Soft Acoustic Sensors Could Monitor Hearts, Recognize Speech

A tiny, wearable acoustic sensor developed by researchers can be used to monitor heart health and recognize spoken words.
Northwestern University/University of Colorado Boulder
A tiny, wearable acoustic sensor developed by researchers can be used to monitor heart health and recognize spoken words.

A soft acoustic sensor that someone can wear like a sticker on their skin can monitor their heartbeat and recognize spoken words, researchers say. Potential applications for the device include diagnosing medical conditions, and letting humans steer robots and play computer games without a handheld device, scientists add.

Previous sensors that could detect acoustic vibrations through the skin "were basically stethoscopes," says study lead author Howard Yu Hao Liu, a materials scientist at the University of Illinois at Urbana-Champaign. They tended to be large and made of rigid materials, which made them difficult to wear and stifled acoustic signals.

In contrast, the new device uses miniaturized, low-power commercial MEMS accelerometers encased in sticky, elastic silicone rubber. The researchers say these accelerometers are tuned to vibration frequencies—ranging from 0.5 to 550 hertz—that are typical of sounds emitted by the body’s vital organs. Stretchable copper wires help connect these accelerometers with amplifiers, resistors, and capacitors.

The scientists detailed their findings online in the 16 November edition of the journal Science Advances.

The new device, which resembles a small Band-Aid, is only 20 millimeters thick, weighs just 213.6 milligrams, and is flexible and stretchable enough to wear on curvy parts of the body such as the neck, the researchers say. The silicone rubber allows for evaporation of human sweat, they add.

In experiments, the device could continuously gather data on several different kinds of acoustic signals at the same time—among them, the opening and closing of heart valves, blood pulsing through the carotid artery in the neck, vibrations of the vocal cords, and even movements in the gastrointestinal tract.

In tests of elderly volunteers at Camp Lowell Cardiology, a private medical clinic in Tucson, Arizona, the device showed that it could detect heart murmurs. Experiments with a commercial ventricular assist device, which helps a heart pump blood, also revealed that the sensors could detect potentially lethal blood clots.

"When put on the human throat, it can be used to control robots or play video games, to serve as a human-machine interface to send commands to a computer," Liu says. For instance, a volunteer was able to control a Pac-Man game by saying "up," "down," "left," and "right." The word recognition accuracy was 90 percent. The sensor could also help people with speech disorders, soldiers in battlefields, and first responders in disaster sites, among others, the researchers say.

The new device also includes electrodes that can record electrical signals from the body. These electrodes can help the sensor monitor how the heart and pacemakers are performing, says study co-senior author Jae-Woong Jeong, an electrical engineer at the University of Colorado at Boulder.

While the sensor currently relies on wires to transmit data, "to make it more practical for use in the real world, we want to make it fully wireless," Jeong says. Future research can also increase the range of vibration frequencies the device can pick up to 2,000 hertz, enabling it to detect the full range of human speech vibrations and act as a microphone, Jeong says.

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