Soft Acoustic Skin Sensor Detects Vibrations from Speech and Heartbeats

Soft Acoustic Skin Sensor Detects Vibrations from Speech and Heartbeats

In 1812, René Laennec invented an acoustic sensor capable of detecting the heart rate of patients. The stethoscope has seen considerable modification over the years, and while modern sensors have been created that perform the same function, they are still made of relatively rigid materials which makes them difficult to wear.

Howard Yu Hao Liu and his team at the University of Illinois at Urbana-Champaign have taken the device a step further and have developed a soft acoustic sensor that can be used to detect the heart rate, as well as pick up other acoustic signals including the voice of the wearer. In contrast to other devices, the tech has been incorporated into a soft, flexible patch that can be worn comfortably on the skin.

The skin patch is just 20 mm thick and smaller than a penny, weighing in at just 213.6 milligrams. The acoustic patch is sufficiently flexible to be worn on virtually any part of the body. The device has been constructed on adhesive silicon rubber, which is permeable to allow sweat to evaporate. The device can be worn comfortably and has been designed for long-lived integration on the skin.

The device incorporates MEMS accelerometers which are tuned to pick up specific vibration frequencies. These allow different acoustic signals to be monitored simultaneously. The MEMS accelerometers are connected to amplifiers and other electrical components using thin copper wires. At present the device does not incorporate any wireless transmitters. Signals detected by the device have to be sent via wires to a companion device, although the researchers believe they can develop a fully wireless version.

In contrast to a standard stethoscope, the device is capable of monitoring multiple acoustic signals at the same time, including vocal cord vibrations, movements in the gastrointestinal tract, blood movement through the carotid artery, and the opening and closing of heart valves. The researchers conducted tests on volunteers at the Camp Lowell Cardiology private medical clinic in Tucson, Arizona, and were able to use the device to detect heart murmurs in patients.

The acoustic sensor has a myriad of applications including monitoring a wide range of medical conditions and analyzing the performance of implanted medical devices such as pacemakers. The team conducted one test with a ventricular assist device and showed that the sensor could be used to detect life-threatening blood clots.

There are also many non-medical applications. Since the sensor can pick up vocal signals – up to 2,000 Hz – it could be used as a microphone to control all manner of electrical devices. The latter was demonstrated by using voice commands to play a game of Pac Man.

A paper explaining the function of the device and its applications – Epidermal mechano-acoustic sensing electronics for cardiovascular diagnostics and human-machine interfaces – has recently been published in the journal Science Advances.

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