Observation of Micropolar Modes from Transmitted Waves in a Multilayer Polystyrene Plate

International audience ; This research investigates the behavior of sound wave propagation through a multilayer micropolar plate composed of expanded polystyrene, examining various incident angles. By integrating theoretical models with experimental methods, we analyze the changes in transmission coefficients across the frequency spectrum, highlighting the dynamic variations in vibrational modes. Using a setup that includes a loudspeaker, a microphone, and a data acquisition system (National Instruments ), we precisely identified the classical Lamb modes below the critical angle and discovered new micropolar modes beyond this critical angle for a single layer of the material. For multilayer configurations with very thin air films between the layers, we observed increased attenuation as well as an augmentation of both Lamb and micropolar modes within the same frequency range of 0-60 kHz. These experimentally validated findings are consistent with theoretical predictions and significantly enhance our understanding of the engineering applications of these materials.