RFID-How does it work?

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An overview about the technology involved

With no line-of-sight requirement radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is an object that can be attached to or incorporated into a product, device, or even person for the purpose of identification using low powered, high frequency radio waves.

Illustration of RFID components

A basic RFID system consists of a tag, or transponder, and a reader, also known as an interrogator. Even if the interrogator is called a “Reader” in the daily terminology, it has always read/write capabilities. Depending on their output power, antenna size and RF frequency, readers have field ranges from one centimeter up to several meters and more. The RFID tag is comprised of a small silicon microchip attached to an antenna and is electronically programmed with unique information, sometimes as little as an ID number, so the item it is attached to can be tracked. Modern RFID tags are much more sophisticated and include embedded non-volatile memory up to a size of 16kbit each. That is space enough to store around 2000 plain ASCII characters in uncompressed form on it. Around 98% of all tags in use are passive types, which do not have an internal power source. They are powered by energy induced in the antenna by the RF signal. For specific applications, active tags with an internal power source and an embedded sensor interfaces (for temperature, pressure etc.) are also available.

During operation, the reader emits electromagnetic waves. The tag antenna is tuned to receive these waves and the tag will identify itself when it detects a signal from a reader that emits a radio frequency transmission. The tag starts absorbing a small portion of the RF energy and sends modulated information back when sufficient energy is acquired from the RF field generated by the reader. In most cases, the data modulation can be accomplished by either direct modulation or FSK or Phase modulation. The reader demodulates the signals received from the tag antenna, and decodes the data for further processing.

Frequency Ranges & Standards

RFID hardware operates over several frequency ranges, where the low-frequency (LF) range has no big impact anymore and is therefore mentioned only for historical reasons. Each of the plain tags shown below are on basic substrates. They could be customized with a specific packaging where different materials, formats and styles could be selected. Combination with other media options for brand protection and/or authentication are easy to implement too.

		Low-frequency (LF) 125 to 134.2 kHz and 140 to 148.5 kHz Typical applications include immobilization systems in automobile, retail, animal identification and access control. Advantages: applications for harsh environments, high immunity to electrical noise. Disadvantages: low memory capacity and reading speed, limited reading distance (≤10cm), no bulk processing.
		High-frequency (HF) 13.56 MHz Typical applications include tagging and tracing of items, ideal for Lab automation and sample coding. Designed as a replacement for the LF technology. Advantages: high reading speed, large memory capacity (16kBit), multi-tag bulk reading possibilities with anti-collision features, global ISO standard (15693/14443/14444), on-chip encryption algorithms. Disadvantages: higher tag price (~50 Euro cent), reading distance limited to ≤2cm (depending on antenna size and transmission protocol).
		Ultra-high-frequency (UHF) 860 MHz to 960 MHz Typical applications include fixed asset tracking, pallet/box identification and supply chain purposes. Advantages: long range reading distance of several meters, memory capacity (10kBit), cheaper tag price (~30 Euro cents) Disadvantages: challenge to detect fluids and other water containing organic materials, higher reader hardware price, no harmonization of frequencies on a world wide basis, privacy and safety considerations required for far-field operation.

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