An electromagnetic coil structure with controllable induced electric field and its construction method

Abstract

This invention discloses an electromagnetic coil structure with controllable induced electric field and its construction method, belonging to the field of non-invasive neuromodulation technology. The electromagnetic coil structure with controllable induced electric field includes at least three coils, each coil consisting of three wire segments forming three endpoints, a, b, and c. Assuming all three coils are located in the same three-dimensional coordinate system, the angle between segment ac and the negative Z-axis is acute in each coil. The at least three coils are spatially symmetrically distributed around the target point. This invention enables arbitrary controllability of the three-dimensional direction of the induced electric field within a small target area, improving the spatial utilization of the non-interference portion between the coil and the stimulation target. Simultaneously, the coil size is small, allowing it to serve as an independent unit for multi-channel parallel stimulation coils, improving coil spatial resolution and experimental controllability.

Description

Technical Field

[0001] This invention relates to an electromagnetic coil structure with controllable induced electric field and its construction method, belonging to the field of non-invasive neuromodulation technology, wherein the nerves include cranial nerves, optic nerves, etc. Background Technology

[0002] Transcranial magnetic stimulation (TMS) is one of the most widely used neurostimulation tools in brain science research and clinical treatment of neurological diseases. Magnetic stimulation generates a rapidly changing magnetic field through instantaneous high-current pulses. This magnetic field induces an electric field in brain tissue, thereby altering cell membrane potential and effectively enhancing or inhibiting neuronal excitability. It avoids the inflammation problems associated with electrical stimulation, which requires increasing stimulation intensity over long-term electrode implantation. TMS offers significant advantages in that it is painless and non-invasive.

[0003] Because the focus and depth of stimulation are mutually restrictive, the effectiveness of deep stimulation needs to be improved. Currently, it is generally believed that the activation region is where the induced electric field is at its maximum. However, the orientation of neurons may not be consistent with the direction of the induced electric field, so the stimulation may not be effective and may easily lead to energy waste. Therefore, some scholars believe that it is necessary to consider the directionality of the electric field when designing coils, but there are currently too few novel structures based on this design.

[0004] Patent CN114247055A proposes several coil structures. Figure 1 The two coil structures proposed in patent CN114247055A that can achieve controllable direction of induced electric field are truly effective. The wire segments OA, OB, OC, and OD shown in Figure (a), and wires ME, MF, and MG shown in Figure (b), are called the "skeleton" structure. The remaining wire segments are collectively referred to as the peripheral structure. As shown in Figure (c), the "skeleton" structure is projected onto the xoy plane as a cross shape, realizing two-dimensional planar controllable stimulation.

[0005] The structure in Figure (a) achieves z-direction stimulation by forming an α angle, which is suitable for stimulating large targets such as the human brain. However, when applied to small animals, the spatial resolution decreases and the peripheral structure interferes with the stimulation, making it difficult to achieve the ideal stimulation effect.

[0006] Adjusting the relative distance between the peripheral structure and the stimulus target, and reducing the number of peripheral structure leads, can improve the stimulation effect. In Figure (b), the three triangles reduce the number of peripheral structure leads, but due to field phase cancellation, stimulation in the z-direction cannot be achieved. Furthermore, the coils in (a) and (b) are interconnected when adjusting the relative distance between the peripheral structure and the stimulus target, changing the distance between the "skeleton" structure and the target point, thus failing to guarantee stimulation efficiency.

[0007] The aforementioned existing technologies suffer from limitations in achieving ideal stimulation effects and in ensuring stimulation efficiency. Due to the anisotropy of brain tissue, skull shape, distance between the skull and cortex, and other biological differences among individuals, the repeatability of stimulation effects from a single large stimulation coil is poor when applied to different individuals. Using multiple small stimulation coils in parallel can enhance spatial selectivity at stimulation sites without moving the coil device, and allows for flexible adjustment of the stimulation direction and intensity at local target points, thereby improving the overall effect and enhancing the universality of the coil structure for different individuals. Therefore, there is a need to design coils that are small in size, simple in structure, can be used in parallel, and can individually achieve arbitrary directional control in three-dimensional space. Summary of the Invention

[0008] This invention proposes an electromagnetic coil structure with controllable induced electric field and its construction method, which can realize a coil structure with arbitrary controllability in three-dimensional direction of induced electric field within a small target area, improve the spatial resolution of the coil and the controllability of the experiment, and solve the problems existing in the prior art.

[0009] An electromagnetic coil structure with controllable induced electric field is provided. The electromagnetic coil structure with controllable induced electric field includes at least three coils. Each coil is formed by three segments of wire, which in turn form three endpoints, namely points a, b and c. Assuming that the at least three coils are all located in the same three-dimensional coordinate system, the angle between segment ac and the negative Z-axis of each coil is an acute angle. The at least three coils are spatially symmetrically distributed around the target point.

[0010] Furthermore, the ac segment conductor is a straight line, while the ab and bc segments conductors are either straight lines or arbitrary curves.

[0011] Furthermore, the space formed by at least three coils around the target point is a regular n-sided space or a spherical space.

[0012] Furthermore, a motorized coil is inserted between at least three coils. The motorized coils are also distributed around the target point and are used to enhance the local electric field.

[0013] Furthermore, when the space surrounding the target point is a regular n-gon, point a in each coil is located at the vertex of the regular n-gon.

[0014] Furthermore, when the space surrounding the target is a spherical space, point a in each coil is located on the surface of the sphere.

[0015] A method for constructing an electromagnetic coil structure with controllable induced electric field, applied to the aforementioned electromagnetic coil structure with controllable induced electric field, includes the following steps:

[0016] S100. At least three coils are radially and symmetrically distributed around the target point. Each coil is formed by three wire segments, which in turn form three endpoints, namely points a, b, and c. The angle between segment ac and the negative direction of the Z-axis is acute. The space formed by the at least three coils around the target point is a regular n-gonal space or a spherical space.

[0017] S200. Each coil is energized to form an electric field.

[0018] Furthermore, following the S100, it also includes:

[0019] S150. If it is necessary to enhance the electric field in a specific direction, a motorized coil shall be added in the required specific direction in addition to at least three coils.

[0020] Furthermore, when the space formed around the target point is a regular n-gon space, point a in each of the at least three coils and the motor coil is located at the vertex of the regular n-gon.

[0021] Furthermore, when the space formed around the target is a spherical space, point a in each of the at least three coils and the motor coil is located on the surface of the sphere.

[0022] The present invention has the following beneficial effects: The electromagnetic coil structure and its construction method for a controllable induced electric field of the present invention can achieve arbitrary controllability of the three-dimensional direction of the induced electric field within a small target area, improving the space utilization rate of the non-interference portion between the coil and the stimulation target. Simultaneously, the coil size is small, allowing it to serve as an independent unit for multi-channel parallel stimulation coils, thus improving the coil's spatial resolution and experimental controllability. Attached Figure Description

[0023] Figure 1 The structure proposed in patent CN114247055A, wherein, Figure 1 (a) is a structure with four rectangular coils; Figure 1 (b) is a three-triangular coil structure; Figure 1 (c) is the projection onto the xoy plane;

[0024] Figure 2 It forms a three-dimensional "skeleton" structure in space;

[0025] Figure 3 It is a coil assembly structure;

[0026] Figure 4 It is a coil array structure;

[0027] Figure 5 It takes the form of three isosceles triangles;

[0028] Figure 6 This is a projection diagram of the coil onto the xoy plane.

[0029] Figure 7 This is a method for implementing induced electric field direction control, wherein, Figure 7 (a) is power-on mode 1; Figure 7 (b) is power-on mode 2;

[0030] Figure 8 The electric field distribution of the cross section below the coil under various energizing methods;

[0031] Figure 9 The electric field distribution on the cross section when the composite current is applied is given, where, Figure 9 (a) is E; Figure 9 (b) is E x ; Figure 9 (c) is E y ; Figure 9 (d) is E z ;

[0032] Figure 10 This is a structural diagram, in which, Figure 10 (a) is a structure with four triangles evenly distributed; Figure 10 (b) is a non-uniformly distributed five triangular structure;

[0033] Figure 11 This is a schematic diagram of a parallel array of three triangular coils. Detailed Implementation

[0034] 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, and 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.

[0035] Reference Figures 2-4 As shown, this invention proposes an electromagnetic coil structure with controllable induced electric field. The electromagnetic coil structure with controllable induced electric field includes at least three coils, each coil is formed by three segments of wire, which in turn form three endpoints, namely points a, b and c. Assuming that the at least three coils are all located in the same three-dimensional coordinate system, then in each coil, the angle between segment ac and the negative direction of the Z-axis is an acute angle. The at least three coils are spatially symmetrically distributed around the target point.

[0036] Specifically, such as Figure 2 As shown, by designing the "skeleton" structure as a separate spatial three-dimensional structure, the angles between the conductors and the negative z-axis are θ1, θ2, ... θ. nThe number of intersecting wires *n* above the target point corresponds to the number of coil groups *m*. As shown in Figure 3, simplifying the outer structure requires minimizing the number of line segments between a→b→c. These segments can be straight lines or arcs, and the connections are unrestricted, resulting in a coil group structure with controllable induced field direction. This not only reduces the number of line segments but also allows for independent adjustment of the outer structure without affecting the relative position of the "skeleton" structure and the target point, and also compensates for... Figure 1 What is missing in (b) is the ability to stimulate in the x, y, and z directions with three “skeleton” line segments.

[0037] like Figure 4 As shown, multiple coil structures form a coil array to stimulate i (i = I, II, III...) target points. The number of "skeleton" structures in each independent unit can be different.

[0038] Furthermore, segment ac is a straight line, while segments ab and bc are either straight lines or arbitrary curves.

[0039] Furthermore, the space formed by at least three coils around the target point is a regular n-sided space or a spherical space.

[0040] Furthermore, a motorized coil is inserted between at least three coils. The motorized coils are also distributed around the target point and are used to enhance the local electric field.

[0041] Furthermore, when the space surrounding the target point is a regular n-gon, point a in each coil is located at the vertex of the regular n-gon.

[0042] Furthermore, when the space surrounding the target is a spherical space, point a in each coil is located on the surface of the sphere.

[0043] A method for constructing an electromagnetic coil structure with controllable induced electric field, applied to the aforementioned electromagnetic coil structure with controllable induced electric field, includes the following steps:

[0044] S100. At least three coils are radially and symmetrically distributed around the target point. Each coil is formed by three wire segments, which in turn form three endpoints, namely points a, b, and c. The angle between segment ac and the negative direction of the Z-axis is acute. The space formed by the at least three coils around the target point is a regular n-gonal space or a spherical space.

[0045] S200. Each coil is energized to form an electric field.

[0046] Furthermore, following the S100, it also includes:

[0047] S150. If it is necessary to enhance the electric field in a specific direction, a motorized coil shall be added in the required specific direction in addition to at least three coils.

[0048] Furthermore, when the space formed around the target point is a regular n-gon space, point a in each of the at least three coils and the motor coil is located at the vertex of the regular n-gon.

[0049] Furthermore, when the space formed around the target is a spherical space, point a in each of the at least three coils and the motor coil is located on the surface of the sphere.

[0050] The following are at least one specific embodiment of the present invention and its effects:

[0051] The following example, using one configuration of three triangular coils, illustrates how to achieve controllable induced field direction. The coil structure is as follows: Figure 5 As shown, the coil consists of three identical isosceles triangles with leg length 'a' and base length 'b'. The coil distribution is as follows: Figure 6 As shown, coils 1 and 2 form angles of 30° with the negative and positive y-axis, respectively. Coil 3 is located in the xoz plane. The three coils are symmetrically distributed in space at 120° intervals, with spherical or regular n-sided gaps reserved in between to prevent overheating of the coils; the radius of the gaps is R.

[0052] When energized in mode 1, the current flowing through the coil group is I. 11 I 12 I 13 And the magnitudes of the currents are equal. 11 =I 12 =I 13 The positive direction of the current is from A to B. The current flowing through coil group 2 in energizing mode is also the same magnitude. 21 =I 22 =I 23 I 31 =I 32 =I 33 The direction of the current is as follows Figure 7 As shown.

[0053] According to Lenz's law, the direction of the induced electric field in the coil is opposite to the direction of the current. The current flowing through the coil is I = 1 A, the frequency is f = 2500 Hz, the radius R is 1.5 mm, the leg length a is 10 mm, and the included angle θ is 120°. Figure 8 Table 1 shows the electric field distribution at a cross section below the coil under three energizing methods. The electric field values ​​at the target point are shown in Table 1. The three energizing methods only produce electric fields in the x, y, and z directions at the target point.

[0054]

[0055] Table 1 (Note: m = 1, 2, 3 represent the energizing method; the current direction is positive from A to B, the same applies below.)

[0056] Therefore, the current required to generate a unit basis vector electric field at the target point can be calculated, as shown in Table 2.

[0057]

[0058] Table 2

[0059] Taking the generation of a vector electric field E(1, 2, -1) V / m at the target point as an example, its component E in the direction of the basis vector is... x =1,E y =2,E z =-1, I j =i 1j +2i 2j -i 3j (j=1, 2, 3), the combined current required to flow through the coil group is (I1, I2, I3)=(0.46×10 3 -3.18×10 3 0.22×10 3 A.

[0060] like Figure 9 The electric field distribution of the cross section containing the target point when the synthetic current is applied is shown. The electric field value generated at the target point (0,0,-0.00675) is consistent with the expectation.

[0061] Figure 10 Other coil structures for magnetic interference methods that can achieve controllable induced field direction for small targets are listed. The structures are divided into symmetrical and asymmetrical distributions; the asymmetrical distribution can enhance the field value in a specific direction. (a) shows a uniform distribution, and (b) shows a non-uniform distribution, which can enhance the electric field component value in the z-direction.

[0062] Coils can serve as local units in parallel coil arrays, enabling flexible stimulation of local target points. (xoy plane projection is shown below.) Figure 11 As shown.

[0063] The above examples are only for helping to understand the method and core idea of ​​the present invention. For those skilled in the art, based on the idea of ​​the present invention, several improvements and modifications can be made in specific implementation methods and application scope, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. An electromagnetic coil structure with controllable induced electric field, characterized in that, The electromagnetic coil structure with controllable induced electric field includes at least three coils, each coil being formed by three segments of wire, thus forming three endpoints, namely points a, b, and c. Assuming that the at least three coils are all located in the same three-dimensional coordinate system, then in each coil, the angle between segment ac and the negative Z-axis is an acute angle. The at least three coils are symmetrically distributed around the target point in space, and the angles formed by adjacent coils are the same. The wire segment ac is a straight line, and the wire segments ab and bc are straight lines or arbitrary curves.

2. The electromagnetic coil structure with controllable induced electric field according to claim 1, characterized in that, The space formed by the at least three coils around the target point is a regular n-sided space or a spherical space.

3. The electromagnetic coil structure with controllable induced electric field according to claim 2, characterized in that, Between the at least three coils, a motorized coil is inserted, which is also distributed around the target point and is used to enhance the local electric field.

4. The electromagnetic coil structure with controllable induced electric field according to claim 3, characterized in that, When the space surrounding the target point is a regular n-sided polygon, point a in each coil is located at the vertex of the regular n-sided polygon.

5. The electromagnetic coil structure with controllable induced electric field according to claim 3, characterized in that, When the space surrounding the target is a spherical space, point a in each coil is located on the surface of the sphere.

6. A method for constructing an electromagnetic coil structure with controllable induced electric field, applied to the electromagnetic coil structure with controllable induced electric field as described in any one of claims 1-5, characterized in that, The method for constructing the electromagnetic coil structure with controllable induced electric field includes the following steps: S100. At least three coils are radially and symmetrically distributed around the target point. Each of the at least three coils is formed by three wire segments, which in turn form three endpoints, namely points a, b, and c. The angle between segment ac and the negative direction of the Z-axis is acute. The space formed by the at least three coils around the target point is a regular n-sided space or a spherical space. S200. Each coil is energized to form an electric field.

7. The method for constructing an electromagnetic coil structure with controllable induced electric field according to claim 6, characterized in that, Following S100 are: S150. If it is necessary to enhance the electric field in a specific direction, a motorized coil shall be added in the required specific direction in addition to the at least three coils.

8. The method for constructing an electromagnetic coil structure with controllable induced electric field according to claim 7, characterized in that, When the space formed around the target point is a regular n-gon space, point a in each of the at least three coils and the motor coil is located at the vertex of the regular n-gon.

9. The method for constructing an electromagnetic coil structure with controllable induced electric field according to claim 7, characterized in that, When the space formed around the target point is a spherical space, point a in each of the at least three coils and the motor coil is located on the surface of the sphere.

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