Abstract:
The present invention is aimed at providing a wireless identification tag which can save information with high reliability that is free from the possibility of being lost or falsified, is not broken or melt in the concrete, can expand directionality of an antenna, be distributed in a cement product to be in an appropriate condition for radio communication, and has good adhesion and affinity with cement or the like. A wireless identification tag  1  mixed in a cement product in the manufacturing procedure thereof in which cement, an aggregate, water, or the like are mixed including a protection body  2  incorporating the wireless identification tag  1  having an antenna portion which can write/read information by radio communication, wherein a concave portion  3  is provided on the surface of the protection body.

Description:
BACK GROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a wireless identification tag used for a quality control system or the like of a concrete product or an architectural structure. Especially, the present invention relates to a wireless identification tag, which is mixed in a production procedure of a cement product in which cement, an aggregate, water or the like are mixed to be used in an architectural structure, using a nonvolatile memory device (FeRAM) having an antenna portion that enables writing/reading of various information such as information regarding a cement product when manufactured. 
     2. Prior Art 
     In a concrete product or a concrete architectural structure related to civil engineering, information such as concrete strength or history of engineering works needs to be examined in case of maintenance or a disaster such as earthquake. Such information has been recorded on paper to be managed with a drawing or the like. However, there is a possibility that the papers are lost or information therein is falsified. Moreover, in recent years, such information is recorded in a database of a computer other than on paper. However, even this cannot prevent possibility of loss or falsification and therefore a conventional concrete quality management system is not exactly reliable for an owner of the concrete architectural structure or a user of the system. 
     Moreover, a method of attaching an IC tag in which distribution management information of an architectural material or the like is recorded to an architectural material or a wall of the architectural structure (e.g., Patent Document 1) or a method of embedding a wireless identification tag in concrete before being hardened (e.g., Patent Documents 2 and 3) has been known. In addition, a wireless identification tag which is mixed in a cement product during a manufacturing procedure thereof in which cement, an aggregate, water, or the like are mixed has been invented (Patent Document 4). 
     [Patent Document 1]: Japanese Unexamined Patent Application Publication No. 2004-141483 
     [Patent Document 2]: Japanese Unexamined Patent Application Publication No. 2005-330729 
     [Patent Document 3]: Japanese Unexamined Patent Application Publication No. 2006-183257 
     [Patent Document 4]: Japanese Unexamined Patent Application Publication No. 2008-63900 
     However, in a case where an IC tag is attached or embedded as in the above-mentioned conventional methods, the IC tag may be exposed from the surface of an architectural material or a wall. Moreover, there is a possibility that the IC tag is broken or lost because it has to be passed through various persons until the tag is provided in the architectural structure and there is also a possibility that information recorded in the IC tag is falsified or the IC tag is replaced by another IC tag in which falsified information is recorded. In addition, in a case where a conventional IC tag is put into concrete, because of its thin and flat shape, there is a possibility that the tag is broken by the great stress applied when the concrete is mixed or cast. Further, in the conventional flat IC tag, a flat antenna is provided on the surface thereof. Because directionality of the antenna in radio communication reaches its peak in a direction orthogonal to the surface of the IC tag, sensitivity is lowered as the IC tag leans, and in a direction parallel to the IC tag surface, neither transmission nor reception can be carried out. Such a narrow directionality has been a problem. 
     A wireless identification tag to be mixed in a cement product, in which cement, an aggregate, water, or the like are mixed, in the manufacturing procedure has been developed. However, in a wireless identification tag to be mixed in the manufacturing procedure of a cement product, if the wireless identification tags concentrate inside of the cement product, it becomes impossible to correctly write/read information and to appropriately carry out radio communication. As a method to extend communication range, for example, it becomes possible to write in/read out information in a long distance if information communication by UHF band or shortwave band is carried out. However, in this case, there occurs a problem such as lowered information storage capacity or strengthened directionality. Therefore, it is required of a wireless identification tag to be distributed in a cement product as evenly as possible and also to be provided in the vicinity of the surface of the cast cement product. 
     Further, for a wireless identification tag mixed in a manufacturing procedure of a cement product to reduce the influence of the wireless identification tag to the cement product strength, it is required to improve adhesion between the cement product and the wireless identification tag. Further, the wireless identification tag itself is required of having strength to endure power applied when cement, an aggregate, water, or the like are mixed or when the mixture is cast, anti-alkaline property enough to endure alkaline property of the cement, and heat-resistance property enough to endure heat generated when mixed. 
     SUMMARY OF INVENTION 
     Therefore, to solve the above-mentioned problems, the present invention is aimed at providing a wireless identification tag to be mixed with cement or the like which can save information with high reliability that is free from the possibility of being lost or falsified, has strength, anti-alkaline property, and heat-resistance property enough to endure mixture with cement or casting of cement, is not broken or melt in the concrete, can expand directionality of an antenna, is distributed in a cement product to be in an appropriate condition for radio communication, and has good adhesion and affinity with cement or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       [ FIG. 1 ] A plan view of a wireless identification tag of the present invention. 
       [ FIG. 2 ] A side view of the wireless identification tag shown in  FIG. 1 . 
       [ FIG. 3 ] A cross-sectional view taken along A-A line of the wireless identification tag shown in  FIG. 1 . 
       [ FIG. 4 ] A cross-sectional view taken along B-B line of the wireless identification tag shown in  FIG. 1 . 
       [ FIG. 5 ] An illustration of a wireless identification tag of a second embodiment of the present invention. 
       [ FIG. 6 ] An illustration of a wireless identification tag of a second embodiment of the present invention. 
       [ FIG. 7 ] An illustration of a concrete quality management system using the wireless identification tag of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view of a wireless identification tag of the present invention,  FIG. 2  is a side view,  FIGS. 3 and 4  are cross-sectional views and  FIG. 5  is a conceptual diagram of a concrete quality management system using the wireless identification tag of the present invention. 
     A wireless identification tag  1  includes a wireless identification tag main body which is covered with a protection body having cubic shape such as sphere, oval, or polyhedron shape (e.g., icosadodecahedron) to have a size of between several millimeters to several tens of millimeters and glass bead-like shape. On the surface of the protection body, a concave portion is formed. 
     In the wireless identification tag  1  of an embodiment of the present invention, a wireless identification tag main body  4  having a shape of a chip is covered with a protection body  2  including thermoplastic resin and the protection body  2  is shaped to have a cubic shape, in the present embodiment, to have an approximately oval shape (straw rice bag shape). The surface of the protection body  2  is dimple processed to provide a plurality of concave portions  3 . 
     The wireless identification tag main body  4  of the embodiment of the present invention is a chip-shaped FeRAM tag including a FeRAM which is a nonvolatile memory using a ferroelectric substance, a power source unit for generating electric current by receiving radio wave from outside and resonating with the radio wave instead of including a battery, an antenna portion for carrying out radio communication in a predetermined frequency bandwidth, and a control unit for controlling them. The FeRAM, the power source unit, and the control unit are mounted on a substrate and covered with an insulating material. Therefore, it is possible to write/read a large amount of information in/from the wireless identification tag main body  4  itself. 
     Compared to an EEPROM used for a conventional IC tag, the FeRAM has a superior performance that enables to rewrite 10 13  times or more, while the EEPROM is enabled to rewrite only 10 5  times or so. Moreover, voltage for writing of the conventional EEPROM is 12V while that for the FeRAM is between DC 1.1V and 3V, which is very low. The FeRAM does not need to include a battery, is sufficient enough to be a passive type which includes a power source unit for generating power by resonating to a radio wave from outside, and has writing speed which is 5000 times faster than the EEPROM used for a conventional IC tag. Data retention period of the FeRAM is 10 years or more. Moreover, when accessed for rewriting, while writing is carried out as a block for a conventional EEPROM or flash memory, the FeRAM can randomly rewrite by a word. The control unit for controlling writing in the FeRAM enables to add information but blocks overwriting so that information which has been written in is not falsified. It is preferable that writing and reading of data is carried out by use of encrypted protocol. Therefore, it is possible to write/read information regarding the architectural structure or other various kinds of information other than information regarding the cement product in about 8 KB memory capacity by use of a write/read apparatus by radio communication any time. 
     In the wireless identification tag  1 , bandwidth of radio wave for radio communication is not especially limited and any bandwidth from LF band to UHF band can be used. However, in the present embodiment, because the wireless identification tag  1  has specific gravity and shape that allows the tag  1  to float on the surface of the cement product as described later, the tag  1  is suitable for radio communication by long wave band which has weak directionality and is relatively not influenced by water, dust, or metal. A reader/writer unit for writing/reading information between the wireless identification tag  1  is a write/read unit for carrying out writing/reading of information by use of electromagnetic induction which occurs between coils. 
     A concave portion  3  is formed on the surface of the protection body  2 . There are a plurality of fine concave portions provided on the surface of the protection body  2  which are dimple processed and a cement product flows into the concave portions to obtain adhesion and affinity between the wireless identification tag  1  and the cement product. Moreover, formation of the concave portion  3  enables to improve strength of the wireless identification tag. In the present embodiment, on 25 spots of both surfaces of the wireless identification tag, that is, a total of 50 spots are dimple processed in injection molding. However, the dimple processing may be carried out to all over the surfaces or part thereof. In addition, depth of the concave portion in the present embodiment is between 0.2 and 0.5 mm or so. However, the present invention is not limited thereto. The concave portion is not limited to dimple processing and a concave hole may be provided on the protection body  2  or a concave portion may be provided by causing the protection body  2  to be curved or by causing the protection body  2  to have a concave lens shape. 
     It is preferable that specific gravity of the wireless identification tag  1  is within a range between 1.3 and 1.9 and in the present embodiment, the specific gravity is set to 1.5. According to a distribution test of the wireless identification tag  1  in concrete, if the tag is formed to have the specific gravity of 1.3 or less, the wireless identification tag  1  floats in the cement product and there is a possibility that the tag is exposed from the cement product surface. If the tag is formed to have the specific gravity of 1.9 or more, the wireless identification tag  1  is not distributed in the cement product and sinks or unevenly distributed therein. It is confirmed that a wireless identification tag  1  having a specific gravity of around 1.5 is distributed in the vicinity of the cement product surface most evenly. That is, in a cement product manufacturing procedure in which an aggregate, cement, water, or the like are mixed, when a plurality of wireless identification tags  1  having specific gravity of 1.5 were thrown into a cement product of 1 cubic meter, the wireless identification tags were provided in a position which was 9.3 cm from the cement product surface on average and standard deviation of 3.826, medium value of 8.00, minimum value of 4.17, and maximum value of 11.83 were obtained. Therefore, even in case of a wireless identification tag  1  having 10 cm or so of writing/reading distance in radio communication, writing/reading of information can be carried out without fail (Table 1). 
     It is preferable that the size of the wireless identification tag  1  is almost same as an aggregate with a cubic volume of between 100 and 300 mm 3 . In the present embodiment, the tag  1  is formed to have an approximately oval shape (straw rice bag shape) with 17 mm in longitudinal direction and 12 mm in lateral direction, affinity of the tag  1  with the cement product is improved, and the tag  1  does not sink in the cement product. The protection body  2  includes thermoplastic resin material and covers a wireless identification tag main body  4  so that the main body  4  is positioned at the center of the protection body  2 . Specifically, the protection body  2  uses alkaline fast resin material which can resist against strong alkaline property of cement with PH 12.0 to 13.0 and temperature of about 100° C. applied when an aggregate, water, cement, or the like are mixed. In the embodiment of the present invention, polyamide resin is used. Especially, when polyamide MXD6 composite resin is used as a material of the protection body  2 , the protection body  2  shows superior mechanical strength and elasticity modulus in a wide temperature range and it is confirmed that change in dimension or degradation in mechanical strength by absorption of water was low when mixed with an aggregate, water, cement, or the like. Here, reny (product of Mitsubishi Engineering-Plastics Corporation) in which polyamide MXD6 composite resin is strengthened by impermeable glass fiber, inorganic filler, or the like is used as the protection body  2  and the wireless identification tag is covered with the protection body  2  to be injection molded. In this case, it is confirmed that the wireless identification tag  1  covered with the protection body  2  to be injection molded can endure load of an average of 197 kgf in longitudinal direction and at least an average of 148 kgf in lateral direction. Moreover, according to an expansion test of the tag by facilitation of alkali-aggregate reaction, if the wireless identification tag  1  was put into the manufacturing procedure of a cement product including an aggregate, water, cement, or the like, an average expansion rate was 0.49%, which hardly gives influence on the cement product after hardened. Moreover, although the protection body  2  includes impermeable glass fiber, any substance having magnetic property such as ferrite is not included. Therefore, there is no influence on radio communication. Here, the thermoplastic resin to be used for the protection body  2  may be, other than polyamide resin, urethane resin, vinyl chloride resin, styrene resin, olefin resin, polyester resin, or the like. 
     Further, as a second embodiment of the present invention, a wireless identification tag  5  includes a FeRAM  51  which is a nonvolatile memory using a ferroelectric substance, instead of including a battery, a power source unit  52  for generating electric current by receiving radio wave from outside and resonating with the radio wave, an antenna portion  53  for carrying out radio communication, and a control unit  54  for controlling them. These components may be provided on a curved surface (or on a bent curvature) of the wireless identification tag having cubic shape along the curvature and be covered with a coating body  6  having a concave portion for protection of the components. If the antenna portion  53  is formed on the curvature, it becomes possible to carry out writing/reading of information without fail. 
     The wireless identification tag  1  having such a configuration is used, for example, in a concrete quality management system. First, a plurality of wireless identification tags  1  in an initial condition are prepared in a ready-mixed concrete company. The tags  1  are mixed in a cement product in the manufacturing procedure in which cement, an aggregate such as gravel, water, or the like are mixed with a ratio of, for example, one tag per one cubic meter. Then, an automatic measuring apparatus provided in a measuring procedure of the cement product measures product characteristic value of the cement product such as water/cement ratio of the cement product, cement admixture, and temperature, and at the same time an IC tag writing apparatus connected to the automatic measuring apparatus automatically writes manufacture information including the product characteristic value measured by the automatic measuring apparatus, manufactured date, and the like in the wireless identification tag  1  when the tag is mixed in. Moreover, the manufacture information written in the wireless identification tag  1  may also be recorded in a central management server  7  for central management of the concrete quality management system depending on the necessity for data link. 
     The cement product in which the wireless identification tags  1  are mixed is carried on the mixer truck  9  and a transporter or the like writes in transportation information such as transportation date in the wireless identification tags  1  mixed in the cement product in the mixer truck  9  by use of the IC tag writing apparatus incorporated in a personal digital assistance (PDA) and set to radio communicate with the tags  1  using an encrypted signal. 
     When the mixer truck  9  arrives at the construction site, a personnel at the site writes in receiving information such as receiving date, test result, and confirmation of mixture of a tag, in the wireless identification tags  1  by use of the IC tag writing apparatus incorporated in a PDA, using an encrypted signal and depending on the necessity, records the information in the central management server  7 . Then, the cement product in which the wireless identification tags  1  are mixed is cast and a concrete building is built. It becomes possible for a general contractor which is in charges of the construction to add record and read building information such as bar arrangement data any time by the unit of construction zone or part of the building using an IC tag write-in unit  10  provided there. After the concrete building is thus complete, it is possible to read various information recorded in the wireless identification tag  1  in the concrete building by use of an IC tag read-out unit  11  which is incorporated in a PDA and set to radio communicate with the tags  1  using an encrypted signal. Moreover, the above-mentioned central management server  7  controls information written in the plurality of wireless identification tags  1  in a plurality of construction sites and provides the information to an constructor, client of the construction, a user, each of industry groups, or the like. Further, in an open memory space which is left open after information regarding the cement product has been written in, wiring information of the building, local information, or other various information may be written in depending on the necessity. 
     According to the above-mentioned configuration, on the surface of a protection body of the present invention which incorporates a wireless identification tag, which is mixed in a cement product in the manufacturing procedure thereof in which cement, an aggregate, water, or the like are mixed and includes an antenna portion for enabling writing/reading of information by radio communication, a concave portion is provided so that cement fills the concave portion provided on the protection body surface to improve adhesion between the wireless identification tag and the cement product. Therefore, the wireless identification tag does not influence the strength of the cement product after hardened and a problem such as collapse of the cement product from the portion where the wireless identification tag is mixed in does not occur. Moreover, it is possible to improve strength of the wireless identification tag itself and the incorporated wireless identification tag is not damaged. 
     The concave portion provided on the protection body surface is formed by dimple processing a plurality of dimples provided on the protection body surface so that cement fills in each of a plurality of fine concave portions provided on the protection body surface to improve adhesion and affinity between the wireless identification tag and the cement product. Moreover, since the concave portion is dimple processed, it becomes possible to equally provide concave portions on the surface of the wireless identification tag and, for example, it becomes possible to form the concave portion simultaneously with the injection molding of the protection body in which the wireless identification tag main body is incorporated. 
     The wireless identification tag is formed to have specific gravity of between 1.3 and 1.9 so that the wireless identification tags can be equally distributed in the vicinity of the surface of the concrete product without sinking in the bottom of the cement product or eccentrically located therein. Therefore, after the cement product is hardened, writing/reading by the IC tag read-out apparatus or write-in apparatus can be carried out without fail. 
     The wireless identification tag is caused to have a cubic volume of between 100 and 300 mm 3  so that the wireless identification tags are mixed with an aggregate such as gravel and equally distributed to have a condition suitable for radio communication in the vicinity of the surface of the cement product without sinking in the bottom of the cement product or eccentrically located therein. Therefore, after the cement product is hardened, writing/reading by the IC tag read-out apparatus or write-in apparatus can be carried out without fail. The protection body includes thermoplastic resin material having anti-alkaline property and therefore even if the protection body is mixed in alkaline cement with PH 12 to 13, the wireless identification tag is not melt or expanded. Therefore, the wireless identification tag is not broken or damaged and strength of the cement product is not influenced. The protection body includes thermoplastic resin material strengthened by glass fiber or inorganic filler. Therefore even if the protection body is mixed in strong alkaline cement, the wireless identification tag is not melt or expanded. Moreover, change in dimension or decrease in strength of the protection body due to absorption of water is small and the protection body can resist against force generated when mixed or compression force applied when cement is cast. Therefore, the wireless identification tag is not broken or damaged and strength of the cement product is not influenced. 
     The protection body has a sphere, oval, or polyhedron cubic shape to resist against force generated when mixed with cement, aggregate, water, or the like or compression force applied when cement is cast. Therefore, the wireless identification tag is not broken or damaged. 
     The wireless identification tag main body includes a so-called FeRAM having a semi-conductor memory device which has semi-conducting material having nonvolatile function and a power source unit for generating electric current by resonating with the received radio wave without incorporating a battery so that faster reading/writing and larger amount of information recording compared to a conventional EEPROM can be carried out. Moreover, low-voltage driving and low power consumption are enabled, the wireless identification tag itself has longer life, and reading/writing of information can be carried out for a long period of time after casting concrete. 
     The wireless identification tag main body has a chip shape including a semi-conductor substrate mounting a semi-conductor which is covered with an insulating material. Therefore, strength of the tag main body can be maintained in the protection body. 
     The antenna portion is formed to have curved surface shape so that directionality of the antenna is expanded compared to a plain antenna for ease of radio communication. 
     The antenna portion is formed to have curved surface shape along cubic shape of the protection body so that directionality of the antenna is further expanded and radio communication can be carried out without fail. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Experiment on distribution of wireless identification tags in 
               
               
                 concrete. Specific gravity: 1.5 
               
             
          
           
               
                   
                 Distance from 
                   
                 Distance from 
               
               
                   
                 right side of 
                 Distance from 
                 upper side of 
               
               
                   
                 front (cm) 
                 front (cm) 
                 front (cm) 
               
               
                   
                   
               
             
          
           
               
                   
                 1 
                 30 
                 3 
                 10 
               
               
                   
                 2 
                 40 
                 10 
                 10 
               
               
                   
                 3 
                 30 
                 10 
                 10 
               
               
                   
                 4 
                 40 
                 10 
                 15 
               
               
                   
                 5 
                 50 
                 10 
                 15 
               
               
                   
                 6 
                 84 
                 9 
                 15 
               
               
                   
                 7 
                 55 
                 15 
                 20 
               
               
                   
                 8 
                 65 
                 15 
                 25 
               
               
                   
                 9 
                 20 
                 7 
                 30 
               
               
                   
                 10 
                 40 
                 7 
                 30 
               
               
                   
                 11 
                 75 
                 2 
                 30 
               
               
                   
                 12 
                 80 
                 14 
                 45 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Description of the reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. 
                 Wireless identification tag 
               
               
                 2. 
                 Protection body 
               
               
                 3. 
                 Concave portion 
               
               
                 4. 
                 Wireless identification tag main body 
               
               
                 5. 
                 Wireless identification tag 
               
               
                 51. 
                 FeRAM 
               
               
                 52. 
                 Power source unit 
               
               
                 53. 
                 Antenna portion 
               
               
                 54. 
                 Control unit 
               
               
                 6. 
                 Coating body 
               
               
                 7. 
                 Concrete quality management system 
               
               
                 8. 
                 Central management server 
               
               
                 9. 
                 Mixer truck 
               
               
                 10. 
                 IC tag write-in unit 
               
               
                 11. 
                 IC tag read-out unit