Imaging Sound Waves in Phononic Metamaterials

Phononic and photonic metamaterials have recently been proposed as analogs for topologically insulating structures, with a variety of potential applications. Most of these systems have been analyzed by simulation only (e.g. in COMSOL Multiphysics), but it has remained challenging to construct them experimentally and to measure their dynamics. Here we demonstrate two approaches to experimentally characterize real systems of topological phononic metamaterials using schlieren optics and a scanning microphone. In the schlieren setup, a mirror with long focal length is used to detect small changes in the refractive index of air using strobed light, which allows dynamic imaging of sound pressure [1]. Furthermore, we have developed a computer numerical control (CNC) scanning microphone with 6 degrees of freedom for dynamic imaging. Our sound wave imaging enables characterization of a topological phononic waveguide and other devices [2].

[1] Crockett & Rueckner, Am. J. Phys. 86, 870 (2018).
[2] Pirie, Sadhuka, Wang, Hoffman, arxiv:1809.09187.