One embodiment of the present invention relates to a method for a reader to transmit and receive a signal to and from a tag, the method comprising: a step in which a first reader transmits a first signal to a tag; and a step in which the first reader receives the first signal reflected on the tag. The timing for the first reader to transmit the first signal is determined by using an offset value based on an ID related to the first reader.

A near-field communication (NFC) device is described. The NFC device includes an antenna configured to radiate an electromagnetic field. The NFC device also includes electronic circuitry coupled to the antenna. The electronic circuitry is configured to receive first data from a unidirectional tag device within a transmission limit. The electronic circuitry is also configured to receive second data from at least one bidirectional tag device after the transmission limit.

Systems and methods for determining an inventory. The methods comprise: placing an RFID tag in a first operational mode in which at least one communication operation or device of the RFID tag is disabled or bypassed; performing first operations by the RFID tag to determine when it is time to begin communications in accordance with the time slotted communications scheme; transitioning an operational mode of the RFID tag from the first operational mode to a second operational mode in which the communication operation(s) or device of the RFID tag is enabled or no longer bypassed, in response to a determination that it is time for the RFID tag to begin communications; and transitioning the operational mode of the RFID tag back into the first operational mode when the RFID tag's communications with a remote tag reader for inventory determination purposes are complete or a time slot has expired.

One embodiment of the present invention relates to a method for a reader to transmit and receive a signal to and from a tag, the method comprising: a step in which a first reader transmits a first signal to a tag; and a step in which the first reader receives the first signal reflected on the tag. The timing for the first reader to transmit the first signal is determined by using an offset value based on an ID related to the first reader.

Systems and methods for determining an inventory. The methods comprise: placing an RFID tag in a first operational mode in which at least one communication operation or device of the RFID tag is disabled or bypassed; performing first operations by the RFID tag to determine when it is time to begin communications in accordance with the time slotted communications scheme; transitioning an operational mode of the RFID tag from the first operational mode to a second operational mode in which the communication operation(s) or device of the RFID tag is enabled or no longer bypassed, in response to a determination that it is time for the RFID tag to begin communications; and transitioning the operational mode of the RFID tag back into the first operational mode when the RFID tag's communications with a remote tag reader for inventory determination purposes are complete or a time slot has expired.

A near-field communication (NFC) device is described. The NFC device includes an antenna configured to radiate an electromagnetic field. The NFC device also includes electronic circuitry coupled to the antenna. The electronic circuitry is configured to receive first data from a unidirectional tag device within a transmission limit. The electronic circuitry is also configured to receive second data from at least one bidirectional tag device after the transmission limit.

Systems and methods for determining an inventory. The methods comprise: placing an RFID tag in a first operational mode in which at least one communication operation or device of the RFID tag is disabled or bypassed; performing first operations by the RFID tag to determine when it is time to begin communications in accordance with the time slotted communications scheme; transitioning an operational mode of the RFID tag from the first operational mode to a second operational mode in which the communication operation(s) or device of the RFID tag is enabled or no longer bypassed, in response to a determination that it is time for the RFID tag to begin communications; and transitioning the operational mode of the RFID tag back into the first operational mode when the RFID tag's communications with a remote tag reader for inventory determination purposes are complete or a time slot has expired.

According to one embodiment, an RFID tag includes a plurality of antenna elements, a switch, and a control circuit. The switch is inserted between the plurality of antenna elements. The control circuit turns off the switch until a specified time elapsed after responding to radio waves from a reader device.

Systems and methods for determining an inventory. The methods comprise: placing an RFID tag in a first operational mode in which at least one communication operation or device of the RFID tag is disabled or bypassed; performing first operations by the RFID tag to determine when it is time to begin communications in accordance with the time slotted communications scheme; transitioning an operational mode of the RFID tag from the first operational mode to a second operational mode in which the communication operation(s) or device of the RFID tag is enabled or no longer bypassed, in response to a determination that it is time for the RFID tag to begin communications; and transitioning the operational mode of the RFID tag back into the first operational mode when the RFID tag's communications with a remote tag reader for inventory determination purposes are complete or a time slot has expired.

A storage unit includes a support bar for hanging items and an RFID antenna provided within a predefined distance of the support bar. When the items hanging from the support bar are adorned with RFID tags, and the RFID antenna emits electromagnetic fields in a direction of the support bar, RFID signals identifying the items are transmitted from the RFID tags to the RFID antenna, thereby enabling a placement or a removal of an item to be automatically registered, or an accounting of the available items to be automatically performed. The RFID antenna may be a portion of a transmission line that uses shields and/or dielectric materials to shape the electromagnetic fields toward a predefined direction, and the locations of items bearing RFID tags on the support bar may be determined by varying the phase of the emitted radiofrequency and determining strengths of RFID signals when the electromagnetic fields are emitted at varying phases.