Adjustable uniform magnetic field generating device with active constant temperature control

Abstract

This invention provides an adjustable uniform magnetic field generator with active constant temperature control, belonging to the technical field of magnetic field generators. It includes: a coil unit for generating a uniform magnetic field in the central region under the action of a driving current; a thermoelectric temperature control unit integrated on the frame of the coil unit for adjusting the temperature of the central region; a power amplifier unit whose output is connected to the coil unit for providing the driving current to the coil unit; and a signal generation and control unit whose output is connected to the input of the power amplifier unit for generating an excitation signal. This invention significantly expands the spatial range of a high-uniformity magnetic field with the same coil size, enabling the formation of a uniform magnetic field with a volume of not less than 300 cm³ and a magnetic field non-uniformity of no more than ±1% in the central region, meeting the stringent requirements for magnetic field spatial uniformity in large-volume sample experiments such as biomedicine and materials science.

Description

Technical Field

[0001] This invention belongs to the technical field of magnetic field generating devices, specifically an adjustable uniform magnetic field generating device with active constant temperature control. Background Technology

[0002] Low-frequency alternating magnetic fields (LF-AMF), as a non-invasive physical modulation method, have shown broad application potential in biomedicine, agricultural and forestry sciences, analytical physics, and materials science. LF-AMF at specific frequencies and intensities can regulate various biological processes, including cell proliferation, apoptosis, differentiation, and migration, and influence the activity of key signaling pathways. Its effects encompass inhibiting tumor cell growth, guiding stem cell differentiation into specific lineages, promoting soft tissue and bone tissue repair, regulating neuronal network synchronization, and even improving plant seed germination rates and crop stress resistance. Simultaneously, LF-AMF also has significant application value in analytical physics and materials science. For example, in experiments such as low-field magnetic resonance, magnetic susceptibility measurement, characterization and functional modulation of magnetic nanomaterials, precisely controllable LF-AMF can serve as a background excitation field or modulation method to probe the microstructure, dynamic response, or magnetic properties of matter.

[0003] These responses are highly dependent on the precise setting of magnetic field parameters (such as frequency, amplitude, waveform, and duration of action), thus imposing stringent requirements on the magnetic field generating system: it must provide a uniform magnetic field environment that is spatially highly uniform, long-term stable, and with flexible adjustable amplitude and frequency in the sample area.

[0004] In typical experimental setups, living or sensitive samples (such as mammalian cells, tissue sections, small model organisms, plant seeds, and even materials or chemical samples used for low-field magnetic resonance) are usually placed directly in the working area at the center of the coil. When an alternating current is passed through the coil to generate the required magnetic field, the conductor resistance inevitably induces Joule heating, causing the coil temperature to rise. This unintended thermal effect can disturb the sample microenvironment temperature through heat conduction or convection, thus introducing "thermal interference" that is difficult to decouple from the pure magnetic field effect. For example, in cell culture, temperature fluctuations of ±0.5°C can significantly alter metabolic rates and gene expression profiles; in neurophysiological recordings, temperature changes affect ion channel dynamics and action potential firing characteristics; in plant development studies, temperature is a crucial factor determining germination, elongation, and stress response; and in precision physical measurements such as low-field magnetic resonance (e.g., for materials characterization, chemical analysis, or geophysical exploration), temperature drift can affect the physicochemical properties of the sample, leading to changes in the sample's magnetic response characteristics and deteriorating measurement repeatability.

[0005] Traditional uniform magnetic field generators are mostly based on standard Helmholtz coils. While simple in structure, their uniform magnetic field area is limited (usually one-third of the coil radius), making it difficult to cover the space required for experimental samples. Furthermore, existing devices mostly focus on diversifying the magnetic field type (e.g., patent CN102653719B) or only temperature control the overall incubator environment, lacking direct, precise, and active management of the heat generated by the uniform magnetic field generator itself (the coil). In terms of drive, efficiency-prioritized switching (Class D) amplifiers or Class B push-pull circuits with crossover distortion are often used, introducing high-frequency harmonic noise that contaminates the theoretically single-frequency magnetic field stimulation signal.

[0006] Therefore, there is an urgent need for an integrated uniform magnetic field generator that can simultaneously solve the three key problems of generating a large-volume uniform magnetic field with high uniformity, driving a low-distortion signal, and directly and precisely controlling the temperature of the sample area. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide an adjustable uniform magnetic field generator with active constant temperature control.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0009] An adjustable uniform strong magnetic field generator with active constant temperature control, comprising:

[0010] A coil unit is used to generate a uniform magnetic field in the central region under the action of a driving current.

[0011] A thermoelectric temperature control unit, integrated on the frame of the coil unit, is used to regulate the temperature of the central region;

[0012] A power amplifier unit, the output of which is connected to the coil unit, is used to provide the driving current to the coil unit;

[0013] The signal generation and control unit has its output terminal connected to the input terminal of the power amplifier unit and is used to generate excitation signals;

[0014] The coil unit is a four-coil structure, and its coil radius and axial spacing are configured such that the magnetic field non-uniformity in the central region does not exceed ±1%.

[0015] As a further improvement: the four-coil structure is a Braunbeck configuration.

[0016] As a further improvement: the power amplification unit is a Class AB linear power amplification unit.

[0017] As a further improvement: the thermoelectric temperature control unit includes:

[0018] A semiconductor cooling chip, the cold side of which is thermally coupled to the frame of the coil unit;

[0019] A temperature sensor is used to detect the temperature of the central region;

[0020] The controller adjusts the operating state of the thermoelectric cooler based on the feedback signal from the temperature sensor.

[0021] As a further improvement, the controller runs a PID control algorithm to dynamically adjust the magnitude and direction of the current in the thermoelectric cooler.

[0022] As a further improvement, a magnetic field detection unit is also included. The probe of the magnetic field detection unit is located in the central working area of ​​the coil unit. The magnetic field detection unit includes a Hall effect gaussmeter, a probe fixing bracket, a signal transmission cable, and a communication interface.

[0023] As a further improvement, it also includes a multi-winding isolation transformer, where the high-voltage winding, after rectification and filtering, supplies power to the Class AB linear power amplifier unit, and the low-voltage winding supplies power to the protection circuit and cooling fan.

[0024] Compared with existing technologies, the beneficial effects of this invention are: by precisely setting the ratio between the coil radius and the axial spacing, the second-, fourth-, and sixth-order non-uniform terms of the magnetic field in the central region are simultaneously eliminated. Compared with traditional Helmholtz coils, which can only eliminate second-order non-uniform terms, this invention significantly expands the spatial range of a high-uniformity magnetic field with the same coil size. It can form a uniform magnetic field with a volume of not less than 300 cm³ and a magnetic field non-uniformity of no more than ±1% in the central region, meeting the stringent requirements for magnetic field spatial uniformity in large-volume sample experiments such as biomedicine and materials science. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall system architecture and signal flow of an embodiment of the present invention.

[0026] Figure 2 This is a structural block diagram of a Class AB linear power amplifier in an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram of the optimized four-coil Braunbeck structure spatial arrangement used in an embodiment of the present invention.

[0028] Figure 4These are schematic diagrams comparing the magnetic field uniformity distribution of embodiments of the present invention with that of traditional structures. In the diagram, (a) is a simulated magnetic field distribution cloud map of the YZ plane of the four coil units in the embodiment of the present invention when a current of 6 A is applied; (b) is a simulated magnetic field distribution cloud map of the XY plane of the four coil units in the embodiment of the present invention when a current of 6 A is applied; (c) is a simulated YZ plane result diagram of a traditional Helmholtz coil (coil spacing equal to radius) under the same excitation conditions; and (d) is a simulated XY plane result diagram of a traditional Helmholtz coil (coil spacing equal to radius) under the same excitation conditions.

[0029] Figure 5 This is a schematic diagram of the coil frame structure and thermoelectric temperature control unit installation in an embodiment of the present invention.

[0030] Figure 6 This is a block diagram illustrating the system working principle of the thermoelectric temperature control unit in an embodiment of the present invention. Detailed Implementation

[0031] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0032] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0033] Please see Figure 1 , Figure 3 and Figure 4 In one embodiment, an adjustable uniform magnetic field generator with active constant temperature control includes:

[0034] A coil unit is used to generate a uniform magnetic field in the central region under the action of a driving current.

[0035] A thermoelectric temperature control unit, integrated on the frame of the coil unit, is used to regulate the temperature of the central region;

[0036] A power amplifier unit, the output of which is connected to the coil unit, is used to provide the driving current to the coil unit;

[0037] The signal generation and control unit has its output terminal connected to the input terminal of the power amplifier unit and is used to generate excitation signals;

[0038] The coil unit is a four-coil structure, and its coil radius and axial spacing are configured such that the magnetic field non-uniformity in the central region does not exceed ±1%.

[0039] The four-coil structure is a Braunbeck configuration.

[0040] In this embodiment, the main body of the device is an electromagnetically shielded enclosure. The interior of the enclosure is divided into three areas: the front houses the control and power supply module, the middle houses the power amplifier module and heat dissipation components, and the rear is the experimental chamber for housing the coil system. The experimental chamber is equipped with an openable and closable shielded door for easy sample loading and unloading. The modules are interconnected via internal cables and are uniformly coordinated and operated by a main control computer.

[0041] The signal generation and control unit includes a direct digital frequency synthesis module and a high-resolution amplitude controller, which are used to generate stable low-frequency analog excitation signals according to the frequency and amplitude parameters set by the user.

[0042] In this embodiment, the geometric parameters of the four-coil structure are determined based on theoretical derivation and optimized through multiphysics simulation. Finally, the coil frame is manufactured using 3D printing technology. This structure is designed to generate a low-frequency alternating magnetic field with a volume of not less than 300 cm³ and a magnetic field non-uniformity of no more than ±1% in the central region. The magnetic field frequency and amplitude can be adjusted according to experimental requirements. When the low-frequency alternating current output from the Class AB linear power amplifier unit flows through the four sets of series-connected circular coils, each set of coils generates a low-frequency alternating magnetic field in space. The four sets of coils are designed according to the Braunbeck system, using an optimized coil radius ratio and axial spacing to design the coil frame, ensuring that the second, fourth, and sixth order non-uniform terms of the magnetic field in the central region are simultaneously zero. Simultaneously, due to the symmetrical distribution of the coils, the odd-numbered gradient terms of the magnetic field in the central region are all zero. This combination of active cancellation of even-order terms and structural elimination of odd-order terms enables a highly uniform magnetic field within a large volume. Since the input current is an AC signal with adjustable frequency (typical range 0.1 Hz - 1 kHz) and controllable amplitude, the combined magnetic field generated by the four coil units is also a low-frequency alternating uniform magnetic field.

[0043] The coil system design is based on classical electromagnetic theory combined with numerical simulation methods. The design is first completed through analytical calculations: a parametric mathematical model of a four-coil Braunbeck structure is established based on the Biot-Savart law and the spherical harmonic function expansion of an axisymmetric magnetic field. To suppress the second, fourth, and sixth-order gradient terms in the spatial magnetic field, a set of equations that the coil radius and axial position must satisfy are derived, and their dimensionless proportional relationships are solved. Subsequently, in the engineering implementation phase, a three-dimensional model including the wire diameter, inter-turn gap, and skeleton material is constructed using finite element simulation software such as COMSOL Multiphysics. With constraints of a magnetic field non-uniformity of ≤±1% in the central region and an effective uniform region volume ≥300 cm³, parametric scanning and multivariate optimization are performed on the analytical solution to determine the final geometric dimensions and winding parameters (including wire diameter, number of turns, and stacking method). The coil skeleton is made of resin with low dielectric loss and good dimensional stability, formed by photopolymerization 3D printing, and is used to support the windings and maintain the required geometric configuration.

[0044] This process, based on classical electromagnetic field theory, begins with a model of a single circular coil. Consider a circular coil of radius R, with N turns, carrying a current I, located in the z=0 plane. According to the Biot-Savart law, the magnetic induction intensity B produced at any point (0,0,z) on the axis is... Z (z) is:

[0045] ;

[0046] in Let be the vacuum permeability, and z be the axial distance from the point of observation to the center of the circular coil.

[0047] A Helmholtz coil consists of two coaxial circular loops of the same radius R, where N is the number of turns and d is the distance between the loops (i.e., the axial distance between the two coil planes). The two loops are located at... The total magnetic flux density B of the Helmholtz coil Helm The sum of the contributions of the two coils:

[0048] ;

[0049] To investigate the effect of coil spacing d on magnetic field uniformity, we treat d as a variable. For B... Helm (z) Calculate the second derivative with respect to z and analyze the curvature characteristics at the center point z=0. Mathematical derivation shows that the second derivative at the center point is 0 only when d = R. At this time, the second-order non-uniformity of the magnetic field distribution is eliminated; simultaneously, due to the coaxial symmetry of the coil, the odd-numbered non-uniformity is also eliminated, and the magnetic field in the central region reaches optimal uniformity. This conclusion theoretically and rigorously explains why Helmholtz coils must satisfy the geometric constraint that "the spacing is equal to the radius".

[0050] Under this optimal condition (d=R), B Helm (z) Taking a Taylor series expansion at z=0, we get:

[0051] ,in It is the magnetic induction intensity at the center point.

[0052] Therefore, the dominant non-uniform term is the fourth-order term. Because the fourth-order term decays extremely rapidly, the Helmholtz coil provides a highly uniform magnetic field only within a small central region (typically the diameter of the uniform region is about 0.3R).

[0053] To eliminate higher-order non-uniform terms (such as fourth-order and sixth-order), a four-coil system (Braunbeck coil) is introduced. Let the positions of the four coils be... Let h1 and h2 be the axial distances from the center of the inner and outer coil planes to the origin (center of the device), respectively. The radii of the inner and outer coils are R1 and R2, respectively, and the currents through the inner and outer coils are I1 and I2, respectively (symmetrically arranged, excited in the same direction). Let the dimensionless variables be β1 = h1 / R1 and β2 = h2 / R2.

[0054] A multipole expansion of the magnetic field near the axis is performed using spherical harmonics and Legendre polynomials. In spherical coordinates (r, θ) (where...) (where θ is the distance from the point of observation to the origin, and θ is the angle with the Z-axis). The axial magnetic fields generated by the two pairs of coils are as follows:

[0055] ;

[0056] Among them, B Z1 (r,θ), B Z2 (r, θ) represent the axial magnetic fields of the large and small coils, respectively; L 2n (β1) is a dimensionless function related to the large coil structure; L 2n (β2) is a dimensionless function related to the small coil structure; P 2n (cosθ) is a 2n-order Legendre polynomial.

[0057] Axial component B of the composite magnetic field Z (r,θ) can be represented as:

[0058] ;

[0059] In the formula, g 2n This represents the 2n-th order magnetic field coefficient.

[0060] When I1=I2=I:

[0061] ;

[0062] To make a uniform magnetic field even more uniform, the following conditions must be met:

[0063] ;

[0064] Among them, g0 is the main event, g 2i The spatial harmonic coefficients characterize the non-uniformity of the magnetic field. The Helmholtz coil eliminates only g2, while the Braunbeck configuration eliminates g2, g4, and g6 simultaneously, reducing the dominant non-uniformity term to g8, thereby significantly expanding the uniform region.

[0065] Solving the above equation, we obtain the geometric parameters of the coil as follows:

[0066] ;

[0067] This set of solutions corresponds to a specific proportional relationship of the coil geometry parameters in the Braunbeck configuration. When the parameters satisfy this relationship, the second, fourth, and sixth order non-uniform terms of the magnetic field in the central region are eliminated, and the remaining dominant non-uniform terms are eighth order and higher.

[0068] In the specific implementation of this device, the design objective is to form a uniform region at the center with a volume of not less than 300 cm³ and a magnetic field non-uniformity of less than ±1%. This objective serves as a constraint, leading to the engineering optimization phase. Using COMSOL Multiphysics finite element simulation software, a fully parametric three-dimensional model was established, including the dimensions of the conductor (diameter, number of turns), the inter-turn gaps, and the skeleton structure. For example... Figure 4As shown in the figure, the area enclosed by the black contour lines represents the effective uniform region with a magnetic field non-uniformity not exceeding ±1%. To quantitatively evaluate the performance differences, this paper constructs two comparative models based on the COMSOL Multiphysics platform: the four-coil model of this invention (parameters R1=0.1m, R2=0.0764m, h1=0.0834m, h2=0.2448m, N=64 turns) and the standard Helmholtz coil model (radius R=0.1m, spacing d = R, N=64 turns), both using the same Litz wire specifications and a 6 A sinusoidal excitation current. By solving the steady-state electromagnetic field and calculating the relative deviation of the magnetic field at each point in space relative to the center point, the ±1% non-uniformity contour surface is plotted. Simulation results show that the ±1% uniform region formed by the four-coil structure of this invention is approximately cylindrical, with a volume larger than that of the uniform region of the traditional Helmholtz coil; at the same time, under the same driving current, the magnetic induction intensity at the center of the four-coil unit of this device reaches 4.7 mT, which is better than the 3.3 mT of the traditional structure. The results confirm that, by synergistically optimizing the radius and axial spacing of the four coils, the four-coil unit of this device outperforms Helmholtz coils in both magnetic field strength and effective uniform region volume. The coil frame is made of resin with dimensional stability and low dielectric loss, and is formed using 3D printing technology. During winding, Litz wire is tightly and neatly wound into the slots, and after completion, insulating tape is used to reinforce and insulate the windings. Finally, the coil assembly is integrated into an electromagnetic shielding cavity.

[0069] Please see Figure 2 In one embodiment, the power amplification unit is a Class AB linear power amplification unit.

[0070] In this embodiment, the Class AB linear power amplifier unit is powered by a symmetrical dual DC power supply, including a differential input stage, a voltage amplification stage, and a push-pull output stage composed of complementary power MOSFETs. It also applies deep global voltage series negative feedback and operates in Class AB mode to reduce crossover distortion.

[0071] In the design of the power amplifier module, a Class AB linear power amplifier is used as the driving unit. This module is used to drive the uniform magnetic field generating coil, which is powered by a symmetrical bipolar DC power supply formed by the high-voltage winding of the multi-winding isolation transformer inside the device after full-bridge rectification and electrolytic capacitor filtering.

[0072] The amplifier employs a multi-stage architecture, consisting of a differential input stage, a voltage amplification stage, a driver stage, and a push-pull output stage. The differential input stage, based on an operational amplifier, receives the low-frequency excitation signal from the preceding stage and provides high input impedance and common-mode rejection. The voltage amplification stage provides the main gain and is connected in parallel with a Miller compensation network to ensure loop stability. The driver stage buffers the gate capacitance load of the high-power MOSFETs. The push-pull output stage consists of complementary power MOSFETs, which are biased to maintain a slightly conductive Class AB state in the static state, effectively eliminating crossover distortion. Furthermore, the system uses a global voltage series negative feedback structure, attenuating the output signal through a resistor network before feeding it back to the input to stabilize the gain. A Zobel network (resistor and capacitor in series) is connected in parallel at the output to compensate for high-frequency phase shift caused by inductive loads and prevent oscillation.

[0073] The working process of a Class AB linear power amplifier unit is as follows: Figure 2 As shown, the low-frequency excitation signal generated by the pre-amplifier first enters the differential input stage composed of operational amplifiers to provide high input impedance and suppress common-mode interference. Subsequently, the signal obtains the main gain through the voltage amplification stage and is stabilized by the Miller compensation network. Then, it enters the driver stage to buffer the gate capacitance load of the high-power MOSFET. Then, the bias circuit of the push-pull output stage puts the complementary power MOSFET in a slightly conducting Class AB state to eliminate crossover distortion. At the same time, the output signal is fed back to the input through the resistor network to form a global voltage series negative feedback, which stabilizes the gain and reduces distortion. It works with the Zobel network to suppress high-frequency oscillation. Finally, the high-fidelity high-current signal after overcurrent protection detection is output to the four-coil unit to generate the required uniform magnetic field.

[0074] In terms of performance, this power amplifier is designed to output continuous power no less than its rated value under a specified load. Its maximum output voltage peak is determined by the supply voltage, and the design ensures that the output voltage swing under full load conditions meets the current and voltage requirements for the drive coil to generate the target maximum uniform magnetic field. Under high-power output conditions, the power devices generate power consumption, which is released as heat. The heat sources mainly consist of two parts: first, ohmic losses caused by the on-resistance of semiconductor devices (such as MOSFETs) in the on-state; since the on-resistance of modern power MOSFETs is typically on the order of milliohms, this dynamic loss accounts for a small proportion of the total power consumption. Second, static power consumption generated by the linear power amplifier due to its quiescent operating point. To reduce crossover distortion, the output stage power transistors maintain a certain bias current even when there is no signal input, resulting in continuous power consumption even when the output power is zero. Therefore, the efficiency of such amplifiers under typical operating conditions is usually less than 50%, with the input electrical energy mainly converted into heat. To manage temperature rise, the power MOSFETs are mounted on low thermal resistance metal heat sinks and equipped with axial fans driven by independent temperature control circuits for forced cooling. The module also includes overcurrent protection circuitry, which detects abnormal currents using a current sampling resistor and a voltage comparator. The output terminal features a network of inductors and RC components to suppress high-frequency oscillations that may occur when driving capacitive loads.

[0075] The power amplifier module achieves high-fidelity, high-power linear amplification of the excitation signal over a wide bandwidth, and its output voltage capability can drive the subsequent uniform magnetic field generating coil to generate an alternating uniform magnetic field of the required intensity.

[0076] Please see Figure 5 In one embodiment, the thermoelectric temperature control unit includes:

[0077] A semiconductor cooling chip, the cold side of which is thermally coupled to the frame of the coil unit;

[0078] A temperature sensor is used to detect the temperature of the central region;

[0079] The controller adjusts the operating state of the thermoelectric cooler based on the feedback signal from the temperature sensor.

[0080] The controller runs a PID control algorithm to dynamically adjust the magnitude and direction of the current in the thermoelectric cooler.

[0081] In this embodiment, the thermoelectric temperature control unit and the four-coil unit of the present invention are structurally integrated to form a closed-loop active temperature control system for regulating the temperature of the coil frame and its central sample area. The system adopts a closed-loop control architecture, including three functional components: temperature sensing, control, and execution. The relevant hardware is installed in a pre-reserved mounting position on the coil frame. Temperature sensing is achieved by multiple digital temperature sensors: one sensor is embedded inside the central stage of the coil frame to measure the temperature at the sample location; another is attached to the surface of the coil winding to detect the coil temperature. The control signal is generated based on the coil temperature. The control system is based on an embedded microprocessor, runs a digital PID algorithm, and calculates and outputs a drive current to the thermoelectric cooler based on the deviation between the user-set target temperature and the measured temperature of the sample area. The execution part uses a semiconductor thermoelectric cooler (TEC), whose cold end contacts the outside of the coil frame through a thermally conductive insulating material, and whose hot end is connected to a copper-aluminum composite heat sink. The heat sink is cooled by an independent axial fan, and the fan speed is adjusted by a pulse width modulation (PWM) signal.

[0082] The thermoelectric temperature control unit also includes a copper-aluminum composite heat dissipation module and an independently driven PWM speed-regulating fan, with the hot surface of the thermoelectric cooling element connected to the heat dissipation module.

[0083] The specific operating flow of the closed-loop control system is as follows: Figure 6 As shown, after the system starts, the user-set target temperature value and the actual temperature value collected in real time by the temperature sensor are simultaneously input to the comparator. The comparator compares the two, calculates the current temperature deviation, and sends the deviation signal to the PID algorithm module. The PID controller dynamically calculates the deviation based on preset proportional, integral, and derivative parameters, generating a corresponding control quantity output to the drive circuit. The drive circuit converts this control quantity into a current or voltage signal suitable for the operation of the thermoelectric cooler (TEC) and applies it to the two ends of the TEC. The TEC performs cooling or heating actions according to the polarity and magnitude of the applied signal—when the actual temperature is higher than the set value, the cold end of the TEC absorbs heat to reduce the temperature of the coil winding area; conversely, it reverses the current to release heat at the hot end to increase the temperature. After the TEC acts on the coil winding, its temperature change is detected again by the temperature sensor attached to the winding surface or embedded in the stage, and the new actual temperature value is fed back to the comparator, forming a closed loop. By continuously cycling the above process, the system achieves high-precision and stable control of the temperature of the coil winding and the sample area, ensuring that the thermal environment fluctuation during the experiment does not exceed ±0.2℃.

[0084] In one embodiment, the device further includes a magnetic field detection unit. The probe of the magnetic field detection unit is located in the central working area of ​​the coil unit. The magnetic field detection unit includes a Hall effect gaussmeter, a probe mounting bracket, a signal transmission cable, and a communication interface.

[0085] In this embodiment, the magnetic field detection unit of the device includes a calibrated Hall effect gaussmeter, a probe mounting bracket, a signal transmission cable, and a communication interface. The gaussmeter main unit is installed in a separate area within the device chassis, physically isolated from the power amplifier module and main power circuit. Its probe is a packaged lateral Hall sensor, fixed below the central stage of the coil system by a non-magnetic rigid bracket. The bracket is adjustable, allowing the probe sensing point to be aligned with the geometric center of the coil during assembly and maintaining its position during use. The probe is connected to the gaussmeter main unit via a double-shielded coaxial cable, with a cable length not exceeding 1.5 meters. The gaussmeter reads the magnetic induction intensity value at a fixed sampling period. The user can activate the gaussmeter's zero-point calibration function before the experiment begins; this function records the sensor offset value under conditions without an external magnetic field and subtracts it from subsequent measurements. The gaussmeter is powered by an independent DC power supply and outputs magnetic field measurement data during experimental operation.

[0086] In one embodiment, the system further includes a multi-winding isolation transformer, wherein the high-voltage winding supplies power to the Class AB linear power amplifier unit after rectification and filtering, and the low-voltage winding supplies power to the protection circuit and cooling fan.

[0087] In this embodiment, the power supply and drive section uses a multi-winding toroidal transformer as the power isolation and distribution unit. The primary winding of the transformer is connected to 220 V / 50 Hz AC mains power, and the secondary winding has three sets of mutually isolated windings: one set outputs 56 V AC, which, after full-bridge rectification and electrolytic capacitor filtering, provides DC operating voltage for the push-pull output stage of the Class AB linear power amplifier module; the other two sets each output 12 V AC, one supplying power to the internal protection circuit of the power amplifier, which includes overcurrent detection and over-temperature shutdown functions, and the other supplying power to the axial cooling fan mounted on an aluminum heat sink. Through the physical isolation of the secondary windings, the power supply of the main power circuit is independent from that of the control and heat dissipation circuits, thereby reducing grounding interference and minimizing the impact of main circuit load changes on sensitive circuits.

[0088] The specific working process of this invention is as follows:

[0089] Initialization and parameter setting: Users set experimental parameters through the host computer software, including the frequency of the uniform magnetic field, the target field strength, and the target temperature of the sample.

[0090] Temperature control subsystem startup: After the system is powered on, the temperature control subsystem begins operation. The embedded controller executes the PID control algorithm and outputs a drive signal to the thermoelectric cooler to adjust the temperature of the central area of ​​the coil frame.

[0091] Uniform magnetic field generation: After the temperature of the sample area reaches the set value, the user activates the uniform magnetic field generation function. The main control unit controls the direct digital frequency synthesizer (DDS) to output a waveform with the target frequency and the initial amplitude corresponding to the preset field strength; this signal is amplified by the power amplifier and then drives the four-coil unit.

[0092] Operation and testing: During the set experimental time, the temperature control subsystem dynamically adjusts the driving current of the thermoelectric cooler according to the deviation between the measured temperature of the sample area and the target value; at the same time, the gaussmeter continuously collects the magnetic induction intensity data of the coil center area.

[0093] Shutdown and Protection: When the experiment ends, the system first stops the DDS output, then cuts off the power amplifier's power supply, causing the coil current to return to zero and the magnetic field to disappear; the temperature control subsystem can continue to operate or enter a low-power state. If an overcurrent or overtemperature abnormality is detected, the protection circuit will immediately cut off the power amplifier's power supply and trigger an audible and visual alarm.

[0094] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0095] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A device for generating an adjustable uniform magnetic field with active constant temperature control, characterized in that, include: A coil unit is used to generate a uniform magnetic field in the central region under the action of a driving current. A thermoelectric temperature control unit, integrated on the frame of the coil unit, is used to regulate the temperature of the central region; A power amplifier unit, the output of which is connected to the coil unit, is used to provide the driving current to the coil unit; The signal generation and control unit has its output terminal connected to the input terminal of the power amplifier unit and is used to generate excitation signals; The coil unit is a four-coil structure, and its coil radius and axial spacing are configured such that the magnetic field non-uniformity in the central region does not exceed ±1%.

2. The adjustable uniform magnetic field generator with active constant temperature control according to claim 1, characterized in that, The four-coil structure is a Braunbeck configuration.

3. The adjustable uniform magnetic field generator with active constant temperature control according to claim 1, characterized in that, The power amplification unit is a Class AB linear power amplification unit.

4. The adjustable uniform magnetic field generator with active constant temperature control according to claim 1, characterized in that, The thermoelectric temperature control unit includes: A semiconductor cooling chip, the cold side of which is thermally coupled to the frame of the coil unit; A temperature sensor is used to detect the temperature of the central region; The controller adjusts the operating state of the thermoelectric cooler based on the feedback signal from the temperature sensor.

5. The adjustable uniform magnetic field generator with active constant temperature control according to claim 4, characterized in that, The controller runs a PID control algorithm to dynamically adjust the magnitude and direction of the current in the thermoelectric cooler.

6. The adjustable uniform magnetic field generator with active constant temperature control according to claim 1, characterized in that, It also includes a magnetic field detection unit, whose probe is located in the central working area of ​​the coil unit. The magnetic field detection unit includes a Hall effect gaussmeter, a probe fixing bracket, a signal transmission cable, and a communication interface.

7. The adjustable uniform magnetic field generator with active constant temperature control according to claim 3, characterized in that, It also includes a multi-winding isolation transformer, with the high-voltage winding supplying power to the Class AB linear power amplifier unit after rectification and filtering, and the low-voltage winding supplying power to the protection circuit and cooling fan.

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