RFID FAQ

Are there different types of RFID?

Yes. There are a number of types of RFID. They differ by:

(1) Power source:

ACTIVE systems - the tags are powered by internal batteries

PASSIVE systems - the tags are powered by readers. They have no internal power source.

BATTERY ASSISTED PASSIVE systems - a hybrid between active and passive systems. The tags contain a small battery

(2) Frequency:

LOW FREQUENCY or LF - operate at frequencies of 400kHZ or less, typically between 125 kHz and 134.2 kHz.

HIGH FREQUENCY or HF - typically operating in the low MHz range

ULTRA HIGH FREQUENCY or UHF - typically operating in the mid-MHz to GHz range.

(3) Chip type

EEPROM which may be:

- OTP or One Time Programmable, if locked; or

- WMRM - Write Many Read Many, or Read/Write, if unlocked.

ROM which is laser-programmed in the factory.

(4) Modulation

There are different types of modulation, including Amplitude shift keying (ASK); Frequency shift keying (FSK); and Phase shift keying (PSK)

(5) Type of communication

Full-duplex communication - both tag and reader send and receive information at the same time

Half-duplex communication - tag and reader must alternate, and cannot send and receive information simultaneously.

With over 30 different types of RFID available, which one do I select?

An RFID technology that is well suited for one project may be completely unsuitable for another. A good understanding of the requirements of the application and the attributes of the technology will help pin-point the right technology for the job. Contact us to discuss your requirements.

Differentiators between RFID systems include:

  • Size, ruggedness and cost of transponders
  • Longevity of transponder
  • Achievable reading distance
  • Transmission speeds
  • Long term operating cost within the intended application
  • Ability or inability to read through or near liquids and different types of solids
  • Readability in the presence of metal and Electro Magnetic Interference (EMI) emitted by nearby equipment
  • Quality of design and assembly (affects all aspects of performance)

What is a passive tag?

Passive tags are powered by the reader (they typically derive their power from the signal emitted by the reader). As a result, passive tags do not have an internal power source, unlike active tags which depend on batteries to send a signal to the reader.

Battery-assisted passive (BAP) tags use a battery to operate the chip, but communicate using power from the reader. The batteries used in active and BAP tags have a typical lifespan of only three to five years. Passive tags do not have this limitation and typically have a longer life expectancy.

Passive tags typically cost less and have fewer failure modes because they contain fewer components and connections.

They can operate across a wider temperature range.

All TROVAN transponders are passive.

What are the differences between low frequency (LF), high frequency (HF) and ultra high frequency (UHF) RFID?

Low frequency RFID systems operate at frequencies below 500kHz, with most systems operating between 125 and 134.2kHz, with ranges of up to 1 meter. The omni-directional read field of LF systems may have low sensitivity to interference.

High frequency RFID systems operate between 3 and 30 MHz. Most HF RFID systems operate at 13.56 MHz with read ranges of up to 1 meter. HF systems are moderately sensitive to interference.

UHF RFID systems operate from 300 MHz to 5.8 GHz. The most significant advantage that high frequency products enjoy is range. The most commonly used UHF system is EPC Gen2 which, in most countries, operates between 900 and 915 MHz. High frequency signals can be focused in a beam, rather than having to be omni-directional, and focused as a beam can achieve greater range. UHF systems are extremely sensitive to interference.

Advantages of high frequency (HF) and ultra high frequency (UHF) tags:

  • May have longer read range in benign environments that have little to no interference (associated with larger tag form factors)
  • Higher data rates (transmit more data in shorter time)
  • Anti-collision systems possible due to higher data rates.

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Disadvantages of high frequency (HF) and ultra high frequency (UHF) tags:

  • Extremely sensitive to electromagnetic interference.
  • May fail in: Presence of rust and metal (the so-called "diode effect"). Water, snow, ice, dew drops.
  • Directionally sensitive: transponder has to be oriented “just right,” because the signal is directed as a beam.
  • May require line-of-sight (like barcode).
  • When supplied as paper labels, very short range HF and UHF tags with printed antennas may be quite low cost (but with many of the same limitations as barcode).


Advantages of low frequency RFID:

  • Reliable operation in harsh environments. Use low frequency RFID tags in wet, dusty, dirty conditions; use in high-impact applications.
  • No line-of-sight constraints. Read low frequency tags through wood, concrete, any non-metallic solids. Hide low frequency RFID tags inside objects. Paint over them.
  • No problem with condensation on LF tags.
  • Easily read them when submersed in water or implanted into living animal tissue.
  • Orientation between tag and scanner in LF systems is not critical. (Signal pattern is essentially omni-directional in LF systems).
  • Optimized LF systems have improved ability to operate in high EMI environments.
  • Optimized LF systems have improved ability to operate attached to metals or in the vicinity of metal objects.


Disadvantages of low frequency tags:

  • Lower data rates.
  • Limited read range.

What are so-called “anti-collision” systems?

The concept behind “anti-collision” systems is this: when several compatible tags are present in a reader’s field at the same time, they can all be read. Though the advantages of the “anti-collision” principle seem obvious, in practice there are several important limitations.

Read times for anti-collision protocols are longer than for standard protocols. As a result, if a single “anti-collision” tag is travelling through a reader’s field at a distance, it is less likely to be detected than a standard tag. If a number of “anti-collision” type tags are moving into and out of the reader’s field, particularly at a distance from the reader, expect a percentage of “no-reads” at lower speeds than would be true for standard tags.

In the most commonly used anti-collision protocols, tags transmit their data sequentially, so only one tag is interacting at a time with the reader. The larger the batch, the longer the read time.

Other factors will cause a percentage of “anti-collision” transponders in a batch not to be detected: for instance, if two transponders are the same distance from the reader, one or both may be “masked.” Also, tags may be masked by the presence of ferrous materials (metals).

Most importantly, there is no way to determine whether each tag present in the batch has been read, unless all items in the batch are counted. In many applications, the physical interaction required to ensure a 100% read rate with “anti-collision” systems effectively does away with the benefits of using them.

And what about NFC tags?

NFC, which stands for Near Field Communication, are HF tags with extremely short read ranges, generally touch tags, or near-touch tags. They may be very low cost paper labels. NFC tags have substantially the same operational limitations as barcode.

Why would I ever use read-only technology if I can use read-write?

There is a place for each.

Read-write tags allow the operator to program relevant information about the asset or animal into the tag itself, for later retrieval with a compatible scanner.

Trovan supplies read-only tags with a laser programmed IC that is programmed with a globally unique ID number – it does not have any intrinsic meaning. The unique ID number is stored in a central database or look-up table together with all relevant data about the asset or animal. Nowadays, with cheap storage on smart phones and tablets and easy access to cloud-based data, read-only tags may provide an economical and more flexible solution in many applications.

Advantages of the read-only approach: types and format of data can be readily changed and expanded as need, without limitation. Access correct and up-to-date data on every asset, even if the asset is not physically available to be scanned. Tag data is most secure in read-only tags, as it is not subject to hacking/reprogramming.

All read-write tags, and competitors’ read-only tags, feature electronically programmed (EEPROM) integrated circuits. Write range is typically comparatively short: 1/3 of achievable read range. And write speed is typically relatively slow: in fact read speed is a fraction of the write speed, which may be a factor in dynamic processes. Electronically programmed ICs are subject to deterioration and limited lifespan, and are subject to hacking and even spontaneous modification via EMI. Tag data is generally accessibly to anyone with a compatible reader, which may compromise strategic and sensitive data.

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