Transcranial magnetic stimulation coil and transcranial magnetic stimulation device

Abstract

The present invention relates to the technical field of medical devices, and discloses a transcranial magnetic stimulation coil and a transcranial magnetic stimulation device. The transcranial magnetic stimulation coil comprises a solenoid and a magnetic core. The solenoid comprises a tube body and a conductor, the tube body extends along a first axis, and the tube body conductor is spirally wound on the side wall of the tube body to form a coil, the tube body is provided with a first side line and a second side line parallel to and coplanar with the first axis, the interval between two adjacent turns of the conductor gradually increases from the first side line to the second side line, and the projection of the end face of the first end of the tube body in the first plane is a straight line and intersects with the first side line and is arranged at an acute angle. The magnetic core is placed inside the tube body and arranged inside the coil, the magnetic core extends along a second axis, the second axis is parallel to the first axis, and the outer side wall of the magnetic core on the side facing the first side line is attached to the inner wall of the tube body, and the outer side wall of the magnetic core on the side facing the second side line is arranged at an interval from the inner wall of the tube body. The present invention improves the focusing of the transcranial magnetic stimulation coil.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and in particular to a transcranial magnetic stimulation coil and a transcranial magnetic stimulation device. Background Art

[0002] Transcranial magnetic stimulation (TMS) is a non-invasive medical device based on electromagnetic induction technology. It uses pulsed magnetic fields to act on the central nervous system, change the membrane potential of cerebral cortical nerve cells, generate induced currents, affect brain metabolism and neural electrical activity, and thus cause a series of physiological and biochemical reactions. It is a magnetic stimulation technology. Because of its advantages such as painless, non-damaging and radiation-free, it is widely used in various fields. The stimulation coil is the load of the pulse current generating circuit and is made of a conductor with a low resistivity. When the shape of the coil is different, the distribution of the induced electric field generated will also be different, which directly affects the focusing, that is, the size of the focusing area at the target point of the patient's head. Under the condition of ensuring the magnetic field strength, the smaller the focusing area, the higher the focusing. Therefore, the design of the coil is the key to TMS research. High focusing can narrow the stimulation range, enhance the pertinence of the stimulation at the patient's target point, and avoid stimulating irrelevant neural tissues in the skull. The existing transcranial magnetic stimulation coils are mainly based on eight-shaped coils and circular coils, with a large magnetic field strength, but the range of stimulation on the patient's head is also large, and the focusing is poor, which affects the treatment effect.

[0003] Based on this, there is an urgent need for a transcranial magnetic stimulation coil and a transcranial magnetic stimulation device to solve the above-mentioned problems. Summary of the invention

[0004] The object of the present invention is to provide a transcranial magnetic stimulation coil and a transcranial magnetic stimulation device, which improve the focusing of the transcranial magnetic stimulation coil and can stimulate the target area of ​​the patient's head in a targeted manner.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A transcranial magnetic stimulation coil, comprising:

[0007] A solenoid, comprising a tube body and a wire, wherein the tube body extends along a first axis, and the wire is spirally wound on a side wall of the tube body to form a coil, a first side line and a second side line parallel to the first axis are arranged on the tube body, the first axis, the first side line and the second side line are all located in a first plane, the interval between two adjacent turns of the wire gradually increases from the first side line to the second side line, and the projection of the end face of the first end of the tube body in the first plane is a straight line and is arranged at an acute angle to the first side line;

[0008] A magnetic core, wherein the magnetic core is placed inside the tube body and arranged inside the coil, the magnetic core extends along a second axis, the second axis is parallel to the first axis, and the outer wall of the magnetic core on the side facing the first side line is attached to the inner wall of the tube body, and the outer wall of the magnetic core on the side facing the second side line is spaced apart from the inner wall of the tube body.

[0009] Preferably, the tube body comprises a first straight wall and a second straight wall, the first straight wall and the second straight wall are both parallel to the first axis, the first straight wall and the second straight wall are connected at an acute angle, and a connecting line between the first straight wall and the second straight wall is the first side line.

[0010] Preferably, the active end of the magnetic core is arranged toward the first end of the tube body, and the end surface of the active end and the end surface of the first end are in the same plane.

[0011] Preferably, a spiral winding groove is provided on the side wall of the tube body, and the wire is placed in the winding groove.

[0012] Preferably, the tube body is a fan-shaped tube, and the magnetic core is a fan-shaped column.

[0013] Preferably, the transcranial magnetic stimulation coil further comprises a shell, and the shell covers the outside of the solenoid.

[0014] Preferably, the shell extends along the third axis, the first axis is arranged in parallel with the third axis, and both ends of the shell along the third axis are blocked with end plates, and the two end plates are perpendicular to the third axis.

[0015] Preferably, the housing is provided with a wire entry hole for the wire to pass through the housing and a wire exit hole for the wire to pass through the housing.

[0016] Preferably, a cross section of the housing perpendicular to the third axis is fan-shaped.

[0017] A transcranial magnetic stimulation device comprises the transcranial magnetic stimulation coil as described above.

[0018] Beneficial effects of the present invention:

[0019] When in use, the first axis is perpendicular to the patient's head, and the first side line is ensured to pass through the target point of the patient's head, and the first end of the tube body is arranged toward the patient's head. At this time, the interval between two adjacent turns of wire in the coil located above the target point of the patient's head along the first axis direction is small, and the interval between two adjacent turns of wire along the first axis direction gradually increases from the first side line to the second side line, that is, the wire is wound more tightly at the first side line. The magnetic field strength at the target point is improved, thereby improving the electric field strength induced at the target point, and increasing the stimulation intensity at the target point. Since the second side line is located in the non-target area and is far away from the target point, the magnetic field strength in the non-target area is reduced, so that the electric field induced in the non-target area is weak, and the action area of ​​the transcranial magnetic stimulation coil is limited to the vicinity of the target point, the action area of ​​the transcranial magnetic stimulation coil is reduced, the focusing area is reduced, and the focusing of the transcranial magnetic stimulation coil at the target point is improved, which is conducive to targeted treatment of the target point and ensures the treatment effect. In addition, when the first end is set toward the patient, the coil at the first side line can be as close to the patient's head as possible, and there is a certain distance between the coil at the second side line and the patient's head, and the distance gradually increases from the first side line to the second side line. The magnetic field generated by the magnetic core and the coil at the first side line is attenuated less during the transmission to the head, while the magnetic field generated by the magnetic core and the coil at the second side line is attenuated more during the transmission to the head, further ensuring that the induced electric field at the target point is strong, and further improving the focusing. The magnetic core is arranged in a close contact with the inner wall of the tube body corresponding to the first side line, and is arranged at intervals with the inner wall of the tube body corresponding to the second side line, further improving the magnetic field strength that can be generated by the coil at the first side line, and the magnetic core is away from the non-target area, reducing the increase in the electric field strength induced by the magnetic core for the non-target area corresponding to the second side line, and further improving the focusing of the transcranial magnetic stimulation coil. The transcranial magnetic stimulation coil provided in this embodiment increases the stimulation intensity at the target point and weakens the stimulation intensity at the non-target area, so that the difference in stimulation intensity between the target point and the non-target area is enlarged, and the focusing of the transcranial magnetic stimulation coil is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a cross-sectional view of a transcranial magnetic stimulation coil provided by an embodiment of the present invention;

[0021] Figure 2 The embodiment of the present invention provides a transcranial magnetic stimulation coil along the Figure 1 Sectional view of section AA;

[0022] Figure 3 It is a structural schematic diagram of a part of the structure of the transcranial magnetic stimulation coil provided in an embodiment of the present invention.

[0023] In the figure:

[0024] 1. solenoid; 11. tube body; 111. first straight wall; 112. second straight wall; 113. first cover; 114. second cover; 12. wire;

[0025] 2. Magnetic core;

[0026] 3. Shell; 31. End plate;

[0027] 4. Winding groove. DETAILED DESCRIPTION

[0028] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0032] This embodiment provides a transcranial magnetic stimulation coil. Specifically, Figure 1-Figure 3As shown, the transcranial magnetic stimulation coil includes: a solenoid 1 and a magnetic core 2. The solenoid 1 includes a tube body 11 and a wire 12, the tube body 11 extends along a first axis, and the wire 12 is spirally wound on the side wall of the tube body 11 to form a coil, and the tube body 11 is provided with a first side line and a second side line parallel to the first axis, the first axis, the first side line and the second side line are all located in the first plane, the interval between two adjacent turns of the wire 12 gradually increases from the first side line to the second side line, and the projection of the end face of the first end of the tube body 11 in the first plane is a straight line and intersects with the first side line and is arranged at an acute angle. The magnetic core 2 is placed in the tube body 11 and arranged inside the coil, the magnetic core 2 extends along a second axis, the second axis is parallel to the first axis, and the outer side wall of the magnetic core 2 on the side facing the first side line is attached to the inner wall of the tube body 11, and the outer side wall of the magnetic core 2 on the side facing the second side line is spaced from the inner wall of the tube body 11. In this embodiment, the angle between the projection of the end surface of the first end of the tube body 11 in the first plane and the first side line is 70°. Figure 2 In terms of the direction in the middle, the first end is located below the tube body 11 and Figure 1 In the figure, the first plane is the AA section. It can be understood that the magnetic core 2 is placed within the range where the wire 12 is wound to form a coil.

[0033] When in use, the first axis is perpendicular to the patient's head, and ensures that the first side line passes through the target point of the patient's head, and the first end of the tube body 11 is set toward the patient's head. At this time, the interval between the two adjacent turns of wire 12 in the coil above the target point of the patient's head is small, and the interval between the two adjacent turns of wire 12 gradually increases from the first side line to the second side line, that is, the wire 12 is wound more tightly at the first side line. The magnetic field strength at the target point is improved, thereby improving the electric field strength induced at the target point, and increasing the stimulation intensity at the target point. Since the second side line is located in the non-target area and is far away from the target point, the magnetic field strength in the non-target area is reduced, so that the electric field induced in the non-target area is weak, and the action area of ​​the transcranial magnetic stimulation coil is limited to the vicinity of the target point, the action area of ​​the transcranial magnetic stimulation coil is reduced, the focusing area is reduced, and the focusing of the transcranial magnetic stimulation coil at the target point is improved, which is conducive to targeted treatment of the target point and ensures the treatment effect. In addition, when the first end is set toward the patient, the coil at the first side line can be as close to the patient's head as possible, and there is a certain distance between the coil at the second side line and the patient's head, and the distance gradually increases from the first side line to the second side line. The magnetic field generated by the magnetic core and coil at the first side line is attenuated less during the process of being transmitted to the head, while the magnetic field generated by the magnetic core and coil at the second side line is attenuated more during the process of being transmitted to the head, further ensuring that the induced electric field at the target point is strong, and further improving the focusing. The magnetic core 2 is arranged in close contact with the inner wall of the tube body 11 corresponding to the first side line, and is spaced from the inner wall of the tube body 11 corresponding to the second side line, further improving the magnetic field strength that can be generated by the coil at the first side line, and the magnetic core 2 is far away from the non-target area, reducing the increase in the electric field strength induced by the magnetic core 2 to the non-target area corresponding to the second side line, and further improving the focusing of the transcranial magnetic stimulation coil. The transcranial magnetic stimulation coil provided in this embodiment increases the stimulation intensity at the target point and weakens the stimulation intensity at the non-target area, so that the difference in stimulation intensity between the target point and the non-target area is enlarged, thereby improving the focusing of the transcranial magnetic stimulation coil.

[0034] In the present embodiment, the magnetic core 2 is solid and made of silicon steel sheet, and the magnetic core 2 is fixed inside the tube body 11 by an adhesive layer. The tube body 11 is provided with a first cover 113 at the first end to prevent the magnetic core 2 from being separated from the tube body 11, thereby ensuring the role of the magnetic core 2 in strengthening the magnetic field strength. The end of the tube body 11 away from the first end is the second end, and the end face of the second end is arranged parallel to the end face of the first end, and a second cover 114 is arranged on the end face of the second end. In other embodiments, the end face of the second end can also be arranged perpendicular to the first axis, which is not limited here. In addition, the covers at both ends of the tube body 11 can be integrally arranged with the tube body 11, or can be separately arranged, and connected by bonding or snapping.

[0035] Specifically, the tube body 11 includes a first straight wall 111 and a second straight wall 112, both of which are parallel to the first axis, and the first straight wall 111 and the second straight wall 112 are connected at an acute angle, and the connecting line between the first straight wall 111 and the second straight wall 112 is a first side line. The first straight wall 111 and the second straight wall 112 connected at an acute angle are provided, which further reduces the focusing area of ​​the magnetic field generated by the wire 12 corresponding to the first side line, improves the focusing, and is conducive to targeted stimulation of the target point on the patient's head.

[0036] Furthermore, the tube body 11 is a fan-shaped tube, and the magnetic core 2 is a fan-shaped column. For the circular columnar tube body 11 and the magnetic core 2, the area of ​​the induced electric field is still annular, so that the area acting at the target point is larger; while the area of ​​the induced electric field on the patient's head of the tube body 11 and the magnetic core 2 with a fan-shaped cross section is a fan-shaped ring. When the first side line is placed above the target point, that is, the tip of the fan-shaped cross section is placed above the target point, the electric field area induced at the target point is reduced, and the focusing at the target point is improved. The radius of the cross-sectional sector of the magnetic core 2 is 5mm, the angle between the two straight sides of the sector is 60°, and the overall height along the first axis is 120mm. The radius of the cross-sectional sector of the tube body 11 is 10mm, the angle between the two straight sides of the sector is 60°, and the overall height along the first axis is 120mm. In other embodiments, the size of the tube body 11 and the magnetic core 2 can be adaptively adjusted, which is not limited here.

[0037] It can be understood that the first side line passes through the apex of the fan-shaped cross section of the tube body 11, and the two straight sides of the magnetic core 2 can coincide with the two straight sides of the tube body 11, which is convenient for positioning and installing the magnetic core 2 and ensures focusing. That is, the tube body 11 is provided with an arc surface at the second side line, and the two ends of the arc surface are respectively connected to the first straight wall 111 and the second straight wall 112, so that the first straight wall 111, the arc surface and the second straight wall 112 are connected end to end to form a fan-shaped tube. In other words, since the first plane is the AA cross section, the straight line where the AA cross section intersects with the arc surface is the second side line. Figure 2 In the first side line Figure 2 On the left side, the second side line is Figure 2 It can be understood that the first plane is sandwiched between the first straight wall 111 and the second straight wall 112, and the first plane intersects the first straight wall 111 and the second straight wall 112 at the first side line, and specifically the angles between the first plane and the first straight wall 111 and the second straight wall 112 are the same, both of which are 30°. The distance between the first axis and the first side line is the same as the distance between the first axis and the second side line.

[0038] In other embodiments, the cross-section of the tube body 11 and the magnetic core 2 perpendicular to the first axis may also be triangular. That is, the tube body 11 is provided with a third straight wall at the second side line, and the two ends of the third straight wall are respectively connected to the first straight wall 111 and the second straight wall 112, so that the first straight wall 111, the third straight wall and the second straight wall 112 are connected end to end to form a tube with a triangular cross-section.

[0039] Preferably, the active end of the magnetic core 2 is arranged toward the first end of the tube body 11, and the end surface of the active end is in the same plane as the end surface of the first end. The end surface of the magnetic core 2 facing the cover is in contact with the cover, which facilitates the placement of the magnetic core 2 inside the tube body 11, avoids the magnetic core 2 shaking inside the tube body 11 when using the transcranial magnetic stimulation coil, and ensures improved practicality.

[0040] Preferably, a spiral winding groove 4 is opened on the side wall of the tube body 11, and the wire 12 is placed in the winding groove 4. The winding groove 4 is provided to facilitate winding the wire 12 on the tube body 11 according to the winding groove 4, thereby simplifying the processing process.

[0041] In this embodiment, the width of the winding groove 4 is 2 mm, the wire 12 is a 1 mm enameled copper wire, and a single-strand wire 12 can be used to wind the tube body 11, or multiple-strand wires 12 can be used to wind the tube body 11. The tube body 11 is made of ABS resin or PVC plastic, and the winding groove 4 can be opened on the tube body 11 after the tube body 11 is processed, or the winding groove 4 can be directly set during the printing process through 3D printing.

[0042] Specifically, the winding groove 4 is a multi-layer spiral structure along the first axis. The winding starting point of the wire 12 is the first layer, and each layer includes three sections. The starting point of the first section of the first layer of the winding groove 4 is at the sharp point of the fan-shaped section of the tube body 11, and reaches the arc surface along the fan-shaped straight edge corresponding to the first straight wall 111. The second section of the first layer bypasses the arc surface, and the plane where the wire 12 at the second section is perpendicular to the first axis. The third section of the first layer starts at the connection between the arc edge and the second straight wall 112, and reaches the sharp point of the fan-shaped section of the tube body 11 along the second straight wall 112, and the end point of the third section is located above the starting point of the first section; the second, third, fourth, and fifth layers of the winding groove 4 are arranged in the same manner as the first layer. The starting points of the winding groove 4 in the first, second, third, fourth, and fifth layers are respectively located 3mm, 13mm, 23mm, 33mm, and 43mm above the sharp point of the first end face of the tube body 11, that is, the winding groove 4 is spaced 10mm apart from the starting points of the first, second, third, fourth, and fifth layers. The end points of the winding groove 4 in the first, second, third, fourth and fifth layers are respectively located at 13mm, 23mm, 33mm, 43mm and 53mm above the tip of the first end face of the tube body 11, that is, the end point of the winding groove 4 in the previous layer is the starting point of the winding groove 4 in the next layer, and the spacing between the starting points of the two layers of winding grooves 4 is 10mm. The wires 12 of the second section of the winding groove 4 in the first, second, third, fourth and fifth layers are respectively located at 23mm, 43mm, 63mm, 83mm and 103mm above the fan-shaped arc edge on the first end face, that is, the spacing between the second sections of the two layers of winding grooves 4 is 20mm. The winding of the winding groove 4 at the tip of the fan-shaped cross section is denser than the winding of the winding groove 4 at the arc edge, which ensures focusing.

[0043] Preferably, the transcranial magnetic stimulation coil also includes a shell 3, which covers the outside of the solenoid 1. The shell 3 protects the solenoid 1, improves the durability of the solenoid 1, avoids damage to the wire 12, and ensures the functionality of the transcranial magnetic stimulation coil.

[0044] Preferably, the housing 3 extends along the third axis, the first axis is arranged parallel to the third axis, and both ends of the housing 3 along the third axis are blocked with end plates 31, and both end plates 31 are perpendicular to the third axis. The end plates 31 of the housing 3 are perpendicular to the third axis, and the end plates 31 can be brought into contact with the patient's head, thereby preventing the tip of the first end face of the tube body 11 from poking the skin and improving practicality. It can be understood that in order to ensure the focusing of the transcranial magnetic stimulation coil, when using the transcranial magnetic stimulation coil provided in this embodiment, the end of the housing 3 close to the first cover 113 is facing the patient's head. In addition, when using the transcranial magnetic stimulation coil provided in this embodiment, the end plate 31 can be used with a spacing of 1 mm between the patient's head.

[0045] Furthermore, the housing 3 is provided with an inlet hole for the wire 12 to pass through the housing 3 and an outlet hole for the wire 12 to pass through the housing 3. The inlet hole and the outlet hole are provided to facilitate the connection of the wire 12 with the power supply device, which is beneficial to supply power to the coil.

[0046] Preferably, the cross section of the shell 3 perpendicular to the third axis is fan-shaped. In this embodiment, the radius of the bottom fan of the shell 3 is greater than 10 mm, the height is 120 mm, and the material of the shell 3 is ABS resin. In other embodiments, the size of the shell 3 is determined according to the size of the spiral tube 1, which is not limited here.

[0047] This embodiment also provides a transcranial magnetic stimulation device. The transcranial magnetic stimulation device includes the above transcranial magnetic stimulation coil. The stimulation intensity at the target point is increased, and the stimulation intensity at the non-target area is weakened, so that the difference in stimulation intensity between the target point and the non-target area is enlarged, which facilitates the transcranial magnetic stimulation device to stimulate the target point in a targeted manner and ensure the treatment effect.

[0048] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A transcranial magnetic stimulation coil, characterized in that: include: A solenoid (1), comprising a tube body (11) and a conductive wire (12), the tube body (11) extending along a first axis, the conductive wire (12) being spirally wound on a side wall of the tube body (11) to form a coil, the tube body (11) being provided with a first side line and a second side line parallel to the first axis, the first axis, the first side line and the second side line all being located in a first plane, the interval between two adjacent turns of the conductive wire (12) gradually increasing from the first side line to the second side line, and the projection of an end face of a first end of the tube body (11) in the first plane being a straight line and being arranged at an acute angle to the first side line; a magnetic core (2), the magnetic core (2) being placed in the tube (11) and arranged inside the coil, the magnetic core (2) extending along a second axis, the second axis being parallel to the first axis, and the outer wall of the magnetic core (2) on the side facing the first side line being in contact with the inner wall of the tube (11), and the outer wall of the magnetic core (2) on the side facing the second side line being spaced apart from the inner wall of the tube (11); The tube body (11) comprises a first straight wall (111) and a second straight wall (112), the first straight wall (111) and the second straight wall (112) are both parallel to the first axis, the first straight wall (111) and the second straight wall (112) are connected at an acute angle, and a connecting line between the first straight wall (111) and the second straight wall (112) is the first side line; A spiral winding groove (4) is provided on the side wall of the tube body (11), and the conducting wire (12) is placed in the winding groove (4).

2. The transcranial magnetic stimulation coil according to claim 1, characterized in that: The active end of the magnetic core (2) is arranged toward the first end of the tube body (11), and the end surface of the active end and the end surface of the first end are in the same plane.

3. The transcranial magnetic stimulation coil according to claim 1, characterized in that: The tube body (11) is a fan-shaped tube, and the magnetic core (2) is a fan-shaped column.

4. The transcranial magnetic stimulation coil according to claim 3, characterized in that: The transcranial magnetic stimulation coil further comprises a shell (3), wherein the shell (3) is coated on the outside of the solenoid (1).

5. The transcranial magnetic stimulation coil according to claim 4, characterized in that: The shell (3) extends along a third axis, the first axis is arranged parallel to the third axis, and both ends of the shell (3) along the third axis are blocked by end plates (31), and the two end plates (31) are perpendicular to the third axis.

6. The transcranial magnetic stimulation coil according to claim 4, characterized in that: The housing (3) is provided with a wire entry hole for the wire (12) to pass through the housing (3) and a wire exit hole for the wire (12) to pass through the housing (3).

7. The transcranial magnetic stimulation coil according to claim 5, characterized in that: The cross section of the housing (3) perpendicular to the third axis is fan-shaped.

8. A transcranial magnetic stimulation device, characterized in that: Comprising a transcranial magnetic stimulation coil as described in any one of claims 1-7.

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