Antennas of RFID Tags

Radio Frequency Identification (RFID) is a rapidly developing technology which uses RF signals for automatic identification of objects. RFID system generally consists of three components: 1) A small electronic data carrying device called a transponder or tag that is attached to the item to be identified, 2) A reader that communicates with the tag using radio frequency signals, 3) A host data processing system that contains the information of the identified item and distributes the information between other remote data processing systems. A typical passive RFID tag consists of an antenna and RFID chip. RFID tags can be active (with battery) or passive (without battery). In particular, passive UHF (860 ~ 960) MHz tags represent a near optimal combination of cost and performance (Hunt et al., 2007). Generally, omni directionality for the tag antenna is preferred to ensure the identification from all directions. The structure of the tag antenna should also be low cost, small in size, have good impedance matching and insensitive to the attached objects to keep performance consistent (Curty et al., 2007). A passive RFID system operates in the following way: RFID reader transmits a modulated RF signal to the RFID tag consisting of an antenna and an integrated circuit chip. The chip receives power from the antenna and responds by varying its input impedance and thus modulating the backscattered signal. Modulation type often used in RFID is amplitude shift keying (ASK) where the chip impedance switches between two states: one is matched to the antenna (chip collects power in that state) and another one is strongly mismatched. The most important RFID system performance characteristic is tag range – the maximum distance at which RFID reader can either read or write information to the tag. Tag range is defined with respect to a certain read/write rate (percentage of successful reads/writes) which varies with a distance and depends on RFID reader characteristics and propagation environment (Nikitin & Rao, 2006). In this chapter, the operation theory of the RFID system is described. The antenna in RFID system is discussed, and the designing considerations of the antennas for RFID applications are presented. Also the design, simulation and implementation of some commonly used antennas in the RFID system are presented and investigated. IE3D electromagnetic simulator based on Method of Moment (MoM) is used to design some of these antennas. Source: Radio Frequency Identification Fundamentals and Applications, Design Methods and Solutions, Book edited by: Cristina Turcu, ISBN 978-953-7619-72-5, pp. 324, February 2010, INTECH, Croatia, downloaded from SCIYO.COM