Patent Publication Number: US-11031673-B2

Title: RF tag antenna, RF tag, and RF tag having conductive body formed therein

Description:
TECHNICAL FIELD 
     The present invention relates to an RF tag antenna, an RF tag, and an RF tag with a conductor. 
     BACKGROUND ART 
     In recent years, in management systems for inventory management of products or parts, logistics management, etc., RFID (Radio Frequency Identification) technology has been utilized. In systems that use the RFID technology, wireless communications are performed between an RF tag and a reader-writer (hereinafter referred to as a “reading device”) and identification information and the like stored in the RF tag is read by the reading device. 
     For example, Patent Literature 1 (Japanese Patent Laid-Open No. 2012-253700) discloses a wireless communication device, its manufacturing method, and a metal article with the wireless communication device which facilitate installation of a radiation conductor and a ground conductor to improve connection reliability between the conductors. 
     The wireless communication device described in Patent Literature 1 comprises an inverted F-type antenna which includes: a dielectric block having a first main surface and a second main surface facing the first main surface; a radiation conductor provided on the first main surface of the dielectric block; a ground conductor provided on the second main surface of the dielectric block; feed conductor for connecting a wireless IC element processing a high-frequency signal to the radiation conductor and the ground conductor; and a short circuit conductor for connecting the radiation conductor to the ground conductor, where at least the radiation conductor, the ground conductor, the feed conductor, and the short circuit conductor are each formed as a flat-plate-shape metal conductor; and the metal conductors are disposed at its radiation conductor part on the first main surface of the dielectric block, at its ground conductor part on the second main surface of the dielectric block, at its feed terminal part mainly on a side of the dielectric block, and at its short circuit conductor part mainly on a side of the dielectric block. 
     Patent Literature 2 (Japanese Patent Laid-Open No. 2007-124696) discloses a wide band antenna apparatus, reduced in height, also available in a communication system where an ultra wide band (UWB) and small-sized antenna apparatus are required, such as a Broadband-PAN (Personal Area Network) utilizing UWB technologies. 
     The wide band antenna apparatus described in Patent Literature 2 is a wide band antenna apparatus that comprises a conductor ground plate and a radiation conductor plate at least portions of which face one another, where a magnetic substance whose relative permeability in the radio frequency in use becomes greater than 1 and approximately equal to or smaller than 8 is interposed between the conductor ground plate and the radiation conductor plate. 
     Patent Literature 3 (Japanese Patent Laid-Open No. 2013-110685) discloses a thin antenna for reading an RFID tag, used in radio wave of the UHF band, and capable of excellently performing communications even when mounted on a metallic component. 
     The thin antenna described in Patent Literature 3 comprises: a magnetic sheet; an antenna section disposed on one surface of the magnetic sheet; and a conductor ground plate disposed at the other surface of the magnetic sheet, where the antenna section and the conductor ground plate are disposed so that at least parts of them are overlapped with each other when viewed in a thickness direction of the magnetic sheet, and the thickness of the magnetic sheet is 200 μm or more and 600 μm or less. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open No. 2012-253700 
     Patent Literature 2: Japanese Patent Laid-Open No. 2007-124696 
     Patent Literature 3: Japanese Patent Laid-Open No. 2013-110685 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the prior-art document 1, an RF tag antenna of an inverted-F type is disclosed. However, there is a problem that long distance reading is not possible even when a dielectric body is used. 
     Also, in Patent Literatures 2 and 3, there is a problem that manufacturing costs increase due to the complexity of the structure such as feeding electrical power using coaxial lines or strip lines, and there is another problem that it is difficult to adjust resonant frequency according to the applications. 
     Also, yet there is another problem that when an RF tag is placed close to a conductor, the resonant frequency is shifted and this may hinder the communications, and still there is another problem that communication is not possible when radio wave is irradiated on the back of the RF tag installation surface. 
     A main object of the present invention is to provide an RF tag antenna, an RF tag, and an RF tag with a conductor which are omnidirectional and have long communication distance. 
     Solution to Problem 
     (1) 
     An RF tag antenna in accordance with one aspect is an RF tag antenna to which an IC chip is mounted, the RF tag antenna including: an inductor pattern section having a C-shape and configured in a form of a flat plate; a notch section formed by cutting out a periphery of the inductor pattern section; an antenna section formed around the notch section; and a ground section provided in continuation with the inductor pattern section and configured in a form of a flat plate. 
     In this case, by virtue of the fact that the IC chip is provided to bridge both ends of the C-shape, a resonant circuit is formed by the inductor pattern section and capacitance inside the IC chip. 
     Also, the resonant circuit enables omnidirectional communications between the RF tag and a reading device, and thinning or miniaturization of the RF tag can be achieved. 
     It should be noted that, in the present embodiment, a thin film indicates a range of thickness of 3 μm or more and 35 μm or less. 
     Also, with regard to the antenna section, any one antenna from among dipole antennas, collinear array antennas, and monopole antennas can be used. 
     (2) 
     An RF tag antenna in accordance with another aspect is an RF tag antenna to which an IC chip is mounted, the RF tag antenna including: an inductor pattern section having a C-shape and configured in a form of a flat plate; a notch section formed by cutting out a periphery of the inductor pattern section; an antenna section formed around the notch section; an insulating substrate having a first surface and a second surface facing the first surface; and a ground section provided in continuation with the inductor pattern section and configured in a form of a flat plate, where the inductor pattern section, the notch section, and the antenna section are formed on the first surface, and the ground section is formed on the second surface. 
     In this case, by virtue of the fact that the IC chip is provided to bridge both ends of the C-shape, a resonant circuit is formed by the inductor pattern section, and capacitances inside the IC chip and the insulating substrate, and an omnidirectional RF tag can be configured. 
     (3) 
     An RF tag antenna in accordance with a still another aspect is an RF tag antenna to which an IC chip is mounted, the RF tag antenna including: an inductor pattern section having a C-shape and configured in a form of a flat plate; a notch section formed by cutting out a periphery of the inductor pattern section; an antenna section formed around the notch section; an insulating substrate having a first surface and a second surface facing the first surface; and a ground section provided in continuation with the inductor pattern section and configured in a form of a flat plate, the inductor pattern section, the notch section, and the antenna section are formed in the first surface, and the ground section is formed on a surface which is an extended surface of the second surface and does not face the first surface. 
     In this case, by virtue of the fact that the IC chip is provided to bridge both ends of the C-shape, a resonant circuit is formed by the inductor pattern section, capacitances inside the IC chip and the insulating substrate, and an omnidirectional RF tag can be configured. 
     Also, by virtue of the fact that the ground section is formed on the surface which is the extended surface of the second surface and does not face the first surface, a further low-profile configuration can be achieved. 
     (4) 
     In an RF tag antenna in accordance with a fourth invention, which is in the context of the RF tag antennas in accordance with one aspect, the other aspect, and the still other aspect, a periphery length of the antenna section may be λ/2, where λ is a frequency of a target radio wave. 
     In this case, since the periphery length of the antenna section becomes λ/2, where λ is the frequency of the target radio wave, the RF tag having a long communication distance can be provided. 
     (5) 
     An RF tag antenna in accordance with a fifth invention, which is in the context of the RF tag antenna in accordance with any one of the other aspect to the fourth invention, the insulating substrate may be made of dielectric. 
     In this case, since the insulating substrate is configured by dielectric, a small RF tag of several millimeters size can be achieved. 
     (6) 
     In an RF tag antenna in accordance with a sixth invention, which is in the context of the RF tag antenna in accordance with any one from the other aspect to the fourth invention, the insulating substrate may be made of polystyrene foam. 
     In this case, since the insulating substrate is made of polystyrene foam, an RF tag of several-centimeters size can be achieved. Also, by using polystyrene foam, the insulating substrate similar to air can be used. 
     Also, a large opening between the antenna section and the ground section can be ensured. 
     (7) 
     In an RF tag antenna in accordance with a seventh invention, which is in the context of the RF tag antenna in accordance with any one from the other aspect to the sixth invention, the insulating substrate may be configured such that a relative permittivity on the first surface side and a relative permittivity on the second surface side may be different from each other. 
     In this case, since the relative permittivity on the first surface side and the relative permittivity on the second surface side are different from each other, the state is apparently the same as the state where a conductive plate is provided, so that the communication distance for communications with the reading device can be extended. 
     It should be noted that with regard to the characteristics that the relative permittivity on the first surface side and the relative permittivity on the second surface side are different from each other, the components on the first surface side and the second surface side may be changed, two different layers may be used to form the insulating substrate, or the insulating substrate may be formed of one layer, and doping may be performed on one side of the first surface side or the second surface side. 
     (8) 
     In an RF tag antenna in accordance with an eighth invention, which is in the context of the RF tag antenna in accordance with any one from the other aspect to the sixth invention, one or more holes may be formed in the insulating substrate, wherein the holes have the same or different diameters and gradually decrease from the first surface side to the second surface side. 
     In this case, since the one or more holes are formed in the insulating substrate, and the holes have the same or different diameters and gradually decrease from the first surface side to the second surface side, the state is apparently the same as the state where a conductive plate is provided, so that the communication distance for communications with the reading device can be extended. 
     (9) 
     In an RF tag antenna in accordance with a ninth invention, which is in the context of the RF tag antenna in accordance with any one from the other aspect to the sixth invention, the insulating substrate may be formed such that a relative permittivity on the first surface side becomes smaller than a relative permittivity on the second surface side. 
     In this case, since the insulating substrate is formed such that the relative permittivity on the first surface side becomes smaller than the relative permittivity on the second surface side, the state is apparently the same as the state where a conductive plate is provided, so that the communication distance for communications with the reading device can be extended. 
     (10) 
     In an RF tag antenna in accordance with a tenth invention, which is in the context of the RF tag antenna in accordance with any one from the other aspect to the eighth invention, the insulating substrate may be configured such that a layer of polystyrene foam is formed on the first surface side and a layer having a relative permittivity higher than the relative permittivity of the polystyrene foam is formed on the second surface side. 
     In this case, since the insulating substrate is formed such that the relative permittivity on the first surface side becomes smaller than the relative permittivity on the second surface side, the state is apparently the same as the state where a conductive plate is provided, so that the communication distance for communications with the reading device can be extended. 
     (11) 
     An RF tag in accordance with still another aspect includes: the RF tag antenna according to any one of claims  1  to  10 ; and an IC chip provided to bridge both ends of the C-shape of the RF tag antenna. 
     In this case, by virtue of the fact that the IC chip bridges both ends of the C-shape, a resonant circuit is formed by the inductor pattern section, and capacitances inside the IC chip and the insulating substrate. Hence an omnidirectional RF tag can be configured. 
     (12) 
     An RF tag with a conductor in accordance with still another aspect includes: the RF tag antenna according to any one of claims  1  to  10 ; an IC chip provided to bridge both ends of the C-shape of the RF tag antenna; and a conductor connected to a ground section of the RF tag antenna directly or electrically via a capacitance. 
     In this case, by virtue of the fact that the IC chip bridges both ends of the C-shape, a resonant circuit is formed by the inductor pattern section, and capacitances inside the IC chip and the insulating substrate. Further, the conductor can be utilized as an antenna. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view that illustrates an example of an RF tag. 
         FIG. 2  is a schematic perspective view that illustrates an example of a back surface of the RF tag. 
         FIG. 3  is a schematic perspective view for explanation of an example of a configuration of an antenna section. 
         FIG. 4  is a top view that illustrates an example of an expanded view of an RF tag antenna. 
         FIG. 5  is a schematic cross-sectional view that illustrates a state where a sheet member is provided on the RF tag. 
         FIG. 6  is a schematic cross-sectional view that illustrates an example where the RF tag is stuck on an electrically conductive member. 
         FIG. 7  is a schematic diagram that illustrates an example of an equivalent circuit of the RF tag and the electrically conductive member. 
         FIG. 8  is a schematic diagram that shows results of a reading experiment of the RF tag. 
         FIG. 9  is a schematic diagram that illustrates another example of an insulating substrate. 
         FIG. 10  is a schematic cross-sectional view that illustrates still another example of the insulating substrate. 
         FIG. 11  is a schematic diagram that illustrates another example of the case where the RF tag is mounted to the electrically conductive member. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment of the present invention will be described hereinbelow with reference to the drawings. In the following explanations, the same components are indicated by the same reference signs. Also, when the same reference signs are assigned to components, they are the same ones which have the same name and the same function. Accordingly, detailed explanations thereof will not be repeated. 
     Present Embodiment 
       FIG. 1  is a schematic perspective view that illustrates an example of an RF tag  100  in accordance with the present embodiment and  FIG. 2  is a schematic perspective view that illustrates an example of the back surface of the RF tag  100 . 
     As illustrated in  FIG. 1 , the RF tag  100  includes an RF tag antenna  110 , an insulating substrate  140 , and an IC chip  500 . Note that the RF tag  100  of  FIG. 1  may be packed by a sheet member  600  (see  FIG. 5 ). 
     The RF tag antenna  110  includes an antenna section  120 , a ground section  130 , an inductor pattern section  150 , and a short-circuit section  160 . 
     Insulating Substrate  140   
     In the present embodiment, the insulating substrate  140  is made of polystyrene foam. Ideally, it is most preferable to fill with air instead of the insulating substrate but, in order to maintain a predetermined interval between the antenna section  120  and the ground section  130  and prevent them from being brought into contact with each other, it is preferable to utilize polystyrene foam having 90% or more by volume of air. Further preferably, it is closed-cell polystyrene foam having 95% or more by volume and 99% or less by volume of air. 
     As a result of this, the spatial distance between the antenna section  120  and the ground section  130  can be maintained as a predetermined interval. As such an interval, an interval of 0.5 mm or more and 3.0 mm or less is preferable. Also, it is desirable that a relative permittivity of the insulating substrate falls within the range from 1% or more and 20% or less. More desirably, the range is 1.01% or more and 1.20% or less, and most desirably 1.01% or more and 1.10% or less, and further most desirably 1.02% or more and 1.08% or less. In the case where polystyrene foam is used as the insulating substrate  140 , it is preferable that the polystyrene foam has a foaming ratio of 15 times or more to 60 times or less (in this case, the relative permittivity will be 1.01% or more and 1.10% or less). 
     In the case where ceramic (whose relative permittivity is higher than 5% and equal to or less than 9%) is used as the insulating substrate  140 , the opening area of the antenna section  120  and the ground section  130  becomes small and the communication distance is reduced, but reduction in the size of the RF tag  100  can be achieved. 
     On the other hand, in the case where a material having the relative permittivity of 1% or more and 5% or less (in particular, 1.01% or more and 1.20% or less) such as polystyrene foam is used as the insulating substrate  140 , then the opening area of the antenna section  120  and the ground section  130  can be maintained as a large area and the communication distance can be extended to several meters to tens of meters. 
     It should be noted that the thickness of the insulating substrate  140  made of polystyrene foam is desirably in the range between 0.5 mm and 3 mm including these values. 
     It should be noted that, in the present embodiment, while the insulating substrate  140  is made of polystyrene foam, this does not constitute a limitation thereto, and any insulator may be used and other foams or materials having insulating property such as polyethylene, polyimide, and thin foam (volara) may be used. 
     As has been described in the foregoing, with regard to the RF tag antenna  110  in accordance with the present embodiment, since polystyrene foam is used as the insulating substrate  140  of the RF tag antenna  110 , an opening area of a certain size can be provided, and the sensitivity of the plate-shaped antenna can be improved. 
     It should be noted that, in the above-described embodiment, while the case has been described where the polystyrene foam is used as the insulating substrate  140 , dielectric may be used. For example, as dielectric, resin, ceramic, paper, etc. may be used. Further, the insulating substrate may have a foam shape, may have one or numerous cavities, and may be made of composite material in which different materials are mixed or stacked. 
       FIG. 3  is a schematic perspective view for explanation of an example of a configuration of the antenna section  120  and  FIG. 4  is a top view that illustrates an example of an expanded view of the RF tag antenna  110 . 
     Antenna Section  120   
     As illustrated in  FIG. 3 , the antenna section  120  is formed by the region enclosed by a side  121 , a side  122 , a side  123 , a side  124 , a side  125 , a side  126 , a side  127 , and a side  128 . 
     In the antenna section  120  of the present embodiment, the value obtained by adding the total value of the sides  121 ,  122 ,  123 ,  124 ,  125 ,  126 ,  127 , and  128  and the total value of the sides  155 ,  154 ,  153 , and  152 , is the value T. The side  152 , the side  153 , the side  154 , and the side  155  define outer periphery of the inductor pattern section  150 . 
     In other words, as illustrated in  FIG. 4 , the value T can be determined as:  120   a + 120   b + 120   c + 120   d + 120   e + 120   f + 120   g.    
     The value T is designed such that it corresponds to any one of λ/4, λ/2, 3λ/4, and 5λ/8 in case the wavelength λ (lambda) of the radio wave is used. 
     In the present embodiment, the value T is designed as half the length of the wavelength λ of the frequency in use. The wavelength λ can be calculated as “propagation speed (light speed (c))/frequency (F). 
     Specifically, in the case where the frequency is 920 MHz, the propagation speed (light speed (c)) is 300 Mm/s, and the value T will be value T=(300÷920 MHz)/2≈163 mm. 
     In this case, the lengths of the individual sides are adjusted such that the value T becomes 163 mm. Note that, since the value T is an approximate value, the numerical value of the value T as such may have an error of around ±5%. This is because it can be brought into conformity with the design specifications through adjustments though the read distance of the RF tag  100  becomes shorter. 
     Also, in the present embodiment, the first waveguide section is made of an aluminum metal thin film. In general, the thin film in the present embodiment is formed with a thickness in the range from 3 μm to 35 μm including these values. 
     The first waveguide section is formed by techniques such as etching or pattern printing. 
     Ground Section  130   
     Next, as illustrated in  FIG. 2 , the ground section  130  is formed by the region enclosed by a side  131 , a side  132 , a side  133 , and a side  134 . 
     The ground section  130  is made of an aluminum metal thin film. In general, the thin film in the present embodiment is formed with a thickness in the range from 3 μm to 35 μm including these values. 
     The ground section  130  is formed by techniques such as etching or pattern printing. 
     Notch Section  170   
     Also, although a notch section  170  is a spatial region and accordingly is not an element constituting the RF tag antenna  110 , for convenience of explanation, the description will be provided with a reference numeral assigned thereto. 
     The notch section  170  is formed by the region enclosed by the side  128 , the side  127 , the side  126 , the side  125 , the side  155 , the side  154 , the side  153 , the side  152 , and the side  151 . 
     Inductor Pattern Section  150   
     As illustrated in  FIGS. 1 and 3 , the inductor pattern section  150  is configured by a shape obtained by cutting out a portion between a side  161  and a side  162  as part of the circuit of a ring shape. In other words, it is configured by the shape of a C of an alphabetic character. 
     In other words, as illustrated in  FIG. 3 , it is configured by the region enclosed by a side  157 , a side  158 , a side  159 , a side  164 , and a side  166  (internal area S). 
     It should be noted that, with regard to the inductor pattern section  150 , while the case has been described in which the portion between the side  161  and the side  162  is cut out, this does not constitute a limitation thereto, and an insulating section may be formed between the side  161  and the side  162 . 
     In the present embodiment, the inductor pattern section  150  is made of an aluminum metal thin film. In general, the thin film in the present embodiment is formed with a thickness in the range from 3 μm to 35 μm including these values. 
     The inductor pattern section  150  is formed by techniques such as etching or pattern printing. 
     Also, the IC chip  500  is provided such that it bridges the side  161  and the side  162  of the inductor pattern section  150 . 
     In the present embodiment, the impedance of the inductor pattern section  150  can be made constant according to the internal area S of the inductor pattern section  150 . 
     IC Chip  500   
     The IC chip  500  is arranged on the upper surface of the RF tag antenna  110  (to be flush with the antenna section  120 ). The IC chip  500  operates based on the radio wave received by the plate-shaped antenna of the RF tag antenna  110 . 
     Specifically, the IC chip  500  in accordance with the present embodiment first rectifies part of the carrier wave transmitted from a reading device and the IC chip  500  generates a power supply voltage necessary for itself to operate. Then the IC chip  500  causes the logic circuit for control in the IC chip  500  and non-volatile memory that stores product specific information or the like to operate by the power supply voltage that has been generated. Also, the IC chip  500  causes a communication circuit or the like for performing transmission and reception of data with the reading device to operate. 
     Sheet Member  600   
       FIG. 5  is a schematic cross-sectional view that illustrates a state where the sheet member  600  is provided on the RF tag  100  of  FIGS. 1 to 4 . 
     As illustrated in  FIG. 5 , with regard to the RF tag  100 , its peripheral sections may be covered by the sheet member  600 . Here, the peripheral sections refer to the entire peripheral section of the RF tag  100 . Note that covering the entire peripheral sections by the sheet member  600  does not constitute a limitation thereto and only the IC chip  500 , the antenna section  120 , and the ground section  130  may be covered. 
     The sheet member  600  is mainly made of polyethylene terephthalate. It should be noted that, in addition to polyethylene terephthalate, one or more types of materials or resins having insulating property such as polyimide and polyvinyl chloride may also be used as the sheet member  600 . 
     The sheet member  600  is used to protect the antenna section  120  and the ground section  130 . For this reason, the sheet member  600  preferably has a thickness of several micrometers or more and several hundred micrometers or less, more preferably about several tens of micrometers. 
     Accordingly, while the sheet member  600  is to be provided in the present embodiment, this does not constitute a limitation thereto, and the sheet member  600  may not be provided and other insulation coating treatments may be used. 
     RF Tag Antenna  110 , IC Chip  500 , and Electrically Conductive Member  900   
       FIG. 6  is a schematic cross-sectional view that illustrates an example where the RF tag  100  depicted in  FIGS. 1 to 5  is stuck on an electrically conductive member  900 . 
     As illustrated in  FIG. 6 , the RF tag  100  is stuck on the electrically conductive member  900  by means of a conductive adhesive, an adhesive layer  450 , or the like. In the present embodiment, the electrically conductive member  900  is made of a metal plate having conductive property. Specifically, it has any appropriate metal portion such as a metal box, a box or a case containing a metal plate, a box or a case containing a metal member. 
     It should be noted that while the conductive adhesive or the adhesive layer  450  is to be used in  FIG. 6 , this does not constitute a limitation thereto, and it may be a conductive double-sided tape, solder, or, any appropriate conductive adhesives such as 1-component or 2-component epoxy resin. 
       FIG. 7  is a schematic diagram that illustrates an example of an equivalent circuit of the RF tag  100  and the electrically conductive member  900 . 
     As illustrated in  FIG. 7 , with regard to the equivalent circuit of the RF tag  100  and the electrically conductive member  900 , the inductor pattern L of the inductor pattern section  150  and the capacitor C b  configured by an internal capacitance of the IC chip  500  are connected in parallel. The inductor pattern L and the IC chip  500  configures a resonant circuit that resonates in the frequency band of the radio wave transmitted from the reading device. 
     The resonant frequency f (Hz) of this resonant circuit is given by the expression (1). The value of the resonant frequency f is tuned such that it falls within the frequency band of the radio wave transmitted from the reading device. 
     
       
         
           
             
               
                 
                   
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     In the expression (1), L a  represents the inductance of the inductor pattern L, and C b  represents the equivalent capacitance inside the IC chip  500 . 
     Here, some components have a capacitor inside the IC chip  500  and the IC chip  500  has stray capacitance. For this reason, when the resonant frequency f of the resonant circuit is to be specified, the equivalent capacitance C b  inside the IC chip  500  is used. 
     In other words, the resonant circuit has a resonant frequency f that has been set with the inductance of the inductor pattern L and the equivalent capacitance C b  inside the IC chip  500  taken into account. It should be noted that, as the C b , for example, it is possible to use a capacitance value disclosed as one of the specification data of the IC chip to be used. 
     As has been described in the foregoing, by using the equivalent capacitance C b  inside the IC chip  500 , no new capacitor needs to be provided. Also, the resonant frequency f of the resonant circuit can be accurately set in the frequency band of the radio wave. 
     In addition, it is also possible to use the capacitor capacitance C of the insulating substrate  140 . As a result, the reading performance of the RF tag  100  can be further improved. Also, the power supply voltage generated by the IC chip  500  can be further increased. 
     Also, as illustrated in  FIG. 7 , since the electrically conductive member  900  can be used in the same or similar manner as the antenna section  120 , the radio wave of the reading device can be received from either the front surface side or the back surface side of the electrically conductive member  900 . 
     It should be noted that while the case has been described in the present embodiment where the sheet member  600  is disposed between the ground section  130  of the RF tag  100  and the electrically conductive member  900 , they may be electrically connected to each other either directly or indirectly. 
     Further, in the present embodiment, the electrically conductive member  900  may be made of a metal plate. Note that, with regard to the “conductor” in the context of the present application, a typical example thereof is “electrical conductivity, metal” in the same manner as in a general lexical meaning. However, the “conductor” is not limited to metal and may be, for example, a human body, a plant, water, the ground, etc. 
       FIG. 8  is a schematic diagram that shows the results of the reading experiment of the RF tag  100  described in  FIGS. 1 to 7 . 
     The symbol  100 M in  FIG. 8  is a curve which indicates a relationship between a frequency (horizontal axis) and a theoretical reading distance (m) (vertical axis) in the case where the reading experiment is done using the reading device from the front surface side of the RF tag  100  in accordance with the present embodiment. 
     And the symbol  101 M is a curve which indicates a relationship between a frequency (horizontal axis) and a theoretical reading distance (m) (vertical axis) in the case where the reading experiment is done using the reading device from the back surface side of the RF tag  100  in accordance with the present embodiment. 
     The symbol  100 N is a curve which indicates a relationship between a frequency (horizontal axis) and a theoretical reading distance (m) (vertical axis) in the case where the reading experiment is done using the reading device from the front surface side of a in-house RF tag (product name 06) of an inverted-F antenna type. 
     And the symbol  100 M is a curve which indicates a relationship between a frequency (horizontal axis) and a theoretical reading distance (m) (vertical axis) in the case where the reading experiment is done using the reading device from the back surface side of the in-house RF tag (product name 06) of the inverted-F antenna type. 
     As illustrated in  FIG. 8 , the RF tag  100  in accordance with the present embodiment is capable of reading with a distance of 13 m if the reading device is used from the front surface side (solid line  100 M). 
     On the other hand, if the reading device is used from the back surface side (solid line  101 M), the RF tag  100  is capable of reading with a distance of 7 m. 
     As a result of this, it has been revealed that the RF tag  100  in accordance with the present embodiment exhibits the same or better performance as the in-house inverted F antenna type RF tag in the case where the reading device is used both from the front surface side (broken line  100 N) and from the back surface side (broken line  101 N). 
     Insulating Substrate 
       FIG. 9  is a schematic diagram that illustrates another example of the insulating substrate  140 . 
     As illustrated in  FIG. 9 , the insulating substrate  140  may be made of a laminate of a polystyrene foam material  145  and a resin material  146 . In the present embodiment, the polystyrene foam material  145  is stacked on the antenna section  120  side, but the resin material  146  may also be stacked on the antenna section  120  side. 
     In the present embodiment, the polystyrene foam material  145  and the resin material  146  are both designed to have the same size length. In the present embodiment, ABS was used as the resin material. Note that ABS is used in the present embodiment but this does not constitute a limitation thereto, and polyethylene, polypropylene, polyvinyl chloride, ceramic, paper, etc. may be used. 
     Specifically, in the polystyrene foam material  145 , the wavelength λ1 is calculated assuming that the relative permittivity of the polystyrene foam material  145  εa is 1.0 and the frequency is 900 MHz. 
     As a result of this, since the antenna section  120  stuck on the polystyrene foam material  145  is not influenced by the relative permittivity, the wavelength λ1 will be λ1=(300/920 MHz)/1 2 ≈333 mm. 
     Meanwhile, in the resin material  146 , the wavelength λ2 is calculated assuming that the relative permittivity of the resin material  146  εb is 5.0, the frequency is 900 MHz, and propagation speed is 300 Mm/s. 
     As a result of this, in the resin material  146 , the wavelength λ2 will be λ2=(300/920 MHz)/5 2 ≈149 mm. 
     It should be noted that ceramic, paper, etc. may be used instead of the resin material  146 . 
     Here, since the value T1 of the antenna section  120  is 333 mm, resonance will take place at 402 MHz of the wavelength 333/149≈2.23 times longer. 
     In other words, this is equivalent to a state where the apparently 744 mm-long ground section  130  is formed. 
     As a result of this, the state can be made to be the same as the state where the RF tag  100  is mounted to a conductive member  900 , and the RF tag  100  having a sufficient communication distance for metal or non-metal applications can be achieved. 
     Insulating Substrate 
       FIG. 10  is a schematic cross-sectional view that illustrates still another example of the insulating substrate  140 . 
     As illustrated in  FIG. 10 , the insulating substrate  140  has a front surface  141  and a back surface  142 . 
     Also, it has one or more holes  143  whose diameter gradually decreases from the front surface  141  to the back surface  142 . Here, the hole  143  is not limited to the one whose diameter continuously decreases and may encompass those the diameter of which decreases in a stepwise fashion. According to such a structure, the insulating substrate  140  is obtained whose relative permittivity differs in the direction of the thickness of the insulating substrate  140 . In the embodiment illustrated in  FIG. 10 , the insulating substrate  140  is obtained whose relative permittivity decreases sequentially toward the antenna section  120  side. 
     In the present embodiment, the case is explained where the hole  143  has a stepwise or conical shape but this does not constitute a limitation thereto, and the hole  143  may be a cylinder, rectangular cylinder, or elliptical cylinder which does not penetrate the insulating substrate  140  from the front surface  141  to the back surface  142  or may also be a conical cylinder, pyramidal cylinder, or elliptical conical cylinder which does not penetrate or penetrates the insulating substrate  140  from the front surface  141  to the back surface  142 . 
     Further, the shape of a cavity portion of the hole may change from the front surface  141  to the back surface  142 . For example, on the front surface  141  side, the hole may be a star-shaped hole and the cross section of the hole may change to a shape of a circle toward the back surface  142  side. 
     Also, in  FIG. 10 , the explanations are given based on the case where the diameters of the holes  143  are the same, but this does not constitute a limitation thereto, and it may be the same or different. 
       FIG. 11  is a schematic diagram that illustrates another example of the case where the RF tag  100  is mounted to the electrically conductive member  900 . 
     As illustrated in  FIG. 11 , the antenna section  120  of the RF tag  100  may be extended until it reaches the back surface side of the insulating substrate  140  and the ground section  130  of the extended RF tag  100  may be mounted to the electrically conductive member  900 . In this case, a low-profile configuration can be achieved. 
     As described above, by changing the relative permittivity on the side of the front surface  141  and the relative permittivity on the side of the back surface  142 , apparently, the ground section  130  which is longer than a predetermined length will be formed, so that the RF tag  100  having a sufficient communication distance for metal or non-metal applications can be achieved. 
     As has been described in the foregoing, according to the RF tag  100  and the electrically conductive member  900 , since the electrically conductive member  900  can be utilized as the antenna section  120  and a large opening area can be provided, the sensitivity of the RF tag  100  can be improved. 
     Also, since the electrically conductive member  900  can be utilized as the antenna section  120 , it is made possible to perform reading by the reading device from the back surface side of the RF tag  100  on which the electrically conductive member  900  is provided. 
     In the present embodiment, the IC chip  500  corresponds to the “IC chip”, the RF tag antenna  110  corresponds to the “RF tag antenna”, the inductor pattern section  150  corresponds to the “inductor pattern section”, the notch section  170  corresponds to the “notch section”, the antenna section  120  corresponds to the “antenna section”, the ground section  130  corresponds to the “ground section”, the front surface  141  corresponds to the “first surface”, the back surface  142  corresponds to the “second surface”, the insulating substrate  140  corresponds to the “insulating substrate”, the value T corresponds to the “periphery length of the antenna section”, the resin material  146  corresponds to the “dielectric”, the polystyrene foam material  145  and the polystyrene foam correspond to the “polystyrene foam”, the hole  143  corresponds to the “one or more holes”, RF tag  100  corresponds to the “RF tag”, the electrically conductive member  900  corresponds to the “conductor”, and the electrically conductive member  900  and the RF tag  100  correspond to the “RF tag with a conductor”. 
     Whilst one preferred embodiment of the present invention has been described in the foregoing, the present invention is not limited thereto. It will be appreciated that other various embodiments may be conceived without departing from the purport and scope of the present invention. Further, while the operations and effects achieved by the features of the present invention have been described in the present embodiment, these operations and effects are merely examples by which the present invention is in no way limited. 
     REFERENCE SIGNS LIST 
     
         
           100  RF tag 
           110  RF tag antenna 
           120  antenna section 
           130  ground section 
           140  insulating substrate 
           141  front surface 
           142  back surface 
           143  hole 
           145  polystyrene foam material 
           146  resin material 
           150  inductor pattern section 
           170  notch section 
           500  IC chip 
           900  electrically conductive member 
         T value