Abstract: A golf distance indicator system provides measurement and display of the distance between a golfer and the pin on the green he is approaching. The system comprises a portable unit carried by the golfer and an target unit located on the pin. With the portable unit, the golfer selects the hole he is playing then activates the system. The portable unit sends a wireless coded message to an intended target unit. When a target unit receives a message, it analyzes the message to see if it should respond. If the target unit determines that it should respond, it sends a coded responding message to the portable unit. When the portable unit receives a responding message, it analyzes the responding message to see if the responding message originates from the intended target unit. If it does, the portable unit calculates a distance based on the elapsed time for the communications and the speed of the communications. The results are displayed on the portable unit.

Abstract: A radio frequency identification system employing a thin, flexible electronic radio frequency identification (RFID) tag having an overall thickness not exceeding approximately 280 microns and the process for its manufacture is disclosed. The RFID tag includes an insulating, flexible substrate having an aperture formed therein for receiving an RFID circuit chip. An antenna forming an integral part of the substrate is electrically connected to circuit chip. A cured adhesive having a portion substantially parallel with the substrate encapsulates the circuit chip so that the chip is operably retained within the substrate aperture.

Abstract: The RF tag system of the present invention minimizes the effect of the RF tag on the overall radar cross section (RCS) of the object with which it is associated, tailors the signal reflected from the tag to match the actual RCS of the object with which it is associated, utilizes an RF tag design that reduces degenerative RF coupling at the tag, and is designed to exploit the operational features of conventional pulse Doppler radars. In accordance with one embodiment of the present invention, a radio frequency tag system is provided including an interrogator and a tag. The tag is secured to an object. The interrogator is configured to generate a transmitted electromagnetic interrogation signal at a predetermined interrogation frequency. The tag comprises an antenna array including a plurality of receiver antennas and a plurality of transmitter antennas.

Abstract: A modulated backscatter communication system (e.g., an Electronic Shelf Label (ESL) system) includes a central node (e.g., a ceiling node) and one or more remote nodes (e.g., ESL tags). The central node transmits a downlink radio signal which is reflectively modulated at a remote node to produce a modulated reflected radio signal. At the remote node, a precise-frequency subcarrier signal is modulated with an uplink information signal to produce a modulated signal which is used to produce the modulated reflected radio signal. At the central node, the modulated reflected radio signal is received, detected and narrowband filtered to obtain the modulated subcarrier signal which is then demodulated to obtain the uplink information signal, with great immunity to close to carrier downlink radio noise and fluorescent light backscatter interference.

Abstract: The invention encompasses a living organism sensing device. Such device comprises a conductive loop extending over a substrate. The loop comprises carbon particles. The device further comprises a circuit which includes the conductive loop as a first circuit component and a transponder as a second circuit component. The transponder is configured to emit a first signal if the loop of conductive material is continuous and a second signal if the loop of conductive material is broken. The second signal is different than the first signal. The invention also encompasses a termite sensing device. Such device includes at least one wooden block, and a conductive loop proximate the wooden block. The loop comprises conductive particles of carbon. The termite sensing device further includes an electrical circuit comprising the conductive loop as a first circuit component and a transponder as a second circuit component.

Abstract: A passive electrical marker has tuned circuits, each of which includes a coil and a capacitance. The tuned circuits are oriented with respect to each other in a predetermined arrangement so as to provide a broader spatial response. A foamed core inside of the tuned circuits maintains the tuned circuits in their respective orientations and protects the tuned circuits from mechanical shock. A shell or housing around the foamed tuned circuits provides environmental protection to the tuned circuits. The tuned circuits can be foamed together in a mold and then placed into the housing. Alternatively, the tuned circuits can be foamed together inside of a housing, which housing maintains the orientations between the tuned circuits during foaming. As still another alternative, the housing can be applied to the outside of the foamed tuned circuits as a coating.

Abstract: A transponder communication device has an interrogation signal generator for generating an interrogation signal, a transmitter for transmitting the interrogation signal to a number of transponders, and a receiver for receiving answers signal from transponders. A transponder has an interrogation signal detector, an answer signal generator, and a state setting controller for setting a state of the transponder. The transponder communication device selects a single transponder from the number of transponders. First, the transponder communication device transmits an initial interrogation signal is transmitted to all transponders when the transponders are in an active state. In dependence of answer signals received from the transponders, the transponder communication device transmits a standby setting signal to at least one transponder at a time to instruct the transponders to adopt a standby state. In the standby state the transponders wait until a single other transponders has been selected.

Abstract: A radio communication system includes an Interrogator for generating and transmitting a radio signal. One or more Tags contained within the radio communication system receive the radio signal. A Backscatter Modulator modulates the reflection of the radio signal using a subcarrier signal, thereby forming a reflected modulated signal. The Interrogator receives and demodulates the reflected modulated signal. Based upon the characteristics of the demodulated signal, the Interrogator can determine the identity of the Tag, and the relative velocity of the Tag with respect to the Interrogator. The Interrogator can also determine if motion exists in the vicinity of the Interrogator, even when no Tag is present, without the need for a separate motion detection system. The characteristics of the demodulated signal, can also be used to determine the characteristics of motion of the Tag, such as the vibrational frequency.

Abstract: An RFID tag circuit provides magnetic decoupling and amplitude modulation. The circuit is made up of a first inductor and a second inductor connected in series, a first capacitor, a second capacitor, and a switch. The circuit includes a first resonant circuit formed from a parallel connection of the series connected first and second inductors, and the first capacitor. The first resonant circuit has a primary resonant frequency. The circuit also includes a second circuit formed from a series connection of the second capacitor and the switch. The series connection of the second capacitor and the switch are connected in parallel to the second inductor. One end of the series connected second capacitor and switch is connected to the common connection between the series connected first and second inductors.

Abstract: A system of vehicle identification with a first interrogator that uses a Lower SideBand (LSB) receiver to receive a modulated signal from a vehicle transponder and a second interrogator that uses an Upper SideBand (USB) receiver to receive another modulated signal. The two interrogators are adjacent to each other at a toll plaza, and operate at different carrier frequencies to force a signal frequency bandgap between communication signals in adjacent vehicle lanes.

Abstract: A method and apparatus for communicating between a host and a motor vehicle, the motor vehicle including an on board computer system having a bus for communicating with a plurality of motor vehicle systems. The apparatus includes an electronic tag having a transceiver for transmitting data to and receiving data from the host, a memory for storing bus requests and bus response data, a decoder for decoding requests from the host, a bus interface for reading data from and writing data to the bus and a conroller. The bus interface for extracting responses from the bus responsive to requests from the host. The responses may be stored in the memory. The controller is responsive to write requests from the host to transfer data to the bus interface and responsive to read requests from the host to transfer data stored in memory back to the host.

Abstract: A transponder 20 for an electronic identification system transponder is characterized in that it presents a high input impedance (>400.OMEGA.) at an input thereof which is directly connected to an antenna 22 with a matched high input impedance. The transponder is aimed at improving the voltage recovered on capacitor C.sub.2 from an interrogation signal and thus the operational range of the system. The modulator 30 of the transponder is arranged to backscatter modulate the interrogation signal at a modulation depth of less than 80%, preferably in the order of 30%. This also results in an improvement of the operational range of the system.

Abstract: A new VIN Reading and Transmitting System for providing a device for automatically detecting a vehicle identification number and transmitting the number to a dispatch station for immediate identification of the vehicle and owner. The inventive device includes a vehicle unit containing the vehicle identification number, a portable unit which enables the vehicle unit to transmit the number which is detected by the portable unit, a digital repeater which receives a signal from the portable unit for transmitting to a receiver at the dispatch office where the number can be utilized to disclose the vehicle and the owner which can be transmitted to the police officer immediately.

Abstract: A novel apparatus for reliably and selectively releasing a data acquisition package from an animal for recovery. The data package comprises two parts: 1) an animal data acquisition device and 2) a co-located release apparatus. One embodiment, which is useful for land animals, the release apparatus includes two major components: 1) an electronics package, comprising a receiver; a decoder comparator, having at plurality of individually selectable codes; and an actuator circuit and 2) a release device, which can be a mechanical device, which acts to release the data package from the animal. To release a data package from a particular animal, a radio transmitter sends a coded signal which is decoded to determine if the code is valid for that animal data package. Having received a valid code, the release device is activated to release the data package from the animal for subsequent recovery.

Abstract: Contactless transmission of information from a passive transponder to a base station takes place in known manner by load modulation in the transponder. The coils of resonant circuits in the base station and in the transponder are coupled to one another, both resonant circuits being tuned as well as possible to the carrier frequency of the base station so that the load modulation of the resonant circuit in the transponder influences the current in the resonant circuit of the base station. Because the two resonant circuits often are not tuned exactly to one another in practice and the transponder is also liable to be moved during the information transmission, it may occur that no signal is recovered by conventional demodulation in the base station.

Abstract: A radio communications system is that can determine the location of an RFID Tag. The radio communication system includes at least one Interrogator for generating and transmitting a modulated radio signal to one or more Tags. The Interrogator is at a known location, and is in motion with respect to the Tag at a known velocity. One or more Tags of the system receive and demodulate the modulated radio signal, which contains a first information signal which specifies which Tag or Tags should respond using Modulated Backscattering. The Tag generates a subcarrier signal, and backscatter modulates the reflection of the radio signal using the subcarrier signal, thereby forming a reflected signal. The Interrogator receives and demodulates the reflected signal. The Interrogator then determines the Tag's relative direction from the location and velocity of the Interrogator, and from the Doppler shift of the subcarrier signal. More than one of such measurements allow the location of the Tag to be determined.

Abstract: A wireless identification device including a housing; circuitry in the housing configured to provide a signal to identify the device in response to an interrogation signal; and a selectively actuated switch supported by the housing and permitting operation of the circuitry only while the switch is actuated. A method of manufacturing a wireless identification device, the method comprising configuring circuitry to provide a signal to identify the device in response to an interrogation signal; coupling the circuitry to a selectively actuated switch, such that the circuitry provides the signal only while the switch is actuated; and encasing the circuitry in a housing such that the switch is actuable from outside the housing by touching a portion of the housing.

Abstract: The present invention provides wireless communication devices, radio frequency identification devices, and methods of forming wireless communication devices and radio frequency identification devices. According to one aspect of the invention, a wireless communication device includes a substrate; communication circuitry supported by the substrate; and a housing over at least a portion of the substrate and including a substantially rigid first housing portion; and a second housing portion configured to have increased flexibility with respect to the first housing portion.

Abstract: An acoustic wave identification transponder device, having a substrate, an electroacoustic transducer generating an acoustic wave in said substrate and a set of encoding elements disposed in a path of the acoustic wave for modifying the acoustic wave, having at least two reflective elements disposed in the acoustic path of the acoustic wave such that an acoustic path length of the acoustic wave on the substrate is longer than twice a largest linear dimension of the substrate. The device preferably includes an angled elongated conductor formed on said substrate, having angle magnitudes whose sum exceeds .pi. radians, said angled elongated conductor defining at least a portion of the acoustic path.

Abstract: Novel means of achieving increased security while still obtaining a low cost, manufacturable device are disclosed and claimed. The first mode of operation is the learn mode which provides means for initial checkout with no security. In the learn mode of operation, the interrogator and transponder may be switched to a predetermined error detection algorithm, i.e. CCITT(Start Mask, CCITT Mask), and certain information is programmed into the transponder memory. During programming, all the bits received from the interrogator are shifted through the preintialized CRC generator. In addition, once the transponder response is sent back to the interrogator, the response is also shifted through a preinitialized CRC generator within the interrogator(which could be a software implementation). Because neither the Cypher Key nor the Function Key are directly readable once programmed, an encryption must be performed to verify the proper Cypher Key and Function Key were programmed into the transponder's memory.

Abstract: An antenna circuit configured for use in a radio frequency data communications device has an antenna constructed and arranged to transfer electromagnetic waves, the electromagnetic waves corresponding to a signal carried by the antenna and generated from a signal source. A Schottky diode is electrically coupled in serial relation with the antenna, and in operation the signal is applied serially across the antenna and the diode in direct relation with electromagnetic waves transferred by the antenna. A bias current supply is also electrically coupled to the Schottky diode and is configurable to deliver a desired bias current across the current. The diode is responsive to the bias current to realize a desired diode impedance such that a desired impedance matched/mis-matched is provided between impedance of the diode and impedance of the antenna when the signal is applied across the antenna circuit, which selectively tunes the antenna circuit by imparting a desired power transfer therein.

Abstract: A method, system, and apparatus for sending data from a base station to an RF tag, whereby the RF tag comprises an "intention to write to memory" field, and the "intention to write to memory" field is written before writing the data and cleared after the data is successfully written. If the data transmission is interrupted and partial data is written to the tag, the "intention to write to memory" field will not have been cleared when the tag is checked at a later time through interrogation by a base station.

Abstract: A transponder antenna is carried by a substrate and is sandwiched between the substrate and a cover sheet. A rectangular opening extends through the cover sheet and receives a signal processing chip adhesively carried in a recess below a cap which covers the opening. The chip is spaced with respect to the antenna so as to facilitate direct or inductive coupling between the chip and antenna. The cap has a protective portion which extends through the cover opening substantially all the way to the substrate so as to prevent accidental contact between the chip, on one hand, and the substrate and/or antenna on tee other.

Abstract: An RF identification transponder comprises a substrate layer, and an array of M*N antenna elements formed on the substrate layer, where M and N are integers. The antenna elements have a common predetermined resonant frequency f.sub.r. The resonant frequency of the transponder's antenna element array allows it to be identified apart from other transponders, each having an antenna element array with a different resonant frequency.

Abstract: A Write Broadcast system and method uses a base station to write sent data associated with no particular destination tag or tags, by radio frequency signal, to all or some selected number (sub group) of tags in a base station field simultaneously. By unselecting the tags that have been successfully written to, and requesting a response from the remaining tags in the field (or sub group), the system determines, by receiving a response to the request, that there are tags in the field (sub group) that were unsuccessfully written to. Another Write Broadcast signal is sent to these tags. The system is useful for quickly (simultaneously) "stamping" information on the tag memory of a large number of tags in the field of the base station.

Abstract: Process for managing concurrent access permitting the successive input or storage of several slave devices (receiver/transmitter) in the field of action of a master device (emitter/reader) so as to render possible the exchange of data in two directions whilst guaranteeing coherent transmission between the master device and each slave device. This process is based on a double temporary address of the slave devices. Upon each command emitted by the reader, two values are transmitted, the first comprising the identification of the next free number and the second the number of the receiver to which the command is directed.

Abstract: A method and apparatus for simultaneously storing a set of read/write or respond-to-order transponders located in a container. The method transmits radiation to read/write trnsponders to energize them, receives identity data transmitted by the transponders, verifies that the identity data are not subject to dispersion, transmits a data group to the transponders, and stores the data group in memories of the transponders. If the identity data are subject to dispersion, the method interrupts radiation transmission in order to deactivate the transponders and then retransmits the radiation until the data are not subject to dispersion so that the data group can be transmitted to the transponders for storage in their memories. In the case of respond-to-order transponders, a signal is also transmitted. If the identity data are subject to dispersion, the signal is retransmitted until the data are not subject to dispersion, and then the data group is transmitted to the transponders and stored in their memories.

Abstract: A novel addressing scheme for an RF-ID system or LAN network is presented in which an interrogator(reader) addresses a set of transponders, each transponder in this set having a common addressing scheme, and the addressed transponders respond only upon the matching of their own address with the received addressing scheme. The addressing scheme comprises a fixed size sub-address and a variable size mask. For example, assuming that the transponder address is 32 bits, the implementation of the addressing scheme can choose 4 bits for the size of the sub-address and 0, 4, 8, 12, 16, 20, 24, 28 bits for the size of the mask. By varying the addressing scheme according to the algorithm in FIG. 4, the reader will in time interrogate all the transponders individually, thus receiving their unique address and achieving the requested exhaustive inventory.

Abstract: A passive radio frequency transponder (RF tag) having a diode rectifier receiver circuit outside the tag power rectification circuit, the tag power rectification circuit supplying power to the electronics of the RF tag. An additional innovative low current circuit protect the signal capacitor from overvoltage produced by the signal diode. An innovative circuit also clips the signal and sharpens it. An innovative low current circuit is used as a comparator to sharpen the signal pulses.

Abstract: An identification and/or sensor system includes a sensor that queries an identification and/or sensor configuration which contains resonators. A receiver receives an answer signal from the identification and/or sensor configuration. The receiver includes a phase-locked loop for converting a resonator decay signal into a signal of constant frequency and constant envelope curve.

Abstract: In one aspect, the present invention provides an air coil 20. The air coil 20 may be made from a strip of electrically conductive material 22 which has an insulating material overlying it. For example, the conductive material may comprise copper. The strip 22 is wound into a coil to perform a plurality of windings. The insulating material electrically insulates each of the windings from adjacent ones of the windings.

Abstract: A system for identifying probe cards including a prober which accepts a number of interchangeable probe cards, each carrying a transponder tag; a magnetic coupling antenna supported above the probe card when it is in use, the transponder tag being substantially located within a magnetic field generated by the magnetic coupling antenna; and circuitry connected to the magnetic coupling antenna for receiving signals emitted by the transponder tag, for deriving data therefrom, and for communicating the data to a central computer which holds information on the probe cards in a memory.

Abstract: A transmitting and receiving system including, a transponder always maintains a transmission function even if circuit constants of circuit elements are deviated or such circuit constants are shifted in association with temperature changes. The transponder includes a transponder coil electromagnetically coupled to an antenna coil through which a response signal is transmitted, a resonance capacitor, a main modulation circuit including a first modulation capacitor, and a supplemental modulation circuit including a second modulation capacitor whose static capacitance value is different from that of the first modulation capacitor. A response signal is transmitted in changing an impedance of a transmitting and receiving portion by the main modulation circuit when a question signal is received and by the supplemental modulation circuit when a correction command signal is received.

Abstract: A system and method for identifying objects. A preferred embodiment employs a radio transceiver on each object. Each article is identified by recording an amplitude at which the respective transceiver exhibits a nonlinearity.

Abstract: System for automatic fuelling of a vehicle and debiting for fuel obtained. A transponder is provide on the vehicle for the positioning of a fuelling robot and includes coded information to be utilized for the debiting function.

Abstract: A device of a vehicle for data transmission to a stationary beacon 91), which has a transceiver, comprising an on-board unit (2) with an antenna (6) for receiving a continuous signal (5), broadcast by the beacon (1), and for transmitting the received signal (5) back after modulation with a data signal (i(t)), is characterized in that the signal (7) transmitted back by the on-board unit (2) is a double-sideband signal. In that case, the on-board unit (2) can be designed as extremely simply and in the simplest case comprises a diode (9) connected to the base of the antenna (6).

Abstract: A method and apparatus for determining the identification number or any other information within a plurality of radiofrequency identification tags within a common field of interrogation utilizes a combination of an isolation state into which the tags may be placed together with bitwise interrogation of the identification number or information followed by selective deactivation. A first bit in the identification number or information is interrogated of all the tags in the field. If any tag responds that the bit is a 1, a 1 is entered into an ID register in a reader and all tags in which a 0 exists in that bit position are deactivated. The process continues until only one tag remains activated. The last activated tag at this point has been completely read and is then placed in an isolated state. The process is begun anew with the remaining nonisolated tags until all tags have been read.

Abstract: An identification mark operating with acoustical surface waves includes at least one reflector having higher reflectivity than a reflectivity of other reflectors.

Abstract: A transponder unit (10) includes an N cycle counter (30) and an M cycle counter (28). The N cycle counter (30) has a different cycle value than the M cycle counter (28). During the transmission of information from the transponder unit (10), the duration for data bits having a binary zero value is controlled by the N cycle counter (30). The duration of data bits having a binary one value is controlled by the M cycle counter (28). The use of different cycle values within the N cycle counter (30) and the M cycle counter (28) allows for the transmission of binary one and binary zero data bits having the same bit length despite different frequencies representing the binary one and binary zero bits respectively.

Abstract: A wireless communications system comprising a first transponder having a plurality of selectable antennas, and having a stack including locations holding data representing antennas, the stack defining an order in which antennas will be used to attempt communication; a second transponder configured to communicate with the first transponder, wherein the first transponder uses an antenna defined by data in one location of the stack for communication with the second transponder, and, if successful communication with the second transponder is not established, the transponder uses an antenna defined by data in another location of the stack.

Abstract: The invention provides a microstrip patch antenna for emitting backscatter-modulated signals in response to a received signal. The antenna has two segments that are connected together by a switch. When the switch is ON, the antenna is a full wave length antenna with its two segments out-of-phase with each other, thus producing minimal backscatter. When the switch is OFF, the two segments of the antenna act in concert with each other to produce a backscatter-modulated signal. Multiple pairs of such antennas can be connected together to make a single antenna with increased signal power.

Abstract: A long range identification system is disclosed for utilizing a radio frequency (RF) signal sent by a calling location, such as a mass transit vehicle, as the energy source to power response apparatus at a responding location, such as a route stop of the transit vehicle. The responding signal is then broadcast within the transit vehicle as audio or as a video display of a signal from a character generator, or as both audio and video.

Abstract: A system and method in which a transponder (14) is operable to transmit an original user account balance to an interrogator (12), which in turn calculates a revised user account balance and transmits the revised user account balance to the transponder (14). In one embodiment of the invention, the transponder (14) is further operable to transmit a verification user account balance back to the interrogator (12), which then compares verification user account balance to the revised user account balance that was earlier calculated and stored in an interrogator memory.

Abstract: Transponder signal collision avoidance system incudes a reader and wireless HDX or FDX type transponders (A, B) are disclosed, interrogated by the reader (R) by alternately powering and then reading through cycles corresponding to a number of possible transponders in the interrogation field. The cycles, which include reader power pulses, signify addresses of respective possible transponders, whether in or out of the field. The transponders for this purpose count reader power pulses by end-of-burst detection, increasing a stored count value with each reader power pulse. The transponder responds to the reader by transmission if and only if a stored count value in a read cycle matches a respective transponder address, preventing the transponders from transmitting telegrams interfering with each other.

Abstract: A method and apparatus for sensing corrosion are provided in which an interrogation unit (14) transmits interrogation pulses and receives responses. A plurality of corrosion sensors (12) are disposed in the structure to be monitored (10), each of the sensors (12) generating an output. A plurality of responders (16) are powered from the interrogation pulses, one each of the responders (16) associated with one each of the sensors (12). The responders (16) are operable to transmit responses to the interrogation pulses based on the corrosion sensors' (12) output.

Abstract: Security devices which are difficult to reproduce include a grid screen metallization pattern. The grid screen metallization pattern may be laid down over a hologram or diffraction grating formed as a surface relief pattern on a substrate, to form a visually identifiable, semi-transparent security device. Additionally, the metallization pattern may include resonant structures in which information about the security device is encoded. In some embodiments of these security devices, the metallization pattern is disposed in accurate registration with the underlying hologram or diffraction grating. These security devices are made by methods which include printing an oil pattern on the substrate. Areas on which oil is deposited do not receive metal during a metallization step. Since these methods do not use caustics, metallization patterns including features which would otherwise trap and hold caustics are possible.

Abstract: In accordance with the present invention, an RFID system has a homodyne receiver having two outputs; the in-phase or I output and the quadrature or Q output. The modulated backscattered signal is composed of an information signal, modulated onto a single frequency subcarrier signal, generating a modulated subcarrier signal; this modulated subcarrier signal is then backscatter modulated onto the incoming RF signal. To demodulate this modulated backscattered signal, the I and Q outputs are combined using an IQ combiner. This IQ combiner introduces a 90.degree. phase shift, with respect to the frequency of the subcarrier signal, onto one of the demodulator outputs and then combines the outputs of the demodulator.

Abstract: A vehicle (V) is fitted with a primary receiver/emitter cell (1) containing a first code (C1) and a secondary receiver/emitter cell (2) containing a second code (C2) as well as a first representation (FR1) of the first code (C1). The two cells receive respectively primary (EIB1, EIA1) and secondary (EIB2) selective interrogations (OI) to which they respond by emitting respectively a primary response (ERB 1, ERA 1) representing the first code (C1) and a secondary response (ERB2) representing the second code (C2). Then the secondary cell (2) responds alone to a complementary interrogation (EIC) which contains a second representation (SR2) of the first and second codes emitted, together with an order.

Abstract: A reader interrogates a transponder attached to a remote object. The transponder includes a microstrip patch antenna having two segments connected together by a switch, each segment being one-half wavelength, the antenna being a full wavelength at the frequency of the interrogating signal. In response to a control signal, the switch is opened and closed, thereby coupling and decoupling the two segments of the microstrip antenna. When the switch is in the closed position, the two segments are out-of-phase with one another, thereby producing a maximum reflected signal. When the switch is in the open position, the two segments act in concert to produce a minimum backscattered signal. The backscatter signal is thus modulated in accordance with the control signal and is received at the reader where it is subsequently decoded to identify the remote object.

Abstract: An RF identification system for generating data indicative of an item that is tagged, and one bit of variable data representative of an external stimulus. An ID code reader is provided and an RF identification tag is coupled to the item that is to be monitored and the ID code reader queries the tag. The tag comprises two RF transponder chips that store a data relating to the item, and an excitation coil coupled thereto. A switch is coupled to the chips and excitation coil, and a capacitor is coupled across the switch. A sensor is coupled to the switch for generating one bit of variable data representative of an external stimulus, such as the pressure in a tire. The ID code reader comprises an exciter and RF excitation coil, and a receiver and an RF receiver coil. The receiver includes phase detection circuitry for detecting a state of the switch by detecting the phase shift between signals received from each of the transponder chips. When the switch is shorted, the effect of the capacitor is nullified.