MIT researchers develop sound-suppressing silk fabric

This innovative fabric, barely thicker than a human hair, contains a special fibre that vibrates when voltage is applied. The researchers used these vibrations to suppress sound in two ways. Firstly, the fabric generates sound waves that cancel out unwanted noise, similar to noise-cancelling headphones but applicable to larger spaces. Secondly, holding the fabric still prevents sound transmission, making it effective for noise reduction in larger areas like rooms or cars.

By using common materials such as silk, canvas, and muslin, the researchers have created practical noise-suppressing fabrics for real-world use, such as office dividers or thin walls.

Yoel Fink, professor in MIT’s departments of Materials Science and Engineering and Electrical Engineering and Computer Science, stated: “Noise is a lot easier to create than quiet. In fact, to keep noise out we dedicate a lot of space to thick walls. Grace’s work provides a new mechanism for creating quiet spaces with a thin sheet of fabric.”

Lead author Grace (Noel) Yang and co-authors from MIT, Case Western University, the University of Wisconsin at Madison, and the Rhode Island School of Design, published their findings in Advanced Materials. Their previous research involved creating fabric microphones by sewing piezoelectric fibres into fabric, which convert vibrations into electrical signals. The new work flips this concept to create a fabric loudspeaker that cancels out sound waves.

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

Applying an electrical signal to the piezoelectric fibre causes it to vibrate, generating sound. The researchers demonstrated this by playing Bach’s ‘Air’ using a 130-micrometre sheet of silk. To suppress sound, the fabric loudspeaker emits sound waves that destructively interfere with unwanted sound waves. However, this technique is effective only over small areas.

To suppress sound in larger spaces, the researchers developed a technique using fabric vibrations to stop sound transmission. For instance, placing the fabric on a shared wall can prevent noise from passing through.

“If we can control those vibrations and stop them from happening, we can stop the noise that is generated, as well,” Yang said.

Surprisingly, the fabric, when held still, reflects sound like a mirror. Experiments showed that both the mechanical properties of the fabric and the size of its pores affect sound suppression efficiency. Silk’s smaller pore sizes make it a better fabric loudspeaker compared to muslin.

The silk fabric, in direct suppression mode, can reduce sound volumes by up to 65 decibels. In vibration-mediated suppression mode, it can reduce sound transmission by up to 75%. These results were achieved through collaboration with various institutions, leveraging expertise in fabric construction, simulations, material characterisation, and airflow measurement.

Future research will explore blocking sounds of multiple frequencies, requiring complex signal processing and additional electronics. The team also plans to study the fabric’s architecture to enhance performance by adjusting the number of piezoelectric fibres, their direction, or applied voltages.

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