Abstract:
An inductor includes a core, a coil disposed about the core, and a shield. The shield and the core are connected to each other so that a closed magnetic loop is formed. The core may be a single piece or made up of a pair of core segments. The shield may include two halves or portions or may include a cover with a base. The core may be unitary with the shield at one or both ends thereof. In embodiments where the shield includes two portions, the portions may have substantially identical geometry and dimensions.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to electrical components, specifically inductors. 
   2. Description of the Related Art 
   The desirability for electrical components that are smaller in size but that have better electrical properties never fades. Often there are trade offs when it comes to designing such components. For example, when size is reduced, one or more of the electrical properties is adversely affected. 
   In the case of inductors, electromagnetic interference (EMI) is one of the properties that is desirably minimized or eliminated. EMI is an unwanted electromagnetic signal which may degrade the performance of an electronic device. To reduce EMI effects caused by inductors, shields are placed about the inductor. Shielded inductors thereby require more space than unshielded types. In addition, the shields require grounding. 
   BRIEF SUMMARY OF THE INVENTION 
   An inductor includes a core, a coil disposed about the core, and a shield. The shield and the core are connected to each other so that a closed magnetic loop is formed. The core may be a single piece or made up of a pair of core segments. The shield may include two halves or portions or may include a cover with a base. The core may be unitary with the shield at one or both ends thereof. In embodiments where the shield includes two portions, the portions may have substantially identical geometry and dimensions. 
   For a given energy storage capability, the inductor of the invention greatly improves upon conventional inductors. For example, the inductor of the invention is able to store the same amount of energy at a volume of about 10 times less than conventional toroidal inductors. In addition, with ratio of width to length of the inductor of the invention may be on the order of 1 to 1, while such ratio for conventional toroidal inductors is on the order of 2 to 1. 
   Other features and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a perspective view of a shielded inductor; 
       FIG. 2  is an exploded perspective view of a shielded inductor; 
       FIG. 3  is an exploded side view of a shielded inductor; 
       FIG. 4  illustrates a closed magnetic loop of a shield and a core of an inductor; 
       FIG. 5  is an exploded perspective view of a shielded inductor; 
       FIGS. 6A and 6B  are side views of the inductor of  FIG. 5 ; 
       FIG. 7  is an exploded perspective view of a shielded inductor; 
       FIG. 7A  is a perspective view of the inductor of  FIG. 7 ; 
       FIG. 8  is an exploded perspective view of a shielded inductor; 
       FIG. 8A  is a perspective view of the inductor of  FIG. 8 ; and 
       FIG. 9  illustrates dimensions of a shielded inductor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 2  in detail, an inductor  10  includes a coil  12  and a shielded core  14 . The coil  12  may have a pair of terminals  16 , and the shielded core  14  may include a first portion  18   a  and a second portion  18   b.    
   As shown in  FIG. 2 , each portion  18  may include a housing  20  having an end wall  22  and a side wall  24 . In the embodiment shown, the side wall  24  of each housing  20  may have a mating edge  26 , which is also shown in FIG.  3 . In addition, a pair of notches  28  may be formed in the side wall  24  for receiving a terminal  16  of the coil  12 . 
   The housing of each portion  18  of the core  14  may also include a core segment  30 , which is shown clearly in FIG.  3 . The core segment  30  may be disposed on an inner surface  32  of the end wall  22 . Each core segment  30  may have an end face  34 . In a number of embodiments, a seat  36  may be defined within each portion  18 , for example, the between the side wall  24  and the core segment  30  for receiving the coil  12 . 
   With additional reference to  FIG. 4 , when the first and second portions  18   a  and  18   b  are engaged together with the coil  12  received by the seats  36 , the mating edges  26  of the side walls  24  of the housings  20  mate with each other as shown by the dashed lines indicated at A to form a magnetically continuous shield  40 . In addition, the end faces  34  of the core segments  30  contact each other as shown by the dashed line indicated at B to form a magnetically continuous core  42 . Accordingly, a closed magnetic loop is formed by the shield  40  and the core  42 , as indicated by magnetic flux lines C. When mounted in an electric circuit, the shield  40  does not require grounding. 
   As shown in  FIG. 1 , when the portions  18  are engaged, the notches  28  of the housing  20  of the first portion  18   a  respectively align with the notches  28  of the housing  20  of the second portion  18   b  to form a pair of apertures  44  in the shield  40  (only one of the apertures is shown in FIG.  1 ). Accordingly, with the coil  12  received by the seats  36  about the core  42 , the terminals  16  may respectively project through the apertures  44  of the shield  40 . 
   In a number of embodiments, for example, as shown in  FIG. 5 , a single notch  28  may be formed in the side wall  24  of each portion  18 . Accordingly, when the portions  18  are secured as shown in  FIGS. 6A and 6B , a pair of apertures  44  are formed in the shield  40  for respectively receiving the terminals  16  of the coil  12 . 
   In other embodiments such as those shown in  FIG. 7 , the shielded core  14  may include a first portion such as a base  50  and a second portion such as cover  52 . The base  50  may include a side wall  54  and a core  56 , with a seat  58  for receiving a coil  60  defined between the side wall  54  and the core  56 . The cover  52  may include a pair of apertures  64  for respectively receiving terminals  64  of the coil  60  when the coil is received in the seat  58 . When the cover  52  is mated with the base  50  and the core  56  as shown in  FIG. 7A , a closed magnetic loop is formed by the base  50 , the cover  52 , and the core  56 , with the terminals  64  projecting through the apertures  64 . 
   In still other embodiments, a single aperture may be utilized. For example, as shown in  FIG. 8 , the shielded core  14  may include a first portion such as a base  70  and a second portion such as cover  72 . The base  70  may include a side wall  74  with a notch  76  formed therein. A core  78  is provided and may be disposed on either the base  70  or the cover  72 ; in the embodiment shown, the core  78  is attached to the cover  72 . When the cover  72  is mated with the base  70  with a coil  80  received about the core  78  as shown in  FIG. 8A , an aperture  82  is formed, and a closed magnetic loop is formed by the base  70 , the cover  72 , and the core  78 , with terminals  84  of the coil  80  projecting through the aperture  82 . 
   In a number of embodiments, the dimensions of the inductor  10  are minimized while still maintaining desirable electrical characteristics. As an example, with reference to  FIG. 9 , an overall height H of the shield core  40  may be less than about 10 mm, with the side wall  24  of each housing having a height h of less than about 5 mm. In addition, the shielded core  40  may have a length L of less than about 10 mm and a width W of less than about 10 mm. Accordingly, in embodiments where the dimensions are approximately equal, a ratio of width W to length L is on the order of 1 to 1. In other embodiments, the width-to-length ratio is less than about 1.5 to 1. 
   As another example, one of the electrical properties for inductors is energy storage, which is a determined by the equation E=½LI 2 , where L is inductance and I is current DC. A desirable characteristic of inductors is volume versus energy storage. If each of the dimensions (i.e., height H, length L, and width L) of the inductor  10  is about 6.8 mm, then a volume of the shield core  40  is about 310 mm 3 . At these dimensions, the inductor  10  may have an inductance of about 400 nH (nanohenrys) at a frequency of about 100 kHz and a current of about 20 amperes DC, and an energy storage of 80 μJ (microjoules). For comparison purposes, a conventional toroidal inductor capable of storing the same amount of energy would need to have a length of about 20 mm, a width of about 20 mm, and a height of about 8 mm, thereby having a volume of about 3,200 mm 3 . Accordingly, the inductor  10  with a columnar core  42  and closed magnetic loop of the present invention reduces the volume by over 10 times for the same energy storage capability. 
   In a number of embodiments, such as that shown in  FIGS. 1 ,  2 , and  3 , the first and second portions  18   a  and  18   b  of the shielded core  14  have substantially identical geometry and substantially equal dimensions. Accordingly, during manufacturing, only a single die, mold, or cast (depending upon the manufacturing process) needs to be made to produce the portions  18  of the shielded core  14  with, e.g. powder iron, thereby reducing costs. In addition, the core segment  30  and the housing  20 , specifically, the end wall  22 , of each portion  18  may be of unitary construction, thereby eliminating manufacturing processes dedicated to producing a separate core and attaching such core to a shield. In other words, an end  86  (see  FIGS. 3 ,  7 , and  8 ) of the core  78  or core segment  30  may be unitary with the shield  14 . 
   With regard to manufacturing, to fabricate t inductor  10 , the coil  12  may be positioned in the seat  36  of the housing  20  of one of the portions  18  with the terminals aligned with the notch or notches  28 . The other portion may then be positioned thereon, with the mating edges  26  and the end faces  34  respectively contacting. The portions  18   a  and  18   b  may be secured together at the mating edges  26  of the side walls  24  with, for example, adhesive such as epoxy. Although the coil  12  may be wound about the core, the coil  12  may be prefabricated, e.g., with an automatic winder, to reduce manufacturing costs. 
   Those skilled in the art will understand that the preceding exemplary embodiments of the present invention provide the foundation for numerous alternatives and modifications thereto. These other modifications are also within the scope of the present invention. Accordingly, the present invention is not limited to that precisely as shown and described in the present invention.