″, y2″),..., (x′ N ′, y′ N ′)]; (x n ″, y n ″) represents the data of the nth interpolation point, specifically:

[0014] x n ″ = x n ′ + ε

[0015]

[0016] Step 6: Combine the sampling point set Q2 and the interpolation point set Q3 in ascending order of magnetic field strength to form a test point set, and perform Lorentz fitting on the test point set again. Take the fitting parameter of the ferromagnetic resonance linewidth as the measurement result of the ferromagnetic resonance linewidth.

[0017] Furthermore, the formula for Lorentz fitting is:

[0018]

[0019] where x is the magnetic field strength, y is the S 21 parameter, A, y0, x c are fitting parameters, and w is the fitting parameter of the ferromagnetic resonance linewidth.

[0020] Furthermore, the interpolation accuracy ε is less than the minimum accuracy of the magnetic field strength.

[0021] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0022] The present invention provides a method for measuring the ferromagnetic resonance linewidth with high precision. It adopts a measurement process of rough sweep, first fine sweep, and second fine sweep with the sweep field stepping decreasing in turn. And based on the fitting parameters of the first fine sweep, the test data of the second fine sweep are interpolated as precision compensation, making the measurement data more convergent, significantly improving the precision of the measurement result; at the same time, the interpolation to achieve precision compensation can effectively solve the problem of insufficient magnetic field precision, reduce the error caused by measurement, make the measurement data obtain a better fitting effect, and further improve the precision of measuring the ferromagnetic resonance linewidth; in addition, the measurement method of the present invention is applicable to common resonance cavity methods and coplanar waveguide methods, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the ferromagnetic resonance linewidth test system of the present invention. Among them, 1 is a sample clamp, 2 is a large magnetic field electromagnet, 3 is a vector network analyzer, 4 is a chiller, 5 is a programmable current source, 6 is a gaussmeter, and 7 is a computer interconnecting each device.

[0024] Figure 2 This is the theoretical curve of the ferromagnetic resonance linewidth in the embodiment of the present invention.

[0025] Figure 3 This is the test curve of the ferromagnetic resonance linewidth obtained by the first fine sweep fitting in the embodiment of the present invention.

[0026] Figure 4 This is the test curve of the ferromagnetic resonance linewidth after precision compensation in the embodiment of the present invention. Detailed implementation manners

[0027] To make the objectives, technical solutions and beneficial effects of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0028] This embodiment provides a method for measuring the ferromagnetic resonance linewidth with high precision, which is implemented based on the ferromagnetic resonance linewidth test system as shown in Figure 1 , and includes: a sample fixture 1, a large magnetic field electromagnet 2, a vector network analyzer 3, a chiller 4, a programmable current source 5, a gaussmeter 6, and a computer 7. Among them, the sample fixture is used to place a sample, which can be a resonant cavity or a coplanar waveguide; the sample fixture is located in the center of the retractable electromagnet, and both ends of the fixture are connected to the vector network analyzer through microwave transmission lines. The vector network analyzer generates an input microwave signal and receives the output microwave signal after resonance; the programmable current source is used to energize the large magnetic field electromagnet so that the large magnetic field electromagnet provides a steady bias magnetic field for the sample. The chiller is used to monitor the temperature of the electromagnet and provide cooling water to cool the electromagnet. The Hall probe of the gaussmeter is located directly above the sample fixture to monitor the magnitude of the bias magnetic field in real time.

[0029] The method for measuring the ferromagnetic resonance linewidth with high precision specifically includes the following steps:

[0030] Step 1: Set the test frequency and the coarse sweep step ε1, and perform a maximum range field sweep at the test frequency (control the output current of the current source to increase from the minimum value to the maximum value in accordance with the preset step, that is, the steady bias magnetic field increases from the minimum value to the maximum value in accordance with the preset step), and obtain the absorption peak of the microwave ferrite sample to be measured, as shown in Figure 2 ;

[0031] Step 2: Set the first fine sweep step ε2, perform a field sweep on the absorption peak, and obtain the sampling point set Q1 = [(x1, y1), (x2, y2),..., (x M , y M )] of the microwave ferrite sample to be measured. (x m , y m ) represents the data of the m-th sampling point of the first fine sweep. Among them, x m is the magnetic field strength of the m-th sampling point, and ym is the S at the m-th sampling point 21 parameter, and M is the number of sampling points in the sampling point set Q1;

[0032] Step 3: Perform Lorentz fitting on the sampling data set Q1 to obtain the resonance curve of the microwave ferrite sample to be measured, as Figure 3 shown; the Lorentz fitting formula is:

[0033]

[0034] where x is the magnetic field strength and y is the S 21 parameter, and A, y0, x c , w are fitting parameters, and w is the ferromagnetic resonance linewidth obtained by fitting;

[0035] The idea of Lorentz fitting mainly uses the least squares method and iterates with the Levenberg-Marquardt optimization algorithm to make the curve fitting effect better;

[0036] Derive the resonance curve to obtain:

[0037]

[0038] Step 4: Set the second fine sweep step ε3, perform a field sweep on the absorption peak, and obtain the sampling point set Q2 of the microwave ferrite sample to be measured = [(x1′, y1′), (x2′, y2′),..., (x′ N , y′ N )], (x n ′, y n ′) represents the data of the n-th sampling point in the second fine sweep, x n ′ is the magnetic field strength of the n-th sampling point, and y′ n is the S at the n-th sampling point 21 parameter, and N is the number of sampling points in the sampling point set Q2;

[0039] Step 5: Set the interpolation accuracy ε, perform accuracy compensation on the sampling point set Q2, that is, interpolate the sampling point set Q2 by numerical differentiation to obtain the interpolation point set Q3 = [(x1″, y1″), (x2″, y2″),..., (x′ N ′, y′ N ′)]; (x n ″, y n ″) represents the data of the n-th interpolation point, specifically:

[0040] x n ″ = x n ′ + ε

[0041]

[0042] Step 6: Merge the sampling point set Q2 and the interpolation point set Q3 in ascending order of magnetic field strength to form a test point set, and perform Lorentz fitting on the test point set again. The fitting curve is as Figure 4 shown, and the fitting parameter w′ is obtained as the measurement result of the ferromagnetic resonance linewidth.

[0043] In summary, in the ferromagnetic resonance linewidth measurement method provided by the present invention, since the S 21 parameter is a constant value during non-ferromagnetic resonance, the present invention first performs a field sweep with the maximum step to obtain the absorption peak during ferromagnetic resonance; then, the step is reduced, and only the absorption peak (the measurement point dense area) is finely swept for the first time. Based on the data point set of the first fine sweep, the resonance curve y of the microwave ferrite sample to be measured is fitted; the step is further reduced, and the absorption peak is finely swept for the second time to obtain the data point set of the second fine sweep, and interpolation is performed on the data point set of the second fine sweep based on the derivative of the resonance curve y of the microwave ferrite sample to be measured to obtain an interpolation point set; finally, the data point set of the second fine sweep and the interpolation point set are merged to obtain the final test point set, and the measurement result of the ferromagnetic resonance linewidth is obtained based on the fitting of the test point set.

[0044] Based on the above measurement process, the field sweep with the maximum step can effectively save the measurement time, and the two fine sweeps with gradually decreasing steps can significantly increase the quantity and accuracy of the test data. Moreover, interpolation with an accuracy less than the minimum magnetic field strength accuracy is performed on the data set of the second fine sweep based on the fitting parameter of the first fine sweep, which can achieve effective accuracy compensation, thereby obtaining more data points, ultimately significantly reducing the fitting error and improving the measurement accuracy; at the same time, the number of data points in the non-ferromagnetic resonance region is effectively reduced, the influence of the linewidth on the fitting process is reduced, and the errors caused by the asymmetry of the S 21 parameter value in the non-ferromagnetic resonance region are reduced.

[0045] The above is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for measuring the ferromagnetic resonance linewidth with high precision, comprising the following steps: Step 1: Set the test frequency and the coarse sweep step ε1, perform a maximum range field sweep at the test frequency, and obtain the absorption peak of the sample to be measured; Step 2: Set the first fine sweep step ε2, where ε2 < ε1. Perform a field sweep on the absorption peak to obtain the sampling point set Q1 = [(x1, y1), (x2, y2),..., (x M , y M )] of the sample to be measured. (x m , y m ) represents the data of the m-th sampling point in the first fine sweep. Here, x is the magnetic field strength, and y is the S 21 parameter; Step 3: Perform Lorentz fitting on the sampling data set Q1 to obtain the resonance curve y of the sample to be measured, and take the derivative of the resonance curve to obtain: where x is the magnetic field strength and y is the S 21 parameter, A and x c are fitting parameters, and w is the fitting parameter of the ferromagnetic resonance linewidth; Step 4: Set the second fine sweep step ε3, where ε3 < ε2, and perform a field sweep on the absorption peak again to obtain the sampling point set Q2 of the sample to be measured = [(x1′, y1′), (x2′, y2′),..., (x N ′, y N ′)], (x n ′, y n ′) represents the data of the nth sampling point of the second fine sweep; Step 5. Set the interpolation accuracy ε, and perform interpolation on the sampling point set Q2 to obtain an interpolation point set Q3 = [(x1″, y1″), (x2″, y2″),..., (x N ″, y N ″)]; (x n ″, y n ″) represents the data of the nth interpolation point, specifically: Step 6: Combine the sampling point set Q2 and the interpolation point set Q3 in ascending order of magnetic field strength to form a test point set, perform Lorentz fitting on the test point set again, and use the fitting parameter of the ferromagnetic resonance linewidth as the measurement result of the ferromagnetic resonance linewidth.

2. The high-precision ferromagnetic resonance linewidth measurement method according to claim 1, characterized in that, The formula for Lorentz fitting is: where x is the magnetic field strength and y is the S 21 parameter, and A, y0, x c are fitting parameters, and w is the fitting parameter of the ferromagnetic resonance linewidth.

3. The high-precision ferromagnetic resonance linewidth measurement method according to claim 1, characterized in that The interpolation precision ε is less than the minimum precision of the magnetic field strength.

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