Patent Publication Number: US-2009231140-A1

Title: Radio frequency identification antenna and apparatus for managing items using the same

Description:
RELATED APPLICATION 
     The present disclosure relates to subject matter contained in priority Korean Application No. 10-2008-011838, filed on Feb. 5, 2008, which is herein expressly incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radio frequency identification (RFID) reader antenna and an apparatus for managing items using the same, and particularly, to an RFID antenna for a shelf using an ultra-high frequency (UHF) band signal and an apparatus for managing items using the same. 
     2. Background of the Invention 
     In general, a radio frequency identification (RFID) technique denotes contactlessly reading out data stored in tags, labels, cards, and the like, each having a compact semiconductor chip by using a wireless (radio) frequency signal. 
     Such RFID technique is implemented such that information related to items and their peripheral circumstances are identified from tags attached on such items by using a wireless frequency signal, which allows collection, storage, processing and tracing of information on each item, resulting in enabling various services, including location measuring of the items, remote control for the items, management of the items, information exchange between the items, and the like. 
     The RFID technique has recently been employed to manage items, such as stock of items, warehousing/delivering of items and selling of items. In particular, by using the RFID technique, an RFID antenna is installed on an item managing shelf and tags are attached to each item, so as to be aware of the current condition of each item in real time, whereby many items can efficiently be managed. 
     The RFID antenna using such mentioned technique and the apparatus for managing items using the RFID tags are disclosed in Japanese Laid-Open Publication No. 2007-70112. Hereinafter, with reference to  FIGS. 1 and 2 , description will be given of configurations of an RFID antenna and an apparatus for managing items using RFID tags disclosed in Japanese Laid-Open Publication No. 2007-70112. 
       FIG. 1  is a view showing a configuration of an apparatus for managing items using an RFID antenna according to the present invention. 
     As shown in  FIG. 1 , an apparatus  1  for managing items using an RFID antenna includes an RFID antenna  15  mounted inside a shelf board  11 , and a converter  16  configured to exchange information, such as an electrical signal or the like, with the RFID antenna  15  and connected to an external computer (not shown) via an interface circuit (not shown). 
     Various shapes of items  17  are placed on the shelf board  11  with RFID tags  18  being attached thereto. The RFID tag  18  is provided with a small loop antenna and a memory having information recorded therein, and an electronic chip is disposed at the center of the loop antenna. 
       FIG. 2  is a view showing a detailed configuration of the related art RFID antenna for a shelf. 
     As shown in  FIG. 2 , the related art RFID antenna  15  is configured in a structure of two loop antennas  23  and  24  being stacked on each other. The RFID antenna  15  operates in a sequentially operating manner that one of the first or second antenna  23  or  24  first operates followed by the other one. Thus, in order to operate the two antennas  23  and  24  disposed on one shelf, a switching circuit is required for sequentially operating each of the antenna  23  and  24  at two RFID readers (not shown) or one RFID reader (not shown). 
     However, radiators (or emitters) of the related art loop antennas  23  and  24  for the shelf can be used only below a high frequency (HF) band (3 MHz˜30 MHz), for example, 13.56 MHz. Since an entire length of a radiator of the loop antenna of 13.56 MHz is relatively much shorter than a wavelength (1λ 0 =22 m) of electric wave on the air, a phase change less occurs on a radiator line. Accordingly, strength and direction of a surface current of the radiator are constant, whereby a null point at which the wave is offset is less generated. 
     Hence, the related art has usually used antennas employing the aforementioned HF band (3 MHz˜30 MHz). 
     However, in recent time, markets are getting extended to an RFID application field using an ultra-high frequency (UHF) band (300 MHz˜3 GHz). 
     An RFID system of the UHF band enables the identification of tags even at a remote distance farther than a valid identification distance of 5 m, and also has very high identification speed and identification rate at a short distance nearer than 50 cm as compared to the HF band. 
     In the RFID system of the UHF band, a far field is usually formed as an electric field such that a tag identification is possible at a remote distance. However, it is operated by a backscattering, and thus is sensitive to its peripheral environment. 
     On the other hand, a near field in the RFID system of the UHF band is usually formed as a magnetic field and operated by a coupling. Thus, it is hardly affected by a material having high permittivity, such as water or metal, so as to provide high identification rate and fast identification speed of an RFIDI reader. 
     However, the antenna of the UHF band uses high operation frequency and short wavelength of an electric wave, thereby to frequently cause a null point at which a signal is not identified at the near field as compared to the antenna of HF band, from the perspective of its physical feature. 
     Furthermore, for the antenna of the UHF band, if the number of items having tags attached thereto are increased, the operation frequency of the antenna is shifted. Accordingly, the RFID reader antenna may be affected by the change in the number of items. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a radio frequency identification (RFID) antenna capable of avoiding a generation of a null point at a near field even using a UHF-band frequency, and an apparatus for managing items using the same. 
     Another object of the present invention is to provide an RFID antenna capable of accurately obtaining information related to RFID tags using a UHF-band frequency even when many items exist or items are massed, and an apparatus for managing items capable of easily identifying a current condition of each item using the same. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a radio frequency identification (RFID) reader antenna including: a feeding portion having one end connected to the RFID reader and another end connected to a ground; and a radiating electrode disposed to be spaced apart from the feeding portion and configured to send or receive a signal of a certain band. 
     The feeding portion and the radiating electrode may be formed inside a dielectric substance or on a surface thereof. 
     The feeding portion and the radiating electrode may be electromagnetically coupled to each other so as to send or receive a signal. 
     The antenna may further include a load resistance connected between the another end of the feeding portion and the ground. 
     The feeding portion may be disposed below the radiating electrode. 
     The antenna may further include an antenna port connected at the one end of the feeding portion. 
     The antenna may further include a sub electrode disposed to be spaced apart from the feeding portion by a certain distance. 
     The antenna may further include a sub resistance connected between one end of the sub electrode and the ground and configured to control an impedance matching. 
     The sub electrode may be disposed in parallel with the feeding portion on the same surface. 
     The sub electrode may be configured as a linear feeding line or strip line including a conductive material. 
     The radiating electrode may be arranged perpendicular to the feeding portion at one end thereof, and arranged vertical to the sub electrode at another end thereof. 
     The certain band may be an ultra high frequency (UHF) band. 
     The radiating electrode may be configured in a shape of a meander. 
     The feeding portion may be at a shelf for storing items thereon. 
     In accordance with one embodiment of the present invention, there is provided an apparatus for managing items including: at least one shelf configured to store items thereon; at least one radio frequency identification (RFID) reader antenna disposed at the shelf, and including a feeding portion having one end connected to an RFID reader and another end connected to a ground, and a conductive radiating electrode spaced apart from the feeding portion by a certain distance for sending or receiving a signal of a certain band to/from an RFID tag attached to each item; and an RFID reader configured to receive information from the RFID tag attached to each item via the RFID reader antenna. 
     The radiating electrode may send or receive a UHF-band signal by an electromagnetic coupling with the feeding portion by being spaced apart therefrom by a certain distance. 
     The RFID reader antenna may be provided in plurality, and the apparatus may further include a switching portion configured to perform a switching operation such that the plurality of RFID reader antennas are sequentially connected to the RFID reader. 
     The RFID reader antenna may further include: a load resistance disposed between another end of the feeding portion and the ground and configured to allow a current applied from the RFID reader to smoothly flow all over the feeding portion; a sub electrode disposed on the same surface as the feeding portion by being spaced apart from the feeding portion by a certain distance and configured to process a signal of the certain band by a coupling with the feeding portion; and a sub resistance connected between the sub electrode and the ground and configured to control an impedance matching. 
     The RFID reader antenna may send or receive a UHF-band signal. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a view showing a configuration of an apparatus for managing items using a related art RFID antenna; 
         FIG. 2  is a view showing a detailed configuration of the RFID antenna for a shelf according to the related art; 
         FIG. 3  is a perspective view of an RFID reader antenna according to the present invention; 
         FIG. 4  is an upper view of the RFID reader antenna according to the present invention; 
         FIG. 5  is a side view of the RFID reader antenna according to the present invention; 
         FIG. 6  is a view showing a magnetic field formed around a feeding portion according to the present invention; 
         FIGS. 7A and 7B  are views showing a correlation between a magnetic field of the feeding portion and a magnetic field formed at adjacent RFID tags according to the present invention; 
         FIGS. 8A and 8   b  are views showing a comparison between an impedance bandwidth of only the feeding portion and an entire impedance bandwidth of the RFID antenna according to the present invention; 
         FIG. 9  is a perspective view showing an apparatus for managing items using an RFID reader antenna in accordance with an embodiment of the present invention; and 
         FIG. 10  is a view showing a configuration of the apparatus for managing items using the RFID reader antenna in accordance with the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Description will now be given in detail of an RFID reader antenna and an apparatus for managing items using the same according to the present invention, with reference to the accompanying drawings. 
       FIG. 3  is a perspective view of an RFID reader antenna  300  according to the present invention,  FIG. 4  is an upper view of the RFID reader antenna  300 , and  FIG. 5  is a side view of the RFID reader antenna  300 . 
     As shown in  FIGS. 3 to 5 , the RFID reader antenna  300  according to the present invention may include a feeding portion  310  formed at a lower portion of a dielectric substrate  301 , and a radiating electrode  320  formed above the feeding portion  310 . Here, the feeding portion  310  and the radiating electrode  320  may be made of a conductive material, and formed inside the dielectric substrate  301  or on the surface of the dielectric substrate  301 . 
     The feeding portion  310  may be configured as a linear feeding line or strip line. An antenna port  311  through which a current is supplied is formed at one end of the feeding portion  310 , and a load resistance  312  is connected to another end of the feeding portion  310 . Also, the load resistance  312  is connected to a ground GND. 
     The radiating electrode  320  is formed above the feeding portion  310  by being perpendicularly spaced apart therefrom by a certain distance. The radiating electrode  320  is implemented by including a plurality of first electrodes  321  arranged in a direction orthogonal to the feeding portion  310 , and a plurality of second electrodes  322  arranged in a direction in parallel with the feeding portion  310 . One ends of the first and second electrodes  321  and  322  are alternately connected to each other, and thus, as shown in  FIGS. 3 to 5 , the radiating electrode  320  can substantially be configured in a shape of meander. Also, a type or size of the dielectric substance of the dielectric substrate  301  may determine a connected angle between the first and second electrodes  321  and  322 , a distance between two adjacent first electrodes  321  or two adjacent second electrodes  322 , and shapes of the first and second electrodes  321  and  322 . The radiating electrode  320  is fed by an electromagnetic coupling with the feeding portion  310 , which allows the antenna  300  to process frequencies of UHF band (i.e., 300 MHz˜3 GHz). 
     In addition, the present invention further provides a sub electrode  330 , which is arranged on the same surface as the feeding portion  310  by being horizontally spaced apart from the feeding portion  310  by a certain distance. The sub electrode  330  may be arranged in parallel with the feeding portion  310  on the same surface, or be configured as a linear feeding line or strip line using a conductive material. The sub electrode  330  may be fed by an electromagnetic coupling with the feeding portion  310 , so as to allow the antenna  300  to process frequencies of the UHF band (i.e., 300 MHz˜3 GHz). 
     One end of the sub electrode  330  is open and another end thereof is connected to a sub resistance  332 . The sub resistance  332  is connected to the ground GND. The sub resistance  332  is used for an impedance matching of the antenna  300 . 
       FIG. 6  is a view showing a magnetic field formed around a feeding portion according to the present invention, and  FIGS. 7A and 7B  are views showing a correlation between a magnetic field of the feeding portion and a magnetic field formed at adjacent RFID tags according to the present invention. 
     Hereinafter, an operation of the RFID reader antenna  300  according to the present invention will be described with reference to  FIGS. 6 ,  7 A and  7 B. 
     First, a signal having a UHF-band frequency is input from an RFID reader (not shown) to the antenna port  311  of the feeding portion  310 . The signal input to the antenna port  311  is applied to the entire feeding portion  310 , thus to generate a magnetic field  410  around the feeding portion  310  as shown in  FIG. 6 . The magnetic field  410  is formed in a clockwise direction  411  around the feeding portion  310  in cooperation with a current flowing direction  313  according to Ampere&#39;s Law. 
     The magnetic field  410  generated around the feeding portion  310  is then applied to the RFID tag  430  attached to an item  400  placed at an adjacent position. Accordingly, the RFID reader (not shown) can contactlessly perform a wireless communication at a short distance with the RFID antenna  430  via the antenna  300 . In  FIG. 6 , reference numeral ‘ 431 ’ denotes a tag antenna of the RFID tag  430 , and ‘ 432 ’ denotes an electronic chip disposed in the RFID tag  430  for storing information. 
       FIG. 7A  is a view showing a magnetic field formed around the feeding portion  310  when a current signal having a UHF-band frequency is applied to the feeding portion  310  in case of only the feeding portion  310  being provided according to the present invention. 
     As shown in  FIG. 7A , when a physical length of the feeding portion  310  is long, a null point is generated by an interval of λ g /2 (here, λ g  denotes a valid wavelength) according to a wavelength of a signal applied. However, at such null point, even if the RFID tag  430  is located near the feeding portion  310 , a case that the RFID reader (not shown) does not identify the RFID tag  430  may occur. 
       FIG. 7B  is a view showing a magnetic field formed around the feeding portion  310 , the radiating electrode  320  and the sub electrode  330  when a current signal having a UHF-band frequency is applied to the feeding portion  310  in case of the feeding portion  310 , the radiating electrode  320  and the sub electrode  330  being provided. 
     As shown in  FIG. 7B , when the radiating electrode  320  is disposed above the feeding portion  310  according to the present invention and the sub electrode  330  is also disposed in parallel with a side surface of the feeding portion  310 , it can be noticed that the null point generated around the RFID reader antenna  300  is removed, as shown in the comparison of  FIG. 7B , due to the affection of a parasitic capacitance by the radiating electrode  320  and the sub electrode  330 . 
     That is, with the configuration according to the present invention, a vector component of the magnetic field is changed by an electromagnetic coupling between the feeding portion  310  and the radiating electrode  320  or an electromagnetic coupling between the feeding portion  310  and the sub electrode  330 , so as to enable a reduction or complete removal of the null point. 
     In particular, with the configuration according to the present invention, the null point can be removed by the electromagnetic coupling between the feeding portion  310  and the radiating electrode  320 . Also, when the sub electrode  330  is further disposed at the feeding portion  310  and the radiating electrode  320 , the null point can further be reduced. 
       FIG. 8  is a view showing a comparison between an impedance bandwidth of only the feeding portion and an entire impedance bandwidth of the RFID antenna according to the present invention. 
       FIG. 8A  shows an impedance bandwidth when only the feeding portion  310  is configured. As shown in  FIG. 8A , it can be seen that a narrow bandwidth  610  is represented when only the feeding portion  310  is disposed. 
     On the other hand,  FIG. 8B  shows an impedance bandwidth when the feeding portion  310 , the radiating electrode  320  and the sub electrode  330  are all disposed. As shown in  FIG. 8B , it can be seen that an impedance bandwidth  620  is increased about three times wider than that when the feeding point  310  is only disposed, in case where the radiating electrode  320  and the sub electrode  330  as well as the feeding portion  310  are all configured. 
     As such, the RFID reader antenna  300  according to the present invention can be implemented such that the impedance bandwidth can be increased by the electromagnetic coupling between the feeding portion  310  and the radiating electrode  320  and the electromagnetic coupling between the feeding portion  310  and the sub electrode  330 , which means that the RFID reader antenna  300  is tolerant to the permittivity of an item located near its upper portion. Accordingly, the RFID reader antenna  300  and the RFID reader (not shown) using the antenna  300  can obtain a constant tag identification rate regardless of the number of items placed on the antenna  300  and the number of tags attached to the items. 
       FIG. 9  is a perspective view showing an apparatus for managing items using an RFID reader antenna in accordance with an embodiment of the present invention, and  FIG. 10  is a view showing a configuration of the apparatus for managing items using an RFID reader antenna in accordance with the embodiment of the present invention. 
     As shown in  FIGS. 9 and 10 , an apparatus  700  for managing items according to the present invention may include shelves  711  for keeping items  400  thereon, RFID reader antennas  300  each disposed on the shelves  711 , and an RFID reader  720  for reading information out of the RFID tags  430  attached to the items  400  via the RFID reader antenna  300 . 
     The shelf  711  is formed of a dielectric substance having a certain permittivity, and has the RFID reader antenna  300  according to the present invention disposed inside thereof or on an upper surface thereof. Also, the shelf  711  may be used as the dielectric substrate  311  according to the present invention. In this case, the feeding portion  310 , the radiating electrode  320 , the sub electrode  330 , the load resistance  312 , the sub resistance  332  and the like may be disposed inside the shelf  711  or on the upper surface of the shelf  711 . 
     The shelf  711  may be disposed at various types of item storage cabinets  5   710 , such as bookcases, bookracks or cabinets, which are divided into a plurality of spaces by the shelves  711  for keeping items on each space. For example,  FIG. 9  shows a bookrack as the item storage cabinet  710 , and also shows may books as the items  400  kept on the item storage cabinet  710 . 
     As aforementioned with reference to  FIGS. 3 to 8 , the RFID reader antenna  300  includes the feeding portion  310 , the radiating electrode  320 , the sub electrode  330 , the load resistance  312  and the sub resistance  332  and the like. Also, the RFID reader antenna  300  can obtain information from the RFID tags  430  using the UHF-band frequency at a short distance by the electromagnetic coupling, and also can remove the null point, even having a wide impedance bandwidth. Accordingly, the RFID reader antenna  300  can acquire a constant tag identification rate regardless of the number of items placed on the antenna  300  and the number of tags attached to the items. 
     The RFID reader  720  is connected to the antenna port  311  of the RFID reader antenna  300  via an antenna cable  730 . The RIFD reader  730  then receives information from the RFID tags  430  attached to the items  400  via the RFID reader antenna  300  to transmit to an external server  750 , thereby comprehensively managing the current condition of items via the server  750 . 
     In addition, the apparatus  700  for managing items according to the present invention may further include a switch portion  740  connected to a plurality of RFID reader antennas  300  and one RFID reader  720 . The switch portion  740  performs a switching operation such that the plurality of RFID reader antennas  300  can sequentially be connected to the RFID reader  720  when a plurality of shelves  711  are disposed on the item storage cabinet  710  and thus the plurality of RFID reader antennas  300  are provided. 
     Such configuration of the apparatus  700  for managing items can increase identification speed and identification rate of the RFID tags at a short distance by using the UHF-band frequency, at libraries, document repositories, warehouses, material management storages or the like, having many books and documents collected or many items stored. Also, the configuration of the apparatus  700  for managing items allows an accurate management of the current condition of each item without any affection by the number of items. 
     An RFID reader antenna according to the present invention is provided with a radiating electrode fed by an electromagnetic coupling with a feeding line via which a current is directly fed, so as to prevent the generation of a null point at a near field even using a UHF-band frequency. 
     The RFID reader antenna according to the present invention can accurately acquire information related to RFID tags without any change in a frequency using the UHF-band frequency even when many items are placed on the RFID antenna. 
     An apparatus for managing items according to the present invention can remarkably enhance identification speed and identification rate of items located at a near distance and also obtain a wide impedance bandwidth without a null point by employing the RFID reader antenna and using the UHF band frequency, so as to enable an accurate management of a current condition of each item regardless of the number of items. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
     As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.