By Marisa Torrieri, Contributing Editor

You can tag cows, you can tag drugs, and you can tag palates. So long as you have picked a good reader, you’re all set, right? Not true, unless you’ve selected the ideal frequency for your particular application. For developers in the RFID space, differences between UHF, HF, and other “F” variations are clear as day. But for the rest of us, the various manifestations, applications, even the very concept of ‘frequency’ can leave us scratching our head. In RFID schemes, a product’s radio frequency (the portion of the electromagnetic spectrum that electromagnetic waves can be generated within) falls into set band constraints – each with its own limitations and benefits.

As such, misconceptions between the two most common RFID frequencies – UHF (ultra high frequency) and HF (high frequency) are fairly common – and fairly dangerous if you’re shopping around for RFID. Purveyors of goods and servicess could pull a fast one on you in trying to woo you with their wares – convincing you to believe any number of egregious misconceptions about a particular band’s limitations.

Symbol’s Alan Melling, Senior Director of Business Development, gives the example of a high-frequency Gen 2 product manufacturer who uses the argument that ultra-high frequency bands compromise security. Such blanket-statement misnomers could fill RFID newbie users with fear – that the security of the product they’re developing could eventually be compromised. And it is simply not true, stresses Mr. Melling.

“I think it’s important to understand that each band has different characteristics and qualities,” adds Sara Shah, RFID industry analyst at ABI Research. “Each one has its own limitations and capabilities and that’s why there are distinct applications evolving in each frequency band.”

And so, it’s important to know the differences, limitations, and benefits of using RFID’s most common frequencies – as well as what’s being done to circumvent challenges. And as more applications begin to emerge, it’s important to know a little something about the big “F” – and what’s being used for closed-loop applications like tagging cattle, or bigger supply chain operations like tagging highly secure pharmaceuticals.

High Frequency Versus Ultra High Frequency

Before mass-market retailers like Wal-Mart or government agencies issued mandates that companies use RFID products that met specific criteria (such as that set forth by EPCGlobal’s Gen 2 specification), RFID was more a curiosity in the supply chain. When the technology was used, it tended to be in closed-loop applications where a single party controlled all aspects of the deployment (in contrast to Gen 2, a global interoperable standard with wide adoption by hundreds of companies).

With standardization and proliferation, the need to understand the different ‘flavors’ of RF tags and readers was underscored. Here’s how they’re different:

Ultra High Frequency: The Gen2 preference for long range, rapid reads

Ultra High Frequency (UHF), the most commonly utilized frequency for Gen 2 supply chain operations, runs in the 902-928 MHz band in North America, and somewhere between 860-960 MHz internationally. UHF is known for its longer read range (typically cited up to 30 feet rather than the three feet maximum typically defined for HF). Generally, the wider the allowable bandwidth, the more information you can transmit in a shorter period of time.

“Most Gen 2 is UHF because its longer read range and higher data rates make it ideal for retail applications,” says Mr. Melling. “If I have to reach 100 palates as they come through the door, I need to have both the range required to read the tags and the throughput to process that data quickly.”

But there are a few disadvantages to UHF. First, the tagging of objects that contain liquid or metal – two elements that can disrupt radio signals. “Metal reflects it and water absorbs it,” notes Sara Shah, ABI Research. Under normal circumstances, the metal in the object being tagged and the tag’s antenna form what’s called a parasitic capacitor the unintentional presence of which can diminish the tag’s ability to receive power from the reader.

The end result: “it looks dead – it won’t respond to a reader,” notes Clarke McAllister, CEO of ADASA. But companies are coming up with clever ways to combat that problem, Mr. McAllister notes. The manufacturer of a portable tag encoder (i.e. a mobile tag issuing device) recently unveiled its FAT tag (Foam Attached Tag)” for businesses interested in attaching Gen2 RFID tags to metal parts and liquid containers in their supply chains. FAT tags are thicker than standard tags (about an 1/8 of an inch thick), so they can reduce the problems that kill signals in these environments.

Adds Ms. Shah: “Some vendors offer solutions that use Ultra High Frequency bands around metal and water environments but they use various techniques to mitigate these issues, like encase the tag in plastic.”

Some concerns have been raised that the spectrum set aside for UHF RFID differs slightly across the globe – 902-928 MHz in North America and 865-868 MHz in Europe, for example. As Symbol’s Melling points out however, this is not a concern if tags are built correctly. Readers may be slightly different, but it is relatively easy to build one tag that works well globally. Even if your product travels through China or Japan, into Europe, and then back to the states, the same tag responds to all the frequency bands. “You’re not moving readers from country to country, you’re moving tags,” Mr. Melling says.

High frequency: Short range, secure, and resistant to metals and liquids

High-frequency (HF) RFID resides within the 13.56 MHz band in North America, and around the globe. As a frequency, it’s older and more established than UHF, but has a shorter wavelength, which means it can generally only be read within a couple of feet (or as little as 10 cm according to key international standards). Because of this, it’s the frequency most associated with today’s RFID-based payment and access control applications like contactless smart cards or event tickets. HF’s most notable advantages are that it works better around metals and liquids than UHF, and that it is well-established internationally.

“The real strength is there’s been a global standard for high frequency tags for a long time, you can pretty much use high frequency bands anywhere in the world no problem,” Mr. Melling says. “But the read range is a limited.” In addition to read range, another limitation is its speed: HF operates much slower than UHF, which is why most mass-market retailers and suppliers use UHF tags and accompanying products. But just as with UHF, there are ways to circumvent the ‘read range’ issue, says Mr. McAllister. “Companies like Impinj have demonstrated that UHF antenna structures can be made to fit onto small bottle caps and such. “There are many examples of how both HF and UHF are breaking barriers in size and speed.”

While HF might not be suitable for moving large containers across a supply chain, it is the frequency of choice for one of the biggest, burgeoning RFID small-scale supply chain operations: pharmaceutical tracking and tracing.

“If you take a look at the use of RFID in pharmaceutical applications, you’re talking about putting very small tags on very small items – the primary focus being track and trace that will enable an electronic pedigree,” says Matt Ream, senior manager of RFID Systems at Zebra Technologies, a printing solutions provider that manufactures HF and UHF RFID labels, among other things. “One of the biggest concerns about UHF technology is that UHF technology has not been approved for use on biological agents.”

In other words, UHF technology could potentially raise the temperature of live biological drugs such as vaccines, and render them ineffective.

Right now Zebra and partner Magellan Technology, developer, manufacturer and licensor of advanced read and write 13.56 MHz RFID systems, are working on a product that makes automated pharmaceutical processes faster and more secure – debunking two myths about slow speeds associated with HF, says Mr. Ream.

As RFID begins to be incorporated into pharmaceutical supply chain operations, a major concern of pharmaceutical manufacturers is slowing down line speeds.

The HF technology Zebra is working on with Magellan can program and verify 45 tags per second, more than six times faster than existing HF and UHF products, Mr. Ream says. The technology runs on ISO 18000-3 Mode 2 technology, yields high read rates, and uses a different modulation technique from other HF technology (called Phase Jitter Modulation or PJM).

“It really communicates differently from frequency modulation and amplitude modulation,” says Mr. Ream. “PJM communicates data by shifting the signal’s phase versus the frequency or the amplitude found in most other RFID systems, allowing you to speed up your primary communication speed.” Additionally, the tag has the ability to return the signal on any one of eight return channels: One output channel from the reader and eight simultaneous return channels, increasing the number of tags you can read by a factor of eight.

Low Frequency: ‘making hay’ with animals and closed loop applications

Low Frequency (LF), the third most commonly used RFID frequency in North America, isn’t a direct competitor in the arena of applications that require any sort of range, but is highly useful for closed-loop applications. Running at frequencies in the bands from 125 kHz to 134.2 kHz, some of the most common LF RFID applications are livestock tagging, Exxon Mobile’s Speedpass, and certain access control applications. Because of its shorter wavelengths, it is better able penetrate objects like glass windows. “(A major application) is the use of Low Frequency tag in automobile ignition systems,” notes Mr. McAllister. In most modern cars, a tiny LF tag is built into the ignition key – a reader in the steering column authenticates the key and allows the car to start.

Looking to the future …

So, will UHF become the dominant standard for all supply chain applications? Will more sophisticated additions continue to help solve the metal-water challenges presented by UHF? What applications will we see more of in the future?

“That’s a huge question,” says Mr. McAllister. “Everyone’s watching with interest what the market’s gonna do – because there’s a number of innovations going on. I perceive a big huge play for either HF or UHF is in item level tagging. The question remains, which one will the market choose to adopt for large scale item-level tagging for pharmaceuticals and retail?”