RFID tag having timing and environment modules

Details RFID tag having timing and environment modules RFID tag having timing and environment modules

1999-10-04

2001-09-25

Lee, Benjamin C. (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S309160, C340S010100, C340S457000, C340S457400, C340S540000, C235S385000

Reexamination Certificate

active

06294997

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio frequency identification (“RFID”) tags, and more particularly, to an RFID tag that can measure time and detect environmental changes.
2. Description of Related Art
In the automatic identification industry, the use of RFID tags has grown in prominence as a way to track data regarding an object to which the RFID tag is affixed. An RFID tag generally includes a semiconductor memory in which digital information may be stored, such as an electrically erasable, programmable read-only memory (EEPROMs) or similar electronic device. Under a technique referred to as “backscatter modulation,” the RFID tags transmit stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator by modifying their antenna matching impedances. The RFID tags can therefore operate independent of the frequency of the energizing field, and as a result, the interrogator may operate at multiple frequencies so as to avoid radio frequency (RF) interference, such as utilizing frequency hopping spread spectrum modulation techniques. The RFID tags may either be passive, in which they extract their power from the electromagnetic field provided by the interrogator, or active, in which they include their own power source.
One of the many advantages of RFID tags is that they can be manufactured in very small, light weight and inexpensive units. Passive RFID tags are particularly cost effective since they lack a power source. In view of these advantages, RFID tags can be used in many types of applications in which it is desirable to track information regarding a moving or inaccessible object. One such application is to affix RFID tags to work pieces moving along a conveyor belt of an assembly line. The RFID tags would contain stored information regarding the particular assembly requirements for the work piece to enable automated equipment to operate on the work piece and perform certain tasks unique to the work piece requirements. This way, products having different assembly requirements can be sent down the same assembly line without having to modify the assembly line for each unique requirement. Another application for RFID systems is to collect information from a moving motor vehicle, such as for vehicle toll collection.
A drawback of conventional RFID tags is that they are not able to measure a given length of time, or more specifically, to measure the time that the RFID tag is exposed to a given environmental condition. This ability would be very desirable for RFID tags attached to items that are sensitive to time and environment, such as perishable foods. A time-tracking feature would enable the seller to determine the precise age of the goods they are selling. This would be beneficial to both the seller, who could maximize his profit, and the consumer, who would be given accurate information regarding the food being bought. Moreover, an RFID tag that can detect and report on environment conditions would be further beneficial in the perishable food applications because conditions such as an unacceptably high or low temperature, humidity, or pressure, as well as exposure to certain undesirable gasses could be monitored to determine the food's freshness. Timing and environmental tracking features would also be beneficial for many other applications including the parcel delivery business where certain items to be shipped could be sensitive to time or environment.
It is therefore an object of the present invention to provide an RFID tag with timing capabilities. It is a further object of the present invention to provide an RFID tag with an environment module to detect certain environmental conditions and measure the length of time that an RFID tag is exposed to the environmental conditions.
SUMMARY OF THE INVENTION
In accordance with the present invention, an RFID tag with timing and environment modules is provided. The RFID tag includes a transmitter/receiver, memory module, antenna module, converter and a timing and environment module. The timing module enables the user, upon interrogating the RFID tag, to determine the precise length of time from the previous charge of the RFID tag. The environment module enables the user to determine how long the RFID tag has been exposed to certain conditions that have been pre-programmed into the RFID tag. These features greatly enhance standard RFID tags because they broaden the range of uses for RFID tags.
In an embodiment of the invention, a timing module is incorporated into a passive RFID tag to keep track of the length of time from previous charge. The timing module may include a resistor coupled to a charging capacitor. The capacitor is initially charged, but over time the charge dissipates from the capacitor. When the RFID tag is subsequently read, the amount of capacitance leak can be determined, and the time can be calculated based on the rate of dissipation. The dissipation rate can be controlled through the use of different valued resistors. For instance, a high value resistor will promote a slow leak while a small value resistor will promote a faster leak. The size of the resistance used in the timing module depends on the application. The time from charging is determined by knowing the value of the resistor and the amount of charge left in the capacitor. A register is located within the timing module and records a number of ticks (i.e., units of time) based on the dissipation of the charge. The value of each tick can be set to correspond with a predetermined time period, e.g., one second, one hour, one week, one year, etc., depending on the particular application. Upon interrogation of the RFID tag, the data from the register is sent to the interrogator so that elapsed time from the last charging can be ascertained.
In another embodiment of the invention, the timing module is combined into a passive RFID tag with an environment module in order to provide a way to ascertain the amount of time that the RFID tag has been exposed to adverse environmental conditions. A micro-sensor may be provided to detect a certain environmental condition and perform a particular function upon the passing of a predetermined threshold. For example, the micro-sensor may be adapted to detect temperature. The detected temperature is then compared against a predetermined threshold value, and when the detected temperature rises above the threshold, the micro-sensor would initialize a timer. The timer would track the number of ticks until the temperature returned to a normal range, in which case the timer would stop. The count of ticks would enable the user to know exactly how long the RFID tag was exposed to the elevated temperature. Alternatively, the micro-sensor may be adapted to react chemically with a substance in the environment, and changes in electrical conductivity of the micro-sensor may be used to determine the length of time that the RFID tag, and the item it is attached to, has been exposed to a certain condition. The micro-sensor may also be sensitive to pressure, and when a certain pressure is exceeded, the micro-sensor will undergo a chemical transformation. Based on the state of the micro-sensor, measured by electrical conductivity upon interrogation, the length of time that the RFID tag was exposed to the elevated pressure can be readily calculated.
A more complete understanding of the RFID tag having a timing and environment module will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings that will first be described briefly.


REFERENCES:
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patent: 5241299 (1993-08-01), Appalucci et al.
patent: 5530702 (1996-06-01), Palmer et al.
patent: 5583819 (1996-12-01), Roesner et al.
patent: 5798694 (1998-08-01), Reber et al.
patent: 5822683 (1998-10-01), Paschen
patent: 5883582 (1999-03-01), Bowers et al

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