RFID Vendors Unite to Promote UHF for Items

Their finding: magnetic coupling, the mechanism HF tags use to transfer energy between the RFID readers and RFID tags. Magnetic coupling works much better for close-range reads, Gokhale says, and is immune to RF interference caused by liquids. UHF tags, he notes, typically operate using electromagnetic coupling, which is better suited to long-range reads.

However, Gokhale adds, if UHF tags and reader antennas are designed to use magnetic coupling, they should be able to match HF performance in terms of short-range reads and immunity to RF interference caused by liquids. "Using existing Gen 2 chips and readers, but designing new antennas for both, Impinj has demonstrated that UHF operating in the near-field can perform as well—and, in most cases, better than HF solutions," he affirms.

Impinj's Vinay Gokhale

"That fundamental issue of using magnetic coupling for UHF tags had not been analyzed," he adds. "When you use magnetic coupling (or near-field communications), you can overcome the commonly held myths people believe about using UHF in item-level tagging."

Using UHF in the near field doesn't affect a tag's or reader's ability to comply with EPCglobal's Gen 2 UHF RFID standard, either. "This is the same Gen 2 protocol that EPCglobal ratified back in December 2004," Gokhale explains. "The only differences are new near-field would be new tag antennas and new reader antennas, which are some of the lowest-cost elements that you can change. But the air protocol is the same."

Now that UHF tags can be designed to operate well for item-level tagging, the group argues, UHF tags are the optimal choice for any RFID implementation, case- and pallet- or item-level. The vendors—and other UHF proponents such as Wal-Mart—argue that by sticking with the same technology, companies won't have to support two different frequencies requiring separate infrastructures. Instead, companies can implement a single platform for numerous RFID applications, resulting in what the group says are significant efficiencies in cost and inventory visibility from the point of manufacture to the point of sale.

"At a very high level, what I try to convey is that technology is merely a tool to achieve an objective—and with RFID, that objective is visibility and the need to be able to identify a product," says Symbol's White. "And it is always beneficial to select the technology that can be applied more broadly across an organization. UHF allows the customer to use one technology to do item-, case- and pallet-level traceability."

If UHF tags can be made to use with magnetic coupling to operate in the near field, that does beg the question: Can HF tags be made to use electromagnetic coupling in the far field? The answer, according to Gokhale, is no. That’s because lower frequencies generate weaker electromagnetic fields than higher frequencies do. HF tags operate at 13.56 MHz, while UHF operates in the 900 MHz range. "That is a 70-times multiple in frequency between the two—and why UHF can work with far-field antennas [antennas that have greater read ranges], and HF can't."