CAMBRIDGE, Mass. — Fabric that can “hear” one’s heartbeat via high-tech fibers has been developed by scientists at the Massachusetts Institute of Technology. The tech could also be used on clothes worn by pregnant women to help them pick up their baby’s heartbeat.
This potentially revolutionary tech could give rise to wearable hearing aids and clothes that can speak to each other. It works by first converting sounds into mechanical vibrations before they are converted again into electrical signals, similar to how the ear works. All fabrics vibrate in response to sounds, although these responses are normally far too small to be audible.
Researchers stitched a single fiber to a shirt’s inner lining, just over the chest region, and found it accurately detected the heartbeat of a healthy volunteer, along with subtle variations in the heart’s “lub-dub” features. They say the possibilities for the new technology are endless.
“It can be integrated with spacecraft skin to listen to accumulating space dust, or embedded into buildings to detect cracks or strains,” says lead author Dr. Wei Yan, who helped develop the fiber as an MIT postdoc, in a statement. “It can even be woven into a smart net to monitor fish in the ocean. The fiber is opening widespread opportunities. Wearing an acoustic garment, you might talk through it to answer phone calls and communicate with others.
“In addition, this fabric can imperceptibly interface with the human skin, enabling wearers to monitor their heart and respiratory condition in a comfortable, continuous, real-time, and long-term manner,” adds Dr. Yan, who is now an assistant professor at the Nanyang Technological University in Singapore.
The researchers say the fabric allows wearers to monitor their heart and breathing in a comfortable way over long periods and could also be used to answer phone calls and communicate.
How do these fibers ‘hear’ sound?
For the study, the team created a flexible fiber that bends when it is woven into fabric. The fabric is made of material that produces an electrical signal when it bends or becomes strained, giving it a way of converting sound vibrations into electrical signals. It can capture a whole range of sounds and can determine the direction noise from sudden sounds such as handclaps are traveling in.
When woven into a shirt’s lining it can detect the subtle features of a wearer’s heartbeat. The fibers can also be made to create sounds, such as recordings of spoken words, that can be picked up by another fabric.
In their quest to make sound-sensing fabrics they looked to the human ear for inspiration. Audible sound travels through air as slight pressure waves. When these waves reach our ear, which is an extremely sensitive and complex three-dimensional organ, our eardrum uses a circular layer of fibers to translate the pressure waves into mechanical vibrations. These vibrations travel through small bones into the inner ear, where our cochlear converts the waves into electrical signals that are sensed and processed by our brain.
As the team did their research they made two important discoveries: that any fabric would need stiff fibers to effectively convert sound waves into vibrations; and that they would need to design a fiber that could bend with the fabric and make electricity in the process.
With this in mind, the team developed a layered block of materials called a preform, made from a piezoelectric layer as well as ingredients to enhance the material’s vibrations in response to sound waves. The resulting preform, about the size of a thick marker, was then heated and pulled into thin, 40-metre long fibers.
They then wove the fiber to a fabric that was lighter than a denim jacket, but thicker than a dress shirt. The team tested the fabric’s sensitivity to directional sound by clapping their hands while standing near the shirt at different angles. The fabric was able to detect the angle of the sound to within one degree at a distance of three meters away.
Researchers envision that a directional sound-sensing fabric could help those with hearing loss to tune in to a speaker amid noisy surroundings.
Finally, the team used the device as a speaker, recording a string of words before feeding the recording to the fibre. The fiber converted the electrical signals to audible vibrations, which a second fibre was able to detect.
“This research offers quite literally a new way for fabrics to listen to our body and to the surrounding environment,” says co-author Yoel Fink. “The dedication of our students, postdocs and staff to advancing research which has always marveled me is especially relevant to this work, which was carried out during the pandemic.”
South West News Service writer Gwyn Wright contributed to this report.