Single-chip sensor
A student at the University of California, San Diego, has developed a single-semiconductor IC that can record biopotentials—tiny voltage signals that inhabit the human skin’s surface—to be used for heart monitoring via a wireless sensor network. The project came about as part of PhD candidate Mike Chi’s effort to simplify biomedical wireless sensor technology and make it more commercially viable. The biopotentials are recorded without any contact with the skin—through clothing, in fact—as data is transmitted wirelessly to remote computers.
“One of the goals of this wireless sensor project is to take the sensing technology out of the typical hospital setting and into the home environment, without constraining the mobility of the patient,” explains professor Gert Cauwenberghs of the bioengineering department at UCSD, under whose guidance Chi is working. “Also, our approach would allow the monitoring of brain activity during exercise, or the monitoring of the health of soldiers in the battlefield, so it can be transformative in that sense.”
Various wireless sensor prototypes for recording biopotentials have been used since the 1960s, but according to Chi, “no one has gotten them past the lab prototype stage. You don’t see them out in the marketplace.” Chi’s efforts have earned him the University’s coveted $80,000 Entrepreneur Challenge prize, which includes $25,000 cash for a commercial startup and $15,000 for legal services. The chip is being readied for commercialization by Cogionics, a company in early stages of development that Chi and colleagues plan to launch after he completes his PhD studies.
Chi cited several problems with cost and reliability, as well as the difficulty of recording clinically relevant electrical signals, as challenges faced by other wireless biomedical sensors, particularly because wireless sensors are more complex than wired versions. “We managed to reduce the circuitry for the sensor into a single IC that makes it more reliable and cheaper to manufacture than other types of sensors,” Chi explains (see the figure). “We have two lab prototypes that are working.”
“The key to developing this chip was our ability to boost the chip’s input impedance to a high enough level to allow it to sense signals from 10 s of µV to about 1 mV,” he adds. “We needed to reduce input capacitance levels to the femtofarad levels, down from the picofarad levels found in conventional input instrumentation amplifiers.” Commercial versions of the chip, which operates from a small battery and senses changes in capacitance, are expected to dissipate about 10 to 20 µW.
The Cogionics team includes Yuchen Cao, a chemistry PhD student; Mehmet Parlak, an electrical and computer engineering PhD student; Ping Wang, a PhD student at the Salk Institute; and Stephen Chen, a PhD student at the Scripps Research Institute.