An introduction to RFID

What's RFID?

RFID stands for Radio Frequency Identification. It is a technology allowing devices to automatically identify information stored in a tag through radio waves. An RFID tag consists of an antenna and a microchip in order to transmit and receive.

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This technology is generally characterized by the use of three important and essential components: the chip, the antenna and the reader.

The evolution of RFID

The use of RFID goes back to World War II, where it was used as a form of radar to locate Allied planes. Below is a quick history of the evolution of this technology.

How does it work?

The operating principle of RFID systems is based on the remote exchange of electromagnetic waves. Specifically, the reader transmits a signal at a given frequency to one or more radio tags located in its reading field and they also transmit a signal back. The electromagnetic field feeds the label and activates the chip.

To transmit the information recorded in the chip, the chip creates an amplitude or phase modulation on the carrier frequency. Once this information is received by the reader, it transforms it into binary code. The operation remains symmetrical in the opposite direction.

The scenario of a radio frequency identification is therefore as follows:

1. The reader transmits energy by radio to activate the tag.
2. It queries the tags nearby.
3. It listens to the answers and eliminates duplicates or collisions between answers.
4. Finally, it transmits the results obtained to the concerned applications.

RFID labels/tags

These little devices are commonly called labels, but they are found under other names (smart labels, smart tags, tags, transponders). They are equipment intended to receive a radio signal and to immediately return a different radio signal containing relevant information. Each tag consists of a microcircuit and an antenna.

Just like the barcode that's read with an optical laser, the RFID tag is also scanned with a reader that retrieves radio frequency signals emitted by this tag.

There are three types of tags:

• Passive tags: Devices that do not require any source of power, except that provided by readers at the time of the scan.
• Active tags: Devices equipped with a battery, allowing them to communicate with the readers. Unlike passive tags, active tags can be read from long distances.
• Semi-active tags: They act as a passive tag for communication and use their battery only to record the data.

The principal characteristics of a tag are:

• Large storage capacity (one or more kilobytes)
• Can be read by a scanner at a distance that can range from a few centimeters to about 200 meters
• Can be read but not necessarily written. It is, however, possible to rewrite the tag and thus recycle it
• Ease of use

Standards

The RFID system is based on a frequency system and has several tag devices, each adapted to the frequencies that suit it. The below protocols define the functionality provided by different types of tags.

The use of these standards allows RFID solution integrators to find systems suitable to the needs of their customers based on verified performance, and which can be a repository even if the tests are not performed on site. It will also allow users to choose from several solutions.

RFID frequency bands

A radio signal has a radius of a few hundred meters, depending on the power of the installation and the frequency used. A radio wave is classified according to its frequency expressed in Hertz (Hz) or cycles per second.

The set of frequencies used for RFID technology is described below.

Low frequency

These are the frequencies ranging from 30 to 300KHz, with a wavelength of 1 to 10 km and a reading distance going up to 10cm.

In RFID, a tag using low frequency is represented by the acronym LF (Low Frequency). Following national or international regulations, LF uses frequencies 125KHz - 134.2 KHZ.

High frequency

All frequencies from 3 to 30MHz, with a wavelength of 10 to 100m and a reading distance of 10cm to 1m.

In RFID, the tag that uses high frequency is represented by the acronym HF (High Frequency) and uses the frequency 13.56MHz to exchange data.

Ultra-high frequency

These are all frequencies from 300 MHz to 3 GHz, with a wavelength of 10 cm to 1 m and a reading distance going up to 200m.

In RFID, the tag using ultra-high frequency is represented by the acronym UHF (Ultra High Frequency) and is based on the frequency band 860MHz - 960MHz.

Conclusion

In this article, we saw a bit of history about RFID and how RFID works theoretically. In the next articles, we will dig deeper into its functioning with concrete examples and the necessary tools to use it.

Sources

• A Brief History of RFID, University of Arizona
• Introduction to the RIFD, French National RFID Center
• EPCglobal: A Universal Standard, Juan Ignacio Aguirre (MIT)