Abstract:
Disclosed herein is an antenna device that includes: a planar coil pattern that surrounds an inner diameter region, the inner diameter region including a center region elongated in a first direction, a first end region positioned at one side in the first direction as viewed from the center region, and a second end region positioned at other side in the first direction as viewed from the center region; and a metal layer that covers the planar coil pattern, the metal layer including a first slit that overlaps a part of the first end region and a second slit that is formed separately from the first slit and overlaps a part of the second end region.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to an antenna device and a portable wireless device provided with the antenna device and, more particularly, to an antenna device suitable for NFC (Near Field Communication) and a portable wireless device provided with the antenna device. 
         [0003]    Description of Related Art 
         [0004]    In recent years, an RFID (Radio Frequency Identification) system is implemented in a portable wireless device such as a smartphone, and such a portable wireless device is provided with an antenna device for performing near field communication with a reader/writer as a communication means. As an antenna device of such a type, those described in Japanese Patent No. 4,687,832, and Japanese Patent Application Laid Open Nos. 2002-111363, and 2013-162195 are known. 
         [0005]    The antenna devices described in the above publications are provided with a planar coil pattern and a metal layer covering the planar coil pattern, wherein an inner diameter region of the planar coil pattern overlaps an opening part of the metal layer. 
         [0006]    In the antenna devices described in the above publications, it is necessary to form an opening part of the metal layer having substantially the same size as that of the inner diameter region of the planar coil pattern. However, in recent years, there are increasing number of portable wireless devices having a metal casing in view of reduction in thickness and weight, improvement in durability against impact of, e.g., dropping, and enhancement in design. In such a case, the metal layer serving as a part of the casing constitutes the antenna device, so that the opening part cannot be freely formed in the metal layer. 
         [0007]    Further, in order to extend a magnetic flux radiated from the antenna device, a planar coil pattern is preferably formed into an elongated rectangular planar shape, not a square shape. In this case, however, in the antenna devices described in the above publications, a very long opening part needs to be formed in the metal layer. To form such an opening part is not realistic particularly when the metal layer constitutes a part of the casing. 
       SUMMARY 
       [0008]    An object of the present invention is therefore to provide an antenna device capable of reducing restrictions on the shape of the metal layer covering the planar coil pattern and extending a magnetic flux, and a portable wireless device provided with the antenna device. 
         [0009]    An antenna device according to the present invention includes a planar coil pattern and a metal layer that covers the planar coil pattern. An inner diameter region surrounded by the planar coil pattern includes a center region elongated in a first direction, a first end region positioned at one side in the first direction as viewed from the center region and a second end region positioned at the other side in the first direction as viewed from the center region. The metal layer includes a first slit that overlaps a part of the first end region and a second slit that is formed separately from the first slit and overlaps a part of the second end region. 
         [0010]    A portable wireless device according to the present invention includes the above antenna device. 
         [0011]    According to the present invention, the separately formed slits are formed at the both sides of the inner diameter region in the longitudinal direction, making it possible to largely extend a magnetic flux radiated from the antenna device and to increase the density of the magnetic flux. Thus, when the antenna device according to the present invention is used as an antenna for NFC, it is possible to increase a communication distance as compared with a conventional one. In addition, a large opening part need not be formed in the metal layer, so that when the metal layer constitutes a part of the casing of the portable wireless device, design restrictions can be reduced. 
         [0012]    In the present invention, the center region, a part of the first end region that does not overlap the first slit, and a part of the second end region that does not overlap the second slit are preferably covered with the metal layer. With this configuration, a metal layer having a large area can be used, which is especially suitable for a case where the metal layer constitutes a part of the casing of the portable wireless device. 
         [0013]    In this case, the width of the inner diameter region in the second direction that crosses the first direction is preferably smaller in the center region than in the first and second end regions. With this configuration, magnetic fluxes at parts of the conductor pattern constituting the planar coil pattern that sandwich the center region cancel each other, so that an eddy current generated in a part of the metal layer that covers the center region can be reduced. 
         [0014]    Further, in this case, it is preferable that the first and second slits extend in the first direction and that the width of each of the first and second slits in the second direction is smaller than the width of each of the first and second end regions in the second direction. With this configuration, a magnetic flux radiated from the antenna device can be intensified. 
         [0015]    In the present invention, the first and second slits may be formed so as to cross the first and second end regions, respectively. With this configuration, the metal layer that covers each of the first and second end portions is divided into two sections, so that a magnetic flux can be intensified further by the metal layer. 
         [0016]    In the present invention, the metal layer may further include a third slit that overlaps the center region. With this configuration, a magnetic flux can be radiated from the center region as well. 
         [0017]    Thus, according to the present invention, there can be provided an antenna device capable of reducing restrictions on the shape of the metal layer covering the planar coil pattern and more widely extending a magnetic flux, and a portable wireless device provided with the antenna device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a schematic perspective view illustrating a configuration of a portable wireless device provided with an antenna device according to a first embodiment of the present invention; 
           [0020]      FIG. 2  is a plan view transparently illustrating a configuration of the antenna device shown in  FIG. 1 ; 
           [0021]      FIGS. 3A and 3B  are cross-sectional views taken along a line A-A of  FIG. 2  and a line B-B of  FIG. 2 , respectively; 
           [0022]      FIG. 4  is a partially enlarged view of the antenna device shown in  FIG. 1 ; 
           [0023]      FIG. 5  is a plan view transparently illustrating a configuration of an antenna device according to a second embodiment of the present invention; 
           [0024]      FIG. 6  is a plan view transparently illustrating a configuration of an antenna device according to a third embodiment of the present invention; 
           [0025]      FIG. 7  is a plan view transparently illustrating a configuration of an antenna device according to a fourth embodiment of the present invention; 
           [0026]      FIG. 8  is a plan view transparently illustrating a configuration of an antenna device according to a fifth embodiment of the present invention; 
           [0027]      FIG. 9  is a plan view transparently illustrating a configuration of an antenna device according to a sixth embodiment of the present invention; 
           [0028]      FIG. 10  is a plan view transparently illustrating a configuration of an antenna device according to a seventh embodiment of the present invention; and 
           [0029]      FIG. 11  is a plan view transparently illustrating a configuration of an antenna device according to an eighth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0030]    Preferred embodiments of the present invention will now be explained in detail with reference to the drawings. 
       First Embodiment 
       [0031]      FIG. 1  is a schematic perspective view illustrating a configuration of a portable wireless device  100  provided with an antenna device  10 A according to the first embodiment of the present invention. 
         [0032]    The portable wireless device  100  illustrated in  FIG. 1  is, e.g., a smartphone and has a thin box-like casing.  FIG. 1  is a view illustrating the portable wireless device  100  as viewed from the back surface side of the portable wireless device  100 . Thus, the front surface of the portable wireless device  100  on which a display and the like are provided faces downward. The casing of the portable wireless device  100  is formed of a combination of resin and metal. A center part  101  corresponding to a wide area on the back surface is mainly formed of a metal layer  30 . The both ends of the casing in the longitudinal direction (y-direction) as viewed from the center part  101  are formed of resin cover layers  102  and  103 , respectively. The reason that the wide area on the back surface of the casing is formed of the metal layer  30  is mainly for improving mechanical strength, magnetic shielding characteristics, and design of the casing. 
         [0033]    The portable wireless device  100  incorporates therein a spiral-shaped planar coil pattern  20 . The majority of the planar coil pattern  20  is covered with the metal layer  30  constituting the casing, so that, actually, the planar coil pattern  20  cannot be seen from outside. As illustrated in  FIG. 1 , first and second slits  31  and  32  are formed in the metal layer  30 . The slit  31  has a shape obtained by cutting, in the x-direction, a part of an edge L 1  of the metal layer  30  extending in the y-direction, and the slit  32  has a shape obtained by cutting, in the x-direction, a part of an edge L 2  of the metal layer  30  extending in the y-direction. The slits  31  and  32  are not connected but separated from each other, so that the metal layer  30  is not divided by the slits  31  and  32 . 
         [0034]    As illustrated in  FIG. 1 , the planar coil pattern  20  partially overlaps the slits  31  and  32 , and parts thereof that overlap the slits  31  and  32 , respectively, are exposed from the metal layer  30 . However, the slits  31  and  32  are embedded by a resin or the like, so that the planar coil pattern  20  is not exposed from the casing. 
         [0035]    The planar coil pattern  20  and the metal layer  30  that covers the planar coil pattern  20  constitute the antenna device  10 A according to the present embodiment. The planar coil pattern  20  is connected to a non-illustrated RF circuit incorporated in the portable wireless device  100 . Thus, the antenna device  10 A according to the present embodiment can be used for, e.g., 13.56 MHz NFC. 
         [0036]      FIG. 2  is a plan view transparently illustrating a configuration of the antenna device  10 A.  FIGS. 3A and 3B  are cross-sectional views taken along a line A-A of  FIG. 2  and a line B-B of  FIG. 2 , respectively. 
         [0037]    In the present embodiment, the planar coil pattern  20  is formed into a rectangular planar shape elongated in the x-direction, and the number of turns thereof is, e.g., four. Thus, a conductor pattern constituting the planar coil pattern  20  has a part extending in the x-direction and a part extending in the y-direction, and the former is longer than the latter. Terminals  21  and  22  illustrated in  FIG. 2  are terminals connected to a non-illustrated RF circuit. The terminal  21  is connected to the outer peripheral end of the planar coil pattern  20 , and the terminal  22  is connected to the inner peripheral end of the planar coil pattern  20  through a crossing part  20   a  that crosses the conductor pattern. As illustrated in  FIGS. 3A and 3B , the planar coil pattern  20  is formed on a single substrate  50  formed of a PET resin, and the crossing part  20   a  that crosses the conductor pattern is formed on, e.g., the back surface of the substrate  50 . 
         [0038]    As illustrated in  FIG. 2 , an inner diameter region  40  surrounded by the planar coil pattern  20  has a rectangular shape elongated in the x-direction. The inner diameter region  40  refers to the XY plane surrounded by the innermost turn of the planar coil pattern  20 . Here, a part of the inner diameter region  40  that is positioned at one end portion (left side in  FIG. 2 ) in the x-direction is defined as a first end region  41 , a part of the inner diameter region  40  that is positioned at the other end portion (right side in  FIG. 2 ) in the x-direction is defined as a second end region  42 , and a region positioned between the first and second end regions  41  and  42  is defined as a center region  43 . In this case, in the present embodiment, a part of the first end region  41  overlaps the slit  31 , and a part of the second end region  42  overlaps the slit  32 . The residual part of the first end region  41 , the residual part of the second end region  42 , and the entire surface of the center region  43  are covered with the metal layer  30 . 
         [0039]    While a geometric characteristic point does not exist at the boundary between the center region  43  and end regions  41  and  42  when the inner diameter region  40  has a simple rectangular shape as in the present embodiment, the center region  43  is defined such that the x-direction thereof is the longitudinal direction. 
         [0040]    As illustrated in  FIG. 2 , the width of each of the slits  31  and  32  in the y-direction is smaller than the width of each of the end regions  41  and  42  in the y-direction. Therefore, both sides of each of the end regions  41  and  42  in the y-direction as viewed from each of the slits  31  and  32  are covered with the metal layer  30 . A part of each of the end regions  41  and  42  that is covered with the metal layer  30  functions as an accelerator that intensifies a magnetic flux generated by the planar coil pattern  20 . Further, a part of the metal layer  30  that is positioned outside the planar coil pattern  20  extends a magnetic flux generated by the planar coil pattern  20 . 
         [0041]      FIG. 4  is a partially enlarged view of the antenna device  10 A, which explains a function obtained when current is made to flow in the planar coil pattern  20 . 
         [0042]    As illustrated in  FIG. 4 , when a counterclockwise current I 1  is made to flow in the planar coil pattern  20 , a magnetic flux φ 1  (see  FIG. 3 ) is generated, and this magnetic flux φ 1  circulates widely around the metal layer  30 . This widens a range of the magnetic flux to thereby increase a communication distance and widen antenna directivity. 
         [0043]    On the other hand, current flows in the metal layer  30  in a direction canceling the magnetic flux φ 1 . Specifically, a current I 2  illustrated in  FIG. 4  flows in the inner diameter region  40  surrounded by the planar coil pattern  20 , and a current I 3  illustrated in  FIG. 4  flows in a region outside the planar coil pattern  20 . The current I 2  generates a magnetic flux φ 2  in the same direction as the magnetic flux φ 1  passing through the slits  31  and  32  and thus serves as an accelerator, thereby further increasing a communication distance. In the present embodiment, the magnetic fluxes φ 2  are generated in the same direction respectively from three edges L 11  to L 13  constituting the slit  31 . The magnetic fluxes φ 2  generated from the respective edges L 11  and L 12  are illustrated in  FIG. 3A , and the magnetic flux φ 2  generated from the edge L 13  is illustrated in  FIG. 3B . 
         [0044]    In the present embodiment, the slits  31  and  32  are positioned at both end portions of the planar coil pattern  20  in the longitudinal direction, so that a region having a high flux density is distributed in two places. This widens the range of the magnetic flux to a large extent to thereby increase a communication distance and widen antenna directivity. Such an effect is considered to be obtained by locating two or more planar coil patterns at different planar positions. In this case, however, not only the number of components is increased, but also wirings need to be provided so as to connect the plurality of planar coil patterns. On the other hand, in the present embodiment, the single planar coil pattern  20  formed on the single substrate  50  is used to constitute the antenna device  10 A, so that the above problem does not occur. 
         [0045]    Thus, when the antenna device  10 A according to the present embodiment is used as an antenna for NFC, it is possible to increase a communication distance as compared with a conventional one without having to make the antenna structure complicate. In addition, a large opening part need not be formed in the metal layer  30 , so that when the metal layer  30  is used as a part of the casing of the portable wireless device  100 , design restrictions can be reduced. 
       Second Embodiment 
       [0046]      FIG. 5  is a plan view transparently illustrating a configuration of an antenna device  10 B according to the second embodiment of the present invention. 
         [0047]    The antenna device  10 B according to the second embodiment differs from the antenna device  10 A according to the first embodiment in that the width of the center region  43  in the y-direction is reduced. Other configurations are basically the same as those of the antenna device  10 A according to the first embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. 
         [0048]    As illustrated in  FIG. 5 , in the present embodiment, of the conductor pattern constituting the planar coil pattern  20 , patterns X 1  and X 2  extending in the x-direction are in proximity to each other at their center portions, with the result that the width of the center region  43  in the y-direction is significantly reduced. The center portions of the respective patterns X 1  and X 2  are portions that define the width of the center region  43  in the x-direction. Although not especially limited, the distance between the innermost turn of the pattern X 1  and the innermost turn of the pattern X 2  is preferably reduced to approximately the same degree as the distance between adjacent wiring patterns. The shape of each of the end regions  41  and  42  is substantially the same as that in the first embodiment. 
         [0049]    With this configuration, a magnetic flux generated by current flowing in the pattern X 1  and a magnetic flux generated by current flowing in the pattern X 2  cancel each other, so that an eddy current generated in a part of the metal layer  30  that overlaps the center region  43  is reduced. As a result, it is possible to obtain higher antenna efficiency than that in the antenna device  10 A according to the first embodiment. 
       Third Embodiment 
       [0050]      FIG. 6  is a plan view transparently illustrating a configuration of an antenna device  10 C according to the third embodiment of the present invention. 
         [0051]    The antenna device  10 C according to the third embodiment differs from the antenna device  10 B according to the second embodiment in that the pattern X 2  linearly extends. Other configurations are basically the same as those of the antenna device  10 B according to the second embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. Even in this configuration, a magnetic flux generated by current flowing in the pattern X 1  and a magnetic flux generated by current flowing in the pattern X 2  cancel each other, so that an eddy current generated in apart of the metal layer  30  that overlaps the center region  43  is reduced. As a result, it is possible to obtain the same effect as that of the antenna device  10 B according to the second embodiment. 
       Fourth Embodiment 
       [0052]      FIG. 7  is a plan view transparently illustrating a configuration of an antenna device  10 D according to the fourth embodiment of the present invention. 
         [0053]    The antenna device  10 D according to the fourth embodiment differs from the antenna device  10 C according to the third embodiment in that the slits  31  and  32  extend passing completely through the end regions  41  and  42 , respectively. Other configurations are basically the same as those of the antenna device  10 C according to the third embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. 
         [0054]    As illustrated in  FIG. 7 , in the present embodiment, the length of each of the slits  31  and  32  in the x-direction is extended. The slit  31  is extended in length in the x-direction so as to cross a pattern y 1  of the conductor pattern surrounding the end region  41  that extends in the y-direction. The slit  32  is extended in length in the x-direction so as to cross a pattern y 2  of the conductor pattern surrounding the end region  42  that extends in the y-direction. As a result, a part of the metal layer  30  that covers the end region  41  is divided in the y-direction into two sections by the slit  31 , and a part of the metal layer  30  that covers the end region  42  is divided in the y-direction into two sections by the slit  32 . 
         [0055]    With this configuration, the current I 2  illustrated in  FIG. 4  flows more smoothly to increase the density of the magnetic flux φ 2 . This makes it possible to obtain higher antenna efficiency than that in the antenna device  10 C according to the third embodiment. 
       Fifth Embodiment 
       [0056]      FIG. 8  is a plan view transparently illustrating a configuration of an antenna device  10 E according to the fifth embodiment of the present invention. 
         [0057]    The antenna device  10 E according to the fifth embodiment differs from the antenna device  10 A according to the first embodiment in that the slits  31  and  32  each extend in the y-direction. Other configurations are basically the same as those of the antenna device  10 A according to the first embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. Even with such a configuration, it is possible to obtain substantially the same effect as that of the antenna device  10 A according to the first embodiment. 
       Sixth Embodiment 
       [0058]      FIG. 9  is a plan view transparently illustrating a configuration of an antenna device  10 F according to the sixth embodiment of the present invention. 
         [0059]    The antenna device  10 F according to the sixth embodiment differs from the antenna device  10 C according to the third embodiment in that the slits  31  and  32  each extend in the y-direction. Other configurations are basically the same as those of the antenna device  10 C according to the third embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. Even with such a configuration, it is possible to obtain substantially the same effect as that of the antenna device  10 C according to the third embodiment. 
       Seventh Embodiment 
       [0060]      FIG. 10  is a plan view transparently illustrating a configuration of an antenna device  10 G according to the seventh embodiment of the present invention. 
         [0061]    The antenna device  10 G according to the seventh embodiment differs from the antenna device  10 D according to the fourth embodiment in that the slits  31  and  32  each extend in the y-direction. Other configurations are basically the same as those of the antenna device  10 D according to the fourth embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. Even with such a configuration, it is possible to obtain substantially the same effect as that of the antenna device  10 D according to the fourth embodiment. 
         [0062]    The above fifth to seventh embodiments are suitable for a case where the slits  31  and  32  are made to extend in the y-direction due to design restrictions. 
       Eighth Embodiment 
       [0063]      FIG. 11  is a plan view transparently illustrating a configuration of an antenna device  10 H according to an eighth embodiment of the present invention. 
         [0064]    The antenna device  10 H according to the eighth embodiment differs from the antenna device  10 A according to the first embodiment in that a slit  33  is additionally formed. Other configurations are basically the same as those of the antenna device  10 A according to the first embodiment. Thus, the same reference numerals are given to the same elements, and overlapping description will be omitted. 
         [0065]    The slit  33  extends in the y-direction, and an end portion thereof reaches the center region  43  in a plan view. With such a configuration, the magnetic flux φ 1  is radiated from a part where the center region  43  and the slit  33  overlap each other, so that it is possible to obtain higher antenna efficiency than that in the antenna device  10 A according to the first embodiment. 
         [0066]    It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention. 
         [0067]    For example, the shape of the planar coil pattern  20  is not limited to those described in the above-described embodiments, but may be a polygonal shape such as a hexagon or an octagon, or an elliptical shape. Further, the number of turns of the conductor pattern constituting the planar coil pattern  20  is not especially limited.