Realization of broadband acoustic metamaterial lens with quasi-conformal mapping

Recently, transformation acoustics has been widely recognized for its ability to convert the acoustic pressure field into desired spatial patterns, resulting in numerous functionalities with unique functionalities. Here, we propose and realize a two-dimensional flattened Luneburg lens using quasi-conformal mapping in the acoustic regime, allowing geometries with curved shapes to be converted into flat systems while the broadband and low-loss properties are preserved. Importantly, such an acoustic metamaterial lens is composed of purely isotropic materials that are easy to obtain via artificial structures. Our results may give rise to various applications, such as medical treatments and novel imaging systems.