In general terms, RFID (Radio Frequency Identification) is a means of identifying a person or object using a radio frequency transmission. The technology can be used to identify, track, sort or detect a wide variety of objects. Communication takes place between a reader (interrogator) and a transponder (Silicon Chip connected to an antenna) often called a tag. Tags can either be active (powered by battery) or passive (powered by the reader field), and come in various forms including Smart cards, Tags, Labels, watches and even embedded in mobile phones. The communication frequencies used depends to a large extent on the application, and range from 125KHz to 2.45 GHz. Regulations are imposed by most countries (grouped into 3 Regions) to control emissions and prevent interference with other Industrial, Scientific and Medical equipment (ISM).

	LF	HF	UHF	Microwave
Frequency Range	< 135 KHz	13.56 MHz	860 - 930 MHz [1]	2.45GHz
Standards Specifications	ISO/IEC 18000-2	ISO/IEC 18000-3 AutoID HF class 1 ISO 15693, ISO 14443 (A/B)	ISO/IEC 18000-6 AutoID class 0, class 1	ISO/IEC 18000-4
Typical Read Range	<0.5m	~ 1m	~4 -5 m[2]	~ 1m
General	Larger Antennas resulting in higher cost tags. least susceptible to performance degradations from metals and liquids	Less expensive than LF tags, Best suited for applications that do not require long range reading of high number of tags. This frequency has the widest application scope.	In volume UHF tags have the potential to be cheaper than LF or HF due to recent advances in IC design. Good for reading multiple tags at long range. More affected than LF and HF by performance degradations from metals and liquids	Similar characteristics to UHF but faster read rates. Drawback is microwaves are much more susceptible to performance degradations from metals and liquids.
Tag power source	Mainly passive using inductive coupling (near field)	Mainly passive using inductive coupling (near field)	Active and passive tags using E-Field back scatter in the far field	Active and passive tags using E-Field back scatter in the far field
Typical applications	Access Control, Animal tagging, Vehicle immobilizers	Smart cards, Access Control, Payment, ID, Item level tagging, baggage control, Biometrics, Libraries, laundries, Transport, Apparel	Supply Chain­pallet and Box tagging, Baggage Handling, electronic toll collection.	Electronic toll collection, Real Time Location of goods.
Notes	Largest installed base due to mature technology. However will be overtaken by higher frequencies	Currently the most widely available high frequency world-wide due to the adoption of smart cards in transport.	Different frequencies and power allocated by different countries US 4W(EIRP) 915MHz, Europe 0.5W (ERP) 868 MHz, [2]	5.8 GHz more or less abandoned for RFID

 

How RFID Works

RFID systems

In a typical system tags are attached to objects. Each tag has a certain amount of internal memory (EEPROM) in which it stores information about the object, such as its unique ID (serial) number, or in some cases more details including manufacture date and product composition. When these tags pass through a field generated by a reader, they transmit this information back to the reader, thereby identifying the object. Until recently the focus of RFID technology was mainly on tags and readers which were being used in systems where relatively low volumes of data are involved. This is now changing as RFID in the supply chain is expected to generate huge volumes of data, which will have to be filtered and routed to the back end IT systems. To solve this problem companies have developed special software packages called savants, which act as buffers between the RFID front end an the IT back end. Savants are the equivalent to middleware in the IT industry.

Communication

The communication process between the reader and tag is managed and controlled by one of several protocols, such as the ISO 15693 and ISO 18000-3 for HF or the ISO 18000-6, and EPC for UHF. Basically what happens is that when the reader is switched on, it starts emitting a signal at the selected frequency band (typically 860 - 915MHz for UHF or 13.56MHz for HF) . Any corresponding tag in the vicinity of the reader will detect the signal and use the energy from it to wake up and supply operating power to its internal circuits. Once the Tag has decoded the signal as valid ,it replies to the reader, and indicates its presence by modulating (affecting) the reader field.

Anti-collision

If many tags are present then they will all reply at the same time, which at the reader end is seen as a signal collision and an indication of multiple tags. The reader manages this problem by using an anti-collision algorithm designed to allow tags to be sorted and individually selected. There are many different types of algorithms (Binary Tree, Aloha....) which are defined as part of the protocol standards. The number of tags that can be identified depends on the frequency and protocol used, and can typically range from 50 tags/s for HF and up to 200 tags/s for UHF.
Once a tag is selected, the reader is able to perform a number of operations such as read the tags identifier number, or in the case of a read/write tag write information to it. After finishing dialoging with the tag ,the reader can then either remove it from the list, or put it on standby until a later time. This process continues under control of the anti collision algorithm until all tags have been selected.