Theoretical and experimental study of micropolar elastic materials using acoustic waves in air

Abstract This study focuses on the development of a theoretical and experimental acoustic method and setup for studying the micropolar behavior of materials. Two types of low density closed-cell foams made from polystyrene (expanded and extruded) materials that were previously reported as materials exhibiting the non-classical elastodynamic behavior were investigated in order to reveal the particular comportment using acoustic waves. Two different types of transducers were employed to provide a large frequency band to study the influence of the Cosserat parameters. The frequency band from 1–40 kHz was covered using a tweeter loudspeaker whereas that from 30–120 kHz, by an air coupled ultrasonic transducer. The materials’ micropolar elastic behavior were revealed through the comparison between the theoretical and experimental transmission coefficients. At the cut-off frequency where the theoretical phase velocity of the transverse acoustic mode was established to be infinite, the acoustic wave transmission by the panels was found to be very small. This makes the Cosserat materials appealing to harmonic noise reduction.