Frequencies

When R.E.M. (and less famously RFID For Dummies) asked, "What's the Frequency, Kenneth?" the answer was pretty cut and dried because Wal-Mart demanded UHF. The world of RFID has changed a lot since the Wal-Mart mandate in 2003. RFID systems operate at various frequencies, which have been allocated by the International Telecommunication Union (ITU) and regional regulatory organizations such as the U.S. Federal Communications Commission (FCC). Although specific frequency bands differ by country or world region, four general frequency bands are used by RFID systems: low frequency, high frequency, ultra-high frequency, and microwave frequency. RFID tags working in each of the bands have different constructions, capabilities, and performance. Each frequency has its own advantages and disadvantages, and no frequency is perfect for all applications, despite what the greeter in the blue smock might tell you.

Low-Frequency Tags

Low-frequency (LF) tags operate at a frequency from 125 kHz to 134 kHz. Passive LF tags are constructed with an induction coil and use near-field inductive coupling for power and communication. An advantage of a low frequency is that the RF waves have great penetration ability, and metals, liquids, or any other "difficult" materials do not pose a problem. This fact also could be a disadvantage because LF waves are hard to shield. However, LF tags are less susceptible to interference than are the tags of other frequencies.

Read ranges of LF passive tags are typically less than half a meter. The read range is highly dependent on the area of the tag's antenna: the larger the area, the longer the read range. LF tags have slower data-transfer rates and are usually read-only . That means that they carry a pre-encoded tag ID, which is then matched to a database in order to retrieve information related to the tag. This feature provides higher data security. Recent developments within the LF tag technology have provided write/rewrite and anticollision capabilities.

The main applications of LF tags are as follows:

• Animal and livestock identification and tracking

• Access control

• Vehicle immobilizers (tags in key fobs)

• Point-of-sale (for instance Mobil/Exxon Speedpass)

• Various applications in closed-loop systems, for example tracking of electronic equipment such as laptops, PCs, or terminals

High-Frequency Tags

High-frequency (HF) tags operate at 13.56 MHz, which is globally accepted and implemented. Passive HF tags include an induction coil and use near-field inductive coupling for power and communication. Passive HF tags provide relatively good performance around liquids and metals, but have short read ranges, usually fewer than 1 meter, most of the time under half a meter. They have higher data-transfer rates than LF tags but are more susceptible to interference. Passive HF tags can be read-only as well as read/write and have anticollision capabilities, which are based around International Organization for Standardization (ISO) standards.

To date, HF tags are the most used tags globally because of their application in smart cards. Other applications include the following:

• Item-level tracking in supply-chain applications

• Access control

• Libraries

• Healthcare and pharmaceutical industry

• Smart shelves

Ultra-High-Frequency Tags

Thanks to the biggest retailers in the world and the largest supply chain in history (the U.S. DoD), there is a new star in the world of RFID-UHF. Passive ultra-high-frequency (UHF) tags operate anywhere from 860 MHz to 960 MHz, while active tags usually operate around 433 MHz. UHF tags have higher data-transfer rates than LF and HF tags and provide many additional capabilities, such as better anticollision and the possibility of locking and killing the tag, which were mostly implemented with electronic product code (EPC) Generation 2 technology.

There are two main types of passive UHF tags. The first type utilizes far-field communication (above one wavelength). The second type, which will be in production in 2007, uses near-field communication (within one wavelength).

Far-field passive UHF tags are made with an antenna that can be etched, stamped, or printed into various shapes. These tags use passive backscatter technology to communicate. A main advantage of these UHF tags over HF and LF tags is their read range, which reaches up to 10 meters, although it typically is around 3–5 meters. Far-field UHF tags do not penetrate water or metals and their performance around these materials is largely diminished, which makes them less suitable for item-level tagging.

Applications of far-field passive UHF tags include the following:

• Case-level and pallet-level tracking (retail, military, and so forth), sometimes item-level

• Baggage tracking

• Toll collection

• Asset tracking

• Antitheft protection

Near-field passive UHF tags were patented back in the mid-1990s but are just now coming into production. The tags have an antenna that is slightly similar to that used in an HF tag, except UHF requires only one loop, so it's not nearly as loopy as an HF tag, and it uses near-field inductive coupling for power and communication. The advantage of using near-field technology is the possibility of water penetration and a better performance around metals; however, it comes with a disadvantage of shorter read ranges. The range should be dictated by the laws of physics, which say that the magnetic field boundary layer is equal to the wavelength divided by 2 times pi. This would mean that the read range of UHF in the near field should be about 33 cm divided by 6, or around 5 cm. However, manufacturers are claiming the ability to read up to 3 feet using UHF near field, although this might be achieved with the help of a small far-field antenna or, more accurately, by using a PE mode wave guide, which may not even be legal according to the FCC-but that's way more detail than you need to know for the CompTIA exam.

This type of tag is being investigated to improve the capabilities of UHF tags that are largely used and mandated in the retail supply chain but historically provided bad performance in conjunction with liquids and metals. Near-field passive tags can be made to support the EPC Generation 2 protocol, and because of their purported performance and read range could be ideal for item-level tagging for such products as apparel and liquor.

Applications of near-field UHF tags include the following:

• Item-level tracking

• Possibly other applications that currently use HF

Note 

You are probably thinking, what is so great about this tag, if the HF tag can do the same thing? Well, near-field UHF tags have much faster data-transfer rates than HF tags (one of the manufacturers claims they're up to 64 times faster) and they can be used for tagging products that are under the UHF mandates. It also provides all the features of the Generation 2 protocol, another innovation that could be a breakthrough in the industry over the next few years.

Microwave Tags

Microwave tags operate at frequencies around 2.45 GHz and sometimes 5.8 GHz. Because of the frequency properties, microwave tags have the highest data-transfer rates of all tags, but the worst performance around liquids and metals. Passive microwave tags use passive backscatter to communicate and have limited read ranges, usually up to 1 meter. This is usually overcome by using active tags, which can achieve longer read distances. Because of fast data transfer, active microwave tags are suitable for use with toll-collection systems.

Table 4.3 provides a comparison of the pros and cons of all four types of frequencies.

Table 4.3: Comparison of Frequencies and Related Tag Capabilities
Open table as spreadsheet

Frequency	Band	Typical Read Range [*]	Pros	Cons	Applications
Low	125–134 kHz	Under 0.5 m	Best performance around water and metal	Slow data transfer Short read range[*]	Animal tracking Immobilizers Access control Speedpass
High	13.56 MHz	Under 1 m	Global standard Higher data-transfer rate than LF	Short read range[*]	Smart cards Smart shelves Access control Libraries Pharma
Ultra-high	860–960 MHz[*] 433 MHz	Around 3 m (up to 10 m)	Higher data-transfer rate than LF and HF Longest read range out of all passive tags[*]	Susceptible to interference Far-field tags have bad performance around water and metals[*]	Retail and DoD mandates[*] Case-level and pallet-level tracking (near-field tags for item-level)[*] Electronic toll collection
Microwave	2.45 GHz, 5.8 GHz	Under 1 m	Highest data-transfer rates	Short read range[*]	Electronic toll collection
[*]Applies to passive tags

Frequencies Used around the World

Because of international, regional, and local regulatory and standardization organizations and the frequencies allocated for a wide variety of purposes, radio frequency bands for RFID differ in various regions of the world. Frequencies were allocated by the ITU to three regions: Region 1, which contains Europe (including the former Soviet Union), the Middle East, and Africa; Region 2, which contains North and South America; and Region 3, which includes Asia, Australia, and Oceania. Within the first two regions the frequencies do not significantly vary by country, but this is not true about Region 3. Table 4.4 summarizes the frequencies per continent or country (as applicable).

Table 4.4: RFID Frequencies by Region
Open table as spreadsheet

ITU Region	Continent or Country	LF	HF	UHF	Microwave
2	North America	125–134 kHz	13.56 MHz	902–928 MHz	2400–2483.5 MHz and 5725–5850 MHz
2	South America	125–134 kHz	13.56 MHz	915 MHz (typically accepted)	2.45 GHz
1	Europe	125–134 kHz	13.56 MHz	865–868 (up to 870) MHz	2.45 GHz
1	Africa	125–134 kHz	13.56 MHz	865–868 (up to 870) MHz (north) 915 MHz (south)	2.45 GHz
3	China	125–134 kHz	13.56 MHz	917–922 MHz (temporary)	2446–2454 MHz
3	China (Hong Kong)	125–134 kHz	13.56 MHz	865–868 and/or 920–925 MHz	2.45 GHz
3	India	125–134 kHz	13.56 MHz	865–867 MHz	2.45 GHz
3	Japan	125–134 kHz	13.56 MHz	952–954 (955) MHz	2.45 GHz
3	Korea	125–134 kHz	13.56 MHz	908.5–914 MHz	2.45 GHz
3	Australia	125–134 kHz	13.56 MHz	918–926 MHz	2.45 GHz
3	New Zealand	125–134 kHz	13.56 MHz	864–868 MHz and 921–929 MHz	2.45 GHz
3	Singapore	125–134 kHz	13.56 MHz	866–869 MHz and 923–925 MHz	2.45 GHz
3	Thailand	125–134 kHz	13.56 MHz	920–925 MHz	2.45 GHz
3	Taiwan	125–134 kHz	13.56 MHz	922–928 MHz	2.45 GHz
3	Malaysia	125–134 kHz	13.56 MHz	868.1 MHz and 919–923 MHz	2.45 GHz

The idea of global supply-chain visibility is more difficult to realize at the UHF level when you look at the variance in UHF spectrum around the world. Generally, a UHF tag that operates on the U.S. frequency will not function adequately in Europe; a tag used in Europe will not work in Korea or Thailand. Fortunately, there is a solution for this problem. Some tag manufacturers (such as OMRON or UPM Raflatac) have or are developing a global tag that works on several different frequencies (within the UHF band), and therefore product manufacturers and distributors will be able to use only one tag for their goods anywhere in the world. The difficulty from a physics perspective is that as the bandwidth gets wider, the ability to tune a tag to respond gets more difficult.