WO2010004491A1

WO2010004491A1 - Toroidal coil arrangement

Info

Publication number: WO2010004491A1
Application number: PCT/IB2009/052895
Authority: WO
Inventors: Alexander C. De Rijck; Hendrik Huisman
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-07-11
Filing date: 2009-07-03
Publication date: 2010-01-14

Abstract

A toroidal coil arrangement is disclosed which comprises a first toroid coil with a first set of windings (10, 11, 12, 13) which progress in a counterclockwise direction along the toroid, and a second toroid coil with a second set of windings (20, 21, 22, 23) which progress in a clockwise direction along the toroid, wherein both toroid coils are electrically connected with each other. This coil arrangement is especially suitable for use as a part of an electronic circuit which is positioned within the examination volume of a magnetic resonance imaging system, because the net axial magnetic field of this coil arrangement is substantially reduced so that disturbing interferences with the functioning of the MRI system, especially with the MR image generation, are accordingly decreased or prevented.

Description

Toroidal coil arrangement

FIELD OF THE INVENTION

The invention relates to a toroidal coil arrangement, especially for use in a magnetic resonance imaging (MRI) system or a magnetic resonance (MR) scanner.

BACKGROUND OF THE INVENTION

As is generally known, MR imaging systems or scanners are provided with an imaging or examination space in which an examination object, usually a patient, is exposed to high static and RF magnetic fields in order to excite magnetic resonance effects in the tissue of the examination object, which resonance effects are detected by means of an RF antenna for generating an MR image of the examination object in a known manner.

For the operation of the MR imaging system or scanner and especially for detecting the magnetic resonance effects, it is often desired to place certain electronic units into the imaging space. Generally, this can cause a disturbance of the generated static or RF magnetic fields, resulting in disturbances of the generated MR image, or the electronic units themselves are detrimentally influenced by the static or RF magnetic fields within the imaging space, both because such the electronic units often comprise inductive elements.

SUMMARY OF THE INVENTION

It has revealed that especially when using such inductive elements in the form of coils, a number of stringent requirements apply in order to decrease or prevent the occurrence of the above and other disturbing interferences:

Ferrite materials e.g. cannot be used because they would greatly distort the generated MR image due to their magnetic properties. Furthermore, the static magnetic field within the MR imaging space would quickly saturate such ferrite materials so that they can no longer work properly.

Even without the presence of ferrite materials, the external field of an inductive element, especially of a coil, can distort the generated MR image. In order to minimize this distortion, the coils should be made as small as possible. Another reason that small coils are required is the fact that the imaging space has a very limited volume. US 6,990,729 discloses coils with a toroid shape (i.e. toroidal coils) and certain methods for manufacturing such coils on a ceramic substrate or PCB (printed circuit board). Even if such a toroidal coil has a smaller external field than a solenoid coil, a toroidal coil generates a net axial magnetic field which is substantially equivalent to the field of a loop of wire positioned in the centre plane of the toroid shape.

Certain attempts have been made to reduce this net axial magnetic field. It can be compensated for either by the addition of a single reverse turn of a winding in the plane of the toroid coil, or by using two windings which are stacked on top of each other. Both these solutions have considerable disadvantages. The reverse winding turn leads to additional manufacturing complexity, whereas using two windings which are stacked on top of each other leads to a wire geometry which is ill-defined, as every turn of the outer winding will need to "hop over" a turn of the inner winding.

One object underlying the invention is to provide a toroidal coil arrangement and an electronic unit comprising a toroidal coil arrangement such that it is especially suitable for use in an MR imaging system or MR scanner, and which is especially provided such that disturbances of the functioning of the MRI system, especially of the MR image generation, due to external stray or leakage fields or the above net axial field of the toroidal coil arrangement are decreased or prevented.

Another object underlying the invention is to provide an electronic unit comprising a toroidal coil arrangement such that it is especially suitable for use in an MR imaging system or MR scanner, without being substantially influenced detrimentally by the static or RF magnetic fields within such an MR imaging system or MR scanner.

The above first object is solved according to claim 1 by a toroidal coil arrangement comprising a first toroid coil with a first set of windings which progress in a counterclockwise direction along the toroid, and a second toroid coil with a second set of windings which progress in a clockwise direction along the toroid, wherein both toroid coils are electrically connected with each other.

The above second object is solved according to claim 15 by an electronic unit provided for being placed into a magnetic resonance imaging system or a magnetic resonance (MR) scanner, the electronic unit comprising a toroidal coil arrangement according to one of claims 1 to 14.

By the counterclockwise and clockwise windings, any net axial field is substantially reduced or prevented. By providing a toroidal coil arrangement, also external stray or leakage fields are largely prevented. Generally, a toroid (the surface of which is called a torus) is according to this invention to be understood as a three-dimensional geometrical form generated by a circle, an ellipse or a rectangle, especially a square, or another closed loop form, which is revolving in the three-dimensional space around the (toroid-) axis which is coplanar with the circle, ellipse, rectangle or closed loop form, respectively, and which axis does not touch this loop form. However, the revolution itself must not be circular (even if this is preferred), but can be e.g. elliptically or can follow another curve having varying distances from the toroid-axis, so that the toroid must not necessarily extend along a circle, but can extend along an ellipse or along another closed loop etc. as well. The subclaims disclose advantageous embodiments of invention.

The embodiments according to claims 2 and 3 are directed on preferred connections wirings of the coil arrangement.

The embodiments according to claims 4 to 6 have the advantage, that the coil arrangement can be realized with very small dimensions. The embodiments according to claims 7 to 9 have the advantage, that the toroidal coil arrangement can be manufactured on a printed circuit board by machine (and not necessarily by hand), so that well reproducible electrical properties are obtained and the manufacturing costs are considerable reduced.

Furthermore, due to the very small external fields, other electronic components or circuits can be placed on top of the toroidal coil arrangement on the same printed circuit board without causing problems due to electromagnetic interferences (EMI). This has the advantage, that space, production cost and production time are saved.

Claims 10 to 14 are directed on preferred embodiments of the layout of a toroidal coil arrangement when realizing it on and within a printed circuit board. It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompanying claims.

Further details, features and advantages of the invention will become apparent from the following description of preferred and exemplary embodiments of the invention which are given with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows a view onto the top of a preferred embodiment of a toroidal coil arrangement according to arrow A in Figure 5; Fig. 2 schematically shows a view onto a cross-section of the toroidal coil arrangement according to Figure 1, along a section line B-B indicated in Figure 5;

Fig. 3 schematically shows a view onto a cross-section of the toroidal coil arrangement according to Figure 1, along a section line C-C indicated in Figure 5; Fig. 4 schematically shows a view onto a cross-section of the toroidal coil arrangement according to Figure 1, along a section line D-D indicated in Figure 5;

Fig. 5 schematically shows a cross-section through the toroidal coil arrangement according to Figure 1, along a section line E-E in Figures 1 to 4; and

Fig. 6 shows a preferred dimensioning of a coil arrangement according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, a preferred embodiment of the invention in the form of a toroidal coil arrangement is described, which comprises a first set of windings that progress in a counterclockwise direction along the toroid, and a second set of windings that progress in a clockwise direction along the toroid, wherein the first set of windings and the second set of windings are electrically connected with each other preferably in series.

Preferably, one of the sets of windings is provided in the form of a first outer toroid coil, and the other set of windings is provided in the form of a second inner toroid coil wherein the windings of the second inner toroid coil are at least partly enclosed by the windings of the first outer toroid coil.

Outer and inner toroid coil is to be understood in this description such that the outer toroid coil comprises windings which enclose a larger area than the windings of the inner toroid coil. By this, the inner toroid coil can extend at least partly within the outer toroid coil. In other words, the windings of the outer toroid coil enclose at least partly the windings of the inner toroid coil, wherein both toroid coils are preferably arranged in a concentrical manner such that they have a common toroid axis.

This configuration has to be distinguished from the configuration with respect to the diameters of the toroid coils, which are measured in a radial direction through the toroid axis (i.e. in a plane perpendicular to the toroid axis). If the inner or outer diameter of the first toroid coil is greater than the inner or outer diameter of the second toroid coil, the first toroid coil encloses at least partly the second toroid coil, seen in a plane perpendicular to the toroid axis, wherein again both toroid coils are preferably arranged such that they have a common toroid axis. Both the above configurations can be used independently from each other, or they can be combined with each other.

The toroidal coil arrangement can be realized as a discrete electric component or as an integrated part of an electronic unit. According to the preferred embodiment, the toroidal coil arrangement is embedded or integrated into a printed circuit board (PCB). The material of the printed circuit board is most preferably a non-magnetic material. The material can be a ceramic material, however it is preferred to use a non-ceramic material like a glass reinforced epoxy because with such a material, a known standard PCB manufacturing process can be used which allows to integrate the toroidal coil arrangement together with other circuitry of a related electronic unit on the same PCB at low cost.

Figures 1 to 5 show such a toroidal coil arrangement according to a preferred embodiment of the invention, embedded into a printed circuit board 1.

Generally, the first outer toroid coil is provided by a plurality of first and second electrically conductive vias 10, 11, extending at least substantially perpendicularly through or into the printed circuit board 1, and a plurality of first and second electrically conductive traces 12, 13 arranged on layers of the printed circuit board 1 (Figures 1 and 2) which traces 12, 13 connect the first and the second vias 10, 11 at or in the region of their first and their opposite second ends, respectively, such that the first outer toroid coil is formed, which according to Figures 1 and 2 progresses in a counterclockwise direction along the circumference of the toroidal coil arrangement.

The second inner toroid coil is provided by a plurality of third and fourth electrically conductive vias 20, 21, extending at least substantially perpendicularly through or into the printed circuit board 1, and a plurality of third and fourth electrically conductive traces 22, 23 arranged on layers of the printed circuit board 1 (Figures 3 and 4) which traces 22, 23 connect the third and the fourth vias 20, 21 at or in the region of their first and their opposite second ends, respectively, such that the second inner toroid coil is formed, which according to Figures 3 and 4 progresses in a clockwise direction along the circumference of the toroidal coil arrangement.

More in details, Figure 1 shows a top view (according to arrow A in Figure 5) onto the printed circuit board (PCB) 1 comprising such a toroidal coil arrangement. In this view, the first vias 10, the second vias 11 and the first traces 12 of the first outer toroid coil are indicated, wherein the first traces 12 each connect the first and the second vias 10, 11 at their first ends. Furthermore, Figure 1 shows the third vias 20 and the fourth vias 21 of the second inner toroid coil. The first and the third vias 10, 20 are arranged in the plane of the PCB 1 preferably along a circle and with a first radial distance from a central toroid-axis G of the toroidal coil arrangement. As can be seen in Figures 1 and 2, the first and the third vias 10, 20 are arranged alternately in the circumferential direction along the same circle and with the same radial distance from the central toroid-axis G. However, the radial distance of the third vias 20 from the central toroid-axis G could also be smaller or greater than the radial distance of the first vias 10.

The second vias 11 are preferably arranged along a circle, concentrically to the circle along which the first and the third vias 10, 20 are arranged, and with a second radial distance from the central toroid-axis G of the toroidal coil arrangement, which second radial distance is smaller than the first radial distance from the central toroid-axis G.

The fourth vias 21 are preferably arranged along another circle, concentrically to the circles of at least one of the first, second and third vias 10, 11, 20, and with a third radial distance from the central toroid-axis G of the toroidal coil arrangement, which third radial distance is smaller than the second radial distance. However, especially in case of a larger toroidal coil arrangement, the third radial distance could be equal to the second radial distance, so that the second and the fourth vias 11, 21 are arranged alternately in a circumferential direction with the same radial distance from the central toroid-axis G. Furthermore, the third radial distance of the fourth vias 21 could even be greater than the second radial distance of the second vias 11 from the central toroid-axis G.

Finally, Figure 1 shows a connection unit 3 with a first and a second connection via 31, 32 for electrically contacting the toroidal coil arrangement. This contacting and the connection of the coils shall be explained below.

Figure 2 shows a cross sectional view along a line B-B through the printed circuit board 1, which line B-B is indicated in Figure 5. Apart from the first to fourth vias 10, 11, 20, 21, Figure 2 shows the plurality of second traces 13 which connect the first and second vias 10, 11 at their second ends such that the first outer toroid coil is formed.

Figure 3 shows a cross sectional view along a line C-C through the printed circuit board 1, which line C-C is indicated in Figure 5. Apart from the first to fourth vias 10, 11, 20, 21, Figure 3 shows the plurality of third traces 22 which connect the third and fourth vias 20, 21 at their first ends such that the second inner toroid coil is formed.

Finally, Figure 4 shows a cross sectional view along a line D-D through the printed circuit board 1, which line D-D is indicated in Figure 5. Again, apart from the first to fourth vias 10, 11, 20, 21, Figure 4 shows the plurality of fourth traces 23, which connect the third and fourth vias 20, 21 at their second ends.

Figure 5 shows a cross section through the printed circuit board 1 along the broken line E-E indicated in Figures 1 to 4. In this Figure 5, the first and the third vias 10, 20 are indicated in common. Furthermore, the second vias 11 and the fourth vias 21 are indicated. This Figure shows that the first outer toroid coil is formed by the first and the second vias 10, 11 which are connected to each other on one (upper) surface of the PCB 1 by the first traces 12 and on the opposite (lower) surface of the PCB 1 by the second traces 13. Furthermore, Figure 5 shows the second inner toroid coil which is formed by the third and fourth vias 20, 21 which are connected to each other at their first ends by the third traces 22 and at their second (opposite) ends by the fourth traces 23 which are both arranged on inner layers (not indicated) of the PCB 1.

Preferably, as indicated in Figure 5, each of the third traces 22 is provided in the form of two single traces which are connected in parallel with the related third and fourth vias 20, 21 and which are arranged on different PCB layers above each other. Accordingly, each of the fourth traces 23 is preferably as well provided in the form of two single traces which are connected in parallel with the related third and fourth vias 20, 21 and which are as well arranged on different PCB layers above each other.

By such each two or more (i.e. multiple) traces connected in parallel, the DC- and AC resistance of the second inner toroid coil is reduced. The same principle could be applied for the first outer toroid coil as well, if e.g. additional layers would be applied onto the outer upper and lower surfaces of the PCB 1, respectively, which layers each bear corresponding additional traces which are each connected in parallel with the related traces 12, 13, below, respectively, as in the case of the second inner toroid coil. As indicated in Figures 1, 2 and 5, the third and fourth vias 20, 21 extend up to the upper and lower surface of the PCB 1. Alternatively to this, the third and fourth vias 20, 21 could also be buried so that they extend within the PCB 1 only up to those layers on which the third and the fourth traces 22, 23, respectively, extend.

Finally, Figure 5 shows the connection unit 3 for electrically connecting the toroidal coil arrangement as follows:

As shown in Figure 1, the first connection via 31 of the connection unit 3 is electrically connected with one of the first vias 10 of the first outer toroid coil. This first via 10 is connected by means of a first trace 12 with a second via 11 which is displaced in a counterclockwise direction along the circumference of the toroid in relation to the first via 10.

According to Figure 2, this second via 11 is connected by means of a second trace 13 with another first via 10, which is displaced in a counterclockwise direction along the circumference of the toroid in relation to this second via 11.

By this, one winding of the first outer toroid coil is closed, and the next first via 10 is again connected according to Figure 1 with the next second via 11 (which is again displaced in the counterclockwise direction) by means of the next first trace 12, and so on.

At the end of the first outer toroid coil (the related "last" first via 10 in circumferential direction is indicated in Figures 2 and 3 with the letter "c"), the second inner toroid coil starts according to Figure 3 by connecting this via c by means of one third trace 22 with one fourth via 21.

According to Figure 4, this fourth via 21 is connected by means of a fourth trace 23 with a third via 20, which is displaced in a clockwise direction along the circumference of the toroid in relation to this fourth via 21. Then, again, this third via 20 is connected by means of another third trace 22 according to Figure 3 with a next fourth via 21 which is displaced in a clockwise direction in relation to the previous third via 20, and so on.

By this, the windings of the second inner toroid coil are closed and progressing in the clockwise direction. At the end of the second inner toroid coil, the related "last" second via 20 is electrically connected according to Figure 4 with the second connection via 32 of the connection unit 3.

By these connections, both windings of both set of windings 10, 11, 12, 13; 20, 21, 22, 23 are wound or oriented in the same direction.

Figure 6 schematically shows the right half of the printed circuit board 1 shown in Figure 5 for explaining exemplary dimensions. The thickness of the entire printed circuit board 1 is in this example about 4.7 mm. The electrically conductive layers on and within the PCB 1 are preferably copper layers.

The outer copper layers by which the first and the second traces 12, 13 are provided, each have a thickness of about 105 μm. The inner copper layers for providing the third and the fourth traces 22, 23 are applied onto a first and a second inner PCB layer each having a thickness of about 100 μm. The inner copper layers on these PCB layers each have a thickness of about 70 μm.

The thicknesses of the inner and the outer copper layers substantially depend on the process which is used for manufacturing the PCB structure. Due to the fact, that the inner copper layers usually have a smaller thickness with such manufacturing processes than the outer copper layers, each of the third and fourth (inner) traces 22, 23 has been provided in the form of two parallel inner copper layers in order to decrease the DC and AC resistance. However, generally and independently from the above dimensions, the inner traces 22, 23 can as well be provided by one or by more than two copper layers. The same accordingly applies for the outer traces 12, 13 for the outer toroid coil as explained above.

The vias 10, 11, 20, 21 each have a diameter of about 1.5 mm and they comprise a conductive (copper) layer with a thickness of about 100 μm.

Generally, while the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, and the invention is not limited to the disclosed embodiments. Variations to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Furthermore, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. Toroidal coil arrangement, comprising a first toroid coil with a first set of windings (10, 11, 12, 13) which progress in a counterclockwise direction along the toroid, and a second toroid coil with a second set of windings (20, 21, 22, 23) which progress in a clockwise direction along the toroid, wherein both toroid coils are electrically connected with each other.

2. Toroidal coil arrangement according to claim 1, wherein the first set of windings (10, 11, 12, 13) and the second set of windings (20, 21, 22, 23) are connected in series.

3. Toroidal coil arrangement according to claim 1, wherein the windings of both set of windings (10, 11, 12, 13; 20, 21, 22, 23) are wound in the same direction.

4. Toroidal coil arrangement according to claim 1, wherein the area enclosed by each one of the windings of one of the set of windings (10, 11, 12, 13) is larger than the area enclosed by each one of the windings of the other set of windings (20, 21, 22, 23).

5. Toroidal coil arrangement according to claim 1, wherein the windings of one of the set of windings (10, 11, 12, 13) extend at least partly into the windings of the other set of windings (20, 21, 22, 23) or at least partly enclose these other windings (20, 21, 22, 23).

6. Toroidal coil arrangement according to claim 1, wherein the first toroid coil encloses at least partly the second toroid coil, seen in a plane perpendicular to an axis (G) of the toroidal coil arrangement.

7. Toroidal coil arrangement according to claim 1, wherein the windings of the first set of windings (10, 11, 12, 13) and the windings of the second set of windings (20, 21, 22, 23) are at least substantially rectangular.

8. Toroidal coil arrangement according to claim 1, which is embedded or integrated into a printed circuit board (1).

9. Toroidal coil arrangement according to claim 8, wherein the printed circuit board (1) is made of a non-magnetic material.

10. Toroidal coil arrangement according to claim 8, wherein the first set of windings (10, 11, 12, 13) is provided by a plurality of first and second electrically conductive vias (10, 11) extending substantially perpendicularly into the printed circuit board (1), and a plurality of first and second electrically conductive traces (12, 13) arranged on layers of the printed circuit board (1), which traces (12, 13) connect the first and the second vias (10, 11) at or in the region of their first and their opposite second ends, respectively, to one another such that the first toroid coil is formed.

11. Toroidal coil arrangement according to claim 10, wherein the second set of windings (20, 21, 22, 23) is provided by a plurality of third and fourth electrically conductive vias (20, 21) extending substantially perpendicularly into the printed circuit board (1), and a plurality of third and fourth electrically conductive traces (22, 23) arranged on layers of the printed circuit board (1), which traces (22, 23) connect the third and the fourth vias (20, 21) at or in the region of their first and their opposite second ends, respectively, to one another such that the second toroid coil is formed.

12. Toroidal coil arrangement according to claim 10 and 11, wherein the first and the third vias (10, 20) are arranged along a common circle and with a first radial distance from an axis (G) of the toroidal coil arrangement.

13. Toroidal coil arrangement according to claim 12, wherein the second and the fourth vias (11, 21) are each arranged along circles and with a second and a third radial distance, respectively, from the axis (G) of the toroidal coil arrangement, wherein the second radial distance is greater than the third radial distance, and wherein the second and the third radial distance is smaller than the first radial distance.

14. Toroidal coil arrangement according to claim 10 and 11, wherein the third and the fourth electrically conductive traces (22, 23) are arranged on layers of the printed circuit board (1) which are positioned between the layers on which the first and the second traces (12, 13) are arranged.

15. Electronic unit provided for being placed into a magnetic resonance imaging system or a magnetic resonance (MR) scanner, the electronic unit comprising a toroidal coil arrangement according to one of claims 1 to 14.