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Interview with Lorenzo Sanchis

"If we gather sound-waves at specific points, we can "absorb" acoustic pollution"


VALENCIA (LAURA GARSANDO). Lorenzo Sanchis carries out his activity at UMDO (Unit of Optoelectronic Materials and Devices) of the Institute for Materials Science (University of Valencia). He has coordinated the research group that developed the first acoustic invisibility cloak that works on three-dimensional objects, particularly on spheres. This means that objects are impermeable to sound waves so that these are diverted in other directions.

The experiment has been carried out in a joint project by researchers from the University of Valencia (theoretical design of the invisibility cloak) and the Polytechnic University of Valencia (testing). Sanchis also took part in the development of an acoustic lens capable of concentrating sound in a particular point, a tool that, once perfected, could be applied to fight acoustic pollution. Somehow shy and quite nervous he confessed «It is my first interview for the press».

–According to the information published in your article, similar tests had previously been run. What does your research add to the existing knowledge on acoustic camouflage?
–It is the first time we successfully run this test on three-dimensional objects, particularly on a sphere covered with rings. But we are also responsible for a previous publication where we explained how we camouflaged a bidimensional object.

–What led you to seek to improve the system?
–We have to take into account that we live in a three-dimensional world. If we wanted to apply the previous findings, they had to be effective on three-dimensional objects. The basis of this research lies on a study we carried out on acoustic lenses, which divert the sound path at will. Just as we get a shining spot if we place a magnifier under the sun, we can make sound waves gather at a particular point in space and thus eliminate it.

–What is the invisibility mechanism made up of and how does it work?
–To be specific, we should point out that, instead of «invisibility» -a term related to light perception- we should talk about «undetectability». Sound waves bounce on objects, and what we have achieved is neutralising this phenomenon in such a way that sound passes through the objects as if they were not there. That is why we say they are acoustically undetectable. The experiment was run on a sphere covered with 60 plastic rings, and what we have done at the University of Valencia is calculating its radius and position in relation to the sphere. For this purpose we have used an optimisation software based on genetic algorithms.

–What is a genetic algorithm?
–They are based on Darwin's laws of evolution: only the fittest survive, the ones capable of transmitting their genetic material to future generations. In this sense, our software has evolved into finding a «specimen» that does what we want it to do: gathering sound waves. 

–How long can the calculations to obtain this effect take?
–We have needed a «super computer» that works in parallel, which means that we have used up to 48 microprocessors working together. We need a strong computing power to find a «fit» specimen among so many generations. Even so, five days of intensive calculations have been necessary to obtain the invisibility cloak for the chosen sphere.

Full text available at Mètode's website.


Laura Garsando. Student of Journalism at the University of Valencia


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