JPH09284038A - Antenna equipment of non-contact data carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the communication distance of a non-contact data carrier to be stable regardless of the arrangement place of an antenna equipment and also to promote more thinning in the antenna equipment by adjacently arranging a soft magnetic body where an effective and magnetical permeability is more than a specified value at the rear surface of a loop antenna. SOLUTION: The loop antenna 1 is contained in a case 2 which is formed by a synthetic resin material, etc., where the effective and magnetic permeability is close to one. Then, the soft magnetic body 3 is arranged on the whole surface of the rear surface of the loop antenna 1. The effective and magnetic permeability when an exciting frequency band is equal to or below 100kHz is more than 100 in the soft magnetic body 3. The soft magnetic body 3 has the drastically high effective and magnetic permeability. When it is adjacently arranged on the rear surface of the loop antenna 1, an electromagnetic field in the rear part of the loop antenna 1 is drawn into the soft magnetic body 3. Therefore, the limitation of the arrangement place is drastically reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna device on the reader / writer side in a contactless data carrier system using a contactless card, a contactless tag or the like.

[0002]

2. Description of the Related Art In recent years, a non-contact type data carrier system has been put into practical use in which a reader / writer reads various kinds of information stored in a non-contact mode carried by a user in a non-contact manner using electromagnetic waves. . In this non-contact data carrier system, there are various types of signal transmission means,
When the electromagnetic induction method is used, the frequency at which signals are exchanged between the antenna device used on the reader / writer side and the contactless card is in the band of several hundred kHz or less, and the loop antenna is used as the antenna type. The effective communication range is generally a relatively short distance within 1 m.

[0003]

The loop antenna used in the non-contact data carrier system of the electromagnetic induction type is optimally adjusted as a single unit and then incorporated in the reader / writer unit or separated by the antenna only. It is installed on a wall surface, a ceiling surface, a floor surface of a building facility, a door, or the like, depending on whether it is housed in the housing. However, in the vicinity of a suitable place to install the antenna, rebar, iron plate, aluminum plate,
Alternatively, there is a tendency that there is a member made of a good conductor such as a signal cable. If such a good conductor member is present close to the antenna, part of the electromagnetic wave power radiated from the loop antenna will be lost due to the effects of eddy currents generated on the surface of the good conductor, which shortens the communication distance and in extreme cases. In some cases, communication cannot be performed unless the card is brought into direct contact with the antenna surface, and there is a problem that the communication sensitivity is greatly affected by the condition of the antenna installation location.

As a countermeasure against this, Japanese Unexamined Patent Publication No. 7-263936
In the gazette, a non-magnetic space such as an air layer and a non-magnetic conductive member such as a copper plate, a silver plate, and an aluminum plate are arranged behind the loop antenna, and the maximum communication distance can be obtained in that state. As described above, a technique has been proposed in which the loop antenna is adjusted and then installed at a desired place. However, while this method is not affected by the conditions of the antenna installation location, in the case of a circular loop antenna with a diameter of about 200 mm, the nonmagnetic space must be 20 to 30 mm or more, which hinders the thinning of the antenna device. There was a problem of being done.

The present invention solves the above-mentioned problems of the prior art, and can keep the communication distance of the non-contact data carrier stable regardless of the installation location of the antenna device. It is an object of the present invention to provide an antenna device for a non-contact data carrier that can promote thinning of the device.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have found that most of the radiation loss of electromagnetic waves caused by the non-magnetic material having high conductivity in the above-mentioned known form being close to the loop antenna is high in conductivity. It is considered that this is caused by the eddy current generated in the material, and from this viewpoint, it was thought that the low conductivity material is preferable. On the other hand, since an electromagnetic wave is one in which an electric field and a magnetic field travel integrally as the front and back sides, it was thought that the electromagnetic field could control the electromagnetic wave. That is, a soft magnetic material having an effective relative permeability (μeff) and a low conductivity higher than that of a magnetic member such as an iron plate is radiated from the antenna by arranging the soft magnetic material close to the side surface other than the direction in which the antenna is radiated. Among the electromagnetic waves, if the supply power is adjusted by taking a configuration in which the electromagnetic waves on the side other than the intended direction are stably absorbed in advance in a time-averaged manner, even if a magnetic material such as an iron plate approaches, that side can be The electromagnetic field is no longer absorbed, and the electromagnetic field generated from the cable is absorbed by the high effective relative permeability material, so the antenna side is not affected and it is thought that a stable radiated electromagnetic field can be secured. As a result of extensive studies, a soft magnetic material having an effective relative magnetic permeability of 100 or more at an excitation frequency of 100 kHz or less was arranged close to the back surface of the loop antenna in order to achieve the above object.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an antenna device of a contactless data carrier according to the present invention. Loop antenna 1
It has a rectangular or circular shape, and is housed in a case 2 formed of a synthetic resin material or the like having a sufficiently small electric conductivity and an effective relative magnetic permeability close to 1. The soft magnetic body 3 is arranged on the entire back surface of the loop antenna 1. The shape of the soft magnetic body 3 may be appropriately determined depending on the shape of the loop antenna 1, such as a rectangle or a circle.

The loop antenna 1 is mounted on the surface of the case 2 in the direction intended for radiation through an antenna mounting bracket or the like (not shown). Also, soft magnetic material 3
Are fixed by adhering the radiation of the loop antenna 1 to a surface in a direction not intended.

FIG. 2 shows the positional relationship between the loop antenna 1 and the soft magnetic material 3 in the antenna device shown in FIG. As shown in FIG. 2, it is ideal that the soft magnetic material 3 larger than the outer peripheral contour of the loop antenna 1 is arranged on the back surface of the opening surface of the loop antenna 1.
If there is any interfering substance in the open □ plane, the soft magnetic body 2 with a hollowed central portion may be placed behind the opening face of the loop antenna 1 as shown in FIG. . When the soft magnetic material 2 cannot be cut through due to material strength or structural problems, the soft magnetic material 2 is divided into a plurality of members as shown in FIG. You can place it in.

The soft magnetic material referred to here is a properly adjusted operating magnetic field (excitation frequency band is 100 kHz or less).
In which the effective relative permeability (μeff) is 100 or more. The low conductivity is included in the definition of the effective relative magnetic permeability, and is not particularly limited.

The soft magnetic material 3 has an extremely high effective relative magnetic permeability, and when it is placed close to the back surface of the loop antenna 1,
The electromagnetic field behind the loop antenna 1 is drawn into the soft magnetic body 3. Further, by adjusting the antenna output in this state, it is possible to reduce the influence when there is a good conductor such as a reinforcing bar, an iron plate, an aluminum plate, or a signal cable on the back surface of the antenna device.

Generally, the coercive force of a soft magnetic material is smaller than that of an iron plate or the like, and the hysteresis loss is small. If a soft magnetic material having a large electric resistance is used, the eddy current flowing on the surface of the soft magnetic material is further reduced. Expressing this with an effective relative permeability that is a typical magnetic characteristic value, the higher the effective relative permeability value, the less the loss of high-frequency power applied to the loop antenna 1, and the presence of a good conductor on the back surface of the antenna device. However, the same communication distance as in the case of the antenna alone can be obtained.

As a more preferable soft magnetic material, a ferrite thin plate with a thickness of about several mm or an amorphous sheet with a thickness of about 10 μm can be considered. By stacking the amorphous sheets, it is possible to further reduce the influence of the good conductor included in the building member on the back surface of the antenna device. Further, the effective relative permeability is further increased and the communication distance can be extended by subjecting the amorphous sheet to a heat treatment of several hundred degrees Celsius in an inert gas or a nitrogen gas to which an appropriate external magnetic field is applied.

When the antenna device is excited at a frequency of several hundreds of kHz, a soft magnetic material capable of maintaining a high effective relative magnetic permeability in the frequency band may be used. In this case, especially ferrite or amorphous is used. preferable. When the antenna device is excited with a lower number of turns than this, a soft magnetic material such as permalloy, silicon steel, or sendust can also be used.

If the operating current of the antenna device of the present invention can be adjusted appropriately, the operating current may be adjusted so as to match the maximum effective relative permeability of the soft magnetic material 3 at that time.

FIG. 5 shows the communicable range of the loop antenna 1 alone, and there is a uniform communicable range 4 before and after the loop antenna 1.

FIG. 6 shows the communicable range of the antenna device of the present invention. According to the antenna device of the present invention, there is almost no communicable range behind the soft magnetic body 3, and the communicable range 4 can be obtained only on the front surface of the loop antenna 1. As shown in the figure, the communicable range hardly changed even when the magnetic material such as the iron plate 5 was present on the back side of the antenna device.

[0019]

As described above, according to the present invention, the soft magnetic material is arranged on the back surface of the loop antenna, and the antenna output is adjusted with the induction electromagnetic field of the loop antenna being drawn into the soft magnetic material. Even if there is a good conductor member such as a reinforcing bar, an iron plate, an aluminum plate, or a signal cable around the antenna device, the communication distance to the opening side of the loop antenna does not change. Therefore, restrictions on the installation location can be significantly reduced. According to the present invention,
Since there is no problem even if the loop antenna and the soft magnetic body are brought into contact with each other, a great effect can be obtained in promoting the thinning of the antenna device.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an antenna device according to the present invention.

FIG. 2 shows an embodiment of the present invention, (A) is a front view, and (B) is a longitudinal sectional view.

FIG. 3 shows a second embodiment of the present invention, (A) is a front view and (B) is a longitudinal sectional view.

FIG. 4 shows a third embodiment of the present invention, (A) is a front view, and (B) is a longitudinal sectional view.

FIG. 5 is a conceptual diagram showing a communicable range of a loop antenna alone.

FIG. 6 is a conceptual diagram showing a communicable range of the antenna device according to the present invention.

[Explanation of symbols]

 1 Loop antenna 2 Case 3 Soft magnetic material 4 Communication range 5 Iron plate

Claims (1)

[Claims] 1. An antenna device for a non-contact data carrier, wherein a soft magnetic material having an effective relative magnetic permeability of 100 or more in an excitation frequency band of 100 kHz or less is arranged close to the back surface of the loop antenna.