First, let’s start with the acronym and what it means: RFID = Radio Frequency IDentification.
If you have ever used an access card or fob to get into a building or passed through an automated toll collection system on a highway, you have used RFID. The definition of RFID is rather broad because it has so many uses.
Now, let’s break down what this means: a system of technologies that allows an object, person, or animal to wirelessly identify itself to another object or person. Hence the words RF (Radio Frequency) and ID (IDentification). To be able to do this in so many usage scenarios, form factors, price points, thermal environments, etc., the technology used for enabling RFID takes many forms. The most common ways of subdividing the technology are by frequency and whether or not the tag is a passive or active device. Let’s first look at the different frequencies.
At the lowest common frequency or LF (Low Frequency), this spans the range of 58-148.5 kHz or 58-148.5 thousand cycles per second. This frequency’s readers have short read range (usually several centimeters), but most importantly, this frequency allows the RF waves to transmit through metals a few millimeters thick as well as liquids. These factors make LF technology very suitable for implanting into animals, but also for access control and electronic article surveillance (EAS) applications. LF is a passive technology in which the tags only respond when energized by an LF RFID Reader. The behavior of the tag changes an incident RF field in a way that a reader can detect a unique ID. This ID may be a single bit in the case of an EAS tag or up to 10s of bits for animal tags.
The next frequency range spans from 1.75-13.56 MHz. This frequency range is called HF, or High Frequency, and includes tags for use in building access, public transportation, and electronic payment systems to name a few. The range of these systems is a few inches to a few feet, depending on the application. HF tags also work relatively well around metals and liquids. HF tags are usually used for proximity applications, for example, the gesture of moving one’s phone or wallet is used to provide access or payment.
The next frequency range is UHF or Ultra High Frequency. UHF RFID spans the 433, 840-960 MHz and the 2.4 GHz range. At this frequency, the RF that is produced allows for relatively efficient wave-like propagation; similar to a radio station, but with reasonable amounts of power consumption for handhelds, laptops, trucks, printers, etc. UHF RFID tags contain a small silicon chip and an antenna paired onto or into an object. This allows one to create tags which can be read from inches to 10s of feet in a passive configuration, and 100s to 1000s of feet if used semi-passively (the tag still changes the RF that comes back to the reader rather than transmitting, but gets a battery to help it out) or actively (an active transmitter).
UHF RFID tags can also be produced relatively inexpensively; the antennas can be etched with chemicals or printed with a printer that can print metals such as copper or aluminum. The lower cost and long range of UHF RFID means that tags can be placed just about anywhere and interrogators (or RFID readers) can read them. This allows computers attached to these interrogators to see the world around them through the RF lens.