Flexible thick film magnetic core material for high frequency current sensor for power cable condition monitoring and preparation method thereof

Abstract

This invention relates to the field of thick and thin film materials for electronic components, specifically to a flexible thick and thin film magnetic core material for high-frequency current sensors used in power cable condition monitoring and its preparation method. The method involves preparing a main component target material using NiO, CuO, ZnO, and Fe2O3 powders as raw materials; and an auxiliary component target material using SiO2, La2O3, CaCO3, and BaTiO3 powders as raw materials. Combined with deposition process control and high-temperature sintering, a soft magnetic ferrite is prepared. A polyimide film is used as a flexible substrate material, and the soft magnetic ferrite material is completely adhered to the flexible substrate material to obtain the flexible thick and thin film magnetic core material. This material exhibits high permeability and low loss, which can significantly improve the detection level of power cables and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the technical field of thick and thin film materials for electronic components, specifically relating to flexible thick and thin film magnetic core materials for high-frequency current sensors used in power cable condition monitoring and their preparation methods. Background Technology

[0002] Partial discharge is a common phenomenon in power cables. If it persists for a long time, it can damage the insulation layer on the cable surface, leading to a decline in insulation performance. In severe cases, it may cause complete insulation breakdown or even explosion, endangering the safe and stable operation of the power grid. Therefore, partial discharge is considered an important indicator of insulation degradation in power cables. The high-frequency current method, as the main detection method for partial discharge, has online monitoring and defect location capabilities and has become one of the most widely used detection methods.

[0003] However, the core material of traditional high-frequency current sensors is usually a rigid ferrite core, which has obvious limitations: on the one hand, although the core material has high sensitivity at high frequencies, it has a narrow bandwidth and high loss, which affects the detection performance; on the other hand, the rigid structure of the sensor requires a large installation space and a direct grounding lead, which limits its application in narrow areas or special equipment. Especially for cable joints with complex structures, traditional rigid high-frequency sensors are difficult to fit into curved surfaces, resulting in low signal coupling efficiency and decreased sensitivity; in scenarios where the sensor needs to be built-in, its size and rigidity also pose significant constraints.

[0004] Flexible high-frequency sensors fabricated using flexible thick-film materials can better adapt to curved surfaces, improve signal coupling, and enhance monitoring capabilities. Existing flexible sensors mostly employ nanocrystalline or magnetic rubber cores, but these still suffer from shortcomings in high-frequency characteristics, temperature stability, and cost. Soft magnetic ferrites offer advantages such as low high-frequency loss, high permeability, and low cost, but their inherent brittleness and difficulty in bending limit their application in flexible sensing.

[0005] Therefore, developing a high-frequency sensing material based on flexible thick-film soft magnetic ferrite, which combines excellent high-frequency performance and flexibility, is of great value for improving the accuracy and applicability of partial discharge monitoring in power cables. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring and a method for preparing the same. By improving the bandwidth and permeability of the flexible thick-film magnetic core material and reducing losses, the invention aims to meet the high-performance requirements of power cable condition monitoring for flexible high-frequency current sensors.

[0007] The technical solution of this invention is: a method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring, comprising:

[0008] The main component target material was prepared using NiO, CuO, ZnO and Fe2O3 powders as raw materials;

[0009] Auxiliary target materials were prepared using SiO2, La2O3, CaCO3 and BaTiO3 powders as raw materials;

[0010] Using pretreated silicon steel sheets as substrates; placing the main component target, auxiliary component target and substrate in the reaction chamber of a vapor deposition device to perform a physical vapor deposition reaction, and finally obtaining a deposition mixture on the surface of the substrate;

[0011] The deposition mixture was sintered and held at a temperature under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a thin film soft magnetic ferrite material.

[0012] Using a polyimide film as a flexible substrate material, the thin-film soft magnetic ferrite material is completely adhered to the flexible substrate material to finally obtain the flexible thick film magnetic core material.

[0013] Preferably, the contents of each raw material used to prepare the main component target material are as follows, based on mass percentage: NiO 8.5%, CuO 4.8%, ZnO 32.5%, and Fe2O3 54.2%;

[0014] The contents of each raw material used to prepare the auxiliary component target material are as follows, based on mass percentage: SiO2 55.5%, La2O3 18.5%, CaCO3 15.5%, and BaTiO3 10.5%;

[0015] Preferably, the preparation of the main component target material using NiO, CuO, ZnO, and Fe2O3 powders as raw materials includes the following:

[0016] The main component powder raw materials NiO, CuO, ZnO and Fe2O3 were mixed with deionized water to obtain the initial mixture A;

[0017] Mixture A is ball-milled to obtain mixture B, and then mixture B is filtered to obtain mixture C.

[0018] Mixture C with polyvinyl alcohol, and then press it into shape to obtain blank D;

[0019] The blank D is placed in a high-temperature sintering furnace and calcined under a nitrogen atmosphere. After natural cooling to room temperature, the desired main component target material can be obtained.

[0020] Preferably, the preparation of the auxiliary component target material using SiO2, La2O3, CaCO3, and BaTiO3 powders as raw materials includes:

[0021] 1) The auxiliary component powder raw materials SiO2, La2O3, CaCO3 and BaTiO3 are thoroughly mixed to obtain mixture E;

[0022] 2) Place the mixture E in a silica crucible, then place it in a high-temperature sintering furnace and calcine it under a nitrogen atmosphere. After calcination, allow it to cool naturally to room temperature to obtain the auxiliary component target material.

[0023] Preferably, the main component powder raw material is mixed with deionized water at a mass ratio of 1:4, and the mixture C is mixed with polyvinyl alcohol at a mass ratio of 4:1.

[0024] Preferably, the pretreatment method for the silicon steel sheet includes:

[0025] The surface of the silicon steel sheet is roughened by mechanical sandblasting: alumina particles are used to blast the surface of the substrate.

[0026] The silicon steel sheet is immersed in an acidic solution, which is a mixture of nitric acid and deionized water in a volume ratio of 1:3.

[0027] Preferably, the main component target, auxiliary component target, and substrate are placed in the reaction chamber of the physical vapor deposition apparatus to perform the physical vapor deposition reaction:

[0028] Adjust the initial vacuum level in the reaction chamber of the physical vapor deposition apparatus to 1×10⁻⁶. -3 ~5×10 -3 Pa, then inert argon gas is introduced as a protective gas, with an argon gas flow rate of 50~200 sccm;

[0029] Adjust the temperature inside the reaction chamber to 200~300℃ and maintain it for 30~60 minutes to preheat the target and substrate.

[0030] Adjust the power of the main component target to 250W~400W, adjust the power of the auxiliary component target to 100~250W, adjust the substrate bias voltage to -50~-70V, and control the deposition time to 120~240 minutes to obtain a deposition mixture on the substrate surface.

[0031] Preferably, the step of sintering and holding the deposited mixture under a nitrogen atmosphere includes: placing the obtained deposited mixture in a high-temperature sintering furnace and sintering it under a nitrogen atmosphere, with a sintering temperature of 950~1100℃, a heating rate of 3~5℃ / min, and a holding time of 3-5 hours.

[0032] Preferably, the step of using a polyimide film as a flexible substrate material and completely adhering the film soft magnetic ferrite material to the flexible substrate material includes:

[0033] An epoxy resin adhesive is evenly applied to the surface of the thin film soft magnetic ferrite material to form an epoxy resin adhesive layer.

[0034] Then, the polyimide film is bonded to the epoxy resin adhesive layer;

[0035] Repeated rolling with a three-roll mill until the thin film soft magnetic ferrite material is uniformly broken and completely separated from the silicon steel sheet, so that the separated and uniformly broken thin film ferrite material is completely adhered to the flexible substrate, and finally a flexible thick film soft magnetic ferrite material can be obtained.

[0036] Furthermore, the present invention also provides a flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring prepared by the above-described method, comprising: a flexible substrate layer and a thin-film soft magnetic ferrite layer thereon.

[0037] This invention provides a flexible thick-film magnetic core material for high-frequency current sensors used in power cable condition monitoring and its preparation method. This method pre-prepares a main component target and an auxiliary component target with uniform composition and high density, providing raw materials for subsequent preparation of high-performance soft magnetic ferrite materials via physical deposition. Experimental results show that the thin-film soft magnetic ferrite prepared using this method possesses good magnetic properties, specifically including high permeability and quality factor, low coercivity and loss, and good transmission impedance over a wide frequency band, meeting the requirements for high-performance soft magnetic ferrite materials in power cable insulation condition monitoring.

[0038] Furthermore, the flexible thick-film magnetic core material provided by this invention can closely fit the curved surface of the cable joint as a sensing material, improving detection sensitivity and adapting to diverse installation environments. It provides more reliable technical support for insulation condition assessment, which is of great significance for ensuring the safe operation of the power grid and improving power supply reliability. Attached Figure Description

[0039] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A flowchart illustrating a flexible thick-film magnetic core material for a high-frequency current sensor for power cable condition monitoring, provided in an embodiment of the present invention.

[0042] Figure 2This is a schematic diagram of the physical vapor deposition equipment used in an embodiment of the present invention;

[0043] Figure 3 These are microstructure characterization diagrams of the thin-film soft magnetic ferrite materials obtained in Examples 1-3 of the present invention;

[0044] Figure 4 This is a schematic diagram showing the magnetic permeability curves of the flexible thick-film soft magnetic ferrite materials obtained in Examples 1-3 of the present invention;

[0045] Figure 5 This is a schematic diagram showing the quality factor results of the flexible thick-film soft magnetic ferrite materials obtained in Examples 1-3 of the present invention;

[0046] Figure 6 This is a schematic diagram showing the transmission impedance results of the flexible thick-film soft magnetic ferrite material obtained in Examples 1-3 of the present invention;

[0047] Figure 7 This is a schematic diagram showing the power loss results of the flexible thick-film soft magnetic ferrite material obtained in Examples 1-3 of the present invention;

[0048] Figure 8 The images are scanning electron microscope images of the thin film soft magnetic ferrite material prepared in this invention; (a) no CaCO3 was added as an auxiliary component, (b) CaCO3 was added in excess (17.0% > 15.5%), (c) the amount of CaCO3 added was insufficient (14.0% < 15.5%), and (d) CaCO3 was added in appropriate amount (15.5%). Detailed Implementation

[0049] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of systems consistent with some aspects of the invention as detailed in the appended claims.

[0050] To achieve both excellent high-frequency performance and flexibility in flexible thick-film soft magnetic ferrites, thereby improving the accuracy and applicability of partial discharge monitoring in power cables, this invention provides a method for preparing flexible thick-film magnetic core materials for high-frequency current sensors used in power cable condition monitoring. Figure 1 As shown, it includes:

[0051] Step 1: Prepare the main component target material using NiO, CuO, ZnO and Fe2O3 powders as raw materials;

[0052] The aforementioned NiO (8.5%), CuO (4.8%), ZnO (32.5%), and Fe2O3 (54.2%) powders are commonly referred to as NiCuZn ferrite. NiCuZn ferrite is an important type of soft magnetic ferrite formed by introducing CuO into NiZn ferrite. The introduction of Cu ions causes lattice distortion and changes in ion occupancy within the NiCuZn ferrite, leading to alterations in its initial permeability Ui and saturation magnetic induction Bs. Furthermore, compared to standard NiZn ferrite materials, NiCuZn ferrite materials have lower sintering temperatures and lower costs. Therefore, to meet the high requirements of power cables for ferrite magnetic properties, this invention selects this precise formulation as the main component target material formulation.

[0053] Preferably, the preparation of the main component target material includes the following steps: 1) mixing the main component powder raw materials NiO (8.5%), CuO (4.8%), ZnO (32.5%) and Fe2O3 (54.2%) with deionized water to obtain an initial mixture A, wherein the mass ratio of the main component powder raw materials to deionized water is 1:4;

[0054] 2) The mixture A was ball-milled at a speed of 650 r / min for 4 h to obtain mixture B. Then, mixture B was filtered to obtain mixture C.

[0055] 3) Mix C with polyvinyl alcohol at a mass ratio of 4:1, and then press it into shape. The molding pressure is 150MPa and the time is 15s to obtain a blank D with dimensions of 50mm×200mm×30mm.

[0056] 4) Place the blank D in a high-temperature sintering furnace and calcine it under a nitrogen atmosphere. The calcination temperature is 600℃ and the time is 3h. After natural cooling to room temperature, the main component target material can be obtained.

[0057] Step 2: Prepare auxiliary target material using SiO2, La2O3, CaCO3 and BaTiO3 powders as raw materials;

[0058] In the auxiliary component formulation, SiO2 has a high resistivity but also a high melting point (1400℃). When used alone as an additive, it is difficult to melt and diffuse to the NiCuZn ferrite grain boundaries at sintering temperatures of 900-1100℃, thus having no positive effect when used alone. La2O3, on the other hand, has a lower melting point. When mixed with SiO2, the overall mixture has a lower melting point, allowing it to melt fully at the subsequent sintering temperature of 900-1100℃, which helps to lower the sintering temperature and increase the density of the ferrite. Simultaneously, it can reduce the amount of low-melting-point oxides used and lower costs. Furthermore, during the sintering process, CaCO3 in the formulation decomposes below 1100℃ to release CO2 gas. This CO2 gas acts as a transport medium during flow, promoting the movement of the high-melting-point additive. Simultaneously, CaO, formed from the thermal decomposition of CaCO3, is also a high-melting-point substance and can accumulate at the grain boundaries during sintering, thus increasing the resistivity of the ferrite. This invention utilizes the gas generated during sintering to promote the movement of high-melting-point additives, resulting in a more uniform distribution. This is more conducive to improving the density and resistivity of ferrite, giving it better magnetic properties. BaTiO3 is also a high-resistivity, high-melting-point material, and choosing it as an additive can further improve the resistivity of ferrite and enhance its magnetic properties.

[0059] The raw materials for preparing the auxiliary target material, by mass percentage, are as follows: SiO2 55.5%, La2O3 18.5%, CaCO3 15.5%, and BaTiO3 10.5%. At this ratio, the mixture of SiO2 and La2O3 softens and maintains sufficient fluidity at 600℃, while also preventing premature decomposition of CaCO3 during the preparation of the auxiliary target material. Furthermore, the 15.5% addition of CaCO3 ensures sufficient gas production, providing a positive effect. Exceeding this ratio would lead to excessive porosity in the ferrite during sintering, negatively impacting its performance. The balance is BaTiO3, which has a high melting point and high resistivity, and can accumulate at grain boundaries, improving magnetic properties.

[0060] Preferably, the preparation of the auxiliary component target material includes the following steps: 1) fully mixing the auxiliary component powder raw materials SiO2 (55.5%), La2O3 (18.5%), CaCO3 (15.5%) and BaTiO3 (10.5%) to obtain mixture E;

[0061] 2) Place the mixture E in a silica crucible with dimensions of 50mm×200mm×30mm, and then place it in a high-temperature sintering furnace for calcination under a nitrogen atmosphere. The calcination temperature is 600℃ and the time is 3h. After natural cooling to room temperature, the desired auxiliary component target material can be obtained.

[0062] Step 3: Using the pretreated silicon steel sheet as the substrate; preferably, the substrate pretreatment includes surface roughening and physical cleaning:

[0063] 1) The surface roughening treatment adopts mechanical sandblasting method, using alumina particles with a particle size of 100 μm to spray the substrate surface, the spraying angle is 60°, and the spraying time is 15 minutes;

[0064] 2) Physical cleaning involves soaking in an acidic solution, which is a mixture of nitric acid and deionized water in a volume ratio of 1:3, for 20 minutes.

[0065] Under these process conditions, the substrate surface can achieve a relatively ideal roughness of approximately 5 μm, which improves the bonding strength between the prepared film and the substrate. The ratio of nitric acid to deionized water is 1:3. If the nitric acid concentration is too high, a violent reaction will occur upon contact with the silicon steel sheet, easily leading to substrate corrosion and increasing the risk during operation. If the concentration is below this level, a passivation reaction will occur on the surface of the silicon steel sheet, affecting the cleaning purpose and efficiency. Therefore, selecting this concentration ratio and soaking time allows for better cleaning of the silicon steel sheet.

[0066] The main component target, auxiliary component target and substrate are placed in the reaction chamber of a physical vapor deposition device to carry out a physical vapor deposition reaction, and finally a deposition mixture is obtained on the surface of the substrate.

[0067] The bonding force between the soft magnetic ferrite and the substrate was significantly improved by roughening the substrate surface and physical cleaning.

[0068] Preferably, the preparation of the deposition mixture on the substrate surface includes:

[0069] 1) Place the prepared main component target, auxiliary component target and pretreated substrate into the reaction chamber, adjust the initial vacuum in the reaction chamber, and then introduce inert argon gas as a protective gas.

[0070] 2) Adjust and maintain the temperature inside the reaction chamber to preheat the target and substrate;

[0071] 3) Adjust the power of the main component target and the auxiliary component target to obtain a deposition mixture on the substrate surface;

[0072] Further optimization includes the following parameters during deposition: adjusting the initial vacuum level in the reaction chamber to 1×10⁻⁶. -3 ~5×10 -3 Pa, then inert argon gas is introduced as a protective gas, with an argon gas flow rate of 50~200 sccm.

[0073] Adjust the temperature inside the reaction chamber to 200~300℃ and maintain it for 30~60 minutes to preheat the target and substrate.

[0074] The power of the main component target is adjusted to 250W~400W, and the power of the auxiliary component target is adjusted to 100~250W. The deposition time is 120~240 minutes, and the substrate bias voltage is -50~-70V during physical deposition. These parameters ensure that argon ions bombard the target material in a sufficient quantity. Furthermore, by adjusting the power, the number of atoms or molecules ejected can be controlled, further controlling the composition of the deposit. The deposition time can control the deposit thickness, thus preparing ferrites with different properties.

[0075] This invention ensures the rational distribution and precise adjustment of the constituent elements of soft magnetic ferrite materials by precisely controlling temperature, pressure and target power, thereby endowing soft magnetic ferrite materials with excellent performance.

[0076] like Figure 2 As shown, the target sputters particles with nanoscale size through argon ion bombardment by physical vapor deposition. The impacted nanoparticles have high surface energy and mainly grow in an island-like manner on the substrate. Since the surface energy of the substrate is lower than that of the nanoparticles, the impacted nanoparticles will preferentially move into the void regions of the substrate. This results in a denser film, reduced porosity, and nanoscale uniform mixing, providing a foundation for the subsequent ferrite sintering process.

[0077] After the physical vapor deposition (PVD) step, the prepared deposit undergoes sintering. Under the selected formulation and PVD process, nanoscale uniform mixing is achieved. During sintering, in the initial stage, the size effect of nanoparticles leads to the formation of more grain boundaries, which reduces the grain boundary dislocation density of the ferrite. As the sintering process continues, the mixture of SiO2 and La2O3 from the auxiliary target material gradually melts in large quantities to form a fluid. This fluid also drives the movement of the nanoscale main components NiO, CuO, ZnO, and Fe2O3, as well as the high-melting-point CaO produced by the high-melting-point decomposition of the nanoscale auxiliary components high-melting-point BaTiO3 and CaCO3. At the same time, CaCO3 decomposes at high temperature to release sufficient gas, which also promotes fluid movement.

[0078] Because the aforementioned nano-sized particles have high specific surface area and surface energy, they are more likely to adsorb and aggregate, forming dense and large grains. Therefore, the ferrite prepared by the method of this invention has the advantages of being dense, having uniform grain boundary size, and large grain size, resulting in better magnetic properties. Traditional secondary sintering methods mainly rely on the fluid formed by the melting of low-melting-point substances to drive the flow of main components and additives. Due to their large size, these components are difficult to aggregate and form large grains, resulting in more voids, smaller and non-uniform grain size, and poorer magnetic properties. By combining the main component and auxiliary component formulations provided in this invention with physical vapor deposition and high-temperature sintering processes, a dense ferrite with uniform grain boundary size and large grain size is prepared, significantly improving the magnetic properties of the ferrite material.

[0079] Step 4: The deposition mixture is sintered and kept at a constant temperature under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a thin film soft magnetic ferrite material;

[0080] Preferably, the sintering process is carried out under a nitrogen atmosphere, with a sintering temperature of 950~1100℃, a sintering heating rate of 3-5℃ / min, and a holding time of 3-5 hours.

[0081] Step 5: Using polyimide film as a flexible substrate material, the thin film soft magnetic ferrite material is completely adhered to the flexible substrate material to finally obtain the flexible thick film magnetic core material.

[0082] Specifically, an epoxy resin adhesive is evenly applied to the surface of the thin-film soft magnetic ferrite material, and then a polyimide film is adhered to the surface as a flexible substrate material, forming a three-layer structure of a thick and thin sheet. The bottom layer is a silicon steel sheet, the middle layer is soft magnetic ferrite, and the top layer is the adhered flexible polyimide film. The entire thick and thin sheet is placed in a three-roll mill and rolled to separate the silicon steel sheet and the soft magnetic ferrite, and to uniformly break the soft magnetic ferrite until the thin-film soft magnetic ferrite material is uniformly broken and completely separated from the silicon steel sheet. At this point, the separated and uniformly broken thin-film ferrite material is completely adhered to the flexible substrate, thus obtaining the thick-film soft magnetic ferrite material. Because there is an epoxy resin adhesive between the soft magnetic ferrite and the polyimide film, the soft magnetic ferrite and the polyimide film will not separate.

[0083] The soft magnetic ferrite prepared in step four is a brittle material and lacks flexibility. By introducing a polyimide film as a flexible substrate in step five, and then adhering the brittle, thick-film soft magnetic ferrite material prepared in step four to the flexible polyimide substrate followed by crushing, a flexible, thick-film soft magnetic ferrite material can be obtained. In other words, by adhering a flexible polyimide substrate and further crushing it, the brittle film ferrite material is transformed into a flexible, thick-film ferrite material.

[0084] To enable those skilled in the art to fully understand and implement the present invention, the following supplementary description of specific embodiments of the present invention is provided in conjunction with a specific application scenario.

[0085] Example 1

[0086] Preparation of main component target material: ① The main component powder raw materials NiO (8.5%), CuO (4.8%), ZnO (32.5%) and Fe2O3 (54.2%) are mixed with deionized water to obtain initial mixture A. The mass ratio of main component powder raw materials to deionized water is 1:4. ② Mixture A is ball-milled at a speed of 650 r / min for 4 h to obtain mixture B. Mixture B is then filtered to obtain mixture C. ③ Mixture C is mixed with polyvinyl alcohol at a mass ratio of 4:1 and then pressed into shape at a pressure of 150 MPa for 15 s to obtain blank D with dimensions of 50 mm × 200 mm × 30 mm. ④ Blank D is placed in a high-temperature sintering furnace and calcined under a nitrogen atmosphere at a temperature of 600 °C for 3 h. After natural cooling to room temperature, the desired main component target material is obtained.

[0087] Preparation of auxiliary component target material: ① The auxiliary component powder raw materials SiO2 (55.5%), La2O3 (18.5%), CaCO3 (15.5%) and BaTiO3 (10.5%) are thoroughly mixed to obtain mixture E. ② Mixture E is placed in a silica crucible with dimensions of 50mm×200mm×30mm, and then placed in a high-temperature sintering furnace for calcination under nitrogen atmosphere protection at a temperature of 1400℃ for 3 hours. After natural cooling to room temperature, the desired auxiliary component target material is obtained.

[0088] Next, the silicon steel sheet substrate needs to be surface treated. The specific methods are as follows: ① Surface roughening treatment adopts mechanical sandblasting method, using alumina particles with a particle size of 100 μm to spray the substrate surface, the spraying angle is 60°, and the spraying time is 15 minutes. ② Physical cleaning adopts acid solution immersion, the acid solution is a mixture of nitric acid and deionized water with a volume ratio of 1:3, and the immersion time is 20 minutes.

[0089] The prepared primary target, secondary target, and pretreated substrate are placed in the reaction chamber of the physical vapor deposition (PVD) apparatus. The primary target, secondary target, and substrate are secured using the existing fixtures of the PVD apparatus. After fixation, the initial vacuum level in the reaction chamber is adjusted to 3 × 10⁻³ Pa. Then, inert argon gas is introduced as a protective gas at a flow rate of 150 sccm to remove residual air from the reaction chamber, ensuring a pure environment and preventing interference from impurities in the subsequent deposition process.

[0090] After preparing the reaction chamber, the temperature inside the chamber was adjusted to 250°C and maintained for 40 minutes to preheat the target and substrate. After preheating, the power of the main component target was adjusted to 300W, the power of the auxiliary component target to 120W, the substrate bias voltage was adjusted to -50V, and the deposition time was controlled to 180 minutes to obtain a deposition mixture on the substrate surface. Finally, the obtained deposition mixture was placed in a high-temperature sintering furnace and sintered under a nitrogen atmosphere at 980°C, a heating rate of 3°C / min, and a holding time of 4 hours to obtain a thin-film soft magnetic ferrite material.

[0091] Apply epoxy resin adhesive evenly to the surface of the thin film soft magnetic ferrite material, then attach a polyimide film to the surface as a flexible substrate material. Use a three-roll mill to repeatedly roll the film until it is uniformly broken and completely separated from the silicon steel sheet. At this point, the separated and uniformly broken film ferrite material is completely adhered to the flexible substrate, thus obtaining a flexible thick film soft magnetic ferrite material.

[0092] Example 2

[0093] Preparation of main component target material: ① The main component powder raw materials NiO (8.5%), CuO (4.8%), ZnO (32.5%) and Fe2O3 (54.2%) are mixed with deionized water to obtain initial mixture A. The mass ratio of main component powder raw materials to deionized water is 1:4. ② Mixture A is ball-milled at a speed of 650 r / min for 4 h to obtain mixture B. Mixture B is then filtered to obtain mixture C. ③ Mixture C is mixed with polyvinyl alcohol at a mass ratio of 4:1 and then pressed into shape at a pressure of 150 MPa for 15 s to obtain blank D with dimensions of 50 mm × 200 mm × 30 mm. ④ Blank D is placed in a high-temperature sintering furnace and calcined under a nitrogen atmosphere at a temperature of 600 °C for 3 h. After natural cooling to room temperature, the desired main component target material is obtained.

[0094] Preparation of auxiliary component target material: ① The auxiliary component powder raw materials SiO2 (55.5%), La2O3 (18.5%), CaCO3 (15.5%) and BaTiO3 (10.5%) are thoroughly mixed to obtain mixture E. ② Mixture E is placed in a silica crucible with dimensions of 50mm×200mm×30mm, and then placed in a high-temperature sintering furnace for calcination under nitrogen atmosphere protection at a temperature of 1400℃ for 3 hours. After natural cooling to room temperature, the desired auxiliary component target material is obtained.

[0095] Next, the silicon steel sheet substrate needs to be surface treated. The specific methods are as follows: ① Surface roughening treatment adopts mechanical sandblasting method, using alumina particles with a particle size of 100 μm to spray the substrate surface, the spraying angle is 60°, and the spraying time is 15 minutes. ② Physical cleaning adopts acid solution immersion, the acid solution is a mixture of nitric acid and deionized water with a volume ratio of 1:3, and the immersion time is 20 minutes.

[0096] The prepared primary target, secondary target, and pretreated substrate are placed in the reaction chamber of the physical vapor deposition (PVD) apparatus. The primary target, secondary target, and substrate are secured using the existing fixtures of the PVD apparatus. After fixation, the initial vacuum level in the reaction chamber is adjusted to 2.5 × 10⁻³ Pa, and then inert argon gas is introduced as a protective gas at a flow rate of 180 sccm to remove residual air from the reaction chamber.

[0097] After preparing the reaction chamber, the temperature inside the chamber was adjusted to 280℃ and maintained for 35 minutes to preheat the target and substrate. After preheating, the power of the main component target was adjusted to 350W, the power of the auxiliary component target to 100W, the substrate bias voltage was adjusted to -60V, and the deposition time was controlled at 150 minutes to obtain a deposition mixture on the substrate surface. Finally, the obtained deposition mixture was placed in a high-temperature sintering furnace and sintered under a nitrogen atmosphere at a temperature of 1000℃, a heating rate of 4℃ / min, and a holding time of 3.5 hours to obtain a thin-film soft magnetic ferrite material.

[0098] Apply epoxy resin adhesive evenly to the surface of the thin film soft magnetic ferrite material, then attach a polyimide film to the surface as a flexible substrate material. Use a three-roll mill to repeatedly roll the film until it is uniformly broken and completely separated from the silicon steel sheet. At this point, the separated and uniformly broken film ferrite material is completely adhered to the flexible substrate, thus obtaining a flexible thick film soft magnetic ferrite material.

[0099] Example 3

[0100] Preparation of main component target material: ① The main component powder raw materials NiO (8.5%), CuO (4.8%), ZnO (32.5%) and Fe2O3 (54.2%) are mixed with deionized water to obtain initial mixture A. The mass ratio of main component powder raw materials to deionized water is 1:4. ② Mixture A is ball-milled at a speed of 650 r / min for 4 h to obtain mixture B. Mixture B is then filtered to obtain mixture C. ③ Mixture C is mixed with polyvinyl alcohol at a mass ratio of 4:1 and then pressed into shape at a pressure of 150 MPa for 15 s to obtain blank D with dimensions of 50 mm × 200 mm × 30 mm. ④ Blank D is placed in a high-temperature sintering furnace and calcined under a nitrogen atmosphere at a temperature of 600 °C for 3 h. After natural cooling to room temperature, the desired main component target material is obtained.

[0101] Preparation of auxiliary component target material: ① The auxiliary component powder raw materials SiO2 (55.5%), La2O3 (18.5%), CaCO3 (15.5%) and BaTiO3 (10.5%) are thoroughly mixed to obtain mixture E. ② Mixture E is placed in a silica crucible with dimensions of 50mm×200mm×30mm, and then placed in a high-temperature sintering furnace for calcination under nitrogen atmosphere protection at a temperature of 1400℃ for 3 hours. After natural cooling to room temperature, the desired auxiliary component target material is obtained.

[0102] Next, the silicon steel sheet substrate needs to be surface treated. The specific methods are as follows: ① Surface roughening treatment adopts mechanical sandblasting method, using alumina particles with a particle size of 100 μm to spray the substrate surface, the spraying angle is 60°, and the spraying time is 15 minutes. ② Physical cleaning adopts acid solution immersion, the acid solution is a mixture of nitric acid and deionized water with a volume ratio of 1:3, and the immersion time is 20 minutes.

[0103] The prepared primary target, secondary target, and pretreated substrate are placed in the reaction chamber of the physical vapor deposition (PVD) apparatus. The primary target, secondary target, and substrate are secured using the existing fixtures of the PVD apparatus. After fixation, the initial vacuum level in the reaction chamber is adjusted to 5 × 10⁻³ Pa, and then inert argon gas is introduced as a protective gas at a flow rate of 80 sccm to remove residual air from the reaction chamber.

[0104] After preparing the reaction chamber, the temperature inside the chamber was adjusted to 200°C and maintained for 60 minutes to preheat the target and substrate. After preheating, the power of the main component target was adjusted to 380W, the power of the auxiliary component target to 220W, the substrate bias voltage was adjusted to -70V, and the deposition time was controlled to 120 minutes to obtain a deposition mixture on the substrate surface. Finally, the obtained deposition mixture was placed in a high-temperature sintering furnace and sintered under a nitrogen atmosphere at a temperature of 1050°C, a heating rate of 5°C / min, and a holding time of 3 hours to obtain the desired thin-film soft magnetic ferrite material.

[0105] Apply epoxy resin adhesive evenly to the surface of the thin film soft magnetic ferrite material, then attach a polyimide film to the surface as a flexible substrate material. Use a three-roll mill to repeatedly roll the film until it is uniformly broken and completely separated from the silicon steel sheet. At this point, the separated and uniformly broken film ferrite material is completely adhered to the flexible substrate, thus obtaining a flexible thick film soft magnetic ferrite material.

[0106] For Examples 1-3, the saturation magnetic flux density and quality factor of Examples 1-3 were tested using an Agilent Technologies E4991B RF impedance meter. The results are as follows: Figure 4 , 5 As shown. The coercivity and power loss of Examples 1-3 were tested using a BH instrument (model SY8232) manufactured by Iwata Corporation. The results are as follows. Figure 7 As shown. According to the State Grid Corporation of China enterprise standard "Q / GDW 11304.5—2015"—Technical Specifications for High-Frequency Partial Discharge Charge Detection Instruments, the transmission impedance of Examples 1-3 was tested, as follows. Figure 6 As shown.

[0107] Specifically, such as Figure 3 The microstructure characterization of the thin-film soft magnetic ferrite materials prepared in Examples 1-3 is shown. It can be seen that the materials prepared in the three examples all have clear grain boundaries, fewer pores, dense structure, large grain size and relatively uniform distribution. The above properties are all beneficial to improving the magnetic properties of the magnetic core and reducing losses.

[0108] With the main component target material composition and the entire preparation method remaining unchanged, a comparison was made between the presence and absence of CaCO3 in the auxiliary component target material formulation, such as... Figure 8As shown, (a) a thin-film soft magnetic ferrite material sample prepared without the addition of CaCO3 as an auxiliary component, (b) with excessive CaCO3 addition (17.0% > 15.5%), (c) with insufficient CaCO3 addition (14.0% < 15.5%), and (d) with appropriate CaCO3 addition (15.5%). It can be seen that when no CaCO3 is added, the prepared sample has very poor fluidity, making it difficult to form grain boundaries. When CaCO3 is added in excess, the sample can form grain boundaries, but due to the excessive CO2 gas generated by decomposition, more pores appear at the grain boundaries, which will reduce the magnetic properties of the material and increase losses. When the amount of CaCO3 added is insufficient, although it can promote the flow of particle components during sintering, the insufficient fluidity results in relatively blurred grain boundaries and extremely uneven distribution of grain boundary size. When the amount of CaCO3 added according to the present invention is used, it can be seen that the prepared sample has clear grain boundaries and relatively uniform size, and the sample can obtain better magnetic properties and lower losses.

[0109] Comparative Example 1

[0110] Comparative NiCuZn ferrite material was prepared using a classic solid-state reaction method, with the following proportions: CuO 5.3 mol%, NiO 13.4 mol%, ZnO 32.3 mol%, and Fe2O3 49.0 mol%. The mixture and a certain amount of deionized water were added to a ball mill and ball-milled for approximately 2 hours, followed by pre-calcination at 850°C for 12 hours. The pre-calcined mixture was cooled, and 0.50 wt% Bi2O3 and 0.3 wt% V2O5 were added. The mixture was then ball-milled a second time for approximately 2 hours. After drying, 10 wt% polyvinyl alcohol (PVA) was added for granulation, and the granules were pressed at 6 MPa for 15 seconds to obtain green bodies. Finally, the green bodies were sintered at 1000°C for approximately 4 hours and cooled in the furnace to obtain Comparative Example 1.

[0111] Comparative Example 2

[0112] Comparative NiCuZn ferrite material was prepared using a classic solid-state reaction method, with the following proportions: CuO 4.8 mol%, NiO 15.7 mol%, ZnO 27.1 mol%, and Fe2O3 52.4 mol%. The mixture and a certain amount of deionized water were added to a ball mill and ball-milled for approximately 2 hours, followed by pre-calcination at 900°C for 12 hours. The pre-calcined mixture was cooled, and 0.30 wt% Co2O3 and 0.2 wt% Nb2O5 were added. The mixture was then ball-milled a second time for approximately 2 hours. After drying, 10 wt% polyvinyl alcohol (PVA) was added for granulation, and the granules were pressed at 6 MPa for 15 seconds to obtain green bodies. Finally, the green bodies were sintered at 1000°C for approximately 4 hours and cooled in the furnace to obtain Comparative Example 2.

[0113] like Figure 4 The diagram shows a comparison of the permeability of the thin-film soft magnetic ferrite materials prepared in Examples 1-3 with that of Comparative Examples 1 and 2. It can be seen that compared with Comparative Examples 1 and 2, Examples 1-3 have better initial permeability and maximum permeability. At the same time, since the frequency range of the high-frequency signals generated by power cables is mainly in the range of 0.001~0.08GHz, it can be seen that the three examples prepared have good permeability in this range, which can meet the performance requirements of power cables for high-performance magnetic cores.

[0114] like Figure 5 The figure shows a comparison of the quality factors of the thin film soft magnetic ferrite materials prepared in Examples 1-3 with those of Comparative Examples 1 and 2. It can be seen that, under the same test conditions, the quality factors of Examples 1-3 are significantly higher than those of Comparative Examples 1 and 2.

[0115] According to the State Grid Corporation of China's enterprise standard "Q / GDW 11304.5—2015"—Technical Specification for High-Frequency Partial Discharge Charge Detection Instruments, the prepared Examples 1-3 and Comparative Examples 1-2 were tested in the range of 0Hz-100MHz, and the results are shown in the figure.

[0116] like Figure 6 As shown in the figure, the results indicate that, within the 0Hz-100MHz range, the transmission impedance of the prepared Examples 1-3 is significantly higher than that of the commercially available Comparative Examples 1 and 2, far exceeding the 5mV / mA ​​specified in the State Grid Corporation of China's enterprise standard "Q / GDW 11304.5—2015". Meanwhile, commercially available similar products have transmission impedances below 5mV / mA ​​in the 20-30MHz and 90-100MHz ranges, indicating that the prepared Examples 1-3 possess better sensitivity and can meet the accurate detection requirements of high-frequency signals from power cables.

[0117] In addition, such as Figure 7 As shown, the power loss of Examples 1-3 and Comparative Examples 1-2 at frequencies of 50 kHz, 10 MHz, 50 MHz and 100 MHz under an external magnetic field of 5 mT was also tested. It can be seen that the flexible thick film soft magnetic ferrite material prepared by the formulation and method of the present invention has lower power loss compared with Comparative Examples 1 and 2.

[0118] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these changes and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing flexible thick-film magnetic core material for high-frequency current sensors used in power cable condition monitoring, characterized in that, include: The main component target material was prepared using NiO, CuO, ZnO and Fe2O3 powders as raw materials; Auxiliary target materials were prepared using SiO2, La2O3, CaCO3 and BaTiO3 powders as raw materials; The contents of each raw material used to prepare the main component target material are as follows, based on mass percentage: NiO 8.5%, CuO 4.8%, ZnO 32.5%, and Fe2O3 54.2%; The contents of each raw material used to prepare the auxiliary component target material are as follows, based on mass percentage: SiO2 55.5%, La2O3 18.5%, CaCO3 15.5%, and BaTiO3 10.5%; Using pretreated silicon steel sheets as the substrate; The main component target, auxiliary component target and substrate are placed in the reaction chamber of a physical vapor deposition device to carry out a vapor deposition reaction and obtain a deposition mixture on the surface of the substrate. The deposition mixture was sintered and held at a temperature under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a thin film soft magnetic ferrite material. Using a polyimide film as a flexible substrate material, the thin-film soft magnetic ferrite material is completely adhered to the flexible substrate material to obtain the flexible thick-film magnetic core material, specifically including: An epoxy resin adhesive is evenly applied to the surface of the thin film soft magnetic ferrite material to form an epoxy resin adhesive layer. Then, the polyimide film is bonded to the epoxy resin adhesive layer; Repeated rolling with a three-roll mill until the thin film soft magnetic ferrite material is uniformly broken and completely separated from the silicon steel sheet, so that the separated and uniformly broken thin film ferrite material is completely adhered to the flexible substrate, and the thick film soft magnetic ferrite material can be finally obtained.

2. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 1, characterized in that, The preparation of the main component target material using NiO, CuO, ZnO, and Fe2O3 powders as raw materials includes the following: The main component powder raw materials NiO, CuO, ZnO and Fe2O3 were mixed with deionized water to obtain the initial mixture A; Mixture A is ball-milled to obtain mixture B, and then mixture B is filtered to obtain mixture C. Mixture C with polyvinyl alcohol, and then press it into shape to obtain blank D; The blank D is placed in a high-temperature sintering furnace and calcined under a nitrogen atmosphere. After natural cooling to room temperature, the desired main component target material can be obtained.

3. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 2, characterized in that, The main component powder raw material is mixed with deionized water at a mass ratio of 1:4, and the mixture C is mixed with polyvinyl alcohol at a mass ratio of 4:

1.

4. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 1, characterized in that, The preparation of auxiliary component target materials using SiO2, La2O3, CaCO3, and BaTiO3 powders as raw materials includes: The auxiliary component powder raw materials SiO2, La2O3, CaCO3 and BaTiO3 are thoroughly mixed to obtain mixture E; The mixture E is placed in a silica crucible and then placed in a high-temperature sintering furnace for calcination under a nitrogen atmosphere. After calcination, it is naturally cooled to room temperature to obtain the auxiliary component target material.

5. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 1, characterized in that, The pretreatment method for the silicon steel sheet includes: The surface of the silicon steel sheet is roughened by mechanical sandblasting: alumina particles are used to blast the surface of the substrate. The silicon steel sheet is immersed in an acidic solution, which is a mixture of nitric acid and deionized water in a volume ratio of 1:

3.

6. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 1, characterized in that, The main component target, auxiliary component target, and substrate are placed in the reaction chamber of a physical vapor deposition apparatus to perform a vapor deposition reaction. Adjust the initial vacuum level in the reaction chamber of the physical vapor deposition apparatus to 1×10⁻⁶. -3 ~5×10 -3 Pa, then inert argon gas is introduced as a protective gas, with an argon gas flow rate of 50~200 sccm; Adjust the temperature inside the reaction chamber to 200~300℃ and maintain it for 30~60 minutes to preheat the target and substrate. Adjust the power of the main component target to 250W~400W, adjust the power of the auxiliary component target to 100~250W, adjust the substrate bias voltage to -50~-70V, and control the deposition time to 120~240 minutes to obtain a deposition mixture on the substrate surface.

7. The method for preparing flexible thick-film magnetic core material for high-frequency current sensors for power cable condition monitoring according to claim 1, characterized in that, The step of sintering and holding the deposited mixture under a nitrogen atmosphere includes: placing the obtained deposited mixture in a high-temperature sintering furnace and sintering it under a nitrogen atmosphere, with a sintering temperature of 950~1100℃, a heating rate of 3~5℃ / min, and a holding time of 3-5 hours.

8. The flexible thick-film magnetic core material for high-frequency current sensors used in power cable condition monitoring, prepared by any one of the preparation methods described in claims 1-7, is characterized in that... include: Flexible substrate and thin film soft magnetic ferrite layer thereon.

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