Systems and methods for location estimation and tracking for passive RFID and wireless sensor networks in accordance with embodiments of the invention are disclosed. In one embodiment, a process for obtaining location information using an RFID reader system includes transmitting a combined interrogation and ranging signal from a plurality of antennas, where the ranging signal is a pseudorandom signal, receiving a backscattered return signal from an RFID tag at one or more receive antennas, extracting an information signal from the return signal and decoding the information signal to obtain RFID tag data, extracting a received ranging signal from the return signal, and estimating a range to the RFID tag based upon correlation between the ranging signal and the received ranging signal.

Apparatus and methods are provided for automatically interrogating a tagged object using radio frequency identification (RFID) when the object is moved. In one embodiment, a worker is outfitted with a wearable RFID system including an RF antenna, an RFID reader, and a holder to hold the antenna and reader during operation. The system is worn by the worker while the worker moves objects from one place to another. When the worker moves an object with an attached RFID tag, the antenna automatically begins scanning for signals from the object's RFID tag. When a RF signal is received by the antenna, the RFID reader collects the signal and transmits it to a host system which processes the signal to obtain information related to the object to which the RFID tag is attached.

A radio frequency identification (RFID) reader is disclosed that allows for selective deep scans of RFID tags. The RFID reader may include a motion detection sensor, a radio frequency transceiver configured to transmit RF energy at first and second frequencies, and a processor. The processor may perform the following steps: (1) when motion is detected by the sensor, commanding the transceiver to transmit RF energy at the first RFID profile; and (2) when motion has not been detect for a predetermined time period, commanding the transceiver to transmit RF energy at the second RFID profile. A method for using the RFID reader to perform selective deep scanning is also disclosed.

Messages may be passed between Radio Frequency Identification (RFID) tags using RFID readers. A first tag with a message intended for a second tag sends the message to an RFID reader. The reader then determines that the destination of the message is the second tag and sends the message to the second tag. The second tag may confirm receipt of the message by sending a receipt confirmation message to the reader for forwarding to the first tag, and/or the reader may itself confirm that the message was sent to the second tag by sending a transmit confirmation message to the first tag.

An RFID reader includes a transmitter, a receiver, and an evaluator. The receiver receives signals from RFID tags within a given number of slots of a time frame with a given frame size and provides a number of successful slots and a number of collided slots. The evaluator sets a modified frame size based on an estimated number of RFID tags which is determined based on the frame size, the number of successful slots, and the number of collided slots. The invention also refers to a corresponding method.

The presence or absence of objects (e.g., medical implements, medical supplies) tagged with transponders may be determined in an environment in which medical procedures (e.g., surgery) are performed via an interrogation and detection system which includes a controller and a plurality of antennas positioned along a patient support structure. The antennas may, for example, be positioned along an operating table, bed, a mattress or pad or a sheet and may be radiolucent. Respective antennas may successively be activated to transmit interrogation signals. Multiple antennas may be monitored for responses from transponders to the interrogation signals. For example, all antennas other than the antenna that transmitted the most recent interrogation signal may be monitored.

Disclosed are various embodiments for verifying that items have been correctly retrieved to fulfill orders or shipments. A plurality of radio frequency identification (RFID) tags are energized with an electromagnetic field emitted from an RFID reader, wherein individual ones of the RFID tags include a sensor. Motion data is reported by the RFID tags and detected via the RFID reader. Subsequently, at least one of the plurality of RFID tags is selected from the plurality of RFID tags based at least in part on the motion data.

A Near Field Communication method performed by a tag reader detects whether a tag is present. The method includes stimulating the tag reader's transmitter to generate an impulse response, evaluating the impulse response generated by the transmitter to obtain an evaluated impulse response, and assessing whether a tag is present based on the evaluated impulse response.

A hand-held antenna system allows medical personnel to ascertain the presence or absence of objects (e.g., medical supplies) tagged with transponders in an environment in which medical procedures are performed. In use, the hand-held antenna system may be positioned proximate a patient at a time after a medical procedure, such as after child birth, so the system can scan the patient's body to determine the presence of objects tagged with transponders. The antenna system includes three antenna elements arranged mutually orthogonal to each other to transmit and receive signals in three coordinate directions. A controller is coupled to the antenna elements to transmit signals to the transponders and to receive response signals. The antenna system may operate in a static scan mode wherein the antenna system is held in a fixed position by a user and a dynamic scan mode wherein the antenna system is moved by a user.

An example radio frequency identification card monitor is disclosed herein. An example radio frequency identification card monitor includes an example detector to identify radio frequency identification cards, a card tracker to track the radio frequency identification card with a proximity of the apparatus, and an interface to provide alerts when the radio frequency identification cards are not within the proximity.