Patent Application
20150380823
The present invention relates to an antenna device for use in, e.g., RFID (radio frequency identification) systems, which communicate with external devices using electromagnetic signals, and a mobile terminal including the same.
Japanese Patent No. 3975918 (Patent Literature 1) discloses an antenna device included in a mobile electronic apparatus for use in RFID systems. The antenna device of Patent Literature 1 includes an asymmetrical coil where two positions are opposed to each other with the center of a coil winding area therebetween and the winding pitch varies between the two positions. On a side having a larger winding pitch, a magnetic body is disposed on the back of a main surface opposed to an IC card; on a side having a smaller winding pitch, a magnetic body is disposed on the main surface opposed to the IC card.
The present disclosure provides an antenna device that can reduce degradation of communication performance depending on the angle which the antenna device forms with the reading surface of a reader/writer, and a mobile terminal including the same.
In one aspect, an antenna device includes an antenna coil and a flat conductor adjacent to the antenna coil. The antenna coil includes a plate-shaped magnetic core having first and second main surfaces and a coil conductor wound around the magnetic core. The antenna coil is configured such that when a communication partner is positioned near the antenna device, the antenna coil is closer than the flat conductor to an antenna of the communications partner. First and second conductor portions of the coil conductor are provided in positions that do not overlap each other in a perspective plan view of the magnetic core. The first conductor portion is adjacent to the first main surface of the magnetic core, and the second conductor portion is adjacent to the second main surface thereof. The first main surface of the magnetic core faces a surface of the flat conductor. The antenna coil is provided in a position which does not overlap the flat conductor or a position which overlaps the flat conductor in a plan view of the flat conductor and the antenna coil.
In a more specific embodiment, the flat conductor may be a ground electrode formed within a circuit substrate. The antenna coil may be disposed on a ground electrode non-formation area of the circuit substrate, the ground electrode non-formation area being an area where the ground electrode is not formed.
In another more specific embodiment, the magnetic core may be a sheet-shaped mixture of a magnetic powder and a resin material or a plurality of sintered magnetic pieces.
In yet another more specific embodiment, the magnetic core is formed so that one end portion thereof is larger than the other portions thereof.
In another aspect of the disclosure, a mobile terminal includes a case and any one of the above-mentioned antenna devices contained in the case.
The inventors realized that when an electronic apparatus including the antenna device described in Patent Literature 1 is held over a reader/writer, communication may be impossible depending on the angle which the antenna device of the electronic apparatus forms with the antenna device of the reader/writer. That is, when the mobile terminal communicates with an IC card in parallel therewith, no significant problem occurs; when the mobile terminal communicates with a fixed reader/writer or the like, the position (angle) of the mobile terminal relative to the reader/writer varies, disadvantageously degrading communication performance.
A first main surface of a magnetic core 1 closely faces a flat conductor 2. A first conductor portion 11 of a coil conductor is adjacent to the first main surface of the magnetic core 1. A second conductor portion 12 thereof is adjacent to a second main surface of the magnetic core 1. An antenna coil composed of the magnetic core 1 and the coil conductor is disposed adjacent to an end portion of the flat conductor 2, forming an antenna device.
As shown in
However, as angles are made from that state, as shown in
A magnetic core 1 can be a rectangular plate-shaped ferrite core. As shown in
The coil conductor CW includes a first conductor portion 11 adjacent to a first main surface MS1 of the magnetic core 1 and a second conductor portion 12 adjacent to a second main surface MS2 thereof. The magnetic core 1 and the coil conductor CW form the antenna coil 21.
The circuit substrate 20 includes a ground electrode formation area GA and a ground electrode non-formation area NGA. A ground electrode within the ground electrode formation area GA is a flat conductor according to the present disclosure.
The antenna coil 21 is mounted on the ground electrode non-formation area NGA of the circuit substrate 20 with the first main surface MS1 of the magnetic core 1 facing the circuit substrate 20. Accordingly, the first main surface MS1 of the magnetic core 1 faces a surface of the ground electrode non-formation area NGA (an extension of a surface of the ground electrode formation area GA). The antenna coil 21 is disposed outside an end portion of the ground electrode formation area GA in a plan view of the antenna coil 21 and the ground electrode formation area GA.
The first and second conductor portions 11 and 12 of the coil conductor are disposed so that the conductor portions do not overlap each other in a plan view of the magnetic core 1 (in a view from the direction of a normal to the first main surface MS1 or second main surface MS2 of the magnetic core 1).
In the state shown in
Both end portions of the coil conductor CW of the antenna coil 21 are connected to predetermined terminal electrodes on the circuit substrate 20. The illustration of this connection structure is no shown.
When θ=0, the magnetic flux from the reader/writer passes through the central portion of the coil conductor CW formation area in a direction approximately perpendicular to the magnetic core 1.
When θ=45°, the magnetic flux from the reader/writer passes through the central portion of the coil conductor CW formation area in a direction of approximately 45° with respect to the magnetic core 1. Here, a magnetic flux passing through the coil conductor CW in an opposite direction as shown in
When θ=90°, the magnetic flux from the reader/writer passes through the coil conductor CW formation area in the surface direction of the magnetic core 1. Here again, the direction of the magnetic flux passing through the coil conductor CW is the same.
Accordingly, the magnetic fluxes passing through the magnetic core in both directions do not cancel out each other, regardless of the value of the angle θ, at which the mobile terminal 201 is held over the antenna device 30 of the reader/writer.
The difference between the antenna coil 22 and the antenna coil 21 shown in
Use of the magnetic core 1 having such a shape can provide improvements in communication performance, such as strengthening of the magnetic flux passing through the magnetic core 1, strengthening of magnetic coupling with the antenna of a communication partner, and increasing of the maximum communication-capable distance. While, in
While, in the antenna coil 22 shown in
The magnetic core 1 shown in
While, in
In such a configuration again, when the mobile terminal is held over the antenna device of the reader/writer as shown in
While
The antenna device 105 includes an antenna coil 21 and a rectangular plate-shaped circuit substrate 20 having the antenna coil 21 mounted thereon. A ground electrode formation area GA is disposed so that it surrounds the antenna coil 21. The other elements are the same as those shown in the first exemplary embodiment.
In such a configuration again, when the mobile terminal is held over the antenna device of the reader/writer as shown in
The circuit substrate 20 includes a ground electrode formation area GA and a ground electrode non-formation area NGA. In this example, a ground electrode is formed in an inner layer of the circuit substrate 20. The area where this ground electrode is formed is the ground electrode formation area GA. The antenna coil 21 is mounted in a position which overlaps both the ground electrode formation area GA and the ground electrode non-formation area NGA of the circuit substrate 20, with a first main surface MS1 of the magnetic core 1 facing the circuit substrate 20. The configuration of the antenna coil 21 is the same as that shown in the first embodiment.
When an angle θ, at which a mobile terminal whose case contains the antenna device 106 is held over an antenna device 30 of a reader/writer, is approximately 45°, a magnetic flux φs passes through the antenna device 106 as shown by broken-line arrows in
As shown in this example, the antenna coil may overlap the ground electrode formation area GA in a plan view. In such a configuration again, when the mobile terminal is held over the antenna device of the reader/writer, magnetic fluxes passing through the magnetic core 1 in both directions do not easily cancel out each other.
However, when the angle θ signal, at which the mobile terminal is held over the antenna device of the reader/writer, is 0°, the ground electrode formation area GA blocks the passage of the magnetic fluxes. For this reason, the communication distance is not increased so much. When the angle θ is 45°, the magnetic flux φc and φs pass through the ground electrode formation area GA. When the angle θ is 90°, the magnetic flux passes it through as shown in
While the ground electrode within the substrate has been shown as an example of the flat conductor in the above-mentioned embodiments, an antenna device can be formed using, for example, as the flat conductor, a shield plate disposed on the back of the liquid crystal panel, a conductive film or conductive foil formed on the inner surface of the case, or the battery pack. Further, the flat conductor is not limited to a rectangular conductor and can have various flat shapes. Further, the flat conductor can be composed of multiple layers rather than a single layer. Further, since the flat conductor is only required to be flat in its main portion, any other portion can include a bend.
In embodiments according to the present disclosure, when an angle the antenna device forms with the antenna of the reader/writer is in the range of 0° to 90°, the magnetic fluxes interlinked with the coil conductor in opposite directions do not equal each other. Thus, communications can be performed stably in the range of 0° to 90° or more or in a wider range.
Further, an antenna device can be easily formed by mounting the antenna coil on the ground electrode non-formation area of the circuit substrate.
Further, if the magnetic core is formed using sintered magnetic pieces, flexibility can be provided to the entire antenna coil. Thus, the magnetic core can be built in the case of a built-in destination electronic apparatus, such as a mobile terminal, with a high degree of freedom.
While exemplary embodiments have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-221626 | Sep 2009 | JP | national |
The present application is a continuation of International Application No. PCT/JP2010/063746 filed Aug. 13, 2010, which claims priority to Japanese Patent Application No. 2009-221626 filed Sep. 25, 2009, the entire contents of each of these applications being incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13339998 | Dec 2011 | US |
| Child | 14849298 | US | |
| Parent | PCT/JP2010/063746 | Aug 2010 | US |
| Child | 13339998 | US |
