Tag – You’re It! the Low Down on RFID Tags

Tag – You’re It! The Low Down on RFID Tags

RFID Tags Use Different Frequencies

Figuring out Radio Frequency Identification (RFID) can seem like a jungle at times. The building blocks are simple enough: RFID tags, RFID antennas and RFID readers. The tough question, when starting out down the RFID road, is what frequency is right for the application and what combination of RFID tags, RFID readers and RFID antennas is the right combination?

RFID tags are classified by frequencies. RFID tags, antennas and readers are tuned just like a radio is tuned to a specific frequency to receive different stations. RFID has different flavors of a similar technology. For example, low frequency RFID and high frequency RFID tags can be used globally without a license.

RFID Tags Are Categorized By Radio Frequency

RFID Frequency Groupings

1.    Low Frequency  RFID Tags[pK1]  (125 kHz or 134.2kHz)

2.    High Frequency RFID Tags (13.56 MHz)

3.    UHF RFID Tags (868 MHz to 956 MHz) a.k.a. GEN2 RFID

4.    Microwave RFID Tags (2.45 GHz)

Individual countries govern the use of various frequencies differently

Ultra-high-frequency (UHF) RFID tags cannot be used globally as there is no single global standard. Europe uses 868 MHz. for its UHF RFID applications while North America uses 915 MHz..  In North America, UHF can be used for RFID unlicensed for 902 - 928 MHz (+/-13 MHz from the 915 MHz center frequency), but restrictions exist for transmission power. In Europe, RFID is regulated by ETSI recommendations EN 300 220 and EN 302 208, and ERO recommendation 70 03. This allows for RFID Tag operation from 865-868 MHz. The North American UHF standard is not accepted in France as it interferes with its military bands For Australia and New Zealand, 918 - 926 MHz are unlicensed, but restrictions exist for transmission power. The use of 2.45GHz Microwave RFID tags are restricted in Israel, China and Japan.

Different vertical markets require different RFID tags as each frequency range has its advantages and disadvantages. Low Frequency RFID tags (LF) are less costly to manufacturer than Ultra High Frequency (UHF) RFID tags. UHF RFID tags offer better read/write range and can transfer data faster then other RFID tags. HF RIFD tags work best at close range and are highly effective at penetrating non-metal objects especially objects with high water content.

 Attention recently has been focused on the supply chain. The initiatives driven by WalMart and the DoD have created a new level of RFID awareness. These initiatives have also accelerated the creation of new RFID GEN 2 standards. GEN 2 is beginning to unseat some legacy RFID practices. 

  Various Types of RFID Tags

There are two types of RFID tags: active RFID tags and passive RFID tags.

Passive RFID tags have no internal power supply. Instead, a small electric current is created in the antenna when an incoming signal reaches it. This current provides enough power to briefly activate the tag, usually just long enough to relay simple information, such as an ID number or product name. Because passive RFID tags do not contain a power supply, they can be very small in size, sometimes thinner than a piece of paper. Passive RFID tags can be activated from a distance of ten millimeters to over six meters away.

Active RFID tags contain an internal power source, which allows for a longer read-range and for a bigger memory on the tag itself. The power source also makes it possible to store information sent by the transceiver. Active RFID tags are larger than passive tags - usually slightly bigger than a coin. They can be read from many meters away and generally have a battery life of about ten years. Advantages of active tags include accuracy, reliability, and superior performance in adverse RFID environments such as water or metal.

The major advantages of active RFID tags is that it can be read at distances of one hundred feet or more and that it may have other sensors that can use electricity for power. Active RFID tags may have longest communication range of any RFID tag.  Active tags can perform independent monitoring and control and initiate communications. These tags can perform diagnostics and be equipped with autonomous networking. The disadvantages of active RFID tags are that the tags cannot function without battery power, which limits the lifetime of the tag. Active RFID tags are more expensive often costing $20 or more per tag. The tag is physically larger, which may limit its use in certain applications. The maintenance costs for an active RFID tag are greater than a passive tag if batteries need to be monitored and replaced. Battery outages in an active RFID tag can result in costly misreads.

Once a frequency range is determined, then it is time to choose an antenna that best fits the application. RFID Antennas are connected to an RFID tag via a cable. Antennas come in all sorts of sizes and shapes. The size and power output of the antenna determines the read range for the application. Large antennas used with Active RFID Tags can have a range of 100 feet or more. Large antennas used with Passive RFID Tags generally have a range of 10 feet of less. There are dock door antennas (some times called Portals) that allow a forklift driver to drive between two antennas. Information can be collected from the tags without the forklift driver having to stop. There are RFID antennas that mount between rollers on conveyors for reading/writing from below. While other antennas are available that mount to the side of or above the conveyors. In many warehouse applications forklift trucks are equipped with an RFID antenna. In retail operations product is tracked by using ‘Smart Shelf’ antennas. Portable handheld readers are usually restricted to using small RFID antennae.

The Right RFID Tag for the Application   

RFID is being used in almost every industry today. The list of applications is endless. Some applications need RFID tags that can handle very harsh environments. Some applications need tags that can be read from a distance. Some applications need tags that can be read at high speed. Some applications need RFID tags that can accept and store data. Other applications need tags that provide an extra layer of security.  Yet other RFID applications may need very low cost tags. There may be a need for a combination of some of these requirements. No one RFID tag satisfies all requirements just as in horse racing where there are horses for courses. When implementing RFID there are specific RFID tags for specific RFID applications. If you know your application requirements and constraints there is probably an RFID tag that is just right.

The four main frequency ranges of tags each have strengths and weaknesses. LF, low frequency RFID, is used for applications that do not require long read ranges. LF RFID has been used for some time and is well accepted for applications such as tagging machinery for maintenance records, asset control, livestock and animal tagging. LF works well in rugged environments and in otherwise RFID unfriendly surfaces such as metal. LF has been and continues to be used in closed loop operations such as POS transaction, automotive security door locks, and laundry tracking. LF tags come in different form factors and sizes and can be designed to operate in extreme environments. LF form factors include glass cylinder, plastic disk, plastic wedge, FOB, nail tags and badge, card or label.

LF RFID penetrates most materials, such as water and body tissue. EMI is one limitation; if used in industrial environments electric motors may interfere with the LF system. Due to the size of the antenna required, the LF transponders are typically more expensive than High Frequency transponders. This limits the frequency to applications where the RFID transponders can be re-used.

The following are some of the benefits and limitations of LF RFID:

• Penetrates most materials well including water and body tissue, which makes it ideal for animal identification






• Tags can easily be embedded into any non-metallic items such as pallets, key fobs, cards etc.






• LF could be affected by electrical noise that may be generated by motors in an industrial environment






• Relatively low data transfer rate (70ms for read command), the lower the frequency the slower the communication






• Transponders are more expensive ($2.00 - $17.00)






• Most LF systems can only read one transponder at a time and does not support simultaneous read of multiple transponders






• Read ranges are from a few centimeters to a couple of meters, depending on the size of the transponders






• Frequency is used worldwide. There are no restrictions

• Currently most access control systems are based on LF, contact-less cards or key fob for security. A read only card can be used simply as identification or a read-write card can be used to maintain access or security information.

 Passive High Frequency (HF) operates at 13.56MHz and is a globally accepted frequency; however, there are some differences with regulations in the different regions of the world. These differences pertain primarily to power and bandwidth. In North America, Industry Canada and the FCC limits the reader antenna power to three watts while in Europe the regulations allow for four watts.

Passive HF is also the basis of numerous standards such as ISO 14443, 15693, 18000-3.

With HF, the signal travels well through most materials including water and body tissue. It is however more affected by surrounding metals compared to Low frequency (LF).

In comparison to LF, the benefits of HF are lower tag costs, better communication speed and the ability to read multiple tags at once.

The length of the antenna is based on the length of the signal wave thus the higher the frequency the shorter the wavelength. For this reason, there is the flexibility that an antenna for a HF RFID tag is small enough that it can be produced by printing it onto a substrate, using conductive ink and then affixing the chip.

Today the cost for HF RFID tags or what are also known as INLAYS is approximately $0.60 to $0.70. As demand increases, we should see prices drop significantly.

RFID tags produced with HF chips are typically less than .1mm in thickness and are available with different sizes of antennas. The larger the tag antenna, the greater the energy capture area the tag has and the greater the communication distance from the reader. Smaller RFID tag sizes may be easier to package into a product but the downside is the reduction of communication distance available.

The capability of the small inlay size allows for it to be embedded into labels. Labels with inlays are called smart labels. Through the use of printers with embedded RFID or external readers not only can smart labels be printed on, but they can also be written to.

With the current power regulations, HF is designed for applications that require a 1m or less of communication range. Orientation of the tags with respect to the reader antenna will have an impact on the communication range. For optimum communication range, both antennas (tag and reader) should be parallel. Having the tag perpendicular to the RFID reader antenna may significantly reduce the communication range.

The higher the frequency, the higher the data throughput and the faster the communications will be between the reader and the tags. This increase in speed allows for the reader to communicate with multiple RFID tags at once. The process of communication with multiple tags is known as Anti-Collision and at HF, a reader can read up to 50 tags per second.

The following are some of the benefits and limitations of HF RFID:

• Penetrates most materials well including water and body tissue






• Not as effective as LF in the presence of metal and water






• Tags can easily be embedded into non-metallic items such as labels, pallets, key fobs, cards etc.






• HF should not be affected by electrical noise that may be generated by motors in an industrial environment. Higher data transfer rate (20ms for read command), the higher the frequency, the faster the communication






• Transponders are less expensive (they can range from: $0.70 - $0.80 CDN)






• Reader can communicate with multiple tags simultaneously






• Read range is less than one meter






• Tags have larger memory capacity






• Frequency is recognized and used globally (no restrictions)






• Global standard: ISO 15693, 14443, 18000-3

 Although most RFID access control systems today are based on LF, using either contact-less cards or key fobs, HF RFID is becoming the technology of choice for new access control and security systems. Their additional memory allows for improved security and the integration of biometrics as part of the security features. Enhanced access control systems have the ability to validate assets, such as computer equipment and other items as one passes through an access control system or portal. Assets embedded with a HF RFID tag can be read and identified within the access control system. Documents and files can easily be identified and tracked as well.

Contact-less Smart Cards or RFID cards are going to be the next generation of credit cards. Credit card companies have been testing HF RFID based on ISO 14443 standards for some time. We should start seeing the deployment of these new cards in the next few years, once retail terminals are upgraded to support RFID capabilities. One of the main reasons for the switch to contact-less smart cards is primarily to the ruggedness and consistent performance levels associated with RFID. When a tag is embedded into a card or other form factors, the tag is essentially protected from the surrounding environment. As for the readers, they can also be encased and protected from the surrounding environment. The second reason for the switch to RFID is the additional memory the tags can store. This allows for better security and protection of privacy issues. By using biometrics and personalized access number improved security can be accomplished.

Ultra High Frequency refers to the frequency range 300 MHz to 3 GHz in the radio spectrum. RFID technology has been developed in different regions of this band, specifically, 433 MHz, 860 -956 MHz and 2.45 GHz. The focus of this section will be specifically on the 860-956 MHz range due to the fact that this range has attracted most R & D investments and is positioned to dominate the UHF passive RFID market space. This technology is also referred to as GEN2.

UHF coming to prominence in the RFID market place is a fairly recent phenomena compared to the more established High Frequency (13.56 MHz) and Low Frequency (125-134.2 kHz) technologies. HF is a robust technology, which works well for item management applications, but fails where read ranges of beyond 1m is required. UHF vendors are targeting the supply chain market where longer read distances are required.

Technologically speaking, RFID in the UHF range differs from High Frequency systems in a number of ways. UHF operates, primarily, in 860-956 MHz range allowing for shorter antennas and longer read distances. RFID Reader-Tag communication is implemented using backs-scatter technology. In this method, tag communicates with the reader by modulating the received signal and radiating it back to the reader. This scheme is fundamentally different than Inductive-coupling method used in HF systems. Moreover, the anti collision (simultaneous reads) feature implementation in UHF is achieved using a protocol based on bit broadcasting as opposed to HF protocol that operates based on the time slot concept. This allows for higher number of tags to be read simultaneously in the UHF range, typically 200 tags as opposed to 50 tags with HF systems.

Although the UHF RFID addresses some shortcomings of the HF RFID, primarily in terms of read range, it has to contend with its own limitations and challenges. Today's UHF systems do not work in the presence of liquids whereas HF and LF work fairly well in such environments. Metal poses a serious challenge for any RFID implementation, more so in the UHF range, however. Moreover, longer read distance becomes a disadvantage in applications such as banking and access control.

One of the biggest challenges that has impeded the wide spread implementation of UHF RFID is lack of globally accepted standards and regulations. In today's global economy, cross continental trade requires goods to be identifiable universally. At the present time, different frequency designations, power and safety regulations are in place in different regions of the world. In North America, UHF operates at 902 - 928 MHz. In Europe, UHF works in the 860 - 868 MHz range whereas Japan uses 950 - 956 MHz.

The following are some of the benefits and limitations of UHF RFID:

• Provides good read distances, typically in the 3-6 m range






• Tags can easily be embedded into solid non-metallic items such as labels, pallets, cards etc.






• High data throughput and faster anti collision scheme facilitate higher read rates. 800 reads is achievable in theory but 200 is the read rate for practical purposes






• UHF Transponders cost less compared to HF due to lower memory capacity and simpler manufacturing process






• Low tag memory, most currently manufactured UHF tags do not have user memory and only carry a 96 bit serial number






• Lack of global standards and regulations. Work is underway to establish a uniform standard acceptable to all regions of the world






• Poor performance around liquids and metals






• Crowded frequency band, 860-960 MHz falls within the ISM (Industrial, Scientific, Medical) band, making it one of the more crowded regions of the spectrum

 There are complicating factors that have somewhat hindered faster progress in the UHF RFID market. As mentioned above, UHF technology suffers from lack of standards and regulations. ISO and EPC Global are the main bodies that work to draw standards and specifications for UHF RFID. However, at times, these two organizations seem to be moving in competing paths, resulting in duplication of efforts and confusion in the market place. This has caused some major vendors and users to delay their entry into the RFID market. At present, EPC standards have defined specification for Class 0, Class 1, and GEN2 tags. At the same time, 18000-6 is the ISO standard for the 900 MHz UHF band. UHF or GEN2 has been tapped as the go ahead technology for the supply chain. GEN2 is also beginning to erode legacy LF and HF solutions as GEN2 price decreases and capability such as greater read distances increases.

About GAO RFID Inc.

GAO RFID Inc. is a leading provider of Radio Frequency Identification (RFID) hardware and solutions to end users worldwide. GAO RFID combines best of breed with low cost RFID readers, RFID tags and enabling-RFID software. We have a wide variety of RFID readers, tags and antennas in all the RFID technologies, Low Frequency (LF), High Frequency (HF), Ultra High Frequency (UHF, Gen 2) as well as Active and Semi-Passive.  GAO RFID’s products and services are easily customized for use in Asset Tracking,  Health care, Supply Chain & Logistics, Event Management, Access Control, Livestock Tracking, Inventory Control & Management, Field Service, Maintenance and Document Authentication.

For more information please visit http://www.GAORFID.com