Abstract:
An apparatus for cooling an electrical component includes a circuit board with the electrical component disposed on the circuit board. The apparatus includes a cover disposed on the circuit board. The cover and the circuit board form a closed cavity in which the electronic component is disposed. The cavity has a first opening for introduction of a fluid and a second opening for discharge of a fluid.

Description:
[0001]    This application claims the benefit of DE 102013215843.2, filed on Aug. 12, 2013, which is hereby incorporated by reference in its entirety. 
       FIELD 
       [0002]    The disclosed embodiments relate to magnetic resonance tomography and cooling an electrical component. 
       BACKGROUND 
       [0003]    In magnetic resonance measurements, the interaction of magnetic torques of atomic nuclei, the nuclear spins, is examined using an external magnetic field. The nuclear spins align themselves in the external magnetic field and precess with a Larmor frequency. The Larmor frequency depends on the value of the magnetic torque of the atomic nucleus when excited by an external electromagnetic alternating field about the axis of orientation in the magnetic field. The atomic nuclei generate an electromagnetic alternating field with the Larmor frequency. 
         [0004]    The external electromagnetic alternating field for exciting the nuclear spins is irradiated by one or more antennas into a sample or into a patient. One possible form of antenna is a body coil, which surrounds the patient or the sample. Local coils are however also used, which may be arranged directly on the patient or the sample. The electromagnetic alternating field generated by the atomic nuclei is also received by the antennas. The same antenna may receive the signal generated, or the nuclear spins may be excited using one type of antenna and the electromagnetic alternating field generated by the atomic nuclei is received by another type of antenna. 
         [0005]    Both during the generation of the high-frequency electromagnetic alternating fields and also during the actuation of the gradient coils for the spatial resolution, powers in the range of kilowatts and voltages of several hundred or thousand volts are used. Hence the actuations also generate power losses of a comparable magnitude and benefit from efficient and high-capacity cooling. Also, because the measured high-frequency signals resulting from the excited nuclear spins are very weak, it is useful to ensure that electromagnetic interference fields generated by the actuations do not unintentionally bleed from the actuations and cause the measured signals to degrade. 
       SUMMARY AND DESCRIPTION 
       [0006]    The scope of the present invention is defined solely by the appended claims and is not affected to any degree by the statements within this summary. 
         [0007]    The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, the disclosed embodiments may provide an apparatus that provides effective and high-capacity cooling, simultaneously reduces stray radiation, and is easy to install. 
         [0008]    An apparatus is described for cooling an electrical component. A magnetic resonance tomography system including the apparatus is also described. The apparatus has a circuit board with an electrical component disposed on the circuit board, and a cover disposed on the circuit board. The cover and the circuit board form a closed cavity in which the electronic component is disposed. The cavity has a first opening for the introduction of a fluid and a second opening for the discharge of a fluid. 
         [0009]    The apparatus enables a fluid for cooling to be fed into the first opening, thereby filling the first cavity and flowing through the cavity, such that the fluid flows out of the second opening. The fluid flows around the component and absorbs heat, which is discharged with the outflowing fluid. The direct contact means that, with a suitable fluid, large volumes of heat may be discharged. 
         [0010]    The magnetic resonance tomography system includes the inventive apparatus. 
         [0011]    In one embodiment, a further cover is arranged on a surface of the circuit board lying opposite the first-named cover. The further cover and the circuit board form a further closed cavity. 
         [0012]    With a further cavity, an electrical component may be cooled from both sides, if a fluid connection exists between the cavities or the further cover has separate openings for the fluid. 
         [0013]    In one embodiment, the first-named cover and the further cover are in contact with the circuit board at opposing locations on the surfaces of the circuit board. 
         [0014]    By mounting the circuit board between two covers, a larger force may be exerted onto the circuit board. The forces exerted by the covers cancel each other out on the opposing sides of the circuit board. As a result, a better seal between the circuit board and the covers may be achieved. 
         [0015]    In one embodiment, the first-named cover and/or the further cover are made from an electrically conductive material. 
         [0016]    An electrically conductive material shields against electromagnetic waves that are emitted by an electrical component. This may apply if two covers fully enclose both sides of the electrical component. 
         [0017]    In one embodiment, the first-named cover and/or the further cover are made from several individual elements. For example, a cover may have a frame that forms side walls of the cavity, and a lid that closes the cavity opposite the circuit board. 
         [0018]    This type of multipart embodiment of the cover is easier to manufacture, e.g., if the lid is made to be flat. The circuit board may be easily accessed if the lid is removed. 
         [0019]    In one embodiment, an electrically conductive sealing mechanism (or seal) is disposed between the individual elements of the first-named cover and/or of the further cover. 
         [0020]    The electrically conductive sealing mechanism creates a circumferential contact that, together with the conductive cover, provides (e.g., ensures) full shielding. 
         [0021]    In one embodiment, the apparatus has an electrically conductive sealing mechanism (or seal) between the first-named cover and/or the further cover and the circuit board. 
         [0022]    The electrically conductive sealing mechanism (or seal) between the circuit board and the first-named and/or further cover also provides (e.g., ensures) reliable shielding with respect to the circuit board. 
         [0023]    In one embodiment, the first-named cover bounds a third cavity with the circuit board. The third cavity is delimited from the first cavity by a wall element. 
         [0024]    With the third cavity, regions of the circuit board containing further components may be shielded without these components having to be sealed against contact with the fluid. In addition, it is not necessary to configure the third cavity to be fluid-proof, which simplifies the construction. 
         [0025]    In one embodiment, a second electrical component is disposed on the wall element in the third cavity, and is in thermal contact with the wall element. 
         [0026]    In this way, heat may be discharged from the second component via heat conduction through the wall element and released to the fluid. 
         [0027]    In one embodiment, the circuit board is coated in the first cavity with an electrically insulating material such that a fluid in the first cavity does not come into contact with an electrically conductive contact of the circuit board or of the first-named component. 
         [0028]    The electrically insulating material prevents electrical currents from unintentionally flowing between contacts through the fluid and interfering with the function of the components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  shows a schematic, plan view of an apparatus in accordance with one embodiment. 
           [0030]      FIG. 2  shows a schematic, cross-sectional view of the apparatus of  FIG. 1  along line II-II of  FIG. 1 . 
           [0031]      FIG. 3  shows a schematic illustration of a magnetic resonance tomography system in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  shows a plan view of an inventive apparatus  100 , in which a lid  112  of the apparatus has been removed. 
         [0033]      FIG. 2  shows a schematic cross-section along a line II-II of  FIG. 1 . In  FIG. 2 , the lid  112  is disposed and illustrated at a location in accordance with one embodiment. 
         [0034]    In the middle of the apparatus is a circuit board  101 , which may have one, two or more layers including circuit paths. Disposed on the circuit board  101  are components  103 ,  104 , which are electrically connected to circuit paths of the circuit board  101 . A first component  103  has a large power loss and in operation warrants high cooling power, as well as a second component  105  with an average power loss and average cooling demands. 
         [0035]    Arranged on the circuit board  101  are wall elements  111  that are constructed as part of a single-piece frame. As is apparent in  FIGS. 1 and 2 , the frame forms several regions that are each separated from one another by a wall  111 . The wall  111  surrounds a region in each case on the outer circumference. Alternatively, several separate frames adjoining one another may be arranged on the circuit board  112 , in order to separate the individual regions from one another. Alternatively, only a single frame may be provided, which merely surrounds a single region. 
         [0036]    The frame or frames are in each case disposed in planar fashion on the side facing the circuit board  101  and opposite a lid  112 , in order to provide as exact a fit as possible with the likewise planar circuit board  101  and the planar lid  112 . 
         [0037]    As is apparent in  FIG. 2 , a lid  112  is disposed on the walls  111 , so that the walls  111  form closed cavities  105 ,  107  with the circuit board  101  and the lid  112 . The first electrical component  103  is disposed on the circuit board  101  in the first cavity  105 . In the third cavity  107  the second electrical component  104  is disposed on a wall  111  adjoining the first cavity  105 . 
         [0038]    The walls  111  or the frame  111  and the lid  112  are made of an electrically and thermally conductive material. This material may, for example, be aluminum or copper, but other metals or alloys with these properties may be used. For example, a resistance against a fluid used as a coolant may also be useful. 
         [0039]    Disposed between lid  112  and walls  111  are sealing mechanisms (or seals)  113 , which seal the respective cavities  105 ,  107  against one another in a fluid-proof manner. In the same way, sealing mechanisms  114  are disposed between the walls  111  and the circuit board  101 , and seal the cavities  105 ,  107  in a fluid-proof manner. The cavity  105 , through which, as explained below, a fluid flows, is hereby made fluid-proof with respect to the adjacent cavities. 
         [0040]    In one embodiment, the sealing mechanisms  113 ,  114  are configured to be electrically conductive, so that, while providing the sealing, a conductive connection also exists between walls  111  and lid  112 , or walls  111  and circuit board  101 . In this way, the cavities  105 ,  107  each form a Faraday cage that restricts electromagnetic waves to the respective cavity  105 ,  106 ,  107  and prevents propagation into the surrounding area. Alternatively, the sealing mechanisms  113 ,  114  may not be conductive themselves, but a separate electrical connection is to be established using other conductive connecting elements such as screws, male multipoint connectors, contact springs or cables. 
         [0041]    In the region which is open to the cavity  105 , an electrically insulating material  102  is applied to the circuit board  101 , and covers the entire surface of the circuit board belonging to the cavity  105  in a fluid-proof manner. The material  102  also covers all metal contacts of the first electrical component  103  provided with an electrical potential and thereby insulates the first electrical component  103  from a fluid provided in the cavity  105 . The electrically insulating material  102  may, for example, be an epoxy resin poured into the cavity  105 , after the frame  101  has been disposed on the circuit board. 
         [0042]    As is apparent from  FIG. 1 , the cavity  105  additionally has two openings  115 ,  116  on walls  111 , through which an exchange of fluid is possible with the interior of the cavity  105 . Thus, for example, a fluid may be introduced as a coolant into the cavity  105  through the fluid feed  115 , and flows around the first electrical component  104  and, in this way, effectively cools the first electrical component  104 . The heated fluid may then be discharged again by way of the second opening  116  as a fluid outflow. The fluid also cools the walls  111  of the cavity  105  and thus the second electrical component  104 , which in the third cavity  107  is in thermal contact with the wall  111  on the opposing side of the wall  111 . Because the transport of heat is degraded because of heat resistance of the wall  111 , the cooling power is reduced with respect to the electrical component  103 . Depending on the electrical circuit and construction of the second electrical component, the second electrical component  104  is electrically insulated with respect to the wall  111  using an insulating mechanism. 
         [0043]    Illustrated in the embodiment in  FIG. 2  on a side of the circuit board  101  opposing the frame  111  is another frame  121  or walls  121  and a lid  122 , which, as already described, likewise bounds cavities  106  with the circuit board  101 . No other electrical components are illustrated in  FIG. 2 , but electrical components may also be arranged in the second cavity  106  and on the adjacent wall  112 . The second cavity  106  also has an electrically insulating material  102  on the surface of the circuit board  101 . Otherwise, the cavities  106  bounded by the frame  121  and the lid  122  correspond in terms of their properties with the previously described cavities  105 ,  107 . For example, the cavities  106  are provided with comparable sealing mechanisms (or seals)  123 ,  124 . 
         [0044]    For optimum cooling, in one embodiment, the circuit board  101  may have openings, through which a fluid flows from the first cavity  105  into the second cavity  106  and back. As a result, cooling of the first component  103  also takes place from the other side of the circuit board  101 . The second cavity  106  may have a separate fluid inflow and fluid outflow or otherwise for the first cavity  105  to be supplied with fluid via the openings in the circuit board  101 . In one embodiment, fluid openings may be in the lids  112 ,  122  instead of in the walls  111 ,  121 . 
         [0045]    In one embodiment, water, e.g., distilled water, is provided as a fluid, because water has a particularly high thermal capacity and does not damage the environment. 
         [0046]    Other fluids such as oils or synthetic liquids may also be used, e.g., liquids resistant to high voltages. The electrically insulating material  102  may then be dispensed with, for example. 
         [0047]    The walls  111  and  121  are in one embodiment in each case arranged adjacently on opposing sides of the circuit board  101 . In this way a larger force may be exerted on the walls, without distorting the circuit board. As a result, a good seal may be achieved between circuit board  101  and the walls  111 ,  121 . Furthermore, the opposing cavities, such as the first cavity  105  and the second cavity  106 , form a common shielding of the circuit board  101  outward through the conducting walls  111 ,  121  and the lids  112 ,  122 . By being bolted to each other, the frames  111 ,  121  and lids  112 ,  122  may, for example, clamp the circuit board  101  between the frames and lids or may be pressed from the outside against the circuit board  101  via additional retaining elements. 
         [0048]    In one embodiment, one or more cavities  105 ,  106  may be provided only on one side of the circuit board  101 . In this case, the circuit board  101  itself shields the interior of the cavity  105 ,  106  by metal layers. The circuit board is pressed firmly enough against the frame  111  via a suitable construction, for example, via a support frame. 
         [0049]      FIG. 3  schematically shows a magnetic resonance tomography system  1 , in which inventive apparatuses  100  are used. 
         [0050]    The magnetic resonance tomography system  1  has a magnet unit  10  with a field magnet  11  that generates a static magnetic field B 0  to align nuclear spins of samples or of a patient  40  in a sample volume. The sample volume is arranged in a passthrough or opening  16  that extends in a longitudinal direction  2  through the magnet unit  10 . The field magnet  11  may be a superconducting magnet that may provide magnetic fields having a magnetic flux density of up to 3 T or higher. For lower field strengths, permanent magnets or electromagnets with normal-conducting coils may also be used. 
         [0051]    Furthermore, the magnet unit  10  has gradient coils  12  configured to overlay the magnetic field B 0  with variable magnetic fields in three spatial directions for the spatial differentiation of the captured imaging regions in the sample volume. The gradient coils  12  may be coils made of normal-conducting wires that may generate fields orthogonal to one another in the sample volume. 
         [0052]    The magnet unit  10  furthermore has a body coil  14  and local coils  15 . Both the body coil  14  and the local coil  15  are also characterized as antennas  14 ,  15  in the following description, because both are suitable for emitting a high-frequency electromagnetic alternating field into their surrounding area. The body coil  14  is used among other things as a transmit coil if as homogeneous as possible an electromagnetic excitation field is to be generated across a large volume. 
         [0053]    A magnetic resonance signal excited by the electromagnetic alternating field of the body coil  14  or of the local coils  15  and by the static magnetic field B 0  in the patient may be received either by the transmit coils  15  or by the separate body coil  14 , which may receive signals from the entire examination region. 
         [0054]    A control unit  20  supplies the magnet unit  10  with the various signals for the gradient coils  12  and the body coil  14  or the local coils  15  and evaluates the signals received. 
         [0055]    Thus the control unit  20  has a gradient control  21  configured to provide the gradient coils  12  with variable currents via feed lines. The variable currents provide the desired gradient fields in the sample volume on a temporally coordinated basis. The gradient control  21 , to actuate the gradient coils  12 , generates signals with a voltage of over a thousand volts and an output of kilowatts at working frequencies in the kilohertz range and multiple harmonic components thereof. It is hence useful for the gradient control to have an apparatus  100  in order to provide sufficient cooling and good shielding combined with simple construction. 
         [0056]    Furthermore, the control unit  20  has a transceiver device  22  configured to generate, for antenna  14 ,  15 , a high-frequency pulse with a predetermined time characteristic, amplitude, phase and spectral power distribution to excite a magnetic resonance of the nuclear spins in the patient  40 . In this case pulse powers in the kilowatt range may be achieved. It is therefore useful for the transceiver device  22  also to have an apparatus  100  in order to provide sufficient cooling and good shielding combined with simple construction. 
         [0057]    The transceiver unit  22  is furthermore configured to evaluate, in terms of amplitude and phase, high-frequency signals received from the body coil  14  or one or more transmit coils  15  and fed to the transceiver unit  22  via a signal line  33 . This relates to high-frequency signals that emit nuclear spins in the patient  40  in response to the excitation by a high-frequency pulse in the magnetic field B 0  or in a magnetic field resulting from an overlay of B 0  and gradient fields. 
         [0058]    Furthermore, the control unit  20  has a controller  23  configured to undertake the temporal coordination of the activities of the gradient control  21  and the transmit devices  22  for the purpose of image capture via magnetic resonance tomography. To this end the controller  23  is connected to the other units  21 ,  22  via a signal bus  25  and exchanges signals with the other units  21 ,  22 . The controller  23  is configured to accept and process signals from the patient  40  evaluated by the transceiver unit  22  or to define and temporally coordinate pulse and signal shapes for the gradient control  21  and the transceiver unit  22 . 
         [0059]    The patient  40  is disposed on a patient couch  30 . The patient couch  30  is used in magnetic resonance tomography. The patient couch  30  has a first support  36  disposed under a first end  31  of the patient couch  30 . So that the support  36  may hold the patient couch  30  in a horizontal position, the support  36  may have a foot that extends along the patient couch  30 . To move the patient couch  30 , the foot may also have a mechanism for movement, such as castors. Apart from the support  36  on the first end  31 , no structural element is disposed between the floor and the patient couch, so that the patient couch may be introduced as far as the first end  31  into the opening  16  of the field magnet  11 .  FIG. 1  shows linear rail systems  34  that movably connect the support  36  to the patient couch  30 , so that the patient couch may travel in the longitudinal direction  2 . To this end the linear rail system has a drive  37  that enables an operator or the controller  23  to move the patient couch  30  in the longitudinal direction  2  in a controlled manner. As a result, regions of the body of the patient may be examined that have a larger extent than the sample volume in the opening  16 . 
         [0060]    It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification. 
         [0061]    While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.