The world is getting noisier. From the hum of traffic outside your window to the sound of your next door TV blaring to sounds from a chef’s room, unwanted noise is still a big problem.
Whether it is deliberately generating sound waves or trying to reduce unwanted noise, noise control is an area full of challenges and opportunities.
Active noise reduction involves the elimination of sounds at low volumes and has become an important application area for headphones and earbuds, which only require a small quiet zone near the eardrum. Large volume sound damage, such as indoors, is mainly achieved through passive methods such as sound reflection using materials with high acoustic impedance or sound absorption usually achieved by fiber structures or insulating foam.
Can sound be dampened by clothing slightly thicker than human hair? Researcher at Massachusetts Institute of Technology (MIT) claims to have achieved this remarkable feat. An interdisciplinary collaboration of researchers from prestigious institutions and colleagues at other major American universities has developed noise-reducing silk fabrics that can be used to create quiet rooms.
The secret is in the fiber
The fabric contains special fibers that vibrate when tension is applied. The researchers used these vibrations to suppress noise in two different ways. One of them is vibrating clothes sound wave that block out unwanted sound to cancel it out, like headphones that work well in small spaces like your ears, but don’t work in large spaces like a room. or a plane.
Another, more impressive way is to hold the fabric up to suppress the vibrations that are important for sound transmission. This prevents sound from being transmitted through the fabric and muffles further away. This second approach allows for noise reduction in much larger spaces such as rooms or cars.
Using common materials such as silk, canvas, and muslin, the researchers created sound-reducing clothing that is practical for use in real-world environments. For example, the fabric can be used to create a partition in an open work space or a thin fabric wall that prevents sound from entering.
“Noise is much easier to create than silence. In fact, to prevent noise, we put a lot of space into thick walls,” the team wrote. “We provide a new mechanism to create a relaxing space with a thin sheet of fabric,” said Prof. Yoel Fink, a materials science and engineering expert who is the study’s senior author.
The lead author of this study is Dr. Grace (Noel) Yang, and her team including MIT graduate student and chemical engineering Dr. Zachary Smith; graduate student at Case Western University in Cleveland, Ohio; Prof. Chu Ma of the University of Wisconsin at Madison; and a graduate student at the Rhode Island School of Design.
Their study has just appeared in the journal Advanced Materials titled “Single-Ply Silk and Cotton Woven Fabric for Acoustic Emissions and Active Sound Damping.”
IN RECENT RESEARCH, they sewed single layers of piezoelectric fibers that produce electrical signals when pressed or bent into the fabric. When environmental noise causes the fabric to vibrate, piezoelectric fibers convert these vibrations into electrical signals that can pick up the sound.
In their new study, the researchers turned their attention to making fabric glues that could be used to reduce sound waves. Applying an electrical signal to a piezoelectric fiber causes it to vibrate, which creates sound. The researchers demonstrated this by playing Bach’s Air using a 130-micrometer sheet of silk mounted on a circular frame.
“Although we can use print to make sound, there is so much noise in our world already. We thought that creating silence could be even more valuable,” Yang explained.
To enable direct noise reduction, the researchers used a silk speaker to emit sound waves that cause destructive interference with unwanted sound waves. They control the vibration of the piezoelectric fibers so that sound waves emitted by the fabric collide with unwanted sound waves hitting the fabric, thus eliminating noise. – but the method is only effective in small areas. Therefore, researchers built on this idea to develop a method that uses fabric vibrations to suppress noise in larger areas such as bedrooms.
Let’s say your next door neighbor is busy watching a sporting event on TV in the middle of the night. You hear noise in your bedroom because the noise in their apartment causes your partition wall to vibrate, which creates sound waves on your side.
To reduce the noise, you can place a silk cloth next to your partition wall, controlling the vibrations in the fibers to make the cloth stay still. This mid-vibration compression prevents sound from being transmitted through the fabric. “If we can control these vibrations and stop them from happening, we can also stop the noise they make,” Yang said.
Surprisingly, the researchers found that holding the cloth still caused the sound to be reflected by the cloth, producing a thin piece of silk that reflected sound like a mirror reflecting light
Their tests also revealed that the mechanical properties of the fabric and the size of its pores affect the efficiency of sound generation. Although silk and muslin have similar mechanical properties, the smaller pore size of silk makes it a better material.
However, the effective pore size also depends on the frequency of the sound wave. If the frequency is low enough, even fabrics with relatively large pores can work effectively, Yang said.
When they tested the silk fabric in direct pressing mode, the researchers found that the fabric could significantly reduce the volume of sound by up to 65 decibels (as loud as an enthusiastic human conversation). In vibration dampening mode, the fabric can reduce sound transmission by up to 75%.
In the future, the team members want to study the use of their material to block sounds of different frequencies. This may require complex signal processing and additional electronics. They also aim to study the fabric’s architecture to see how things like the number of piezoelectric needles, the direction of the seams, or the applied tension change performance.
“There are a lot of switches that we can flip to make this moisturizer really effective. We want to get people thinking about how to control structural vibrations to dampen noise. This is just the beginning,” Yang concluded.
2024-05-12 19:04:11
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