JP2009065280A - Antenna unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna unit having a wide directivity in a direction substantially perpendicular to the center axis of a loop antenna. <P>SOLUTION: The antenna unit includes a loop antenna with which winding of the element is carried out with at least one or more time surroundings, and a magnetic member arranged near the loop antenna. The loop antenna as a whole is arranged on one surface of the magnetic member. The magnetic member is prepared with a larger size compared to the loop antenna so as to make the formation range of magnetic field produced from the loop antenna in a direction substantially perpendicular to the center axis of a loop antenna wider than in the state that magnetic member is not arranged. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device having a loop antenna.

  Conventionally, as an antenna device having a loop antenna, for example, as shown in Patent Documents 1 and 2, an antenna device including a magnetic member is known.

In the antenna devices disclosed in Patent Documents 1 and 2, the magnetic member is arranged between the metal member and the loop antenna and in the vicinity of the loop antenna, thereby reducing the influence of the metal member (for example, eddy current loss in the metal member). I try to reduce it.
JP 2006-41986 JP 2002-298095 A

  Incidentally, the antenna devices disclosed in Patent Documents 1 and 2 are applied to a wireless communication medium such as an IC card and a wireless communication medium such as a non-contact type IC card reader, and the size of the magnetic member is a loop. It is almost the same size as the antenna (see FIG. 1 of Patent Document 1 and FIGS. 1 and 2 of Patent Document 2). The generation range of the magnetic field generated from the loop antenna is narrower than the state in which the magnetic member is not disposed in a direction substantially perpendicular to the central axis of the loop antenna due to the magnetic collection on the magnetic member (Patent Document 2). 2 and 3). As described above, the antenna devices disclosed in Patent Documents 1 and 2 are antenna devices having a narrow directivity in a direction substantially perpendicular to the central axis of the loop antenna.

  In view of the above problems, an object of the present invention is to provide an antenna device having a wide directivity in a direction substantially perpendicular to the central axis of a loop antenna.

  In order to achieve the above object, an invention according to claim 1 is an antenna device comprising: a loop antenna in which an element is wound with at least one or more turns; and a magnetic member arranged in the vicinity of the loop antenna. The loop antenna is entirely arranged on one surface of the magnetic member, and the magnetic member has a magnetic field generated in a direction substantially perpendicular to the central axis of the loop antenna. It is characterized in that it is large with respect to the loop antenna so as to be wider than the state where it is not arranged.

  As described above, according to the present invention, the magnetic member is sufficiently large with respect to the loop antenna, and the magnetic lines of force pass through the magnetic member having a smaller magnetic resistance than the external atmosphere. Therefore, the direction is substantially perpendicular to the central axis of the loop antenna. The magnetic field lines reach farther from the loop antenna than in the state where the magnetic member is not disposed. As a result, the antenna device has a wide directivity in the direction substantially perpendicular to the central axis of the loop antenna (in other words, when used as a transmitter, the transmission area in the direction substantially perpendicular to the central axis of the loop antenna is wide, When used as an antenna, the antenna device has a wide receiving area in a direction substantially perpendicular to the central axis of the loop antenna.

  In the first aspect of the present invention, as described in the second aspect, a body constituting member that constitutes a vehicle body is suitable as the magnetic member. Thus, if it is a vehicle body structural member, it has a sufficient size to expand the directivity in the direction substantially perpendicular to the central axis of the loop antenna. The number of parts of the antenna device can be reduced.

  In the first or second aspect of the invention, as described in the third aspect of the invention, the loop antenna is preferably configured to be wound around the one surface of the magnetic member in a plurality of height directions. According to this, the directivity in the direction substantially perpendicular to the central axis of the loop antenna can be widened as compared with the configuration in which the loop antenna is wound in a plane parallel to one surface of the magnetic member.

  In the invention according to any one of the first to third aspects, as described in the fourth aspect, the central axis of winding of the loop antenna may be substantially perpendicular to one surface of the magnetic member. According to this, directivity can be balanced in a direction substantially perpendicular to the central axis of the loop antenna.

  In the invention according to any one of claims 1 to 4, as described in claim 5, a columnar core made of a magnetic material may be provided, and a loop antenna may be wound around the core. According to this, since the lines of magnetic force pass through the core having a lower magnetic resistance than the external atmosphere, the directivity can be further expanded. In this case, as described in claim 6, when the core is magnetically coupled to the magnetic member, the magnetic resistance can be further reduced and the directivity can be further expanded.

  In the invention according to any one of claims 1 to 4, as described in claim 7, a convex portion may be formed on one surface of the magnetic member, and a loop antenna may be wound around the convex portion. According to this, not only the convex portion functions as a core, but also the directivity can be further expanded because the convex portion is a part of the magnetic member. In addition, since the core as a separate member is unnecessary, the configuration of the antenna device can be simplified.

  In the invention according to any one of the first to seventh aspects, as described in the eighth aspect, it is preferable that the magnetic member is formed using a material having a relative permeability higher than 10 with respect to a use frequency. According to this, the directivity in a direction substantially perpendicular to the central axis of the loop antenna can be effectively widened as compared with a magnetic member made of a material having a relative permeability of 10 or less.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of the antenna device according to the first embodiment. FIG. 2 is a plan view of FIG. 1 viewed from the loop antenna arrangement side.

  The antenna device according to the present embodiment is, for example, as an antenna device of a smart key system disposed in a vehicle interior (a transmitter from the vehicle side to the key side for detecting whether a key exists in the vehicle interior). It is configured.

  As shown in FIGS. 1 and 2, the antenna device 100 includes a loop antenna 20 wound around a core 10 and a magnetic member 30 disposed in the vicinity of the loop antenna 20 as main parts.

  The core 10 is formed of a known magnetic body capable of forming a magnetic circuit against a magnetic field generated from the loop antenna 10, preferably a columnar shape using a ferromagnetic material of known magnetic bodies as a magnetic material. A loop antenna 20 is wound around.

  In the present embodiment, the core 10 having a rectangular cross section (rectangular shape) is formed using Ni-Zn ferrite as a material. Further, in a state where one end of the core 10 is in contact with the one surface 31 of the magnetic member 30 so that the longitudinal direction of the core 10 is substantially perpendicular to the one surface 31 (XY plane shown in FIG. 1) of the magnetic member 30. It is fixed. That is, the core 10 is magnetically coupled to the magnetic member 30.

  The loop antenna 20 is a kind of transmission line whose end is short-circuited. The element is wound with at least one or more turns according to the operating frequency (having one or more loops), and a power source is connected to both ends of the element. It is a thing. As the form of the loop antenna 20, it is possible to employ any form as long as at least the central axis of the loop antenna 20 (loop part) has a component in the vertical direction (height direction) with respect to the one surface 31 of the magnetic member 30. . Further, the shape of the loop portion is not particularly limited.

  In the present embodiment, as a transmitter for a smart key, a plurality of conductive wires (copper wires) as elements are arranged on the surface of the core 10 along the longitudinal direction of the core 10 so as to have an electrical length corresponding to a use frequency of 134 kHz. It is wound around. That is, the loop antenna 20 is wound a plurality of times along a direction substantially perpendicular to the one surface 31 of the magnetic member 30 (Z-axis direction shown in FIG. 1), and the central axis of the loop antenna 20 (loop portion) is magnetic. It is substantially perpendicular to one surface 31 of the member 30. Further, the loop shape is rectangular corresponding to the outer shape of the core 10.

  Like the core 10, the magnetic member 30 is formed of a known magnetic body that can form a magnetic circuit against the magnetic field generated from the loop antenna 20, preferably a ferromagnetic body of known magnetic bodies, as a magnetic material. is there. Specifically, as will be described later, a material having a relative permeability (magnetic material permeability / vacuum permeability) of more than 10 with respect to the operating frequency, and more preferably a material having a relative permeability of 50 or more is used. It is good to adopt what was formed. In addition, the magnetic member 30 has the entire loop antenna 20 disposed on one surface 31 of the magnetic member 30, and the generation range of the magnetic field generated from the loop antenna 20 is substantially perpendicular to the central axis of the loop antenna 20 (see FIG. 1 in a direction perpendicular to the Z-axis shown in FIG. 1 so as to be larger than the state in which the magnetic member 30 is not disposed. In other words, the magnetic member 30 is sufficiently large with respect to the loop antenna 20 so as to widen the transmission area of the loop antenna 20 in a direction substantially perpendicular to the central axis of the loop antenna 20.

  In the present embodiment, a steel plate (for example, a floor) as a body constituting member constituting the vehicle body is used as the magnetic member 30, and the loop antenna 20 is provided on the inner surface (one surface 31) of the body steel plate (magnetic member 30). Has been placed.

  Next, the effect of the antenna device 100 configured as described above will be described with reference to FIGS. 3A and 3B are schematic cross-sectional views showing a distribution of magnetic lines of magnetic field generated from the loop antenna 20. FIG. 3A shows this embodiment (in the case where the magnetic member 30 is provided), and FIG. The case where there is no member 30 is shown. 3A and 3B, arrows are attached to both ends of the lines of magnetic force in consideration of switching of magnetic poles due to a high-frequency current flowing through the loop antenna 20.

  In the antenna device 100 shown in the present embodiment, the central axis of the loop antenna 20 (loop portion) is substantially perpendicular to the one surface 31 of the magnetic member 30, and the magnetic member 30 is disposed in the vicinity of the loop antenna 20. ing. Therefore, when a high frequency current is passed through the loop antenna 20 at the time of transmission, the magnetic force lines 40 of the magnetic field generated from the loop antenna 20 are magnetic members having a smaller magnetic resistance than the external atmosphere (air), as shown in FIG. 30 will pass through. Here, the magnetic member 30 is sufficiently larger than the loop antenna 20, and the magnetic circuit is not limited by the size of the magnetic member 30. Therefore, the magnetic field lines 40 reach far away from the loop antenna 20 as compared with the configuration in which the magnetic member 30 shown in FIG. It becomes.

  As described above, according to the antenna device 100 according to the present embodiment, the magnetic field generation range in the direction substantially perpendicular to the central axis of the loop antenna 20 is wider than the configuration in which the magnetic member 30 is not disposed. In other words, in the direction substantially perpendicular to the central axis of the loop antenna 20, the interval between the magnetic force lines 40 is widened (the magnetic flux density is low). That is, the antenna device has a wide directivity in a direction substantially perpendicular to the central axis of the loop antenna 20 (wide transmission area).

  Particularly in this embodiment, the body steel plate of the vehicle is used as the magnetic member 30. Therefore, since the magnetic member 30 has a sufficient size with respect to the loop antenna 20, the directivity in a direction substantially perpendicular to the central axis of the loop antenna 20 can be widened. In addition, since a separate magnetic member is unnecessary, the number of components of the vehicle-mounted antenna device 100 can be reduced.

  Moreover, in this embodiment, the loop antenna 20 is wound around the core 10, and the magnetic force line 40 passes through the core 10 whose magnetic resistance is smaller than that of the external atmosphere (air). Further, the core 10 is magnetically coupled to the magnetic member 30, and the magnetic resistance between the core 10 and the magnetic member 30 is reduced. Therefore, since the magnetic force lines 40 reach farther from the loop antenna 20, the directivity in the direction substantially perpendicular to the central axis of the loop antenna 20 can be made wider.

  In the present embodiment, the loop antenna 20 is wound a plurality of times along a direction substantially perpendicular to the one surface 31 of the magnetic member 30 (Z-axis direction shown in FIG. 1). Therefore, compared to the configuration in which the loop antenna 20 is wound in a plane parallel to the one surface 31 of the magnetic member 30, the height of the magnetic member 30 relative to the one surface 31 is substantially perpendicular to the central axis of the loop antenna 20. Directional directivity can be widened.

  In the present embodiment, the central axis of the loop antenna 20 (loop part) is substantially perpendicular to the one surface 31 of the magnetic member 30. Therefore, although the central axis of the loop antenna 20 (loop part) has a component in the vertical direction (height direction) with respect to the one surface 31 of the magnetic member 30, it is not substantially perpendicular to the one surface 31 of the magnetic member 30 ( Compared to the case of being inclined with respect to one surface 31 of the magnetic member 30), the directivity balance is improved in a direction substantially perpendicular to the central axis of the loop antenna 20 (in other words, the XY plane shown in FIG. 1). Can be taken.

  In the present embodiment, a magnetic member 30 that is sufficiently larger than the loop antenna 20 is disposed in the vicinity of the loop antenna 20. Therefore, the magnetic field generated from the loop antenna 20 does not appear on the opposite side of the loop antenna 20 (the back side of the one surface 31 of the magnetic member 30) through the magnetic member 30. Therefore, even if a metal member is disposed on the back side of the one surface 31 of the magnetic member 30, the magnetic member 30 can reduce the influence of the metal member.

  In addition, this inventor examined the relationship between the relative magnetic permeability of the magnetic member 30 and magnetic field intensity (electric field strength conversion value) by simulation. The results are shown in FIGS. 4 (a) to (c) and FIGS. 5 (a) to (c). FIG. 4 is a diagram showing the relationship between the relative magnetic permeability of the magnetic member and the magnetic field strength (electric field strength converted value), where (a) is the relative magnetic permeability 1, (b) is the relative magnetic permeability 5, and (c) is the magnetic permeability. The case of relative permeability 10 is shown. 5A shows the case where the relative permeability is 50, FIG. 5B shows the case where the relative permeability is 100, and FIG. 5C shows the case where the relative permeability is 1000. 4A to 4C and FIGS. 5A to 5C, the center of the one surface 31 of the magnetic member 30 is set as the center coordinate, and the center of the one surface 31 of the magnetic member 30 (loop antenna). 20 shows the magnetic field strength on the Z-X plane (on one surface 31 of the magnetic member 30) passing through (the central axis of 20). Further, the loop antenna 20 is illustrated in a simplified manner.

  In this simulation, a 1000 mm square steel plate with a thickness of 3 mm was adopted as the magnetic member 30, and the center thereof was matched with the central axis of the loop antenna 20. In addition, a rectangular (rectangular) core having a cross section of 9 mm × 3.5 mm and a length of 20 mm is adopted as the core 10, and a wire diameter of 0.5 mm, 10.2 mm × 4. A rectangular loop antenna having a length of 7 mm and a length of 15 mm was employed. The analysis was performed by the finite element method with the core 10 being ferrite, the element of the loop antenna 20 being copper, the operating frequency being 134 kHz, and the antenna current being 11A.

  As a result, as shown in FIGS. 4A to 4C, when the relative permeability was 1, 5, and 10, almost no change in the magnetic field strength was confirmed. On the other hand, as shown in FIGS. 5A to 5C, when the relative permeability is 50, 100, 1000, the larger the relative permeability, the more in the X-axis direction (substantially the center axis of the loop antenna 20). The magnetic field strength is strong at the same position in the vertical direction), and the interval between the same magnetic field strengths (for example, the interval between 130 and 140) is wide. This suggests that the magnetic field lines 40 reach far from the loop antenna 20.

  From the above, when the magnetic member 30 is formed using a material having a relative permeability larger than 10 with respect to the operating frequency, the loop antenna is formed as compared with the case where the magnetic member 30 is formed using a material having a relative permeability of 10 or less. It was revealed that the directivity in the direction substantially perpendicular to the central axis can be effectively widened. Further, more preferably, when the magnetic member 30 is formed using a material having a relative permeability of 50 or more, it is clear that the directivity in a direction substantially perpendicular to the central axis of the loop antenna can be more effectively widened. became.

(Second Embodiment)
Next, a second embodiment of the present invention will be described based on FIG. FIG. 6 is a schematic cross-sectional view illustrating a schematic configuration of the antenna device according to the second embodiment.

  Since the antenna device according to the second embodiment is often in common with that according to the first embodiment, a detailed description of the common parts will be omitted below, and different parts will be described mainly. In addition, the same code | symbol shall be provided to the element same as the element shown in 1st Embodiment.

  In the first embodiment, an example in which the antenna device 100 includes the core 10 separately from the magnetic member 30 and the loop antenna 20 is configured by winding an element around the core 10. On the other hand, in this embodiment, as shown in FIG. 6, the antenna device 100 does not have the core 10, the convex portion 32 is formed on the one surface 31 of the magnetic member 30, and the element is formed on the convex portion 32. The loop antenna 20 is configured by being wound. That is, the core 10 is replaced with the convex portion 32. About another point, it is the same as the structure shown in 1st Embodiment.

  Thus, according to the antenna device 100 according to the present embodiment, the convex portion 32 exhibits the same function as the core 10 shown in the first embodiment. Further, the convex portion 32 is configured as a part of the magnetic member 30, and there is no magnetic resistance between the convex portion 32 and the magnetic member 30. Therefore, the directivity in the direction substantially perpendicular to the central axis of the loop antenna can be made equal to or wider than that of the antenna device 100 shown in the first embodiment. Moreover, since the core 10 as a separate member is not necessary, the configuration of the antenna device 100 can be simplified.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the present embodiment, an example is shown in which an element is wound around the core 10 or the convex portion 32 to constitute the loop antenna 20, and the loop antenna 20 is in a predetermined positional relationship with respect to the magnetic member 30. However, a configuration without the core 10 or the convex portion 32 may be adopted. The loop antenna 20 may be fixed to the magnetic member 30 with a holder made of a nonmagnetic material, or the loop antenna 20 may be directly formed on the one surface 31 of the magnetic member 30.

  In the present embodiment, an example in which the loop antenna 20 is wound a plurality of times along a direction substantially perpendicular to the one surface 31 of the magnetic member 30 is shown. However, the loop antenna 20 may be configured to be wound a plurality of times in a plane parallel to the one surface 31 of the magnetic member 30.

  In the present embodiment, an example in which the central axis of the loop antenna 20 (loop portion) is substantially perpendicular to the one surface 31 of the magnetic member 30 is shown. However, any configuration may be employed as long as the central axis of the loop antenna 20 has a component in the direction perpendicular to the one surface 31 of the magnetic member 30 (height direction). For example, although the central axis of the loop antenna 20 has a component in the vertical direction (height direction) with respect to the one surface 31 of the magnetic member 30, it is not substantially perpendicular to the one surface 31 of the magnetic member 30 (one surface of the magnetic member 30). It is good also as a structure (it is diagonal with respect to 31).

  In the present embodiment, an example in which the core 10 is magnetically coupled to the magnetic member 30 has been shown. However, a configuration in which both are not magnetically coupled may be used. In this case, since the magnetic resistance between the core 10 and the magnetic member 30 is increased, the directivity is narrower than that in the configuration in which the magnetic coupling is performed.

  In this embodiment, the body steel plate is used as the magnetic member 30, and the antenna device 100 is shown as an example applied as a transmitter in a smart key system of a vehicle. However, the antenna device 100 can also be applied as a receiver. In this case, the antenna device 100 having a wide reception area in a direction substantially perpendicular to the central axis of the loop antenna 20 can be obtained. Further, the magnetic member 30 is not limited to the body steel plate, and the application range of the antenna device 100 is not limited to the smart key system.

It is typical sectional drawing which shows schematic structure of the antenna device which concerns on 1st Embodiment. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of the antenna device according to the first embodiment. FIG. 2 is a plan view of FIG. 1 viewed from the loop antenna arrangement side. It is typical sectional drawing which shows magnetic field line distribution of the magnetic field produced from the loop antenna, (a) shows this embodiment, (b) has shown the case where there is no magnetic member as a comparative example. It is a figure which shows the relationship between the relative magnetic permeability of a magnetic member, and magnetic field intensity (electric field strength conversion value), (a) is the relative magnetic permeability 1, (b) is the relative magnetic permeability 5, (c) is the relative magnetic permeability 10 Shows the case. It is a figure which shows the relationship between the relative magnetic permeability of a magnetic member, and magnetic field intensity (electric field strength conversion value), (a) is relative magnetic permeability 50, (b) is relative magnetic permeability 100, (c) is relative magnetic permeability 1000. Shows the case. It is typical sectional drawing which shows schematic structure of the antenna device which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Core 20 ... Loop antenna 30 ... Magnetic member 31 ... One side 32 ... Convex part 40 ... Magnetic field line 100 ... Antenna apparatus

Claims (8)

A loop antenna in which the element is wound with at least one or more turns;
A magnetic member disposed in the vicinity of the loop antenna,
The loop antenna is all disposed on one surface of the magnetic member,
The magnetic member generates a magnetic field generated from the loop antenna with respect to the loop antenna so that a generation range of the magnetic member is wider than a state in which the magnetic member is not disposed in a direction substantially perpendicular to the central axis of the loop antenna. An antenna device characterized by being provided large.   The antenna device according to claim 1, wherein the magnetic member is a body constituting member that constitutes a vehicle body.   The antenna device according to claim 1, wherein the loop antenna is wound around a surface of the magnetic member in a plurality of height directions.   The antenna apparatus according to any one of claims 1 to 3, wherein a central axis of winding of the loop antenna is substantially perpendicular to one surface of the magnetic member. It has a columnar core made of magnetic material,
The antenna device according to claim 1, wherein the loop antenna is wound around the core.   The antenna device according to claim 5, wherein the core is magnetically coupled to the magnetic member. A convex portion is formed on one surface of the magnetic member,
The antenna device according to claim 1, wherein the loop antenna is wound around the convex portion.   The antenna device according to claim 1, wherein the magnetic member is formed using a material having a relative permeability higher than 10 with respect to a use frequency.

Images