is that multiple tags can be read at the same time and in bulk very quickly. Finally, the tags can be easily embedded into any nonmetallic object, enabling the tags to work in harsh environ- ments and providing permanent identification for the life of the object. However, the environment into which RFID will be implemented must be carefully consid- ered because factors such as the presence of metal, electrical noise, extreme tem- peratures, liquids, and physical stress may affect performance. RFID Readers RFID readers are used to query RFID tags in order to obtain identification, loca- tion, and other information about the object the tag is embedded in. In addition, Chapter 15 WMANs, WLANs, and WPANs the reader antenna sends RF energy to the RFID tag antennas, which use that energy to power up the microchip. There are two types of RFID readers: Read-only-These readers can only query or read information from a nearby RFID tag; they cannot write information to tags. They are found in fixed, stationary applications as well as portable, handheld varieties. Read/write-These readers, also known as encoders, read and also write information in RFID tags. RFID encoders can be used to program informa- tion into a blank RFID tag. A common application is to combine this type of RFID reader with a barcode printer to print smart labels. A smart label con- tains a UPC barcode on the front and an RFID tag embedded on the back. RFID Frequencies Even though no global body currently governs RFID frequencies (each country can set its own rules), there are four main frequency bands for RFID tags, as shown in Table 15.9. Table 15.9 RFID Frequency Bands Frequency Typical Frequency Band Range Tag Cost Description Applications Low (LF) 125KHz-134.2KHz 3 ft. (1 m) US$1+ Short reading Pet and ranch ani- ranges, slow read mal identification, 140 KHz-148.5KHz speeds, and lower car key locks High (HF) 13.56MHz 3 ft. (1 m) US$0.50 Longer read Library book iden- ranges and fast tification, cloth- reading speeds ing identification, smart cards U