Researchers design sound-canceling silk to reduce noise transmission in a large room

We live in a very noisy world. From the hum of traffic outside the window to the next-door neighbor’s TV and the sounds of a co-worker’s cubicle, unwanted noise is still a resounding problem.

In order to overcome the din, an interdisciplinary collaboration of researchers at MIT and elsewhere developed a sound-canceling silk fabric that could be used to create quiet spaces. An open access paper on the research appears Advanced materials.

The tissue, which is barely thicker than a human hair, contains a special fiber that vibrates when tension is applied. The researchers harnessed these vibrations to suppress sound in two different ways.

In one, the vibrating tissue generates sound waves that interfere with unwanted noise to cancel it out, like noise-canceling headphones, which work well in a small space like the ears, but don’t work in large enclosures like rooms or airplanes.

In the other, more surprising technique, the fabric is held still to suppress the vibrations that are key to sound transmission. This prevents noise from being transmitted through the fabric and mutes the volume further. This second approach makes it possible to reduce noise in much larger spaces such as rooms or cars.

By using common materials such as silk, cloth, and muslin, the researchers created noise-canceling fabrics that would be practical to implement in real-world spaces. For example, this fabric could be used to make dividers in open workspaces or thin fabric walls that prevent sound from passing through.

“Noise is much easier to create than silence. In fact, to avoid noise, we dedicate a lot of space to thick walls. [First author] Grace’s work provides a new mechanism for creating quiet spaces with a thin sheet of fabric,” says Yoel Fink, professor in the Departments of Materials Science and Engineering and Electrical and Computer Engineering, principal investigator of the Electronics Research Laboratory, and author main. of a paper on the canvas.

The lead author of the study is Grace (Noel) Yang. Co-authors include MIT graduate students Taigyu Joo, Hyunhee Lee, Henry Cheung, and Yongyi Zhao and others.

Silky silence

The sound-canceling silk builds on the group’s previous work creating fabric microphones.

In this research, they sewed a single strand of piezoelectric fiber into the fabric. Piezoelectric materials produce an electrical signal when squeezed or bent. When a nearby noise causes the fabric to vibrate, the piezoelectric fiber converts these vibrations into an electrical signal, which can capture the sound.

In the new work, the researchers turned that idea on its head to create a fabric speaker that can be used to cancel sound waves.

“Although we can use fabrics to create sound, there is already so much noise in our world. We thought creating silence could be even more valuable,” says Yang.

Applying an electrical signal to the piezoelectric fiber causes it to vibrate, which generates sound. The researchers demonstrated this by playing Bach’s “Air” with a 130-micrometer sheet of silk mounted on a circular frame.

To enable direct sound suppression, the researchers use a silk cloth speaker to emit sound waves that destructively interfere with unwanted sound waves. They control the vibrations of the piezoelectric fiber so that the sound waves emitted by the tissue are opposed to the unwanted sound waves impinging on the tissue, which can cancel the noise.

However, this technique is only effective in a small area. So the researchers built on this idea to develop a technique that uses fabric vibrations to suppress sound in much larger areas, such as a bedroom.

Let’s say your next door neighbors are playing foosball in the middle of the night. You hear noise in your bedroom because the sound from his apartment vibrates the shared wall, which forms sound waves next to you.

To suppress this sound, the researchers could place the silk fabric on your side of the shared wall, controlling the vibrations of the fiber to force the fabric to stay still. This vibration-mediated suppression prevents sound from being transmitted through the tissue.

“If we can control these vibrations and prevent them from occurring, we can also stop the noise being generated,” says Yang.

A mirror for sound

Surprisingly, the researchers found that holding the fabric still causes sound to reflect off the fabric, resulting in a thin piece of silk that reflects sound like a mirror does with light.

His experiments also revealed that both the mechanical properties of a tissue and the size of its pores affect the efficiency of sound generation. Although silk and muslin have similar mechanical properties, silk’s smaller pore sizes make it a better fabric speaker.

But the effective pore size also depends on the frequency of the sound waves. If the frequency is low enough, even a fabric with relatively large pores could work effectively, Yang says.

When they tested the silk fabric in direct suppression mode, the researchers found that it could significantly reduce the volume of sounds by up to 65 decibels (about as loud as enthusiastic human conversation). In vibration-mediated suppression mode, the fabric could reduce sound transmission by up to 75 percent.

These results were only possible thanks to a robust group of collaborators, says Fink. Graduate students from the Rhode Island School of Design helped the researchers understand the details of fabric construction; scientists at the University of Wisconsin in Madison performed simulations; Case Western Reserve University researchers characterized materials; and chemical engineers in Smith’s group at MIT used their expertise in gas membrane separation to measure air flow through tissue.

Moving forward, the researchers want to explore using their fabric to block sound of multiple frequencies. This would likely require complex signal processing and additional electronics.

In addition, they want to further study the architecture of the fabric to see how changing things like the number of piezoelectric fibers, the direction in which they are sewn, or the applied stresses could improve performance.

“There are a lot of knobs we can turn to make this sound-suppressing fabric really effective. We want people to think about controlling structural vibrations to suppress sound. This is just the beginning,” says Yang.

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site covering news about MIT research, innovation, and teaching.