Fabric to “listen” to the sound of your heart | MIT News

Is there a problem with listening? Just turn your shirt up. This is the idea behind the new “acoustic fabric” developed by MIT engineers and collaborators at the Rhode Island School of Design.

The team designed a fabric that acts like a microphone, first converting sound into mechanical vibrations and then into electrical signals, much like audible.

All fabrics vibrate in response to audible sounds, but these vibrations are on the nanometer scale and are usually too small to be perceived. To capture these imperceptible signals, researchers have created flexible fibers that, when woven into the cloth, bend with the cloth like seaweed on the surface of the sea.

The fiber is designed with a “piezoelectric” material that produces an electrical signal when bent or mechanically deformed, and the fabric provides a means of converting sound vibrations into an electrical signal.

The fabric can capture sounds in the decibel range, from quiet libraries to busy roads, and determine the exact direction of sudden sounds like clapping. When woven into the lining of the shirt, the fabric can detect the wearer’s subtle heartbeat characteristics. Fibers can also be created to produce sounds, such as spoken language recordings, that can be detected by another fabric.

A study detailing the design of the team is today Nature.. Wei Yan, the lead author who helped develop the fiber as a MIT postdoc, sees many uses for listening fabrics.

“Wearing acoustic wear allows you to answer calls and communicate with others,” says Yang, an assistant professor at Nanyang Technological University in Singapore. “In addition, this fabric can inadvertently come into contact with human skin, allowing the wearer to monitor heart and respiratory status in a comfortable, continuous, real-time, long-term manner.”

Yan’s co-authors include Grace Noel, Gabriel Loke, Tural Khudiyev, Juliette Marion, Juliana Cherston, Atharva Sahasrabudhe, Joao Wilbert, Irmandy Wicaksono, MIT professors John Joannopoulos and Yoel Fink, Anais Missakian and Elizabeth Meik. of Design (RISD), Lei Zhu from Case Western Reserve University, Chu Ma from the University of Wisconsin-Madison, and Reed Hoyt from the US Army Institute for Environmental Medicine.

Sound layer

Fabric is traditionally used to attenuate or reduce sound. Examples include soundproofing in concert halls and carpets in living spaces. However, Fink and his team have worked for years to reconstruct the traditional role of fabrics. They focus on extending the properties of the material to make the fabric more functional. The team was inspired by the human ear when looking for ways to make sound-sensitive fabrics.

The audible sound travels through the air as a slight pressure wave. When these waves reach our ears, the eardrum, a very sensitive and complex three-dimensional organ, the eardrum, uses a circular layer of fibers to convert pressure waves into mechanical vibrations. These vibrations travel through small bones to the inner ear, where the cochlea converts the waves into electrical signals that the brain senses and processes.

Inspired by the human auditory system, the team sought to create soft, durable, comfortable, and sound-detectable fabric “ears.” Their research has led to two important discoveries. Such fabrics need to incorporate hard or “highly elastic” fibers in order to effectively convert sound waves into vibrations. The team then needs to design a fiber that can bend with the fabric and generate electrical output in the process.

With these guidelines in mind, the team has developed a layered block of material called a preform, made from a piezoelectric layer and ingredients to enhance the vibration of the material in response to sound waves. The resulting preform, almost the size of a thick marker, was heated and pulled like a toffee into fine fibers 40 meters long.

Lightweight listening

Researchers tested the sensitivity of the fiber to sound by attaching the fiber to Mylar’s suspended seat. They used a laser to measure the vibration of the sheet and thus the fibers, depending on the sound played from nearby speakers. The sound varied in decibels between a quiet library and a busy road. In response, the fiber vibrated, producing a current proportional to the reproduced sound.

“This shows that the performance of the fibers on the membrane is comparable to that of a handheld microphone,” says Noel.

Next, the team woven fibers with traditional threads to create a panel of drapeable, machine washable fabrics.

“It feels like a jacket that’s lighter than denim, but heavier than a dress shirt, and almost lightweight,” says Make Region, who woven the fabric using a standard loom.

She sewed a panel on the back of the shirt, and the team tested the fabric’s sensitivity to directional sounds by clapping hands while standing at different angles to the shirt.

“The fabric was able to detect sound angles within 1 degree at a distance of 3 meters,” says Noel.

Researchers believe that directional sound-sensing fabrics may help people with deafness tune in to speakers in noisy environments.

The team also sewed a fiber into the lining of the shirt just above the chest area to accurately detect the heartbeat of healthy volunteers, along with subtle changes in the heart’s S1 and S2, or “love dub” functions. I found that I did. In addition to monitoring his heart rate, Fink also considers the possibility of incorporating acoustic fabrics into maternity wear to enable him to monitor the heart rate of his baby’s fetus.

Finally, the researchers reversed the function of the fiber to act as a speaker rather than as a sound detector. They recorded a series of spoken words and sent the recordings to the fiber in the form of applied voltage. The fiber converted the electrical signal into an audible vibration, which the second fiber could detect.

In addition to wearable hearing aids, garments that communicate, and garments that track vital signs, the team is looking at uses other than garments.

“It can be integrated with the spacecraft’s skin to hear (accumulate) space dust, or it can be embedded in buildings to detect cracks and strains,” Yan suggests. “It can even be woven into a smart net to monitor sea fish. Fiber opens up a wide range of opportunities.”

“The learning in this study provides a whole new way for fabrics to listen to our body and the environment around us,” says Fink. “The dedication of students, postdocs and staff to carry out research that has always surprised me is particularly relevant to this research conducted during the pandemic.”

This study was partially supported by the US Army Institute through the National Oceanic and Atmospheric Administration’s Soldier Nanotechnology Institute, SeaGrant NOAA.