Attenuating Noise: They Test New Materials to Create Silent Spaces

A fabric as thin as a hair has been designed to suppress noise in a room. Very good news in the face of growing noise pollution in our cities.

noise suppression
A fabric has been created almost as thick as human hair capable of suppressing unwanted noise. Credit: MIT News

Researchers at the Massachusetts Institute of Technology (MIT) have published the result of a multidisciplinary study to develop a silk fabric capable of suppressing unwanted sound.

By analyzing the behavior of traditional tissues, their characteristics as emitters or sound suppressors could be determined. It could be found that the size of the pores in relation to the thickness of the tissue, directly influences their ability to mitigate sound. The behavior of a particular tissue caught the attention of scientists: silk.

When attaching a piezoelectric actuator wire to the surface of a silk fabric (or what is the same, applying voltage), the latter is capable of emitting vibrations of 70 decibels (bB). By analyzing this behavior, it was possible to verify that it was capable of suppressing or attenuating the surrounding sound by implementing these two techniques: the first by direct acoustic interference and the second by suppression of the surrounding vibrations.

With direct interference, the "vibrating" fabric generates sound waves that interfere with unwanted noise to cancel it. In this case, a decrease of up to 37 bB in the intensity of the unwanted sound could be recorded.

In the second technique, the tissue remains "motionless", that is, the vibrations that are the ones that transmit the sound are practically suppressed, therefore, it cannot travel beyond the border that silk fabric means. Thus it was possible to reduce the amplitude of the vibration waves by 95%, achieving the reduction of the intensity of the transmitted sound by up to 75%. This result confirms the applicability of this technique in large spaces, such as aircraft rooms and cabins.

What acoustic insulation materials have we had until today?

To improve the comfort and privacy of homes, as well as the protection of people in industrial environments where noisy machinery is present, without forgetting the acoustics in entertainment venues, for many years the most diverse materials have been used as acoustic insulators.

industrial noise
In industries, on many occasions, effective sound isolation is lacking.

Polyurethane foam is widely used for its versatility, because in addition to its ability to absorb and disperse sound waves, reducing the transmission of noise, it is an efficient thermal insulator. But its flammability and toxicity put it at a disadvantage for some applications.

Acoustic plasterboards (commercially known as Pladur), in addition to giving a good finish to the constructions, improve the acoustic insulation of the premises, and in addition to being flame retardant, they provide thermal insulation.

Copopren is another insulating material that is made by ethylene and propylene copolymers, used to acoustically isolate spaces, although its greatest application has been in reducing vibrations in machinery.

Aerogel is a solid, ultra-light material, consisting of a three-dimensional lattice of Silica atoms.

Aerogel is another of the many materials developed for decades for acoustic insulation, and is one of the most used in recent years in aerospace industry applications. It is the most expensive of the materials available today, so its use is aimed at applications where high efficiency in sound reduction is required.

Will silk prevail in the future?

The reduction of unwanted noises persists as a challenge in daily life. Facing this challenge using the versatility offered by the use of silk fabrics, to implement acoustic insulation systems that are increasingly efficient, cost-effective and with the least impact on the environment, hopefully it will be the way in the coming years. It is still too early to affirm it. That is why this research contributes to the transit to safer environments for our hearing health.

Reference source:

Yang, G. H.; et. al. Single Layer Silk and Cotton Woven Fabrics for AcousticEmission and Active Sound Suppression. Wiley Online Library. MIT.