JP2006279180A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the sensibility of an antenna while avoiding the enlargement of the whole device containing a circuit board. <P>SOLUTION: An antenna device 10 has an approximately rectangular plate-shaped core body 12, a spool 13 fitted on the outer periphery of the core body 12 and an antenna coil 14 wound on the periphery of the spool 13. The core body 12 is divided into a plate-shaped upper core 12a constituting the top face of the core body 12 and an approximately plate-shaped lower core 12b constituting the underside of the core body 12, and an integral core is configured by combining these cores 12a and 12b. Since the circuit board 11 is surrounded by the core body 12, a magnetic flux in the Z direction projected to the main surface of the upper core 12a or the lower core 12b is passed through the reverse side through a side wall section 12W and does not interfere in the circuit board 11. Consequently, the antenna coil having a high sensibility and an antenna device can be achieved without increasing the substantial occupied area of the antenna coil. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to an antenna device in which an antenna coil and an electronic circuit connected thereto are integrated.

  In general, a wound antenna coil has a higher detection sensitivity as the opening area of the coil increases due to the principle of detecting the magnetic field component of electromagnetic waves by electromagnetic induction. Normally, these antenna coils are formed by being wound around a magnetic material such as ferrite. Therefore, in order to obtain high detection sensitivity, it is advantageous to increase the cross-sectional area of the magnetic material as much as possible. However, this means an increase in the size of the antenna coil, which is difficult to apply to portable devices and the like that are required to be reduced in size and height.

  12A and 12B are diagrams schematically showing a configuration of a conventional general antenna device, where FIG. 12A is a top view and FIG. 12B is a view from the direction of arrow A in FIG. FIG.

  As shown in FIG. 12A, a conventional antenna device 40 has a configuration in which an antenna coil 42 is wound around a magnetic rod-like core 41. The mounting range of the circuit component 43 related to the antenna coil 42 is as indicated by a broken line. 12B, reference numeral 44 denotes an end face of the magnetic rod-like core 41, and reference numeral 45 denotes a circuit board on which the antenna coil and related circuit components are mounted.

  When attempting to increase the cross-sectional area of the rod-shaped core 41 in order to increase the sensitivity of the antenna coil 42, the mounting area of the antenna coil 42 on the circuit board 45 increases if the cross-sectional area is expanded toward the inner surface of the circuit board 45. As a result, the mounting area of the other circuit components 43 is deprived. Further, if the cross-sectional area is widened in the vertical direction of the circuit board 45, the height of the antenna coil 42 increases, so that it becomes impossible to meet the demand for a low profile. That is, the method of increasing the cross-sectional area of the rod-shaped core in order to improve the sensitivity of the antenna coil is extremely unacceptable in portable devices and the like that are required to be reduced in size and height.

  In order to improve this difficulty, a method of increasing the cross-sectional area of the core, that is, improving the electromagnetic wave detection sensitivity by integrating the circuit board and the rod-shaped core and winding a coil around the circuit board is also known. (See Patent Documents 1 and 2). In this case, however, the width of the core is limited to the width of the substrate, and if the thickness is increased, the overall size is increased. These are essentially an extension of the above-described concept of the rod-shaped antenna, and an increase in the size of the apparatus cannot be avoided if the antenna sensitivity is increased.

  On the other hand, the structure which wound the coil around the outer periphery of the cylindrical core is also known (see Patent Documents 3 and 4). However, in this case, the external magnetic flux passes only through the thin cylindrical portion, and sufficient antenna characteristics cannot be obtained.

There is also known a structure in which the cross-sectional area of one end face or both end faces of the core is increased while keeping the core diameter of the portion around which the coil is wound (see Patent Documents 5 and 6). However, simply increasing the cross-sectional area of the end portion for higher sensitivity will eventually increase the mounting area of the antenna coil itself, so it will change the pressure on the mounting area of other circuit components. Absent. Furthermore, when this antenna coil is mounted on a circuit board, in order for external magnetic flux to be introduced into the core, parts should not be placed near both ends of the antenna coil or on its extension line. There is also the problem that it introduces significant limitations.
Japanese Patent Laid-Open No. 08-135264 JP-A-10-117107 JP 2003-294869 A JP 07-129867 A JP 2004-153649 A JP 2004-274609 A

  As described above, various methods are known as methods for improving the sensitivity of the antenna coil. However, if the sensitivity of the antenna coil is improved, the antenna device inevitably increases in size. No effective solution has been proposed.

  Accordingly, an object of the present invention is to provide an antenna device with improved antenna sensitivity while avoiding an increase in size of the entire device including a circuit board.

  The object of the present invention includes a magnetic body having a cavity, a circuit board at least partially housed in the cavity of the magnetic body, and a coil that converts a magnetic field component passing through the magnetic body into an electric current. Achieved by the antenna device.

  In the present invention, the magnetic body is preferably composed of two flat plate portions sandwiching both surfaces of the circuit board and a connecting portion connecting the flat plate portions, and the coil is disposed on the outer periphery of the connecting portion. It is preferably wound.

  In the present invention, the connecting portion may be a side wall portion provided along at least one side of the flat plate portion, or may be a convex portion provided near the center of the flat plate portion.

  In this invention, it is preferable that the said connection part is provided through the said circuit board.

  In this invention, it is preferable that the area of the said circuit board is larger than the said cavity part of the said magnetic body, and a part of said circuit board is arrange | positioned outside the said cavity part of the said magnetic body.

  In the present invention, it is preferable that a holding member for holding the coil is further provided on the outer periphery of the magnetic body.

  In the present invention, it is preferable that a terminal or a conductive wire connected to the circuit board is further provided, and the terminal or the conductive wire is drawn to the outside through a gap where the connecting portion of the magnetic material does not exist.

  It is preferable that the magnetic body has a higher loss at a frequency higher than a frequency band used as an antenna.

  ADVANTAGE OF THE INVENTION According to this invention, the antenna apparatus which improved the antenna sensitivity can be provided, avoiding the enlargement of the whole apparatus including a circuit board.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is an exploded perspective view schematically showing a configuration of an antenna device according to a preferred embodiment of the present invention, and FIG. 2 is a perspective view showing a state in which each component shown in FIG. 1 is assembled.

  As shown in FIGS. 1 and 2, the antenna device 10 includes a substantially rectangular flat plate core body 12 that houses a circuit board 11, a winding frame (bobbin) 13 provided on the outer periphery of the core body 12, and a winding. An antenna coil 14 is provided around the frame 13.

  The circuit board 11 is a board on which electronic components are mounted. For example, components such as capacitors and resistors necessary for realizing an antenna device are mounted together with an antenna coil that converts a magnetic field component into a current. Of course, a circuit or an electronic component for realizing another function may be mounted.

  The core body 12 is divided into a flat upper core 12a constituting the upper surface thereof and a substantially flat lower core 12b constituting the lower surface thereof, and these are combined to constitute an integral core. Both the upper core 12a and the lower core 12b are made of a magnetic material. Side walls 12W are integrally provided on two sides along the longitudinal direction (X direction in the figure) of the lower core 12b. When the upper core 12a and the lower core 12b are combined, the presence of the side wall 12W A cavity is formed between the two, and the circuit board 11 is accommodated in the cavity. That is, the lower core 12b and the upper core 12a are in a container-lid relationship. Moreover, since the side wall part is not formed in two sides orthogonal to the longitudinal direction of the lower core 12b, the core main body of this embodiment is a cylindrical body which has a space | gap in the both ends of a X direction.

  As the magnetic body used for the core body 12, for example, ferrite represented by Ni—Zn or Mn—Zn can be used. It is preferable that the magnetic body used for the core main body 12 of this embodiment has a higher loss at a frequency higher than the use frequency band of the antenna. Generally, an antenna coil has frequency selectivity because it is combined with a capacitor to form a parallel resonance circuit or a series resonance circuit. The selectivity is determined by the Q value of the formed resonance circuit. Therefore, signals in unnecessary frequency bands other than the frequency band in which the antenna coil 14 is used are attenuated. However, the Q value of the resonance circuit can obtain only a mathematically determined attenuation characteristic depending on the characteristics of the antenna coil and the capacitor. Therefore, by giving a loss in the unnecessary frequency band to the magnetic material itself, it is possible to form a resonance circuit having a larger attenuation characteristic that is away from the mathematical limitation described above. Therefore, the magnetic material used in combination with the antenna coil should have as much loss as possible in the unnecessary frequency band.

  The frequency band in which the antenna coil 14 is used is generally from a long wave band to a short wave band, and is at most several hundreds MHz band. On the other hand, a portable device that is assumed to incorporate this antenna device may have a transmission function of several hundred MHz or more. Therefore, in order to suppress the influence of the high frequency noise generated from the portable device, it is preferable in the present embodiment to use a magnetic body having higher loss characteristics in a high frequency band. Furthermore, the effective attenuation characteristic in the unnecessary frequency band possessed by the magnetic material has an effect of suppressing the signal in the unnecessary band that the antenna apparatus is trying to radiate. That is, the core main body 12 also exhibits a function as a shield against a signal in an unnecessary band. An example of the magnetic body having such characteristics is a ferrite core. Since the magnetic body has such loss characteristics, unnecessary high-frequency components are not induced in the antenna coil, so that the antenna characteristics can be improved. Of course, it is more preferable that the loss characteristic of the magnetic material is larger in a frequency band lower than the used frequency band. And in order to give the above characteristics, the core main body 12 can also be comprised by combining several magnetic body from which a characteristic differs.

  On the other hand, the winding frame 13 is made of a non-magnetic material such as a resin. In the present embodiment, the inner diameter dimension of the winding frame 13 substantially matches the dimension of the core body 12, and the winding frame 13 is disposed on the outer periphery of the core body 12 by fitting the winding frame 13 into the core body 12. Here, the outer periphery of the core body is the periphery of the main surface of the flat core. A plurality of lead terminals 15 are provided at both ends of the winding frame 13. The lead terminal 15 is enclosed or press-fitted when the winding frame 13 is molded, or is bonded after molding to be integrated with the winding frame 13 and passes through the inside of the winding frame 13 as shown. One end of the lead terminal 15 is connected to the circuit board 11, and the other end is drawn out through the gap of the core body 12. The lead terminal 15 is used not only as a terminal for connecting to an external circuit, but also as a terminal for connecting the circuit board 11 and the antenna coil 14. The lead terminal 15 can be provided without passing through the inside of the winding frame 13, but in that case, the lead terminal 15 may be covered with an insulating material so as not to interfere with the antenna coil 14 and the core body 12. preferable. It is also possible to use a conducting wire.

  3 is a side sectional view of the antenna device along the line BB in FIG. 2, and FIG. 4 is a side sectional view along the line CC in FIG.

  As shown in FIGS. 3 and 4, the circuit board 11 is sandwiched between the upper core 12a and the lower core 12b, and the winding frame 13 and the antenna coil 14 are arranged on the outer periphery thereof. Therefore, the magnetic flux passes through the upper core 12a, the side wall portion 12W, and the lower core 12b, is linked to the antenna coil 14, and induces a signal current in the antenna coil 14 by electromagnetic induction. In this embodiment, since the width of the circuit board 11 and the inner diameter of the winding frame 13 are substantially equal, the winding frame 13 also serves to fix the movement of the circuit board in the X direction by pressing the circuit board 11 from both sides. You can also As shown in FIG. 4, since the circuit board 11 is surrounded by the core body 12, when a magnetic field component in the Z direction is present, the magnetic flux incident on the main surface of the upper core 12a or the lower core 12b is the side wall portion 12W. Through the other side.

  FIG. 5 is a magnetic flux distribution diagram showing a simulation result when the core body 12 of the present embodiment is placed in a static magnetic field. The static magnetic field is generated using a Helmholtz coil. As apparent from FIG. 5, the external magnetic flux incident substantially perpendicularly to the flat plate portion of the core body 12 selectively passes through the side wall portions on both sides and reaches the opposite flat plate portion. This means that all the magnetic flux incident on the inside of the antenna coil 14 can pass through the core body 12 to the opposite side and can be linked to the antenna coil 14. Further, since the magnetic flux distribution is formed so as to avoid the hollow portion of the core body 12, the magnetic flux does not adversely affect the circuit board 11 accommodated in the core body 12.

  FIG. 6 is a side view of the antenna device and shows a state where the antenna device is mounted on a motherboard.

  As shown in FIG. 6, the antenna device 10 is fixed on the mother board 16, and the circuit board accommodated in the antenna apparatus 10 is connected to the circuit on the mother board 16 through the lead terminals 15. In addition, it is preferable not to arrange a conductive pattern or an electronic component in the region 16S on the lower surface of the mother board 16 at the mounting position of the antenna device 10 so as not to hinder the passage of magnetic flux interlinking with the antenna coil 14.

  As described above, according to the antenna device 10 of the present embodiment, the cross-sectional area of the antenna coil 14 and the core body 12 around which the antenna coil 14 is wound can be made to be approximately the same as the area of the circuit board 11. Since it is much larger than the one wound around the conventional rod-shaped core, the external magnetic flux can be collected effectively. Therefore, the sensitivity of the antenna coil 14 can be greatly improved by increasing the number of magnetic fluxes linked to the antenna coil 14.

  Further, according to the present embodiment, the core body 12 having a structure surrounding the circuit board 11 is provided so that the magnetic flux can pass through the antenna coil 14 even if the circuit board 11 exists inside the antenna coil 14. Therefore, the magnetic flux passes through the core body 12 without interfering with the circuit board 11 and is linked to the antenna coil 14. That is, in this embodiment, it can be said that the occupied area of the antenna coil 14 and the core body 12 and the occupied area of the circuit board 11 are effectively overlapped without impairing the respective functions. Therefore, there is no problem that the mounting area of other circuit components on the circuit board is deprived due to the increase in size of the antenna element, and an increase in the size of the entire apparatus including the circuit board can be avoided.

  In the said embodiment, although the core main body 12 consisted of the upper core 12a and the lower core 12b, and demonstrated the case where the side wall part 12W was provided in two sides along the longitudinal direction of the lower core 12b, Various other shapes are possible.

  FIG. 7 is a schematic perspective view showing another shape of the core body.

  The core main body 17 of FIG. 7 has a side wall portion 17W provided not only on the lower core 17b but also on the upper core 17a. That is, the cross-sectional shapes of the two upper and lower magnetic bodies are both U-shaped, and by combining these vertically and symmetrically, a wider cavity is formed, and the magnet that connects the upper and lower two flat plate portions is formed. A path is formed. In such a structure, since the shapes of the upper core 17a and the lower core 17b are the same, the handling of the core during assembly is facilitated, and the manufacturing cost can be reduced.

  FIG. 8 is an exploded perspective view schematically showing another embodiment of the antenna device.

  As shown in FIG. 8, the antenna device 20 is characterized in that a circuit board 21 larger than the opening area of the antenna coil 14 is used. Only a partial region 21X of the circuit board 21 is sandwiched between the upper core 12a and the lower core 12b. In the region 21X on the circuit board 21 sandwiched between the upper core 12a and the lower core 12b, electronic components are mounted as in the surrounding region. In the present embodiment, components such as capacitors and resistors necessary for realizing the antenna device 20 together with the antenna coil 14 may be mounted in the region 21X or may be mounted in a surrounding region. When mounted in the surrounding area, it is not necessary to connect the antenna coil 14 and the electronic components on the circuit board 21 via the lead terminals 15. The circuit board 21 is provided with a hole 21H for penetrating the side wall of the lower core 12b. After the side wall of the lower core 12b is fitted into the hole 21H from the lower side of the circuit board 21, the antenna coil 14 is mounted. Since the winding frame 13 around which the antenna coil 14 is wound is fitted into the lower core 12b from above, and then the upper core 12a is combined thereabove, the antenna device 20 is completed. Even when configured in this manner, the same effects as those of the antenna device 10 described above can be obtained.

  FIG. 9 is an exploded perspective view schematically showing still another embodiment of the antenna device.

  As shown in FIG. 9, the antenna device 30 is characterized in that a magnetic path that connects the upper core 18a and the lower core 18b is formed at substantially the center thereof. In the present embodiment, a columnar convex portion 18P is integrally formed substantially at the center on the lower core 18b side, and this is connected to the upper core 18a on the opposite side to form a magnetic path. Only a partial region 31X of the circuit board 31 is sandwiched between the upper core 18a and the lower core 18b.

  In the region 31X on the circuit board 31 sandwiched between the upper core 18a and the lower core 18b, electronic components are mounted as in the surrounding region. The circuit board 31 is provided with a hole 31H for penetrating the convex portion 18P of the lower core 18b. After the convex portion 18P of the lower core 18b is fitted into the hole 31H from the lower side of the circuit board 31, an upper side thereof is provided. A winding frame 32 around which the antenna coil 14 is wound is fitted into the frame. Furthermore, the antenna device 30 is completed by combining the upper core 18a on the upper side. Even when configured in this manner, the same effects as those of the antenna device 10 described above can be obtained. In addition, although the convex part 18P of this embodiment is a column shape, it may be a prismatic shape, for example, and even if the convex part 18P is provided not only in the lower core 18b but in both the upper core 18a and the lower core 18b. Good.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention, and these are also included in the scope of the present invention. Needless to say.

  For example, in the above embodiment, the core body 12 is configured by a combination of two magnetic bodies including the upper core 12a and the lower core 12b. However, the core body 12 may be divided into any number, and further divided. It does not have to be done. That is, any magnetic body having a cavity that can accommodate at least part of the circuit board can be used as the core body of the present invention.

  Moreover, in the said embodiment, although the side wall part 12W is provided in two sides along the longitudinal direction of the lower core 12b or the upper core 12a, you may provide in two sides orthogonal to a longitudinal direction. Moreover, it is not limited to two sides, but may be three sides or only one side. Furthermore, it is possible to provide side walls on all four sides. However, if the lead terminals 15 are provided on all four sides, the lead terminals 15 cannot be drawn out, and some care is required such as forming a gap in the core body 12 for drawing the lead terminals 15 to the outside.

  Further, in the present invention, as a member that connects the flat plate portion of the upper core 12a and the flat plate portion of the lower core 12b, in addition to the side wall portion 12W, a form such as a convex portion 18P shown in FIG. In consideration of these, the core body 12 only needs to be composed of two flat plate portions sandwiching both surfaces of the circuit board 11 and a connecting portion that connects the flat plate portions, and can take various forms within the range. It is.

  In the above embodiment, the lead terminal 15 is provided for connecting the circuit board 11 to an external circuit such as a motherboard. However, if the circuit board 11 in the core body 12 does not need to be connected to the external circuit, As shown in FIG. 10, the lead terminal 15 can be omitted. In this case, there is no problem even if side walls are formed on all four sides of the core body. Further, if the antenna coil 14 can be correctly wound around the core body 12, it is possible to omit the winding frame 13 and directly wind the antenna coil 14 around the core body 12 as shown in FIG. 11. It is. Furthermore, as a member for holding the antenna coil 14 on the outer periphery of the core body 13, another member can be employed instead of the winding frame 13. As another holding member, for example, an insulating tape can be used, and it can be dealt with by winding the antenna coil 14 directly on the side surface of the core body 12 and affixing the insulating tape thereon.

FIG. 1 is an exploded perspective view showing a configuration of an antenna device according to a preferred embodiment of the present invention. FIG. 2 is a perspective view showing a state in which the components shown in FIG. 1 are assembled. FIG. 3 is a side sectional view of the antenna device taken along line BB in FIG. FIG. 4 is a side sectional view of the antenna device taken along the line CC of FIG. FIG. 5 is a magnetic flux distribution diagram showing a simulation result when the core body 12 of the present embodiment is placed in a static magnetic field. FIG. 6 is a side view of the antenna device and shows a state where the antenna device is mounted on the mother board 16. FIG. 7 is a schematic perspective view showing another shape of the core body. FIG. 8 is a schematic perspective view showing another embodiment of the antenna device. FIG. 9 is a perspective view showing still another embodiment of the antenna device. FIG. 10 is a perspective view showing still another embodiment of the antenna device. FIG. 11 is a perspective view showing still another embodiment of the antenna device. 12A and 12B are diagrams schematically showing a conventional antenna device, in which FIG. 12A is a top view, and FIG. 12B is a side view as viewed from the direction of arrow A in FIG. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna apparatus 11 Circuit board 12 Core 12a Upper core 12b Lower core 12W Side wall part 13 Winding frame (bobbin)
14 Antenna coil 15 Lead terminal 16 Motherboard 16S Antenna device mounting region 17 Core body 17a Upper core 17b Lower core 17W Side wall portion 18a Upper core 18b Lower core 18P Protruding portion 20 Antenna device 21 Circuit board 21H Hole 21X Antenna device mounting region 30 Antenna device 31 Circuit board 31H Hole 31X Mounting area 32 of antenna device Winding frame 40 Antenna device 41 Bar-shaped core 42 Antenna coil 43 Circuit component 44 End surface 45 of bar-shaped core Circuit board

Claims (10)

  An antenna device comprising: a magnetic body having a hollow portion; a circuit board at least partially housed in the hollow portion of the magnetic body; and a coil for converting a magnetic field component passing through the magnetic body into an electric current.   The antenna device according to claim 1, wherein the magnetic body includes two flat plate portions sandwiching both surfaces of the circuit board, and a connecting portion that connects the flat plate portions.   The antenna device according to claim 2, wherein the coil is wound around an outer periphery of the connecting portion.   The antenna device according to claim 2, wherein the connecting portion is a side wall portion provided along at least one side of the flat plate portion.   The antenna device according to claim 2, wherein the connecting portion is a convex portion provided near the center of the flat plate portion.   The antenna device according to claim 2, wherein the connecting portion is provided so as to penetrate the circuit board.   The antenna device according to claim 6, wherein an area of the circuit board is larger than the cavity of the magnetic body, and a part of the circuit board is disposed outside the cavity of the magnetic body. .   The antenna device according to claim 1, further comprising a holding member for holding the coil on an outer periphery of the magnetic body.   9. A terminal or a conductive wire connected to the circuit board is further provided, and the terminal or the conductive wire is drawn out through a gap where the connecting portion of the magnetic material does not exist. The antenna device according to any one of the above. The antenna device according to claim 1, wherein the magnetic body has a higher loss at a frequency higher than a frequency band used as an antenna.

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