This sound-absorbing silk can create quiet spaces

We live in a very noisy world. From the hum of traffic outside your window to the next door neighbor’s blaring television to the sounds coming from a co-worker’s cubicle, unwanted noise remains a resounding problem.

To cut through the noise, an interdisciplinary collaboration of researchers at MIT and beyond has developed a sound-absorbing silk fabric that could be used to create quiet spaces.

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

In one, the vibrating fabric generates sound waves that interfere with unwanted noise to cancel it out, similar to noise-canceling headphones, which work well in a small space like your ears but don’t work in large speakers like parts or planes.

In the other, more surprising technique, the fabric is held still to eliminate the vibrations essential for sound transmission. This prevents noise from being transmitted through the fabric and attenuates the volume beyond. This second approach helps reduce noise in much larger spaces like rooms or cars.

Using common materials like silk, canvas, and muslin, researchers created noise-canceling fabrics that would be practical to implement in real-world spaces. For example, one could use such fabric to create partitions in open work spaces or thin fabric walls that block sound from passing through.

“Noise is much easier to create than silence. In fact, to avoid noise, we devote 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 lead author of a paper on fabric.

The study’s lead author is Grace (Noel) Yang SM ’21, PhD ’24. Co-authors include MIT graduate students Taigyu Joo, Hyunhee Lee, Henry Cheung and Yongyi Zhao; Zachary Smith, Robert N. Noyce Career Development Professor of Chemical Engineering at MIT; graduate student Guanchun Rui and Professor Lei Zhu of Case Western University; graduate student Jinuan Lin and assistant professor Chu Ma of the University of Wisconsin-Madison; and Latika Balachander, graduate student at the Rhode Island School of Design. An open access article on the research recently appeared in Advanced materials.

A silky silence

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

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

In their new work, the researchers reversed this idea to create a fabric speaker that could be used to cancel out sound waves.

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

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

To enable direct sound suppression, researchers use a silk fabric 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 fabric are opposed to unwanted sound waves hitting the fabric, which can cancel out the noise.

However, this technique is only effective on 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, like a bedroom.

Let’s say your next door neighbors are playing foosball in the middle of the night. You hear noise in your room because the noise in their apartment vibrates your shared wall, which forms sound waves on your side.

To suppress this sound, researchers could place the silk fabric on your side of the common 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 stop them from happening, we can also stop the noise being generated,” says Yang.

A mirror for sound

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

Their experiments also revealed that a fabric’s mechanical properties and its pore size affect the efficiency of sound generation. Although silk and muslin have similar mechanical properties, silk’s smaller pores 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 an enthusiastic human conversation). In vibration suppression mode, the fabric could reduce sound transmission by up to 75%.

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

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

Additionally, they want to further study the architecture of the fabric to see how changes such as the number of piezoelectric fibers, the direction in which they are sewn, or the voltages applied could improve performance.

“We can use lots of buttons to make this sound-absorbing fabric really effective. We want to get people thinking about controlling structural vibration to suppress sound. This is just the beginning,” says Yang.

This work is supported, in part, by the National Science Foundation (NSF), the Army Research Office (ARO), the Defense Threat Reduction Agency (DTRA), and the Wisconsin Alumni Research Foundation.