JP4062288B2 - Chip coil for antenna and chip coil antenna - Google Patents

Description

  The present invention relates to an antenna chip coil and a chip coil type antenna, and more particularly to an antenna chip coil and a chip coil type antenna that are incorporated in a reader / writer for a non-contact IC card.

  2. Description of the Related Art Conventionally, an IC card reader / writer that performs non-contact communication using magnetic field coupling is known. The IC card reader / writer incorporates, for example, a coil-type transmitting / receiving antenna described in Patent Document 1. As shown in FIG. 19, the coil-type transmitting / receiving antenna includes an antenna coil 105 and a circuit board 130 on which the antenna coil 105 is mounted.

  The antenna coil 105 includes a magnetic core 110 and a winding 120. The magnetic core 110 has a flat plate shape, and an annular groove 111 is formed on the upper surface along the outer periphery. Therefore, a relatively rectangular parallelepiped shaft column 112 protrudes from the central portion of the magnetic core 110.

  The winding 120 is wound around the shaft column a plurality of times and is accommodated in the annular groove 111. Terminal portions 121 and 122 of the winding 120 are led out from the annular groove 111 and connected to a transmission / reception circuit (not shown).

  The antenna coil 105 is installed at a substantially central portion of the circuit board 130. Although not shown, a large-area ground pattern is formed on the lower surface of the circuit board 130.

By the way, in this kind of antenna coil, it is required to reduce the leakage magnetic flux and improve the antenna efficiency. However, in Patent Document 1, no particular countermeasure is taken for this point.
JP-A-8-279714

  SUMMARY OF THE INVENTION An object of the present invention is to provide an antenna chip coil that can reduce the leakage of magnetic flux as much as possible and improve antenna efficiency, and a chip coil antenna using the antenna coil.

In order to achieve the above object, an antenna chip coil according to the present invention comprises:
(A) An antenna chip coil comprising a magnetic core composed of a lower collar part and a trunk part provided perpendicular to the lower collar part, and a winding wound around the trunk part. ,
(B) the lower collar portion is made of an anisotropic magnetic body having an easy magnetization axis disposed in a direction parallel to the main surface of the lower collar portion;
It is characterized by.

  With the above configuration, a magnetic flux directed mainly upward (in the vertical direction) is generated from the open upper surface of the body portion of the magnetic core. Further, the directivity in the horizontal direction is also controlled by the shape of the lower collar part of the magnetic core. Since the lower collar portion of the magnetic core is made of an anisotropic magnetic material having an easy magnetization axis disposed in a direction parallel to the main surface of the lower collar portion, the lower core portion penetrates downward from the bottom surface of the lower collar portion. Leakage magnetic flux is reduced as compared with an isotropic magnetic material such as a Ni—Zn system, and the antenna efficiency is increased. As the anisotropic magnetic material, a hexagonal ferrite material can be suitably used.

  The chip coil antenna according to the present invention includes the antenna chip coil having the above-described characteristics and an electrode portion to which a terminal end of the winding is electrically connected. With the above configuration, a chip coil type antenna having an antenna chip coil with good antenna efficiency is obtained.

  Furthermore, the chip coil antenna according to the present invention has a plurality of antenna chip coils arranged close to each other, and each antenna chip coil is electrically connected so that the magnetic flux generated in each antenna chip coil has the same polarity. Connected. As a result, the magnetic flux generated by the current flowing through each of the antenna chip coils is canceled out between the adjacent antenna chip coils, and a magnetic flux distribution equivalent to one large coil is obtained. Therefore, the communication distance with the IC card can be increased.

  The antenna chip coil according to the present invention has excellent directivity of magnetic flux directed upward from the open upper surface of the body portion of the magnetic core, and less leakage magnetic flux penetrates downward from the bottom surface of the lower collar portion. Thus, the antenna efficiency can be improved, and even a small antenna chip coil can increase the communication distance with the IC card.

  Hereinafter, embodiments of a chip coil for an antenna and a chip coil antenna according to the present invention will be described with reference to the accompanying drawings.

[First embodiment, FIGS. 1 to 9]
FIG. 1 is an external perspective view of a chip coil antenna 1, and FIG. 2 is a vertical sectional view thereof. The chip coil antenna 1 includes a vertically wound chip coil 5. The chip coil 5 includes a magnetic core 51 composed of a lower collar part 51a and a body part 51b, a winding 52 wound around the body part 51b, and a nonmagnetic material 53 having a flat upper surface. .

  The body 51b of the magnetic core 51 has a bottom joined to the lower collar 51a and is provided perpendicular to the lower collar 51a. That is, the chip coil 5 is an open magnetic circuit type coil that opens the magnetic flux φ upward with the open upper surface 51ba of the body portion 51b as the upper side, and functions as an antenna coil.

  The winding 52 is generally a copper wire coated with an insulating film such as polyurethane. Both end portions 52a of the winding 52 are electrically connected to the electrode 6 formed from the bottom surface to the side surface of the lower collar portion 51a by a method such as thermocompression bonding.

  Further, a nonmagnetic material 53 is formed so as to cover the open upper surface 51ba of the body portion 51b and the upper surface of the winding 52. The reason why the upper surface of the non-magnetic material 53 is planar is that, as shown in FIG. 3, when the chip coil antenna 1 is mounted on the circuit board 16, the suction by the suction nozzle of the mounting machine can be reliably performed. At the same time, the winding 52 is prevented from being disturbed during suction by the suction nozzle. For example, the non-magnetic material 53 is formed by immersing the magnetic core 51 around which the winding 52 is wound in a resin bath from the open upper surface 51ba side of the body 51b to the upper part of the winding 52 and the upper part of the body 51b. After the resin is applied, it is formed by lifting the resin from the resin bath and curing the resin with light or heat. At this time, the resin bath may be immersed so that the resin is also formed on the outer peripheral surface of the winding 52. Moreover, the nonmagnetic material 53 may be formed by sticking a plate-shaped member.

  For example, as shown in FIG. 4, the circuit board 16 on which the chip coil antenna 1 is mounted is incorporated in a reader / writer 31 for a non-contact IC card. Although not shown, in addition to the chip coil antenna 1, a transmission / reception circuit and the like are provided on the upper surface of the circuit board 16. A large-area ground electrode is provided on the lower surface of the circuit board 16.

  The circuit board 16 is attached to the inner bottom of the insulating case 35. FIG. 5 is an electric circuit block diagram of the IC card reader / writer 31 thus obtained.

  The chip coil antenna 1 having the above configuration is excellent in the directivity of the magnetic flux φ directed mainly upward (in the vertical direction) from the open upper surface of the body 51b of the magnetic core 51. The communication distance with the IC card 20 can be increased. On the other hand, the magnetic flux φ from the bottom of the body 51b mainly passes through the lower flange 51a and escapes to the side surface of the lower flange. Therefore, the chip coil antenna 1 has a structure in which the generated magnetic flux φ hardly generates an eddy current in the large-area ground electrode provided on the lower surface of the circuit board 16.

  Here, in order to further strengthen the directivity of the magnetic flux φ directed upward from the open upper surface 51ba of the body 51b of the magnetic core 51, as shown in FIG. It may be higher than the height H1 of the body portion 51b. At this time, a step is formed between the open upper surface 51ba of the trunk portion 51b and the upper surface of the winding 52, but the flatness of the upper surface of the nonmagnetic material 53 is increased by increasing the thickness of the nonmagnetic material 53 of the open upper surface 51ba. Is secured.

  7 to 9 are magnetic flux density distribution diagrams when the height H2 of the winding 52 is gradually increased. A curve indicated by a symbol A in the figure indicates a magnetic flux density distribution at a position of 6.5 mm upward from the surface of the circuit board 16. Similarly, symbols B, C, D, and E indicate magnetic flux density distributions at positions of 7.5 mm, 8.5 mm, 9.5 mm, and 10.5 mm upward from the surface of the circuit board 16, respectively.

  At this time, all the inductances of the chip coil 5 were 0.944 μH, the relative permeability of the magnetic core 51 was 1600, and a current of 1.0 A was passed through the winding 52. Further, when the height H2 of the winding 52 is 5.5 mm, the number of turns of the winding 52 is 10 turns, and when the height H2 is 6.0 mm, the number of turns of the winding 52 ′ is 10.9 turns. When the height H2 is 6.5 mm, the number of turns of the winding 52 ″ is 11.8 turns.

  In order to increase the radiation efficiency (antenna efficiency) of the magnetic flux φ without degrading the directivity of the magnetic flux φ, the lower collar portion 51a and the trunk portion 51b of the magnetic core 51 are made of different materials. The imaginary part of the complex relative permeability of the material constituting the lower collar part 51a is lower than the imaginary part of the complex relative permeability of the material constituting the body part 51b in the operating frequency band of the chip coil antenna 1. Set to. That is, a low-loss material is used for the lower collar portion 51a that does not directly relate to the upward directivity of the magnetic flux φ. For example, when used in an IC card reader / writer, in the 13.56 MHz band, the imaginary part of the complex relative permeability of the material constituting the lower collar part 51a is the complex relative permeability of the material constituting the body part 51b. The material may be selected so as to be lower than the imaginary part.

  Furthermore, as a method for increasing the antenna efficiency, an anisotropic magnetic body (in which an easy axis of magnetization is disposed in a direction parallel to the main surface 51a ′ of the lower core portion 51a of the lower core portion 51a of the magnetic body core 51). For example, there is a method of manufacturing with a hexagonal ferrite material. Since the hexagonal ferrite material exhibits magnetic anisotropy, the leakage magnetic flux penetrating downward from the bottom surface of the lower collar portion 51a by arranging the easy magnetization axis in a direction parallel to the main surface of the lower collar portion 51a. Is less than isotropic magnetic materials such as Ni-Zn. Accordingly, the leakage magnetic flux does not easily reach the large-area ground electrode provided on the lower surface of the circuit board 16, and the eddy current loss at the ground electrode is reduced. As a result, the radiation efficiency of the magnetic flux φ does not deteriorate, and the communication distance with the IC card 20 can be increased.

  Table 1 below shows experimental conditions of an example of the present invention in which the lower collar portion 51a is made of a hexagonal ferrite material in which an easy magnetization axis is arranged in a direction parallel to the main surface 51a ′. In addition, experimental conditions for the conventional example are also shown.

  FIG. 10 schematically shows the distribution of magnetic field lines in the present invention example in (A) and in the conventional example in (B). As apparent from FIGS. 10A and 10B, the magnetic field lines shown in FIG. 10A, which is an example of the present invention, are slightly more in the A portion than the magnetic field lines shown in FIG. 10B, which is a conventional example. Ascending upward (Z-axis direction), it can be seen that the leakage magnetic flux from the bottom surface of the lower flange 51a to the lower side is reduced. According to the experimental results, the Q value of the conventional example was 548, whereas the Q value of the example of the present invention was 654, which was about 1.2 times that of the conventional example. However, the Q value here is a numerical value that does not consider the loss of the winding 52 itself.

[Second and third embodiments, FIGS. 11 and 12]
A chip coil antenna 1A shown in FIG. 11 includes a magnetic core 51 having a disk-shaped lower collar 51a. A chip coil antenna 1B shown in FIG. 12 includes a magnetic core 51 having a prismatic body 51b. In these chip coils 5, no electrode is formed on the lower flange portion 51 a, and the end portion 52 a of the winding 52 is led out to the outside and soldered to the electrode provided on the circuit board.

[Fourth embodiment, FIG. 13]
In the chip coil antenna 1 </ b> C shown in FIG. 13, a nonmagnetic case 61 covers the open upper surface of the body 51 b of the magnetic core 51 and the upper surface of the winding 52. The upper surface of the nonmagnetic case 61 is flat.

[Fifth Embodiment, FIGS. 14 and 15]
In the chip coil antenna 1D shown in FIG. 14, in the body 51b of the magnetic core 51, the area of the open upper surface 51ba is smaller than the area of the bottom surface joined to the lower collar 51a. A taper is provided on the outer peripheral surface 51bb. Thereby, the directivity of the magnetic flux φ directed upward from the open upper surface 51ba of the body 51b of the magnetic core 51 can be further increased.

  FIG. 15 shows the magnetic flux density distribution of the chip coil antenna 1D. At this time, the inductance of the chip coil 5 was 0.944 μH, the relative permeability of the magnetic core 51 was 1600, and a current of 1.0 A was passed through the winding 52. The winding 52 was wound 12.1 turns. FIG. 6 shows the detailed dimensions of the chip coil 5. The dashed-dotted line of FIG. 6 displays the taper-shaped outer peripheral surface 51bb.

[Sixth embodiment, FIGS. 16 and 17]
As shown in FIG. 16, the chip coil antenna 80 has a plurality of (four) chip coils 5 provided on the circuit board 16 in an axially symmetrical manner. Each chip coil 5 may be electrically connected in series or in parallel, but the magnetic flux generated by each chip coil 5 has the same polarity.

  As a result, the magnetic flux generated by the current flowing in each of the chip coils 5 is canceled by the portion between the adjacent chip coils 5, and a magnetic flux distribution equivalent to one large coil is obtained equivalently. Therefore, the communication distance with the IC card 20 can be increased. Furthermore, at this time, as shown in FIG. 17, if the chip coil 5 is once attached to the magnetic substrate 85 and then attached to the circuit board 16 and wired, the magnetic flux can be more reliably offset, so that a more remarkable effect can be obtained. It is done. As a result, the communication distance between the chip coil antenna 80 and the IC card 20 can be increased.

[Other embodiments]
The antenna chip coil and the chip coil antenna according to the present invention are not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof. For example, an annealed copper wire coated with polyurethane or the like is generally used for the winding 52, but a sheet-like flat plate winding 52 as shown in FIG. The structure which fits in the trunk | drum 51b may be sufficient.

1 is a perspective view showing a first embodiment of a chip coil antenna according to the present invention. FIG. 2 is a vertical sectional view of the chip coil antenna shown in FIG. 1. The perspective view which shows the state which mounted the chip coil type | mold antenna shown in FIG. 1 on the circuit board. FIG. 2 is a schematic configuration diagram of an IC card reader / writer incorporating the chip coil antenna shown in FIG. 1. FIG. 5 is an electric circuit block diagram of the IC card reader / writer shown in FIG. 4. FIG. 2 is a partially enlarged cross-sectional view showing the relationship between the height of a magnetic core of the chip coil antenna shown in FIG. 1 and the height of a winding. The graph which shows magnetic flux density distribution. The graph which shows magnetic flux density distribution. The graph which shows magnetic flux density distribution. Explanatory drawing which shows the distribution state of a magnetic force line typically. The perspective view which shows 2nd Example of the chip coil type | mold antenna which concerns on this invention. The perspective view which shows 3rd Example of the chip coil type antenna which concerns on this invention. Sectional drawing which shows 4th Example of the chip coil type | mold antenna which concerns on this invention. Sectional drawing which shows 5th Example of the chip coil type | mold antenna which concerns on this invention. The graph which shows magnetic flux density distribution. The perspective view which shows 6th Example of the chip coil type antenna which concerns on this invention. The perspective view which shows another Example. The perspective view which shows the modification of the chip coil type | mold antenna shown in FIG. The perspective view which shows the conventional coil type | mold antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A, 1B, 1C, 1D, 80 ... Chip coil type antenna 5 ... Chip coil 6 ... Electrode 51 ... Magnetic body core 51a ... Lower collar part 51a '... Main surface 51b ... Trunk part 52, 52', 52 '' ... Winding

Claims (4)

A chip coil for an antenna comprising a magnetic core composed of a lower collar part and a trunk part provided perpendicular to the lower collar part, and a winding wound around the trunk part,
The lower collar portion is made of an anisotropic magnetic body having an easy magnetization axis disposed in a direction parallel to the main surface of the lower collar portion;
A chip coil for an antenna.   The antenna chip coil according to claim 1, wherein the anisotropic magnetic body is a hexagonal ferrite material.   A chip coil antenna comprising: the antenna chip coil according to claim 1; and an electrode portion to which a terminal portion of the winding is electrically connected.   The plurality of antenna chip coils are arranged close to each other, and the antenna chip coils are electrically connected so that magnetic fluxes generated by the antenna chip coils have the same polarity. 4. The chip coil antenna according to 3.

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