3D Printed Metamaterials

[ewen.daviau]

Hi !
I am both acoustician, enginner and accordion maker and I look for a meta material which could make a one way sound barrier.
Do you have any idea ?

 

[Patrick Bateman]

Nearly all of them can do that. The main challenges are:

1) the metamaterial has to be quite large to work at a low frequency

2) 3D printing the metamaterials is tricky; if you wanted to print an entire wall of them, it would take weeks to finish the print.

All of the metamaterials are mostly just closed transmission lines, and you can simulate closed transmission lines in Hornresp.

To elaborate on that a bit:

A transmission line is tuned to a single frequency. You can make a transmission line that will attenuate sound to a high degree; 20dB of rejection is possible. A metamaterial is basically an array of those transmission lines. So you're creating a series of transmission lines, tuned to specific frequencies, to absorb sound.

Having said all that, I kinda lost interest in metamaterials for treating a room, because a couple of plants and a curtain are way less work, cheaper, don't look weird, etc. Sometimes the existing solutions are best.

IMHO, the best application of metamaterial is on the speaker driver itself, like KEF does

 

[ewen.daviau]

Ok, I would like to implement this in accordions, make a wall (approximately a4 format (210 x 287 mm size) so that the sound could go out but that extrenal sound could not pollute a internal microphone inside the instrument.
I wounder if it's possible to at least do a little improvement withing this size.
There is an exemple here : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4910075/pdf/srep28023.pdf
but I don't really understand the design , ie how they mix the labythinth and the hybrid metastructure.

Few questions :
1) What is the minial surface of every transmission line ?
2) Does anyone made a parametric file on Cad software to design metamaterials ?