LTS2 is a team of researchers led by Prof. Pierre Vandergheynst working within the Institute of Electrical Engineering of the EPFL, one of the two Swiss federal institutes of technology. The main part of our research activities focuses on modern challenges in data processing.
The joint expertise of the acoustic group extends the LTS2 research landscape to audio engineering and electroacoustics.
— Nonlinear distortions are not favored in audio systems, except in the cases where they contribute to the DNA of music genres (eg. heavy metal or electronic music). However, nonlinear membrane sound absorbers are known to allow absorbing acoustic energy through a physical phenomenon known as Targeted Energy Transfer. When triggered by high enough sound pressure levels, energy can be transferred from the incident sound pressure to higher harmonics vibration components of the membrane, leading to a net loss of energy in the acoustic domain, as thoroughly described in the literature on Nonlinear Energy Sinks. This is exactly the aim of the Nonlinear ElectroAcoustic Resonators (NEAR) presented in our paper, published in Physical Review Applied [1], where a loudspeaker is used as an active membrane absorber, through an hybrid active impedance control scheme. Such device tweaks the loudspeaker to act as an “active” nonlinear membrane resonator, mimicking the behavior of a cubic stiffness, exhibiting Target Energy Transfer phenomena even for excitation levels that are 1’000 times lower than the one reported in the literature. This study paves the way to a new generation of Active Nonlinear Energy Sinks, outperforming the existing concepts so far, for better sound absorption at low frequencies.
— Have you ever visited a Wikipedia page to answer a question, only to find yourself clicking from page to page, until you end up on a topic wildly different from the one you started with? If so, not only are you not alone, but chances are that other people have taken the same roundabout route from, say, “Game of Thrones” to “Dubrovnik” to “tourist attraction” to “world’s biggest ball of twine”.
— Most naturally occurring materials have a disordered atomic structure that interferes with the propagation of both sound and electromagnetic waves. When the waves come into contact with these materials, they bounce around and disperse – and their energy dissipates according to a highly complex interference pattern, diminishing in intensity. That means it’s virtually impossible to transmit data or energy intact across wave-scattering media and fully leverage the potential of wave technology. For an example, you need look no further than your smartphone – the geolocation function works less well inside buildings where radiofrequency waves scatter in all directions. Other potential applications include biomedical imaging and geological surveying, where it’s important to be able to send waves across highly disordered media.
