Electronic identification systems typically comprise two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems are operable to provide such communications via a wireless medium.
One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee of the present application and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system including an interrogator and a transponder such as a tag or card.
The communication system can be used in various identification and other applications. The interrogator is configured to output a polling signal which may comprise a radio frequency signal including a predefined, code. The transponders of such a communication system are operable to transmit, reflect or backscatter an identification signal responsive to receiving an appropriate polling signal. More specifically, the appropriate transponders are configured to recognize the predefined code. The transponders receiving the code subsequently output a particular identification signal which is associated with the transmitting transponder. Following transmission of the polling signal, the interrogator is configured to receive the identification signals enabling detection of the presence of corresponding transponders.
Such communication systems are useable in identification applications such as inventory or other object monitoring. For example, a remote identification device is attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output the appropriate identification signal. Generating the identification signal identifies the presence or location of the article or object.
Such identification systems configured to communicate via radio frequency signals are susceptible to incident RF radiation. Reflected RF radiation can cause problems in environments having metal structures. For example, application of transponders to objects comprising metal may result in decreased or no performance depending on the spacing of the transponder antenna to the nearest metal on the object.
Therefore, there exists a need to reduce the effects of incident RF radiation upon the operation of communication devices of an electronic identification system.