JP2006042059A - Radio communication apparatus and impedance controlling method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication apparatus for RFID, with which the transmitting/receiving characteristics can be improved, the design and manufacture of which is facilitated, and the manufacturing cost of which can be reduced, as regards a radio communication apparatus suitable for a radio tag to be attached to various objects in an RFID (moving body identification) system. <P>SOLUTION: The radio communication apparatus is provided with a case body 5 that stores a substrate 2, a radiation conductor 3 disposed on the substrate 2 and a communication control module (tag IC) 4 electrically joined on the radiation conductor 3 and consists of a dielectric substance, and a parasitic element 6 is disposed on the surface of the case body 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless communication apparatus suitable as a wireless tag attached to various objects in an RFID (mobile object identification) system.

  One radio communication system is an RFID (Radio Frequency-Identification) system. This RFID system is a system having a read / write function, and includes an interrogator and a wireless tag. The wireless tag stores information according to instructions from the interrogator and transmits the stored information.

  As a wireless tag used in an RFID system, particularly in the micro domain, a wireless tag with a built-in battery is often used in the field of factory automation (FA), but the technology of a wireless communication circuit using semiconductor technology. Due to the progress, wireless tags that do not have a battery that obtains driving power from signals based on an interrogator have been developed, and various applications are being studied in many fields. This wireless tag is expected to be further utilized particularly in logistics and distribution.

  FIG. 4 is a diagram showing a basic configuration of the RFID system 11. The RFID system 11 includes an interrogator 13 and a wireless tag 12. This RFID system basically operates as follows.

  First, a signal emitted from the interrogator 13 is received by an antenna element (not shown) in the wireless tag 12 and guided to a tag IC (not shown) in the wireless tag 12. The guided signal is processed in the tag IC. For example, in the case of a reading instruction from the interrogator 13, the input signal is modulated by the stored information in the tag IC and is radiated from the antenna element again. The signal radiated to the interrogator 13 is received by the antenna element of the interrogator 13, and the function as an RFID is realized.

  By the way, this RFID system has various methods such as an electromagnetic induction method, an electromagnetic coupling method, and a radio wave method. In any case, the RFID system is composed of an interrogator and a wireless tag. It has an antenna portion made of a conductor. In a radio frequency RFID system that has begun to spread in general, a signal having a frequency of 2.45 GHz or a UHF band of 915 MHz is used. As a tag IC of the wireless tag in both of these use frequency bands, a common tag IC can be used regardless of the use frequency.

  On the other hand, the antenna unit must be designed and manufactured according to the frequency used. In addition, the designed and manufactured wireless tag needs to be adjusted for impedance of the wireless tag in order to achieve matching with the circuit side.

  As described above, in the conventional wireless tag, the antenna unit has to be designed and manufactured separately according to the operating frequency, which increases the manufacturing cost. Even if the design and manufacture of the antenna portion of the wireless tag is accurately managed, the impedance of the wireless tag varies due to slight differences in the shape of the antenna portion. However, the transmission / reception characteristics deteriorated.

Patent Documents 1 and 2 disclose a wireless communication device with high radiation efficiency, wide application, easy manufacture, and low manufacturing cost. Means for matching impedance with the circuit side is disclosed in Patent Documents 1 and 2. The antenna length itself was adjusted (see Patent Document 1 and Patent Document 2 below). However, in the conventional manufacturing process, there is no means for adjusting the impedance after the antenna portion is covered by the case body. When the impedance adjustment between the wireless tag and the circuit side is not accurately performed, reflection occurs at the antenna input end on the circuit side, and as a result, power cannot be supplied to the antenna unit, and transmission / reception characteristics are significantly deteriorated.
JP2003-298464A JP 2002-353735 A

  An object of the present invention is to provide an RFID wireless communication apparatus that improves transmission / reception characteristics, is easy to design and manufacture, and can reduce manufacturing costs.

  The above object is a wireless communication apparatus comprising a case body made of a substrate, a radiating conductor provided on the substrate, and a dielectric that houses a communication control module electrically connected to the radiating conductor, This is achieved by providing a parasitic element on the surface of the case body. The case body made of a dielectric material in the present invention is not limited to a case body made of only a dielectric material, and a part of the case body is made of a material other than a dielectric material without departing from the effects of the present invention. May be.

  In the wireless tag of the present invention, when there is one parasitic element provided on the surface of the case body, the impedance of the wireless tag can be adjusted by changing the area thereof, and there are two parasitic elements. When provided as described above, the impedance of the wireless tag can be adjusted by increasing or decreasing the distance between them.

  According to the present invention, when there is one parasitic element on the case body, the impedance can be increased by reducing the area, and conversely, the impedance can be reduced by increasing the area of the parasitic element. Can be lowered.

  Also, when there are two parasitic elements in the case body, the impedance can be lowered by reducing the distance between them, and conversely, the impedance can be raised by increasing the distance between them. Can do.

  This is because the parasitic element provided on the case body plays a role as an impedance adjustment element, so that the impedance of the wireless tag can be changed.

  Hereinafter, the present invention will be described in detail. The present invention corresponds to a wireless communication apparatus in which a communication frequency of the wireless communication apparatus is 2.45 GHz or a signal having a UHF band of 915 MHz is used.

  FIG. 1 is a perspective view of a wireless communication apparatus according to the first embodiment of the present invention. The substrate 2 used in the wireless tag 1 is made of a material having excellent high-frequency characteristics, that is, a low dielectric loss, such as a glass epoxy resin substrate (FR-4). This substrate is a dielectric having a substantially rectangular parallelepiped shape, a relative dielectric constant of 4 to 5, and a dielectric loss of about 0.021.

  The shape of the radiation conductor 3 is not particularly limited, but it is desirable that the radiation conductor 3 has a rectangular shape in consideration of manufacturing advantages. The radiating conductor is made of gold, silver, copper, or other conductive metal, and is made of silver in the present invention.

  Further, a tag IC 4 serving as a communication control module is electrically connected on the radiation conductor. The electrical connection means that a signal is transmitted in the present invention.

  The tag IC 4 is realized by a semiconductor integrated circuit, has a demodulation unit, a modulation unit, and a memory unit for storing information, and is arranged in an in-plane region where a radiation conductor is formed. The tag IC4 demodulates the signal received by the radiation conductor 3 in the demodulator, and when the demodulated signal issues a response command, the tag IC4 writes the specified information in the memory unit. The tag IC4 does not need to have a function corresponding to both the response command and the write command, and may have only a function corresponding to the response command.

  More preferably, the case body 5 made of a dielectric that houses the substrate, the radiating conductor on the substrate, and the tag IC electrically joined to the radiating conductor is made of only a dielectric.

  As this dielectric, for example, ceramic having a relative dielectric constant of 5 to 100 and a dielectric loss of about 0.001 is used. The case body is formed so as to cover both the radiation conductor and the tag IC by providing a gap as an air layer so as not to contact the tag IC.

  One parasitic element 6 is formed on the surface of the case body. In the present invention, the parasitic element is printed with a silver paste having a thickness of about 10 μm. The parasitic element is not particularly limited as long as it is a conductor, and may be a thick metal film of a conductor such as gold, copper, or aluminum.

  The parasitic element can change the impedance of the wireless tag depending on the size of the area. For example, when the impedance of the wireless tag is larger than the desired impedance, the area of the parasitic element may be increased in accordance with the impedance to be obtained. In addition, when the impedance of the wireless tag is smaller than the desired impedance, the area is preferably reduced.

  As described above, by changing the area of the parasitic element, the impedance can be adjusted regardless of the shape of the antenna portion.

  FIG. 2 is a perspective view of a wireless communication apparatus according to the second embodiment of the present invention.

  Also in the present embodiment, the configuration in which the case body made of a dielectric covers the substrate, the radiation conductor provided on the substrate, and the communication control module electrically connected on the radiation conductor is the same as that of the first embodiment. There is no change.

  In the second embodiment, the impedance of the wireless tag is adjusted by providing two parasitic elements on the surface of the case body and adjusting the distance between them. For example, when the impedance of the wireless tag is larger than the desired impedance, the distance between the two parasitic elements may be shortened according to the impedance to be obtained. Further, when the impedance of the wireless tag is smaller than the desired impedance, the distance may be increased.

  Thus, by providing a parasitic element, impedance adjustment can be performed without being influenced by the shape of the antenna portion.

  In any of the first and second embodiments, a dielectric made of the same material as the case body may be provided on the lower side of the substrate, that is, on the side where the communication control module is not disposed.

  At this time, the lower dielectric is preferably the same size as the substrate, and the substrate is preferably about 0.3 mm or less.

  The present invention is particularly useful in the case where both a wireless tag having a usage frequency of 2.45 GHz and a usage frequency of 915 MHz is manufactured.

  As described above, the wireless tag has to design and manufacture an antenna unit corresponding to the use frequency. As described above, according to the present invention, the antenna unit corresponding to both use frequencies is shared. Can do.

  In general, when the use frequency of the wireless tag is reduced, the antenna needs to be enlarged in order to obtain sufficient antenna output. However, according to the present invention, it is possible to inexpensively manufacture a wireless communication device having excellent transmission / reception characteristics without causing an increase in the size of the antenna.

  Hereinafter, the present invention will be specifically described by way of examples.

  On a glass epoxy substrate having a thickness of about 2 mm, after drying, a silver paste was applied to a thickness of about 10 μm and a size of 10 mm × 50 mm to form a radiation conductor. Then, the communication control module was joined on the radiation conductor with solder, and a wireless tag having a usage frequency of 2.45 GHz was produced without using a case body. The antenna length at this time, that is, the length in the longitudinal direction of the radiation conductor was 50 mm.

  Similarly, when a wireless tag having a use frequency of 915 MHz was produced without using a case body, the antenna length was required to be about 160 mm.

  Therefore, when this 915 MHz wireless tag is covered with a case body using a dielectric having a relative dielectric constant of 7 to 8, the antenna length is set to 50 mm, so that transmission / reception characteristics equivalent to those of the wireless tag not using the case body are obtained. was gotten. Further, for adjusting the impedance, a parasitic element was produced on the case body by printing using silver paste to a thickness of 10 μm and a length × width of 3 mm × 3 mm.

  Using this parasitic element, the impedance of the wireless tag was adjusted in order to achieve matching with the circuit side.

  As described above, according to the present invention, the antenna of the 2.45 GHz wireless tag and the antenna of the 915 MHz wireless tag can be shared, and the manufacturing cost can be greatly reduced.

  The above-described invention can be used for a wireless communication device used in an RFID system.

1 is a perspective view showing a first embodiment of the present invention. It is a perspective view which shows the 2nd Embodiment of this invention. It is sectional drawing which shows the 1st Embodiment of this invention. 1 is a diagram illustrating a basic configuration of an RFID system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wireless communication apparatus 2 Board | substrate 3 Radiation conductor 4 Communication control module (tag IC)
5 Case body 6 Parasitic element 11 RFID system 12 Wireless tag 13 Interrogator

Claims (4)

  A wireless communication device comprising a substrate, a radiating conductor provided on the substrate, and a case body made of a dielectric material that houses a communication control module electrically connected to the radiating conductor, on the surface of the case body A wireless communication apparatus comprising a parasitic element.   The wireless communication apparatus according to claim 1, wherein the parasitic element is a metal conductor.   The impedance adjustment method for a wireless communication device according to claim 1, wherein the impedance of the wireless communication device is adjusted by changing the area of the parasitic element. . The impedance adjustment method for a wireless communication device according to claim 1, wherein the impedance of the wireless communication device is adjusted by changing a distance between the plurality of parasitic elements. Impedance adjustment method.

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