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The history of RFID technology dates back to the Second World War. The British military commenced the first usage of this technology to differentiate between a friend aircraft from a foe aircraft. In the 1950s and 1960s, a number of researches about RFID techniques were published and the theory of RFID was developed. In the 1970s and 1980s, the academic institution of the Los Alamos Scientific Laboratory was established which focused on toll payment systems, which were widely applied on different situations such as roads, tunnels, bridges and so on. They developed Ultra-High Frequency (UHF) passive RFID tags for animal tracking. RFID systems were also used for commercial purposes in various applications related to warehouse management, smart cards, and anti-theft systems. The 1990s was a decade that the RFID system was standardized and developed widely. In the 2000s, EPCglobal Inc. was founded to continue works on the Electronic Product Code (EPC) technology. RFID systems are now a part of our daily lives (Symonds, Ayoade, & Parry, 2009).
Components of RFID Systems
Radio Frequency Identification (RFID) systems apply a small device to send and receive Radio Frequency (RF) signals. The major components of RFID systems are tag (or transponder), reader (or transceiver), and server (Liu & Bailey, 2009), as it is shown in Figure 1.
A tag attached to an object is used to identify the object uniquely. The reader can read and write the information on the tags, and communicate with the server. The server obtains the data from the reader and stores this information.
These components work together through transmitting electromagnetic waves. First, the reader sends a query signal to the tags in the interrogation zone of the reader. The tags thereafter send out their unique identification data to the reader. The reader receives the signals and converts them into a form of data that can be used by the computer. Then, the reader transfers the data to the server, and the server stores this data to the database. The database server manages and stores all data related to the tags, such as the electronic product code data and previous identification information (Huang, 2009).
RFID tags are categorized in three major groups: passive, semi-passive, and active tags, as they are shown in Figure 2 (Liu & Bailey, 2009).
Figure 2. Passive, semi-passive and active tags respectively
The differences among the passive, semi-passive, and active, tags (Kim, Lee, Jung, Maeng, & Park, 2010) stem from their power source, cost and processing capability. In the passive tags, the required power is provided by the reader’s radio frequency signals. These types of tags are low in cost, and run very simple functions; while active tags have their own battery power source, and send back their data to the reader by using the battery power. It works like a simple computer. In semi-passive tags, there are batteries same as the active tags, but the required power to transmit the tags’ data is provided by the reader, which is the only difference. These types of tags can read the sensors. Active tags and semi-passive tags are expensive because of their hardware complexity. Table 1 compares the different properties and features of passive, semi-passive and active tags.
Table 1. Comparison of passive, semi-passive and active tags
| Type of Tags | Power Source | Cost | Processing Capability |
| Passive (a) | Harvesting RF energy | Least expensive | Almost none |
| Semi-Passive (b) | Battery & RF energy | More expensive | Ability to read sensors |
| Active (c) | Battery | Most expensive | Like a very small computer |