Method and system for demagnetizing magnetic shielding device based on controllable magnetic coupling attenuation

Abstract

The invention relates to the technical field of precise electromagnetic regulation and control and extremely weak magnetic environment construction, and discloses a magnetic shielding device demagnetization method and system based on controllable magnetic coupling attenuation, a primary excitation unit and a secondary induction unit are coupled through a magnetic field, and the spatial magnetic coupling coefficient between the primary excitation unit and the secondary induction unit is continuously adjustable. The spatial magnetic coupling coefficient between the secondary induction coil and the constant power frequency magnetic field source is continuously changed through the mutual inductance regulation and control unit, so that the secondary induction unit passively generates pure sinusoidal current of which the amplitude strictly follows the attenuation law of the spatial magnetic coupling coefficient. Through programming control of the space magnetic coupling coefficient, linear or exponentially attenuated demagnetization current can be generated to act on the permalloy shielding body, so that efficient demagnetization is realized. According to the method, the inherent direct-current bias and high-frequency switching noise of a traditional electronic demagnetization power supply are substantially reduced fundamentally, the output current spectrum is pure, demagnetization is thorough, and the residual magnetic field is remarkably reduced.

Description

A demagnetizing method and system for a magnetic shielding device based on controllable magnetic coupling attenuation Technical Field

[0001] This invention relates to the field of precision electromagnetic control and the construction of extremely weak magnetic environments, specifically to a demagnetization method and system for a magnetic shielding device based on controllable magnetic coupling attenuation. Background Technology

[0002] The magnetically shielded chamber is a core facility that shields against external magnetic field interference and provides an ultra-low noise, static magnetic environment for high-precision magnetic measurements (such as magnetoencephalography (MEG) and superconducting quantum interference devices (SQUIDs). To ensure its performance, the shield, made of a soft magnetic material with high permeability (such as permalloy), must be periodically demagnetized to completely eliminate residual magnetism and internal magnetic noise, thereby ensuring the high stability and purity of the magnetic field environment inside the chamber.

[0003] In existing technologies, the mainstream approach typically uses an electronically programmable AC power supply to drive the demagnetizing coil. Demagnetization is achieved by actively controlling the power output to generate a gradually decaying power frequency current. However, this approach suffers from the inherent limitations of active electronic circuits, resulting in the following fundamental and insurmountable drawbacks:

[0004] 1. DC bias contamination: The power amplifier (whether linear or switching) in the final stage of the demagnetizing power supply has inherent DC offset voltage and current. This DC component does not synchronously return to zero when the demagnetizing current waveform decays to zero, but instead transforms into a fixed residual bias magnetic field after demagnetization. This fixed magnetic field directly contaminates the "magnetic zero point" used as the measurement reference inside the shielded chamber, becoming an uncalibrable source of systematic error.

[0005] 2. High-frequency electromagnetic noise (EMI) injection: To achieve precise and efficient control of current amplitude, such power supplies generally employ switching technologies such as pulse width modulation (PWM) or phase control. In addition to the fundamental power frequency, their output current spectrum inevitably contains abundant high-frequency switching harmonics and broadband noise. This high-frequency noise energy can easily be conducted through the power lines and coupled into the shielded enclosure, severely interfering with the ultra-sensitive detectors operating inside, manifesting as an increase in background noise or signal distortion.

[0006] Therefore, a novel demagnetization technology is urgently needed to avoid the problems of DC bias pollution and high-frequency electromagnetic noise injection caused by the inherent characteristics of electronic circuits in existing technologies, and to generate a demagnetizing current with smooth amplitude decay, no DC component, and pure spectrum, so as to achieve efficient and deep demagnetization of magnetic shielding devices. Summary of the Invention

[0007] This invention provides a demagnetization method and system for a magnetic shielding device based on controllable magnetic coupling attenuation, in order to avoid the problems of DC bias pollution and high-frequency electromagnetic noise injection introduced by the inherent characteristics of electronic circuits in the prior art.

[0008] In a first aspect, the present invention provides a demagnetizing system for a magnetic shielding device based on controllable magnetic coupling attenuation. The system includes: a primary excitation unit, a secondary induction unit, and a mutual inductance control unit. The primary excitation unit and the secondary induction unit are coupled via a magnetic field. The spatial magnetic coupling coefficient between the primary excitation unit and the secondary induction unit is continuously adjustable. The output terminal of the secondary induction unit is connected to the demagnetizing coil of the magnetic shielding device. The primary excitation unit generates an alternating main magnetic field with stable frequency and amplitude. The mutual inductance control unit drives the relative spatial configuration or magnetic circuit state between the secondary induction unit and the primary excitation unit to change according to a predetermined law based on a preset timing function, causing the spatial magnetic coupling coefficient to monotonically attenuate from its design maximum value to a zero state. The zero state refers to the spatial magnetic coupling coefficient being zero, or the spatial magnetic coupling coefficient fluctuating within a positive value range near zero with its fluctuation amplitude not exceeding a preset threshold. The secondary induction unit senses and generates a sinusoidal current with an amplitude that attenuates synchronously with the spatial magnetic coupling coefficient. This sinusoidal current acts on the shielding device through the demagnetizing coil, thereby demagnetizing the magnetic shielding device.

[0009] This invention provides a demagnetizing system based on controllable magnetic coupling attenuation of a magnetic shielding device. By continuously changing the spatial magnetic coupling coefficient between the secondary induction coil and a constant power frequency magnetic field source through a mutual inductance control unit, the secondary induction unit passively generates a pure sinusoidal current whose amplitude strictly follows the attenuation law of the spatial magnetic coupling coefficient. Through programmed control of the spatial magnetic coupling coefficient, a demagnetizing current with linear or exponential decay can be generated and applied to the permalloy shielding body, thereby achieving efficient demagnetization. This method fundamentally and significantly reduces the inherent DC bias and high-frequency switching noise of traditional electronic demagnetizing power supplies, resulting in a pure output current spectrum, thorough demagnetization, and a significantly reduced residual magnetic field.

[0010] In one optional implementation, the preset timing function is a linear function or an exponentially decaying function.

[0011] In one optional implementation, the coupling differential equations between the primary excitation unit and the secondary induction unit are as follows:

[0012] in, This is the power supply voltage for the primary excitation unit. The circuit resistance of the primary excitation unit. This refers to the loop current of the primary excitation unit. The loop inductance of the primary excitation unit. The spatial magnetic coupling coefficient, This is the loop current of the secondary sensing unit. The loop resistance of the secondary sensing unit. The loop inductance of the secondary sensing unit, For time.

[0013] In one optional implementation, the coupling magnetic flux between the primary excitation unit and the secondary induction unit is:

[0014] The spatial magnetic coupling coefficient between the primary excitation unit and the secondary induction unit is:

[0015] in, This refers to the coupling magnetic flux between the primary excitation unit and the secondary induction unit. The location of the secondary sensing unit. The number of coil turns of the secondary induction unit. To generate a magnetic field distribution in space for the primary excitation unit, The coil normal of the secondary induction unit. The effective area of ​​the coil of the secondary induction unit. This is the constant amplitude of the primary excitation unit.

[0016] In one optional embodiment, the primary excitation unit includes: an iron core, an excitation coil, and a current stabilizing circuit, wherein the excitation coil is uniformly wound around the outer periphery of the magnetic circuit of the iron core, the excitation coil is supplied with an industrial frequency AC power supply, and a current stabilizing circuit is connected in series in the power supply circuit of the excitation coil.

[0017] In one optional embodiment, the secondary induction unit includes a secondary induction coil and a monitoring coil, wherein the secondary induction coil is fixedly coupled to the monitoring coil and arranged coaxially, the secondary induction coil is used to induce a sinusoidal current whose amplitude decays synchronously with the spatial magnetic coupling coefficient, and the monitoring coil is used to non-invasively monitor the decay process of the demagnetizing current.

[0018] In one optional embodiment, the mutual inductance control unit includes: a displacement mechanism, a position sensor, and a position closed-loop controller. The displacement mechanism is drively connected to the secondary sensing unit and drives the secondary sensing unit to perform linear displacement or rotation about an axis relative to the primary excitation unit, thereby adjusting the spatial magnetic coupling coefficient. The position sensor is mounted on the moving end of the displacement mechanism and is used to collect the actual position data of the secondary sensing unit in real time and transmit the position feedback signal to the position closed-loop controller. The position closed-loop controller pre-stores the feedback signal received from the position sensor and compares it in real time with a preset curve, outputting a pulse width modulation control signal to the displacement mechanism.

[0019] Secondly, the present invention provides a demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation, and a demagnetization system for a magnetic shielding device based on controllable magnetic coupling attenuation according to the first aspect above or any corresponding embodiment thereof. The method includes: adjusting the primary excitation unit to a spatial configuration that is fully coupled with the secondary induction unit, so that the spatial magnetic coupling coefficient between the two reaches the design maximum value; activating the power supply circuit of the primary excitation unit to establish an initial saturated magnetic field around the shield of the magnetic shielding device; triggering the mutual inductance control unit to drive the relative magnetic coupling between the secondary induction unit and the primary excitation unit according to a preset timing function. The spatial configuration or magnetic circuit state changes according to a predetermined law, causing the spatial magnetic coupling coefficient to monotonically decay from its design maximum value to zero. The zero state refers to the spatial magnetic coupling coefficient being zero, or the spatial magnetic coupling coefficient fluctuating within a positive range near zero with its fluctuation amplitude not exceeding a preset threshold. Based on the magnetic field coupling between the primary excitation unit and the secondary induction unit and the decay change of the spatial magnetic coupling coefficient, a sinusoidal current with an amplitude that decays synchronously with the spatial magnetic coupling coefficient is induced in the secondary induction unit. The sinusoidal current acts on the shielding device through the demagnetizing coil to demagnetize the magnetic shielding device.

[0020] This invention provides a demagnetizing method for a magnetically shielded device based on controllable magnetic coupling attenuation. By continuously changing the spatial magnetic coupling coefficient between the secondary induction coil and a constant power frequency magnetic field source, the secondary induction unit passively generates a pure sinusoidal current whose amplitude strictly follows the attenuation law of the spatial magnetic coupling coefficient. Through programmed control of the spatial magnetic coupling coefficient, a demagnetizing current with linear or exponential decay can be generated and applied to the permalloy shield, thereby achieving efficient demagnetization. This method fundamentally and significantly reduces the inherent DC bias and high-frequency switching noise of traditional electronic demagnetizing power supplies, resulting in a pure output current spectrum, thorough demagnetization, and a significantly reduced residual magnetic field.

[0021] In an optional embodiment, the method further includes: when the spatial magnetic coupling coefficient decays to zero, stopping the control action of the mutual inductance control unit, so that the secondary induction unit and the primary excitation unit enter a completely decoupled state; after maintaining the decoupled state for multiple power cycles, cutting off the power supply circuit of the primary excitation unit.

[0022] In one optional implementation, the method further includes: acquiring the loop current of the primary excitation unit in real time and comparing the loop current with a preset current; and dynamically adjusting the parameters of the current stabilizing circuit based on the comparison result. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 is a principle block diagram of a demagnetization system for a magnetic shielding device based on controllable magnetic coupling attenuation according to an embodiment of the present invention; Figure 2 is a flowchart of a demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation according to an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0027] This invention provides a demagnetization system for a magnetic shielding device based on controllable magnetic coupling attenuation, as shown in Figure 1. It includes a primary excitation unit, a secondary induction unit, and a mutual inductance control unit. The primary excitation unit and the secondary induction unit are coupled via a magnetic field, and the spatial magnetic coupling coefficient between them is continuously adjustable. The output of the secondary induction unit is connected to the demagnetizing coil of the magnetic shielding device. The primary excitation unit generates an alternating main magnetic field with stable frequency and amplitude. The mutual inductance control unit drives the relative spatial configuration or magnetic circuit state between the secondary induction unit and the primary excitation unit to change according to a predetermined law based on a preset timing function, causing the spatial magnetic coupling coefficient to monotonically decay from its design maximum value to zero. Zero refers to a spatial magnetic coupling coefficient of zero, or a spatial magnetic coupling coefficient fluctuating within a positive range near zero with a fluctuation amplitude not exceeding a preset threshold. The secondary induction unit senses and generates a sinusoidal current whose amplitude decays synchronously with the spatial magnetic coupling coefficient. This sinusoidal current acts on the shielding device through the demagnetizing coil, thereby demagnetizing the magnetic shielding device.

[0028] Specifically, the primary excitation unit is a constant current alternating magnetic field generation module, whose function is to output an amplitude. and angular frequency Highly stable alternating magnetic flux Its internal implementation mainly involves the core material, the number of coil turns, and the current-stabilizing circuit. Here, it is only necessary to ensure that its output characteristic is an alternating main magnetic field with a constant (or approximately constant) amplitude. This unit provides a high-permeability magnetic circuit through the core, ensuring that the magnetic flux generated by the excitation coil is concentrated and has a sufficiently large amplitude, thereby determining the main magnetic flux. Spatial distribution and intensity; it is usually connected to the mains power U P (corresponding angular frequency) This forms a stable magnetic field excitation source.

[0029] The core function of the mutual inductance control unit is to receive preset timing function commands. , usually for example The functional relationship is given, and a physical quantity with a real-time spatial magnetic coupling coefficient of M(t) is output, satisfying the following conditions: The functional relationship is achieved internally through various physical mechanisms such as linear displacement, rotation about an axis, and adjustment of magnetic circuit parameters. Essentially, it represents an abstract function instruction. A conversion module that transforms data into a specific physical quantity M(t). The preset timing function is either a linear function or an exponentially decaying function.

[0030] The secondary induction unit contains a secondary induction coil, whose coil frame is typically made of a non-magnetic material to avoid introducing additional nonlinear hysteresis effects and ensure the deterministic nature of the secondary circuit parameters. The output of the secondary induction unit is connected to a demagnetizing coil on a magnetically shielded barrel or shielded cabin made of permalloy or nanocrystalline soft magnetic material. The core function of this unit is to form a magnetic field coupling with the primary excitation unit, and to output a decaying induced current based on the real-time M(t) output by the mutual inductance control unit. Its core relationship is determined by Faraday's law of electromagnetic induction, namely... By applying a value from the design maximum M to M(t) max A preset timing function that smoothly and monotonically decays to near zero can passively and synchronously induce a pure sinusoidal current whose amplitude strictly follows the decay law in the secondary circuit connected to the demagnetizing coil.

[0031] The spatial magnetic coupling coefficient M(t) between the two coupled coils of the primary excitation unit and the secondary induction unit is established as a directly programmable real-time control variable. By changing the spatial relative configuration between the two coupled coils through the actuator of the mutual inductance control unit, M(t) is precisely controlled to smoothly decay from its maximum value to near zero according to a preset timing function. This is based on Faraday's law of electromagnetic induction. This controlled change in mutual inductance will actively generate a decaying alternating current in the secondary induction coil with a constant frequency and an amplitude envelope that strictly follows the change of M(t). This current can directly drive the demagnetizing coil surrounding the magnetic shielding barrel or magnetic shielding chamber.

[0032] This invention provides a demagnetizing system based on controllable magnetic coupling attenuation of a magnetic shielding device. By continuously changing the spatial magnetic coupling coefficient between the secondary induction coil and a constant power frequency magnetic field source through a mutual inductance control unit, the secondary induction unit passively generates a pure sinusoidal current whose amplitude strictly follows the attenuation law of the spatial magnetic coupling coefficient. Through programmable control of the spatial magnetic coupling coefficient, a demagnetizing current with linear or exponential decay can be generated and applied to the permalloy shielding body, thereby achieving efficient demagnetization. This method fundamentally and significantly reduces the inherent DC bias and high-frequency switching noise of traditional electronic demagnetizing power supplies, resulting in a pure output current spectrum, thorough demagnetization, and a significant reduction in residual magnetic field. The system structure is simplified and reliable, making it particularly suitable for ultra-high sensitivity measurement systems with extremely demanding electromagnetic environment requirements, such as magnetoencephalography (MEG) and superconducting quantum interference devices.

[0033] In one alternative implementation, the complete electromagnetic behavior of the system can be described by the following coupled circuit equations. Let the primary loop parameter be resistance. With inductance The secondary circuit parameter is resistance. With inductance The coupling differential equations between the primary excitation unit and the secondary induction unit are as follows:

[0034] in, This is the power supply voltage for the primary excitation unit. The circuit resistance of the primary excitation unit. This refers to the loop current of the primary excitation unit. The loop inductance of the primary excitation unit. The spatial magnetic coupling coefficient, This is the loop current of the secondary sensing unit. The loop resistance of the secondary sensing unit. The loop inductance of the secondary sensing unit, For time.

[0035] Specifically, to achieve precise control of the demagnetizing current waveform, the amplitude of the primary excitation magnetic field must be kept constant during the demagnetizing process. This can be achieved by connecting a large inductive reactance in series in the primary circuit. Under this condition, the primary current can be approximated as a stable sinusoidal quantity independent of load and mutual inductance changes:

[0036] in, For a constant amplitude, This is the angular frequency of the power supply.

[0037] The above Substituting into the secondary equation, we obtain a result containing only secondary variables. With spatial magnetic coupling coefficient The equation:

[0038] Expand the differential terms:

[0039] Define the system's two key time scales, with the communication cycle as follows:

[0040] The characteristic time of mutual inductance change is:

[0041] The effective implementation of this application depends on adiabatic slow-change conditions, that is, the change in mutual inductance must be slow enough to satisfy:

[0042] Or equivalent:

[0043] Therefore, the equation can be simplified to:

[0044] The first-order linear steady-state particular solution of the equation (i.e., the main component of the demagnetizing current) is:

[0045] Among them, the current amplitude is The system gain constant is The impedance angle is .

[0046] This relation This indicates that the instantaneous amplitude of the secondary demagnetizing current is affected by the spatial magnetic coupling coefficient. Real-time, linear modulation. Therefore, the problem of generating complex attenuating current waveforms is precisely transformed into modulation of the spatial magnetic coupling coefficient. The problem of programming time-series trajectories.

[0047] In practical systems, by The small additional current caused by the term It can be obtained from the complete equation. Its magnitude satisfies:

[0048] It can be seen that the frequency components of this error current are mainly distributed in It is near its lower harmonics, but its amplitude is relative to the main current. Suppressed approximately The error term is several times higher, and importantly, it does not contain any DC component.

[0049] Under the premise that the change in the spatial magnetic coupling coefficient is sufficiently slow, the demagnetizing current generated by this system It is a frequency locked to the power supply frequency. The amplitude envelope strictly follows the changes of the programmed function, and the harmonic distortion is extremely low. This mathematical characteristic theoretically guarantees the accuracy, repeatability, and electromagnetic compatibility of the demagnetization process.

[0050] In one alternative implementation, it is assumed that the primary coil generates a magnetic field distribution in space as follows: The secondary coil is The turn, whose center moves along the x-axis, is located at... The coil normal is The coupling magnetic flux between the primary excitation unit and the secondary induction unit is:

[0051] The spatial magnetic coupling coefficient between the primary excitation unit and the secondary induction unit is:

[0052] in, This refers to the coupling magnetic flux between the primary excitation unit and the secondary induction unit. The location of the secondary sensing unit. The number of coil turns of the secondary induction unit. To generate a magnetic field distribution in space for the primary excitation unit, The coil normal of the secondary induction unit. The effective area of ​​the coil of the secondary induction unit. This is the constant amplitude of the primary excitation unit.

[0053] Specifically, it is generally obtained through calibration. Curve. Displacement is controlled by motion commands. according to Exercise, among which Based on the above design logic, this application constructs and implements an electromagnetic induction system with the spatial magnetic coupling coefficient M(t) as the core time-controlled variable. Through precise mapping and closed-loop control of displacement-mutual inductance, the attenuation law of the demagnetizing current is ensured to be highly consistent with the design target.

[0054] Furthermore, supported by the aforementioned theoretical model, a systematic parameter matching and optimization design needs to be completed. Its core objective is to ensure that the demagnetization process simultaneously meets the triple requirements of sufficient field strength, reasonable duration, and optimal energy efficiency. To achieve the optimal demagnetization effect, the key parameters of the system need to be collaboratively designed and optimized based on the following physical constraints: 1. Initial demagnetization field strength constraint: at the start of demagnetization, Spatial magnetic coupling coefficient Peak intensity of alternating magnetic field acting on shielding material It must significantly exceed the coercivity of the material. This is to ensure that all magnetic domains can be effectively flipped. From secondary peak current Geometric factors of the demagnetizing coil Decision, that is Therefore, the design must meet the following strength requirements: .in, The safety factor, typically determined based on material properties and process requirements, is used in engineering. This inequality defines the required maximum peak value of the secondary current. The lower limit.

[0055] 2. Maximum spatial magnetic coupling coefficient Determination and Implementation: Based on the core relational formula The system constant At power frequency Main magnetic flux amplitude and total impedance of secondary circuit Given that the goal is known or predictable, we can work backward to deduce how to achieve it. Required maximum spatial magnetic coupling coefficient This value is achieved by optimizing the following physical factors: 1) the ampere-turns of the primary excitation unit. 2) The cross-sectional area of ​​the iron core, the length of the magnetic circuit, and the permeability of its material, in order to maximize... 3) Dimensions and number of turns of the secondary induction coil in the "fully coupled" configuration And its spatial overlap with the primary excitation magnetic field.

[0056] 3. Total decay time Engineering design: Total duration of the demagnetization process This is a key process parameter. It depends on the condition that the change in mutual inductance is sufficiently slow. It must be much longer than the power cycle. For large magnetic shielding structures, a timeframe between 30 seconds and several minutes is typically selected based on their size, material thickness, and number of layers. Longer [timeframes]... It facilitates the full and uniform relaxation of magnetic domains, thereby obtaining a lower final remanence, but it will reduce processing efficiency. The selection of the actuator directly determines the speed planning of the actuator.

[0057] 4. Secondary circuit impedance Optimization: for given incentive conditions ( , Maximize the initial demagnetizing current Efforts should be made to minimize the total impedance magnitude of the secondary circuit. Specific measures include: 1) using wires with a sufficiently large cross-sectional area to wind the demagnetizing coil and connecting circuits to reduce resistance. 2) Optimize the geometry of the demagnetizing coil (e.g., optimize the wire diameter and number of turns). While meeting the requirements for coverage and field uniformity, avoid excessive inductance. Too large, to prevent infection resistance This becomes dominant, thus limiting the current amplitude. The goal is to make the circuit moderately inductive or close to resistive at the operating frequency to maximize power transfer.

[0058] In one optional embodiment, the primary excitation unit includes: an iron core, an excitation coil, and a current-stabilizing circuit. The excitation coil is uniformly wound around the outer periphery of the magnetic circuit of the iron core, and is supplied with an industrial frequency AC power supply. A current-stabilizing circuit is connected in series in the power supply circuit of the excitation coil.

[0059] Specifically, the iron core is made of a soft magnetic material with high permeability to construct a low-resistivity closed magnetic circuit. This efficiently confines the magnetic field generated by the excitation coil within the iron core, significantly reducing magnetic flux leakage. This ensures that the magnetic field strength meets the requirements for secondary induced current generation while also making the magnetic field distribution more concentrated and uniform. The outer periphery of the iron core's magnetic circuit specifically refers to its effective magnetic conduction path. The excitation coil is wound in this region to ensure that the magnetic field generated by the coil penetrates the iron core's magnetic circuit to the maximum extent, maximizing magnetic flux utilization. Simultaneously, the excitation coil is wound around the outer periphery of the iron core's magnetic circuit with equal spacing and number of layers, ensuring a uniform magnetic field distribution within the iron core's magnetic circuit after energization, thereby providing a stable coupling magnetic flux for the secondary induction unit.

[0060] When the excitation coil is connected to the power frequency AC power supply, according to Ampere's circuital law, an alternating magnetic field synchronized with the current frequency (power frequency 50Hz) will be generated in the iron core magnetic circuit. The current stabilizing circuit is connected in series with the excitation coil to form a power supply circuit, which can directly control the current flowing through the coil in real time in a closed loop, offsetting disturbances such as power grid fluctuations and load impedance changes, and ensuring that the amplitude of the excitation current is constant.

[0061] Furthermore, a real-time feedback closed-loop control module based on a Hall current sensor is added to the primary excitation unit. This control module can dynamically compensate for disturbances such as grid voltage fluctuations and changes in the primary-side reflected equivalent impedance caused by variations in the spatial magnetic coupling coefficient M(t), ensuring the primary current amplitude throughout the demagnetization process. and the main magnetic flux it generates By maintaining a constant value, the potential interference of the aforementioned disturbances on the consistency of the output demagnetizing current waveform is fundamentally avoided, providing a core guarantee for the purity and accuracy of the attenuation law of the secondary induced current.

[0062] In one optional embodiment, the secondary induction unit includes a secondary induction coil and a monitoring coil. The secondary induction coil and the monitoring coil are fixedly coupled and coaxially arranged. The secondary induction coil is used to induce a sinusoidal current whose amplitude decays synchronously with the spatial magnetic coupling coefficient. The monitoring coil is used to non-invasively monitor the decay process of the demagnetizing current.

[0063] Specifically, the secondary induction coil, based on the principle of electromagnetic induction, induces a pure sinusoidal current whose amplitude decays smoothly and synchronously with the spatial magnetic coupling coefficient. It uses non-magnetic materials to avoid introducing nonlinear hysteresis effects and ensure the determinism of the secondary circuit parameters. When the primary excitation unit provides a stable alternating main magnetic field, and the mutual inductance control unit drives M(t) to decay monotonically from its maximum value, the coupling magnetic flux of the secondary induction coil changes synchronously with M(t). According to Faraday's law of electromagnetic induction, a sinusoidal current with a frequency locked to the power frequency and an amplitude decaying with M(t) is induced. This current is directly supplied to the demagnetizing coil of the magnetic shielding device.

[0064] Furthermore, to avoid introducing sensing elements such as series sampling resistors and current transformers that may generate noise or waveform distortion in the secondary output circuit where extremely low noise is required, this application adopts a non-intrusive monitoring scheme. Specifically, a third winding is added as a monitoring coil, tightly coupled (with a fixed relative position) to the secondary induction coil, and the two are arranged coaxially to improve magnetic coupling efficiency. The voltage induced in this monitoring coil... It is proportional to the rate of change of the secondary demagnetizing current, that is ,in This is the fixed mutual inductance between the secondary induction coil and the monitoring coil. Through... By performing integration and calibration on the signal, the secondary demagnetizing current can be reconstructed with high fidelity. Complete waveform and real-time amplitude This provides a precise basis for real-time monitoring, data recording, and closed-loop quality control of the demagnetization process, and does not interfere with the passive characteristics and current purity of the main demagnetization circuit throughout the process.

[0065] In one optional embodiment, the mutual inductance control unit includes a displacement mechanism, a position sensor, and a position closed-loop controller. The displacement mechanism is drively connected to the secondary sensing unit and drives the secondary sensing unit to perform linear displacement or rotation about an axis relative to the primary excitation unit, adjusting the spatial magnetic coupling coefficient. The position sensor is mounted on the moving end of the displacement mechanism and is used to collect the actual position data of the secondary sensing unit in real time, transmitting the position feedback signal to the position closed-loop controller. The position closed-loop controller pre-stores the feedback signal received from the position sensor and compares it with a preset curve in real time, outputting a pulse width modulation control signal to the displacement mechanism.

[0066] Specifically, the displacement mechanism receives PWM control signals from the controller and drives the secondary induction unit to move precisely relative to the primary excitation unit. Continuous control of the mutual inductance is achieved through the relative spatial configuration between the primary and secondary induction coils. Changes in the relative spatial configuration include linear displacement (adjusting the distance between the two coils) or rotation around an axis (adjusting the area of ​​the two coils facing each other). The position sensor collects the actual position data of the secondary induction unit in real time, converting the physical displacement into a standard electrical signal and feeding it back to the position closed-loop controller, providing a reliable actual value reference for closed-loop control. After receiving this feedback signal, the position closed-loop controller compares it in real time with a pre-stored displacement-time target curve, calculates the deviation between the actual position and the target position, and then corrects the motion state of the displacement mechanism by dynamically adjusting the duty cycle of the PWM signal, ensuring that the secondary induction unit strictly follows the preset trajectory.

[0067] Furthermore, when employing a spatial displacement control paradigm, the displacement mechanism driving the secondary sensing unit is equipped with a high-precision position feedback device (i.e., the aforementioned position sensor). The control algorithm will monitor the motion trajectory of the secondary sensing unit. The core of S-shaped velocity curve planning is to strictly limit the acceleration of displacement, ensuring a smooth and continuous velocity change for the secondary sensing unit throughout its entire process from startup and uniform operation to shutdown. This completely eliminates instantaneous vibration and impact interference caused by sudden changes in mechanical acceleration. This design further ensures the spatial magnetic coupling coefficient. The high smoothness of the variation function effectively suppresses the minute electromagnetic noise that may be introduced by mechanical vibration coupling, providing a pure magnetic field environment for the demagnetization process.

[0068] This invention provides a demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation. The demagnetization system for a magnetic shielding device based on controllable magnetic coupling attenuation according to the above-described embodiments is shown in Figure 2. The method includes: step S1, adjusting the primary excitation unit to a spatial configuration that is fully coupled with the secondary induction unit, so that the spatial magnetic coupling coefficient between the two reaches the design maximum value.

[0069] Specifically, the secondary induction unit is placed in a spatial configuration that is fully coupled with the primary excitation unit, at which point the spatial magnetic coupling coefficient between the two reaches its design maximum value. Under this stable coupling state, the peak value of the open-circuit induced voltage in the secondary circuit is... or peak short-circuit current Perform measurements and record them. The above measurement data will serve as the core basis for system status self-check and benchmark calibration, used to verify the magnetic field output stability of the primary excitation unit, the induction performance of the secondary induction unit, and the matching degree of the coupling relationship between the two units, ensuring that the working status of each core component is normal and that the coupling state is highly consistent with the design expectation, laying the foundation for the accurate implementation of the subsequent demagnetization process.

[0070] Step S2: Start the power supply circuit of the primary excitation unit to establish an initial saturated magnetic field around the shield of the magnetic shielding device.

[0071] Specifically, the demagnetizing coil of the magnetic shielding device is first connected to the secondary circuit, and then the power supply circuit of the primary excitation unit is started. The system then enters the initial strong field establishment phase. This phase needs to be maintained for a short, fixed duration. The purpose is to utilize the maximum current in the secondary circuit. The generated strong alternating magnetic field effectively overcomes the initial magnetic viscosity effect of the shielding material, ensuring that all magnetic domains inside the shielding can be fully activated and enter a state that can be precisely driven and orderly flipped by the subsequent decaying magnetic field, laying a solid foundation for deep demagnetization.

[0072] Step S3: Trigger the mutual inductance control unit to drive the relative spatial configuration or magnetic circuit state between the secondary induction unit and the primary excitation unit to change according to a predetermined law according to a preset timing function, so that the spatial magnetic coupling coefficient monotonically decays from the design maximum value to the zero state. The zero state means that the spatial magnetic coupling coefficient is zero, or the spatial magnetic coupling coefficient fluctuates in the positive value range near the zero value and its fluctuation amplitude does not exceed the preset threshold.

[0073] Specifically, the mutual inductance control unit is triggered to strictly follow the preset timing function. The coupling control process is initiated by precisely altering the spatial relative configuration between the primary excitation coil and the secondary induction coil, causing the spatial magnetic coupling coefficient to smoothly decay from its design maximum value to near zero. In the axial displacement control paradigm, this process corresponds to controlling the displacement mechanism, which drives the secondary induction unit to move precisely along a preset displacement-time trajectory. This trajectory corresponds one-to-one with the timing function through a pre-calibrated mapping curve, ensuring that changes in the spatial position of the secondary induction unit can be directly converted into a preset decay law for the spatial magnetic coupling coefficient.

[0074] Step S4: Based on the magnetic field coupling between the primary excitation unit and the secondary induction unit and the attenuation change of the spatial magnetic coupling coefficient, a sinusoidal current with an amplitude that decays synchronously with the spatial magnetic coupling coefficient is induced in the secondary induction unit. The sinusoidal current acts on the shielding device through the demagnetizing coil to demagnetize the magnetic shielding device.

[0075] Specifically, the entire preset attenuation period Internally, based on Faraday's law of electromagnetic induction and the principle of mutual inductance coupling, the demagnetizing current generated in the secondary circuit... Its amplitude envelope will smoothly and synchronously decay in real time and accurately following the programming law of the spatial magnetic coupling coefficient of the time-series function. After the demagnetizing current flows through the demagnetizing coil of the magnetic shielding device, it forms an alternating magnetic field with synchronously decaying amplitude. This magnetic field can drive the magnetic domains inside the shield to relax and reset in an orderly manner, thereby performing deep demagnetization of the shield without additional pollution.

[0076] This invention provides a demagnetizing method for a magnetically shielded device based on controllable magnetic coupling attenuation. By continuously changing the spatial magnetic coupling coefficient between the secondary induction coil and a constant power frequency magnetic field source, the secondary induction unit passively generates a pure sinusoidal current whose amplitude strictly follows the attenuation law of the spatial magnetic coupling coefficient. Through programmed control of the spatial magnetic coupling coefficient, a demagnetizing current with linear or exponential decay can be generated and applied to the permalloy shield, thereby achieving efficient demagnetization. This method fundamentally and significantly reduces the inherent DC bias and high-frequency switching noise of traditional electronic demagnetizing power supplies, resulting in a pure output current spectrum, thorough demagnetization, and a significantly reduced residual magnetic field.

[0077] In an optional implementation, the method further includes: step S51, when the spatial magnetic coupling coefficient decays to zero, stopping the control action of the mutual inductance control unit, so that the secondary induction unit and the primary excitation unit enter a completely decoupled state.

[0078] Step S52: After maintaining the decoupled state for multiple power cycles, the power supply circuit of the primary excitation unit is cut off.

[0079] Specifically, when the system monitors the spatial magnetic coupling coefficient in real time When the position signal of the secondary induction unit (or the corresponding induced voltage signal of the monitoring coil) decays to zero, the control action of the mutual inductance control unit automatically terminates, and the secondary induction unit and the primary excitation unit officially enter a completely decoupled state. To avoid the impact of power outage on the demagnetization effect, this decoupled state needs to be maintained for 3 to 5 power cycles. After the magnetic field environment stabilizes, the power supply circuit of the primary excitation unit can be safely disconnected.

[0080] To quantitatively evaluate the demagnetization effect, a high-sensitivity magnetometer (such as an optically pumped magnetometer or a superconducting quantum interference device, SQUID) can be placed inside the magnetic shielding device to accurately measure its residual static magnetic field strength. By determining whether this residual static magnetic field value is lower than the preset target technical indicator (such as ≤1nT), the final verification of the single demagnetization process effect is completed, ensuring that the shielding body meets the requirements for use in ultra-high sensitivity magnetic measurement.

[0081] In an optional implementation, the method further includes: step S61, acquiring the loop current of the primary excitation unit in real time and comparing the loop current with a preset current.

[0082] Step S62: Dynamically adjust the parameters of the current stabilizing circuit based on the comparison results.

[0083] Specifically, high-precision detection elements such as Hall current sensors are used to collect the loop current of the primary excitation unit in real time; simultaneously, this real-time loop current is dynamically compared with a preset current, and the deviation between the two is calculated. The preset current is a fixed value pre-calculated according to the demagnetization process requirements, and its stability directly determines the main magnetic flux. The amplitude stability is important. Real-time current is easily affected by factors such as grid voltage fluctuations and reflection impedance fluctuations caused by changes in secondary mutual inductance, which can lead to slight deviations. This step can capture current deviations in a timely manner, providing a basis for subsequent regulation.

[0084] Based on the current deviation value obtained in step S61, the controller automatically outputs adjustment commands to dynamically adjust the core parameters of the current stabilizing circuit. If the loop current is greater than the preset current, it indicates that the primary current is too large. The loop current can be reduced by decreasing the duty cycle of the power devices in the current stabilizing circuit or increasing the equivalent impedance of the series controllable reactance. If the loop current is less than the preset current, it indicates that the primary current is too small. In this case, the above parameters are adjusted in reverse to increase the loop current.

[0085] In one specific embodiment, in order to quantitatively verify the technical superiority of this application, the same magnetic shielding chamber was demagnetized using the magnetic shielding device demagnetization system based on controllable magnetic coupling attenuation of this application and the traditional electronic programmable power supply demagnetization scheme, respectively. Systematic tests and comparative analyses were conducted from multiple core performance dimensions such as DC bias current level, current background noise, residual magnetic strength of the shielding body, and magnetic noise of the space inside the shielding chamber.

[0086] 1. Compared to traditional electronic solutions, the demagnetizing current waveform exhibits obvious digital quantization steps and high-frequency switching noise. The smoothness of its attenuation envelope is limited by the resolution of the digital-to-analog converter and the switching characteristics of the power devices. In contrast, the current waveform output by the proposed solution is a pure sine wave with a highly smooth and continuous attenuation trend in its amplitude envelope, completely free of digital steps or high-frequency switching harmonics. This verifies the unique advantage of the mutual inductance gradual change control principle in generating an ideal attenuation waveform.

[0087] 2. Comparison of Power Supply Noise Floor and DC Bias: The peak-to-peak value of the power supply noise floor of an electronic power supply is approximately 0.645A, and it also has a non-negligible DC bias component of approximately 3.987mA. These non-ideal components can be directly injected into the degaussing coil, potentially contaminating the highly sensitive magnetically shielded environment. In contrast, the peak-to-peak value of the power supply noise floor in this application is only 0.178mA, which is almost negligible compared to the noise floor of an electronic power supply. Furthermore, the DC bias component is also almost negligible, at only approximately 0.126mA.

[0088] 3. Comparison of Magnetic Noise Inside the Shielded Chamber: After demagnetization using a conventional power supply, the magnetic noise spectrum inside the chamber showed a significant increase in multiple frequency bands (especially at low frequencies and switching frequency harmonics), indicating that additional magnetic field disturbances remained after the demagnetization process. After demagnetization using this application, the overall magnetic noise spectrum inside the chamber decreased to a lower level, and the spectrum was flat, approaching the noise floor limit of the shielded chamber. This proves that this method can achieve deeper and "cleaner" demagnetization, maximizing the restoration of the magnetic silence characteristics of the shielded space.

[0089] 4. Residual Remanent Magnetism: For the specific shielding material used in this experiment, fluxgate magnetometer measurements showed that after demagnetization with a traditional electronic power supply, the residual remanent magnetism of the shielding material is typically in the range of 1–2 nT. However, after demagnetization using the method described in this application, the residual remanent magnetism can be stably reduced to the range of 0–1 nT, with some areas reaching sub-nanotesla levels. This improvement of approximately 0.5–2 nT in remanent magnetism is of crucial value for systems pursuing extreme shielding performance (such as magnetoencephalography, magnetocardiography, or ultra-low field magnetic resonance imaging applications).

[0090] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A demagnetization system for a magnetic shielding device based on controllable magnetic coupling attenuation, characterized in that, The system includes a primary excitation unit, a secondary induction unit, and a mutual inductance control unit. The primary excitation unit and the secondary induction unit are coupled via a magnetic field, and the spatial magnetic coupling coefficient between them is continuously adjustable. The output of the secondary induction unit is connected to the demagnetizing coil of a magnetic shielding device. The primary excitation unit generates an alternating main magnetic field with stable frequency and amplitude. The mutual inductance control unit drives the relative spatial configuration or magnetic circuit state between the secondary induction unit and the primary excitation unit to change according to a predetermined law based on a preset timing function, causing the spatial magnetic coupling coefficient to monotonically decay from its design maximum value to zero. Zero refers to the spatial magnetic coupling coefficient being zero, or the spatial magnetic coupling coefficient fluctuating within a positive value range near zero with its fluctuation amplitude not exceeding a preset threshold. The secondary induction unit senses and generates a sinusoidal current whose amplitude decays synchronously with the spatial magnetic coupling coefficient. This sinusoidal current acts on the shielding device through the demagnetizing coil, thereby demagnetizing the magnetic shielding device.

2. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The preset timing function is a linear function or an exponentially decaying function.

3. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The coupling differential equations between the primary excitation unit and the secondary induction unit are as follows: in, This is the power supply voltage for the primary excitation unit. The circuit resistance of the primary excitation unit. This refers to the loop current of the primary excitation unit. The loop inductance of the primary excitation unit. The spatial magnetic coupling coefficient, This is the loop current of the secondary sensing unit. The loop resistance of the secondary sensing unit. The loop inductance of the secondary sensing unit, For time.

4. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The coupling magnetic flux between the primary excitation unit and the secondary induction unit is: The spatial magnetic coupling coefficient between the primary excitation unit and the secondary induction unit is: in, This refers to the coupling magnetic flux between the primary excitation unit and the secondary induction unit. The location of the secondary sensing unit. The number of coil turns of the secondary induction unit. To generate a magnetic field distribution in space for the primary excitation unit, The coil normal of the secondary induction unit. The effective area of ​​the coil of the secondary induction unit. This is the constant amplitude of the primary excitation unit.

5. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The primary excitation unit includes an iron core, an excitation coil, and a current stabilizing circuit. The excitation coil is uniformly wound around the outer periphery of the magnetic circuit of the iron core. The excitation coil is supplied with an industrial frequency AC power supply, and a current stabilizing circuit is connected in series in the power supply circuit of the excitation coil.

6. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The secondary induction unit includes a secondary induction coil and a monitoring coil, wherein the secondary induction coil and the monitoring coil are fixedly coupled and coaxially arranged, the secondary induction coil is used to induce a sinusoidal current whose amplitude decays synchronously with the spatial magnetic coupling coefficient, and the monitoring coil is used to non-invasively monitor the decay process of the demagnetizing current.

7. The demagnetization system of the magnetic shielding device based on controllable magnetic coupling attenuation according to claim 1, characterized in that, The mutual inductance control unit includes a displacement mechanism, a position sensor, and a position closed-loop controller. The displacement mechanism is driven by the secondary sensing unit and is used to drive the secondary sensing unit to perform linear displacement or rotation about an axis relative to the primary excitation unit, thereby adjusting the spatial magnetic coupling coefficient. The position sensor is installed at the moving end of the displacement mechanism and is used to collect the actual position data of the secondary sensing unit in real time and transmit the position feedback signal to the position closed-loop controller. The position closed-loop controller receives the feedback signal from the position sensor and compares it with a preset curve in real time, and outputs a pulse width modulation control signal to the displacement mechanism.

8. A demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation, characterized in that, Based on the demagnetization system of a magnetic shielding device based on controllable magnetic coupling attenuation according to any one of claims 1-7, the method includes: adjusting the primary excitation unit to a spatial configuration fully coupled with the secondary induction unit, so that the spatial magnetic coupling coefficient between the two reaches the design maximum value; activating the power supply circuit of the primary excitation unit to establish an initial saturated magnetic field around the shield of the magnetic shielding device; triggering the mutual inductance control unit to drive the relative spatial configuration or magnetic circuit state between the secondary induction unit and the primary excitation unit to change according to a predetermined law according to a preset timing function, so that the spatial magnetic coupling coefficient monotonically attenuates from the design maximum value to a zero state, wherein the zero state refers to the spatial magnetic coupling coefficient being zero, or the spatial magnetic coupling coefficient fluctuating in a positive value range near zero and its fluctuation amplitude not exceeding a preset threshold; based on the magnetic field coupling between the primary excitation unit and the secondary induction unit and the attenuation change of the spatial magnetic coupling coefficient, a sinusoidal current with an amplitude that attenuates synchronously with the spatial magnetic coupling coefficient is induced in the secondary induction unit, and the sinusoidal current acts on the shielding device through the demagnetizing coil to achieve demagnetization of the magnetic shielding device.

9. The demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation according to claim 8, characterized in that, The method further includes: when the spatial magnetic coupling coefficient decays to zero, stopping the control action of the mutual inductance control unit, so that the secondary induction unit and the primary excitation unit enter a completely decoupled state; after maintaining the decoupled state for multiple power cycles, cutting off the power supply circuit of the primary excitation unit.

10. The demagnetization method for a magnetic shielding device based on controllable magnetic coupling attenuation according to claim 8, characterized in that, The method further includes: acquiring the loop current of the primary excitation unit in real time and comparing the loop current with a preset current; and dynamically adjusting the parameters of the current stabilizing circuit based on the comparison result.

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