Multifunctional acoustic devices based on unbalanced gain–loss materials

The realization of multifunction by simply combining acoustic devices together is always attractive, but it is never an easy task due to the complexity of most acoustic metamaterials. In this paper, a kind of unbalanced gain–loss acoustic metasurface is designed, which can work as an energy amplifier, suggesting that it may be applied to an acoustic signal detector or a sensor. In addition, an acoustic negative refraction system is established by simply putting two of these metasurfaces together, which can produce negative refraction for the acoustic waves from different directions and different incident angles, even focusing and imaging with precisely selected parameters. These functions are quite rare for materials without the double-negative-parameter. This work provides a new route to use the gain/loss materials and achieve multifunctions without complex design