A dual magnetic permeability composite assembled nanocrystalline magnetic core and a preparation method thereof

Abstract

This invention discloses a dual-permeability composite assembled nanocrystalline magnetic core and its fabrication method, relating to the field of nanocrystalline magnetic components technology. The core includes a casing, an isolation sheet, a low-permeability nanocrystalline core unit, and a high-permeability nanocrystalline core unit. The low-permeability and high-permeability nanocrystalline core units are compositely disposed within the same casing, with the isolation sheet disposed at their interface. The low-permeability nanocrystalline core unit is used to withstand high starting current, surge impact, or DC bias conditions, reducing the risk of core saturation; the high-permeability nanocrystalline core unit is used to improve magnetic coupling efficiency in the 1kHz–1MHz frequency band. This invention can achieve both high-current anti-saturation performance and wide-band high magnetic coupling performance without significantly increasing the core volume, and is compatible with existing PCB layouts and standardized assembly processes.

Description

Technical Field

[0001] This invention relates to the field of nanocrystalline magnetic components, specifically to a dual-permeability composite assembled nanocrystalline magnetic core and its preparation method. Background Technology

[0002] Nanocrystalline magnetic cores are core magnetic components in electromagnetic compatibility, power conversion, signal transmission, and magnetic coupling devices. Nanocrystalline materials typically possess high permeability, low loss, and excellent frequency characteristics, making them widely used in common-mode inductors, filters, transformers, magnetic coupling devices, and automotive electronic magnetic components.

[0003] Existing nanocrystalline magnetic cores typically employ a single permeability structure design, meaning that only one type of magnetic material with a specific permeability level is used within the same core. While these cores can meet the requirements of certain applications, they still exhibit significant shortcomings under complex conditions. For instance, low-permeability cores generally possess good anti-saturation capabilities and can withstand large starting currents, surge currents, or impact currents, but their magnetic coupling ability is relatively insufficient, limiting their electromagnetic interference suppression and energy conversion accuracy in the mid-to-high frequency range. High-permeability cores, while possessing higher magnetic coupling efficiency and improving filtering, coupling, or conversion performance, are prone to magnetic saturation under high current or surge impacts, leading to decreased filtering performance, increased losses, and even affecting device reliability.

[0004] Therefore, it is difficult for a single permeability nanocrystalline magnetic core to simultaneously achieve both high-current anti-saturation performance and wide-bandwidth high magnetic coupling performance. Especially in applications such as automotive electronics, industrial power supplies, motor drives, and power electronic conversion, devices often need to withstand high startup currents, surge impacts, steady-state high-frequency operation, and complex load variations. If only a low permeability magnetic core is used, the steady-state high-frequency magnetic coupling capability is insufficient; if only a high permeability magnetic core is used, it is prone to saturation under high-current conditions.

[0005] To compensate for the shortcomings of a single magnetic core, existing technologies employ solutions that combine multiple magnetic cores. However, such solutions typically require increasing the number of magnetic cores or expanding the mounting space, resulting in larger device size and compromising compatibility with existing printed circuit board layouts and standardized assembly processes. Furthermore, distributing multiple magnetic cores can lead to issues such as inconsistent magnetic circuits, difficulties in assembly and positioning, increased localized losses, complex heat dissipation paths, and decreased reliability.

[0006] Furthermore, existing single magnetic cores, under complex operating conditions, must bear all magnetic losses, which can easily lead to localized overheating, increased magnetostriction, or material stress concentration, thus affecting the long-term service life and operational stability of the core. For automotive-grade or industrial applications, magnetic devices typically need to meet long-term high reliability requirements, which traditional single-permeability cores can no longer adequately meet. Summary of the Invention

[0007] The purpose of this invention is to provide a dual-permeability composite assembled nanocrystalline magnetic core and its preparation method, which solves the problem that existing single-permeability nanocrystalline magnetic cores cannot simultaneously achieve anti-saturation performance and high magnetic coupling performance.

[0008] In a first aspect, this application provides a dual-permeability composite assembled nanocrystalline magnetic core, comprising a protective shell, a low-permeability nanocrystalline magnetic core unit, a high-permeability nanocrystalline magnetic core unit, and a magnetic circuit isolation structure; the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are layered and disposed within the same protective shell, the low-permeability nanocrystalline magnetic core unit is disposed at the magnetic circuit input end, the high-permeability nanocrystalline magnetic core unit is disposed at the magnetic circuit output end, and the magnetic circuit isolation structure is disposed between the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit to reduce magnetic interference between the two types of magnetic core units.

[0009] In a preferred embodiment, the initial permeability of the low permeability nanocrystalline magnetic core unit is in the range of 1000 to 5000; and the initial permeability of the high permeability nanocrystalline magnetic core unit is in the range of 10000 to 50000.

[0010] In a preferred embodiment, the saturation magnetic flux density Bs of the low permeability nanocrystalline core unit is ≥1.2T, which is used to withstand the impact of large starting current or surge current; the high permeability nanocrystalline core unit is used to improve magnetic coupling efficiency in the 1kHz to 1MHz frequency band; wherein, both the low permeability nanocrystalline core unit and the high permeability nanocrystalline core unit are FeSiBNbCu-based iron-based nanocrystalline cores.

[0011] In a preferred embodiment, both the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are toroidal wound magnetic cores, and are coaxially layered within the protective shell.

[0012] In a preferred embodiment, the magnetic circuit isolation structure is a non-magnetic isolation component, which is disposed between the bonding surfaces of the low permeability nanocrystalline magnetic core unit and the high permeability nanocrystalline magnetic core unit; wherein, the non-magnetic isolation component is a non-magnetic epoxy insulating sheet with a thickness ranging from 0.05 mm to 0.5 mm.

[0013] In a preferred embodiment, the protective shell is a non-magnetic flame-retardant engineering plastic protective shell, and a shielding structure and an encapsulation and fixing structure are provided inside the protective shell; wherein, the encapsulation and fixing structure is a thermally conductive epoxy resin potting compound, which fills the gap between the low magnetic permeability nanocrystalline magnetic core unit, the high magnetic permeability nanocrystalline magnetic core unit and the protective shell.

[0014] Secondly, this application provides a method for preparing a dual-permeability composite assembled nanocrystalline magnetic core, comprising: preparing a low-permeability nanocrystalline magnetic core unit and a high-permeability nanocrystalline magnetic core unit respectively; performing surface pretreatment on the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit; setting a magnetic circuit isolation structure between the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit; layering the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit into the same protective shell, such that the low-permeability nanocrystalline magnetic core unit is located at the magnetic circuit input end and the high-permeability nanocrystalline magnetic core unit is located at the magnetic circuit output end; injecting an encapsulation and fixing material into the protective shell and curing it to obtain the dual-permeability composite assembled nanocrystalline magnetic core.

[0015] In a preferred embodiment, FeSiBNbCu-based amorphous ribbons are prepared using a melt quenching process, and the amorphous ribbons are wound to form low-permeability toroidal cores and high-permeability toroidal cores, respectively. The wound cores are then subjected to crystallization annealing treatment at a protective atmosphere of 540°C to 580°C for 20 to 60 minutes.

[0016] In a preferred embodiment, the magnetic circuit isolation structure is a non-magnetic epoxy isolator, which is fixed to the side end face of the low permeability nanocrystalline magnetic core unit near the high permeability nanocrystalline magnetic core unit.

[0017] In a preferred embodiment, the encapsulation and fixing material is a thermally conductive epoxy resin potting compound, which is cured at 100℃~140℃ for 20min~60min after potting.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention integrates low-permeability nanocrystalline magnetic core units and high-permeability nanocrystalline magnetic core units into the same protective shell to form a dual-permeability layered composite structure, which overcomes the limitation that a single permeability magnetic core cannot simultaneously achieve both anti-saturation performance and high magnetic coupling performance.

[0019] 2. The present invention sets the low permeability nanocrystalline magnetic core unit at the magnetic circuit input end, and utilizes its high saturation magnetic flux density characteristics to withstand the impact of large starting current, surge current or current change, which can reduce the risk of magnetic core saturation and improve stability under complex working conditions.

[0020] 3. The present invention sets a high permeability nanocrystalline magnetic core unit at the magnetic circuit output end, and utilizes its high initial permeability to improve the magnetic coupling efficiency in the 1kHz to 1MHz frequency band, thereby improving the electromagnetic interference suppression capability, energy conversion accuracy or signal transmission performance.

[0021] 4. This invention forms an isolation gap or magnetic interference suppression region between high and low permeability magnetic core units through a magnetic circuit isolation structure, enabling the two types of magnetic core units to work collaboratively according to magnetic circuit partitions, reducing magnetic interference and additional losses caused by direct coupling of materials with different permeability.

[0022] 5. This invention integrates two magnetic core units with different permeabilities into the same housing, achieving composite magnetic properties without significantly increasing the overall volume, and is compatible with existing printed circuit board layouts and standardized assembly processes.

[0023] 6. This invention reduces the risk of localized overheating when a single magnetic core bears the losses under all operating conditions by using layered composite and magnetic circuit division of labor to share the losses.

[0024] These or other aspects of this application will become more apparent from the description of the following embodiments. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the magnetic permeability composite assembled nanocrystalline magnetic core provided in the embodiments of this application; Figure 2 A schematic diagram of the isolation sheet, the low permeability nanocrystalline magnetic core unit, and the high permeability nanocrystalline magnetic core unit provided in the embodiments of this application; Figure 3 A three-dimensional view of a dual-permeability composite assembled nanocrystalline magnetic core provided in the embodiments of this application; Figure 4 A top view of a dual-permeability composite assembled nanocrystalline magnetic core provided in this application embodiment.

[0027] Explanation of reference numerals in the attached figures: 1. Sheath; 2. Insulating plate; 3. Low permeability nanocrystalline magnetic core unit; 4. High permeability nanocrystalline magnetic core unit. Detailed Implementation

[0028] The following description, in conjunction with the accompanying drawings, further illustrates a specific embodiment of the present invention. This specific embodiment uses a toroidal nanocrystalline magnetic core commonly used in automotive electronics and industrial equipment for electromagnetic interference suppression, energy conversion, or signal magnetic coupling as an example, enabling those without expertise to understand the function of each component and the implementation steps. It should be noted that the dimensions, temperature, time, permeability grade, and material grade described below are used to illustrate specific ways in which the present invention can be implemented and do not limit the scope of protection of the present invention. For ease of understanding by those not skilled in the art, the term "permeability" as used in this specification can be understood as the ability of a magnetic material to conduct magnetic flux. Low-permeability magnetic cores are less prone to saturation under high current, making them suitable for withstanding large starting currents and surge impacts; high-permeability magnetic cores are more sensitive to weak magnetic fields or high-frequency signals, making them suitable for improving magnetic coupling efficiency. Existing single-permeability magnetic cores typically only favor one of these properties. This invention places magnetic core units of two permeability grades within the same housing 1, allowing the low-permeability nanocrystalline magnetic core unit 3 to first handle saturation resistance, and the high-permeability nanocrystalline magnetic core unit 4 to then handle high magnetic coupling, thereby forming a layered, cooperative magnetic circuit.

[0029] The "input terminal" and "output terminal" mentioned in this specification are functional positions defined according to the main transmission direction of the large current impact or the signal to be processed in the magnetic circuit. During actual assembly, the input terminal can be marked on the housing 1 using arrows, grooves, colored dots, laser characters, or the positioning surface of the assembly fixture. If the current direction of the application circuit is opposite, the installation direction only needs to be adjusted accordingly during circuit design or assembly; this does not affect the structural principle of the invention.

[0030] In this specific embodiment, the low-permeability nanocrystalline magnetic core unit 3, the high-permeability nanocrystalline magnetic core unit 4, the protective shell 1, and the insulating sheet 2 are all related to... Figures 1 to 4 The corresponding reference numerals in the attached diagrams. The encapsulation and fixing structure and the shielding structure can be housed within the protective shell 1.

[0031] Combination Figures 1 to 4 The dual permeability composite assembled nanocrystalline magnetic core of this embodiment includes a low permeability nanocrystalline magnetic core unit 3, a high permeability nanocrystalline magnetic core unit 4, a protective shell 1, an isolation sheet 2, an encapsulation and fixing structure, and a shielding structure.

[0032] Low permeability nanocrystalline magnetic core unit 3 Figure 2As shown, it is a toroidal wound magnetic core. The function of the low-permeability nanocrystalline magnetic core unit 3 is to withstand the large starting current, DC bias current, or surge current, preventing the entire magnetic core from rapidly saturating when a large current enters. In this embodiment, the low-permeability nanocrystalline magnetic core unit 3 is made of FeSiBNbCu-based iron-based nanocrystalline material, with an initial permeability of 2000 and a saturation magnetic flux density Bs≥1.2T. The low-permeability nanocrystalline magnetic core unit 3 can be obtained by winding an iron-based amorphous strip with a thickness of 14μm to 30μm into a toroidal blank and then crystallizing and annealing it. For those unfamiliar with magnetic core manufacturing, it can be understood as follows: first, the thin strip material is wound into a toroidal shape, and then heat-treated to form a nanocrystalline structure and obtain the desired magnetic properties.

[0033] High permeability nanocrystalline magnetic core unit 4 Figure 2 As shown, it is also a toroidal wound magnetic core. The function of the high-permeability nanocrystalline magnetic core unit 4 is to improve the magnetic coupling efficiency in the 1kHz to 1MHz frequency band, thereby improving electromagnetic interference suppression, energy conversion accuracy, or signal transmission stability. In this embodiment, the high-permeability nanocrystalline magnetic core unit 4 is made of FeSiBNbCu-based iron-based nanocrystalline material with an initial permeability of 20,000. Compared with the low-permeability nanocrystalline magnetic core unit 3, the high-permeability nanocrystalline magnetic core unit 4 is more suitable for handling steady-state or mid-to-high frequency coupled signals, but it is more prone to saturation under large current surges. Therefore, this invention does not allow it to directly bear the impact of large currents at the input end.

[0034] The housing 1 is used to house and fix the low-permeability nanocrystalline magnetic core unit 3 and the high-permeability nanocrystalline magnetic core unit 4. The housing 1 is preferably made of PPS+GF30 non-magnetic flame-retardant engineering plastic through integral injection molding, with a long-term temperature resistance of up to 150℃ and a flame retardant rating of V-0. Here, "non-magnetic" means that the housing itself does not actively participate in magnetic circuit conduction to avoid altering the partitioning function of the high and low permeability magnetic core units; "flame retardant" and "temperature resistant" are used to meet the safety and reliability requirements of environments such as automotive electronics and industrial power supplies. The external dimensions of the housing 1 are preferably consistent with traditional single-permeability nanocrystalline housings of the same specifications, so that users do not need to redesign PCB mounting holes, limiting structures, or surrounding component layouts when replacing products.

[0035] like Figure 1 , Figure 3 and Figure 4 As shown, the low permeability nanocrystalline magnetic core unit 3, the high permeability nanocrystalline magnetic core unit 4, and the insulating sheet 2 are arranged in a layered composite manner within the same protective shell 1. Figure 3This diagram illustrates the structure of a toroidal composite magnetic core after radial sectional cutting. The left and right sides represent the two sidewall sections formed after the toroidal core is cut open. In each sidewall section, low-permeability nanocrystalline magnetic core unit 3 and high-permeability nanocrystalline magnetic core unit 4 are arranged adjacent to each other, with a separator 2 placed at their interface. The middle section is an assembly channel through which a cavity or conductor passes. In use, the low-permeability nanocrystalline magnetic core unit 3 is located on the magnetic circuit input side and initially withstands the large current surge, while the high-permeability nanocrystalline magnetic core unit 4 is located on the magnetic circuit output side and performs broadband magnetic coupling.

[0036] Isolator 2 uses a 0.05mm–0.5mm non-magnetic epoxy isolator as an optimized structure for the magnetic circuit gap between high and low permeability nanocrystalline magnetic core units. It is sandwiched at the junction of the two magnetic core end faces to construct a controllable and uniform magnetic reluctance gap, solving the problems of magnetic flux disorder and mutual interference loss caused by direct bonding of the two magnetic cores. The isolator itself has no magnetic permeability and will not form a short-circuit magnetic bridge. It moderately increases the interfacial magnetic reluctance, weakens the unintended magnetic flux coupling between high and low permeability materials, and avoids the additional heat generation and performance degradation caused by local magnetic flux concentration.

[0037] Structurally, the isolator is coaxially matched and cut to fit the magnetic core, and fixed to the output end face of the low permeability magnetic core. Assembly and positioning are simple, and with the help of thermally conductive potting compound, the gap can be maintained stably for a long time. Preferably, the isolator can be fixed to the output end face of the low permeability magnetic core by adhesive. The thickness can be adjusted as needed: a thin isolator is selected for small-size, high-frequency coupling scenarios to ensure magnetic coupling efficiency; a thicker isolator is added for high surge conditions to enhance the magnetic isolation effect.

[0038] This gap structure does not cut off the main magnetic circuit, but only controls the magnetic flux path in sections. The low-permeability magnetic core at the input end and the high-permeability magnetic core at the output end can each perform their own functions. It retains the combined advantages of the low magnetic unit's anti-saturation and the high magnetic unit's wide-band and high-efficiency coupling, while reducing the overall magnetic loss and steady-state temperature rise, improving the long-term reliability of the device. It is suitable for complex high-current operating conditions such as automotive and industrial power supplies, and the assembly is compatible with standardized processes without increasing the overall size of the magnetic core.

[0039] The encapsulation and fixing structure is disposed in the gap between the protective shell 1 and the two magnetic core units. In this embodiment, the encapsulation and fixing structure is a thermally conductive epoxy resin potting compound. After the potting compound cures, it serves three purposes: first, it fixes the two magnetic core units inside the protective shell, preventing displacement during transportation and vibration; second, it provides buffer protection for the magnetic core units, reducing the risk of brittle fracture of the nanocrystalline magnetic cores; and third, it transfers the heat generated during the operation of the magnetic cores to the protective shell, which helps to reduce local temperature rise. The shielding structure can be a shielding layer, shielding ribs, isolation wall, or local shielding sheet disposed on the inner wall of the protective shell 1, used to reduce external electromagnetic interference and unintended coupling between the two magnetic core units.

[0040] Before implementing this plan, prepare the following components and materials: two sets of FeSiBNbCu amorphous ribbons, one protective shell, a non-magnetic epoxy insulating sheet, thermally conductive epoxy resin potting compound, anhydrous ethanol, positioning fixtures, heat-resistant adhesive or dispensing equipment, an oven, and conventional magnetic performance testing equipment.

[0041] The external dimensions of the low-permeability nanocrystalline magnetic core unit 3 and the high-permeability nanocrystalline magnetic core unit 4 should match the internal mounting cavity of the housing 1. During implementation, the dimensions can be determined according to the following principles: after the magnetic core unit is placed in the housing, a potting gap of 0.1mm to 1.0mm should be reserved between the outer periphery and the inner wall of the housing; the end faces of both magnetic core units that contact the insulating sheet 2 should remain flat; the through holes or channels in the middle should meet the space requirements for conductors, wire harnesses, or PCB components to pass through. If the housing 1 uses the traditional single-permeability magnetic core specification, the total assembly width or total assembly height of the two magnetic core units should not exceed the original internal space of the housing.

[0042] The housing 1 preferably has a positioning step, a limiting rib, or a positioning groove on its inner wall. The positioning step is used to define the axial position of the low-permeability nanocrystalline magnetic core unit 3 and the high-permeability nanocrystalline magnetic core unit 4, the limiting rib is used to prevent the magnetic core units from wobbling left and right before potting, and the positioning groove is used to accommodate the insulating sheet 2. For housings without a positioning structure, temporary tooling fixtures can also be used to maintain the position and spacing of the two types of magnetic core units before potting.

[0043] This embodiment employs a melt-quenching process to prepare FeSiBNbCu-based amorphous ribbons. Specifically, raw materials such as iron, silicon, boron, niobium, and copper are melted according to a commonly used formula for iron-based nanocrystalline materials to form an alloy melt, which is then rapidly cooled to form an amorphous ribbon. This amorphous ribbon is then wound and crystallized through annealing to form a nanocrystalline magnetic core. If the personnel lack the necessary conditions for ribbon preparation, FeSiBNbCu-based amorphous ribbons or prefabricated toroidal magnetic cores can be directly purchased.

[0044] When preparing the low-permeability nanocrystalline magnetic core unit 3, the amorphous ribbon is wound into a ring-shaped blank according to the target outer diameter, inner diameter, and height. During the winding process, the edges of the ribbon should be kept as flat as possible to avoid local warping, wrinkling, or breakage. After winding, the outer end of the ring can be fixed with heat-resistant tape or temporary clamps to prevent loosening before annealing. Subsequently, the ring-shaped blank is placed in an argon protective atmosphere for crystallization annealing. The annealing temperature is preferably 540℃~580℃, and the annealing time is preferably 30min. After annealing, it is cooled in the furnace or slowly cooled in a protective atmosphere to reduce internal stress. By adjusting the annealing temperature, holding time, external magnetic field, or subsequent stress treatment, the initial permeability is controlled within the range of 1000~5000, preferably 2000, and the saturation magnetic flux density Bs≥1.2T.

[0045] When preparing the high-permeability nanocrystalline magnetic core unit 4, the amorphous ribbon is also wound into a toroidal blank and subjected to crystallization annealing. To obtain a higher initial permeability, an annealing regime more suitable for high magnetic permeability can be selected, such as a stable crystallization temperature in the range of 540℃ to 580℃, and the holding time is controlled to be 20 min to 60 min, so that its initial permeability reaches the range of 10,000 to 50,000, preferably in the 20,000 range. The permeability and loss of the high-permeability nanocrystalline magnetic core unit 4 should be tested in the frequency band of 1kHz to 1MHz to confirm that it can undertake the high magnetic coupling function at the output end.

[0046] After the two types of magnetic core units are fabricated, they undergo visual and dimensional inspections. Visual inspection includes checking for cracks, chipped corners, delamination, loose strips, obvious burrs, or uneven end faces. Dimensional inspection includes outer diameter, inner diameter, height, end face flatness, and the fit clearance with the housing mounting cavity. Minor burrs can be removed using tools that do not introduce magnetic contamination; cores with cracks, chipped corners, or severe looseness should be discarded.

[0047] Before assembly, wipe the outer surfaces, end faces, and inner hole surfaces of the low-permeability nanocrystalline magnetic core unit 3 and the high-permeability nanocrystalline magnetic core unit 4 with anhydrous ethanol to remove dust, oil, and hand sweat. After wiping, allow the magnetic core units to air dry naturally at room temperature, or briefly dry them at 50℃~80℃ for 10min~20min to ensure that there is no obvious residual liquid on the surface. The purpose of surface pretreatment is to improve the bonding reliability of the separator and the adhesion of the potting compound.

[0048] Next, install the isolation sheet 2. Taking a 0.1mm non-magnetic epoxy isolation sheet as an example, first cut the isolation sheet according to the contact end face shape of the low permeability nanocrystalline magnetic core unit 3 and the high permeability nanocrystalline magnetic core unit 4, ensuring that its outer contour does not exceed the outer edge of the magnetic core and that the inner hole does not obstruct the conductor channel. Apply a small amount of heat-resistant non-magnetic adhesive evenly to the end face of the low permeability nanocrystalline magnetic core unit 3 near the high permeability nanocrystalline magnetic core unit 4, and then attach the isolation sheet to it. During attachment, ensure that the isolation sheet is flat, without warping or obvious air bubbles, and that the center of the isolation sheet is aligned with the center of the magnetic core.

[0049] If a liquid resin insulating layer is used instead of an insulating sheet, a layer of non-magnetic epoxy resin with a thickness of 0.05 mm to 0.5 mm can be coated on the end face of the low permeability nanocrystalline magnetic core unit 3, pre-cured until it does not flow, and then assembled with the high permeability nanocrystalline magnetic core unit 4. Regardless of whether an insulating sheet or a resin insulating layer is used, the core requirement is that the insulating structure itself is non-magnetic, does not form a short-circuit magnetic bridge, and can maintain a stable thickness between the two types of magnetic core units.

[0050] Place the housing 1 on the positioning fixture, ensuring the input end mark on the housing faces the operator or the fixture's reference side. First, insert the low-permeability nanocrystalline magnetic core unit 3 into the input end mounting cavity of the housing 1, ensuring its outer circumference or end face aligns with the positioning step inside the housing. Do not directly strike the magnetic core with hard metal tools during installation; instead, use a plastic or rubber pressure block to gently press it into place to prevent cracking of the nanocrystalline magnetic core.

[0051] Then, with the side with the insulating plate 2 facing towards the high-permeability nanocrystalline core unit 4, the high-permeability nanocrystalline core unit 4 and the low-permeability nanocrystalline core unit 3 are stacked and assembled, and then installed into the mounting cavity of the protective shell 1. After assembly, the low-permeability nanocrystalline core unit 3, the insulating plate 2, and the high-permeability nanocrystalline core unit 4 should be aligned... Figure 3 As shown, the cores are arranged adjacent to each other in the cross-section of the toroidal core sidewall, and the central cavity or conductor channel must not be blocked by the isolation plate 2. If a coaxial layered structure is adopted, the center holes of the two core units should be basically aligned; if the structure is adjusted to a front-to-back or top-to-bottom stacked structure according to product specifications, the isolation plate 2 should also be located at the joint surface of the two core units.

[0052] During assembly, three positional relationships should be checked: First, the low-permeability nanocrystalline core unit 3 must be on the input side and should not be installed backwards with the high-permeability nanocrystalline core unit 4; second, the separator 2 must be sandwiched at the interlayer bonding surface of the two core units and should not be omitted, offset to the central cavity, or offset to the inner wall of the housing; third, sufficient space should be left between the two core units and the housing 1 for the flow of potting compound. If reversed installation or misalignment of the separator is found, reassembly should be performed before potting.

[0053] To ensure consistency in mass production, a dedicated assembly fixture can be used. This fixture includes a housing positioning base, an input end anti-foolproof protrusion, a core pressing block, and a center positioning post. The housing positioning base is used to fix the housing 1, the input end anti-foolproof protrusion ensures the housing orientation is unique, the center positioning post passes through the core through-hole to ensure coaxiality, and the core pressing block is used to press the two types of core units to the same height or a predetermined position. With this fixture, even if the operator is not familiar with the working principle of the core, they can complete the assembly by following the sequence of "place the housing, lower the magnetic core, attach the insulating sheet, raise the magnetic core, and press it into place."

[0054] After completing the layered composite assembly, thermally conductive epoxy resin potting compound is injected into the housing 1. Before potting, the two-component epoxy resin can be mixed according to the supplier's specified ratio and degassed. Degasting can be done by vacuum degasing or static degasing. During potting, the compound should be slowly injected from one side of the housing, allowing it to flow along the inner wall of the housing and the gaps around the outer periphery of the magnetic core, gradually filling the gaps between the low-permeability nanocrystalline magnetic core unit 3, the high-permeability nanocrystalline magnetic core unit 4, and the housing 1. During the potting process, avoid sealing a large number of air bubbles into the bottom of the magnetic core or near the insulating sheet.

[0055] The amount of potting compound should be sufficient to cover the magnetic core unit and form a stable encapsulation structure. Insufficient potting compound may cause the magnetic core to loosen under vibration; excessive potting compound may overflow the casing and affect subsequent assembly. After potting, the tooling can be slightly vibrated or a short vacuum can be applied to allow air bubbles to rise and dissipate. For automotive electronics applications, epoxy potting compound with a temperature resistance of 120℃ or higher and certain thermal conductivity and insulation properties is preferred.

[0056] The preferred curing conditions are baking at 120℃ for 30 minutes, but this can be adjusted to 100℃~140℃ for 20 minutes~60 minutes depending on the potting compound system. After curing, allow it to cool naturally to room temperature before inspecting the finished product's appearance. Appearance inspection items include: whether the potting compound is fully cured, whether there are obvious bubbles or cracks on the surface, whether the casing is deformed, whether the magnetic core is exposed, whether the isolator is displaced, and whether the input and output terminal markings are clear. If further improvement in moisture resistance is required, an insulating and moisture-proof coating can be applied to the exposed interfaces after curing.

[0057] To ensure that the finished product can achieve the technical effects of this invention, the following tests can be performed on the dual-permeability composite assembled nanocrystalline magnetic core.

[0058] First, appearance and dimensional inspection. Using calipers or specialized gauges, inspect the core's external dimensions, through-hole dimensions, sheath height, and positioning structure dimensions to confirm that it matches the appearance of a conventional single-permeability core of the same specification or meets the requirements of the mounting drawings. This inspection serves to demonstrate that the invention will not occupy additional PCB layout space.

[0059] Second, initial permeability testing. The finished product is placed in a magnetic performance testing fixture, and the equivalent permeability is tested at 100kHz or the product's specified frequency. For this embodiment, the high permeability functional area at the output end should exhibit high permeability characteristics in the range of 18000–22000; the low permeability functional area at the input end should exhibit low permeability characteristics in the range of 1800–2200. Actual testing can confirm this through equivalent testing of partitioned samples, process samples, or the finished product.

[0060] Third, anti-saturation performance testing. A DC bias current or a simulated large starting current is applied to the magnetic core, and the permeability retention rate or the decrease in inductance is detected. In this embodiment, under a 50A bias condition, the permeability retention rate of the dual-permeability composite magnetic core is preferably not less than 80%, which is used to prove that the low permeability nanocrystalline magnetic core unit 3 can withstand the anti-saturation function of large input current.

[0061] Fourth, magnetic loss and temperature rise detection. Overall magnetic loss was tested at 100kHz, a specified magnetic flux density, or a specified operating current, and temperature rise was tested under continuous operation at 50A for 1 hour at an ambient temperature of 25°C. In this embodiment, the overall magnetic loss can be reduced by more than 25% compared to a single permeability core, and the steady-state temperature rise can be reduced from approximately 60°C to approximately 45°C for a traditional low permeability core, indicating that the two core units share the losses through magnetic circuit division of labor.

[0062] Fifth, reliability testing. Refer to AEC-Q200 for 500 cycles of high and low temperature cycling from -40℃ to 125℃, and refer to IEC60068-2-78 for 1000 hours of damp heat aging at 85℃ / 85%RH. If, after testing, the magnetic core shows no cracks, the potting compound shows no obvious cracking, and the magnetic properties show no abnormal attenuation, then the structure is suitable for long-term use in automotive electronics or industrial equipment.

[0063] To illustrate the technical effects of this invention, the dual-permeability composite assembled nanocrystalline magnetic core in this embodiment is compared with a single low-permeability magnetic core and a single high-permeability magnetic core. During the comparative test, all three types of magnetic cores used similar external dimensions and the same installation conditions; the single low-permeability magnetic core used a 2000-level nanocrystalline magnetic core, the single high-permeability magnetic core used a 20000-level nanocrystalline magnetic core, and the sample of this invention uses a low-permeability nanocrystalline magnetic core unit 3 and a high-permeability nanocrystalline magnetic core unit 4 assembled in the same protective shell 1. The test results are shown in Table 1 below.

[0064] Table 1. Comparison of core performance between dual-permeability composite assembled nanocrystalline magnetic cores and traditional single-permeability magnetic cores. As shown in Table 1, the dual-permeability composite assembled nanocrystalline magnetic core of the present invention retains the high current withstand capability of low-permeability magnetic cores while achieving a wideband magnetic coupling capability close to or reaching that of high-permeability magnetic cores. Unlike simply using two magnetic cores side by side, the present invention achieves compact composite assembly through the same protective shell 1, insulating sheet 2, and potting fixing structure, while maintaining compatibility with standard single magnetic cores in terms of external dimensions and assembly process.

[0065] Without altering the core concept of dual permeability synergy, layered composite assembly, and magnetic circuit isolation, the low-permeability nanocrystalline magnetic core unit 3 and the high-permeability nanocrystalline magnetic core unit 4 can also be replaced by other magnetic materials or materials with similar permeability levels. Examples of alternative materials are shown in Table 2 below.

[0066] Table 2 Comparison of Performance of Alternative Materials for Low / High Permeability Core Units As shown in Table 2, the low-permeability nanocrystalline magnetic core unit 3 can be replaced with other magnetic materials that possess high saturation magnetic flux density and resistance to high current saturation; the high-permeability nanocrystalline magnetic core unit 4 can be replaced with other magnetic materials that possess high initial permeability and wideband magnetic coupling capability. The selection of replacement materials should follow these principles: the input material should prioritize resistance to saturation and DC bias stability, and the output material should prioritize magnetic coupling efficiency in the target frequency band. An isolation plate 2 should still be provided between the two.

[0067] In addition to material substitution, the composite assembly structure can also be adjusted. For example, the low permeability nanocrystalline magnetic core unit 3 and the high permeability nanocrystalline magnetic core unit 4 can be coaxially stacked, side-by-side partitioned, front-to-back series partitioned, or multiple alternating partitioned structures; the isolation sheet 2 can be made of epoxy isolation sheet, ceramic isolation sheet, non-magnetic plastic isolation sheet, resin isolation layer, or an integrally molded isolation wall; the protective shell 1 can be made of PPS, PBT, PA, LCP, or other engineering plastics that meet the requirements of temperature resistance, insulation, flame retardancy, and non-magnetic properties.

[0068] When the dual-permeability composite assembled nanocrystalline magnetic core of the present invention is connected to the circuit, when a large current is generated during circuit startup, motor drive, power conversion, or surge impact, the large current first acts on the low-permeability nanocrystalline magnetic core unit 3. Because the initial permeability of the low-permeability nanocrystalline magnetic core unit 3 is relatively low and the saturation magnetic flux density is high, it can still maintain a good permeability retention rate under large current and will not enter the saturation state as quickly as the high-permeability magnetic core.

[0069] After being processed by the low-permeability nanocrystalline core unit 3, the magnetic circuit or the signal to be coupled continues to enter the high-permeability nanocrystalline core unit 4. The high-permeability nanocrystalline core unit 4 utilizes its higher initial permeability to improve the magnetic coupling efficiency in the 1kHz to 1MHz frequency band, thereby enhancing EMI suppression, energy conversion, or signal magnetic coupling effects. In other words, the low-permeability nanocrystalline core unit 3 is equivalent to first "withstanding" the large current surge, while the high-permeability nanocrystalline core unit 4 is responsible for "coupling" the steady-state or mid-to-high frequency signal.

[0070] The isolator 2 forms a stable gap between the two types of magnetic core units, reducing magnetic flux disturbances caused by direct coupling between materials with high and low permeability. The encapsulation and fixing structure keeps the two types of magnetic core units in a fixed position and conducts operating heat to the protective shell 1; the shielding structure further reduces external interference and unintended internal coupling. Thus, this invention achieves composite magnetic properties of high current withstand capability and wideband, high-efficiency magnetic coupling without significantly increasing the core volume.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, combinations, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-permeability composite assembled nanocrystalline magnetic core, characterized in that, The device includes a protective shell, a low-permeability nanocrystalline magnetic core unit, a high-permeability nanocrystalline magnetic core unit, and a magnetic circuit isolation structure. The low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are layered and disposed within the same protective shell. The low-permeability nanocrystalline magnetic core unit is disposed at the magnetic circuit input end, and the high-permeability nanocrystalline magnetic core unit is disposed at the magnetic circuit output end. The magnetic circuit isolation structure is disposed between the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit to reduce magnetic interference between the two types of magnetic core units.

2. The dual-permeability composite assembled nanocrystalline magnetic core according to claim 1, characterized in that, The initial permeability of the low-permeability nanocrystalline magnetic core unit is in the range of 1000 to 5000; the initial permeability of the high-permeability nanocrystalline magnetic core unit is in the range of 10000 to 50000.

3. The dual-permeability composite assembled nanocrystalline magnetic core according to claim 1, characterized in that, The saturation magnetic flux density Bs of the low permeability nanocrystalline magnetic core unit is ≥1.2T, which is used to withstand the impact of large starting current or surge current. The high permeability nanocrystalline magnetic core unit is used to improve magnetic coupling efficiency in the 1kHz to 1MHz frequency band. The low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are both FeSiBNbCu-based iron-based nanocrystalline magnetic cores.

4. The dual-permeability composite assembled nanocrystalline magnetic core according to claim 1, characterized in that, Both the low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are toroidal wound magnetic cores, and are coaxially layered within the protective shell.

5. The dual-permeability composite assembled nanocrystalline magnetic core according to claim 1, characterized in that, The magnetic circuit isolation structure is a non-magnetic isolation component, which is disposed between the bonding surfaces of the low permeability nanocrystalline magnetic core unit and the high permeability nanocrystalline magnetic core unit. The non-magnetic insulating component is a non-magnetic epoxy insulating sheet with a thickness ranging from 0.05 mm to 0.5 mm.

6. The dual-permeability composite assembled nanocrystalline magnetic core according to claim 1, characterized in that, The protective shell is a non-magnetic flame-retardant engineering plastic protective shell, and a shielding structure and an encapsulation and fixing structure are provided inside the protective shell; The encapsulation and fixing structure is a thermally conductive epoxy resin potting compound, which fills the gap between the low permeability nanocrystalline magnetic core unit, the high permeability nanocrystalline magnetic core unit, and the protective shell.

7. A method for preparing a dual-permeability composite assembled nanocrystalline magnetic core as described in any one of claims 1 to 6, characterized in that, include: Low-permeability nanocrystalline magnetic core units and high-permeability nanocrystalline magnetic core units were prepared respectively; Surface pretreatment is performed on the low permeability nanocrystalline magnetic core unit and the high permeability nanocrystalline magnetic core unit; A magnetic circuit isolation structure is provided between the low permeability nanocrystalline magnetic core unit and the high permeability nanocrystalline magnetic core unit; The low-permeability nanocrystalline magnetic core unit and the high-permeability nanocrystalline magnetic core unit are layered and installed in the same protective shell, with the low-permeability nanocrystalline magnetic core unit located at the magnetic circuit input end and the high-permeability nanocrystalline magnetic core unit located at the magnetic circuit output end. The encapsulation and fixing material is injected into the protective shell and cured to obtain the dual permeability composite assembled nanocrystalline magnetic core.

8. The preparation method according to claim 7, characterized in that, FeSiBNbCu amorphous ribbons were prepared using a melt quenching process, and the amorphous ribbons were wound to form low-permeability toroidal cores and high-permeability toroidal cores, respectively. The wound magnetic core was subjected to crystallization annealing treatment at a protective atmosphere of 540℃~580℃ for 20min~60min.

9. The preparation method according to claim 7, characterized in that, The magnetic circuit isolation structure is a non-magnetic epoxy isolator, which is fixed to the end face of the low permeability nanocrystalline magnetic core unit near the high permeability nanocrystalline magnetic core unit.

10. The preparation method according to claim 7, characterized in that, The encapsulation and fixing material is a thermally conductive epoxy resin potting compound, which is cured at 100℃~140℃ for 20min~60min after potting.

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