Abstract: A pulse-listen electronic article security (EAS) system for detecting the presence of a security tag within a detection zone is disclosed. The EAS system includes a transmitter for radiating a first electromagnetic signal into the detection zone. The first electromagnetic signal is a time sequence of RF bursts emitted during each of a plurality of contiguous frame intervals in which the duration of each of the frame intervals is one of a plurality of different values. The EAS system also includes a receiver synchronized with the transmitter for receiving a second electromagnetic signal re-radiated from a security tag in the detection zone in response to the first electromagnetic signal. The receiver provides an output signal if a security tag is detected.

Abstract: An apparatus for measuring electrical characteristics of a resonant circuit without physically contacting the resonant circuit. The EAS system includes a numerically controlled oscillator for generating an alternating electric signal, the frequency of the alternating electric signal varying in accordance with a numerical frequency control signal; a transmitting antenna connected to the numerically controlled oscillator for establishing an electromagnetic field within a measurement zone; a receiving antenna for sensing disturbances to the electromagnetic field within the measurement zone; a receiver for receiving signals from the receiving antenna representative of disturbances to the electromagnetic field and for determining the Q and center frequency of the resonant circuit; and a clock having a substantially fixed frequency connected to the numerically controlled oscillator.

Abstract: A resonant circuit tag includes an integrated circuit for storing data and an antenna circuit for generating a first local field and resonating at a first predetermined radio frequency. A second circuit including an inductive coil selectively generates a second local field such that a sum of the first and second local fields approaches zero. The second circuit thus allows the resonant tag to be selectively decoupled from its environment.

Abstract: An article inventory control system for articles, such as books, uses RFID tags attached to each article. Each tag has a unique identification or serial number for identifying the individual article. An inventory database tracks all of the tagged articles and maintains circulation status information for each article. Articles are checked out of the library using a patron self-checkout system. Checked out articles are returned to the library via patron self-check in devices. The shelves are periodically scanned with a mobile RFID scanner for updating inventory status.

Abstract: A rotating field antenna is provided which includes a figure eight shape loop, a center loop magnetically coupled to the figure eight shape loop, and a drive element for driving the figure eight loop. The figure eight shape loop has an upper loop, a lower loop and a crossover region therebetween. The center loop overlaps at least a portion of the crossover region and at least a portion of one or both of the upper and lower loops. The center loop has no direct or physical electrical connection to the offset figure eight shape loop. Magnetic induction produces a 90-degree phase difference between the phase of the figure eight loop and the phase of the center loop. The antenna thereby produces a rotating composite field when driven by the drive element. The figure eight loop and the center loop are coplanar. The drive element may be an amplified voltage source which has a fundamental frequency of about 13.

Abstract: Briefly stated a tag includes a dielectric substrate having first and second opposite principal surfaces. An electrical circuit having an electrically conductive pattern is formed on at least one of the principal surfaces of the dielectric substrate, the conductive pattern including a gap which establishes an electrical open circuit. An electrically conductive composition including electro-conductive particles is provided for bridging the gap in the conductive pattern to temporarily establish an electrical closed circuit which resonates when exposed to electromagnetic energy at a frequency within a predetermined frequency range.

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: An electronic system verifies that an article has been tagged with an electronic article surveillance marker. The marker includes a resonant circuit for use in detecting the presence of the article by receiving an interrogation signal and returning a response signal. In the system, the physical presence of an article is detected using an article presence detector which outputs an article presence signal upon physical detection thereof. An interrogation zone is monitored with an interrogator for disturbances in the form of a response signal caused by the presence of a marker within the interrogation zone. The interrogator outputs an interrogator output signal when a marker is detected in the interrogation zone. The article presence signals and the interrogator output signals are received in a processor.

Abstract: An electronic security system uses a set of predefined RFID tags. Each tag is associated with, and attached to, an article or packaging for an article. Each tag includes unique tag information which is logged into a computerized database that contains a record for each of the tags in the set. A detection zone is monitored with an interrogator which detects RFID tags. When an RFID tag is detected, the database records are compared to the tag information and an appropriate database response is output. A deactivation event may be performed on the tag when legitimate access is obtained to the tagged article. The deactivation event may be electronic, physical or virtual. One type of RFID tag used in the system may physically deactivated by altering the state of a circuit element associated with the tag so that the tag cannot return a response signal. Another type of RFID tag used in the system has electronically alterable tag information.

Abstract: An article inventory control system for articles, such as books, uses RFID tags attached to each article. Each tag has a unique identification or serial number for identifying the individual article. An inventory database tracks all of the tagged articles and maintains circulation status information for each article. Articles are checked out of the library using a patron self-checkout system. Checked out articles are returned to the library by being deposited into an exterior smart book drop which reads the RFID tag and automatically checks the article back in. Article data from the exterior smart book drop are used to generate reshelving reports for efficiently reshelve the articles. Articles which are used in the library, but not checked out, are returned to interior smart book drops within the library for reshelving. The interior smart book drops capture data regarding in-house use of articles. The data are used to generate historical usage reports.

Abstract: Noise reduction schemes are provided in a radio frequency identification (RFID) system for use with RFID intelligent tags. Fiber optics are used to communicate analog tag response signals from the output of the receiver circuit to the input of a tag response signal analyzing module, which includes a digital signal processor (DSP). The fiber optics creates electrical isolation between these circuit elements breaking ground loops, stopping internal switching noise from the DSP from entering the receiver circuitry, and preventing common mode signals from interfering with the desired RFID tag signal.

Abstract: Noise reduction schemes are provided in a radio frequency identification (RFID) system for use with RFID intelligent tags. Amplitude and phase noise is minimized by starting with a low noise crystal oscillator having an output frequency which is an integer multiple n of the desired RF field frequency, and then dividing this frequency by the integer multiple n. One or more cascaded flip-flops are used for the frequency dividing. Both outputs of the final stage flip-flop are used to drive the transmitter antenna to produce a continuous wave signal.

Abstract: A highly efficient resonant switching driver circuit includes a matching reactance coupled between an output resonant circuit and a driver circuit. The matching reactance performs a series to parallel impedance match from the driver circuit to the output resonant circuit.

Abstract: A multiple loop antenna is provided which may be connected to either a transmit circuit, a receive circuit, or a transmit/receive circuit. When powered by a transmit circuit, the antenna generates radio frequency magnetic fields in an area or zone proximate to the antenna, but which are substantially canceled at a distance approximately one wavelength and more from the antenna, thereby defining a surveillance zone proximate to the antenna. Radiating loop segments of the antenna are centered around a common feed point and are geometrically symmetrical, such that currents are precisely controlled in each loop segment. A crossover element electrically connects the loop segments. The crossover element includes a pair of spaced, parallel conductors.

Abstract: A method of reading multiple RFID tags located in a field of an interrogating antenna is based on periodic transmissions from the tags with large, non-transmission intervals between transmissions. The non-transmission intervals are fixed for a given tag, but are random between tags due to manufacturing tolerances in electrical components from which the tag is constructed, such that no coordination of transmissions from the interrogating antenna is required.

Abstract: A multiple loop antenna is provided which may be connected to either a transmit circuit, a receive circuit, or a transmit/receive circuit. When powered by a transmit circuit, the antenna generates radio frequency magnetic fields in an area or zone proximate to the antenna, but which are substantially canceled at a distance approximately one wavelength and more from the antenna, thereby defining a surveillance zone proximate to the antenna. The loop antenna includes a first, upper loop and a second, lower loop. The upper and loser loops lie in separate, spaced, parallel planes and are preferably disposed at a fixed angle with respect to the surveillance zone.

Abstract: A resonant tag used with an electronic article surveillance system for detecting the presence of the tag within a surveilled area utilizing electromagnetic energy at a frequency within a predetermined detection frequency range includes a resonant circuit capable of resonating at a frequency within the predetermined detection frequency range. The resonant circuit includes an inductor formed at least in part on a surface of a dielectric substrate of the tag. The inductor is formed with a discontinuity or gap, causing an electrical open circuit. The open circuit is closed with a fuse secured proximate to the gap and wirebonded to the portions of the inductor proximate to the gap. The fuse is melted by a current greater than a predetermined level flowing therethrough. Such a high current may be induced in the inductor by an external electromagnetic field. Melting of the fuse causes an open circuit condition, which alters the frequency at which the tag resonates.

Abstract: A resonant tag circuit useful as an electronic security device includes a layered planar structure having a dielectric substrate, a resonant circuit carried on both sides of the dielectric substrate and a semiconductive material having an ionizable salt dissolved therein. The semiconductor material provides a sermiconductive bridge across an activation or deactivation point in the circuit and connects the conductive circuit on both sides of the activation or deactivation point. The resonant tag circuit of this invention is stabilized against premature operation of the activation or deactivation point from electrostatic discharge.

Abstract: A security tag used with an electronic article surveillance system for detecting the presence of the tag within a surveilled area utilizing electromagnetic energy at a frequency within a predetermined detection frequency range includes a dielectric substrate having first and second opposing principle surfaces, a peripheral outer edge, and a resonant circuit capable of resonating at a frequency within the predetermined detection frequency range. The security tag also includes a guard member, in one embodiment a discontinuous conductive member, effectively electrically isolated from the resonant circuit, extending along at least a portion of the peripheral outer edge of the substrate for surrounding at least a portion of the resonant circuit. The guard member electrically isolates the resonant circuit to facilitate testing of the resonant circuit during an early stage of the manufacturing process when the resonant circuit is in web form.