Developing new materials that can block 94% of sound with 3D printers, can be applied to realize silent drones and measures against noise pollution

A mechanical engineer at Boston University has developed a new " acoustic metamaterial " that can block 94% of the sound. If this is used for Dron 's propellers, aircraft turbines, MRI equipment etc, it can almost entirely eliminate the bumpy sounds, which may lead to resolution of noise pollution which tends to be problematic in cities.

Phys. Rev. B 99, 024302 (2019) - Ultra-open acoustic metamaterial silencer based on Fano-like interference
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.024302

BU Engineers Develop New Acoustic Metamaterial and Noise Cancellation Device | Research
https://www.bu.edu/research/articles/researchers-develop-acoustic-metamaterial-noise-cancellation-device/

"Soundproof walls currently in use are literally thick and heavy walls," said Reza Ghaffarivardavagh, one of the researchers involved in developing acoustic metamaterials capable of blocking 94% of the sound. A sound baffle , which is a type of existing soundproof board, helps to contain sound in the facility by placing it on the wall of a concert hall, but it is not suitable for suppressing sound in the place where the air current flows. For example, in places where air flow can not be blocked as in the exhaust port of a jet engine, soundproof boards like sound baffles can not demonstrate its effect, so mechanics working nearby, etc. will protect the ear from the roaring sound emitted by the engine I have to work with my earplug attached.

Ghaffarivardavagh, who was involved in developing acoustic metamaterial with high acoustic insulation, received a bachelor's degree in Mechanical Engineering from Sharif Institute of Technology in Tehran, Iran, enrolled in the graduate school of Boston University and in the laboratory of Professor Xin Zhang I am a student trying to acquire a doctorate. Originally he lived in major cities other than Boston, but he seems to be surprised at Boston, especially the noise caused by the airplane flying overhead and the car running on the street is badly noisy.

Therefore, Mr. Ghaffarivardavagh and Professor Zhang who were familiar with the problem which the existing soundproofing board has had are thinking "Can not design a structure that can maintain breathability while blocking noise?", Mathematically Approach and 3D printing technology are used. And, we will develop "a ring-shaped structure created according to mathematically perfect specification" that only blocks sound while maintaining air flow. "I have been working on developing metamaterials for over 10 years but it was Reza who brought an amazing idea of combining acoustics and metamaterials.The sound metamaterial is a relatively new field So this is the future, "said Professor Zhang of the Boston University Faculty of Engineering.

Professor Ghaffarivardavagh and Professor Zhang said, "Sounds are born of very small vibrations of the air, so we aimed to quell the oscillation.When we want to make the interior of the structure hollow, We need to keep in mind that it will be a "path through which sound will travel". " They calculated the dimensions and specifications of the metamaterials and constructed acoustic metamaterials so that only sounds are emitted from the open structure rather than air. According to two people, basically it is a feature of the acoustic metamaterial developed by "the place to shield the sound so as to cancel the sound by directly transmitting the sound coming into the metamaterial."

As a test two people created a structure that can turn off the sound from the speaker. We model physical dimensions that most effectively block noise based on calculations and output them with plastic using a 3D printer. You can see how much sound insulation effect by acoustic metamaterial made with 3D printer with sound insulation has in the following movie. The speaker is placed in the back, the pipe placed in front of the speaker is the path of sound. And round parts attached to the tip of the pipe are acoustic metamaterials with sound insulation effect. When the acoustic metamaterial is removed from the pipe in the middle of the movie, a loud noises will be heard in the surroundings, so you can realize how high the sound insulation effect of the sound metamaterial is.

Acoustic Metamaterial Noise Cancellation Device - YouTube


As a result of the analysis, it turned out that by using the acoustic material, it succeeded in blocking almost all sounds of 94% of the noise. By blocking the sound emitted from the speaker with the sound metamaterial, "the sound emitted from the speaker is not perceivable by the human ear".

As acoustic metamaterials made as prototypes have proven to be very effective, researchers are drawing up ideas on how to quiet the daily noises using acoustic metamaterials. Professor Zhang said, "Drone is a very hot topic, Amazon and others are interested in delivering goods using a drone," says the sound metamaterial to a drones with noisy fan rotation noise I hope that a big demand will be born if a drone with high quietness is born. Ghaffarivardavagh also said, "The cause of the drones 'noise is in the upward movement by the fans, if we can arrange an open sound insulation structure under the drones' fans, we can cancel the noise emitted from the drone towards the ground "I tell you.

Also, by placing an acoustic metamaterial in a fan or air conditioning system in a house or company, you can eliminate the noise caused by fan rotation. Since the sound metamaterial developed by the two persons does not need to shield the airflow so as to obtain sound insulation effect, it is possible to enhance the silence while keeping the air of the house and the office firmly, but with the conventional soundproof board etc. Is different and is an excellent point.

Furthermore, Mr. Ghaffarivardavagh and Professor Zhang think that we can use the acoustic metamaterial to reduce the noise pollution by transportation etc, and "We think that the structure we devise is ultra lightweight, openable, beautiful and We can use the acoustic metamaterial designed by us as a tile or brick to make a wall to eliminate sound. "

In addition, according to Mr. Ghaffarivardavagh, acoustic metamaterials are completely customizable in shape, so the structure does not need to be ring-shaped. Mr. Ghaffarivardavagh says, "The shape can be designed to be a cube or a hexagon, if you want to make a wall you can really have any shape, such as a hexagon shape", making a sound insulation wall with a honeycomb structure It is also possible.

According to Professor Zhang, the noise reduction method used in the acoustic metamaterial can be adapted to almost all environments, so the possibilities are infinite, "The idea is to create an object that can block any sound mathematics It is that it can be designed in a way. "