Abstract:
In a device and method to install a coil in a circuit, the coil is installed on a substrate and the inductance value of the coil installed on the substrate is adjusted with a test circuit board. The substrate is then installed in the circuit. This enables an efficient installation of the coil.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention concerns methods for installing a coil in a circuit and devices for this purpose. 
         [0003]    2. Description of the Prior Art 
         [0004]    Magnetic resonance systems for the examination of patients by magnetic resonance tomography are known from, for example, DE 103 142 15 B4. 
         [0005]    The front end electronics of the transmission path of a conventional magnetic resonance system (MR system) normally include a series circuit composed of different function units such as, for example, a transmission path crossover switch, a 90° hybrid circuit, a phase shifter and a transmission/reception diplexer. In nearly all of these units, high-current air-core coils formed by silver-plated copper wire are used. In order to be able to ensure correct functioning of the front end electronics, each of these coils should exhibit an inductance value that is predetermined for it within narrow tolerances. Due to unavoidable heat that arises during losses, the components may heat to temperatures of over 100° C. The execution of the coils as through components (i.e. components that proceed through the circuit board) prevents the presence (and thus the use) of continuous mass on the back side of the circuit board and therefore makes cooling of the module more difficult. 
         [0006]    It is known for the air-core coils to be soldered into the module as geometrically predefined through components that are subsequently adjusted by pinching (manual corrective deformation of the coils) until the entire front end electronics satisfies its specifications. This is made difficult due to the high integration of function units in the transmission path front end, because measurement interfaces between the sub-units cannot be provided without additional measures. Such interfaces interfere for space reasons as well as due to the damping or additional reactive parasitic elements associated therewith. 
         [0007]    Without interfaces a multidimensional optimization exists in which m measurement parameters must be adjusted with n coils, with each coil affects multiple measurement parameters. Overall, the complicated adjustment represents a significant cost factor in such modules. 
         [0008]    A simplification of the adjustment or even a complete absence of adjustment can be achieved by the use of narrow-tolerance components at the critical positions. With regard to capacitors, for example, various manufacturers offer their components with tolerances of +−2% or even +−1%. 
         [0009]    Such narrow-tolerance modules are not available for the coils made of silver wire. Even with a suitable pre-adjustment of the coils by the manufacturer, for components installed as through components the problem still exists that the originally specified inductance value can be adulterated in the installation of the module due to different insertion depths or mechanical tolerances of the hole spacing. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to enable efficient and cost-effective installation of coils in a circuit, in particular a circuit of a magnetic resonance apparatus. 
         [0011]    The above object is achieved in accordance with the present invention in a method to install a coil in a circuit on a circuit board, including the steps of initially installing the coil on a substrate, testing the inductance of the coil on the substrate before attaching the substrate to a circuit board, and subsequently installing the substrate with the tested coil thereon on a circuit board to incorporate the coil in a circuit of the circuit board. 
         [0012]    The above object also is achieved in accordance with the invention by a magnetic resonance system having a circuit formed on a circuit board, the circuit including a coil that is mounted on a substrate, with the coil and the substrate connected to the circuit board as an SMD (surface mounted device). 
         [0013]    According to the invention, the adjustment of coils (in particular of an MR front end electronics module) can be significantly simplified; a subsequent adjustment can even be entirely omitted. 
         [0014]    In an advantageous through-installation of the coil on the substrate, a sufficient stability of the SMD module results so that it can also be adjusted given wire diameters greater than 1 mm by pinching (corrective deformation) of the coil. A tearing of SMD pads due to forces occurring in the adjustment is also avoided by the through-installation. 
         [0015]    In an embodiment of the carrier as an SMD module, a continuous mass surface (and therefore an efficient cooling of the module) is enabled. 
         [0016]    Attachment of the coil on the substrate by a rigid connection avoids the connection between the coil and the substrate changes significantly upon soldering of the substrate with the adjusted coil into a circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIGS. 1A and 1B  show examples of embodiments of pre-adjustable SMD coils on a substrate carrier. 
           [0018]      FIG. 2  shows the installation of a substrate of an SMD coil (of the type shown in the embodiment in  FIG. 1 ) in a test version. 
           [0019]      FIG. 3  shows installation of a carrier of an SMD coil in a circuit of an MR apparatus. 
           [0020]      FIG. 4  schematically illustrates a known magnetic resonance tomography system, 
           [0021]      FIG. 5  schematically shows the arrangement of a front end and transmission path in an MR apparatus, as a block diagram. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]      FIG. 4  shows a magnetic resonance apparatus  1  with a displaceable patient bed  2 , with which a patient  3  is examined. The patient  3  is moved in the patient bed  2  in the Z-direction (i.e. in the axial direction) through the imaging region of the magnetic resonance apparatus  1 . 
         [0023]      FIGS. 1A and 1B  show examples of embodiments of pre-adjustable SMD coils for circuits in the transmission path of a magnetic resonance apparatus  1 . 
         [0024]    In  FIG. 1A , on a substrate  5  made of low-loss material (for example RO4350) the two ends  8   a ,  8   b  of a coil  8  that are inserted through the substrate  5  are contacted by soldering. In addition to a solder connection  14  such as that in  FIG. 1 , a rigid connection can also be used (for example by riveting the coil ends  8   a ,  8   b  into recesses of the substrate  5 ) in order to prevent that the connection between the coil and the substrate from shifting upon soldering of the adjusted coil. 
         [0025]    A connection with known SMD pads  6 ,  7  also can be produced according to the example in  FIG. 1B . A connection without SMD pads can also ensue according to the example in  FIG. 1B , for example, with curved ends of the coil that can possibly be additionally soldered. 
         [0026]    The coil  8  can be mechanically predefined (for example by the coil ends  8   a ,  8   b  being folded for the recesses in the substrate) and thermally unloaded before the mounting on SMD substrate  5 . 
         [0027]    The coil  8  installed on the substrate  5  can be adjusted to the desired inductance value in a test circuit  9 , for example according to  FIG. 2 . 
         [0028]    The substrate  5  on which the coil  8  is already mounted is here inserted with a force F (for example manually) into clamp contacts of the test circuit located on a test circuit board, and the coil  8  is then tuned in a known manner (for example by pinching); its inductance is thus set to a desired value. 
         [0029]    Given use of a suitable test circuit (for example a resonant circuit), tolerances of below 1% could be achieved by such testing. The coil is thereby adjusted, for example with a resonant circuit, so that a no-load operation (phase angle of the input reflection factor=0°) occurs at the input of the resonant circuit. 
         [0030]      FIG. 3  shows a section of a circuit board of a circuit  10  that can be populated with the substrate  5  of the coil  8  (after the adjustment of the coil  8  in the arrangement according to  FIG. 2 ). For example, this can ensue by a solder connection  11  between the substrate  5  of the coil  8  (that is fashioned here as an SMD module) and the circuit  10 . Recesses in the form of blind holes  15 ,  16  can be provided in the circuit board  10 . The blind holes produce a safe spacing between the ends  8   a ,  8   b  of the coil  8  (in particular given execution according to the right side of  FIG. 1 ) and the circuit board  10 . A base metallization  12  on the underside of the circuit  10  forms a continuous mass that can be cooled well. 
         [0031]    The adjustment of the front end electronics module can be significantly simplified by the use of mechanically reliable, narrow-tolerance coils; ideally, a subsequent adjustment can even be entirely foregone. 
         [0032]    The invention has been described in the context of a coil for the transmission path of an MR system, but it can also be used in other configurations. 
         [0033]      FIG. 5  schematically shows an arrangement of a front end electronics unit  58  of an MR apparatus  1  and a local transmission coil  56  as a block diagram. Test signals  53  and reception signals of the whole-body resonator and/or of the local transmission coil  56  of the MR apparatus are transferred between a controller with an evaluation device  51  and the front end electronics unit  54 , for example. The front end electronic unit  58  is connected with the whole-body resonator  1  via connections  55 ,  59  to send and to receive. 
         [0034]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.