Mortise type splicing ferrite magnetic shielding device and method

Abstract

This invention discloses a tenon-and-mortise splicing ferrite magnetic shielding device and method. Addressing the limitations of existing ferrite magnetic shielding methods, such as limited overall size, severe magnetic leakage, difficulty in multi-layer adaptation, high cost, and poor maintenance flexibility, as well as the stringent shielding requirements of medical equipment and high-precision atomic magnetometers in complex magnetic environments, this invention introduces a core design of "modular fan-ring units + tenon-and-mortise interlocking structure" and corresponding splicing methods. These methods utilize stepped surface contact tenons to increase the splicing contact area to ensure magnetic flux continuity, multi-layer coaxial positioning benchmarks to optimize tolerance adaptation, independent replacement and cleaning of modular fan-rings, tooling assistance, and performance calibration splicing processes. These improvements enhance magnetic shielding effectiveness and multi-layer adaptation accuracy, while reducing vertical and inter-layer magnetic leakage. Furthermore, based on the modular design and tenon-and-mortise structure characteristics, breakthroughs have been achieved in the fabrication of large-diameter magnetic shielding and independent maintenance of individual fan-rings, reducing the cost of large molds and the overall lifecycle maintenance cost of the equipment.

Description

Technical Field

[0001] This invention relates to the fields of quantum precision measurement and magnetic shielding technology, specifically to a tenon-and-mortise type ferrite magnetic shielding device and method. Background Technology

[0002] In the field of magnetic field measurement technology, with the continuous increase in the requirements for the accuracy of extremely weak magnetic field detection in applications such as geophysical exploration, biomagnetic imaging, and quantum physics experiments, the sensitivity of magnetometers has become a core competitive indicator. From the early fluxgate magnetometers (sensitivity approximately 1 nT / Hz¹)... / ²), Superconducting quantum interference device (SQUID, sensitivity approximately 1 fT / Hz¹) / ²), to the current mainstream SERF atomic magnetometer (sensitivity has broken through 0.1 fT / Hz¹ / ²), the sensitivity of magnetometers has achieved a leap of several orders of magnitude. This increase in sensitivity inevitably leads to an exponential upgrade in the demand for noise shielding: on the one hand, the tolerance threshold of higher-sensitivity magnetometers to background magnetic field noise is significantly reduced. For example, the SERF atomic magnetometer needs to suppress the background magnetic field to ≤1nT to maintain a spin-free relaxation-free operating state, far lower than the requirements of traditional magnetometers for the magnetic field environment; on the other hand, the increased sensitivity makes the instrument more sensitive to various endogenous and exogenous magnetic noises. External environmental factors such as the geomagnetic field, power frequency electromagnetic interference, and stray magnetic fields generated by internal instrument components (such as heating systems and circuit modules) all become key factors restricting measurement accuracy. In this context, the magnetic shielding system is no longer an auxiliary component of the magnetometer, but a core support that determines whether its sensitivity can be fully utilized. Especially for ultra-high-sensitivity devices like the SERF atomic magnetometer, the performance of the magnetic shielding directly determines whether it can move from the laboratory to engineering applications. With the increasing demand for the ability to detect extremely weak magnetic fields, the SERF atomic magnetometer has been widely used in geophysical exploration, biomagnetic imaging (such as magnetoencephalography (MEG) and magnetocardiography (MCG)) and basic physics experiments (such as dark matter detection and quantum gravity measurement) due to its extremely high sensitivity and wide frequency response characteristics in the field of ultra-weak magnetic field detection.

[0003] In the field of electromagnetic shielding technology, ferrite magnetic shielding benefits from its high initial permeability (μ). i ≥5000), low high-frequency magnetic loss (P cv With a magnetic field strength of ≤250mW / cm³@10kHz, 0.2T and excellent high-frequency magnetic field suppression capabilities, it has become a core shielding component in medical devices (such as fetal magnetocardiography), precision electronic instruments (such as superconducting quantum interference devices), and high-end magnetic sensing devices (such as high-precision atomic magnetometers). Especially in the high-precision atomic magnetometer scenario, it needs to provide an ultra-low magnetic noise environment for atomic spin precession (typically requiring magnetic noise ≤5fT / Hz in the 1Hz-100Hz frequency band¹). / ²), the performance of ferrite magnetic shielding directly determines the detection sensitivity and measurement accuracy of the instrument.

[0004] However, existing ferrite magnetic shielding technology still faces three major technical bottlenecks in practical applications, which severely restrict its application in large-size, multi-layer, and high-precision scenarios:

[0005] Firstly, monolithic circular ferrite magnetic shielding faces a significant size bottleneck. Limited by the integral molding process of ferrite materials—specifically, during the integral ring pressing process, when the diameter exceeds 27cm, it is difficult to ensure the uniformity of pressing force circumferentially on the blank, easily leading to insufficient edge density. Furthermore, during the sintering stage, uneven thermal stress caused by the large blank size can cause ring deformation, with a roundness error ≥1mm. Therefore, under current technology, the diameter of monolithic circular ferrite magnetic shielding is generally difficult to exceed 27cm. This limitation prevents it from meeting the requirements of large medical equipment, such as whole-body magnetic physiological imaging instruments and large-aperture atomic magnetometers, which require a shielding space diameter ≥30cm, creating a significant application barrier.

[0006] Secondly, existing spliced ​​magnetic shielding suffers from significant magnetic leakage, resulting in insufficient shielding effectiveness. To overcome size limitations, the industry often adopts a "brick-type splicing" solution. However, in this solution, adjacent ferrite blocks only have linear contact, causing magnetic flux to break at the splicing interface due to contact gaps. Vertical magnetic leakage is generally ≥0.8μT, which cannot meet the low magnetic leakage requirements of high-precision equipment. As for "multi-layer composite magnetic shielding" designed for higher shielding requirements, each layer of rings needs to be molded independently. The dimensional deviation of a single layer accumulates over multiple layers, leading to tolerance mismatch between inner and outer layers, coaxiality error ≥0.5mm, and thus forming interlayer gaps (≥0.1mm). Interlayer magnetic leakage can reach ≥1.2μT, severely damaging the synergistic effect of multi-layer shielding and causing an overall magnetic shielding effectiveness decrease of more than 30%.

[0007] Thirdly, existing structures are costly, lack maintenance flexibility, and are not economically viable. On the one hand, the development cost of molds for integral circular ferrite magnetic shielding is high. For example, a dedicated mold for a 27cm diameter integral circular ring needs to cover the entire ring size, and the mold material (Cr...)... 12 MoV has high losses, requires high machining precision (tolerance grade IT6), has expensive single-set mold development costs, and is only compatible with a single size, resulting in poor versatility; if the permeability of a local area of ​​the ring is substandard due to sintering defects (e.g., μ), it will cause further problems. i If the density is less than 4500, the entire ring must be scrapped, with a material loss rate of ≥15%. On the other hand, multi-layer composite magnetic shielding relies on high-precision calibration for interlayer fit. During maintenance, all layers must be disassembled to replace the faulty layer, and the coaxiality must be recalibrated after reinstallation (taking ≥4 hours). This results in low maintenance efficiency and high cost, further increasing the total life cycle cost of the equipment.

[0008] In recent years, with the expansion of applications of high-precision atomic magnetometers in fields such as geomagnetic detection and weak magnetic imaging of organisms, the demand for magnetic shielding has been upgraded to a comprehensive requirement of "large diameter (≥30cm) + low magnetic leakage (vertical magnetic leakage ≤0.3μT, interlayer magnetic leakage ≤0.5μT) + low cost + easy maintenance". Existing ferrite magnetic shielding structures can no longer meet the above requirements. Therefore, developing a ferrite magnetic shielding structure that can overcome size limitations, suppress magnetic leakage, reduce costs and is easy to maintain has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing ferrite magnetic shielding, such as the difficulty in exceeding a 27cm diameter overall ring, severe vertical magnetic leakage in brick-like splicing, imperfect matching of internal and external tolerances and prominent interlayer magnetic leakage in multi-layer composite structures, high manufacturing costs, and the inflexibility of requiring complete ring replacement for local maintenance. This invention provides a tenon-and-mortise splicing ferrite magnetic shielding device and method. Through the tenon-and-mortise structure design with protruding tenons and grooves between the fan rings, it overcomes the limitations of large-diameter magnetic shielding fabrication, enabling complete ring splicing of over 30cm. Furthermore, the precise mechanical fit of the tenons and mortise optimizes the tolerance compatibility of multi-layer magnetic shielding, while increasing the contact area enhances magnetic flux continuity, simultaneously suppressing vertical and interlayer magnetic leakage. The modular fan ring design also reduces the cost of large molds and supports independent replacement of individual fan rings, thus constructing a magnetic shielding system that combines large-size adaptability, low magnetic leakage performance, low cost, and high maintenance flexibility, meeting the stringent shielding requirements of medical equipment, high-precision atomic magnetometers, and other devices operating in complex magnetic environments.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A mortise and tenon splicing ferrite magnetic shielding device adopts a core design of "modular fan ring unit + mortise and tenon interlocking structure", including N (N≥2, N=8 in this embodiment) mortise and tenon splicing ferrite fan rings (hereinafter referred to as "fan rings"), which are the basic shielding units; each fan ring has a pre-set protrusion or groove at both ends of its circumference, and the protrusion and groove form a mortise and tenon structure, which enables the detachable and precise splicing of each fan ring, ultimately forming a closed annular magnetic shield; wherein, the protrusion and groove at the splicing point of the fan rings are set opposite to each other to cooperate with each other.

[0012] Preferably, the tenon and mortise structure is a stepped surface contact structure, specifically: the tenon has 2-3 steps along the thickness direction of the fan ring, each step being 1 / 2-1 / 3 the height of the fan ring thickness and 1 / 8-1 / 4 the width of the fan ring arc length; the groove has a corresponding stepped groove matching the tenon, and the fit gap between the tenon and the groove is controlled to 0.02-0.05mm with IT7 grade mold precision. Compared with the traditional brick-type splicing "linear contact", this structure increases the splicing contact area of ​​adjacent fan rings by 3-5 times. It can not only ensure the continuous transition of magnetic flux at the splicing interface by increasing the contact area and avoid magnetic flux breakage caused by contact gap, but also form a "maze-like" magnetic flux path through multiple steps, which conforms to the characteristic of magnetic flux "closing along a high permeability path", extending the leakage magnetic path and further suppressing vertical leakage magnetic field to ≤0.3μT.

[0013] As a preferred option, for multi-layer composite magnetic shielding scenarios, a "coaxial positioning reference" is added to the tenon and mortise structure of each fan ring: using the inner circle reference surface of the fan ring (surface roughness R) as the reference. a Using a positioning reference of ≤0.8μm (achieved through diamond wheel polishing), the outer circular tenon of the inner fan ring and the inner circular groove of the outer fan ring are precisely matched in radial dimension (tolerance grade IT7) and circumferential position (alignment deviation ≤0.1mm). Through the mechanical positioning effect of the tenon and mortise structure, the coaxiality error of the multi-layer fan ring is controlled to ≤0.1mm, which completely solves the problem of fitting gap caused by the accumulation of inner and outer diameter tolerances in traditional multi-layer composite magnetic shielding, thereby eliminating the interlayer magnetic leakage channel and making the interlayer magnetic leakage ≤0.5μT.

[0014] Furthermore, this invention also provides a splicing method for the above-mentioned tenon-and-mortise type fan ring spliced ​​ferrite magnetic shield to ensure splicing accuracy and magnetic shielding performance, specifically including the following steps:

[0015] S1: Fan Ring Pretreatment and Screening

[0016] Before splicing, the tenon and mortise surfaces (protruding tenon end face and groove inner wall) of each fan ring are cleaned using pure water as the cleaning medium and ultrasonic cleaning equipment at a frequency of 40kHz for 10 minutes to remove dust, oil, and other impurities adhering to the tenon and mortise surfaces, thus preventing impurities from increasing the splicing gap. After cleaning, a magnetic performance testing platform built with Helmholtz coils is used to test the uniformity of magnetic permeability of each fan ring. The magnetic permeability of the central area of ​​the fan ring is used as a benchmark. If the error between the magnetic permeability of any area and the benchmark value is ≤5%, it is judged as a qualified fan ring, and unqualified fan rings are rejected to prevent the magnetic performance defects of a single fan ring from affecting the magnetic shielding effectiveness of the entire ring.

[0017] S2: Positioning fixtures assist in splicing

[0018] A positioning fixture is manufactured using non-magnetic stainless steel (magnetic permeability μ≤1.005). The inner circular surface of the fixture is adapted to the outer circular surface of the fan ring, and eight positioning grooves matching the arc surface of the fan ring are evenly opened in the circumference of the fixture. The curvature tolerance of the positioning grooves is controlled to ±0.02mm. The qualified fan rings selected in step S1 are embedded one by one into the positioning grooves. The circumferential position of the fan ring is calibrated by the circumferential scale (accuracy 0.01mm) engraved on the surface of the fixture to ensure that the circumferential misalignment error of adjacent fan rings is ≤0.2mm. After calibration, the fan ring is pushed to make the protrusions of adjacent fan rings align with the grooves. The tight connection is achieved by relying on the interference fit of the tenon structure (interference controlled to 0.01-0.03mm). Only a non-magnetic thermally conductive pad (thickness 0.01mm) needs to be filled in the small gap between the protrusion and the groove to eliminate the gap. No additional adhesive is required to avoid the introduction of magnetic loss or the impact on subsequent disassembly and maintenance by the adhesive.

[0019] S3: Post-assembly performance testing and calibration

[0020] After the ring is assembled, a laser diameter gauge (measurement accuracy ±0.01mm) is used to check the outer diameter of the ring, ensuring that the outer diameter reaches 30cm ±0.5mm. At the same time, a roundness meter is used to check the roundness error of the ring, requiring the roundness error to be ≤0.5mm. After the outer diameter and roundness are qualified, a fluxgate magnetometer (measurement accuracy 0.01μT) is used in a shielding effectiveness testing anechoic chamber (external magnetic field ≤50nT) to check the initial magnetic leakage of the ring, focusing on the magnetic leakage intensity perpendicular to the ring surface, requiring the vertical magnetic leakage to be ≤0.3μT. If the magnetic leakage test fails, the position of the positioning groove of the positioning fixture is adjusted to adjust the tenon and mortise fit clearance, and the ring is reassembled and tested again until the magnetic leakage requirement is met, ensuring that the magnetic shielding performance of the entire ring meets the standard.

[0021] Preferably, the non-magnetic stainless steel material is 316L with a magnetic permeability μ≤1.005.

[0022] Preferably, the non-magnetic thermal pad is made of polytetrafluoroethylene.

[0023] This invention presents a mortise and tenon splicing ferrite magnetic shielding device and method, with "modular fan ring + mortise and tenon interlocking" as the core. The fan ring has protruding tenons and grooves at both ends to form a mortise and tenon structure, which can be disassembled and precisely spliced ​​into a closed ring magnetic shield. Structurally, a stepped surface contact mortise and tenon is preferred. The steps and matching stepped grooves increase the contact area and maintain magnetic flux continuity to suppress vertical magnetic leakage. In multi-layer scenarios, the fan ring mortise and tenon is positioned with the inner circle reference surface as a coaxial reference, which optimizes the multi-layer matching accuracy and eliminates inter-layer magnetic leakage. At the same time, a corresponding splicing method is provided, including fan ring mortise and tenon surface cleaning and screening, non-magnetic stainless steel tooling to assist splicing, and overall ring size and magnetic leakage detection and calibration. Specific materials are preferred to optimize performance. This invention can solve a series of bottlenecks in existing ferrite magnetic shielding, such as the limited overall ring size, brick-type splicing vertical magnetic leakage, multi-layer composite tolerance and inter-layer magnetic leakage, as well as the high cost and poor maintenance flexibility of the overall design.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) This invention takes into account the functions and working requirements of each device, breaks through the bottleneck of size and multi-layer adaptation, breaks the traditional process limitation of the diameter of the whole ferrite ring ≤27cm, and the diameter of the whole ring after splicing exceeds 30cm; at the same time, through the precise design of the tenon and mortise structure, it solves the problem of matching the internal and external tolerances of the multi-layer composite ferrite magnetic shield, and achieves the perfect cooperation of the multi-layer magnetic shield.

[0026] (2) By using a tenon-and-mortise splicing ferrite magnetic shielding device and method, the tenon-and-mortise structure is used to increase the contact area of ​​the fan ring, which not only greatly reduces the vertical magnetic leakage when splicing a single ring, but also eliminates the interlayer magnetic leakage between multiple layers of magnetic shielding, realizing the continuous transition of magnetic flux on the single ring splicing surface and the multi-layer contact surface, and comprehensively improving the magnetic shielding effectiveness.

[0027] (3) The present invention reduces the production cost of large ferrite rings. Based on the modular design that reduces costs and improves efficiency, the cost of the tenon and mortise splicing mold is reduced by more than 40% compared with the overall ring mold. Furthermore, each fan ring can be replaced independently. Compared with the traditional whole ring or multi-layer composite magnetic shielding, the maintenance cost is reduced by 70%, which greatly improves the flexibility and economy of use.

[0028] (4) The present invention can achieve high-precision scene adaptation, and the magnetic noise level is lower than that of the traditional integral ring of the same material thickness. It is adapted to high-precision atomic magnetometers, medical magnetic physiological imaging and other scenarios with strict requirements for magnetic environment, helping atomic magnetometers and other equipment to break through performance bottlenecks and improve instrument sensitivity and biological weak magnetic signal detection level.

[0029] This invention solves a series of bottleneck problems in existing ferrite magnetic shielding technology, including the size limitation caused by process constraints of the overall circular magnetic shielding, the vertical magnetic leakage problem caused by insufficient contact area of ​​the brick-type splicing structure, the internal and external tolerance matching problem and interlayer magnetic leakage defects of multi-layer composite magnetic shielding, as well as the problems of high manufacturing cost of the overall structure and insufficient maintenance flexibility of replacing the whole ring when local damage occurs.

[0030] This invention provides an innovative solution for the need for large-size, multi-level magnetic shielding, and plays a key supporting role in the miniaturization of medical equipment and the performance upgrade of high-precision instruments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of the mortise and tenon type fan ring splicing ferrite magnetic shield of the present invention; in the figure, the overall layout of the mortise and tenon splicing and the connection relationship of the mortise and tenon structure between each fan ring can be seen intuitively, clearly showing that it breaks through the traditional overall ring diameter limitation and achieves large-diameter magnetic shielding by splicing.

[0032] Figure 2 This is a structural schematic diagram of a single tenon-and-mortise ferrite fan ring of a tenon-and-mortise splicing ferrite magnetic shielding device according to the present invention; the diagram shows in detail the external dimensions (in mm) of a single fan ring, as well as the specific shape and size ratio of the tenon and mortise structures (protruding tenons and grooves) on both sides of the fan ring used for splicing.

[0033] Figure 3 This is a partially enlarged schematic diagram of the splicing effect of the mortise and tenon structure of the present invention; the diagram further magnifies the details of the mortise and tenon structure, clearly showing the fitting method of the tenon and groove, the surface flatness, etc., which helps to understand its working principle of increasing the contact area, ensuring the continuity of the magnetic flux interface, and reducing vertical magnetic leakage.

[0034] Figure 4 This is a simulation result diagram of the magnetic flux of the contact surface of the tenon and mortise structure of a tenon and mortise splicing ferrite magnetic shielding device of the present invention. In the figure, the black arrows represent the direction of magnetic flux density, and the cross-sectional color represents the magnetic flux density modulus. The figure clearly shows the magnetic flux continuity of the contact surface of the tenon and mortise structure, and intuitively demonstrates the effect of the tenon and mortise design on the suppression of magnetic leakage.

[0035] Figure 5 This is a photograph of a specific embodiment of the mortise and tenon splicing ferrite magnetic shielding device of the present invention; in the figure, the completed splicing closed ring magnetic shielding body is precisely spliced ​​together by 8 mortise and tenon ferrite fan rings with the same structure.

[0036] Figure 6This is a photograph of a tenon-and-mortise spliced ​​ferrite magnetic shielding device of the present invention applied to a spin-free relaxation exchange atomic magnetometer; in the figure, the white arrow marks the specific location of the tenon-and-mortise spliced ​​ferrite magnetic shielding device applied to the spin-free relaxation exchange atomic magnetometer.

[0037] Figure 7 This is a simulation comparison result of a mortise and tenon type splicing ferrite magnetic shielding device and a brick type splicing ferrite magnetic shielding device according to the present invention.

[0038] Figure 8 These are photographs of a specific embodiment of a single multi-stage step in a mortise and tenon splicing ferrite magnetic shielding device according to the present invention; the left image is a top view of a single multi-stage step fan ring, and the right image is a detail of the mortise and tenon structure splicing surface of the specific embodiment of the multi-stage step.

[0039] Figure 9 The images show a specific embodiment of a mortise and tenon splicing ferrite magnetic shielding device of the present invention, consisting of two multi-level steps. The left image shows details of the mortise and tenon splicing surface of the two multi-level steps, while the right image is a top view of the spliced ​​two multi-level steps. Detailed Implementation

[0040] The present invention will become clearer from the following detailed description with reference to the accompanying drawings and preferred embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0041] The present invention discloses a mortise and tenon type splicing ferrite magnetic shielding device, characterized in that: it includes N mortise and tenon type ferrite fan rings, N≥2, wherein the fan rings are basic shielding units; each fan ring has a pre-set tenon or groove at both ends of its circumference, the tenon and groove forming a mortise and tenon structure, and the mortise and tenon structure enables the detachable splicing of each fan ring to form a closed annular magnetic shield; wherein, the tenon and groove at the splicing point of the fan rings are arranged oppositely to each other for mutual cooperation.

[0042] Among them, the pre-set tenons or grooves at both ends of each fan ring include: a tenon at one end of the fan ring and a groove at the other end; or tenons or grooves at both ends of the fan ring.

[0043] Preferably, one end of the fan ring is provided with a protruding tenon and the other end is provided with a groove; this design only requires several mortise and tenon ferrite fan rings with the same structure to be spliced ​​together to form a closed ring magnetic shield.

[0044] Both ends of the fan ring are provided with protruding tenons or grooves. Specifically, both ends of the first fan ring are provided with protruding tenons, and both ends of the second fan ring are provided with grooves. The first fan ring and the second fan ring are a pair, and several pairs of the first fan ring and the second fan ring are joined together with tenons and mortise to form a closed annular magnetic shield.

[0045] For example, see Figure 1 , Figure 3 and Figure 5 It consists of 8 identical mortise and tenon ferrite fan rings, with a tenon and a groove pre-set at both ends of the circumference of each fan ring. The tenon and groove form a mortise and tenon structure, which enables the fan rings to be detachably and precisely spliced ​​to form a closed annular magnetic shield.

[0046] For example, the dimensions of a single tenon-and-mortise ferrite fan ring can be found in [reference needed]. Figure 2 Those skilled in the art should understand that other sizes of tenon-and-mortise ferrite fan rings can be designed according to target requirements, which will not be shown here.

[0047] In one embodiment, the device includes multiple multi-layer tenon-and-mortise ferrite fan rings. Both ends of the multi-layer tenon-and-mortise ferrite fan rings are respectively provided with staggered tenons and grooves. The tenons and grooves form a tenon-and-mortise structure. The tenon-and-mortise structure is a stepped surface contact structure. The tenon-and-mortise structure enables the detachable splicing of each fan ring to form a closed multi-layer annular magnetic shield. The tenons and grooves at the splicing points of the fan rings are arranged oppositely to cooperate with each other.

[0048] Those skilled in the art should understand that the staggered tenons and grooves at both ends of the multi-layer tenon-and-mortise ferrite fan ring can be consistent or inconsistent. It is only necessary to ensure that the tenons and grooves at the splicing points of two adjacent multi-layer tenon-and-mortise ferrite fan rings are set oppositely to cooperate with each other. Preferably, the tenons or grooves at corresponding positions at both ends of the multi-layer tenon-and-mortise ferrite fan ring are opposite. This design only requires several multi-layer tenon-and-mortise ferrite fan rings with consistent structures to form a closed multi-layer annular magnetic shield through tenon-and-mortise splicing.

[0049] See Figure 8 and Figure 9 An exemplary embodiment is shown of a three-layer tenon-and-mortise ferrite fan ring (the number of layers is determined along the thickness direction of the fan ring), wherein the tenons or grooves at corresponding positions at both ends of the three-layer tenon-and-mortise ferrite fan ring are opposite (see [reference]). Figure 8 In the right image, the upper left part is a tenon, and the corresponding position on the other end is a groove; the middle left part is a groove, and the corresponding position on the other end is a tenon; the lower left part is a tenon, and the corresponding position on the other end is a groove; the upper right part is a groove, and the corresponding position on the other end is a tenon; the middle right part is a tenon, and the corresponding position on the other end is a groove; the lower right part is a groove, and the corresponding position on the other end is a tenon. Several of these three-layer tenon-and-mortise ferrite fan rings can be joined together to form a closed three-layer annular magnetic shield.

[0050] Example:

[0051] like Figure 6As shown, this embodiment illustrates the magnetic shielding requirements of a high-precision atomic magnetometer (magnetic shielding diameter ≥ 30cm, magnetic noise ≤ 5fT / Hz¹ / ² in the 1Hz frequency band) using the mortise and tenon splicing ferrite magnetic shielding device and method of the present invention as an example. The specific implementation parameters and process steps are as follows:

[0052] In specific implementation, the single-piece tenon-and-mortise type ferrite fan ring is made of high-permeability Mn-Zn ferrite material (model PC40), and its performance indicators meet the following requirements: initial permeability μ i ≥5000 (Test conditions: frequency 1kHz, magnetic field strength 0.1mT), saturation magnetic flux density B s ≥0.5T (test conditions: room temperature 25℃), magnetic loss P cv ≤250mW / cm³ (test conditions: frequency 10kHz, magnetic flux density 0.2T) to ensure magnetic shielding effectiveness and stability.

[0053] In specific implementation, such as Figure 2 As shown, the inner radius of a single fan ring is R1 = 11cm, the outer radius is R2 = 15cm (thickness 4cm), the central angle is α = 45° (360° / 8), and the dimensions of the tenons at both ends in the circumferential direction are: height 2cm, width 2.5cm. The groove depth is the same as the tenon height, and the surface roughness R of the tenon / groove is... a ≤0.8μm, to avoid surface burrs affecting the contact effect.

[0054] In practice, the fan ring is prepared by a "dry pressing + high temperature sintering" process: first, ferrite powder (particle size ≤ 5μm) is dry pressed under a pressure of 20MPa, and then sintered in a reducing atmosphere (N2:H2=95:5) at 1300℃±10℃ for 4h, with the cooling rate controlled at 5℃ / min to ensure that the material density is ≥95% and to avoid uneven magnetic permeability caused by internal pores.

[0055] In practice, the tenon and mortise surfaces of each fan ring are cleaned before splicing using ultrasonic cleaning with pure water at a frequency of 40kHz for 10 minutes. The uniformity of magnetic permeability of each fan ring is tested using a Helmholtz coil (error ≤5% is acceptable), and unqualified units are removed to avoid affecting the overall shielding performance of the ring.

[0056] In practice, a non-magnetic stainless steel (magnetic permeability μ≤1.005) positioning fixture is used to assist in the splicing. The fixture has 8 positioning grooves that match the arc surface of the fan ring (arc tolerance ±0.02mm). Qualified fan rings are embedded into the positioning grooves one by one. The position of the fan ring is calibrated by the circumferential scale of the fixture to ensure that the circumferential misalignment error of adjacent fan rings is ≤0.2mm. During splicing, the interference fit of the mortise and tenon structure (interference amount 0.01-0.03mm) is used to achieve a tight connection. Except for filling the gaps, no additional adhesive is required.

[0057] In practice, after the splicing is completed, the outer diameter of the entire ring is checked to ensure that the outer diameter reaches 30cm±0.5mm and the roundness error is ≤0.5mm; at the same time, the initial magnetic leakage of the entire ring is checked by a fluxgate magnetometer to ensure that the magnetic leakage in the vertical direction is ≤0.3μT. If it is not qualified, it is recalibrated by adjusting the tenon and mortise fit gap.

[0058] Taking the three-layer annular magnetic shield of the present invention as an example, the present invention, through the above-mentioned structural design and implementation process, forms significant technical advantages in magnetic performance, economy, maintainability and applicability, as detailed below:

[0059] The magnetic properties of this invention exhibit a magnetic noise level of 3.8-4.0 fT / Hz in the 1Hz-100Hz frequency band. 1 / 2 Compared to traditional 27cm thick monolithic circular ferrite magnetic shielding of the same material (magnetic noise 4.5-4.8 fT / Hz), 1 / 2 It reduces noise by 15%-20% compared to traditional multi-layer composite magnetic shielding (magnetic noise 5.2-5.5 fT / Hz). 1 / 2 This reduces noise levels by 25%-30%, meeting the requirements of high-precision atomic magnetometers, biological weak magnetic imaging, and other equipment for ultra-low magnetic noise environments. (See also...) Figure 4 and Figure 7 Simulation results show that when the assembly error is 0.1mm, the central magnetic field of the ferrite magnetic shielding device using mortise and tenon splicing is 11.088nT, while that of the magnetic shielding using brick-type splicing is 18.845nT. The comparison demonstrates that the mortise and tenon splicing structure can more effectively suppress magnetic leakage, significantly improve magnetic shielding efficiency, and drastically reduce the magnetic field strength in the central region, better meeting the stringent requirements of medical equipment and high-precision atomic magnetometers for low-magnetic environments. Vertical magnetic leakage is ≤0.3μT, and interlayer magnetic leakage is ≤0.5μT, representing a more than 60% improvement in magnetic leakage suppression compared to traditional brick-type splicing (vertical magnetic leakage ≥0.8μT) and traditional multi-layer composite (interlayer magnetic leakage ≥1.2μT). This improvement is attributed to the mortise and tenon structure design, which effectively avoids magnetic flux breakage and leakage at the splicing and interlayer interfaces.

[0060] The modular fan-ring design of this invention significantly reduces mold size. For example, a 30cm diameter ring requires a traditional integral ring mold, necessitating the development of new equipment such as a high-tonnage die-casting machine, with estimated costs exceeding one million yuan. This invention's single-piece fan-ring mold only needs to cover 1 / 8 of the ring size, with a total mold development cost of approximately 48,000 yuan, greatly reducing costs. Traditional integral rings, if local magnetic permeability is unsatisfactory (e.g., in a certain region μ...), can lead to a significant reduction in costs. i <4500), the entire ring needs to be scrapped, and the material loss rate is ≥15%; the present invention uses single-piece fan ring pre-inspection to remove only unqualified units (loss rate ≤1%), thereby increasing the material utilization rate by more than 90% and significantly reducing production costs.

[0061] This invention relies on the interference fit of the mortise and tenon structure to achieve splicing. The disassembly and replacement of a single fan ring does not require damage to the entire ring structure. The faulty fan ring can be separated by a special non-magnetic pry tool. The replacement process takes ≤30 minutes. Compared with the traditional whole ring replacement, which requires disassembling the equipment and removing the entire ring and takes 2-3 hours, the efficiency is improved by more than 80%.

[0062] The structural design of this invention allows for adjustment of the number of fan rings (e.g., 6 or 10 rings) and their thickness (e.g., 3cm or 5cm) according to actual needs, adapting to magnetic shielding requirements of different diameters (30cm-50cm) and different numbers of layers (1-3 layers). It can be applied not only to high-precision atomic magnetometers but also extended to medical devices (e.g., fetal magnetocardiography), electronic instruments (e.g., superconducting quantum interference devices), and other fields, solving the technical bottlenecks of traditional magnetic shielding in large-size, multi-layer scenarios and possessing broad engineering application value.

[0063] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A mortise and tenon joint type spliced ferrite magnetic shielding device, characterized in that: It includes N mortise-and-tenon ferrite fan rings, where N≥2, and the fan rings are basic shielding units; convex tenons or grooves are preset at both circumferential ends of each fan ring, and the convex tenons and grooves form a mortise-and-tenon structure. Through this mortise-and-tenon structure, detachable splicing of each fan ring is achieved to form a closed annular magnetic shielding body; among them, the convex tenons and grooves at the splicing position of the fan rings are arranged oppositely to cooperate with each other; the mortise-and-tenon structure is a stepped surface contact structure, and the height of each step is 1 / 2 - 1 / 3 of the thickness of the fan ring, and the width is 1 / 8 - 1 / 4 of the arc length of the fan ring; a stepped groove matching the convex tenon is correspondingly opened in the groove, and the fitting gap between the convex tenon and the groove is controlled within 0.02 - 0.05 mm by the precision of a preset mold; the mortise-and-tenon structure is used to increase the contact area of the fan ring, enhance the continuity of magnetic flux, and suppress vertical magnetic leakage and interlayer magnetic leakage.

2. The device according to claim 1, wherein: For the multi-layer composite magnetic shielding scenario, a coaxial positioning reference is added to the mortise-and-tenon structure of each layer of fan rings. Taking the inner circular reference surface of the fan ring as the positioning reference, the outer circular surface convex tenon of the inner layer fan ring and the inner circular surface groove of the outer layer fan ring form a precise match in terms of radial dimension and circumferential position.

3. A splicing method for the mortise and tenon type splicing ferrite magnetic shielding device according to any one of claims 1-2, characterized in that, It includes the following steps: S1: Pretreatment and screening of fan rings. Clean the mortise-and-tenon surfaces of single fan rings, detect the magnetic permeability uniformity of single fan rings, and screen qualified fan rings. S2: Auxiliary splicing with a positioning tooling. Use a non-magnetic stainless steel positioning tooling, embed the qualified fan rings into the tooling positioning grooves and calibrate their positions, and achieve a tight connection through the interference fit of the mortise-and-tenon structure. S3: Performance detection and calibration after splicing. Detect the dimensional accuracy and magnetic leakage performance of the whole ring. If it is unqualified, adjust the mortise-and-tenon fitting gap and then splice and detect again.

4. The method according to claim 3, wherein: In step S1, pure water is used as the cleaning medium for the cleaning treatment, and ultrasonic cleaning equipment is used for cleaning; the magnetic permeability uniformity detection is based on the magnetic permeability of the central area of the fan ring, and fan rings with errors within a preset range are screened.

5. The method according to claim 3, wherein: In step S2, the positioning tooling is circumferentially provided with positioning grooves matching the arc surfaces of the fan rings, and the positions of the fan rings are calibrated through the circumferential scale of the tooling. After the convex tenons and grooves of adjacent fan rings are butted, a non-magnetic heat-conducting gasket is filled in the tiny gap.

6. The method according to claim 3, characterized in that: In step S3, detect the outer diameter dimension and roundness error of the whole ring, and use a magnetometer to detect the magnetic leakage intensity of the whole ring, with a focus on detecting the magnetic leakage perpendicular to the ring surface direction.

7. The method according to claim 3, wherein: The magnetic permeability of the non-magnetic stainless steel ≤1.005; The non-magnetic stainless steel material is 316L.

8. The method according to claim 5, wherein: The non-magnetic heat-conducting gasket material is polytetrafluoroethylene.

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