BACKGROUND

Radio-Frequency Identification (RFID) systems typically include RFID readers, also known as RFID reader/writers or RFID interrogators, and RFID tags. RFID systems can be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are useful in product-related and service-related industries for tracking objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its package. The RFID tag typically includes, or is, a radio-frequency (RF) integrated circuit (IC).

In principle, RFID techniques entail using an RFID reader to inventory one or more RFID tags, where inventorying involves at least singulating a tag and receiving an identifier from the singulated tag. “Singulated” is defined as a reader singling-out one tag, potentially from among multiple tags, for a reader-tag dialog. “Identifier” is defined as a number identifying the tag or the item to which the tag is attached, such as a tag identifier (TID), electronic product code (EPC), etc. An “inventory round” is defined as a reader staging RFID tags for successive inventorying. The reader transmitting a Radio-Frequency (RF) wave performs the inventory. The RF wave is typically electromagnetic, at least in the far field. The RF wave can also be predominantly electric or magnetic in the near or transitional near field. The RF wave may encode one or more commands that instruct the tags to perform one or more actions. The operation of an RFID reader sending commands to an RFID tag is sometimes known as the reader “interrogating” the tag.

In typical RFID systems, an RFID reader transmits a modulated RF inventory signal (a command), receives a tag reply, and transmits an RF acknowledgement signal responsive to the tag reply. A tag that replies to the interrogating RF wave does so by transmitting back another RF wave. The tag either generates the transmitted back RF wave originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in several ways.

The reflected-back RF wave may encode data stored in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a time, a destination, an encrypted message, an electronic signature, other attribute(s), any combination of attributes, and so on. Accordingly, when a reader receives tag data it can learn about the item that hosts the tag and/or about the tag itself.

RFID systems are sometimes characterized as interrogator-talks-first or as tag-talks-first. In the former, a tag backscatters data after receiving a command instructing it to do so. In the latter, a tag backscatters data upon receiving RF energy. Regardless of the type, RFID systems typically schedule or queue the tag backscatter using anticollision algorithms to avoid multiple tags backscattering at the same time. These anticollision algorithms include slotted-Aloha, random timeslotting and a host of other scheduling algorithms as will be known to those practiced in the art.

An RFID tag typically includes an antenna section, a radio section, a power-management section, and frequently a logical section, a memory, or both. In some RFID tags the power-management section included an energy storage device such as a battery. RFID tags with an energy storage device are known as battery-assisted, semi-active, or active tags. Other RFID tags can be powered solely by the RF signal they receive. Such RFID tags do not include an energy storage device and are called passive tags. Of course, even passive tags typically include temporary energy- and data/flag-storage elements such as capacitors or inductors. In some embodiments, an RFID tag is attached to its host item. In other embodiments, an RFID tag may be an integral part of its host item.

BRIEF SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter.

RFID tags in reader-talks-first systems have been historically unable to draw the attention of a reader to a timely environmental input, because the reader controls the tag's communication timing, not the tag itself. The reader sends a command initiating an inventory round, thereby staging tags for successive inventorying, and each tag identifies itself at its allotted time or in its allotted timeslot, optionally sending its environmental data at that time. The timing or time-slotting of the tag's reply has historically been independent of environmental inputs, but in many cases a reader's ability to extract value from the environmental input depends on the reader knowing when the tag's environment changes. To address this shortcoming, embodiments are directed to an RFID tag IC that advances its reply based on environmental inputs such as temperature, humidity, chemical composition, RF energy, light, and the like, to alert a reader in a timely fashion that something important is happening. Specifically, embodiments are directed to RFID tag ICs sensing changes in their environment, and upon sensing such changes adjusting their reply timing to reply more promptly to a reader. In a simple but not-limiting analogy, consider a tag population queued for inventory. Upon one tag sensing a change in its environment, the one tag may respond sooner to the reader then it would have absent the sensed change, or join an inventory round based on sensing the change when it may not have joined otherwise, or in some other fashion advance or modify the timing of its communications, thereby enabling the reader to learn about and potentially act on the environmental change.

An RFID tag so configured to advance its response as a consequence of an environmental change may do so by adjusting a reply timer, changing a reply timeslot, changing a timing characteristic of a communications protocol, exiting a sleep state, replying immediately upon sensing the environmental change, entering an inventory round configured for such advanced-reply tags, entering an inventory round it wasn't currently participating in, or in a variety of other ways.

An RFID tag so configured to advance its response as a consequence of an environmental change may indicate the environmental change in its backscattered reply by adjusting a flag or indicator value, transmitting additional or different data to the reader, altering the RF characteristics of its reply, altering the timing of its reply or in a variety of other ways.

An RFID tag so configured to advance its response as a consequence of an environmental change may sense the environmental change by comparing a measured value to a threshold, mean, limit-value or boundary condition; comparing a measured rate-of-change to a threshold, mean, limit-value or boundary condition; or by otherwise sensing the change in the myriad ways known to those skilled in the art. In some embodiments the tag may tune or adjust the magnitude of its response advancement with a parameter of the environmental change, such as a magnitude of the change, a derivative of the magnitude of the change, a time since a prior change, a presence of multiple changes, or another parameter of the change.

In some embodiments an RFID reader may initiate a standard inventory round and a tag, sensing the environmental change, my alter its behavior in, or choose to enter, that standard inventory round because of the change. In other embodiments an RFID reader may initiate a special inventory round looking for tags that sense environmental changes, such as one in which only environmental-change-sensing tags reply, or one in which tags remain dormant or asleep until they sense an environmental change and reply, or one in which the reader allows environmental-change-sensing tags to alter a parameter of a communications protocol. In yet other embodiments an RFID reader, upon hearing a response from a tag that has sensed an environmental change, may broadcast a command (i.e. send a command to multiple tags) temporarily silencing other tags so it can focus on the tag with the environmental change. In some embodiments the broadcast command may be configured for the purpose of so initiating or notifying or silencing, whereas in other embodiments the broadcast command may be a repurposed standard command containing a waveform or pattern that performs the initiating or notifying or silencing. In yet other embodiments the broadcast command may be a sequence of commands.

According to some examples, an RFID IC may provide an environmental alert by performing a first measurement of an environmental parameter at a first time and comparing the first measurement to either a baseline value or a second measurement of the environmental parameter at a second time to determine a difference. If the difference meets a threshold, then the IC may provide the alert by (a) participating in an inventory round, else not participating in the inventory round; (b) advancing a currently scheduled reply in an ongoing inventory round, else not advancing the reply; and/or (c) replying multiple times in an inventory round.

According to other examples, an RFID IC may provide an environmental alert by performing a first measurement of an environmental parameter at a first time, performing a second measurement of the environmental parameter at a second time, and determining a change in the environmental parameter based on the first and second measurements (e.g., a rate-of-change of the environmental parameter). If the determined change meets a threshold, then the IC may provide the alert by (a) participating in an inventory round, else not participating in the inventory round; (b) advancing a currently scheduled reply in an ongoing inventory round, else not advancing the reply; and/or (c) replying multiple times in an inventory round.

The environmental parameter measurement in the above examples may be a received RF power, a received RF frequency, a rate-of-change of the power or frequency or any other RF parameter as will be known to those skilled in the art.

Regardless of the methodology the RFID IC uses to alert the reader, the IC may further include in its reply an indication that it is signaling an environmental change using one or more reply bits or by modifying a waveform feature in its reply.

These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.

