HI,
The Radio Frequency Identification (RFID) technology was developed during World War-2 as a tool to identify friend and foes. It has come a long way in the last 50+ years and is now making inroads into everyday life. RFID is the use of radio frequencies to read information on a small device known as a tag. RFID can be usually read electronically even when obscured or disoriented. The object of any RFID system is to carry data in suitable transponders, generally known as tags, and to retrieve data, by machine-readable means, at a suitable time and place to satisfy particular application needs.
From a functional point of view, an RFID system consists of four components:
Tags: into which identification data can be embedded. These are devices that identify the item to which they are attached. RFID tags are also called transponders.
Readers: Those communicate wirelessly with the tags.
Writers: Those are used to write data to the tags. They come as separate units or inbuilt with the Readers.
Software application (Middleware) that reads/writes data to/from tags through the reader. The application software (in a workstation or pc) initiates all communications between the reader and the tags. Both the reader and the tags are equipped with antennas that receive and emit electromagnetic waves.
RFID Readers
An RFID reader accomplishes two tasks:
• It receives commands from the application software (read middleware)
• It communicates with tags
Readers may be handheld or mounted on a particular object. In the case of handheld readers, the workstation (loaded with the application software), the reader and the antenna are all part of one device. Data exchanged with tags may be stored and transferred to a main processing unit at a later stage depending on the application. An RFID reader is practically a bridge between the application software and the antenna that radiates radio waves towards the tags. The radio waves emitted by the antenna propagate in the surrounding space. As a result, data travels wirelessly towards the tags that are in the vicinity of the antenna.
How does a reader work?
In "RFID speak", one hears the terms reader and coupler used interchangeably. Basically they are the same thing – devices that allow a PC or other device to talk to tags and either read their data or program them with new data. Readers are either inductively coupled or use propagation coupling (this is why the term coupler is used). They both do the same thing but use different methods to generate the required radio waves.
In practice, readers that use propagation coupling can generally read over longer distances. Both the reader and the tag, have antenna that are tuned to the same frequency to allow communications to take place.
The range that can be achieved by a reader is a function of Reader power. The reader power is measured in watts.
The "form factor" of the transponder (the bigger the tag’s antenna the better the read distance)
Environmental factors – these vary according to frequency, for example at 13.56Mhz the presence of metal can detune both the tag and the antenna whilst at 2.45Ghz line of site is a pre-requisite.
In theory, if you provide enough power you can read a tag at any distance. In practice, too much power will cause certain materials (like humans for example) to heat up and possibly become damaged. For this reason, most countries set limits on frequency and maximum power that can be used. The UHF band has one major advantage over 13.56 MHz - under US regulations it can achieve reading distances of two or three meters, suitable for applications such as container identification. However reading distance is reduced to 0.7 meters under European regulations and in Japan, for example, UHF cannot be used at all. Recently the Government of India has opened the band of 865-867 Mhz for UHF RFID applications. All other frequencies in the UHF RFID band 860 – 960 Mhz require specific licenses from the Government before being put to use.
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