Ferrite magnetic core for radio frequency transformer, preparation method of ferrite magnetic core and radio frequency transformer

Abstract

The invention relates to a ferrite magnetic core of a radio frequency transformer, a preparation method of the ferrite magnetic core and the radio frequency transformer, the magnetic core comprises a main formula and a dopant formula, the total proportion of the main formula is 100 mol%, and the main formula is composed of 52-54 mol% of Fe2O2, 25-27 mol% of MnO and 18-20 mol% of ZnO; on the basis of the total weight of the main formula, the dopant formula comprises the following components in parts by weight: 300 to 600 ppm of Bi2O2, 400 to 700 ppm of Co2O3, 200 to 500 ppm of V2O5, 600 to 900 ppm of MoO, 300 to 600 ppm of Cr2O3, 350 to 650 ppm of SiO2 and 200 to 550 ppm of TiO2. The beneficial effects are that the energy transmission efficiency can be improved, the signal distortion can be reduced, the system performance is stable, and the reliability of the radio frequency transformer can be effectively improved when the device is used in the radio frequency transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic and communication systems, and in particular to a ferrite core for a radio frequency transformer, a preparation method thereof, and a radio frequency transformer. Background Art

[0002] As an indispensable key component in modern electronic and communication systems, RF transformers are widely used in various fields such as mobile communication equipment, wireless network equipment, satellite communication systems, etc. It plays multiple roles between different RF circuits, including but not limited to impedance matching, signal isolation, voltage conversion, and power transfer. These functions are essential to ensure the normal operation and performance of the system. The basic structure of the RF transformer includes a primary coil, a secondary coil, and a magnetic core, among which the choice of the magnetic core has a decisive influence on the overall performance of the transformer.

[0003] The material and structure of the core determine its heat dissipation performance, leakage inductance, noise level, and winding arrangement, which are key factors affecting the efficiency and stability of RF transformers. Ferrite cores are widely used within a certain frequency range due to their cost-effectiveness and good magnetic properties. However, with the development of communication technology and application requirements, especially in the fields of ultra-high frequency communication systems and millimeter wave radars, the limitations of traditional ferrite cores have gradually emerged, specifically the following points:

[0004] High-frequency losses and bandwidth limitations: High-permeability or manganese-zinc ferrite cores exhibit high losses at very high frequencies and have limited bandwidth, which limits their application in scenarios with extremely high frequency requirements, such as ultra-high frequency communication systems and millimeter-wave radars.

[0005] Magnetic core saturation phenomenon: For ferrite cores made of manganese-zinc high magnetic permeability materials, when the magnetic field strength passing through exceeds a certain threshold, magnetic core saturation phenomenon will occur. This means that the magnetic permeability drops sharply and the inductance will also be greatly reduced, which will lead to nonlinear distortion of the signal, destroy the linear relationship between the input and output signals, and seriously affect the signal quality of the RF system.

[0006] Temperature sensitivity: The performance parameters of high permeability ferrites will change significantly with temperature. When the temperature rises, the permeability may decrease, causing the inductance and other performance parameters of the RF transformer to change, affecting its normal operation and stability under different temperature environments. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a ferrite core for a radio frequency transformer, a preparation method and a radio frequency transformer, which solve the problems of high-frequency loss and bandwidth limitation, core saturation and temperature sensitivity when the existing high magnetic permeability ferrite core is used in the radio frequency transformer, thereby solving the technical problem that limits the application of high magnetic permeability ferrite cores in radio frequency transformers.

[0009] (II) Technical solution

[0010] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0011] In a first aspect, an embodiment of the present invention provides a ferrite core for a radio frequency transformer, including a main formula and a dopant formula:

[0012] The main formula has a total ratio of 100 mol%, specifically composed of 52-54 mol% of Fe2O3, 25-27 mol% of MnO and 18-20 mol% of ZnO;

[0013] Based on the total weight of the main formula, the dopant formula includes Bi2O3 300-600ppm, Co2O3 400-700ppm, V2O5 200-500ppm, MoO 600-900ppm, Cr2O3 300-600ppm, SiO2 350-650ppm and TiO2 200-550ppm.

[0014] As a preferred embodiment of the present invention, the ferrite core for radio frequency transformer has a main formula consisting of 53.6-54 mol% Fe2O3, 26.4-27 mol% MnO and 18.9-19.7 mol% ZnO;

[0015] Relative to the total weight of the main formula, the dopant formula includes Bi2O3 500-600ppm, Co2O3 400-600ppm, V2O5 300-500ppm, MoO 700-850ppm, Cr2O3 400-500ppm, SiO2 400-600ppm and TiO2 200-500ppm.

[0016] As a preferred embodiment of the present invention, the ferrite core for radio frequency transformer has a main formula consisting of 53.9 mol% Fe2O3, 26.9 mol% MnO and 19.2 mol% ZnO;

[0017] Relative to the total weight of the main formula, the dopant formula includes Bi2O3580ppm, Co2O3550ppm, V2O5370ppm, MoO750ppm, Cr2O3450ppm, SiO2600ppm and TiO2500ppm.

[0018] In a second aspect, an embodiment of the present invention provides a method for preparing the ferrite core for a radio frequency transformer according to the first aspect, comprising the following steps:

[0019] S1. Primary ball milling: weigh the main formula ingredients, add deionized water, and grind and mix thoroughly to obtain the main formula mixture;

[0020] S2, pre-burning: After drying the main formula mixture, place it at 880-950℃ for 2-4h, cool it with the furnace, and obtain the pre-burned material;

[0021] S3, secondary ball milling and granulation: adding dopant formula components and deionized water to the pre-burned material, grinding to obtain slurry, drying the slurry and then granulating to obtain material powder;

[0022] S4, molding and sintering: the granulated powder is pressed into a green body, and then sintered to obtain a manganese-zinc ferrite core.

[0023] As a preferred embodiment of the present invention, in the preparation method, in S4, the sintering process specifically includes a temperature rising section, a temperature holding section and a temperature falling section;

[0024] The control program of the temperature rising section is: the oxygen content in the protective atmosphere is 21%, and the temperature rises to 1050℃;

[0025] The control program of the insulation section is:

[0026] The first stage: the temperature is increased from 1050°C to 1380°C at 1.3-2.7°C / min, wherein the oxygen content in the protective atmosphere during the period from 1050°C to 1300°C is 21%, and the oxygen content in the protective atmosphere during the period from 1300°C to 1380°C is 1%;

[0027] The second stage: at 1380°C, the oxygen content in the protective atmosphere is 21% and maintained for 300 minutes, then the oxygen content is adjusted to 5% and maintained for 30 minutes;

[0028] The third stage: the temperature drops from 1380℃ to 1000℃ at a rate of 2.9-4℃ / min, and the corresponding oxygen content gradually drops to 0;

[0029] The control program of the cooling stage is: cooling from 1000°C to room temperature at 1-3.5°C / min in a nitrogen atmosphere.

[0030] As a preferred embodiment of the present invention, in the preparation method, in S4, in the first stage of the control program of the insulation stage, the temperature rises from 1050°C to 1300°C at a corresponding heating rate of 1.3-1.32°C / min; the temperature rises from 1300°C to 1380°C at a corresponding heating rate of 2.5-2.67°C / min;

[0031] In the third stage, the temperature drops from 1380℃ to 1300℃, and the corresponding cooling rate is 2.96-3℃ / min; the temperature drops from 1300℃ to 1000℃, and the corresponding cooling rate is 3.33-3.85℃ / min.

[0032] As a preferred embodiment of the present invention, in the preparation method, in S4, ZnO powder is added to the sintering environment, and 0.4-0.5 g of ZnO powder is added per kilogram of green body.

[0033] As a preferred embodiment of the present invention, in the preparation method, in S4, the green body is any one of a ring-shaped, single-hole, double-hole and four-hole shape.

[0034] As a preferred embodiment of the present invention, the preparation method further comprises S5, insulating coating, depositing a polyparaxylene film layer on the surface of the green body, the film layer having a thickness of 19-21 μm.

[0035] In a third aspect, an embodiment of the present invention provides a radio frequency transformer, comprising the ferrite core described in the first aspect or the ferrite core prepared by the preparation method described in the second aspect and a core wire wound on the ferrite core, wherein the core wire is a Φ0.1 mm enameled copper wire.

[0036] (III) Beneficial effects

[0037] The beneficial effects of the present invention are as follows: the ferrite core and preparation method for radio frequency transformer and radio frequency transformer of the present invention, wherein the ferrite core material optimizes the dopant formula on the basis of the main formula, wherein TiO2 forms a high resistance layer at the grain boundary, improves the resistivity, reduces the eddy current loss of high permeability materials, and improves the temperature coefficient of the material. The combination of 400-700ppm Co2O3 and 200-550ppm TiO2 improves the wide temperature characteristics of the material and smoothes the positive temperature curve of the material in the range of 30-120°C. Cr2O3 is dissolved in spinel, which plays a role in improving the saturation flux density and Curie temperature. Bi2O3 plays a role in reducing the sintering temperature and increasing the contact surface of the solid phase reaction. MoO plays a role in refining the grains, improving the initial permeability and quality factor of the material, and reducing the core loss. V2O5 promotes and controls the growth of grains during the sintering process, improves the sintering density and initial permeability. SiO2 can reduce hysteresis loss by reducing the interaction between magnetic particles. Compared with the existing technology, the saturation magnetic induction intensity and initial magnetic permeability μi of the ferrite core are significantly improved, and a high magnetic permeability material that can maintain good magnetic properties at high frequencies has been determined, so that the high magnetic permeability material core can achieve low insertion loss and high impedance matching in the high-frequency environment of the RF transformer, and at the same time improve the wide temperature characteristics of the material. Application in RF transformers can improve energy transmission efficiency, reduce signal distortion, improve signal transmission quality, stabilize system performance, and effectively improve the reliability of RF transformers.

[0038] In the sintering process, at the initial stage of the heat preservation stage, as Fe 3+ Reduction decomposition releases oxygen, which increases the oxygen content in the reaction environment. At this time, the oxygen content is temporarily reduced to 1%, which is conducive to the establishment of a balanced oxygen partial pressure and promotes Fe 3+ The reduction reaction proceeds in a positive direction. As the insulation time increases, the reducing property in the system increases, and timely recovery of the oxygen content can prevent ZnO from volatilizing, avoid the generation of vacancies between ferrite grains, and ensure the microstructure and magnetic permeability of the material.

[0039] From the middle and late stage of the insulation stage to the cooling stage, the oxygen content is adjusted to 5% and gradually dropped to 0 to avoid excessive oxidation near 1050°C, which would cause overoxidation of Mn3O4 to Mn2O3 and MnO2, and prevent the precipitation of non-magnetic Mn2O3 from reducing the material magnetic permeability ui.

[0040] Add ZnO powder to the sintering environment, 0.4-0.5g ZnO powder for each kilogram of green body. ZnO powder decomposes at high temperature to produce zinc vapor and oxygen, which helps to maintain the sintering atmosphere and prevent the core from being oxidized when sintered in a reducing atmosphere. It also helps to control the oxygen partial pressure in the furnace and maintain a suitable sintering environment. Sprinkling an appropriate amount of ZnO powder helps the physical and chemical reactions during the sintering process, promotes the growth and densification of ferrite material grains, and thus improves the density and performance of the core.

[0041] A polyparaxylene film layer with a thickness of 19-21μm is deposited on the surface of the green body to form a dense protective film on the surface of the green body, which can improve the coupling effect between the magnetic core and the coil, reduce contact resistance and signal loss, and improve the performance of the RF transformer. It can also reduce the generation of parasitic capacitance and inductance, increase signal transmission speed, increase signal distortion, etc. At the same time, the film layer with a thickness of 19-21μm is conducive to the perforation and winding of a smaller magnetic core while meeting the above performance.

[0042] The core wire is Φ0.1mm enameled copper wire, which has a smaller diameter and a more compact coil structure, which can reduce the parasitic capacitance and inductance of the coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The permeability-temperature curve of the manganese-zinc ferrite core prepared in Example 1;

[0044] Figure 2 The manganese-zinc ferrite core prepared in Example 1;

[0045] Figure 3 This is the manganese-zinc ferrite core prepared in Example 1. DETAILED DESCRIPTION

[0046] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0047] The ferrite core and preparation method for radio frequency transformer and radio frequency transformer proposed in the embodiment of the present invention, wherein the ferrite core material optimizes the dopant formula on the basis of the main formula, wherein TiO2 forms a high resistance layer at the grain boundary, improves the resistivity, reduces the eddy current loss of high permeability materials, and improves the temperature coefficient of the material. The combination of 400-700ppm Co2O3 and 200-550ppm TiO2 improves the wide temperature characteristics of the material and smoothes the positive temperature curve of the material in the range of 30-120°C. Cr2O3 is dissolved in spinel, which plays a role in increasing the saturation flux density and Curie temperature. Bi2O3 plays a role in reducing the sintering temperature and increasing the contact surface of the solid phase reaction. MoO plays a role in refining the grains, improving the initial magnetic permeability and quality factor of the material, and reducing the core loss. V2O5 promotes and controls the growth of grains during the sintering process, improves the sintering density and initial magnetic permeability. SiO2 can reduce hysteresis loss by reducing the interaction between magnetic particles. Compared with the existing technology, the saturation magnetic induction intensity and initial magnetic permeability μi of the ferrite core are significantly improved, and a high magnetic permeability material that can maintain good magnetic properties at high frequencies has been determined, so that the RF transformer can achieve low insertion loss and high impedance matching at high frequencies, while improving the wide temperature characteristics of the material. Application in RF transformers can improve energy transmission efficiency, reduce signal distortion, improve signal transmission quality, stabilize system performance, and effectively improve the reliability of RF transformers.

[0048] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0049] Example 1

[0050] This embodiment provides a method for preparing a ferrite core for a radio frequency transformer, which specifically includes the following steps:

[0051] (1) Primary ball milling: weigh the main formula ingredients according to the following proportions, wherein Fe2O3 is 53.9 mol%, MnO is 26.9 mol% and ZnO is 19.2 mol%, add deionized water, grind and mix thoroughly to obtain a main formula mixed material, dry the main formula mixed material, place it at 880-950°C for 2-4 hours, and cool it with the furnace to obtain a pre-burned material;

[0052] (2) Secondary ball milling and granulation: Based on the total mass of the premix, add the following dopant ingredients to the pre-sintered material: Bi2O3 580ppm, Co2O3 550ppm, V2O5 370ppm, MoO 750ppm, Cr2O3 450ppm, SiO2 600ppm, TiO2 500ppm; then add deionized water and grind to obtain a slurry, dry the slurry and granulate it to obtain a powder;

[0053] (3) Molding and sintering: The granulated powder is pressed into a double-hole green body, and then placed in a sintering furnace for sintering to obtain a manganese-zinc ferrite core. The sintering parameters are shown in Table 1. ZnO powder is added around the bowl or on the bowl cover. 0.4-0.5 g of ZnO powder is added per kilogram of green body.

[0054] (4) Surface treatment: The sintered manganese-zinc ferrite core is treated with solid Parylene (polyparaxylene powder) in an evaporation chamber to gradually absorb heat and sublimate as the temperature rises. The sublimated dimer gas enters the cracking chamber. At a temperature of 660-700°C, the molecular bonds of the dimer are broken to form an active Parylene monomer with two dangling bonds. Finally, the Parylene monomer is sent to a vacuum deposition chamber at room temperature to polymerize and deposit on the surface of the ferrite core, eventually forming a dense protective film with a thickness controlled at 19-21 μm, thereby finally preparing a finished manganese-zinc ferrite core.

[0055] Table 1 Sintering parameters of manganese zinc ferrite core

[0056]

[0057]

[0058] In Table 1, in the 8th program-controlled section of the sintering process of the magnetic core green body, that is, at the beginning of the heat preservation stage, as Fe 3+ Reduction decomposition releases oxygen, which increases the oxygen content in the reaction environment. At this time, the oxygen content is temporarily reduced to 1%, which is conducive to the establishment of a balanced oxygen partial pressure and promotes Fe 3+ The reduction reaction proceeds in a positive direction. As the insulation time increases, the reducibility in the system increases, and timely recovery of the oxygen content can prevent the volatilization of ZnO in the green body, avoid the generation of vacancies between ferrite grains, and ensure the microstructure and magnetic permeability of the material.

[0059] After the 11th program-controlled section, that is, in the cooling stage of the insulation stage, the oxygen content is adjusted to 5% and gradually dropped to 0, which can avoid the oxidation rate being too fast near 1050°C, causing Mn3O4 to be overoxidized to Mn2O3 and MnO2, and preventing the precipitation of non-magnetic Mn2O3 from reducing the material magnetic permeability ui.

[0060] The prepared manganese-zinc ferrite core was subjected to electrical performance tests according to the items in Table 2. The test results are shown in Table 2 for details.

[0061] Example 2

[0062] The present embodiment provides a method for preparing a ferrite core for a radio frequency transformer, which differs from the embodiment 1 in that: in step (2), secondary ball milling and granulation: based on the total mass of the premix, the dopant formula components are added to the pre-burned material in the following amounts: Bi2O3500ppm, Co2O3400ppm, V2O5500ppm, MoO850ppm, Cr2O3450ppm, SiO2400ppm, TiO2200ppm; the remaining steps are the same.

[0063] Example 3

[0064] This embodiment provides a method for preparing a ferrite core for a radio frequency transformer, which differs from Embodiment 2 in that:

[0065] (1) First ball milling: Weigh the main formula ingredients according to the following proportions, where Fe2O3 is 54 mol%, MnO is 26 mol% and ZnO is 20 mol%; the remaining steps are the same.

[0066] Example 4

[0067] This embodiment provides a radio frequency transformer, which adopts the finished manganese-zinc ferrite core prepared in Example 1 and is wound with Φ0.1mm enameled copper wire as the core wire. The specific winding method refers to the prior art. The double-hole core structure can provide more magnetic circuit options, reduce the parasitic capacitance between coils at high frequencies, and improve circuit performance. At the same time, the two holes of the double-hole core increase the heat dissipation area, thereby improving the heat dissipation performance of the core.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing a ferrite core for a radio frequency transformer, which differs from Example 1 in that: in step (2), secondary ball milling and granulation: based on the total mass of the premix, the following dopant formula components are added to the pre-burned material in the following amounts: Bi2O3650ppm, Co2O3550ppm, V2O5800ppm, MoO600ppm, Cr2O3700ppm, SiO2200ppm, TiO2700ppm; the remaining steps are the same.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing a ferrite core for a radio frequency transformer, which differs from Example 1 in that: in step (2), secondary ball milling and granulation: based on the total mass of the premix, the following dopant formula components are added to the pre-burned material in the following amounts: Bi2O3700ppm, Co2O3800ppm, V2O5300ppm, MoO750ppm, Cr2O3600ppm, SiO2800ppm, TiO2900ppm; the remaining steps are the same.

[0072] Table 2 Test conditions and test results of manganese zinc ferrite core electrical properties

[0073]

[0074] In addition, for ease of comparison, the dopant formulas are organized into Table 3 below.

[0075] Table 3 Adulteration formula

[0076]

[0077] Based on the above embodiments and comparative examples, the comparative analysis is as follows in combination with Table 2 and Table 3:

[0078] Compared with Example 2, Example 1 is the best example. Figure 2 and Figure 3 The manganese-zinc ferrite core prepared in Example 1 is shown to have the best electrical performance test results, and the saturation magnetic induction intensity and initial magnetic permeability are significantly higher than those of Comparative Example 1 and Comparative Example 2. The initial magnetic permeability of the core of Example 1 is up to 7500; the saturation magnetic flux density is up to 400mT, and the loss factor is the lowest, as low as 2.2×10 -6 ; Its Curie temperature is 140°C, which meets the operating temperature of the RF transformer. That is, the magnetic core prepared in Example 1 is a magnetic material with high magnetic permeability and low loss, and at the same time significantly reduces the magnetic core loss and insertion loss. It is a high magnetic permeability material that can maintain good magnetic properties at high frequencies, so that the RF transformer can achieve low insertion loss and high impedance matching at high frequencies.

[0079] Among them, TiO2 forms a high resistance layer at the grain boundary, which increases the resistivity, reduces the eddy current loss of high magnetic permeability materials, and improves the temperature coefficient of the material. The combination of 400-700ppm Co2O3 and 200-550ppm TiO2 improves the wide temperature characteristics of the material, see Figure 1, smoothing the positive temperature curve of the material in the range of 30-120℃. Cr2O3 is dissolved in spinel, which increases the saturation flux density and Curie temperature. Bi2O3 reduces the sintering temperature and increases the contact surface of the solid phase reaction. MoO refines the grains, increases the initial magnetic permeability and quality factor of the material, and reduces the core loss. V2O5 promotes and controls the growth of grains during the sintering process, increases the sintering density and initial magnetic permeability. SiO2 can reduce the hysteresis loss by reducing the interaction between magnetic particles.

[0080] Comparison of Example 1 with Comparative Example 1 shows that when the addition amount of TiO2 exceeds 550ppm, the initial magnetic permeability and saturation magnetic flux density of the magnetic core are significantly reduced; and the loss factor is significantly increased.

[0081] Comparison of Example 1 with Comparative Example 2 shows that when the addition amounts of Co2O3 and TiO2 exceed the given range, and the amount of SiO2 exceeds the given range, the three components cannot directly or synergistically play a role in reducing hysteresis loss, and the loss factor increases significantly.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ferrite core for a radio frequency transformer, characterized in that: Including main formula and adulterant formula: The main formula has a total ratio of 100 mol%, specifically composed of 52-54 mol% of Fe2O3, 25-27 mol% of MnO and 18-20 mol% of ZnO; Based on the total weight of the main formula, the dopant formula includes Bi2O3 300-600ppm, Co2O3 400-700ppm, V2O5 200-500ppm, MoO 600-900ppm, Cr2O3 300-600ppm, SiO2 350-650ppm and TiO2 200-550ppm.

2. The ferrite core for a radio frequency transformer according to claim 1, characterized in that: The main formula consists of 53.6-54 mol% Fe2O3, 26.4-27 mol% MnO and 18.9-19.7 mol% ZnO; Relative to the total weight of the main formula, the dopant formula includes Bi2O3 500-600ppm, Co2O3 400-600ppm, V2O5 300-500ppm, MoO 700-850ppm, Cr2O3 400-500ppm, SiO2 400-600ppm and TiO2 200-500ppm.

3. The ferrite core for a radio frequency transformer according to claim 1, characterized in that: The main formula consists of 53.9 mol% Fe2O3, 26.9 mol% MnO and 19.2 mol% ZnO; Relative to the total weight of the main formula, the dopant formula includes Bi2O3 580ppm, Co2O3 550ppm, V2O5 370ppm, MoO750ppm, Cr2O3 450ppm, SiO2 600ppm and TiO2500ppm.

4. A method for preparing a ferrite core for a radio frequency transformer according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Primary ball milling: weigh the main formula ingredients, add deionized water, and grind and mix thoroughly to obtain the main formula mixture; S2, pre-burning: After drying the main formula mixture, place it at 880-950℃ for 2-4h, cool it with the furnace, and obtain the pre-burned material; S3, secondary ball milling and granulation: adding dopant formula components and deionized water to the pre-burned material, grinding to obtain slurry, drying the slurry and then granulating to obtain material powder; S4, molding and sintering: the granulated powder is pressed into a green body, and then sintered to obtain a manganese-zinc ferrite core.

5. The preparation method according to claim 4, characterized in that: In S4, the sintering process specifically includes a temperature rising stage, a temperature holding stage and a temperature falling stage; The control program of the temperature rising section is: the oxygen content in the protective atmosphere is 21%, and the temperature rises to 1050℃; The control program of the insulation section is: The first stage: the temperature is increased from 1050°C to 1380°C at 1.3-2.7°C / min, wherein the oxygen content in the protective atmosphere during the period from 1050°C to 1300°C is 21%, and the oxygen content in the protective atmosphere during the period from 1300°C to 1380°C is 1%; The second stage: at 1380°C, the oxygen content in the protective atmosphere is 21% and maintained for 300 minutes, then the oxygen content is adjusted to 5% and maintained for 30 minutes; The third stage: the temperature drops from 1380℃ to 1000℃ at a rate of 2.9-4℃ / min, and the corresponding oxygen content gradually drops to 0; The control program of the cooling stage is: cooling from 1000°C to room temperature at 1-3.5°C / min in a nitrogen atmosphere.

6. The preparation method according to claim 5, characterized in that: In S4, in the first stage of the control program of the insulation stage, the corresponding heating rate from 1050℃ to 1300℃ is 1.3-1.32℃ / min; the corresponding heating rate from 1300℃ to 1380℃ is 2.5-2.67℃ / min; In the third stage, the temperature drops from 1380℃ to 1300℃, and the corresponding cooling rate is 2.96-3℃ / min; the temperature drops from 1300℃ to 1000℃, and the corresponding cooling rate is 3.33-3.85℃ / min.

7. The preparation method according to claim 4, characterized in that: In S4, ZnO powder is added to the sintering environment, and 0.4-0.5 g of ZnO powder is added per kilogram of green body.

8. The preparation method according to claim 4, characterized in that: In S4, the green body is in any one of a ring shape, a single-hole shape, a double-hole shape, and a four-hole shape.

9. The preparation method according to claim 5, characterized in that: The process also includes S5, insulating coating, depositing a polyparaxylene film layer on the surface of the green body, with a film layer thickness of 19-21 μm.

10. A radio frequency transformer, characterized in that: It comprises a ferrite core as described in any one of claims 1 to 3 or a ferrite core prepared by the preparation method as described in any one of claims 4 to 9 and a core wire wound on the ferrite core, wherein the core wire is a Φ0.1 mm enameled copper wire.

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