Abstract:
A tag includes a housing, an antenna disposed within the housing, and circuitry within the housing that is electrically coupled to the antenna. A battery within the housing is electrically coupled to the circuitry, the battery being positioned so as to avoid significant interference with electromagnetic fields associated with the antenna. A tag holder can be detachably coupled to a radio frequency tag, and has structure facilitating attachment of the tag holder to an object other than a tag. A tag includes a circuit and an antenna, the antenna having a plurality of conductive segments and capacitors that are coupled in series to form an endless loop.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to radio frequency identification (RFID) technology and, more particularly, to a configuration for an RFID Tag.  
       BACKGROUND  
       [0002]     One known application for radio frequency identification (RFID) technology is to track a mobile object, such as a shipping container. A device known as a “tag” is provided on the object to be tracked. The tag typically includes circuitry coupled to an antenna, and a battery to power the circuitry. The tag can transmit radio signals, and some tags can also receive radio signals. Existing tags have been generally adequate for their intended purposes, but have not been satisfactory in all respects.  
       SUMMARY OF THE INVENTION  
       [0003]     One of the broader forms of the invention involves an apparatus having a tag that includes: a housing; an antenna disposed within the housing; circuitry disposed within the housing and electrically coupled to the antenna; and a battery disposed within the housing and electrically coupled to the circuitry, the battery being positioned so as to avoid significant interference with electromagnetic fields associated with the antenna.  
         [0004]     Another of the broader forms of the invention involves an apparatus having a tag holder that can be detachably coupled to a radio frequency tag, and that has structure facilitating attachment of the tag holder to an object other than a tag.  
         [0005]     Still another of the broader forms of the invention involves an apparatus with a tag that includes a circuit and an antenna, the antenna having a plurality of conductive segments and a plurality of capacitors that are coupled in series to form an endless loop.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which:  
         [0007]      FIG. 1  is a diagrammatic perspective view of an apparatus that is a radio frequency identification (RFID) tag, and that embodies various different aspects of the invention.  
         [0008]      FIG. 2  is a diagrammatic perspective view of the tag, taken from a different direction.  
         [0009]      FIG. 3  is a sectional view, taken along the section line  3 - 3  in  FIG. 2 .  
         [0010]      FIG. 4  is a diagrammatic fragmentary side view of a selected portion of the tag.  
         [0011]      FIG. 5  is a diagrammatic perspective bottom view of the tag, with a housing bottom part removed so that the interior of the tag is visible.  
         [0012]      FIG. 6  is a diagrammatic perspective bottom view of the housing bottom part.  
         [0013]      FIG. 7  is a diagrammatic exploded perspective view of a top part of the housing, showing an underside thereof.  
         [0014]      FIG. 8  is a diagrammatic exploded perspective view of the tag, with the bottom part omitted for clarity.  
         [0015]      FIG. 9  is a diagrammatic fragmentary sectional view showing a portion of  FIG. 3  in an enlarged scale, and also showing an end portion of a serial cable coupled to a serial interface connector of the tag.  
         [0016]      FIG. 10  is a diagrammatic perspective view showing the tag with an optional tag holder.  
         [0017]      FIG. 11  is a diagrammatic fragmentary view of one half of a main circuit board, showing details of the structure of a loop antenna thereon.  
         [0018]      FIG. 12  is a diagrammatic perspective view showing the upper side of the housing bottom part.  
     
    
     DETAILED DESCRIPTION  
       [0019]      FIG. 1  is a diagrammatic perspective view of an apparatus that is a radio frequency identification (RFID) tag  10 .  FIG. 2  is a diagrammatic perspective view of the tag  10 , taken from a different direction.  FIG. 3  is a sectional view of the tag  10 , taken along the section line  3 - 3  in  FIG. 2 .  
         [0020]     The tag  10  includes an elongate housing  12  having a top part  13  and a bottom part  14  ( FIG. 3 ). The housing parts  13  and  14  are each made from a high-impact plastic material that is rigid and durable. A variety of suitable plastics and other materials are known to persons skilled in the art. During final assembly of the tag, the top and bottom parts  13  and  14  are ultrasonically welded to each other using known techniques, in order to secure the parts  13  and  14  together, and in order to seal the interior of the housing from external environmental factors such as moisture, humidity, dust, and so forth.  
         [0021]     As best seen in  FIG. 3 , the top part  13  of the housing has a top wall  17 , and two sidewalls  18  and  19  that extend downwardly from opposite sides of the top wall  17 . The sidewalls  18  and  19  extend at an angle to each other. Consequently, the housing  12  is somewhat wedge-shaped, and tapers in width in an upward direction. In the disclosed embodiment, the sidewall  19  is oriented to extend at an angle of approximately 60° with respect to the plate-like bottom part  14 .  
         [0022]     As best seen in  FIGS. 1 and 2 , the housing top part  13  has approximately vertical end walls  21  and  22  provided at opposite ends thereof. A flange  23  extends around the entire periphery of the lower end of the top part  13 , or in other words along lower edges of the sidewalls  18 - 19  and the end walls  21 - 22 .  
         [0023]     The housing top part  13  has two concave recesses  26  and  27  located in diametrically opposite corners. At each of these corners, the flange  23  has a respective vertical hole  28  or  29  extending therethrough. Not-illustrated screws or bolts can be inserted through the holes  28  and  29  in order to fixedly mount the tag  10  on any of a variety of different types of objects, for example a not-illustrated shipping container of a known type. The concave recesses  26  and  27  provide sufficient space so that a mounting screw or bolt can be easily accessed with a screwdriver or a wrench.  
         [0024]     With reference to  FIGS. 1 and 2 , the housing  12  includes a removable battery cover  33 , which is physically separate from the top and bottom parts  13  and  14 . In the disclosed embodiment, the battery cover  33  is made from the same material as the top and bottom parts  13  and  14 , but it could alternatively be made from any other suitable material. The battery cover  33  threadedly engages an opening that is provided in the end wall  22  of the top part  13 , as discussed in more detail later. The battery cover  33  has a slot  34 . A not-illustrated coin or screwdriver can be manually inserted into the slot  34 , in order to facilitate manual rotation of the battery cover  33  for the purpose of removing and installing it. The peripheral edge of the battery cover  33  is knurled, as shown at  35 , so that a person can get a good manual grip on the battery cover  33  for the purpose of removing or installing it.  
         [0025]     A projection  41  extends horizontally outwardly from the sidewall  18 , at a location near the top of the sidewall  18 , and spaced a short distance from the concave recess  26 .  FIG. 4  is a diagrammatic fragmentary side view of a portion of the tag  10 , including the projection  41 . As best seen in  FIGS. 3 and 4 , the projection  41  has an end surface  40  at the outer end thereof. A recess  42  extends horizontally into the projection  41  from the end surface  40 . Two parallel orientation ribs  43  and  44  are provided within the recess. Still referring to  FIGS. 3 and 4 , three spaced metal contacts  46 ,  47  and  48  are provided at an inner end wall of the recess  42 . With reference to  FIG. 3 , these contacts each have a flat head that is disposed against the inner end wall, and each have a stem of smaller diameter that extends through an opening in the inner end wall. The contacts  46 - 48  collectively serve as a serial connector disposed within the recess  42 .  
         [0026]     With reference to  FIG. 2 , a flexible rubber strip  51  has one end fixedly secured to the top part  13  of the housing, in the region of the concave recess  26 . An integral rubber stopper  52  is provided at the other end of the strip  51 , and can be removably inserted into the recess  42  with a friction fit, in order to seal the recess  42  against external environmental factors such as moisture, humidity, dust and so forth. For clarity,  FIGS. 3 and 4  each show the recess  42  without the stopper  52 .  
         [0027]     With reference to  FIG. 2 , a battery orientation indicator  56  is provided on the sidewall  18 , near the battery cover  33 . The indicator  56  may be molded into the material of the housing, or may be a label that is adhesively secured to the sidewall  18 . The indicator  56  shows the proper orientation for a replaceable battery in the tag  10 . In  FIG. 2 , reference numeral  57  diagrammatically designates a region where an adhesive label may optionally be applied to the sidewall  18 . Similarly, with reference to  FIG. 1 , reference numerals  58  and  59  diagrammatically indicate regions where other adhesive labels may optionally be applied to the sidewall  19 . The labels  57 - 59 , if present, can carry indicia providing information such as the name and address of the manufacturer of the tag, a name or trademark associated with the tag, instructions regarding use of the tag, a model number and/or serial number of the tag, a barcode, or any other appropriate information.  
         [0028]      FIG. 5  is a diagrammatic perspective bottom view of the tag  10 , with the bottom part  14  removed so that the interior of the tag is visible.  FIG. 6  is a diagrammatic perspective bottom view of the bottom part  14 . As evident from  FIG. 6 , the bottom part  14  has an approximately rectangular shape, with two opposite corners  71  and  72  that are slightly rounded. The other two corners have circular cut-outs  73  and  74 .  
         [0029]     With reference to  FIGS. 3 and 5 , the peripheral flange  23  of the housing top part  13  has a recess  81  extending along the inner side thereof. The peripheral edge of the recess  81  conforms in shape to the peripheral edge of the plate  14 . In the assembled configuration of the tag, the recess  81  receives the peripheral edges of the plate  14 . A peripheral groove  82  is provided in a surface of the recess  81 . As shown in  FIG. 3 , the bottom part  14  has on its upper side two parallel peripheral ribs  83  and  84  that extend along the entire periphery of the bottom part. The rib  83  is received within the peripheral groove  82 , and the peripheral rib  84  is disposed adjacent inner surfaces of the sidewalls  18 - 19  and the end walls  21 - 22 . As shown in  FIGS. 3 and 6 , the underside of the bottom part  14  has a planar base surface  87 .  
         [0030]     With reference to  FIGS. 3 and 5 , the top part  13  of the housing  12  has a plurality of integral ribs within the interior thereof, two of which are indicated by reference numerals  91  and  92 . The rib  91  designates a U-shaped rib, which extends along inner sides of the top wall  17  and each of the sidewalls  18  and  19 . The rib  92  is an L-shaped rib, which extends along inner sides of the sidewall  19  and the top wall  17 . The ribs provide structural reinforcement for the housing, and also facilitate support within the housing of a main printed circuit board  101  and an auxiliary printed circuit board  102 .  
         [0031]     For example, with reference to  FIG. 3 , the U-shaped rib  91  has a recess  107  that receives one side edge of the main circuit board  101 , and has a surface  106  that engages the circuit board  101  near an opposite side edge thereof. The bottom part  14  of the housing has several spaced transverse ribs on its upper side, one of which is visible at  108  in  FIG. 3 . The rib  108  has a recess  109  that receives a side edge of the circuit board  101 . It will be noted that the circuit board  101  is adjacent and parallel to the sidewall  19 , and thus extends at an angle with respect to the base surface  87  of the bottom part  14 . Other ribs cooperate with the auxiliary circuit board  102 , in order to hold it in place. Thus, when the housing parts  13  and  14  have been ultrasonically bonded together, the circuit boards  101  and  102  are each retained in the proper position within this housing  12 .  
         [0032]     As noted above, the circuit board  101  extends at an angle with respect to the base surface  87  of the bottom part  14 . More specifically, the circuit board  101  extends at an angle in the range of 50° to 90° with respect to the base surface  87 . In the illustrated embodiment, the angle is approximately 60°.  
         [0033]      FIG. 7  is a diagrammatic exploded perspective view of the top part  13  of the housing  12 , showing an underside thereof. With reference to  FIGS. 5 and 7 , a cylindrical battery access opening  121  extends through the end wall  22  of the top part  13 , and has threads  122  at its outer end. The top part  13  has a battery compartment defined by a sidewall  123 , an end wall  124 , and a cover  127 . The sidewall  123  and end wall  124  are integral to the top part  13 , and the cover  127  is a separate arcuate part that is fixedly secured to the top part  13 , for example by ultrasonic bonding, or by a suitable adhesive of a known type. In the disclosed embodiment, the cover  127  is made of the same material as the top part  13 . However, it could alternatively be made of any other suitable material.  
         [0034]     A metal plate  131  has a circular lower part that is disposed against the end wall  124 , and that supports a conical coil spring  132 . The plate  131  has an outwardly projecting tab  133 , which extends through a slot  134  provided in the cover  127 .  
         [0035]     An annular metal strip  137  is fixedly mounted within the opening  121 , slightly inwardly from the threads  122 . The strip  137  has an upwardly projecting tab  138 , which extends through aligned slots  141  and  142  provided in the cover  127  and the top part  13 .  
         [0036]     The battery cover  33  has threads  146 , which are engageable with the threads  122  in the opening  121 . A seal ring  147  is provided around the cover  33 , in order to seal the opening  121  against entry of environmental factors such as moisture, humidity, dust, and so forth. In the disclosed embodiment, the seal ring  147  is made from a silicon rubber material, but it could alternatively be made from any other suitable material. The inner end of the cover  33  has two axial slots  151  on diametrically opposite sides thereof, only one of which is visible in  FIG. 7 . A metal contact has a C-shaped strip  152  that is received within a circular recess provided in an inner end surface of the cover  33 . Two resilient tabs  153  and  154  project outwardly from opposite sides of the strip  152 , and are each received within a respective one of the two slots  151 . An integral spring strip  157  has one end secured to the strip  152 , and is bent to have a slightly arcuate shape. When a battery is disposed within in the battery compartment, the spring  132  engages one end of the battery. The other end of the battery engages the spring strip  157 , and the resilient tabs  153  and  154  slidably engage the annular strip  137 . Thus, one end of the battery is electrically coupled to the tab  133 , and the other end of the battery is electrically coupled to the tab  138 .  
         [0037]      FIG. 8  is a diagrammatic exploded perspective view of the tag  10 , with the bottom part  14  omitted for clarity.  FIG. 8  shows a battery  166  that is removably disposed within the battery compartment. In the disclosed embodiment, the battery  166  is a lithium cell of a known type, in order to permit the tag  10  to operate as long as possible before the battery  166  eventually becomes discharged. However, the battery  166  could be a known type of battery other than a lithium cell. Further, as new battery technologies are developed, a battery conforming to a new technology could be used at  166 , for example if it has a longer operational life then is possible with current battery technology.  
         [0038]      FIG. 8  shows a side of the main circuit board  101  that was not visible in prior figures. The electrically conductive runs etched on the printed circuit board  101  include a loop  171  that has an approximately rectangular shape, and that functions as an antenna. The loop antenna  171  is provided on an end portion  172  of the circuit board  101 . The structure of the loop antenna  171  is discussed in more detail later. The opposite end portion  173  of the circuit board  101  has an electronic circuit of a type that is known in the art. This circuit uses the loop antenna  171  to send and receive signals in a known manner. The details of the electronic circuitry and the format and content of the radio frequency signals are well known in the art, and are therefore not described here in detail.  
         [0039]     As evident from  FIG. 8 , the loop antenna  171  is provided on the end portion  172  of the circuit board that is remote from the battery compartment containing the battery  166 . This is because many battery cells have a metal case. The relative positions of the loop antenna  171  and the battery  166  that are shown in  FIG. 8  minimize the extent to which the metal case of the battery  166  can interfere with radio frequency signals being transmitted and/or received using the loop antenna  171 .  
         [0040]     As mentioned earlier, the circuit board  101  extends at an angle in the range of 50° to 90° with respect to the base surface  87  of the bottom part  14 , and this angle is approximately 60° in the illustrated embodiment. The reason for this angle relates in part to the fact that the loop antenna  171  is on the circuit board. In many applications, the tag  10  will be mounted so that the bottom part  14  is adjacent or disposed against a metal surface. The angle of the circuit board  101  is intended to optimize reception and propagation of radio frequency signals by the loop antenna  171 , based on a balancing of various competing design considerations. These design considerations include the overall height of the loop, the aspect ratio of the loop, the shielding effect of a metal surface when the tag  10  is mounted adjacent such a surface, and the beam forming that results from reflections of radio frequency waves from such an adjacent metal surface. Orienting the circuit board  101  at an angle also helps keep the housing  12  of the tag more streamlined and compact.  
         [0041]     With reference to  FIG. 5 , the auxiliary circuit board  102  is electrically coupled between the main circuit board  101  and the contacts  46 - 48  of the serial interface connector located within the recess  42 . The auxiliary circuit board  102  carries a serial interface circuit, which handles serial communications through the contacts  46 - 48  of the serial interface connector. The serial interface circuit includes a relatively large capacitor  181 , as well as other components that are not specifically shown in the drawings.  
         [0042]      FIG. 9  is a diagrammatic fragmentary sectional view showing a portion of  FIG. 3  in an enlarged scale, and also showing an end portion  201  of a serial cable that can be coupled to the serial interface connector. The end  201  of the cable has been removably inserted with a friction fit into the recess  42  that contains the serial interface contacts  46 - 48 . The cable end  201  has two grooves that each receive a respective one of the orientation ribs  43  and  44 . The cable end  201  also has three axially-movable pins of a known type, one of which is visible at  206 . Each of the pins is electrically coupled to a not-illustrated wire within the cable. Each pin is biased axially outwardly by a respective spring, one of which is indicated diagrammatically at  207 . The outer end of each of the resiliently-biased pins engages a respective one of the three contacts  46 - 48  of the serial connector. For example,  FIG. 9  shows the outer end of the pin  206  engaging the contact  47 .  
         [0043]      FIG. 10  is a diagrammatic perspective view that shows the tag  10 , and also an optional tag holder  251 . As discussed above, the housing  12  of the tag  10  has two openings  28  and  29  that can be used with screws or bolts to mount the tag on an object such as a shipping container. The tag holder  251  represents a different approach for mounting the tag  10  on an object. In particular, the tag holder  251  can be mounted on the object, and then the tag  10  can be easily inserted into and removed from the tag holder  251 .  
         [0044]     In more detail, the tag holder  251  includes a base part  254 , and the tag can be inserted into and removed from the base part  254  in directions parallel to the double-headed arrow  255  in  FIG. 10 . In the disclosed embodiment, the base part  254  is made from the same material as the housing  12  of the tag  10 . However, the base part  254  could alternatively be made from any other suitable material. The base part  254  has holding portions  256 - 259 , which slidably receive the flange  23  on the tag  10  in order to retain the tag  10  on the tag holder  251 . The base part  254  has a resilient tongue  266  with a rib  268  at the outer end. The base part  254  has several mounting holes, two of which are indicated by reference numerals  271  and  272 . Screws or bolts can be inserted through the holes  271  and  272 , in order to securely mount the tag holder  251  to an object such as a shipping container. The tag  10  can then be easily inserted into and removed from the tag holder  251 , without any need to remove screws or bolts.  
         [0045]     In this regard, as the tag  10  is slid into the tag holder  251 , the tongue  266  is pressed downwardly against its inherent resilience by the tag. Then, when the tag  10  reaches a fully inserted position, the inherent resilience of the tongue  266  moves the tongue  266  partway back to its original position, so that the rib  268  moves to a position adjacent the flange  23  on the tag. Engagement of the rib  268  and the flange  23  then prevents the tag  10  from moving out of the tag holder  251 . In order to remove the tag  10 , the outer end of the tongue  266  is manually pressed downwardly, so as to move the rib  268  out of alignment with the flange  23 . The tag  10  can then be slid out of the tag holder  251 .  
         [0046]     The tag holder  251  also includes a U-shaped magnetic part  276 , which is fixedly secured to the base part  254  and extends around three sides thereof. The magnetic part  276  is capable of magnetically holding the tag holder  251  and the tag  10  on a metal surface, such as a wall of a steel shipping container. Thus, where the tag holder  251  is to be mounted to an object that is made of metal, it is not necessary to use bolts or screws to mount the tag holder  251 . This avoids the need to drill holes in the object to receive screws or bolts. The magnetic part  276  can optionally be omitted, leaving just the base part  254  to serve as the tag holder.  
         [0047]      FIG. 11  is a diagrammatic fragmentary view of the half of the main circuit board  101  that carries the loop antenna  171 , and shows the structure of the loop antenna  171  in more detail. The loop antenna  171  is approximately rectangular, and has four sides. The loop antenna  171  includes a plurality of conductive segments  301 - 305  and a plurality of capacitors  311 - 316  that are electrically coupled so as to form the endless loop. In the disclosed embodiment, the segments  301 - 305  are conductive runs that were etched from a layer of metal during fabrication of the circuit board. The circuit board also has two conductive runs  321  and  322  that respectively electrically couple the conductive segments  305  and  304  to the circuitry on the circuit board  101 . Each of the four sides of the rectangular loop  171  has at least one of the capacitors  311 - 316  at a location between the ends thereof.  
         [0048]     The conductive segments  301 - 304  are each an approximately L-shaped segment, and each define a respective corner of the approximately rectangular loop  171 . The capacitor  311  is coupled between adjacent ends of the conductive segments  304  and  305 , the capacitor  312  is coupled between adjacent ends of the conductive segments  305  and  301 , the capacitors  313  and  314  are electrically coupled in parallel with each other between adjacent ends of the conductive segments  301  and  302 , the capacitor  315  is coupled between adjacent ends of the conductive segments  302  and  303 , and the capacitor  316  is coupled between adjacent ends of the conductive segments  303  and  304 . In the disclosed embodiment, the capacitor  314  is a variable trim capacitor with a value of about 1 pf, and the capacitors  311 ,  312 ,  313 ,  315  and  316  have respective fixed values of about 18 pf, 4.7 pf, 4.0 pf, 5 pf and 4.7 pf. However, these specific capacitance values are exemplary, and other capacitance values could be used under other circumstances, for example to tune the loop  171  for use at a different frequency.  
         [0049]     The loop  171  is a tuned circuit with both capacitive and inductive characteristics. In this regard, the conductive segments  301 - 305  collectively define an inductor, and the capacitors  311  and  312  together define a capacitance, the value of the capacitor  312  being selected to tune the loop to a selected frequency. In the disclosed embodiment, the selected frequency is 433 MHz. However, it would alternatively be possible to use some other frequency as the selected frequency. If the capacitors  313 - 316  were omitted, there would be a relatively high impedance in the loop at a point located along the conductive segment  301  near the capacitor  312 . This high impedance would cause the tuned frequency to be subject to undesirable variation if an object such as a metal element or a person&#39;s hand is moved into proximity with the loop  171 . Stated differently, this proximity effect changes the tuned characteristic of the antenna, thereby decreasing the gain of the antenna at the selected frequency. The capacitors  313 - 316  are therefore provided to counteract this proximity effect, in particular by reducing the effective impedance around the loop. The variable trim capacitor  314  is provided to facilitate tuning of the loop  171  during actual production.  FIG. 11  shows one specific configuration for the loop antenna  171 , but it will be recognized that a variety of modifications to this configuration are possible while still utilizing unique aspects of the invention that are embodied within the loop antenna  171 .  
         [0050]      FIG. 12  is a diagrammatic perspective view showing the upper side of the bottom part  14 . As mentioned earlier, several transverse ribs are provided on the top surface of the bottom part  14 , one of which is visible at  351  in  FIG. 12 . As also discussed earlier, there are many applications in which the tag  10  will be mounted with the bottom part  14  adjacent a metal surface. The presence of such a conductive surface can affect the tuned characteristic of the loop antenna  171 . In order to minimize the extent to which such an external conductive surface can affect the operation of the loop antenna  171 , a layer of copper foil  352  is provided over about two-thirds of the top surface of the bottom part  14 , in particular at the end of the bottom part  14  that is aligned with the loop antenna  171 . The copper foil covers several of the transverse ribs, including the rib that is visible at  108  in  FIG. 3 . The copper foil  352  is not electrically coupled to any other circuitry within the tag  10 , and serves as a counter-electrode for the loop antenna  171 .  
         [0051]     Although one selected embodiment has been illustrated and described in detail, it should be understood that various substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims. Moreover, to the extent that the foregoing description uses directional terms such as top, bottom, side, inner and outer, these terms are used only for convenience in relation to how the disclosed structure is oriented in the drawings, and should not be considered to be limiting as to the scope of protection.