The different types of RFID Systems
RFID systems are broken down by the frequency band within which they operate, frequency refers to the size of the radio waves used to communicate between the system components. RFID systems operate in low frequency (LF), high frequency (HF) and ultra-high frequency (UHF) bands. Radio waves behave quite different at each of the mentioned frequencies with advantages and disadvantages associated with using each frequency band.
A lower frequency, results in a shorter read range and a slower data read rate, but increased capabilities for reading near or on metal or liquid surfaces. Systems operating at higher frequencies generally have faster data transfer rates and longer read ranges than lower frequency systems, but are more sensitivity to radio wave interference caused by liquids and metals in the environment.
LF, low frequency
The LF band covers frequencies from 30 KHz – 300 KHz. LF RFID systems mostly operate at 125 KHz, although there are some that operate at 134 KHz. The LF frequency band provides a short read range of about 10 cm and has slower read speed than the higher frequencies, but is relatively insensitive to radio wave interference. Applications include access control and livestock tracking. Standards for LF animal-tracking systems are defined in ISO 14223, and ISO/IEC 18000-2. The LF spectrum is not a truly global standard due to slight differences in frequency and power levels throughout the world.
HF, high frequency
The HF band ranges from 3 – 30 MHz. Most HF RFID systems operate at 13.56 MHz resulting in read ranges between 10 centimeter and 1 meter. HF systems are moderately sensitivity to environmental interference. HF RFID technology is commonly used in ticketing, library, payment, and data transfer applications. Several HF RFID standards are in place, such as the ISO 15693 standard for tracking items, and the ECMA-340 and ISO/IEC 18092 standards for Near Field Communication (NFC). NFC is a short-range technology that is commonly used for data exchange between devices.
UHF, ultra-high frequency
The UHF frequency band covers the range from 300 MHz – 3 GHz. Systems complying with the UHF Gen2 or RAIN RFID standard use the 860 to 960 MHz band. While there is some variance in frequency from region to region, UHF Gen2 RFID systems in most countries operate between 900 and 915 MHz. The read range of passive UHF systems can be as long as 12 m, and UHF RFID has a must faster data transfer rate than systems using LF or HF frequencies. UHF RFID is the most sensitive of the three to interference, but many UHF product manufacturers have found ways of designing tags, antennas, and readers to keep performance high even in difficult environments. Passive UHF tags are easier and therefore much cheaper to manufacture than LF and HF tags. UHF RFID is used in a wide variety of applications, ranging from retail inventory management, pharmaceutical anti-counterfeiting and wireless device configuration. Most new RFID projects are using UHF opposed to LF or HF, making UHF the fastest growing segment in the RFID market. The UHF frequency band is regulated by a single global standard called the ECPglobal Gen2 (ISO 18000-6C) UHF standard.
Active RFID Systems
RFID systems as described so far are all so-called “passive” RFID systems using tags that use no power source. In active RFID systems, tags have their own transmitter and power source. Most often the power source is a battery. Active tags broadcast their own signal to transmit the information stored on their microchips to readers in the range.
Active RFID systems mostly operate in the ultra-high frequency (UHF) band and offer ranges of up to 100 m. In general, active tags are relatively expensive (around € 40,– each) and are used on larger valuable objects, such as rail cars, big reusable containers, and other assets that need to be tracked over long distances. Two main types of active tags can be distinguished: transponders and beacons.
Are “woken up” when they receive a signal from a reader and respond by transmitting a signal back which is received by the reader. The transponders do not actively radiate radio waves until they receive a reader signal, this way conserving battery life.
Are used in most real-time locating systems (RTLS), in order to track the location of an asset or person continuously. Beacons are not powered on by the reader’s signal. Instead, they emit signals at pre-set intervals. Depending on the level of locating accuracy that is required by the user, beacons can be set to emit signals every few seconds, once an hour or once a day. Each beacon’s signal is received by reader antennas positioned in the perimeter of the area being monitored, and communicates the tag’s ID information. The position is determined depending on the readers that read the beacon’s signal.
Passive RFID Systems
In passive RFID systems, the reader and antenna send radio signals to the tag. RFID tags use the transmitted signal to power on, and reflect energy back to the reader (back scatter).
Passive RFID systems operate in low frequency (LF), high frequency (HF) or ultra-high frequency (UHF) radio bands. Ranges of passive system are limited by the power of the tag’s backscatter (the radio signal reflected from the tag back to the reader), and are typically less than 10 m. Because passive tags do not have a power source or transmitter, and only require a tag chip and antenna, they are cheaper, smaller, and easier to manufacture than active tags.
Passive tags are offered in many different formats, depending on the specific RFID application requirements. For example tags may be mounted on a substrate, or sandwiched between an adhesive layer and a paper label to create smart flexible RFID labels. Passive tags may also be embedded in a variety of hard ware devices or packages to make the tag resistant to extreme temperatures or harsh chemicals and environments.
Passive RFID solutions are useful for many applications, and are commonly deployed to track goods in the supply chain, to inventory assets in the retail industry, to authenticate products such as pharmaceuticals, and to embed RFID capability in a variety of devices. Passive RFID can even be used in warehouses and distribution centres, in spite of its shorter range, by setting up readers at choke points to monitor asset movement.
Battery-Assisted Passive (BAP) Systems
A Battery-Assisted Passive RFID tag is a type of passive tag that incorporates a crucial active tag feature. While most passive RFID tags use only the energy from the RFID reader’s signal to “power on” the tag’s chip and backscatter to the reader, BAP tags use an integrated power source (usually a battery) to “power on” the chip, resulting in that all of the captured energy from the reader can be used for backscatter.
| ||Active RFID||Passive RFID||Battery-Assisted Passive (BAP)|
|Tag Power Source||Internal to tag||Energy transfer from the reader via RF||Tag uses internal power source to power on, and energy transferred from the reader via RF to backscatter|
|Availability of Tag Power||Continuous||Only within field of reader||Only within field of reader|
|Required Signal Strength from Reader to Tag||Very Low||Very high (must power the tag)||Moderate (does not need to power tag, but must power backscatter)|
|Available Signal Strength from Tag to Reader||High||Very Low||Moderate|
|Communication Range||Long Range (100m or more)||Short range (up to 10m)||Moderate range (up to 100m)|
|Sensor Capability||Ability to continuously monitor and record sensor input||Ability to read and transfer sensor values only when tag is powered by reader||Ability to read and transfer sensor values only when tag receives RF signal from reader|