Abstract:
Method and systems to detect tampering in a physical article are described herein. A method includes receiving, at a first point in time, at least two response signals from at least one RF tag in a set of RF tags associated with the physical article; forming a first response signature for the physical article based on the received response signals; receiving a second response signal from at least one other RF tag in the set of RF tags associated with the physical article at a second point in time; assessing a relative spacing between the RF tags associated with the physical article has changed from the first point in time to the second point in time; and determining tampering of the physical article as a result of the spacing assessment.

Description:
This application is a continuation of U.S. patent application Ser. No. 11/525,298 entitled “THREE DIMENSIONAL RF SIGNATURES” to Ashwood-Smith et al., filed Sep. 22, 2006. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to Radio Frequency (RF) tags and, more particularly, to three dimensional RF tag signatures. 
     2. Description of the Related Art 
     Radio Frequency tags, also known as Radio Frequency Identification (RFID) tags use electromagnetic radiation to temporarily charge a circuit, which may be programmed to wirelessly transmit a data code. If the data transmitted by the circuit is received by an RF tag reader, it is possible to determine that the RF tag is in the proximity of the RF tag reader. By causing different chips to transmit different RF tag codes, the identity of the RF tag may be determined, which will allow a RF tag processing system interfaced with the RF tag reader to uniquely place that RF tag in a particular place at a particular point in time. Thus, by associating the RF tags with individual articles that are to be tracked, it is possible to keep track of many different articles electronically. RF tags may be used in many applications, and the number of applications of RF tags has been increasing dramatically in the last few years. For example, RF tags are used in retail establishments to keep track of merchandise, in manufacturing to keep track of inventory, in corporations for example in building access badges, and in many other fields. 
       FIG. 1  shows an example RF tag. As shown in  FIG. 1 , a standard RF tag  10  includes a coil  12  that will be used to capture electromagnetic radiation to produce a current. As is well known, changing an electromagnetic field relative to a coil will cause an electrical current to flow in the coil. Thus, by modulating an electromagnetic field it is possible to cause a current to be generated in the coil of an RF tag. Where the coil  12  is connected to an electromagnetic circuit  14 , and the electrical current is used to power to circuit  14 . The circuit may be used for many different things, but generally is configured to transmit a tag response including a tag code that may be read by a RF tag reader  20  (see  FIG. 2 ). RF tags are well known, and many different types and sizes/shapes of RF tags and circuits have been developed. 
     As shown in  FIG. 2 , in operation a RF tag reader  20  generates a strong electromagnetic field  22  which will cause a current to be generated in any RF tags within a given distance of the RF tag reader. When an RF tag  10  comes into proximity of the RF tag reader  20 , the RF tag will generate the tag response  24  which may be sensed by the reader  20  if the tag is sufficiently close to the reader  20 . 
     RF tags provide an indication of presence of the tag relative to the reader, but generally do not provide an indication of where the RF tag is located within the reader&#39;s field of view. While it is possible to use an RF tag reader that has one or more directional antennas to help determine the relative position of the RF tag, doing so reduces the ability of the RF tag reader to detect the presence of RF tags outside of the directional antenna beam. 
     Similarly, when an RF tag is associated with an article, for example where RF tags are to be used to track boxes of merchandise or luggage, sensing the presence of an RF tag will enable the reader to determine the rough location of a particular article at that particular point in time. The RF reader is not able however, to determine the state of the article or whether the article has been damaged or altered since the last time the RF tag presence was sensed. Accordingly, while RF tags are very useful for tracking where articles are at particular points in time, it would be advantageous to provide a way in which the RF tags could provide additional information about the articles being tracked. 
     SUMMARY 
     Three dimensional RF tag signatures may be obtained from a three dimensional RF tag or multiple two or three dimensional RF tags so that information in addition to presence information may be obtained. In one embodiment, a three dimensional RF tag having two or more power coils disposed in non-coplanar planes, enables the coils to experience different levels of excitation from an electromagnetic field associated with the RF tag reader. This information may be transmitted along with the RF tag response to enable the orientation of the RF tag relative to the RF tag reader to be determined. In another embodiment, multiple RF tags (either standard RF tags or three dimensional RF tags) may be used on a given article and a response signature from the article as a whole may be recorded. The three dimensional response signature thus collected may be compared with previous versions of the response signature to determine if the article has been altered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present invention are pointed out with particularity in the appended claims. The present invention is illustrated by way of example in the following drawings in which like references indicate similar elements. The following drawings disclose various embodiments of the present invention for purposes of illustration only and are not intended to limit the scope of the invention. For purposes of clarity, not every component may be labeled in every figure. In the figures: 
         FIG. 1  is a functional block diagram an RF tag; 
         FIG. 2  is a functional block diagram of the interaction between an RF tag reader and an RF tag; 
         FIG. 3  is a functional block diagram of an RF tag having three non-coplanar power coils according to an embodiment of the invention; 
         FIG. 4  is a diagram showing the electrical interconnection of the power coils an circuit of the RF tag of  FIG. 3  in greater detail; 
         FIG. 5  is a diagram of an article having a plurality of RF tags; 
         FIG. 6  is a functional block diagram of an RF tag reader obtaining a three dimensional signature from an article such as the article of  FIG. 5 ; 
         FIG. 7  is a flow chart illustrating a process of determining a relative orientation of an RF tag from a signature of a three dimensional RF tag, such as the RF tag of  FIGS. 3-4 , according to an embodiment of the invention; 
         FIG. 8  is a flow chart illustrating a process of comparing a three dimensional RF tag signature from an article having a plurality of RF tags, such as the article shown in  FIGS. 5-6 , with a previous signature for the same article according to an embodiment of the invention; and 
         FIG. 9  is a functional block diagram of a computer system configured to implement an RF tag processing system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description sets forth numerous specific details to provide a thorough understanding of the invention. However, those skilled in the art will appreciate that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, protocols, algorithms, and circuits have not been described in detail so as not to obscure the invention. 
       FIG. 3  illustrates an example of a RF tag having more than one power coil, in which the power coils are not formed to be co-planar. By using non-co-planar power coils, the several power coils will generate different amounts of power when subjected to a directional electromagnetic field. The chip may transmit a power coil value indicative of the amount of power, current, voltage, or another measurable quantity, that it received from each power coil in connection with generating its tag response. These power coil values may be used by the RF tag reader or RF tag processing system to deduce an orientation of the RF tag relative to the RF tag reader. 
     In the embodiment shown in  FIG. 3 , the three dimensional RF tag  30  includes three power coils  12 X,  12 Y, and  12 Z. The three power coils are connected to the circuit  32  and provide power to the circuit. Although the embodiment shown in  FIG. 3  has three power coils, the invention is not limited in this manner as two power coils or a larger number of power coils may be used as well. Additionally, although the embodiment shown in  FIG. 3  has the power coils disposed on orthogonal planes, this is merely a preferred embodiment. The invention is not limited to this particular embodiment as other types of three dimensional RF tags having more than one power coil disposed in a non-planar fashion may have the power coils disposed on differently oriented planes. 
       FIG. 4  provides additional details about how the power received from the several power coils is used by the circuit  32 . As shown in  FIG. 4 , the power received from each of the power coils  12 X,  12 Y, and  12 Z is added together to form an input power to the circuit  32 . Additionally, the electrical signals from the power coils  12 X,  12 Y, and  12 Z are each measured by the RF tag. The RF tag may measure the power from the power coils, the amount of current being generated, the voltage, or another electrical characteristic derivable from measuring the output of the power coils. 
     Once the RF tag has taken measurements of the power coils, it will transmit the tag code  34  along with power coil values to the RF tag reader via an antenna  36 . The power coil values are indications of the electrical characteristics of the several power coils and may be actual readings of the characteristic that is being measured, or one or more values derived from the measured characteristic. The tag code may be a standard tag code, and the rest of the circuit that is configured to actually transmit the data may be the same as a standard RF tag, except that instead of transmitting only a tag code the RF tag will also transmit the power coil values as well. 
     The amount of current generated in a given coil depends not only on the strength of the electromagnetic field, but also on the orientation of the coil relative to the field. If a RF tag reader is transmitting electromagnetic (EM) radiation, the direction of the radiation over the area occupied by the three dimensional RF tag may be considered to be relatively constant in one direction, given the size of a typical RF tag relative to the distance to the RF tag reader. By placing the power coils in different planes such as the orthogonal planes shown in  FIGS. 3 and 4 , the power coils will therefore be oriented at different angles relative to the EM radiation source. Thus, different currents should be produced in each of the power coils of the RF tag. If the tag has a known geometry, such as if the tag is formed to have three power coils on three mutually orthogonal planes as shown in  FIGS. 3 and 4 , the orientation of the tag relative to the reader may be determined. 
     The amount of current generated in a given coil may be expected to be dependent on the strength of the EM field at the RF tag. If a point EM source radiating in all directions is used to generate the EM field, then the strength of the radiation should be expected to drop off on the order of d.sup.3, where d is the distance from the point source to the RF tag. By measuring the magnitude of the electrical response in these power coils, a rough estimate of the distance between the RF tag and the tag reader may be obtained. 
     The distance and/or orientation information obtainable from an RF tag having multiple non-co-planar power coils may be used in many different applications. For example, in manufacturing, a stationary RF reader may use RF tags to identify when particular parts are approaching a manufacturing station. Knowing the orientation of the RF tag may enable the RF tag reader to determine if the part has been incorrectly placed on the conveyance system, may help the RF tag reader to know where the part is within its field of view, and may help in other ways. For example, knowing the orientation of a tag may enable the system to know if the article associated with the tag is up-side-down. 
     Similarly, where the location of the RF tag has been fixed and the RF tag reader is mobile, knowing the direction from the reader to the RF tag, and optionally the distance between the reader and the RF tag, may help the RF tag reader stay on a desired side of the fixed RF tags. This may be useful, for example in connection with self-propelled vehicles and in other applications. For example, if the RF tags are embedded in a roadway, the three dimensional signatures may enable an RF tag reader in an automobile to know whether it is traveling on the left side or right side of the RF tags. 
     The several example applications described herein are not intended to limit application of the invention to one or two fields, but rather have been provided to show some practical utility for the invention. The invention is thus not limited to the use of the inventive three dimensional RF tag signatures in these several applications, since the signatures may be used in many different ways that are too numerous to list herein. 
     Although an embodiment has been described in which multiple antennas are connected to a given circuit, according to another embodiment of the invention, multiple RF tags  10  associated with an article may be used to generate a three dimensional signature for the article. These RF tags may be conventional tags such as the tag shown in  FIG. 1 , may be tags such as the RF tags discussed above in connection with  FIGS. 3 and 4 , or may be differently configured RF tags.  FIG. 5  shows one example of this where three RF tags  52  are placed at different locations on an article  50 . Since the RF tags will provide a spatial signature for the article that is dependent on their position on the article, changing the position of one or more of the RF tags will cause the three dimensional signature for the article to change. Detecting a change in the RF signature may thus enable a system to determine that the article has been altered between readings. This may be useful, for example, where security is an issue and it is important to detect whether tampering has occurred. Similarly, although an embodiment will be described in which the RF tags have been applied to an article, the invention is not limited in this manner as the RF tags may also be applied to a set of articles that are required to be kept together. 
     The signature will be unique to the article and depend on the orientation of the RF tags, the placement of the RF tags, and possibly the configuration of the article as well. For example, the RF tags may be distributed to form a spatial signature for the article. The RF tags may also be set to respond at different times so that the set of RF tags is able to form a temporal signature. Similarly, the response of one or more of the RF tags may be encoded, so that the signature is encoded. Thus, the three dimensional signature may include spatial signatures, time signatures, coding signatures, and combinations of these types of signatures. 
     Once an initial three dimensional RF signature is received for a given article, the signature may be stored for use at a later time. When a new signature is received for the article, the new signature may be compared with the stored signature to determine if the two signatures are sufficiently alike. If the signatures are sufficiently similar, it may be inferred that the RF tags or the relative placement of the RF tags has not been disturbed. If the signatures are sufficiently dissimilar, it is possible that the article has been tampered with, and an appropriate notification may be provided. 
     The three dimensional signature provided by a set of RF tags disposed within a given volume may be used in many different applications. For example, a signature may be obtained from a box of items. If the signature changes, it may be that the box has been opened. Similarly from a security standpoint, if one or more RF tags are associated with a piece of luggage, detecting a change in the luggage signature may indicate that the luggage has been opened, which may indicate that something has been stolen or added to the piece of luggage. In either instance, further inspection of the luggage may be warranted. The three dimensional signatures may be used in other applications as well and the invention is not limited to these several mentioned applications. 
       FIG. 6  shows an embodiment of a reader that may be configured to obtain RF signatures from a set of RF tags disposed within a volume. As shown in  FIG. 6 , responses  60  from tags  10  may be gathered by an antenna  62  and passed to an RF tag reader  64 . The antenna may be integrated into the RF tag reader  64  and the invention isn&#39;t limited by the manner in which the response from the individual RF tags are collected by the RF tag reader  64 . 
     The response from the RF tags  52  will be input to processing circuitry  66  where the tag codes  68  for the various RF tags will be extracted. In addition, the particular manner in which the RF tags responded may be stored as an RF signature  70  for the article. The tag codes and/or signature may be transmitted to a central area for further processing and/or storage. The invention is not limited by the particular manner in which these values are used once they have been obtained. However, as described above, multiple signatures from the same article  50  may be compared over time to determine if the article has been changed in a way that would change the RF signature of the article. 
     The RF tags  52  may be standard RF tags  12  described above in connection with  FIGS. 1-2 , or may be RF tags  30  that are configured to also provide an indication of the electrical characteristics of at least one of their power coil(s). For example, each RF tag may be configured to transmit not only its tag code, but also an indication of at least one electrical characteristic associated with its power coil. This may be implemented as discussed above in connection with  FIGS. 3-4 . The relative power levels of the several RF tags when interrogated from a particular angle and/or distance may provide information as to whether any of the RF tags have been moved relative to the location of the RF tag reader, and thus provide a way for tampering to be detected from an RF tag signature associated with a given set of RF tags. 
       FIGS. 7 and 8  show two processes that may be used to implement embodiments of the invention. As shown in  FIG. 7 , power from antennas in multiple dimensions may be used to power an RF tag ( 100 ). The power level (or other electrical characteristic) from each antenna may then be transmitted along with the RF tag code to a tag reader ( 102 ). The tag reader or an associated RF tag processing system will interpret the power levels from the antennas to determine an orientation of the RF tag relative to the RF tag reader ( 104 ). Alternatively, the tag reader may pass this information back to a central RF tag processing system that may then interpret the power levels of the antennas to determine the orientation of the RF tag relative to the RF tag reader. The particular location where this process happens will depend on how the invention is implemented and the invention is not to be limited in this manner to any particular implementation. 
     Where the tag reader is mobile, the mobile tag reader may be able to determine its position based on the orientation information obtained from a fixed RF tag ( 106 ). Similarly, where the tag reader is fixed, the location of the RF tag may be determined by analyzing the power levels recorded by the RF tag ( 108 ). The relative location information may then be used in many different ways depending on the particular application being implemented. 
     In the process shown in  FIG. 8 , when an article containing multiple RF tags enters an EM field associated with a tag reader ( 110 ), the RF tags in the article are powered by the EM field and emit a tag code, optionally in conjunction with information about the electrical characteristics of their one or more power coils ( 112 ). The combination of tag codes, the order in which the RF tags respond, the encrypted/unencrypted nature of the tag codes, and the other characteristics associated with the transmissions from the RF tags on the article are used to form a signature for the article as a whole ( 114 ). The RF tag codes may then be compared with expected RF tag codes to identify the article and to determine whether all of the expected RF tags have responded ( 116 ). The signature may also be checked against a previous signature for the article to determine if the signature has changed significantly ( 118 ). The signatures for the article may be used in many different ways as well, depending on the particular application being implemented. 
       FIG. 9  shows a functional block diagram of a RF tag processing system embodied as a computer system  120  that may be used to enable three dimensional RF signatures to be used to understand information about articles associated with the RF tag(s). In the embodiment shown in  FIG. 9 , the computer system  120  includes one or more input/output ports  122  to enable RF tag information to be received from one or more RF tag readers. The input/output ports may be standard network ports configured to enable the RF tag readers and the RF tag processing system to be interconnected by a communication network. Alternatively the input/output ports may be serial ports or other types of ports, for example where the RF tag reader(s) are directly connected to the computer system. Although the embodiment shows the computer system as separate from the RF tag readers, alternatively the processing functions described in connection with  FIG. 9  may be performed by processing circuitry integrated with one or more of the RF tag readers. Thus, part of the functionality described as being attributable to the RF tag processing system may be distributed and instantiated in the RF tag reader or another component associated with the RF tag processing system. Similarly, some of the processing may be implemented on the RF tags themselves, particularly in connection with the three dimensional RF tags, and the invention is not limited to an embodiment in which all of the processing is done in the precise manner described herein. 
     The computer system includes a processor  124  containing control logic  126  configured to enable the processor to perform the functions associated with the RF tag processing system described herein. Specifically, the control logic may be connected to a memory  128  containing software and/or data that will enable the computer system to process RF tag responses, individually and collectively, to enable three dimensional information to be extracted from the RF tag responses. 
     In the embodiment shown in  FIG. 9 , the memory  128  includes RF tag software  130  enabling the RF processing system to maintain a correlation between RF tags and the articles with which they are associated. Many commercial systems have been developed to track articles using RF tags, and the RF tag software  128  in  FIG. 9  may be configured to implement article tracking features in a manner similar to one or more of these commonly available systems. For example, the RF tag software may access a database of RF tags  132  and associated articles so that the system may provide information associated with particular articles to an operator of the RF processing system. Similarly, the RF tag software may have access to a database of RF tag readers  134  to determine the physical location of the readers that are providing RF tag information to the RF tag processing system. 
     The RF tag processing system shown in  FIG. 9  also includes multiple power coil RF tag direction determination software  136 . The software  136  may be a software module that is incorporated into the RF tag software  130  or may be a stand-alone software program. The software  136  may be configured to perform the process shown in  FIG. 7  and described in greater detail in connection with  FIGS. 3-4 . In connection with this, the software  136  may access the RF tags database  132  to obtain characteristic and/or calibration information for particular tags, and may also access the RF tag reader information database  134  to obtain information about particular RF tag readers so that it can determine how the power coil information should be interpreted for a particular RF tag and with reference to the particular RF tag reader that registered the RF tag response. 
     The RF tag processing system may also include multiple RF tag article signature software  138  which, like the software  136 , may be incorporated into the RF tag software  130  or may be a stand-alone software program. The software  138  may be configured to perform the process shown in  FIG. 8  and described in greater detail in connection with  FIGS. 5-6 . In connection with this, the software  138  may be configured to receive RF tag signature information associated with an article, or to create a RF tag signature from multiple RF tags associated with a given article, and optionally then to compare the RF tag signature with a previous RF tag signature for the article. RF tag signatures from combinations of RF tags associated with a given article may be stored in an article signatures database  140  to enable different signatures for the same article to be compared at different points in time to detect tampering with the article. 
     The control logic  126  may implement one or more processes in addition to those shown here, or as an alternative to those shown here, to enable the computer system to implement an RF tag processing system that can generate and/or use three dimensional RF tag signatures. Many other standard components of the computer system have not been illustrated to avoid obfuscation of the more relevant aspects. As is well known in the art, a complete computer system will include many additional components that have not been shown here. 
     The functions described above may be implemented as a set of software program instructions that are stored in a computer readable memory and executed on one or more processors. However, it will be apparent to a skilled artisan that all logic described herein can be embodied using discrete components, integrated circuitry such as an Application Specific Integrated Circuit (ASIC), programmable logic used in conjunction with a programmable logic device such as a Field Programmable Gate Array (FPGA) or microprocessor, a state machine, or any other device including any combination thereof. Programmable logic can be fixed temporarily or permanently in a tangible medium such as a read-only memory chip, a computer memory, a disk, or other storage medium. Programmable logic can also be fixed in a computer data signal embodied in a carrier wave, allowing the programmable logic to be transmitted over an interface such as a computer bus or communication network. All such embodiments are intended to fall within the scope of the present invention. 
     It should be understood that various changes and modifications of the embodiments shown in the drawings and described in the specification may be made within the spirit and scope of the present invention. Accordingly, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not in a limiting sense. The invention is limited only as defined in the following claims and the equivalents thereto.