Experimental study of one-dimensional acoustic metamaterials of sound-soft inclusions.*

We are studying the properties of a one-dimensional acoustic metamaterial. The metamaterial consists in a periodical array of rectangular cross section pillars, made of a sound penetrable material (air) built-in a medium with higher acoustic impedance (Polydimethylsiloxane). We are focused on the acoustic response, when the periodicity of the array is several orders of magnitude lower than the wavelength of the incident wave. The problem is being studied experimentally and theoretically, using homogenization methods (Marigo, 2018, RSPA; Maurel, 2014, JASA) to simulate acoustic response of the array and comparing these results with the experimental measurements. Using lithography and soft lithography techniques, we fabricate the metamaterial, shaping a microscale periodical structure of rectangular cross section air bubbles within a Polydimethylsiloxane media. In order to reproduce a one-dimensional array, the air bubbles are pillars with a length, normal to its cross section, four orders of magnitude larger than the periodicity of the structure. We study experimentally the acoustic wave transmitted and reflected by the metamaterial. We find that it behaves as a perfect reflector for a wide range of frequencies.