Empa develops ultra-thin sound absorbers for facades

(CONNECT) Novel sound-absorbing panels from Empa were able to reduce traffic noise by up to 4 decibels during their first test in a Zurich driveway. According to a report by the institute, they are four times thinner than conventional insulation material and just as effective. They are also weatherproof and therefore suitable for exterior walls. They were developed by Empa's Acoustics/Noise Reduction department together with the Dübendorf materials manufacturer de Cavis.

According to Empa, the noise "literally gets lost" in the irregular pores of the mineral gypsum and cement foams of which they are made. This is because the varying pore structure of the foams forces the air particles to take a longer route to get into and out of the material. This creates the impression of a much thicker absorber for the sound waves, despite its low thickness.

The team uses several porous layers for the panels. It not only varies the thickness of the individual layers and the size of the pores, but also provides it with tiny holes.

The researchers can determine in advance exactly what the ultra-thin panels made of gypsum or cement foams need to look like for a specific application in order to absorb noise particularly efficiently. To this end, they have developed a computer model that simulates how air flows through the pores of the material. The most efficient pore structure can then be produced in a targeted manner. "If only the very low frequencies or only the very high frequencies need to be absorbed for a particular application, we can achieve this with a combination of material properties and perforations with almost no restrictions," explains Empa researcher Bart Van Damme in a video.

The material is now to be further developed with a suitable industrial partner and produced on a larger scale. The aim is to create customised sound absorbers for applications with limited space and high design requirements. ce/mm