A low-loss hexagonal ferrite material in S and C bands and a preparation method thereof

Abstract

A low-loss hexagonal ferrite material in S and C bands and its preparation method, belonging to the technical field of ferrite material preparation. The hexagonal ferrite material includes a main phase and an additive. The main phase is Ba5Cu 2‑x Ni x Ti3Fe 12 O 31 , where x = 0.5 to 1, and the additive is SiO2; the additive accounts for 0.5 to 1.5 wt% of the mass of the main phase; by changing the ratios of Cu 2+ , Ni 2+ , the magnetocrystalline anisotropy, magnetic permeability and natural resonance frequency are regulated, and the real part of the magnetic permeability μ' ≥ 1.8, the magnetic loss tangent tanδ m ≤ 0.08, the real part of the dielectric constant ε' ≥ 10, and the dielectric loss tangent tanδ d ≤ 0.01 are achieved in the S and C bands. It can be used for the miniaturization of Sub-6GHz antennas, improving the antenna bandwidth and reducing the impedance mismatch.

Description

Technical Field

[0001] The present invention belongs to the technical field of ferrite material preparation, and particularly relates to an S- and C-band low-loss hexagonal ferrite material and a preparation method thereof. Background Art

[0002] With the rapid development of wireless communication systems applied to consumer electronics products, the Internet of Things, intelligent driving, and implantable electronic devices, the next-generation wireless communication systems have an urgent need for high-frequency, broadband, miniaturized, and lightweight antennas. Since the antenna size is mainly determined by the electromagnetic wave wavelength in the antenna substrate, high-dielectric constant materials have been widely used in the field of antenna miniaturization. However, the antenna miniaturization technology based on high-dielectric materials has two obvious problems: one is the concentration of electric field energy and the excitation of surface waves, resulting in reduced antenna efficiency and narrowed bandwidth; the other is the large difference between the impedance of high-dielectric materials and the environmental impedance, which brings difficulties to impedance matching.

[0003] Compared with high-dielectric materials, magnetodielectric materials have smaller capacitance, so the electromagnetic field energy distribution is more uniform, which is beneficial to increasing the efficiency and bandwidth of antennas. In addition, the impedance of magnetodielectric materials has a small difference from the environmental impedance, which helps to achieve impedance matching over a wide frequency band. For example, in 2019, Roger Company in the United States launched the world's first commercial magnetodielectric material - 555 laminate, whose characteristic impedance is close to 1, and the miniaturization factor is equivalent to that of a high-dielectric material with a dielectric constant of 30, and it can be used as an antenna substrate below 500 MHz. However, there is currently no commercial magnetodielectric material product for 5G antennas operating in the S (2 - 4 GHz) and C bands (4 - 8 GHz). Hexagonal ferrite is an important type of magnetodielectric material, which is divided into uniaxial, conical, and planar types according to the angle between its easy magnetization axis and the c-axis of the unit cell. The natural resonance frequency of the permeability of uniaxial hexagonal ferrite is high, but the permeability is low; the natural resonance frequency of the permeability of planar hexagonal ferrite is low, but the permeability is high. The permeability and natural resonance frequency of hexagonal ferrite are closely related to the in-plane and out-of-plane magnetocrystalline anisotropy fields. Metal ion substitution can change the angle between the easy magnetization axis of hexagonal ferrite and the c-axis, affecting the in-plane and out-of-plane magnetocrystalline anisotropy fields, thereby realizing the regulation of permeability, magnetic loss, and natural resonance frequency. For example, Patent CN106573848B prepared planar Z-type and Y-type hexagonal ferrite composites through the combined substitution of Co 2+ and Ir 2+ ions, and its real part of permeability at 0.65 - 0.85 GHz is 4.6 - 7.6, the tangent of magnetic loss angle is 0.07 - 0.29, the real part of dielectric constant is 6.5 - 8.1, and the tangent of dielectric loss angle is 0.05 - 0.09. Patent CN107428556B prepared Mo suitable for the UHF band by the solid-phase reaction method 2+Ion-doped Co2Z-type hexagonal ferrite composite materials have a real part of permeability of 7.6 - 8.6, a magnetic loss tangent of 0.07 - 0.12, a real part of dielectric constant of 6.6 - 8.7, and a dielectric loss tangent of 0.002 - 0.003 at 0.8 - 1 GHz. Patent CN105322297A discloses a magnetodielectric antenna applicable to the L band (1 - 2 GHz), in which the Co2Y-type hexagonal ferrite used has a real part of permeability of 2.2 - 2.5 and a magnetic loss tangent of 0.04 - 0.05 at 2.1 GHz. Patent CN103209773B prepared an M-type hexagonal ferrite for Bluetooth antennas by the sol-gel method, which has a real part of permeability of 1.37, a magnetic loss tangent of 0.13, a real part of dielectric constant of 22.2, and a dielectric loss tangent of 0.1 at 2.45 GHz. However, most of the traditional hexagonal ferrites reported so far are only applicable to below the L band, and have a low permeability (<2) and a high magnetic loss tangent (>0.1) in the S band and even higher C band, which is not conducive to the miniaturization application of low-loss 5G antennas. Summary of the Invention

[0004] The object of the present invention is to provide a low-loss hexagonal ferrite material and its preparation method for the S and C bands in view of the problems existing in the background technology. Through ion substitution and preparation process regulation, the present invention realizes the characteristics of high permeability and dielectric constant, low magnetodielectric loss and high cut-off frequency of the material.

[0005] The core idea of the present invention: The 5G antenna miniaturization technology based on high-dielectric materials has problems such as low efficiency, narrow bandwidth, and difficult impedance matching. An effective solution is to use microwave magnetodielectric materials. However, traditional microwave magnetodielectric materials are limited by the cut-off frequency and magnetodielectric loss and are difficult to meet the application requirements of the Sub-6GHz band. Based on the unique crystal structure of 18H hexagonal ferrite, the present invention uses Cu 2+ -doped 18H hexagonal ferrite. The Cu 2+ -doped 18H hexagonal ferrite has uniaxial magnetocrystalline anisotropy, and its permeability natural resonance frequency is greater than the C band but the permeability is less than 1.5. By introducing Ni 2+ substitution, the easy magnetization axis is turned from the c-axis of the unit cell to the hexagonal plane, thus realizing the transformation from uniaxial type to planar type, reducing the natural resonance frequency and increasing the permeability. Cu 2+ and Ni 2+ can jointly and precisely regulate the in-plane and out-of-plane magnetocrystalline anisotropy fields of 18H hexagonal ferrite, realizing a continuously variable permeability natural resonance frequency and low-loss characteristics covering the S and C bands. Secondly, due to the unique crystal structure of 18H hexagonal ferrite, Cu 2+ and Ni 2+The combination can reduce the magnetic moment precession damping coefficient, enhance the natural resonance of magnetic permeability, reduce the half-width of natural resonance, reduce the dispersion of magnetic loss, and achieve low-loss characteristics at high frequencies. Thirdly, the combination of low-melting-point CuO, NiO and high-melting-point SiO2 additives can promote sample densification while inhibiting abnormal grain growth, making the grain size small and uniform. The SiO2 additive with high resistivity is enriched at the grain boundary, which can effectively increase the grain boundary resistivity and reduce the high-frequency magnetic dielectric loss of the material. Therefore, the present invention is based on an 18H hexagonal ferrite material with a new crystal structure, through Cu 2+ 、Ni 2+ The direction of the easy magnetization axis of 18H hexagonal ferrite is jointly regulated to achieve a combination of the high natural resonance frequency of uniaxial hexagonal ferrite and the high magnetic permeability of planar hexagonal ferrite. SiO2 additives are used to achieve a microstructure with high density, uniform fine grains and high resistance grain boundaries, and the CuNi 18H hexagonal ferrite material with high magnetic permeability, dielectric constant and low magnetic dielectric loss for application in S and C frequency bands is prepared.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A low-loss hexagonal ferrite material in the S and C bands, the hexagonal ferrite material comprising a main phase and an additive, the main phase being Ba5Cu 2-x Ni x Ti3Fe 12 O 31 , where x = 0.5 to 1, the additive is SiO2; the additive accounts for 0.5 to 1.5 wt% of the main phase; by changing the Cu 2+ 、Ni 2+ ratio, in the S and C bands, the real part of the magnetic permeability μ'≥1.8 and the magnetic loss tangent tanδ m ≤0.08, real part of dielectric constant ε'≥10, dielectric loss tangent tanδ d ≤0.01.

[0008] A method for preparing a low-loss hexagonal ferrite material in the S and C frequency bands comprises the following steps:

[0009] S1. Ingredients: According to the chemical formula Ba5Cu 2-x Ni x Ti3Fe 12 O 31 Calculate and weigh BaCO3, CuO, NiO, TiO2, Fe2O3 raw material powders, where x = 0.5 to 1;

[0010] S2. First ball milling: The raw powder obtained in step S1 is mixed evenly in a ball mill, and the ball milling time is 2 to 4 hours;

[0011] S3. Pre-sintering: Dry the primary ball-milled abrasive obtained in step S2, and then pre-sinter it at 1050 - 1150 °C for 3 - 5 hours to obtain the CuNi 18H hexagonal ferrite pre-sintered material;

[0012] S4. Doping: Add SiO2 dopant equivalent to 0.5 - 1.5 wt% of the mass of the pre-sintered CuNi 18H hexagonal ferrite material obtained in step S3;

[0013] S5. Secondary ball-milling: Ball-mill the mixed powder obtained in step S4 in a high-energy ball mill for 6 - 10 hours, and the average particle size of the milled powder is 0.6 - 1.0 μm;

[0014] S6. Forming: Dehydrate the slurry obtained in step S5 to control the water content of the slurry between 30 wt% - 35 wt%, and then press the dehydrated slurry into a green body in a rotating magnetic field forming machine. The forming magnetic field strength is 0.6 - 1.0 T, the forming pressure is 80 - 120 MPa, and the pressure holding time is 40 - 60 s;

[0015] S7. Sintering: Place the green body obtained in step S6 in a sintering furnace and sinter it at 1100 - 1200 °C for 3 - 5 hours to obtain the low-loss hexagonal ferrite material.

[0016] For the sample obtained in step S7, use an X-ray diffractometer to analyze the sample phase composition; use a scanning electron microscope to observe the sample microstructure; use a vibrating sample magnetometer to measure the hysteresis loops of the sample parallel and perpendicular to the c-axis to characterize its anisotropy; use a vector network analyzer and a coaxial air line fixture to measure the complex permeability spectrum and complex permittivity spectrum of the sample.

[0017] The main technical indicators of the low-loss hexagonal ferrite material prepared by the present invention: in the S band and C band, the real part of the permeability μ' ≥ 1.8, the magnetic loss tangent tanδ m ≤ 0.08, the real part of the permittivity ε' ≥ 10, the dielectric loss tangent tanδ d ≤ 0.01.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] A low-loss hexagonal ferrite material in the S and C frequency bands provided by the present invention can regulate the magnetocrystalline anisotropy, permeability and natural resonance frequency by changing the Cu 2+ , Ni 2+ ratio, making it suitable for the S and C frequency bands; the microstructure of high density, uniform fine grains and high-resistance grain boundaries is beneficial to improving the permeability and permittivity of hexagonal ferrite and reducing the high-frequency magneto-dielectric loss; the prepared hexagonal ferrite is a magneto-dielectric material, which can be used for the miniaturization of Sub-6GHz antennas, improve the antenna bandwidth and reduce the impedance mismatch. Brief Description of the Drawings

[0020] Figure 1 It is the X-ray diffraction pattern of the hexagonal ferrite materials obtained in Examples 1 to 4;

[0021] Figure 2 It is the scanning electron microscope photograph of the hexagonal ferrite materials obtained in Examples 1 to 4;

[0022] Figure 3 It is the hysteresis loop of the hexagonal ferrite materials obtained in Examples 1 to 4;

[0023] Figure 4 It is the complex permeability spectrum of the hexagonal ferrite materials obtained in Examples 1 to 4; wherein, μ' is the real part of the permeability and μ" is the imaginary part of the permeability. Detailed Description of the Invention

[0024] The following further technical descriptions of the core idea and technical solutions of the present invention are provided through examples, but the present invention is not limited to these examples.

[0025] The specific preparation methods of Examples 1 to 4 include the following steps:

[0026] 1. Ingredient preparation: According to the chemical formula of CuNi 18H hexagonal ferrite Ba5Cu 2-x Ni x Ti3Fe 12 O 31 calculate and weigh the raw material powders of BaCO3, CuO, NiO, TiO2, and Fe2O3. The molar percentages of the raw material powders in Examples 1 to 4 are shown in the following table:

[0027]

[0028] 2. Primary ball milling: Mix the raw material powders obtained in step 1 evenly in a ball mill, and the ball milling time is 2 hours;

[0029] 3. Pre-sintering: Dry the primary ball milled material obtained in step 2, and then pre-sinter it at 1100 °C for 4 hours to obtain the CuNi 18H hexagonal ferrite pre-sintered material;

[0030] 4. Doping: Add 1.0 wt% of SiO2 dopant equivalent to the mass of the pre-sintered material to the CuNi 18H hexagonal ferrite pre-sintered material obtained in step 3;

[0031] 5. Secondary ball milling: Ball mill the mixed powder obtained in step 4 in a high-energy ball mill for 6 to 10 hours, and the average particle size of the milled powder is 0.8 μm;

[0032] 6. Shaping: The slurry obtained in step 5 is dehydrated to control the water content of the slurry within 30 wt%, and then the dehydrated slurry is pressed into a green body under a rotary magnetic field forming machine. The forming magnetic field strength is 0.8 T, the forming pressure is 100 MPa, and the pressure holding time is 40 s;

[0033] 7. Sintering: The green body obtained in step 6 is placed in a sintering furnace and sintered at 1150 °C for 4 hours to obtain the low-loss hexagonal ferrite material.

[0034] Characterize and test the phase composition, microstructure, and magnetic properties of the sample obtained in step 7. Analyze the phase composition of the sample using an X-ray diffractometer; observe the microstructure of the sample using a scanning electron microscope; measure the hysteresis loops parallel and perpendicular to the c-axis of the sample using a vibrating sample magnetometer to characterize its anisotropy; measure the complex permeability spectrum and complex permittivity spectrum of the sample using a vector network analyzer and a coaxial air line fixture. It can be known from the tests that the real part of the permeability μ', magnetic loss tangent tanδ m , real part of the permittivity ε', dielectric loss tangent tanδ d , and natural resonance frequency f0 of the permeability of Examples 1-4 at the optimal operating frequency are as follows in the table.

[0035]

[0036] In summary, based on 18H hexagonal ferrite, the present invention uses Cu 2+ , Ni 2+ to jointly regulate the direction of the easy magnetization axis and the magnetocrystalline anisotropy field, and combines the high melting point SiO2 additive technology to prepare a CuNi 18H hexagonal ferrite material with high permeability (μ'≥1.8) and permittivity (ε'≥10), and low magnetodielectric loss (tanδ m ≤0.08, tanδ d ≤0.01) suitable for the S and C frequency bands. Its magnetodielectric loss in the S and C frequency bands is lower than that of most known polycrystalline hexagonal ferrites. These results prove the feasibility of preparing low-loss 18H hexagonal ferrites in the S and C frequency bands by the traditional solid-state reaction method, providing a material basis for designing miniaturized 5G antennas based on magnetodielectric materials, thereby improving the antenna bandwidth and impedance characteristics.

[0037] It is understood that the present invention is described by way of some embodiments. Those skilled in the art will appreciate that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A low-loss hexagonal ferrite material in S and C bands, characterized in that, The hexagonal ferrite material includes a main phase and an additive. The main phase is Ba5Cu 2-x Ni x Ti3Fe 12 O 31 , where x = 0.5 to 1, and the additive is SiO2; the additive accounts for 0.5 to 1.5 wt% of the mass of the main phase.

2. A preparation method of an S- and C-band low-loss hexagonal ferrite material, characterized in that, It includes the following steps: S1. Ingredients: According to the chemical formula Ba5Cu 2-x Ni x Ti3Fe 12 O 31 calculate and weigh the raw material powders of BaCO3, CuO, NiO, TiO2, and Fe2O3, where x = 0.5 - 1; S2. Primary ball milling: Mix the raw material powder obtained in step S1 evenly in a ball mill, and the ball milling time is 2 - 4 hours; S3. Pre-sintering: Dry the primary ball milled material obtained in step S2, and then pre-sinter it at 1050 - 1150 °C for 3 - 5 hours to obtain a CuNi 18H hexagonal ferrite pre-sintered material; S4. Doping: Add SiO2 dopant equivalent to 0.5 - 1.5 wt% of the mass of the pre-sintered material to the CuNi 18H hexagonal ferrite pre-sintered material obtained in step S3; S5. Secondary ball milling: Ball mill the mixed powder obtained in step S4 for 6 - 10 hours, and the average particle size of the powder after ball milling is 0.6 - 1.0 μm; S6. Forming: Dehydrate the slurry obtained in step S5 to control the water content of the slurry between 30 wt% - 35 wt%, and then press the dehydrated slurry into a green body in a rotating magnetic field forming machine. The forming magnetic field strength is 0.6 - 1.0 T, the forming pressure is 80 - 120 MPa, and the pressure holding time is 40 - 60 s; S7. Sintering: Place the green body obtained in step S6 in a sintering furnace and sinter it at 1100 - 1200 °C for 3 - 5 hours to obtain the low-loss hexagonal ferrite material.

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