Low-Power Processor Enables Disposable Wireless Vital-Signs Monitor

A bandage-sized vital-signs monitor powered by a printed battery

6 February 2008—Hospitals, home patients, the elderly, and even top athletes could benefit from a new disposable wireless electronic patch designed to monitor vital signs, according to researchers at Toumaz Technology. Monday, at the IEEE International Solid State Circuits Conference, in San Francisco, Toumaz engineers described an ultralow-power system-on-chip (SOC) that runs a wireless body-area network capable of sensing temperature, heart rate, respiration, electrocardiogram (ECG) signals, and other vital signs.

There are other wireless vital-signs monitors, says Alison Burdett, director of technology at Toumaz, in Abingdon, England, and a member of the Sensium development team. None of the others, however, fit in an ultrathin patch, are cheap enough to be disposable, and consume as little power as Sensium does. ”We aren’t claiming a new paradigm,” she says. ”But existing systems are generally quite expensive and bulky, and they need reasonable batteries. In that respect, our system is state-of-the-art.”

The Sensium contains a wireless transceiver that consumes just 2.6 milliamperes to transmit and 2.1 mA to receive from a power supply of just under 1 volt. ”A key challenge we faced was to keep peak power consumption as low as possible without sacrificing the integrity and reliability of the data,” Burdett says. One way was to integrate into the chip many systems and functions usually done using power-consuming software. In addition to the transceiver, the chip integrates a digital controller, a temperature sensor, an interface for up to three vital-signs sensors, and signal-processing circuitry. The team also designed a custom communications protocol, which responds quickly to weak signals and assures data reliability.

The transceiver operates in the 862- to 870-megahertz European Short-range Device (SRD) frequency bands and the 902- to 928-MHz North American Industrial, Scientific and Medical (ISM) bands. Up to eight transceivers can connect on a single frequency to a base station located in a hospital ward.

From there, data are forwarded to hospital computer systems. ”We developed software infrastructure up to a certain point, allowing data to be put in a server,” says Burdett. ”We’re working with Oracle, which has implemented a system for electronic medical records.”

The Toumaz chip runs on a printed zinc-based battery manufactured by Israel’s Power Paper. The battery is very cheap, says Burdett, ”and unlike lithium-based batteries, it is environmentally friendly.” The battery has a lifetime of around five days, a period after which electronic patches generally begin to look old, irritate the skin, and need to be replaced anyway, she adds.

The printed battery also contributes to the system’s low cost. But mostly the cost is achieved by integrating all the monitor’s functionality into a single 4 millimeter by 4 mm by 3 mm slice of silicon instead of spreading it over several chips as other manufacturers do, says Burdett. ”It’s really the integration and assembly that add to costs.” In addition to the low-power chip, the vital-signs monitor patch includes two or more noninvasive sensors and, depending on the vital signs to be monitored, can be as small as 25 mm on a side. Once the patch is mass-produced, Burdett expects an initial price of between US $5 and $10, and she expects it will eventually fall below $5.

Toumaz has conducted clinical testing of the vital-signs monitor chip, but the patch ”still needs to go through the safety check,” Burdett says. A commercial launch date has not yet been set.

About the Author

JOHN BLAU writes about technology from Düsseldorf, Germany. For IEEE Spectrum, he detailed the role of technology in securing the soccer World cup in 2006, and more recently he explained German resistance to carbon caps on European cars (June 2007).

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