Abstract:
Methods and apparatus, including computer program products, for a power conserving active RFID label. A system for performing radio frequency (RF) communications includes a radio frequency identification (RFID) tag attached to one or more items to be tracked, the RFID tag configured to receive a request and a time interval indicating a time for determining a temperature and a battery voltage, and to adjust the time interval at a time of determining the temperature and the battery voltage if the detected voltage is less than a predetermined voltage, and an interrogator communicatively coupled to one or more antennas to transmit one or more requests to the RFID tag and to receive one or more responses, at least one response including a time, temperature and battery voltage.

Description:
BACKGROUND 
     The present invention relates to radio frequency identification (RFID), and more particularly to a power conserving active RFID label. 
     RFID is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency (RF) portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. With RFID, the electromagnetic or electrostatic coupling in the RF (radio frequency) portion of the electromagnetic spectrum is used to transmit signals. A typical RFID system includes an antenna and a transceiver, which reads the radio frequency and transfers the information to a processing device (reader) and a transponder, or RF label, which contains the RF circuitry and information to be transmitted. The antenna enables the integrated circuit to transmit its information to the reader that converts the radio waves reflected back from the RFID label into digital information that can then be passed on to computers that can analyze the data. 
     SUMMARY 
     The present invention provides methods and apparatus, including computer program products, for a power conserving active RFID label. 
     In one aspect, the invention features a radio frequency identification (RFID) tag including a substrate, an antenna on the substrate, and an integrated circuit operably coupled to a temperature sensor and to the antenna to receive a time interval from a RFID interrogator, the time interval indicating a time for determining a temperature and a battery voltage, the integrated circuit configured to adjust the time interval at a time of determining the temperature and the battery voltage if the detected voltage is less than a predetermined voltage. 
     In another aspect, the invention features a radio frequency identification (RFID) interrogator including one or more antennas, a receiver communicatively coupled to at least one of the one or more antennas to receive a response from a radio frequency identification (RFID) tag, the response including time, temperature and battery voltage, a transmitter communicatively coupled to at least one of the one or more antennas to transmit requests, and a control unit communicatively coupled to the transmitter and the receiver, wherein the receiver is configured to receive the response and adjust a time interval in the RFID tag for determining a temperature and a battery voltage if the battery voltage in the response is less than a predetermined voltage. 
     In another aspect, the invention features a system for performing radio frequency (RF) communications, the system including a radio frequency identification (RFID) tag attached to one or more items to be tracked, the RFID tag configured to receive a request and a time interval indicating a time for determining a temperature and a battery voltage, and to adjust the time interval at a time of determining the temperature and the battery voltage if the detected voltage is less than a predetermined voltage, and an interrogator communicatively coupled to one or more antennas to transmit one or more requests to the RFID tag and to receive one or more responses, at least one response including a time, temperature and battery voltage. 
     Other features and advantages of the invention are apparent from the following description, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary active radio frequency identification (RFID) label. 
         FIG. 2  is a block diagram of an exemplary RFID interrogator. 
         FIG. 3  is a flow diagram. 
         FIG. 4  is a flow diagram. 
         FIG. 5  is a flow diagram. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Radio frequency identification (RFID) labels can be intelligent or just respond with a simple identification (ID) to radio frequency (RF) interrogations. The RFID label can contain memory. This memory can be loaded with data either via an interrogator, or directly by some integrated data gathering element of the RFID label, for example, an environmental sensor. This data is retrieved some time later. 
     As shown in  FIG. 1 , an exemplary active RFID label  10  includes an antenna  12 , a transceiver  14 , a microcontroller  16 , a temperature sensor  20  and a battery  22 . Microcontroller  16  includes several elements including a memory  18 . Memory  18  can include a power conservation process  100 , fully described below. Temperature sensor  20  senses and transmits temperature data to memory  18  at intervals of time. When triggered by RF interrogation via transceiver  14 , microcontroller  16  fetches the data (i.e., time stamp and temperature) and sends it out to an interrogator as multiplexed data packets from transceiver  14 . In this manner, a historical temperature log stored in memory  18  in the active RFID label  10  can be retrieved. Temperature logging is limited by the size of memory  18  and/or life of battery  22 . 
     In some examples, RFID label  10  stores a voltage of its battery  22  along with a time and a temperature at each time interval. 
     As shown in  FIG. 2 , an exemplary RFID interrogator  50  includes an antenna  52 , transceiver  54 , memory  56 , central processing unit (CPU)  58  and optional user interface (UI)  60 . The RFID interrogator  50  performs Time Division Multiplexing (TDM) with the transceiver  54  and antenna  52 . Data (e.g., time, temperature and/or battery voltage) downloaded from the RFID label  10  can be stored in memory  56 . 
     The RFID interrogator  50  can be used to program the active RFID label  10  to record or log a temperature and/or battery voltage in memory  18  with a time interval starting at an initial time. At each time interval, e.g., every hour, the active RFID label  10  records a time, temperature and/or battery voltage in memory  18 . The RFID interrogator  50  can download the time, temperature and/or battery voltage data from memory  18  to memory  56 . 
     Over a period of service, i.e., the recording and storing of time/temperature/voltage, the life of the RFID label battery  22  in the active RFID label  10  can diminish and eventually fail. In one example, if the active RFID label  10  detects reduced voltage in the battery  22 , the active RFID label  10  can increase the time interval for temperature and/or voltage readings, thus conserving the remaining life of the battery  22 . For example, if the initial time interval in the active RFID label  10  is sixty minutes, the active RFID label  10  will log a time, temperature and/or voltage every sixty minutes. If the active RFID label  10  detects a voltage in the battery is less than 80% capacity, for example, the active RFID label  10  will increase the time interval for readings to, for example, one hundred twenty minutes. At subsequent readings, the active RFID label  10  will increase the time interval for readings as the battery  22  continues to deteriorate, i.e., as a voltage in the battery  22  decreases with each reading, and the active RFID label  10  can continue to increase the time interval for temperature and/or voltage readings, thus extending the remaining life of the battery  22 . 
     In another example, stored data received from the RFID label  10  can be analyzed by the RFID interrogator  50 . More specifically, from stored voltage data, the RFID interrogator  50  can determine whether the most recent voltage of the battery  22  is too low, or has dropped below a selected value, or that the voltage of the battery  22  is decreasing at too rapid a rate. In any event, the RFID interrogator  50  can instruct the RFID label  10  to increase its time interval of temperature and/or voltage readings or the RFID interrogator  50  can adjust its frequency of interrogations of RFID label  10 . 
     In another example, the RFID label  10  does not store any time, temperature and/or voltage data. Instead, during each interrogation of RFID label  10 , the RFID interrogator  50  requests the RFID label  10  for a current battery voltage and/or temperature. The RFID interrogator  50  can store temperatures and/or voltages over time. In addition, the RFID interrogator  50  can determine to increase its time interval between interrogators based on the currently polled battery voltage. 
     As shown in  FIG. 3 , the power conservation process  100  includes receiving ( 102 ) an initial time interval. Process  100  determines ( 104 ) whether the time interval is reached. If the time interval is reached, process  100  detects ( 106 ) a time from its internal clock, a temperature from its temperature sensor and voltage of its power supply, e.g., battery. 
     Process  100  determines ( 108 ) whether the detected voltage has reached a selected reduced level. If the detected voltage has not reached a selected reduced level, process  100  stores ( 110 ) the detected time and temperature. 
     If the detected voltage reached the selected reduced level (or less), process  100  increases ( 112 ) the time interval and stores ( 110 ) the detected time and temperature. 
     Process  100  then determines ( 104 ) whether the increased time interval is reached. 
     Process  100  can be incorporated into the memories of other types of RFID labels. For example, process  100  can be used with beacon tags. In general, a beacon tag is an active RF tag that can be factory set to transmit a periodic RF signal used for location, process and presence detection and tracking. Typically, these devices are placed into non-metallic enclosures and transmit an RF signal to an RFID reader located at a distance of  3 - 10  meters. As the power decreases, process  100  can increase the time at which the period RF signal is transmitted. 
     In another embodiment, memory  56  contains a time interval process  200 . As shown on  FIG. 4 , the time interval process  200  includes sending ( 202 ) an interrogation signal to a RFID label. Process  200  receives ( 204 ) a response signal from the RFID label containing the label&#39;s log of times, temperatures and voltages. 
     Process  200  determines ( 206 ) whether the most recent measured voltage of the label battery is below a minimum voltage. If the most recent voltage of the label is below a minimum, process  200  sends ( 208 ) a signal to the RFID label lengthening its time interval. 
     Process  200  determines ( 210 ) whether the rate of voltage decrease of the label battery exceeds a specified rate. The rate of decrease in battery voltage is determined by the RFID interrogator from the received store of battery voltages received from the RFID label during the interrogation. If the rate of decrease of battery voltage exceeds the specified rate, process  200  sends ( 208 ) a signal to the RFID label lengthening its time interval. 
     In another embodiment, memory  56  contains a polling interval process  300 . As shown in  FIG. 5 , the polling interval process  300  includes sending ( 302 ) an interrogation signal to a RFID label. Process  300  receives ( 304 ) a response signal from the RFID label containing the current battery voltage in the RFID label. 
     Process  300  determines ( 306 ) whether the current battery voltage in the RFID label is below a specified minimum. If the current battery voltage is below the specified minimum, process  300  lengthens ( 308 ) a time to sending its next interrogation signal. 
     Embodiments of the invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments of the invention can be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine readable storage device or in a propagated signal, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. 
     Method steps of embodiments of the invention can be performed by one or more programmable processors executing a computer program to perform functions of the invention by operating on input data and generating output. Method steps can also be performed by, and apparatus of the invention can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry. 
     It is to be understood that the foregoing description is intended to illustrate and not to limit the scope of the invention, which is defined by the scope of the appended claims. Other embodiments are within the scope of the following claims.