## 4 Radio Frequency Identification  
RFID is an emerging technology that makes use of wireless communication. The protocol was originally developed for short-range product identification, typically covering the 2 mm - 2 m read range, and has been promoted as the replacement technology for the optical bar-code found, with the use of EPC (Electronic Product Code). RFID has the ability to allow energy to penetrate certain goods and to read a tag that is not visible [37]. There are many distinct protocols used in the various RFID systems, some using the lower end of the spectrum (135 KHz) and others using the super high frequency (SHF) at 5.875 GHz:  
There are various standards involved in RFID:  
* ISO/IEC 7816 is the standard for contact chip cards [6]. * ISO/IEC 1443 is for contactless proximity cards operating at 13.56 MHz [7]. * ISO/IEC 15693 is for contactless vicinity cards operating at 13.56 MHz [8]. * ISO/IEC 18000 is for item management air interface, defining the parameters for air interface in different frequencies: \(<\) 135 kHz, 13.56 MHz, 2.45 GHz, 5.8 GHz, 860-930 MHz and 433 MHz [9]. * ISO 11784, ISO 11785 and ISO 14223 are standards for the radio-frequency identification of animals [3-5]. RFID systems are comprised of three main components: the tag or transponder, the reader or transceiver that reads and writes data to a transponder, and the computer containing database and information management software [38]. RFID tags can be active, passive or semi-passive. Passive and semi-passive RFID send their data by reflection or modulation of the electromagnetic field that was emitted by the Reader. The typical reading range is between 10 cm and 3 m. The battery of semi-passive RFID is only used to power the sensor and recording logic. The communication of active \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Bluetooth** & **ZigBee** \\ \hline Standards & IEEE 802.15.1 & IEEE 802.15.4 \\ Data rate & 1 Mb s\({}^{-1}\) & 20-250 kb s\({}^{-1}\) \\ Latency (time to establish a & \(<\) 10 s & 30 ms \\ new link) & & \\ Frequencies & 2.4 GHz & 2.4 GHz \\ No. of nodes & 8 & 65,000 \\ Range & 8 m (Class II, III) to 100 m (Class I) & 1-100 m \\ Modulation & FHSS \({}^{2}\) & DSSS \({}^{1}\) \\ Network topology & _Ad hoc_ piconets & _Ad hoc_, star, mesh \\ Data type & Audio, graphics, pictures, files & Small data packet \\ Battery life & 1 week & \(>\) 1 year \\ Extendibility & No & Yes \\ \hline \hline \end{tabular} \({}^{1}\) DSSS: Direct Sequence Spread Spectrum. \({}^{2}\) FHSS: Frequency Hopped Spread Spectrum.  
\end{table} 
Table 1: Comparison between Bluetooth and ZigBee. RFID is powered by his own battery. This enables higher signal strength and extended communication range of up to 100 meters; but the implementation of active communication requires larger batteries and more electronic components. The typical price of active RFID is between five or ten times the price of semi-passive ones [39]. RFID has been successfully applied to food logistics and supply chain management processes because of its ability to identify, categorize, and manage the flow of goods [39-42]. Also, electronic identification of cattle using RFID is a common practice in many farms [43]. However, recent developments in RFID hardware outfitted with sensors extend its range of application. [PERSON] _et al_. developed a RFID passive tag with a chemical sensor and its optoelectronic interface. The device is battery-free, has the size of a credit card and is compatible with the ISO 15693. It measures pH in the range 5.0-8.5, using wireless energy transfer to power the sensor and read its response [44]. There are commercial active and semi-passive tags that can collect temperature information [45,46]. Other semi-passive tags outfitted with sensor are under development, like humidity [47,48], shock/vibration [49], light [48,50] and concentration of gases, such as acetaldehyde or ethylene [51]. In agriculture, active tags are very interesting, especially for animal behavior studies.