Abstract:
Methods and apparatuses for tiered RFID communication are provided, inter alia, for privacy and security in at least certain embodiments. An RFID tag includes first and second memory locations respectively storing first and second identifiers. The tag is configured to respond to an identification query with the first identifier until receipt of a command code. After receipt of the command code, the tag is configured to respond to the identification query with the second identifier. The first identifier can be permanently disabled for privacy. In a one embodiment, the first identifier is an electronic product code, and the second identifier is a recycling identifier, hazardous waste information, or regulatory disposal requirement. In another embodiment, the first and second identifiers can identify the tag&#39;s associated item with differing levels of specificity for improved security.

Description:
RELATED APPLICATION 
     This application claims benefit and priority to provisional application 60/904,590 filed on Mar. 2, 2007. The full disclosure of the provisional application is incorporated herein in its entirety by reference. 
    
    
     FIELD OF THE TECHNOLOGY 
     The present invention generally relates to the field of radio frequency identification (RFID) devices, and particularly to RFID devices and methods for using and making same. 
     BACKGROUND 
     Goods and other items may be tracked and identified using an RFID system. An RFID system includes at least one tag and a reader. The tag is a small transponder typically placed on an item to be tracked. The reader, sometimes referred to as an interrogator, includes a transceiver (alternatively, separate transmitter and receiver) and one or more antennas. The antennas emit electromagnetic (EM) waves generated by the transceiver, which, when received by tag, activates the tag. Once the tag activates, it communicates using radio waves back to the reader, thereby identifying the item to which it is attached. 
     There are three basic types of RFID tags. A beam-powered tag is a passive device which receives energy required for operation from EM waves generated by the reader. The beam powered tag rectifies an EM field and creates a change in reflectivity of the field which is reflected to and read by the reader. This is commonly referred to as continuous wave backscattering. A battery-powered semi-passive tag also receives and reflects EM waves from the reader; however a battery powers the tag independent of receiving power from the reader. An active tag, having an independent power supply, actively transmits EM waves which are then received by the reader. 
     Communication between the tag and reader is defined by an air interface communication protocol. For example, RFID tags can be implemented using (i) EPCglobal&#39;s Class 1 Generation 2 UHF Air Interface Protocol Standard Version 1.0.9: (“Gen 2”); or (ii) ISO/IEC 18000-6:2004 Information technology—Radio frequency identification for item management—Part 6: Parameters for air interface communications at 860 MHz to 960 MHz (type A, B, or C devices). These protocols are incorporated by reference herein. 
     However, the above protocols may not adequately address privacy and security concerns for certain RFID applications. For privacy, an RFID tag can be permanently disabled as described as one embodiment in U.S. Pat. No. 6,933,848, entitled “System and Method for Disabling Data on Radio Frequency Identification Tags,” assigned to Alien Technology Corporation, which is incorporated by reference herein. All of the efficiencies provided by RFID technology are lost with a permanently disabled tag. It would be advantageous for a tag to provide privacy, and yet continue to provide useful information (such as, a recycling identifier, hazardous waste information, or regulatory disposal requirements). 
     For security, a conventional tag can be locked, whereby individual memory banks cannot be read directly. In the supply chain, it may be prudent in some circumstances for a tag not to identify its associated item. For example, if the tag identifies a controlled pharmaceutical substance, one may want to conceal this fact during transport in the supply chain. But, if the tag&#39;s electronic product code (EPC) is inaccessible, the efficiencies provided by RFID technology are lost. A tag that affords security and continues to supply useful information (such as, a less specific EPC) is highly desirable. 
     The above protocols provide for reprogramming a tag with a new ID (“identifier”), however reprogramming a tag requires that the information to be programmed be available at the point where the ID is changed, and may require that many bits are programmed at the tag. For example, if it is desirable to replace an EPC with a recycle code, the best party to determine the proper recycle code may be the party that originally commissioned the tag, (programming it with its primary ID) rather than the retailer, consumer or other party who would decommission the tag from the supply chain and convert the tag into a recycle tag. If the recycle code or other recycle code is available in another memory segment of the tag, preexisting protocols would require that it be read out of the tag and then programmed into the ID memory of the tag, requiring multiple commands and taking substantial time. 
     From the above, it is seen that methods and apparatuses for “tiered” RFID devices having identifiers arranged in layers of an operating procedure, as described below, can provide many benefits. 
     SUMMARY OF THE DESCRIPTION 
     Methods and apparatuses for tiered RFID communication are provided for privacy and security. An RFID tag includes first and second memory locations respectively storing first and second identifiers. The tag is configured to respond to an identification query with the first identifier until receipt of a command code. After receipt of the command code, the tag is configured to respond to the identification query with the second identifier. 
     In a one embodiment, the first identifier is an electronic product code, and the second identifier is a recycling identifier, hazardous waste information, or regulatory disposal requirement for the item associated with the tag. This is also useful for end-of life disposal of battery tags themselves. The first identifier can be permanently disabled or erased for privacy. The first and second identifiers can also identify the tag&#39;s associated item with differing levels of specificity for improved security. 
     In another embodiment of the present invention, a method of operating an RFID reader includes transmitting a first query to a tag and receiving a first identifier. The reader transmits a command sequence to the tag specifying that it is to change its ID to an alternative ID stored in the tag. If any reader transmits a query at anytime after the command sequence, it will receive a second identifier in response from such tag. 
     In yet another embodiment of the present invention, a method for operating a tag includes receiving an interrogating RF signal. The interrogating RF signal provides power to the tag. After an arbitration sequence, the tag returns a first identifier to the reader. The tag receives a reveal code, or a conceal code, from the interrogator. The tag compares the reveal code from the interrogator to a code determined by, or alternatively stored on, the tag. If the comparing results in a successful match, the tag transmits a second identifier in response to any received identification query. If the comparing results in an unsuccessful match, the tag creates a persistent timeout interval, which prevents further attempts. 
     In yet another embodiment of the present invention, a method for operating a tag includes receiving an interrogating RF signal. After an arbitration sequence, the tag returns a first identifier to the reader. The tag receives a “kill” or “access” or similar code or command sequence (e.g., any command permitted by an RFID air-interface protocol or the like) from the interrogator using the same sequence of commands that conventional tags use for killing, accessing security functions, or other functions on those tags. The tag compares one or more codes received from the interrogator to one or more codes determined by, or alternatively stored on, the tag for this special purpose. If the comparing results in a successful match, rather than “killing” or going into the “access” mode, the tag transmits a second identifier in response, or alternatively changes permanently to a secondary ID and responds to further queries with the secondary ID. If the comparing results in an unsuccessful match, the tag responds in the same fashion as a conventional tag (e.g. by product an EPC). In a specific embodiment for enhanced security, one may not distinguish operation of a tag according to this invention to a conventional tag until receipt of a valid code and/or command sequence. The invention can be applied as a hidden custom feature operating consistent with a conventional protocol. It should be understood that to ensure complete anonymity of a disguised tag among conventional tags, the disguised tag should avoid inconsistent power usage as compared to conventional tags. In other words, in one embodiment, a disguised tag may use power only as expected with conventional tags, at least until the disguised tag receives a valid code and/or command sequence. 
     Various additional objects, features, and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1  illustrates a simplified flow diagram for a method according to an embodiment of the present invention. 
         FIG. 2  illustrates another simplified flow diagram for a method according to an embodiment of the present invention. 
         FIG. 3A  illustrates a simplified flow diagram for a method according to an embodiment of the present invention.  FIGS. 3B-C  show a simple example of tag memory that can be used in this or other embodiments of the present invention. 
         FIG. 4  illustrates an exemplary recycling system according to an embodiment of the present invention. 
         FIG. 5  shows an example of an RFID system according to one embodiment of the present invention. The figure includes a RFID reader and multiple RFID tags. 
         FIG. 6  shows an exemplary embodiment of an RFID tag according to an embodiment of the present invention. The exemplary tag includes an antenna, receiver/transmitter, and a controller, among other things. 
         FIG. 7  shows an example of an RFID tag according to another embodiment of the present invention. In particular, it illustrates an exemplary embodiment of a controller typically found in an RFID tag. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of the present invention. However, in certain instances, well known or conventional details are not described in order to avoid obscuring the description of the present invention. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one. 
       FIG. 1  illustrates a simplified flow diagram of a method  100  for tiered RFID according to an embodiment of the present invention. In operation  102 , a reader issues a query to command a tag to respond with its identifier along with any other information required by the air interface protocol (e.g., EPC, handle, cyclic redundancy check (CRC)). In response to the query, the tag responds in operation  104  with a first identifier. A reader query can include a bit pointer and mask to sub-select tags in a population matching the mask. In that case, matching tags may reply in operation  104  with a truncated response beginning with bit(s) of the first identifier that follow the mask. 
     Next, in operation  106 , a reader issues a REVEAL code to the tag. The REVEAL code instructs the tag to respond to queries with a second identifier in lieu of the first identifier. The second identifier, in this embodiment, provides increased product specificity over the first identifier. For example, the first identifier can simply indicate the item is an analgesic product, while the second identifier can indicate a particular morphine product. It should be noted that throughout this specification, a REVEAL code can be interchangeable with a CONCEAL code. The CONCEAL code instructs the tag to respond to queries with a less specific second identifier instead of the first identifier. 
     The REVEAL code (or CONCEAL code) can be specified by a user, factory pre-programmed (randomly or deterministically at factory), or calculated by an algorithm. The reader may also transmit a CRC along with the REVEAL code for one or multiple bit error detection. For example, the CRC can be 8, 16, 32, 64 bits long or more. The authentication process may use public-key cryptography or elliptic curve algorithms for key exchange or the like. Additional details of cryptography and elliptic curve algorithms are provided by (i) Neal Koblitz, An Elliptic Curve Implementation of the Finite Field Digital Signature Algorithm, 1998, Springer-Verlag Berlin Heidelberg, LNCS 1462, pp. 327-337; (ii) Diffie-Hellman, New Directions in Cryptography, November 1976, IEEE Transactions on Information Theory, pp. 644-654; (iii) “Public Key Cryptography for the Financial Services Industry: Elliptic Curve Key Agreement and Transport Protocols,” ANSI X9.63, Oct. 5, 1997, pp. 45-47; (iv) Koblitz, Neal, “Elliptic Curve Cryptosystems,” Mathematics of Computation, January 1987, pp. 203-209, vol. 48, No. 177, each of which is incorporated by reference herein. Embodiments of the present invention can use implement one or more error detection and/correction techniques, such as odd or even parity check, low-density parity-check code, turbo codes (as described in U.S. Pat. No. 5,406,570, which is incorporated by reference), or block codes and convolutional codes (e.g., Reed-Solomon error correction block codes, Viterbi-decoded short constraint length convolutional codes, or the like). 
     A REVEAL code calculated by an algorithm can be the result of a Boolean function (AND, OR, NOT, XOR, NOR, or combinations thereof) of a predetermined sequence and a tag handle. For example, the REVEAL code can be the XOR of the predetermine sequence and tag handle. The tag handle is a pseudorandom number generated by a tag and transmitted to the reader, whereby the reader can use the handle to provisionally identify such tag. If the range of allowed handles is sufficiently large in comparison to an expected tag population (e.g., 16, 32 or more bit handle), the handle is likely to uniquely identify the tag. If additional security is warranted, the REVEAL code can be implemented as two or more codes in a multi-operational procedure. For example, the REVEAL code can comprise of both (i) an XOR of a first predetermined sequence and a first handle and (ii) a multiplicative product of a second predetermined sequence and a second handle, wherein each of (i) and (ii) are transmitted separately to the tag. The first and second predetermined sequences and handles can be the same in certain embodiments. 
     Referring to  FIG. 1 , the tag may observe a REVEAL code in operation  108  transmitted by the reader. The tag verifies that the REVEAL code is valid by comparing the observed REVEAL code to a REVEAL code stored on the tag. For security and privacy, the REVEAL code stored on the tag is permanently locked and inaccessible, or at least password protected after initial commission of the tag. The tag&#39;s verification can include, among other things, (i) matching the codes, (ii) algorithmic operations prior to the matching codes, (iii) calculating a CRC for a code and comparing to a received CRC and (iv) combinations thereof. 
     In respective operations  110  and  112 , the tag can indicate receipt of a valid or invalid REVEAL code to the reader. Tag confirmation, for purposes of this specification, can be transmission of the REVEAL code, handle, pre-programmed code, or other sequence to the reader. If the reader does not receive a valid tag confirmation, it can re-transmit the REVEAL code. In a specific embodiment, a second attempt to process a REVEAL code can be subject to a persistent timeout interval as more fully described below. In operations  114  and  116 , assuming a valid REVEAL code is verified by the tag, a reader may issue a query and the tag will respond with a second identifier. 
     In respective operations  110  and  112 , the tag may emulate a command sequence which is available on conventional tags under a particular protocol, and may not indicate receipt of a valid or invalid “reveal” command sequence to the reader (or simply respond in a manner consistent with the particular protocol). For example, the invention can be a hidden custom feature providing anonymity of a disguised tag operating according the present invention. In operations  114  and  116 , assuming a valid command sequence or key exchange is verified by the tag, a reader may issue a query and the tag will respond with a second identifier. 
       FIG. 2  illustrates another simplified flow diagram for a method  200  of tiered RFID according to an embodiment of the present invention. In operation  202 , a reader issues a REVEAL code and CRC therefor. This can be done at a consumer point of sale (e.g., cash register, check-out line, self check-out station, in-store kiosk, automated teller machine, or the like) during a purchase of an item associated with a tag. The tag next observes a valid REVEAL code and CRC in operation  204 . Responsive to a valid REVEAL code, the tag disables a first identifier and enables a second identifier in operation  206 . Operation  206  can be accomplished using many techniques that will be clear to one skilled in the art based on the teachings contained this specification. One example would be to overwrite a specific memory location storing the first identifier with the second identifier. 
     An alternative implementation of operation  206  is to redirect a memory pointer from a first memory location to a second memory location storing the respective identifiers. If a memory pointer is redirected, the first memory location can still be overwritten to make the first identifier permanently irrecoverable. However, certain RFID application may require their first and second identifiers be reused depending on the context. For example, a tag may respond to queries with a first identifier outside a controlled area (such as a hospital, pharmacy, clinic, and the like) and respond with a second identifier inside the controlled area. This is particularly advantageous if the tagged item is repeatedly moved between controlled and non-controlled areas. 
     Another alternative implementation of operation  206  is to set a flag at the tag. The flag can be used by the logic of the tag to determine which information is to be replied as the ID during an inventory. The setting of the flag may also make the original ID of the tag inaccessible, or the tag may erase the original ID, either immediately or at a later opportunity. 
     Method  200  may also include a persistent timeout interval (not shown in  FIG. 2 ) for additional security. The persistent timeout interval prevents a rapid succession of attempts to “crack” the REVEAL code. If the timeout period is sufficiently long, it may take hours, days, weeks, or years to attempt all permutations of the REVEAL code, thus preserving privacy and/or security. Techniques for persistent data for passive tags are described in U.S. Pat. No. 6,942,155 (assigned to Alien Technology) and U.S. Pat. No. 7,116,240 (apparently assigned to Impinj, Inc.), both are incorporated by reference herein. 
       FIG. 3A  illustrates a simplified method  300  according to an embodiment of the present invention. A reader issues and tag receives a valid RECYCLE code in operations  302  and  304 . Responsive to the RECYCLE code in operation  306 , the tag disables its EPC and enables access to recycle information. Recycle information can include, without limitation, constituent materials of the item, hazardous waste information, regulatory requirements, recycling center information, redemption value of the item (e.g., beverage containers). A reader, not necessarily the reader that transmitted the REVEAL code, can read the tag&#39;s recycle information in operation  308 . The tagged item can then be automatically sorted in operation  310  based on the recycle information stored on the revealed tag, and finally disposed or recycled in the appropriate manner in operation  312 .  FIGS. 3B-C  show a simple example of tag memory that can be used in method  300  or other embodiments of the invention. 
       FIG. 4  illustrates an exemplary recycling system  400  according to an embodiment of the present invention. System  400  includes a reader  402  coupled to antennas  404   a ,  404   b  and computer  406 . Reader  402  can be operating in a bistatic, monostatic, or multistatic mode with the antennas. As illustrated in  FIG. 4 , tags  408   a ,  408   b  are physically coupled to items to be identified. These items are moved along a conveyer and recycle codes read by reader  402 . This recycle information is provided to automatic sorter  410 . Sorter  410  can segregate items based on their respective recycle information using magnets, sifters, centrifuges, fluid separators, vacuum loaders, or other known techniques to divert items (or a constituent material, gas, liquid, or sludge) to an appropriate branch line, bin, receptacle, compactor, or hopper. Automatic sorting can provide greater efficiency over manual sorting requiring visual inspection of items. It can also reduce or eliminate the need for private consumers to pre-sort their refuse before collection. Although  FIG. 4  depicts a distributed system  400 , an alternative system can include a reader, antennas, computer, and automatic sorter integrated into a single piece of equipment. In a specific embodiment, system  400  can also include decontamination equipment (e.g., to wash, heat, or sterilize) and containment equipment for hazardous waste. Decontaminants can include alcohol solution, ethylene oxide, water, detergent, hydrogen peroxide, sodium hydroxide, chloramines solutions, hot steam, hot air stream, and the like. 
       FIG. 5  illustrates an exemplary radio frequency identification (RFID) system  500 , which includes an RFID reader  501  and a plurality of RFID tags  531 ,  533 ,  535 , . . . , and  539 . The system can be either a reader-talks-first or tag-talks-first system using passive, semi-passive, or active tags. Reader  501  typically includes a receiver  519  and a transmitter  523  (alternatively, a transceiver), each of which is coupled to an I/O (input/output) controller  517 . The receiver  519  may have its own antenna  521 , and the transmitter  523  may have its own antenna  525 . It will be appreciated by those in the art that the transmitter  523  and the receiver  519  may share the same antenna provided that there is a receive/transmit switch which controls the signal present on the antenna and which isolates the receiver and transmitter from each other. The receiver  519  and the transmitter  523  may be similar to receiver and transmitter units found in conventional readers. In North America, the receiver and transmitter for RFID typically operate in a frequency range of about 915 megahertz (e.g., 902 MHz-928 MHz) using spread spectrum techniques (e.g., frequency hopping). In Europe, the frequency range is about 866 megahertz (e.g., 865.7 MHz-867.7 MHz). Other regions have set aside, or are in the process of setting aside, frequency ranges for operation—these ranges of operation typically lie somewhere in the overall range of 200 MHz to 5 GHz. Each is coupled to the I/O controller  517  which controls the receipt of data from the receiver and the transmission of data, such as commands, from the transmitter  523 . The I/O controller is coupled to a bus  515  which is in turn coupled to a microprocessor  513  and a memory  511 . 
     There are various different possible implementations for the processing system represented by elements  511 ,  513 ,  515 , and  517 , which may be used, for example, in the exemplary RFID reader  501  of  FIG. 5 . In one embodiment, the microprocessor  513  is a programmable microcontroller, such as an 8051 microcontroller or other well-known microcontrollers or microprocessors (e.g. a PowerPC microprocessor) and the memory  511  includes dynamic random access (DRAM) memory. Memory  511  may also include a non-volatile read only memory for storing data and software programs. The memory  511  typically contains a program which controls the operation of the microprocessor  513  and also contains data used during the processing of tags as in the interrogation of tags. In some embodiments of the present invention, the memory  511  would typically include a computer program which causes the microprocessor  513  to decode received tag data with the appropriate tag-to-reader protocol scheme. The reader  501  may also include a network interface (not shown in figure), such as an Ethernet interface, universal bus interface, or Wi-Fi interface (such as IEEE 802.11, 802.11a, 802.11b, 802.16a, Bluetooth, Proxim&#39;s OpenAir, HomeRF, HiperLAN and others), which allows the reader to communicate to other processing systems through a network, including without limitation an inventory management system, central store computer, personal computer, or database server. The network interface would typically be coupled to the bus  515  so that it can receive data, such as the list of tags identified in an interrogation, from either the microprocessor  513  or from the memory  511 . 
       FIG. 6 . shows an example of one implementation of a radio frequency identification (RFID) tag which may be used with the present invention. The tag  600  includes an antenna  601  (alternatively, two, three or more antennas) which is coupled to a receive/transmit switch  603 . This switch is coupled to the receiver and demodulator  605  and to the transmitter and modulator  609 . A controller unit  607  is also coupled to the receiver/demodulator  605  and to the transmitter/modulator  609 . The particular exemplary RFID tag shown in  FIG. 6  may be used in various embodiments of the present invention in which data is maintained in a memory (not shown in figure). The receiver and demodulator  605  receives signals through the antenna  601 , e.g., interrogation signals from a reader (not shown in figure), and the switch  603  and demodulates the signals and provides these signals to the controller unit  607 . Commands received by the receiver  605  are passed to the controller of the unit  607  in order to control the operation of the tag. Any additional data received by the receiver  605  is also passed to the control unit  607 , and this data may include handshaking data (e.g., parameters for a tag-to-reader encoding protocol). The transmitter and modulator  609 , under control of the control unit  607 , transmits responses to the commands or other processed data through the switch  603  and the antenna  601  to the reader. It will be appreciated by those skilled in the art that the transmitter may be merely a switch or other device which modulates reflections from an antenna, such as antenna  601 . 
     In certain embodiments of the present invention, RFID tags may be designed with a small integrated circuit (IC) area, a small memory, atomic transactions to minimize tag state storage requirements, and the like. This type of design will lower the tag production cost, thereby enabling wide-scale adoption of RFID labeling in a variety of industries, for example, in the supply chain.  FIG. 7  shows an example of a low cost tag  700 . The tag  700  includes an antenna  701  and an integrated circuit (IC)  703 , coupled together. Tag IC  703  implements the command protocol and contains data such as an EPC. The antenna  701  receives the reader-generated interrogation signals and reflects the interrogation signal back to the reader in response to a modulation signal created by the tag IC  703 . The exemplary tag IC  703  comprises a radio frequency (RF) interface and power supply  711 , data detector and timing circuit  713 , command and control  715 , data modulator  717 , and memory  719 . In one embodiment, command and control  715  may include static logic (such as a state machine) which implements communication protocols according to various embodiments of the present invention. 
     The RF interface and power supply  711  converts the RF energy into the DC power required for the tag IC  703  to operate and provides modulation information to the data detector and timing circuit  713 . The RF interface also provides a means of coupling the tag modulation signals to the antenna for transmission to the reader. The data detector and timing circuit  713  demodulates the reader signals and may generate timing and data signals used by the command and control  715 , including a subcarrier sequence. The command and control  715  coordinates all of the functions of the tag IC  703 . The command and control  715  may include state logic to interpret data from the reader, perform the required internal operations, and determine if and/or how the tag will respond to the reader. The memory  719  contains the EPC, which may be associated with the tagged item. The data modulator  717  translates the binary tag data into a tag-to-reader encoded signal that is then applied to the RF interface  711  and transmitted to the reader (e.g., reader  501  of  FIG. 5 ). In one embodiment, IC  703  is a NanoBlock™ IC made by Alien Technology Corporation of Morgan Hill, Calif. 
     The design and implementation of RFID tags can be characterized in terms of layers. For example, a physical and environmental layer characterizes the mechanical, environmental, reliability and manufacturing aspects of a tag, an RF transport layer characterizes RF coupling between reader and tag, and a communication layer characterizes communications/data protocols between readers and tags. Various different implementations of tags at different layers can be used with embodiments of the present invention. It is understood that the implementations of the tags are not limited to the examples shown in this description. Different tags or communication devices can use methods and apparatuses of the embodiments of the present invention for communication according to the needs of the particular application. 
     In one embodiment of the present invention, a tag may be fabricated through a fluidic self-assembly process. For example, an integrated circuit (e.g.,  703  of  FIG. 7 ) may be fabricated with a plurality of other integrated circuits in a semiconductor wafer. The integrated circuit will include, if possible, all the necessary logic of a particular tag, possibly excluding the antenna  701 . Thus, all the logic shown in the tag  700  would be included on a single integrated circuit and fabricated with similar integrated circuits on a single semiconductor wafer. Each circuit may be programmed (or pre-programmed) with a unique identification code and then singulated (and shaped) from the wafer. Integrated circuit block can be singulated by many techniques, including those described in U.S. patent No. application Ser. No. 11/546,683 filed on Oct. 11, 2006, entitled “Block Formation Process”, which is incorporated by referenced. Integrated circuit blocks are next suspended in a fluid. The fluid is then dispersed over a substrate, such as a flexible substrate, to create separate tags. Receptor regions in the substrate would receive at least one integrated circuit, which then can be connected with an antenna on the substrate to form a tag. An example of fluidic self-assembly (FSA) is described in U.S. Pat. No. 6,864,570, entitled “Method for Fabricating Self-Assembling Microstructures,” which is incorporated by reference herein. 
     Alternatively, other conventional or unconventional assembly methods may be used to construct the radio frequency tag. Silicon integrated circuits, formed using standard CMOS processes can be bonded to an antenna using robotic techniques (e.g., pick and place methods, surface mounted flip chips, and the like), vibratory assembly techniques, or a wire bonding construction. The chip can be placed in a carrier, such as a lead frame or a strap, or be bonded directly to an antenna. Strap attachment may be accomplished in automatic web processes using Alien Technology Corporation&#39;s high speed strap attach machine (HiSAM™ machine). The chip need not be made of silicon—devices built from semiconductors such as GaAs, or even organic semiconductors, can achieve the benefits derived from these communication methods. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. For example, the invention has been described in detail for reader-talk-first systems, but the invention can be applied to tag-talk-first systems. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.