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Tagging items With barcodes or symbols that facilitate optical character recognition has long been used to identify and track product inventories, baggage, paper checks, or other movable items susceptible to misplacement or loss. Unfortunately, such optically perceptible tags must remain visible for identi? cation, and can be easily rendered unread able by surface marks or other damage. To improve tracking reliability, attempts have been made to use radiofrequency based electronic tags. Such tags typically have a semiconductor memory for data storage, processing logic, and a small antenna for broadcasting data, all embedded in rugged epoxy, thermoplastic, or other suitable plastic containers. Data storage capacity typically ranges from a feW bits to many kilobits, With 64 bits being typical. Tags can include read only memory (ROM), elec trically programmable or erasable (EPROM and EEPROM), or even? ash …