Ultracapacitor Offers 75-Foot Read Range for Passive Tags

By Mary Catherine O'Connor

Storing energy from a small solar panel enables the passive UHF S/Cap tag to perform like a battery-assisted tag.

Enable IPC, a technology-development startup located in Madison, Wisc., has announced the availability of its new passive ultrahigh-frequency (UHF) RFID tag, known as the S/Cap tag, which it claims can be read from a distance of 75 feet. The tag, designed for asset-tracking applications, performs like a battery-assisted tag, but instead of a battery uses an ultracapacitor to boost the inlay's read distance.

An ultracapactitor is a very powerful capacitor—a device used to store an electric charge, which can be utilized with or without a battery. Ultracapactitors can take and release a charge faster than batteries can, as well as withstand more charges and discharges than batteries can accommodate.

The S/Cap tag

South Korean tag manufacturer RF Camp provides the EPC Gen 2-compliant UHF passive RFID inlay used in the S/Cap. RF Camp has also announced plans to resell and distribute the S/Cap tag in South Korea. EM Microelectronic supplies its EM4324 integrated circuit for the inlay. The ultracapacitor is connected on a circuit board to both the tag's chip—via a bonding pad originally designed to mount a battery to the chip for a battery-assisted passive (BAP) tag—and its antenna.

The S/Cap tag is the first in a line of RFID tags that Enable IPC plans to produce, all using ultracapacitors (also known as supercapacitors) rather than batteries to extend the tag's range.

The ultracapacitor still requires a power source to obtain the energy it stores, the company notes. The S/Cap employs a small solar panel mounted on the tag's face to power the ultracapacitor. This means it works well outdoors, says David Walker, Enable IPC's CEO. However, he says, the solar panel can still generate power from indoor light. Even if the tag is placed in darkness for many days, he adds, it will still remain readable, since it is a passive tag that receives energy from a reader—but the extended range, made possible by the solar power, will be lost.

In the presence of light, Walker explains, the S/Cap tag has a read range of 75 feet. Metallic surfaces or other conductive materials, he notes, can detune the RF antenna and reduce the range, as with an ordinary UHF tag, but the company is currently developing a metal-mount version, designed to overcome this limitation.

The ultracapacitor is used to extend the passive tag's signal strength, and thus increase its range. The S/Cap is designed to compete with BAP tags, rather than with active tags, which are powered by a battery and typically transmit their signal to receivers, rather than utilizing power from the interrogator to backscatter data back to the reader.

Why use an ultracapacitor rather than the thin-film battery often found in BAP tags? One reason, Walker says, is that ultracapacitors offer greater power density, and can take a charge more quickly than batteries can. But their key benefit for RFID tags designed for tracking assets, he says, is a longer life.

An ultracapacitor has up to 1,000 times a battery's cycle life—that is, the number of charges and discharges that a battery can perform before it begins to fail. "The real competitive advantage to the S/Cap is in the lifespan," Walker states. "My understanding is that with BAP tags, [vendors] say they'll last two, three or five years, but in reality, the tags often have a shorter lifespan."

The S/Cap tag, Walker reports, will outlast the RFID chip and other tag components. "The limiting factor for lifespan on the tag is not the ultracapacitor," he says. "It's more like the data retention on the chip, which is probably around 10 years." Enable IPC offers a seven-year limited warranty on the tag.

The S/Cap tag is currently available, and costs between $12 and $15 per tag, depending on volume. According to Walker, Enable IPC has already secured an order for 1.5 million S/Cap tags from a company involved in the RFID industry, though he declines to name that firm.

Moreover, Enable IPC is presently developing energy-storage technologies and products for renewable energy applications. The company is also researching the use of nanotechnology in developing ultracapacitors, through its SolRayo subsidiary.