A new electronic tattoo picks up on subtle noises inside the human body, including the sound of your heart, muscles and gastrointestinal tract.
The skin patch could be used in medical monitoring, to detect irregular heartbeats, for example. It could also act as a human-machine interface to use your voice to control video games.
“Our body generates a lot of different sounds,” says Howard Liu at the University of Illinois at Urbana-Champaign. “By designing sensors with a lightweight and thin construction, we are able to capture sounds or vibration signals from our skin.”
The device consists of sensors encased in a flexible silicone shell and flanked on either side by electrodes. It sticks to the skin like a plaster or temporary tattoo and measures just 20 millimetres across. You can stick it on almost any part of the body and it will pick up sounds and vibrations from 0.5 to 550 Hertz – everything from a heartbeat to speech.
The team thinks the patch could be useful for monitoring a broad range of medically significant sounds. In one demonstration, they asked eight people at Camp Lowell Cardiology clinic in Tucson, Arizona, to wear it on their chest. The device detected the patients’ heart murmurs and could tell what type they were, an echocardiogram confirmed.
The researchers think the patch could keep tabs on biological implants, alerting doctors to potential medical issues or mechanical failures. As an experiment they introduced blood clots into a heart pump called a left ventricular assistive device, or LVAD. The blood clots changed the sound made by the LVAD, an anomaly the technology should be able to pick up.
Liu says the patch could also enable people to communicate with drones or prosthetics by voice command.
In one experiment, the team placed the device on people’s throats and set them up with a voice-controlled game of Pac-Man. The sensors listened to the vibrations of the players’ vocal cords, as they said “up”, “down”, “left” or “right” to move the Pac-Man avatar in real time (see video).
As the patch uses vibrations, it can pick out what people are saying even if the sound of their voice is drowned out by background noise, which offers an advantage over other voice control systems.
An algorithm learned to recognise these four basic commands, which the patch was able to capture in quiet and noisy conditions.
“What you’re capturing is the vibration directly from your throat,” says Liu. “If you capture signals of this kind directly, you’re basically immune from all these surrounding noises.”
“This type of signal – these low-frequency signals that one can get from muscle activities, from the heart, all of that – basically opens a new dimension of information, extra to the one that is typically recorded,” says Reza Bahmanyar at Imperial College London in the UK.
He says the miniaturisation of electronics and the development of biocompatible materials have made such devices possible.
“The way this collection of known technologies is used to produce something that is actually comfortable and usable by a patient – that is what I would call the added value here,” he says.