Flashbacks – amusing acoustic discoveries in recent years
Acoustics, like any other science, is driven by new discoveries and development of knowledge in the field. However, it’s also worth remembering past discoveries which made it possible for the field to move forward.
We would like to draw your attention to two interesting phenomena discovered and described in 2014 – acoustic invisibility and the longest echo measured.
The phenomenon of acoustic invisibility was described in 2014 by academics from Duke University. They created so called “acoustic invisibility cloak” – a 3D, pyramid-shaped object made of layers of perforated plastic. It’s uniqueness stems from the unusual property – the cloak is a barrier against sound waves. It means that when sound waves reach it, their trajectory is changed in a way that both acoustic waves as well as the cloak itself are undetectable. What makes it possible is the use of metamaterials – specially produced materials with properties that can’t be found in nature – as well as it’s specific shape and distribution of holes on it.
Some of the potential practical use of acoustic cloaking is in military or in architectural acoustics.
Full article on acoustic invisibility can be found here: https://www.extremetech.com/extreme/178362-the-worlds-first-acoustic-invisibility-cloak-has-been-created-by-duke-university.
In 2014, scientists induced the longest echo that ever occurred in a man-made construction. The world record has been set in Scotland, in an underground tunnel built for fuel storage during WWII. The discovery was a result of an experiment conducted by Prof. Trevor Cox from Salford University, who fired a shotgun in a tunnel, using a pistol loaded with blanks. The reverberation time after the shot was 112 seconds, which is 15 more than the previous world record from 1970.
Results of the conducted experiment may be used in research on acoustics in concert halls.
You can read more about this phenomenon here: https://www.bbc.com/news/uk-scotland-highlands-islands-25757937.