RFID Basics

By Jack Shandle

February 26, 2007

A basic Radio Frequency Identification (RFID) system consists of: an antenna; a transceiver with a decoder; and a transponder (also known as an RFID tag). Without software to utilize the information derived from reading the tags, however, the system would have little practical value. So it is wise to include middleware as a component.

A transponder, or tag, is electronically programmed with unique information sometimes as little as an identification number so the item it is attached to can be located and tracked. Some RFID tags are much more sophisticated. Electronic passports based on RFID technology, for example, can include biometric data about the passport holder and encryption capability as well.

When an antenna is packaged with a transceiver and decoder, it becomes an RFID reader. Depending on their output power and RF frequency, readers have ranges of from an inch to 100 feet or more. When an RFID tag passes through the reader's active zone, it detects the reader's activation signal. The reader decodes the data encoded in the tag's RFID chip and the data is sent over the wired communication infrastructure to corporate, institutional, of governmental databases where it is included in databases.

In the basic system, the antenna emits RF signals to activate the tag and read and write data to it.

Antennas are available in a variety of shapes and sizes depending on the application. They can be attached to any number of retail items such as clothing, inserted under the skin of livestock, or mounted on toll booths to monitor traffic passing by on a freeway.

When a steady stream of tags is expected in the application, the electromagnetic field produced by an antenna can be on all the time. But if constant interrogation is not required, the field can be activated by a sensor.

Tags vary in their technological sophistication and capabilities. Regardless of the type of tag, however, since there are always far more tags than readers in a system cost is a controlling factor. In many systems, the tags are discarded or destroyed.

Software consists of the embedded systems software that runs the hardware and middleware, which connects the local RFID system to corporate, governmental or institutional databases. In almost all RFID applications, middleware is by far the single most expensive part of the system.

Figure 1: RFID system components.

Passive RFID Tags

Passive RFID tags do not have internal power supply. Instead, they are powered by energy induced in the antenna by the RF signal. Most passive tags transmit by backscattering the carrier signal from the reader. The engineering challenge is to design an antenna that can collect power from the incoming signal and transmit it to the outbound backscatter signal. The response of a passive RFID tag is not necessarily just an ID number; the tag chip can contain non-volatile EEPROM for storing data.

Hitachi, Ltd. presently holds the record for the smallest passive tag. Its mu-Chip measuring 0.15x0.15mm (not including the antenna) is thinner than a sheet of paper. (7.5 micrometers). It transmits a unique 128-bit ID number hard coded into the chip as part of the manufacturing process and has a read range of 30 cm.

The lowest cost RFID tags cost about 5 cents each. Adding an antenna creates a tag that varies from the size of a postage stamp to the size of a post card. Passive tags have practical read distances ranging from about 10 cm to a few meters. Their simple design means that a printing process can be used to manufacture passive tags.

Active RFID tagsActive have an internal power source, which makes them more reliable and provides a wider range of operation. Their higher reliability is derived from the tag's ability to conduct a session with a reader during which transmission errors can be detected and corrected.

Many active tags have practical ranges of hundreds of meters, and a battery life of up to 10 years. Active tags can have a range of up to 300 feet and they typically have larger memories than passive tags, as well as the ability to store additional information sent by the transceiver. Presently, the smallest active tags are about the size of a coin and sell for a few dollars.

Due to the wide range of applications RFID continues to develop based on new standards and improvements in the technology and design. A few of these challenges include HF gen 2 standards, Near Field UHF technology, as well as mature and off-the-shelf hardware and sensor technology.

RFID Frequencies

RFID operate over several frequency ranges.,br>

• Low-frequency (LF): 125 to 134.2 kHz and 140 to 148.5 kHz. Typical applications include immobilization systems in automobiles, retail, and animal identification and it's tracking through the human food chain.
• High-frequency (HF): 13.56 MHz. Typical applications include tagging of rental items like books or uniforms, public transportation ticketing pharmaceuticals and other item tagging.
• Ultra-high-frequency (UHF): 860 MHz to 960 MHz. Typical applications include fixed asset tracking, baggage handling, and supply chain applications.

Standards

Although organizations such as EPC Global and AIM/ are involved in standardizing physical and system attributes, there is no global public body that governs the frequencies used for RFID on a world wide basis.

As a result, countries and regions have chosen independently which frequency bands are reserved for the use of RFID. LF and HF RFID tags can be used globally, with power levels harmonized on a global basis simplifying the desing of labels and readers.

For UHF frequencies, however, the situation is a bit more challenging. The heavily used frequency range of 860 MHz to 960 MHz was chosen for UHF RFID and this is creating challenges for the unified solutions. It will be no easy task to get the approval for the usage of RFID at UHF in all countries. But without a global standard, UHF companies that operate on a global scale will struggle to implement it cost effectively.

Multiple Frequencies, Varied Applications

LF and HF frequencies have been heavily utilized for RFID rollouts utilizing passive systems. Standardized LF and HF technologies have been available since 1995, while UHF has been available since 2001.

LF systems have an advantage in applications that have harsh operating conditions. High immunity to electrical noise and encryption technology are two decided advantages. A range of 1.5 metres can be reached. LF is also suitable applications involving liquids, organic materials and metals because it does not scatter when it meets these surfaces.

LF is already the major technology in: animal identification, access control, asset management solutions for gas cylinder, beer kegs and other high valued products. LF's range, performance and cost are being improved with new IC designs and more mature readers in the market.

An HF system is considered appropriate in applications where items are tagged and read/ write ranges of up to 1.5 metres are required. Encryption algorithms allow for protected data on the IC and EAS features in the tag, make anti theft prevention possible.

Typical applications today include tagging of library books, CDs and DVDs, pharmaceutical products for counterfeit prevention and many applications which require a very precise read and write environment.

New encryption algorithms are being used in HF to make the technology even more secure for short ranges. Faster protocols are being introduced to improve the reading and anti-collision speed. Additionally, new regulations are being worked on to allow for more power to be used to increase the read and write distance of the HF solutions.

UHF RFID

UHF is typically used for applications where of several meters are required. These include pallet and case identification in warehouses, as well as car authentication in a factory for production control purposes.

In the UHF space, only Far Field UHF technology has been available until recently, making identification of fluids and other organic material virtually impossible. Today the industry is working on Near-Field UHF (NF UHF) to get around these problems. With NF UHF, read distances of approximately 30 cm can be achieved, allowing for some item level tagging.

Figure 1 provides an overview of the performance of LF, HF, and UHF systems across several key areas. Tag construction will be discussed in the next few paragraphs.

Figure 2: Metals, field characteristics and tag construction are challenging for NF UHF.

Whereas HF and LF tags tend to have typical coil configurations that allow generic label designs, UHF tags come in many different configurations as they need to be optimized to the material the labels to which they are attached. This is largely due to the fact that UHF signals interact with tagged articles or adjacent materials more than HF or LF.

FF UHF is well characterized but work continues on optimizing hardware and software to solve application specific requirements. These include improving read rates, optimizing reader fields and working on the harmonization of regulations to allow UHF to be used on a world wide basis.

In 2006, work began on NF UHF has to analyze how it can be used to achieve item-level tagging.

Ongoing Research

With so much improvement in all three frequency ranges, it was becoming more difficult to choose the best frequency range for a specific application, particularly in choosing between HF and UHF.

Early in 2006, Deutsche Post World Net launched an initiative to evaluate industry usage of RFID across several industries including fashion, pharmaceutical and electronics. Other members of the DHL Innovation Initiative included IBM, Intel, Philips Semiconductors (now NXP Semiconductors) and SAP.

By including both HF and UHF systems in its testing and evaluations, the Initiative's goal was to determine optimum RFID solution for various applications within target industries.

Key factors being considered were the readability and writability of RFID tags under differing environmental conditions, when applied to the many materials found in a typical logistic environment.

Safety and Privacy

Two important considerations for deployment of RFID systems are privacy and safety.

Privacy issues largely revolve around the range in which the RF signal can be read or written as well as the use of security enhancing technologies like password protection and cryptology and destroy commend where required.

Cryptology technologies are well proven and deployed at large for HF, some LF solutions but not yet in UHF solutions.

Since the power of HF RFID signals drops off rapidly from the interrogator antenna, it has an inherent advantage over the far-field operation of typical UHF RFID chips. UHF fields can, however, be contained by using near field coupling between the interrogator antenna and the tagýthe technique used in the aforementioned NF UHF.

Health issues are still a matter of active study by regulatory agencies around the world. Allowable exposure is expressed in terms of power density. For a specific system with a known transmit power and frequency, this means that a minimum exposure distance can be calculated.

Regulatory bodies also make a distinction between allowable occupational exposure and allowable radiation exposure for the general public. Since the general public is not subject to more or less continuous exposure, the minimum distance is greater than for occupational exposure. Since NF UFH is a relatively new technology in terms of its use in RFID applications, it is not clear as of this time how the health issues will be sorted out.

Conclusion

Although the industry has, in the past, used LF or HF for item-level tagging and UHF for pallet and case-level tagging, NF UHF makes it possible to use NF UHF for item-level tagging. .

Initiatives to find the most cost effective technology for different applications are well underway. While technical efficiency is important, the studies also look at privacy, health, and security concerns that are often written into regulations.

There are also initiatives to harmonize a second-generation standard for HF, similar to the UHF Gen 2 standard already agreed to by EPCGlobal and ISO.

But it remains clear that there is no one-size-fits all solution for RFID. In countries where both HF and UHF frequencies can be utilized, issues such as tag performance repeatability, privacy, reliability, scalability and cost may tip the balance toward one frequency choice or the other. By making both available, system integrators have the option of determining the most appropriate solution and deploying it.

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Jack Shandle is the site editor of WirelessNetDesignline. He holds BS in Electrical Enginering from the University of Pennsylvania and a MS in Communications from Temple University. Presently a freelance writer and editor, he formerly held management positions at several major electronics publications and can be reached at jshandle@earthlink.net. Copyright 2005 ý CMP Media LLC