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Negative refraction plays an important role in acoustic wave manipulation andimaging. However, conventional systems based on acoustic metamaterials sufferfrom the limits induced by loss-related and resolution issues. In this work, aparity-time (PT)-symmetric system is introduced to realize loss-freebidirectional acoustic negative refraction. The system is composed of a pair oflocally PT-symmetric multi-layer metasurfaces sandwiching a region of freespace, which also forms a global PT-symmetry. The property of bidirectionalnegative refraction, which is rare for regular PT-symmetric structures, isrelated to the coexistence of amplification and absorption in the locallyPT-symmetric metasurfaces at their PT broken phases. Such metasurfaces canfreely switch their states between coherent perfect absorber (CPA) andamplifier depending on the direction of incidence. Our results provide a newphysical mechanism for realizing bidirectional functions in PT-symmetricsystems.

Bidirectional acoustic negative refraction based on a pair of metasurfaces with both local and global PT-symmetries