WO2009147552A1

WO2009147552A1 - Rotary power transformer and computer tomography gantry comprising same

Info

Publication number: WO2009147552A1
Application number: PCT/IB2009/052035
Authority: WO
Inventors: Christoph Loef; Peter Luerkens
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2008-06-02
Filing date: 2009-05-15
Publication date: 2009-12-10
Anticipated expiration: 2010-12-02

Abstract

A rotary transformer (101, 201, 301) for a computer tomography gantry (91) for contactlessly transferring electrical energy from a stationary part (92) of the gantry to a rotary part (93) of the gantry and a CT gantry comprising such rotary transformer are proposed. The rotary transformer comprises: - a first core (103, 203, 303) comprising a magnetically conductive material and including a first winding window (107, 207, 307) having a first winding window volume, - a second core (105, 205, 305) comprising a magnetically conductive material and including a second winding window (109, 209, 309) having a second winding window volume, - first windings (111, 211, 311) arranged within the first winding window, - second windings (113, 213, 313) arranged within the second winding window. At least one of the first and second windings fill the respective first and second winding windows volumes only partially, and a geometrical arrangement of at least one of the first and the second windings within the respective first and second winding windows is adapted such that a leakage inductance (Ln, Li2) induced by the respective one of the first and second windings is adapted to a resonance requirement imposed by a high frequency power source (121) to be connected to the first windings or imposed by an energy consumer arrangement connected to the second windings. By suitably adapting the leakage inductance by varying the positioning of windings within winding windows, the need for additional separate inductances in resonant tank circuits can be overcome.

Description

Rotary power transformer and computer tomography gantry comprising same

FIELD OF THE INVENTION

The present invention relates to a rotary power transformer for contactlessly transferring electrical energy from a stationary part to a rotary part of a computer tomography (CT) gantry and to a CT gantry comprising such transformer.

BACKGROUND OF THE INVENTION

For high power CT applications, the X-ray tube power must usually be transferred from a power supply connected to a stationary part of a CT device to a rotary part of a gantry which comprises inter alia the X-ray tube and an X-ray detector and which may rotate around an object to be examined. The energy transfer from the stationary part to the rotary part of the gantry has been conventionally realized by means of mechanical slip-rings where flexible electrical connectors fixed to the stationary part slide along an energy receiving surface on the rotary part or vice versa.

However, with respect to the mechanical outline, the power which has to be transferred to the gantry and the lifetime of the mechanical slip-ring, the slip-ring arrangement cannot be used for high power applications having e.g. X-ray tube powers in access of e.g. 60 kW and applications with high rotational gantry speed.

Accordingly, newer CT high power transmission concepts for transferring electrical energy to the rotating part of the gantry may be based on contact-less rotary transformers instead of slip-rings. Therein, the rotary transformer may show a circular outline in which the inner diameter may be determined by a given inner bore of the CT system. The rotary power transformer may comprise first or primary windings on a first core arranged on the stationary part of the gantry and second or secondary windings on a second core arranged on the rotary part of the gantry. Upon application of a high- frequency AC voltage to the primary windings, electrical power can be inductively transferred from the primary windings to the secondary windings and, accordingly, energy can be provided from the stationary part of the gantry to the rotary part of the gantry in a contactless way, i.e. without mechanical contact for energy supply between the stationary and the rotary part.

Fig. 1 schematically shows a conventional rotary transformer 1. The rotary transformer 1 comprises a first and a second core 3, 5 made with a magnetically conductive material. The cores 3, 5 each comprise two winding windows 7, 9. Accordingly, both cores 3, 5 have an E-shape. The E-shaped cores 3, 5 are arranged opposite to each other such as to have a symmetry with respect to a symmetry axis S. First windings 11 are arranged in the winding window 7 of the first core 3. Second windings 13 are arranged in the winding window 9 of the second core 5. Therein, the entire volume of the winding windows 7, 9 is filled with first and second windings 11, 13, respectively, i.e. the windings 11, 13 which are arranged adjacent to each other within one winding window 7, 9 are in direct mechanical contact to each other and the first windings 11 in the first core 3 are separated from the second windings 13 in the second core 5 only by a small air gap 15 between the two cores 3, 5.

In such arrangement, the first core 3 may be fixed to a stationary part of a CT gantry whereas the second core 5 may be fixed to a rotary part of the gantry. While the rotary part of the gantry may rotate with respect to the stationary part of the gantry as indicated by the arrow r in Fig. 1, energy might be transferred contactlessly from the stationary part to the rotary part using magnetical inductance between the first windings 11 and the second windings 13.

While conventional contactless power transformers are usually operated at medium frequencies in the range of typically 20 kHz to 100 kHz, future high power CT applications may need power transformers which are adapted to the application of high-frequency voltage supply, e.g. in a range of 100kHz to 300kHz, for the energy transmission from a first stationary part to a second rotary part of the transformer. To effectively achieve high-frequency operation, a topology with a resonant tank circuit may be used.

Fig. 2 schematically shows a circuitry for contactlessly transferring energy from an energy source 21 including an inverter and being arranged on a stationary part as to be arranged rotatively with respect to a fixed energy source 21. Electrical energy coming from the energy source 21 is contactlessly transferred to the consumer 23 by the rotary transformer 1. Therein, the first windings 11 forming a first inductance L_wi are connected in series to a first capacitor Ci. In order to adapt the circuitry to a resonance requirement when high-frequency voltage is supplied by the energy source 21 , an additional external inductance L₆₁ is connected in series. A similar resonant tank circuit is provided on the rotary part 27 including a capacitor C₂ connected in series with an inductance L_w2 provided by the second winding 13 of the rotary transformer 1 and an external inductance L_e2. However, it is to be noted that the capacitor C2 may be optional only and that particularly the circuit including the consumer may be provided without such capacitor.

SUMMARY OF THE INVENTION

There might be a need for a rotary transformer and for a CT gantry comprising such rotary transformer wherein an arrangement for contactlessly transferring energy from a stationary energy source to a rotary energy consumer may be simplified.

These needs may be met by the subject-matter according to one of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims and in the following description.

According to a first aspect of the present invention, a rotary transformer for a computer tomography gantry for contactlessly transferring electrical energy from a stationary part of the gantry to a rotary part of the gantry is proposed. The rotary transformer comprises: a first core comprising a magnetically conductive material and including a first winding window having a first winding window volume, a second core comprising a magnetically conductive material and including a second winding window having a second winding window volume, first windings arranged within the first winding window and second windings arranged within the second winding window. At least one of the first and second windings fill the respective first and second winding window volumes only partially. Therein, a geometrical arrangement of at least one of the first and second windings within the respective first and second winding windows is adapted such that a leakage inductance induced by the respective one of the first and second windings is adapted to a resonance requirement imposed by a high-frequency power source to be connected to the first windings and/or imposed by an energy consumer arrangement connected to the second windings. A gist of the present invention may be seen as being based on the following idea:

Future approaches for high power CT applications will need an effective transfer of high power from a stationary energy source to a rotary energy consumer. While conventional CT applications using rotary transformers are usually operated at medium AC frequencies in the range of typically 20 kHz to 100 kHz, future approaches might be operated at 100 kHz and 300 kHz. The inventors of the present application have found that for such high frequency applications, lower values of a resonance inductance within each of the resonant tank circuits of the stationary part and of the rotary part of the gantry may be required. The present invention is based on the idea that such lower inductance values may be provided by the first and/or second windings of the rotary transformer itself instead of providing separate, external inductance elements L_ei, L_e2 as in prior art approaches.

The inventors of the present application have realized that the first and second windings in the rotary transformer do not only have their intrinsic magnetizing inductance which mainly depends on the number of windings, i.e. the length of the windings, and the cross-sectional area of an air gap between the first, stationary core and the second, rotary core of the transformer but also depend on the so-called leakage inductance. Therein, the leakage inductance has been found as being mainly dependent on the relative position of the windings within winding windows of the respective first and second cores. The inventors had the idea not to fill the volumes of the respective winding windows completely with the respective first and second windings but to only partially fill these winding window volumes. Accordingly, there are air spaces remaining within winding windows. The idea is to arrange the first and/or second windings within the respective first and/or second winding windows geometrically in such a way such that the leakage inductance, which mainly depends on such geometrical arrangement and the resulting air spaces, will be such that the leakage inductance together with the intrinsic magnetizing inductance of the respective windings may sum up to a value which is suitably adapted to an external capacitance such as to fulfil a resonance requirement within the respective circuitry when a high-frequency power source is connected to the circuitry. As the windings may be arranged within the cores such as to achieve a resonance inductance solely with the respective first or second windings, no additional external inductance element may be necessary. Accordingly, the circuitry for the resonant tank circuit(s) may be simplified. Furthermore, at high-frequency, it is required to reduce proximity losses in the litz winding strands and thus the fill factor will be less than in prior art approaches at identical or lower losses in the windings.

In the following, further possible features, details and advantages of embodiments of the present invention are mentioned.

The rotary transformer of the present invention may be adapted for contactlessly transferring a high amount of electrical energy, e.g. up to 150 kW, from a stationary part to a rotary part of a CT gantry. It comprises two cores each comprising a magnetically conductive, preferably ferro-magnetical material such as ferrite. The cores may have a circular or toroidal shape and may be arranged adjacent to each other, preferably co-axially. A first core may be attached to the stationary part of the gantry whereas a second core may be attached to the rotary part of the gantry. Both cores include winding windows having a specific volume. In other words, the cores each comprise spaces which are at least partially enclosed by the magnetically conductive material of the core and in which windings of an electrical conductor may be arranged. Accordingly, the magnetic field induced by an electrical current flowing in the windings may be mainly guided within the cores. The windings may be made with litz strands. A plurality of windings may be wound with a single strand.

It may be important that at least one of the winding windows of the first and second cores are not completely but only partially filled with windings. In other words, less windings may be fitted within the winding window than would fit in there if all windings would be arranged in close contact to each other and in close contact to the walls of the winding window within the core. Again in other words, there may be free air spaces within a winding window. A cross-section of such an air space may be larger than a cross-section of a winding. The cross-section of all air spaces within a winding window may even be larger than the cross-section of all windings within a winding window. Particularly, when the first and second cores do have an open surface where there is no magnetically conductive material and where windings could be arranged, according to an idea of the present invention, no windings are arranged directly at such surface but an air space is remained free adjacent to such surface.

The presence of free spaces within the winding windows may enable a variation of a geometrical arrangement of the windings in the respective winding windows. Accordingly, the positioning of the windings can be selected such that a leakage inductance occurring in the respective core and mainly depending on the size and position of free spaces within the winding window may be adjusted such that the entire inductance of the respective core may be suitably fulfil a resonance requirement which may be imposed by the fact that the windings of the respective core are part of a resonant tank circuit. Such resonant tank circuit may include a high-frequency power source including a high-frequency inverter connected in series to an external capacitor and to the first windings within the first stationary core. Alternatively, the resonant tank circuit may include an energy consumer arrangement such as an X-ray source attached to a rotary part of a CT gantry wherein the consumer arrangement may be connected to a high-frequency inverter further being connected in series to an external capacitor and to the second windings within the second core. Therein, not only the number of windings, i.e. the length of the litz strands, but also the geometrical arrangement of the windings within the winding windows may be suitably adapted such that the resulting inductance of the windings including the magnetizing inductance and the leakage inductance may be adjusted such that, in dependence of the capacitance of the external capacitor and of the frequency provided by the respective inverter, resonance can be obtained within the resonant tank circuit. Accordingly, no separate external inductance component is required for the resonant tank and the overall circuitry is simplified.

According to an embodiment of the present invention, the first and second cores are arranged adjacent to each other and an air gap between the first and second cores is smaller than an air gap between the first and second windings arranged within the respective first and second winding windows of the first and second cores. In other words, in the rotary transformer, there is usually an air gap between the first core of the stationary part and the second core of the rotary part. This air gap is usually kept as small as possible, for example in the range of a few mm or less. Usually the winding windows within the cores have their openings in a direction towards the opposing other core. Whereas in conventional rotary transformers, the winding windows were completely filled with windings such that the air gap between the opposing cores substantially corresponds to the air gap between the windings arranged within the respective winding windows of the cores, in the presently proposed rotary transformers, the winding windows are not completely filled with windings such that free spaces may remain which may enlarge the air gap between the windings arranged in the distinct cores when compared to the air gap between the cores themselves. The size of such air gap between the windings of the distinct cores may be suitably selected in order to adjust the resulting leakage inductance as explained further above.

According to a further embodiment of the present invention, a geometrical arrangement of the first windings within the first winding window differs from a geometrical arrangement of the second windings within the second winding window such that a leakage inductance induced by the first windings differs from a leakage inductance induced by the second windings upon connection to a high-frequency power source. In other words, the windings within the first core may be positioned at a different location than the windings in the second core. Accordingly, the leakage inductance in the first core may differ from the leakage inductance in the second core as a result of an asymmetrical arrangement of the windings within the distinct cores. Such asymmetrical distribution of leakage inductances may be advantageous as the resonance requirements in a first circuitry within the stationary part of the gantry may differ from the resonance requirements within a second circuitry within the rotary part of the gantry. For example, the leakage inductance may be increased in the first circuitry and decreased in the second circuitry. By shifting the leakage inductance either more to the primary side or the secondary side, the electrical resonance function of the transformer may be influenced. According to a further embodiment of the present invention, at least one of the first and second cores has an E-shaped cross-section. Therein, the cross-section may be taken radially with respect to a circular or toroidal shape of a core. The "E"- shape allows to better contain any stray magnetic fields in a vicinity of the cores. Furthermore, the "E"-shape contains two distinct winding windows such that the windings may be arranged in a first winding window in a direction opposite to the direction of windings arranged in a second winding window which may improve the overall characteristic of the magnetic field induced by the core.

According to a further embodiment of the present invention, the first and second cores are arranged symmetrically with respect to a cross-sectional view thereof. For example, in case the cores have a toroidal shape and are arranged one adjacent to the other, the first, left core may have an "E"-shaped cross-section whereas the second, right core may have an "Ξ"-shaped cross-section with a mirror-symmetry to the first core. Alternatively, the first and second cores may be provided as a radially outter first toroidal core and a radially inner second toroidal core both having for example an E- shape wherein the openings of the "E" are directed towards each other. Such symmetrical arrangement of the first and second cores may be advantageous for the overall distribution of the magnetic field.

According to a further embodiment of the present invention, the first and second windings are arranged symmetrically with respect to a symmetry plane provided by the first and second core in a cross-sectional view. In other words, when the cores both have for example an "E"-shape, and are arranged symmetrically to each other, the first and second windings are arranged at the same position within the "E" of the cores. Such arrangement of the first and second windings may provide a homogeneous magnetic field distribution.

According to an alternative embodiment of the present invention, the first and second windings are arranged asymmetrically with respect to a symmetry plane provided by the first and second cores in a cross-sectional view. In contrast to the previous embodiment, the first and second windings may be arranged at different positions within for example the "E" of the first and second cores. Accordingly, the size and position of free air spaces within the winding windows may differ in the first and second cores such that the leakage inductance induced in the first and second cores may be influenced differently. Accordingly, the leakage inductance may be adjusted to different resonance requirements in the stationary first resonant tank circuit and in the rotary second resonant tank circuit. According to a second aspect of the present invention, a computer tomography gantry is proposed comprising a rotary transformer as described above with respect to the first aspect of the present invention and further comprising a high- frequency power source associated with the stationary part of the gantry and connected to the first windings of the rotary transformer and further comprising a power consumer associated with the rotary part of the gantry and connected to the second windings of the rotary transformer.

According to an embodiment of the present invention, the high-frequency power source and the first windings are part of a first resonant tank circuit and a geometrical arrangement of the first windings within the first winding window of the first core is adapted such that a leakage induced by the first windings is adapted to a resonance requirement imposed by the first resonant tank circuit. The first resonance tank circuit may further comprise an inverter and an external capacitor. A resonance requirement may then be determined by the frequency of an AC current provided by the high-frequency power source and/or the inverter and by the magnitude of the capacitance of the external capacitor such that, knowing these parameters, the magnitude of an inductance necessary for resonant characteristics may be determined and accordingly the position and size of the windings in the winding windows, which are necessary to achieve the desired leakage inductance, may be determined.

According to a further embodiment of the present invention, the power consumer and the second windings are part of a second resonant tank circuit and a geometrical arrangement of the second windings within the second winding window is adapted such that a leakage inductance induced by the second windings is adapted to a resonance requirement imposed by the second resonant tank circuit.

It has to be noted that aspects and embodiments of the invention are described with reference to different subject-matters. In particular, some embodiments are described with reference to the rotary transformer whereas other embodiments are described with reference to the CT gantry. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination or features belonging to one type of subject-matter also any combinations between features relating to different subject-matters are considered to be disclosed with this application.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments defined above and further details of the present invention may be apparent from exemplary embodiments to be described hereinafter with reference to the figures but to which the invention is not limited.

Fig. 1 shows a conventional rotary transformer; Fig. 2 shows a circuitry for a conventional rotary transformer; Fig. 3 shows a rotary transformer according to an embodiment of the present invention; Fig. 4 shows a circuitry for a rotary transformer according to an embodiment of the present invention;

Fig. 5 shows a cross-sectional view of an alternative embodiment of a rotational transformer according to an embodiment of the present invention having enlarged air spaces;

Fig. 6 shows a cross-sectional view of an alternative embodiment of a rotational transformer according to the present invention having asymmetrical winding arrangements; Fig. 7 shows a CT gantry according to an embodiment of the present invention.

All illustrations in the drawing are only schematically and not to scale. Similar elements are indicated with similar reference signs throughout the drawings. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Fig. 3 shows a rotary transformer 101 according to an embodiment of the present invention. The rotary transformer 101 comprises a first core 103 and a second core 105 made from a magnetically conductive, ferromagnetic material such as iron. Both cores 103, 105 have an E-shape and are arranged adjacent and opposing to each other such that the openings of the E-shape are directed to the opposing E-shaped core. Therein, the openings of the E-shape serve as winding windows 107, 109 within the respective cores 103, 105. First windings 111 are arranged in the winding window 107 of the first core 103 and second windings 113 are arranged in the winding window of the second core 105.

However, the winding windows 107, 109 are not completely filled with windings 111, 113. Instead, all winding windows 107, 109 are only partially filled such that free spaces 117 not being filled with any windings 111, 113 remain within each of the winding windows 107, 109. Accordingly, whereas the cores 103, 105 are arranged in close neighbourhood to each other with a gap 115 between the two cores 103, 105 having a width w_g of only a few mm, within the winding windows 107, 109, air spaces not filled with windings 111, 113 remain such that the air gap between the first and second windings 111, 113 having a width w_a is substantially larger than the air gap 115 between the cores 103, 105.

Due to the fact that the winding windows 107, 109 are only partially filled with windings 111, 113, an increased leakage conductance may occur within the rotary transformer 101. Therein, the magnitude of the leakage inductance strongly depends on the position of the windings 111, 113 within the winding windows 107, 109. Particularly, the induced leakage inductance strongly depends on the air spaces 117 between the first windings 111 in the first core 103 and the second windings 113 in the second core 105. Accordingly, by varying and suitably adapting the number of windings 111, 113 and their positioning within the winding windows 107, 109, the resulting leakage inductance can be suitably adapted. As schematically shown in Fig. 4, a stationary part 125 of a computer tomography gantry comprises an power source 121 and a stationary part of a rotary transformer 101. The energy source 121 comprises an inverter for providing a high- frequency AC voltage and is connected to the first windings 111 of the rotary transformer 101. The circuitry further comprises a capacitor 129 having a capacitance Ci and being connected in series between the power source 121 and the rotary transformer 101. The first windings 111 induce both, an intrinsic magnetical inductance L_wi depending mainly on the number and length of the windings 111 and a leakage inductance Ln depending mainly on the positioning of the first windings 111 within the first winding window 107. These two inductances L_wi, Ln, can be interpreted as being connected in series. Accordingly, as the leakage inductance LIl can be influenced by suitably positioning the first windings 111 within the first winding window 107, an overall inductance Li of the stationary part of the rotary transformer 101 can be suitably adapted such that a resonance requirement of the circuit comprising the first capacitor 129 with the capacitance Ci and the first windings 111 with the inductance Li can be fulfilled. In a similar way, a rotary part 127 of the CT gantry comprises an energy consumer 123 such as an X-ray tube being connected in series to a second capacitor 131 and to the second windings 113 of the transformer 101. Therein, the leakage inductance L₁₂ can be suitably adapted to fulfil a resonance requirement depending on the capacitance C2 and the overall inductance L₂. Figs. 5 and 6 show alternative embodiments of rotary transformers 201,

301 in cross-section. As shown in Fig. 5, first and second windings 211, 213 are arranged at outermost regions within the first and second winding windows 207, 209 in order to maximize the free air space 217. In the embodiment shown in Fig. 6, the first and second windings 311, 313 are arranged asymmetrically with respect to a symmetry plane S provided by the first and second cores 303, 305. Accordingly, the respective leakage inductances Ln, Li₂ may differ in the first, stationary core 303 and the second, rotary core 305 and may be adapted for the respective resonance requirement in the stationary part and in the rotary part of a CT gantry.

Fig. 7 shows an exemplary embodiment of a computer tomography gantry (91) arrangement. The gantry (91) comprises a stationary part (92) connected to a high frequency power source (98) and rotary part (93) adapted to rotate relative to the stationary part (92). An X-ray source (94) and an X-ray detector (95) are attached to the rotary part (93) at opposing location such as to be rotatable around a patient positioned on a table 97. The X-ray detector (95) and the X-ray source (94) are connected to a control and analysing unit (99) adapted to control same and to evaluate the detection results of the X-ray detector (95).

Finally, it should be noted that the terms "comprising", "including", etc. do not exclude other elements or steps and the term "a" or "an" does not exclude a plurality of elements. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

1, 101, 201, 301 rotary transformer

3, 103, 203, 303 first core

5, 105, 205, 305 second core

7, 107, 207, 307 first winding window

9, 109, 209, 309 second winding window

11, 111, 211 , 311 first windings

13, 113, 213 , 313 second windings

15, 115 air gap

117, 217, 317 free air space

21, 121 energy source

23, 123 energy consumer

25, 125 stationary part

27, 127 rotary part

129 first capacitor

131 second capacitor

91 computer tomography gantry

92 stationary part

93 rotary part

94 X-ray source

95 X-ray detector

97 table

98 energy source

99 analysing unit

Claims

CLAIMS:

1. A rotary transformer (101, 201, 301) for a computer tomography gantry (91) for contactlessly transferring electrical energy from a stationary part (92) of the gantry to a rotary part (93) of the gantry, the rotary transformer comprising: - a first core (103, 203, 303) comprising a magnetically conductive material and including a first winding window (107, 207, 307) having a first winding window volume,

- a second core (105, 205, 305) comprising a magnetically conductive material and including a second winding window (109, 209, 309) having a second winding window volume,

- first windings (111, 211, 311) arranged within the first winding window, - second windings (113, 213, 313) arranged within the second winding window, wherein at least one of the first and second windings fill the respective first and second winding windows volumes only partially, and wherein a geometrical arrangement of at least one of the first and the second windings within the respective first and second winding windows is adapted such that a leakage inductance (Ln, Li₂) induced by the respective one of the first and second windings is adapted to a resonance requirement imposed by a high frequency power source (121) to be connected to the first windings or imposed by an energy consumer arrangement connected to the second windings.

2. The rotary transformer according to claim 1 , wherein the first and second cores are arranged adjacent to each other and wherein an air gap (115, 215, 315) between the first and second cores is smaller than an air gap between the first and second windings arranged within the respective first and second winding windows of the first and second cores.

3. The rotary transformer according to claim 1 or 2, wherein a geometrical arrangement of the first windings within the first winding window differs from a geometrical arrangement of the second windings within the second winding window such that a leakage inductance induced by the first windings differs from a leakage inductance induced by the second windings upon connection to a high frequency power source.

4. The rotary transformer according to one of claims 1 to 3, wherein at least one of the first and second cores has an E-shaped cross section.

5. The rotary transformer according to one of claims 1 to 4, wherein, in a cross sectional view, the first and the second cores are arranged symmetrically.

6. The rotary transformer according claim 5, wherein, in a cross sectional view, the first and the second windings are arranged symmetrically with respect to a symmetry plane provided by the first and second cores.

7. The rotary transformer according claim 5, wherein, in a cross sectional view, the first and the second windings (311, 313) are arranged asymmetrically with respect to a symmetry plane provided by the first and second cores.

8. A computer tomography gantry comprising: a rotary transformer according to one of claims 1 to 7; a high frequency power source (121) associated with the stationary part (92) of the gantry (91) and connected to the first windings (111) of the rotary transformer (101, 201, 301); a power consumer (123) associated with the rotary part (93) of the gantry (91) and connected to the second windings (113, 213, 313) of the rotary transformer.

9. The computer tomography gantry according to claim 8, wherein the high frequency power source and the first windings are part of a first resonant tank circuit and wherein a geometrical arrangement of the first windings within the first winding window is adapted such that a leakage inductance induced by the first windings is adapted to a resonance requirement imposed by the first resonant tank circuit.

10. The computer tomography gantry according to claim 8 or 9, wherein the power consumer and the second windings are part of a second resonant tank circuit and wherein a geometrical arrangement of the second windings within the second winding window is adapted such that a leakage inductance induced by the second windings is adapted to a resonance requirement imposed by the second resonant tank circuit.