Multi-pole-moment multi-layer low-magnetic-field flexible film electric heater and design method thereof

Abstract

The invention discloses a multi-pole-moment multi-layer low-magnetic-field flexible film electric heater and a design method thereof, and belongs to the technical field of electric heaters. The heater aims to solve the problem that the performance of a precision sensor is affected due to large magnetic field interference of a heater in the prior art. The heater comprises at least two electric heating layers, and each layer comprises at least four wire sections. The core is as follows: 1) N wire sections in each layer are configured in a specific current direction to form an intra-layer multi-pole-moment magnetic field suppression configuration; and (2) an interlayer multi-pole-moment magnetic field suppression structure is formed among the multiple electric heating layers through specific current direction configuration. The invention further discloses a corresponding systematic design method which comprises the steps of determining the number of wires / layers, configuring the current direction in the layers / between the layers, optimizing the layout and conducting simulation verification. The magnetic field generated by heating current and the gradient thereof can be remarkably reduced, and the method is suitable for precise instruments with harsh requirements for the magnetic field environment.

Description

Technical Field

[0001] The present invention relates to the technical field of electric heaters, and in particular to a low magnetic field flexible thin film electric heater for precision sensors, and more specifically to a multi-pole moment multi-layer low magnetic field flexible thin film electric heater and a design method thereof for use in magnetic field environment sensitive devices such as nuclear magnetic resonance inertial sensors. Background Art

[0002] Nuclear magnetic resonance (NMR) inertial sensor is a high-precision angular velocity sensor, which works on the principle of atomic magnetic resonance effect. The output signal of this type of sensor has extremely high requirements on the uniformity and stability of the main magnetic field and is very sensitive to external stray magnetic fields.

[0003] In the NMR inertial sensor system, the atomic gas chamber, as the core sensitive element, needs to be precisely heated to maintain the required atomic number density. At the same time, key components such as lasers in the system also require temperature control to stabilize their output power and wavelength. These temperature control requirements are usually achieved through electric heaters. However, the heating current will inevitably generate a magnetic field, which will interfere with the main magnetic field and directly affect the accuracy and stability of the sensor.

[0004] With the continuous development of NMR inertial sensor technology, system performance indicators continue to improve, and integration and miniaturization have become important trends. This means that components such as heaters are getting closer and closer to core sensitive elements (such as atomic gas chambers), which puts more stringent requirements on the non-magnetic or low-magnetic properties of heaters. Therefore, designing a heating element with efficient magnetic field suppression capabilities is of great significance for improving the performance of NMR inertial sensors and achieving miniaturization and integration.

[0005] Existing low magnetic field heater solutions, such as Figure 1 As shown, a method of overlapping and thermally compounding two flexible heating films (1, 2) with the same wiring pattern is usually adopted. This structure attempts to offset part of the magnetic field through reverse current. However, this solution has the following defects: 1) Incomplete overlap of current paths due to process limitations: Due to the process requirements of welding leads (usually welding is performed on the same side of the heater), it is difficult for the current path near the solder joint to achieve complete mirror overlap of the upper and lower layers, resulting in incomplete magnetic field cancellation.

[0006] 2) Thermal composite error: The two heating films may introduce alignment errors during the thermal composite process, resulting in the inability to accurately overlap the upper and lower layers of the electric heating lines, affecting the magnetic field suppression effect.

[0007] 3) Single-layer configuration limitations: traditional serpentine wire or simple two-strand winding [such as Figure 16 (a)] The single-layer routing method has limited magnetic field suppression capability, especially in the near field area.

[0008] Therefore, the existing technical solutions are difficult to meet the requirements of high-performance and high-integration NMR inertial sensors for extremely low magnetic field interference of heaters, and there is an urgent need for a heater structure design with better magnetic field suppression ability and its systematic design method. Summary of the Invention

[0009] The present invention aims to overcome the technical defects in the prior art, such as insufficient magnetic field suppression ability of low magnetic field heaters, large process limitations, and unclear design methods. It provides a multi-pole moment multi-layer low magnetic field flexible thin film electric heater with significantly improved magnetic field suppression ability and its systematic design method to meet the requirements of ultra-low magnetic field environments for high-precision devices such as nuclear magnetic resonance inertial sensors.

[0010] To solve the above technical problems, the present invention proposes a multi-pole moment multi-layer low magnetic field flexible thin film electric heater, which is characterized by including: At least two flexible substrates; A conductive layer disposed on the flexible substrate, and the conductive layer is patterned to form at least two electrothermal layers; Each electrothermal layer includes at least N wire segments (N = 2J, J is a positive integer greater than or equal to 1, preferably J≥2, that is, at least 4) arranged along a predetermined path, and the N wire segments form a multi-pole moment magnetic field suppression configuration in the transverse direction (within the layer); The at least two electrothermal layers also form a multi-pole moment magnetic field suppression configuration in the longitudinal direction (between layers).

[0011] Further, the in-layer multi-pole moment magnetic field suppression configuration is achieved by the following method: The N wire segments are divided into multiple groups, and a predetermined current direction is assigned to each group, such that the current direction configurations of adjacent wire segments or adjacent wire segment groups satisfy the multi-pole moment cancellation condition.

[0012] For example, when N = 4, the current direction configuration of the four wire segments is preferably (+--+).

[0013] For example, when N = 8, the eight wire segments can be divided into four groups, with two wire segments in each group. The overall current direction configuration can be (+--+), and the current direction configuration of the two wire segments in each group is (+-) or (-+), forming an octupole moment configuration such as (+-,-+,-+,+-).

[0014] For example, when N = 16, the sixteen wire segments can be divided into four groups, with four wire segments in each group. The overall current direction configuration can be (+--+), and the current direction configuration of the four wire segments in each group is also (+--+) or its reverse, forming a sixteen-pole moment configuration such as (+--+,-++-,-++-,+--+). This grouping and current direction configuration rule can be recursively applied.

[0015] Furthermore, the layout configuration of each layer of the electrothermal layer is optimized to enhance the magnetic field suppression effect and adapt to the manufacturing process. For example, an optimized octupole configuration (such as configuration D or E) as shown in Figure 2 is adopted, and the lead pads originally located at the center of the pattern are moved to the edge of the layout (such as the Figure 2 square position) to avoid wire crossing and ensure the flatness of the core area of the heating film, which is beneficial to multi-layer stacking and fitting.

[0016] Furthermore, the interlayer multipole magnetic field suppression configuration is realized by the following method: The number of layers M of the electrothermal layer is preferably 2K (K is a positive integer greater than or equal to 1, that is, at least two layers).

[0017] The M layers of electrothermal layers are assigned a predetermined current direction according to their positions in the stacked structure, so that the current direction configurations of adjacent layers or adjacent layer groups in the longitudinal direction (interlayer) satisfy the multipole cancellation condition.

[0018] For example, when M = 4, the current direction configuration of the four electrothermal layers from the top layer to the bottom layer is preferably (+--+), forming an interlayer quadrupole.

[0019] Furthermore, the multipole multi-layer low-magnetic-field flexible thin-film electric heater uses polyimide as the flexible substrate material and resistance alloys such as constantan alloy as the conductive layer material.

[0020] The present invention also proposes a design method for a multipole multi-layer low-magnetic-field flexible thin-film electric heater, which is characterized by including the following steps: Determine the number of single-layer wires and current distribution: Select the number of wires N of a single-layer electrothermal layer as 2J (J is a positive integer greater than or equal to 1, preferably J≥2).

[0021] According to the multipole magnetic field suppression principle, determine the current direction configuration of N wires. Adopt a recursive grouping method, and the basic configuration is the (+--+) configuration of 4 wires or the (+-) configuration of 2 wires to achieve the optimal in-layer magnetic field suppression.

[0022] Design the single-layer layout configuration: Based on the selected number of wires and current distribution, design the specific wire routing path to form in-layer multipole configurations such as octupole and hexadecapole.

[0023] Optimize the layout, for example, move the lead pads in the central area to the edge, avoid wire crossing, ensure the flatness of the heating film, and consider the limitations of the actual processing technology (such as line width and line pitch).

[0024] Determine the number of layers and interlayer current distribution: Select the number of layers M of the electrothermal layer to be 2K (K is a positive integer greater than or equal to 1, preferably K≥2, for example, 4 layers), and utilize the advantage that the layer spacing is much smaller than the in-layer wire spacing.

[0025] According to the multi-pole moment magnetic field suppression principle, determine the current direction configuration of the M-layer electrothermal layer in the longitudinal direction. Similarly, a recursive grouping method can be adopted, and the basic configuration is the (+--+) configuration of 4 layers to achieve the optimal inter-layer magnetic field suppression.

[0026] Integrated design and simulation verification: Combine the optimized single-layer layout configuration with the determined number of layers and the inter-layer current distribution to form a complete multi-pole moment multi-layer heater structure model.

[0027] Perform magnetic field simulation calculations on the designed heater model through electromagnetic simulation software (such as COMSOL, etc.), evaluate the magnetic field strength and magnetic field gradient generated in the target area (such as the center of the gas chamber), verify the effectiveness of the design, and perform iterative optimization according to the simulation results.

[0028] Fabrication and testing: Fabricate a heater sample using the flexible circuit board manufacturing process according to the final design scheme.

[0029] Build a test platform, for example, use a high-precision magnetometer to measure the magnitude and distribution of the magnetic field generated by the heater under different excitation currents, compare with the simulation results, and verify the actual magnetic field suppression effect.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1) Significantly improve the magnetic field suppression ability: By adopting the multi-pole moment configuration design both within and between layers, especially using the smaller inter-layer spacing to achieve efficient cancellation, and combining with the optimized current direction configuration, the heater proposed by the present invention can suppress the stray magnetic field generated by the heating current to an extremely low level (such as 8.4 pT / mA measured in experiments), which is more than 5 times higher than that of the traditional structure.

[0031] 2) Reduce the magnetic field gradient: The multi-pole moment configuration not only reduces the absolute value of the magnetic field but also effectively reduces the magnetic field gradient, which is crucial for applications such as NMR sensors that require a highly uniform magnetic field.

[0032] 3) Systematic design method: The present invention provides a set of clear design rules and processes, including wire quantity selection, in-layer / inter-layer current configuration principles, layout optimization strategies, and simulation verification methods, providing guidance for designing high-performance low-magnetic-field heaters.

[0033] 4) Improve sensor performance and integration: The significantly reduced magnetic field interference helps improve the signal-to-noise ratio, accuracy, and stability of NMR inertial sensors. At the same time, the low magnetic characteristics also enable the heater to be closer to the sensitive elements, facilitating the miniaturization and integration of the sensor system.

[0034] 5) Good process compatibility: The optimized layout design (such as the outward movement of pads) takes into account the actual manufacturing and assembly requirements, facilitating the precise alignment, bonding of multi-layer structures, and the flat fitting with the heated device, ensuring heating efficiency and reliability. Brief Description of the Drawings

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0036] Figure 1 is a schematic diagram of the structure of a traditional low-electromagnetic heater in the prior art.

[0037] Figure 2 is a schematic diagram of the optimized layout configuration design in the embodiment of the present invention.

[0038] Figure 3 is a schematic diagram of the analysis model of the influence of the number of wires on the magnetic field.

[0039] Figure 4 is a simulation comparison diagram of the influence of the number of wires on the magnetic field.

[0040] Figure 5 is a schematic diagram of the analysis model of the influence of the current direction on the magnetic field.

[0041] Figure 6 is a simulation comparison diagram of the influence of the current direction configuration on the magnetic field.

[0042] Figure 7 is a design diagram of different multipole moment configurations.

[0043] Figure 8 is a simulation comparison diagram of the magnetic fields generated by different layout configurations.

[0044] Figure 9 is a simulation calculation model diagram of the multi-layer structure.

[0045] Figure 10 is a schematic diagram of the multi-layer heating film structure. (a) is a schematic diagram of the wire configuration of the multi-layer heating film, and (b) is a schematic diagram of the current direction distribution in the cross-section.

[0046] Figure 11It is a simulation comparison diagram of the influence of the number of layers on the magnetic field. (a) is a double-layer heating film, and (b) is a four-layer heating film (+--+).

[0047] Figure 12 It is a simulation comparison diagram of the influence of the interlayer current sequence on the magnetic field.

[0048] Figure 13 It is a simulation model diagram of a magnetometer testing the magnetic field of a heating film.

[0049] Figure 14 It is a magnetic field distribution diagram generated by a double-layer heating film.

[0050] Figure 15 It is a magnetic field distribution diagram generated by a four-layer heating film.

[0051] Figure 16 It is a design diagram and a physical diagram of a common configuration and an optimized octupole plate configuration, where (a) is configuration A and (b) is configuration D.

[0052] Figure 17 It is a physical diagram of a multipole heating film.

[0053] Figure 18 It is a magnetic field diagram generated by a multi-layer heating film under different configurations.

[0054] Explanation of reference numerals: 1. Upper electrothermal layer; 2. Lower electrothermal layer; 3. Upper covering film of the lower heater; 4. Upper covering film of the upper heater; 5. Lower covering film of the lower heater; 6. Lower covering film of the upper heater. Detailed implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0056] Embodiment 1: A four-layer octupole low-magnetic-field flexible thin-film electric heater The purpose of this embodiment is to provide an ultra-low magnetic-field flexible thin-film electric heater for heating the gas chamber of an NMR inertial sensor.

[0057] Design principles and processes: 1. Single-layer design: 1) Number of wires and current distribution: Based on theoretical analysis and simulation ( Figure 4 , Figure 6), Selecting an even number of wires has better magnetic field suppression ability. Further, to form an effective multipole moment, the number of wires N = 8 (J = 3) is selected. For 8 wires, according to the recursive grouping principle (+--+) applied to two-layer grouping and combined with the intra-group (+-) configuration, the optimal current direction configuration is (+-,-+,-+,+-), forming an intra-layer octupole moment.

[0058] 2) Layout configuration: Comparing Figure 7 Configuration A (traditional double-strand winding), B, C, D, E (all with octupole design ideas but different details) in, the simulation results ( Figure 8 ) show that the octupole configurations (B - E) have significantly improved magnetic field suppression ability compared to the traditional configuration A. To solve the problems brought by the central pad (affecting flatness, heat accumulation, and lead crossing), an optimized design as shown in Figure 2 is adopted, leading the central lead to the lower left corner pad of the layout (at the square) through ingenious wiring. In this embodiment, configuration D [as shown in (b) in Figure 16 is selected as the single-layer layout. The main body of this configuration maintains an octupole structure with a line width of 0.2 mm and a spacing of 0.2 mm (meeting the parameters in Table 1), adapting to the processing technology.

[0059] 2. Multi-layer design: 1) Selection of the number of layers: Theory and simulation show that the more layers there are, the better the magnetic field suppression effect achieved by the small inter-layer spacing. Selecting the number of layers M = 4 (K = 2) can not only obtain a significant improvement in magnetic field suppression (compared to the double layer) but also take into account the feasibility of the manufacturing process (inter-layer alignment).

[0060] 2) Inter-layer current distribution: For the 4-layer structure, based on simulation ( Figure 12 ), three inter-layer current configurations of (+--+), (++--), and (+-+-) are compared. The results show that the (+--+) configuration (i.e., the top and bottom layer currents are in the same direction, and the middle two layer currents are in the opposite direction) has the best inter-layer magnetic field suppression effect, forming an inter-layer quadrupole moment.

[0061] 3. Overall structure: 1) The finally designed heater is a four-layer structure, and each layer adopts the optimized octupole configuration D shown in (b) in Figure 16 .

[0062] 2) By adjusting the inter-layer lead connection method, the (+--+) configuration of the four-layer currents is achieved. As shown in Figure 10 , a positive current is passed through the top layer (Layer 1) and the bottom layer (Layer 4), and a reverse current is passed through the middle two layers (Layer 2 and Layer 3). Figure 10 The current direction of the lead area cross-section is shown schematically in (b) in

[0063] 3) The heater thus formed creates an octupole suppression magnetic field in the transverse direction (within the layer) and a quadrupole suppression magnetic field in the longitudinal direction (between the layers), achieving multi-dimensional and multi-level magnetic field cancellation.

[0064] Materials and Manufacturing: The heater substrate material is selected as polyimide.

[0065] The conductive layer material is selected as constantan alloy, which has a relatively stable resistivity (see Table 1).

[0066] It is processed using flexible printed circuit (FPC) manufacturing technology, including processes such as conductive layer etching, multi-layer lamination, cover film, and pad treatment. The layers are laminated through an adhesive, and the layer spacing is approximately 43 μm. The outer dimensions of the heater are approximately 11 mm x 5 mm, and the resistance is approximately 40 Ω (see Figure 17 and Table 1).

[0067] Table 1 Statistical Table of Main Technical Parameters of the Heater

[0068] Simulation Verification: 1) Influence of the number of layers: By comparing the curves of Configuration D in Figure 8 (single layer), Figure 11 in (a) (double layer) and Figure 11 in (b) (four layers), it can be seen that as the number of layers increases from 1 to 4, the magnetic field strength at the same distance (such as z = 7 mm, the center of the simulated gas chamber) decreases significantly.

[0069] 2) Influence of configuration: At each number of layers, Configuration D (optimized octupole) shows significant magnetic field suppression advantages compared to Configuration A (traditional double-strand pair winding), especially more obvious in the single layer and double layer. In the four-layer structure, although the inter-layer suppression effect is dominant, Configuration D is still slightly better than Configuration A (about 16 times improvement).

[0070] 3) Influence of inter-layer current configuration: Figure 12 shows that for the four-layer Configuration D, the magnetic field generated by the inter-layer current configuration of (+--+) is much smaller than that of the double-layer (+-) configuration, and also much smaller than incorrect four-layer configurations such as (++--) or (+-+-), verifying the effectiveness of the inter-layer quadrupole design.

[0071] 4) Magnetic field distribution: A simulation model as shown in Figure 13 is established to simulate the relative position (spacing 7 mm) between the heater (Configuration D) and the NMR sensor gas chamber. Figure 14 (double layer) and Figure 15(Four layers) respectively show the magnetic field distributions in the air chamber region (within the frame lines). By comparison, it can be seen that the magnetic field intensity (0.3136 pT / mA at the center of the air chamber) and magnetic field gradient generated by the four-layer heater are much smaller than those of the double-layer heater (18.3683 pT / mA at the center of the air chamber), and the maximum magnetic field intensity also drops from 28.9 pT / mA to about 2 pT / mA.

[0072] Experimental tests: Samples of single-layer, double-layer, and four-layer heaters with configurations A and D were fabricated (as Figure 16 shown).

[0073] The magnetic fields generated by the samples under different excitation currents (mainly the z-axis component perpendicular to the heating film direction) were measured using a high-precision magnetometer. The test results are as Figure 18 shown.

[0074] The results show that: 1) The magnetic field output of all samples has a good linear relationship with the excitation current.

[0075] 2) For the same number of layers, the magnetic field generated by configuration D is significantly lower than that of configuration A.

[0076] 3) For the same configuration, increasing the number of layers can significantly reduce the generated magnetic field.

[0077] 4) The four-layer optimized octupole heater (configuration D, 4 layers) in this embodiment shows the best magnetic field suppression effect. The measured magnetic field is as low as about 8.4 pT / mA, which is a significant improvement compared to the traditional double-layer double-strand winding structure (configuration A, 2 layers, no data is explicitly given but it is much higher than this value from the trend) and the single-layer optimized structure (configuration D, 1 layer), verifying the effectiveness of the multi-pole multi-layer design, which is consistent with the simulation results trend. Experiments prove that its magnetic field suppression ability is more than 5 times higher than that of the conventional heating film.

[0078] The four-layer octupole low-magnetic-field flexible thin-film electric heater designed in this embodiment, by combining the in-layer octupole configuration and the inter-layer quadrupole configuration, and optimizing the layout design, realizes an extremely low associated magnetic field (about 8.4 pT / mA) and a low magnetic field gradient. This heater and its design method can effectively solve the magnetic interference problem of heating elements in precision instruments such as NMR inertial sensors, contribute to improving the performance of the instruments, and promote their miniaturization and integration.

[0079] Example 2: A double-layer octupole low-magnetic-field flexible thin-film electric heater The purpose of this embodiment is to provide a low-magnetic-field flexible thin-film electric heater with a relatively simple structure and still having good magnetic field suppression ability, which is suitable for application scenarios with certain requirements for cost or manufacturing complexity but still needs to be significantly better than traditional heaters.

[0080] Design Principles and Structure: Number of Layers Selection: Select the number of layers M = 2 (K = 1). This is the minimum number of layers to achieve interlayer magnetic field suppression, and the structure is relatively simple.

[0081] Single - layer Design: Number of Conductors and Current Distribution: Keep the same in - layer design as in Example 1, that is, select the number of conductors N = 8 (J = 3), and adopt the in - layer octupole current configuration (+ -, - +, - +, + -).

[0082] Layout Configuration: Also adopt the optimized configuration D in Example 1 [as shown in (b) of Figure 7 、 Figure 16 , ensure that the core area is flat and the pads are located at the edges.

[0083] Interlayer Current Distribution: For the double - layer structure (M = 2), the most effective interlayer magnetic field suppression configuration is the magnetic dipole moment, that is, the current directions of the two layers are opposite. The configuration is (+ -), that is, a positive current is passed through the top layer and a negative current is passed through the bottom layer.

[0084] Overall Structure: The heater is a double - layer structure, and each layer adopts the octupole layout of configuration D. Through lead connection, the current directions of the top layer and the bottom layer are opposite.

[0085] Materials and Manufacturing: The materials and manufacturing processes are similar to those in Example 1. A polyimide substrate and constantan alloy conductors are used, and it is manufactured by the FPC process. The layer spacing is also about 43μm.

[0086] Performance Expectation and Verification Reference: Simulation Results: Refer to (a) of Figure 11 which shows the magnetic fields generated by double - layer heating films with different configurations. Configuration D (double - layer octupole) has a significant improvement in magnetic field suppression ability compared with configuration A (double - layer traditional pair - winding) (about 5.6 times improvement at z = 7mm). At the same time, by comparing (a) of Figure 11 with (b) of Figure 11 , it can be seen that the magnetic field value of the double - layer configuration D is higher than that of the four - layer configuration D, indicating that the four - layer structure has a better suppression effect. Figure 14 shows the magnetic field distribution of the double - layer configuration D heater near the gas chamber. The magnetic field at the center of the gas chamber is about 18.3683 pT / mA, and the maximum internal magnetic field is 28.9315 pT / mA. This is much lower than the unoptimized single - layer structure but higher than the four - layer structure in Example 1 (0.3136 pT / mA at the center).

[0087] Experimental Results: Refer to Figure 18The measured data therein shows the relationship between the magnetic field and current for the curve marked as "Configuration D - bilayer". Its slope (representing the magnetic field generated per unit current) is significantly lower than that of "Configuration A - bilayer" and "Configuration D - monolayer", but higher than that of "Configuration D - quadruple layer". This is consistent with the trend of the simulation results, verifying the effectiveness of the bilayer octupole design. Although the effect is not as good as that of the quadruple - layer octupole, it is still a significant improvement. The instruction manual mentions that "the bilayer multipole heating film can reduce the magnetic - field gradient, but the effect is halved". Here, "halved" should be understood as a discount compared to the quadruple - layer structure, but there is still a significant improvement compared to the traditional structure.

[0088] The bilayer octupole heater of this embodiment realizes good magnetic - field suppression effect and a certain reduction in magnetic - field gradient through the combination of in - layer octupoles and inter - layer magnetic dipoles. Its performance is significantly better than that of traditional heaters, and the structure is simpler than that of the quadruple - layer. It is suitable for applications with high performance requirements but limited cost and complexity.

[0089] Example 3: A quadruple - layer sixteen - pole low - magnetic - field flexible thin - film electric heater The purpose of this embodiment is to demonstrate the possibility of extending the design method of the present invention to a higher - order in - layer multipole configuration (sixteen - pole) to explore further improvement in magnetic - field suppression performance, especially in the region very close to the heating film or in scenarios with higher requirements for the in - layer gradient.

[0090] Design principle and structure: Number of layers selection: Keep the same number of layers M = 4 (K = 2) as in Example 1 to utilize the excellent inter - layer magnetic - field suppression effect brought by the quadruple - layer structure.

[0091] Single - layer design: Number of wires and current distribution: Select the number of wires N = 16 (J = 4). According to the principle of recursive grouping and the basic configuration (+--+), divide the 16 wires into four groups, with 4 wires in each group. The overall current direction is configured as (+--+). The 4 wires within each group are also configured as (+--+) or its reverse (-++-). For example, a possible sixteen - pole current configuration is (+--+,-++-,-++-,+--+).

[0092] Layout configuration: Based on the 16 wires and their current configuration, design the corresponding layout. The optimization idea of Configuration D in Example 1 can be referred to: arrange the overall configuration symmetrically or antisymmetrically around the central region, and move all lead pads to the edge of the layout. Since the wires are denser, the line width and line pitch may need to be adjusted according to the process capabilities, or increase the heater length while keeping the total width unchanged.

[0093] Inter - layer current distribution: Keep the same inter - layer quadruple - pole configuration (+--+) as in Example 1.

[0094] Overall Structure: The heater has a four-layer structure, and each layer adopts a specially designed 16-pole moment layout. Through lead connections, a (+--+) current direction configuration is achieved among the four layers.

[0095] Materials and Manufacturing: The materials and manufacturing processes are similar to those in Example 1. However, due to the increase in the number of wires within a single layer, higher requirements may be imposed on etching accuracy and alignment accuracy.

[0096] Performance Expectations and Verification References: Theoretical and Simulation Expectations: According to the multi-pole moment theory, higher-order multi-pole moments (16-pole moment vs. 8-pole moment) have a faster magnetic field decay near the source. Therefore, theoretically, the 16-pole moment configuration may have better magnetic field suppression than the 8-pole moment in the region very close to the heating film surface.

[0097] For positions slightly farther away (such as z = 7 mm), the main magnetic field suppression effect comes from the inter-layer quadrupole moment. Therefore, it is expected that the magnetic field value at z = 7 mm in this embodiment (four-layer 16-pole moment) compared with that in Example 1 (four-layer 8-pole moment) may not improve as significantly as from the traditional configuration A to the 8-pole moment, but there may still be a small improvement or better performance in terms of magnetic field gradient.

[0098] Special electromagnetic simulations are required to quantitatively evaluate the specific performance of the four-layer 16-pole moment design and compare it with the four-layer 8-pole moment. Refer to Figure 8 the comparison of single-layer multi-pole moment configurations in

[0099] Experimental Verification: Processable samples can be made and tested to directly compare the measured magnetic field data of the four-layer 16-pole moment and the four-layer 8-pole moment.

[0100] The four-layer 16-pole moment heater in this embodiment demonstrates the scalability of the design method of the present invention by adopting a higher-order in-layer multi-pole moment (16-pole moment) and combining an optimized inter-layer quadrupole moment configuration. It is expected to maintain the excellent far-field suppression ability of the four-layer structure while potentially providing further optimization in near-field suppression or in-layer gradient uniformity. It is applicable to application scenarios with extreme requirements for magnetic field suppression and gradient uniformity.

[0101] Example 4: A Four-Layer Low-Magnetic-Field Flexible Thin-Film Electric Heater Using an Alternative 8-Pole Moment Layout This example aims to illustrate that even if an 8-pole moment layout design slightly different from that in Example 1 (configuration D) (such as configuration C) is adopted, as long as the core multi-pole moment design principles (number of layers, in-layer / out-layer current configuration) are followed, very excellent magnetic field suppression effects can still be obtained.

[0102] Design Principles and Structure: Layer Selection: Keep M = 4 (K = 2).

[0103] Single - layer Design: Number of Conductors and Current Distribution: Keep N = 8 (J = 3), and adopt an in - layer octupole current configuration (+ -,- +,- +, + -).

[0104] Layout Configuration: Adopt Figure 7 Configuration C shown in. Configuration C is also an octupole design, but its conductor arrangement is slightly different from that of Configuration D (for example, the distance between the left - right two groups of four - wires may be slightly larger than that of Configuration D / E). It is also assumed that the pad - out optimization has been applied.

[0105] Inter - layer Current Distribution: Keep an inter - layer quadrupole configuration (+ - - +).

[0106] Overall Structure: The heater is a four - layer structure, and each layer adopts an octupole layout of Configuration C. Through lead connections, the (+ - - +) current direction configuration among the four layers is achieved.

[0107] Materials and Manufacturing: The materials and manufacturing processes are the same as those in Example 1.

[0108] Performance Expectation and Verification Reference: Simulation Results: Refer to Figure 11 (b) in, which shows the magnetic fields generated by four - layer heating films of different configurations. It can be seen that the simulation curves of Configuration C (four - layer octupole, alternative layout) and Configuration D (four - layer octupole, optimized layout) are very close, and both are far better than Configuration A (four - layer traditional counter - winding). At z = 7mm, the difference in magnetic field values between Configuration C and Configuration D is very small. This indicates that under the strong four - layer inter - layer suppression effect, although the specific implementation methods of the in - layer octupole layout (such as C and D) may bring slight differences, as long as it is an effective octupole design, a good overall effect can be achieved. Figure 8 The single - layer simulation comparison of also shows that Configurations B, C, D, and E are all significantly better than A, and D and E have a slight advantage because the conductor grouping is more compact.

[0109] Experimental Verification: Four - layer samples of Configuration C can be processed and compared with four - layer samples of Configuration D. It is expected that the measured results will also show that the performances of the two are very close and both are far better than the traditional configuration.

[0110] In this embodiment, a four-layer octupole heater with layout of configuration C is adopted to verify the robustness of the core design principle of the present invention. Even if there are some changes in the in-layer layout (such as configuration C vs configuration D), as long as the key elements of even layers, even wires, in-layer multipole current configuration, and inter-layer multipole current configuration are followed, excellent magnetic field suppression performance can be achieved. This provides more flexibility for practical design.

[0111] Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings in this specification, those skilled in the art can understand that they can make various modifications, substitutions, and variations to these embodiments without departing from the spirit and scope of the present invention. These modifications, substitutions, and variations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A multi-pole moment multi-layer low magnetic field flexible thin film electric heater, characterized in that: include: at least two layers of flexible substrate; A conductive layer disposed on the flexible substrate, wherein the conductive layer is patterned to form at least M electric heating layers, wherein M is a positive integer greater than or equal to 2; Each of the electric heating layers comprises at least N wire segments arranged along a predetermined path, wherein N is a positive integer greater than or equal to 4, and the current directions of the N wire segments are configured so as to form a multi-pole moment magnetic field suppression configuration in the plane of the electric heating layer; Furthermore, the current directions of the at least M electric heating layers are configured according to their positions in the stacked structure so as to form a multi-pole moment magnetic field suppression configuration in a direction perpendicular to the plane of the electric heating layer.

2. The electric heater according to claim 1, characterized in that: In the intra-layer multipole moment magnetic field suppression configuration, the number N of the wire segments is 2J, where J is a positive integer greater than or equal to 2.

3. The electric heater according to claim 2, characterized in that: The intra-layer multipole moment magnetic field suppression configuration is achieved by dividing the N wire segments into multiple groups and assigning a predetermined current direction to each group or each wire segment. The current direction configuration satisfies the recursive multipole moment cancellation condition, and the basic configuration is that the current direction of four adjacent or grouped wire segments is (+--+) or the current direction of two adjacent or grouped wire segments is (+-).

4. The electric heater according to claim 3, characterized in that: When N=8, the current directions of the eight wire segments are configured as (+-, -+, -+, +-) or an equivalent form thereof, forming an intra-layer octupole moment.

5. The electric heater according to claim 1, characterized in that: The layout configuration of each electric heating layer is an optimized multipole configuration, wherein the pads for drawing out current are arranged at the edge area of ​​the layout to avoid the crossing of the wires in the heating core area and to maintain flatness.

6. The electric heater according to claim 1, characterized in that: In the interlayer multipole moment magnetic field suppression configuration, the number of layers M of the electric heating layer is 2K, and K is a positive integer greater than or equal to 1.

7. The electric heater according to claim 6, characterized in that: The interlayer multipole moment magnetic field suppression configuration is achieved by assigning predetermined current directions to the M layers of electric heating layers. The current direction configuration satisfies the recursive multipole moment cancellation condition, and the basic configuration is that the current direction of four adjacent or grouped electric heating layers is (+--+).

8. The electric heater according to claim 7, characterized in that: When M=4, the current directions of the four electric heating layers from the top layer to the bottom layer are configured as (+--+), forming an interlayer quadrupole moment.

9. The electric heater according to claim 1, characterized in that: The electric heater is applied to a temperature control system of a nuclear magnetic resonance inertial sensor.

10. A method involving the multi-pole moment multi-layer low magnetic field flexible thin film electric heater according to any one of claims 1 to 9, characterized in that: The following steps are involved: a) determining the number of wires in a single electric heating layer as N, and determining the current direction configuration of the N wires according to the multipole moment principle within the layer; b) designing an optimized layout configuration of a single-layer electric heating layer based on the result of step a), including a wire path and a pad position; c) determining the number of layers M of the electric heating layer and determining the current direction configuration of the M layers of electric heating layer according to the principle of interlayer multipole moment; d) combining said steps b) and c) to form a complete multi-layer heater structure; e) The magnetic field suppression performance of the designed heater structure is verified and optimized through electromagnetic simulation.

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