new Literature Review

figure1: RFID basic concept

RFID acts as a signal mirror. For centuries we have known how to communicate messages with just a mirror by flashing the sun reflection to the direction of the recipient. The flashes are sequenced to represent a code known by the recipient, for example Morse code that communicates intelligence without the necessity of an infrastructure that establishes physical contact such as telegraph line. So, messages can be sent through air simply by reflecting radiated sunlight. That is the basic idea behind RFID, except that instead of using radiated sunlight as our communication medium, we reflect radio waves as shown in Figure 1. The basic theory underlying RFID technology has been discovered that the introduction of a conductive material into an electric or magnetic field could alter the field characteristics. That occurs because the conductive material both absorbs and reflects the energy in the field. If the field is a radio frequency or RF, the conductive material is capable of imparting a reflection of the source field radiation. RFID technology takes advantage of that characteristic by manipulating the sequence and rate at which that reflection occurs, called modulation. RFID tags are designed to deliberately reflect the source RF in sequences that are interpreted as information in the form of digital data

Radio-frequency identification (RFID) is the wireless non-contact use of radio-frequency electromagnetic fields to transfer data, for the purposes of automatically identifying and tracking tags attached to objects. The tags contain electronically stored information. Some tags are powered by and read at short ranges (a few meters) via magnetic fields (electromagnetic induction). Others use a local power source such as a battery, or else have no battery but collect energy from the interrogating EM field, and then act as a passive transponder to emit microwaves or UHF radio waves (i.e., electromagnetic radiation at high frequencies). Battery powered tags may operate at hundreds of meters. Unlike a barcode, the tag does not necessarily need to be within line of sight of the reader, and may be embedded in the tracked object