Abstract: A method for interleaving time slots in a multi-antenna system for communication with RFID tags is disclosed. An example is shown for an eight antenna system. A first four antennas arranged side-by-side are sequentially energized to interrogate RFID transponders. A second set of four antennas arranged side-by-side, the first of which is adjacent to the last of the first set of antennas. A four-antenna sequence is performed for the first four antennas and a second four antenna sequence is performed for the second set of antennas. The first and second four antenna sequences are offset by only a marginal amount, sufficient to ensure that a transponder signal received four antennas away from an active antenna is not acknowledged because the receive window for the non-active antenna is delayed.

Abstract: An RFID tag having a non-volatile memory and a piezoelectric sensor. The piezoelectric sensor produces an electrical charge that momentarily supplies electrical power to the RFID tag when subjected to a mechanical force and the electrical power is sufficient to record data in the non-volatile memory. The piezoelectric sensor is affixed to an article such that an attempt to tamper with the article produces sufficient mechanical force on the piezoelectric sensor to record data evidencing the tampering in the non-volatile memory.

Abstract: A system carried by a vehicle for computing tolls using a global position satellite (GPS) signal receiver, a communications link, and compact toll lane information provided by a service center. Toll lane information is organized by travel monitoring point. Data for each point includes a latitude and longitude coordinate and either lane shape information or a coordinate offset from a similar lane. A driver interface module is used in conjunction with the OBU to allow selection of occupancy and to display toll information to the driver to allow for use in HOT lanes and to support congestion pricing models with zero or minimal infrastructure cost.

Abstract: A multi-protocol RFID interrogating system employs a synchronization technique (step-lock) for a backscatter RFID system that allows simultaneous operation of closely spaced interrogators. The multi-protocol RFID interrogating system can communicate with backscatter transponders having different output protocols and with active transponders including: Title 21 compliant RFID backscatter transponders; IT2000 RFID backscatter transponders that provide an extended mode capability beyond Title 21; EGO™ RFID backscatter transponders, SEGO™ RFID backscatter transponders; ATA, ISO, ANSI AAR compliant RFID backscatter transponders; and IAG compliant active technology transponders. The system implements a step-lock operation, whereby adjacent interrogators are synchronized to ensure that all downlinks operate within the same time frame and all uplinks operate within the same time frame, to eliminate downlink on uplink interference.

Abstract: When multiple readers for RF transponders have to be placed in close proximity, such as in adjacent lanes of a highway toll barrier, they can be set to operate at different frequencies. When signals from two adjacent ones of the readers interfere, the resulting signal includes interference terms whose frequencies equal the sum of the reader frequencies and the difference between the reader frequencies. To remove such interference terms while passing the desired terms, a tag includes a low-pass or other frequency-selective filter.

Abstract: Systems, tags and methods for disabling transponders used in electronic toll collection or other RFID systems, wherein the transponders include an antenna and RFID circuitry. The transponders can be selectively disabled by positioning (e.g., pivotably moving) a disabling member having a metallic portion to an operative position over the antenna of the RFID system, whereupon the metallic portion is coupled to the antenna in such a manner as to disable the RFID circuitry so long as the disabling member is at the operative position. The RFID circuitry is arranged to be automatically enabled upon removal of the disabling member from the operative position (e.g., pivoting the disabling member back to an inoperative position).

Abstract: A multi-mode, preferably dual mode, radio frequency identification (RFID) tag is adapted for automatic detection of whether a RFID reader located within communication range of the RFID tag is transmitting a continuous wave (CW) or modulated wave types of RF signal, and accordingly, mandating a response from the tag in read-only (RO) mode or read/write (R/W) mode, respectively. The tag includes means for designating one of the RO and R/W operating modes as a default mode of the tag, and for switching the tag from its default mode to its other operating mode, and vice versa, according to a rule for determining the frequency of occurrence of a selected event related to signal type of the reader. A device-implemented method of this automatic detection, and a method of fabricating the tag, are also disclosed.

Abstract: Distance to a modulated backscatter tag is measured with a RFID reader that measures changes in phase with frequency of modulated backscattered RF signals. Measured distances are linked to a specific tag. The effects of other sources of reflected and interfering signals are mitigated. The techniques eliminate the need for high RF bandwidth used in time-of-flight methods, and may be used with linear, limiting or other types of amplifiers in the reader receiver. Unambiguous distance to a tag may be found using the derivative of phase with RF frequency of the modulated signal backscattered by a tag. The distance to a tag can be measured with an accuracy on the order of a centimeter. The techniques utilize the characteristics of cooperative backscatter tags (transponders, labels, etc.). New readers implement the techniques which may use unmodified tags.

Abstract: In a protocol for preserving the privacy of communications between a RFID reader and a RFID tag, two distinct actions are taken. First, the reader and the tag must be mutually authenticated as being authorized participants in the communications. After that process is successfully completed, the authenticity of each authorized participant must be validated prior to each subsequent communication between reader and tag.