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Lots of people talk about it and many people use it: RFID has been around a while and many RFID applications are getting more and more popular. But what is it exactly? At Nedap we often are asked about straightforward and comprehensive ways of explaining the basics of RFID and how to position different forms of RFID. Here’s an attempt to shed some light on what seems to be the magic communication of RFID readers with RFID tags.

What does RFID mean?

RFID is an acronym for Radio Frequency Identification. And this says it all: RFID is a word to describe all techniques that use radio waves to identify something. Usually RFID systems consist of the following components:

– A reader, that is connected to (or integrated with)
– An antenna, that sends out a radio signal
– A tag (or transponder) that returns the signal with information added

Sometimes the communication is one-way: it is only the tag that sends information to the reader. Sometimes it is bidirectional. But the basic principle is always used to identify a tag (or transponder). The tag is carried by a person, an animal or an object and usually contains a number (in a certain format).

RFID readers and antennas are sometimes integrated and sometimes more than one antenna is connected to one reader. The antenna is the part that actually transmits and receives the radio signal. The reader is the part that deals with the generation of the signal, the modulation, the conversion of information, etc.

What is RFID used for?

Readers are usually connected to another system. Let’s use an access control system as an example. The carrier would be a company employee. This person would have an access control card as a RFID tag. The reader would be a smartcard reader that is mullion mounted next to secured doors. The reader would be connected to an access control system.

In the access control system access rights for people are stored and people are linked to a number. This number is also stored on the RFID card. If the access control system gets information from the reader, it will look in its database to check if this person has access rights. If so, the system would be sending a signal to a door that it can be opened.

There are many variations to this setup. A wide variety of RFID systems have been implemented in the world. Livestock management systems deal with identification of cattle to automate feeding and milking or optimize heat detection. Vehicle access control systems use RFID in buses, taxis and ambulances to allow to them secure and convenient access to bus depots, taxi stands or first help entrances. Retail stores use RFID for securing goods and inventory checking. Logistics departments use RFID to track parcels in warehouses and during transport. Libraries use RFID to identify books and members in elf service applications. Billions of RFID tags are used in our world on a daily basis in millions of applications.

OK, but how does that work?

The principle of all RFID systems are basically the same: a reader sends out a radio signal. Once a RFID tag gets in reach of this signal, it will be powered in a certain way (sometimes inductive, sometimes in other ways). Inside the tags is a chip that is able to perform some logical behavior and that contains some information in its memory.

When the tag is powered, it will start returning a radio signal to the reader. The basic concept for many wider range systems is referred to as “modulated backscatter”. In basic terms the idea is that the tag reflects the reader signal (you could compare it to a mirror for radio waves), but when it reflects the signal, it slightly changes the modulation using a certain protocol. The reader understands these changes and is able to decode the information.

Both the reader and the tag will be transmitting radio signals in a certain frequency so they are interoperable. Some well known and often used RFID frequencies are:

Frequency (approximate range) Name Example
120 – 125 kHz Low Frequency (LF) Nedap and HID Prox cards
13,56 MHz High Frequency (HF) MIFARE and HID iClass cards
868 – 928 MHz Ultra High Frequency (UHF) EPC Gen II tags and cards
2,45 – 5,8 GHz Microwave Vehicle Identification & Tolling

Some of the RFID tags are powered using a battery, these are the so-called active or semi-active transponders. Other tags do not require a battery. These are often referred to as passive badges.

The read range of these RFID systems varies enormously and depend not only on the frequency that is used, but on many other things, like tag sensitivity and antenna size. Passive access control cards that operate at LF or HF frequencies, often offer a limited read range of a few centimeters, while systems that operate at UHF or microwave frequencies sometimes offer a read range of more than ten meters.

Why does EPC Gen II matter?

There are billions of RFID tags being used in millions of applications. Unfortunately until a few years ago not much has been achieved in standardizing the communication between reader and chip. In the past few years usage of the UHF frequency has become increasingly popular. This has to do lot with the introduction of the EPC Gen II standard.

EPC Gen II is short for EPCglobal UHF Class 1 Generation 2. EPCglobal (a joint venture of GS1 and GS1 US) has introduced this standard for the use of usually passive RFID tags and the Electronic Product Code (EPC) in the identification of many items in may applications worldwide.

One of the missions of EPCglobal was to unify the wide variety of protocols that existed in the RFID world in the nineties. The second generation interface was introduced in 2004. Many UHF readers and UHF tags nowadays have embraced this standard, making them a lot more interoperable. A Gen II version 2 standard is in the making, which will introduce encryption to improve tag authentication.

EPC tags are not only used in generic supply chain operations, but also in more specific applications of vehicle access control and building access control.