R&D Firm Developing Passive Ultra-Wideband RFID

By Dave Friedlos

April 8, 2008—Martec, a research and development firm based in Las Vegas, says it is developing an RFID system that uses ultra-wideband (UWB), that employs passive or semi-active tags instead of the active tags traditionally used in UWB systems. The company is currently testing the technology, called Passpulse, at its Australia-based research lab, and plans to commercially release the system next year.

A passive tag has no internal battery and instead is powered entirely by incoming radio frequency signals from an interrogator. A semi-active tag, also known as a battery-assisted passive (BAP) tag, contains a battery to operate its microchip, but still depends on the reader's incoming radio frequency signals to power its outgoing signal.

Martec's head of research, Artem Muchkaev, says that by eliminating the need for a battery and instead drawing all their energy from an interrogator's signal, Passpulse passive tags will cost less than active tags. The Passpulse design also allows for charging of the battery in the semi-active tag through pulses from the interrogator, thereby prolonging battery life. Consequently, the battery can be cheaper because it is of a smaller capacity and its lifetime is extended through recharging.

The Passpulse semi-active tag will be more expensive than the passive version, Muchkaev says, depending on read range, storage type and quantity, but will still be cheaper than active tags. "Most UWB systems in the market today use active tags that cost anything from $20 to $100," he states. "Our goal is to bring the cost of Passpulse [passive] tags down initially to just $2, and eventually, maybe even $1."

According to Muchkaev, UWB technology offers several advantages over traditional RFID systems. For one thing, UWB operates by emitting a series of short encoded pulses across a band of frequencies simultaneously, reducing the potential for interference caused by the reflection of RF frequencies between tags and readers. The signal's large bandwidth, he notes, makes it harder to eavesdrop on UWB transmissions.

All UWB systems utilize what's known as pulse position modulation (PPM) to transmit data, Muchkaev says. "As the pulses are short, they can have larger amplitudes, which charges the capacitor in the tag faster to increase the tag's power supply efficiency that allows longer reading range," he explains.

UWB transmissions have greater range than traditional radio frequency communications, Muchkaev says, and are less prone to inaccurate read results. Semi-active tags will provide even more accurate read rates, he says, because the battery feeding the circuits allows for shorter pulses.