A collaborative project between researchers from MIT and elsewhere has developed a sound-suppressing silk fabric that could be used to create quiet spaces.
- The fabric, which is barely thicker than a human hair, contains a special fibre that vibrates when a voltage is applied to it.
HOW IT WORKS: The researchers leveraged the vibrations to suppress sound in two different ways.
- In one, the vibrating fabric generates sound waves that interfere with an unwanted noise to cancel it out, similar to noise-cancelling headphones, which work well in a small space like your ears but do not work in large enclosures like rooms or planes.
- In the other, the fabric is held still to suppress vibrations that are key to the transmission of sound. This prevents noise from being transmitted through the fabric and quiets the volume beyond. This second approach allows for noise reduction in much larger spaces like rooms or cars.
- By using common materials like silk, canvas and muslin, the researchers created noise-suppressing fabrics which would be practical to implement in real-world spaces.
- For instance, one could use such a fabric to make dividers in open workspaces or thin fabric walls that prevent sound from getting through.
THE SCIENTISTS: The study’s lead author is Grace (Noel) Yang. Co-authors include MIT graduate students Taigyu Joo, Hyunhee Lee, Henry Cheung, and Yongyi Zhao; Zachary Smith, the 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 at Madison; and Latika Balachander, a graduate student at the Rhode Island School of Design.
- An open-access paper about the research appeared recently in Advanced Materials.
BUILDING ON: The sound-suppressing silk builds off the group’s prior work to create fabric microphones. In that research, they sewed a single strand of piezoelectric fibre into fabric. Piezoelectric materials produce an electrical signal when squeezed or bent. When a nearby noise causes the fabric to vibrate, the piezoelectric fibre converts those vibrations into an electrical signal, which can capture the sound.
- In the new work, the researchers flipped that idea to create a fabric loudspeaker that can be used to cancel out soundwaves. Applying an electrical signal to the piezoelectric fibre causes it to vibrate, which generates 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, the researchers use a silk fabric loudspeaker to emit sound waves that destructively interfere with unwanted sound waves. They control the vibrations of the piezoelectric fibre so that sound waves emitted by the fabric are opposite of unwanted sound waves that strike the fabric, which can cancel out the noise.
- However, this technique is only effective over a small area. So, the researchers built off this idea to develop a technique that uses fabric vibrations to suppress sound in much larger areas, like a bedroom.
THE PROPERTIES: The researchers found that holding the fabric still causes sound to be reflected by the fabric, resulting in a thin piece of silk that reflects sound like a mirror does with light.
- Their experiments also revealed that both the mechanical properties of a fabric and the size of its pores affect the efficiency of sound generation. While silk and muslin have similar mechanical properties, the smaller pore sizes of silk make it a better fabric loudspeaker.
- But the effective pore size also depends on the frequency of sound waves. If the frequency is low enough, even a fabric with relatively large pores could function effectively.
What they said:
Noise is a lot easier to create than quiet. In fact, to keep noise out 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.
— Prof Yoel Fink (Senior Author)
Departments of Materials Science and Engineering and Electrical Engineering and Computer Science
MIT
