SECTION I: Understanding Radio Frequency IDentification (RFID)
INTRODUCTION TO RFID
Simply put, RFID is a form of automatic identification. However, its capabilities surpasses the traditional forms of auto ID technologies such as barcoding and magstripe, allowing to enhance and improve current applications and processes or enabling new identification and tracking applications not feasible or possible through traditional auto ID technologies in the past.
In the past 10 years, RFID has emerged as an innovative mainstream technology expanding beyond its proprietary and obscure application base in the decades previous. Today, RFID is considered an enabling technology, numerous applications and implementations across a wide range of industries and markets are testaments that the technology is beyond the hype curve and is solving problems and delivering real value on the ground.
RFID in principle is a simple technology, yet it is powerful, feature-rich and functional. At the highest level, RFID systems can be classified into active, passive and semi passive types with further grouping based on the frequency band they operate in, most notably, low frequency (LF – 125 KHz to 135 KHz), high frequency (HF – 13.56 MHz), ultra high frequency (UHF – 433 MHz and 868 MHz-956 MHz) and microwave (2.4 GHz). We will discuss the characteristics of different types and different frequencies in more detail in later sections of this whitepaper.
Figure one shows the main components of a typical RFID system. The focal point in an RFID system is the RFID tag or transponder. The IC based RFID (as opposed to polymer based chipless RFID) in its simplest form comprises of an integrated circuit chip and an antenna mounted onto a substrate or an enclosure. The chip consists of a microprocessor, memory and RF communication, command control as well as data storage and processing. Depending on the type of technology, active, semi active or passive and the operating frequency, they vary in data storage, communication method and power source.
- Type : active , passive, semi active
- Frequency, LF, HF, UHF , microwave
- Electrical field , magnetic field
- Reader talks first vs. tag talks first
- Memory: read only (RO), Read-Write (R/W)
- Antenna – gain, polarity
The transponders communicate via radio frequency to a reader, which has its own antennas. The readers can interface through wired or wireless medium to a main computer. Transponders are also known as smart or radio tags. The memory will vary, depending on the manufacturer, from just a few characters to kilobytes.
The two most common types of RFID technologies are Active and Passive. Active RFID transponders are self-powered and tend to be more expensive than Passive. Having power on board allows the tag to have greater communication distance and usually larger memory capacity. The most common application for Active RFID is for highway tolls such as the Highway 407 in Toronto, ON, Canada.
As for passive RFID transponders, which are available with chips and without chips, they have no internal power source therefore require external power to operate. The transponder is powered by an electromagnetic signal that is transmitted from a reader. The signal received will charge an internal capacitor on the transponder, which in turn will then supply the power required to communicate with the reader.
A BAP RFID (battery assisted passive) tag is fundamentally different than an active RFID tag because it utilizes the “reader-talks-first” principle. The batteries on BAP tags are activated only when scanned by a reader. Once activated, it uses the power of the battery. Once read, the tag goes back to “sleep”, which helps extend the tag’s battery life. The ISO/IEC 18000-6:20103 BAP RFID standard implements sophisticated tag selection capabilities, allowing readers to only request responses from tags meeting certain selection criteria. Using the “reader-talks-first” principle, combined with the sophisticated tag selection capabilities, readers can inventory all tags on a programmable periodic basis while also constantly inventorying tags based on certain selection criteria (e.g. only read tags that have alarm events).
Because of the high sensitivity of the BAP tag, the RFID reader’s receiver sensitivity also should be high to be able to receive this signal. Keep in mind that high reader sensitivity does not help the performance of standard passive tags because performance in this case is limited by the reader-to-tag link. Lower sensitivity readers will still work, but they will provide shorter read distances.
Some of the most common uses of passive RFID today are for security and access control, payment, animal identification, waste management, work-in-process, asset tracking and electronic commerce.
Whether we are talking about active or passive RFID, the features and benefits are the same.
The following details some of the benefits:
- Transponders can be read from a distance and from any orientation, thus they do not require line of sight to be read.
- Transponders have read and write capabilities, which allow for data to be changed dynamically at any time.
- Multiple transponders can be read at once and in bulk very quickly.
- RF-Tags can easily be embedded into any non-metallic product. This benefit allows the tag to work in harsh environments providing permanent identification for the life of the product.
It is important to take the environment into consideration when implementing RFID. For example, metal, electrical noise, extreme temperatures, liquids and physical stress can create a challenge and may affect performance. For seamless integration, RFID Canada highly recommends that a site survey and testing be done. System implementation will be reviewed in Section VI.
Today, most implementations involve passive technology. For this reason, this document is based solely on passive RFID. There are different frequency bands which passive technology operates within.
Low and high frequency RFID operate on the inductive coupling principle. That is, the energy is transferred from the reader to the tag through shared magnetic field. The amount of transferred energy is proportional to the size of the transmitting and receiving antennas as well as the tag ability to operate at the resonance frequency. The resonant frequency is a state in which the impedance is at its minimum, allowing for maximum current flow in the circuit. The resonance frequency is a function of the inductance and capacitance of the tag circuit. The quality of a resonant circuit is measured by Q factor. The higher the Q factor, the higher the amount of energy transfer. Although higher energy transfer is desirable, the higher Q factor results in reduced bandwidth.
UHF RFID tags communicate with the reader using the backscatter principle. This is the same technique used in radar technology. The term backscatter refers to the portion of the transmitted signal that is reflected back 180 degrees opposite the direction of the incident signal, as opposed to random scattering that is lost in the space. The tag will send back data by means of varying the load of the received signal. The reader senses the varying field and demodulates the signal to retrieve tag data.
Currently, available UHF passive tags can contain a hybrid antenna which can operate with both the near-field and far-field components produced by the reader antenna. This appears as the combination of two topologies – a closed loop to inductively couple the magnetic near-field and a dipole to couple the electric far-field. Such a tag can be used in a dual mode to take advantage of the different properties of each mode using a single tag design.
Of all the various frequency bands RFID operates within, there isn’t one that can address all applications. In essence, there is no super RFID frequency band; in other words, “one frequency does not fit all”. For this reason, the next three sections will review the most common passive RFID frequencies.