JP2007006123A - Mobile device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile device provided with a data communication function, which is capable of obtaining a required sensitivity even with a small-sized magnetic antenna coil. <P>SOLUTION: A reception sensitivity is improved by utilizing an influence of a magnetic field 3 having an opposite polarity caused by an eddy current which is generated in a metallic component constituting a part of the mobile device having a RFID tag mounted thereon when performing RFID communication, and a magnetic antenna coil 27 is disposed in the vicinity of a metallic plate 30 constituting a part of the mobile device having the RFID tag mounted thereon, in an extension direction of a metallic plate surface 30a thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a portable device having a data communication function using electromagnetic induction or electromagnetic coupling, and particularly relates to the arrangement of a magnetic antenna coil for improving transmission / reception sensitivity.

An RFID tag (Radio Frequency Identification TAG) has been conventionally used as an electromagnetic induction type or electromagnetic coupling type near field data communication technology. The configuration of the RFID communication is shown in FIG. RFID communication is composed of a read ride terminal (hereinafter referred to as an R / W terminal) 60 for reading / writing information in a tag and a tag 61.
The R / W transceiver circuit 62 supplies, for example, a 13.56 MHz transmission signal to the R / W antenna 63. Since an alternating current of 13.56 MHz flows through the R / W antenna 63, a magnetic flux proportional to the alternating current is generated around the R / W antenna 63. This magnetic flux is, for example, amplitude modulated (ASK: Amplitude Shift Keying) based on data transmitted to and received from the tag 61.

On the tag 61 side, electric power is generated by a mutual induction action in a resonance circuit 67 including capacitors 66 connected to both ends of the T antenna 65 on the tag 61 side that is linked to the magnetic flux 64. This power is stabilized by the power supply circuit 68 and activates the IC chip 72 including the T transmission / reception circuit 69, the CPU 70, and the memory 71.
The activated IC chip 72 demodulates the data contained in the flux linkage 64 by the T transmission / reception circuit 69, and the CPU 70 rewrites the data in the memory 72 based on the demodulated data. It operates so that it may transmit to R / W terminal 60 via.

Since the memory 71 is composed of a ROM or an EEPROM (Electrically Erasable Programmable Read Only Memory) that can be electrically written and erased, data is retained even if the IC chip is not activated during non-communication. Some products have a power supply on the RFID tag side, but those composed of no power supply as described above are the mainstream.
RFID tags with such features of no power supply and small size are widely used for inventory management and IC cards that record personal information. Also, for example, mobile phones and portable audio devices themselves An RFID tag may be mounted on a device having a power supply or display function as an additional function for a purpose other than the function originally possessed by the device.

The T antenna 65 of the RFID tag 61 is roughly divided into two types. One is a disk-shaped antenna using a circular air-core coil, and the other is a rod-shaped antenna in which an insulation-coated copper wire such as an enameled wire is wound around a rod-shaped ferrite core.
When an RFID tag is mounted on a portable device as an additional function, a rod-shaped antenna is often used because it is not particularly desirable to increase the size of the portable device.
JP 2002-157568 A (paragraph 0008)

When the interlinkage magnetic flux for communication intersects with a conductive member such as iron, aluminum, or copper, an eddy current is generated in the conductive member, and a magnetic flux in a direction that cancels the interlinkage magnetic flux is generated by the eddy current. In order to avoid the influence of the magnetic flux due to the eddy current, conventionally, the rod-shaped antenna is generally disposed away from the metal member in the portable device.
For the purpose of not affecting the mobile device side where the RFID tag is mounted as an additional function, there is a problem that even if a small rod-shaped antenna is adopted, the mobile device is enlarged by being disposed away from the metal member. .

Further, the communication distance of the RFID tag is in the range of several millimeters to several tens of millimeters. However, in order to obtain this communication sensitivity, there is a limit even if a magnetic material such as ferrite or permalloy having a high magnetic permeability is used. In order to obtain the required sensitivity, there was a problem that the cross-sectional area of the core was increased.
The present invention has been made in view of these points, and it is an object of the present invention to provide a portable device capable of obtaining necessary sensitivity even with a small magnetic antenna coil.

  The present invention reversely uses the influence of the eddy current magnetic field, and approaches the metal plate constituting a part of the portable device on which the RFID tag is mounted in the extending direction of the metal plate surface. And place the magnetic antenna coil.

  The density of the external magnetic flux intersecting with the magnetic antenna coil is improved by the metal plate constituting a part of the portable device close to the magnetic antenna coil according to the present invention. As a result, the sensitivity required for RFID communication is improved and the portable antenna can be made compact because the magnetic antenna coil is close to the metal plate.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
〔principle〕
The principle of the present invention will be described with reference to FIG. FIG. 1A shows a state in which the magnetic field lines 1 run in a uniform magnetic field. In this state, when the metal plate 2 is disposed so as to be orthogonal to the lines of magnetic force as shown in FIG. 1B, an eddy current flows on the surface of the metal plate 2 due to the interlinkage magnetic flux. Due to this eddy current, a magnetic field 3 having a reverse polarity is generated in a direction to block the magnetic field lines 1.

  The magnetic field lines 1 bypass the metal plate 2 in the vicinity of the plate end surface of the metal plate 2 due to the antipolar magnetic field 3. As a result, the magnetic flux density of the detouring portion 4 is increased. The magnetic antenna coil is disposed on the portion 4 having a high magnetic flux density, and the coil surface thereof is parallel to the metal plate 2. With this configuration, the sensitivity can be improved.

A first embodiment of the present invention based on the above principle is shown in FIG. The mobile device 20 is a foldable mobile phone composed of a lower case 21 and an upper case 22, and an LCD panel 23 is disposed on the upper case 22. A battery 25 is accommodated in the lower case 21 in which the operation switch 24 is disposed, and a substrate 26 on which various IC elements and electronic components are mounted is accommodated along with the battery 25. For example, a magnetic antenna coil 27 is disposed close to the battery 25 between the battery 25 and the substrate 26.
The positional relationship between the battery 25 and the magnetic antenna coil 27 is extracted and shown in FIG. In general, a lithium ion secondary battery having a width of 25 mm, a length of 35 mm, and a thickness of several millimeters is used for a mobile phone.

Assuming this, a metal plate 30 having a width of 25 mm, a length of 35 mm, and a thickness of 1 mm is prepared. A square with a side of a cross-section of 3 mm in the vicinity of the short side of the metal plate 30 and having a height of An experimental environment was prepared in which a magnetic antenna coil 27 in which an insulation-coated copper wire was wound around a 4 mm rod-shaped core was arranged. A magnetic field 31 is applied from an R / W terminal (not shown) from a direction orthogonal to the plate surface 30a of the metal plate 30, and the position of the magnetic antenna coil 27 is changed to allow the RFID reception distance (R / W terminal and tag and The distance was determined. The material of the metal plate 30 is iron.
In this way, the metal plate 30 and the magnetic antenna coil 27 are arranged, a magnetic field 31 is applied from a R / W terminal (not shown) from a direction orthogonal to the plate surface 30a of the metal plate 30, and the position of the magnetic antenna coil 27 is changed. An experiment was conducted to determine the distance at which RFID can be received (the distance between the R / W terminal and the tag).

The experimental results are shown in FIG. The horizontal axis is the distance between the magnetic antenna coil 27 and the metal plate 30, the distance d in the extending direction of the metal plate surface 30a is expressed in mm, and the vertical axis is the distance between the R / W terminal capable of receiving data and the tag. Is expressed in mm.
When the distance d is large, that is, when the magnetic antenna coil 27 is separated from the metal plate 30, the reception distance is short, and the closer the magnetic antenna coil 27 is to the metal plate 30, the longer the reception distance is.
When the number of turns t (hereinafter referred to as the number of turns) of the insulated copper wire is 11 turns, the distance d is 10 mm and the reception distance is about 14.3 mm, but the principle is explained in the range where the distance d is 5 mm or less. The effect of a region with a high magnetic flux density begins to appear, and the reception distance suddenly increases from a distance d of 2 mm. In particular, the reception distance becomes almost maximum in a range of a little less than 1 mm to 0 mm. When the reception distance when the distance d is about 10 mm and the reception distance when the distance d is 1 mm or less are compared, an improvement of about 150% can be seen.

The experiment was performed by changing the number of turns of the insulation-coated copper wire wound around the core from 10 turns (10 t) to 15 turns (15 t) as a parameter of the experiment shown in FIG. 4, but the reception distance increases as the number of turns increases. There was no such tendency. However, the reception distance of 12 turns (12 t) and 13 turns (13 t) is particularly large when the distance d is in the range of 0 to 1 mm.
Thus, in an experiment using a magnetic antenna coil using a relatively small core with a cross section of 3 mm square and a height of 4 mm, the effect of extending the reception distance by bringing the magnetic antenna coil closer to the metal plate was obtained. It was confirmed that

  This effect can be similarly confirmed on the end face in the longitudinal direction of the metal plate.

There are metal parts other than the battery in the portable device on which the RFID tag is mounted, and the same effect can be obtained between these metal parts. FIG. 4 shows an example of a metal part that constitutes a part of the portable device. FIG. 4 shows a schematic diagram of the modular structure of the portable device when the folding case structure as shown in FIG. 2 is not taken.
FIG. 4A is a cross-sectional view showing an example in which the magnetic antenna coil 27 is arranged in such a portable device. The LCD panel 50 is driven by an LCD driver substrate 51 disposed on the back surface thereof. On the LCD driver substrate 51, a drive signal for driving the display element (segment) and a drive signal for the common electrode (common) are wired, and interference due to the frequency signal of the drive signal becomes a problem in the design of portable devices. Often becomes.

  In order to prevent the interference, an electromagnetic shielding plate 53 may be provided between the wireless board (hereinafter referred to as RF board) 52 and the LCD driver board 51. This electromagnetic shielding plate 53 is also a metal plate, and the reception distance of RFID communication can be improved by arranging the magnetic antenna coil 27 at a position close to the electromagnetic shielding plate 53 as in the case of the battery described above. . The electromagnetic shielding plate 53 actually has a thickness of 1 mm or less, and when the magnetic antenna coil 27 having a height of about 4 mm is simply placed close to the electromagnetic shielding plate 53, the electromagnetic shielding plate 53 interferes with the LCD driver substrate 51 and is assembled. It will not be possible. Therefore, for example, the concave portion 54 is formed over a part of the LCD driver substrate 51 so that the magnetic antenna coil 27 does not interfere in the thickness direction.

Another example is shown in FIG. In a portable device with a display function, the connection between the LCD panel 50 and the LCD driver substrate 51 is omitted in FIG. 5, but there are cases where the connection is made with conductive rubber (zebra rubber). In this case, the LCD panel 50, the LCD driver board 51, and the main circuit board 55 are pressed by a metallic circuit pressing plate 56 having elasticity, thereby ensuring the conduction of the conductive rubber and the circuit block. Are designed to be integrated.
The circuit holding plate 56 is also a metal plate, and it is possible to improve the reception distance of RFID communication by arranging the magnetic antenna coil 27 at a position close to the circuit holding plate 56 as described above. .

It is a figure which shows the principle of this invention. It is a figure which shows 1st Example of this invention. It is a figure which shows an experimental environment. It is a figure which shows an experimental result. It is a figure which shows an example of the metal component which comprises a part of portable apparatus. It is a figure which shows the structure of RFID communication.

Claims (3)

In a portable device having a data communication function using an electromagnetic induction method or an electromagnetic coupling method, a part of which is made of a metal plate, and provided with a magnetic antenna coil for the data communication function,
The portable device, wherein the magnetic antenna coil is disposed close to an end of the metal plate in an extending direction of the metal plate surface. The mobile device according to claim 1,
The portable device, wherein the magnetic antenna coil is disposed within 5 mm in the extending direction of the metal plate surface from the end of the metal plate. The portable device according to claim 1 or 2,
A portable device, wherein the metal plate is a power battery or an electromagnetic shielding plate.

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