  Acoustic metamaterials have become a novel and effective way to control sound
waves and design acoustic devices. In this study, we design a 3D acoustic
metamaterial lens (AML) to achieve point-to-point acoustic communication in
air: any acoustic source (i.e. a speaker) in air enclosed by such an AML can
produce an acoustic image where the acoustic wave is focused (i.e. the field
intensity is at a maximum, and the listener can receive the information), while
the acoustic field at other spatial positions is low enough that listeners can
hear almost nothing. Unlike a conventional elliptical reflective mirror, the
acoustic source can be moved around inside our proposed AML. Numerical
simulations are given to verify the performance of the proposed AML.
