Abstract
Negative refraction plays an important role in acoustic wave manipulation and imaging. However, conventional systems based on acoustic metamaterials suffer from the limits induced by loss-related and resolution issues. In this work, a parity-time (PT)-symmetric system is introduced to realize loss-free bidirectional acoustic negative refraction. The system is composed of a pair of locally PT-symmetric multi-layer metasurfaces sandwiching a region of free space, which also forms a global PT symmetry. The property of bidirectional negative refraction, which is rare for general PT-symmetric structures, is related to the coexistence of amplification and absorption in the locally PT-symmetric metasurfaces at their PT-broken phases. Such metasurfaces can freely switch their states between coherent perfect absorber (CPA) and amplifier depending on the direction of incidence. Our results provide a physical mechanism for realizing bidirectional functions in acoustic PT-symmetric systems.
Highlights
Negative refraction plays an important role in acoustic wave manipulation and imaging
Besides the exceptional point (EP), there exists another type of singular points denoted as coherent perfect absorber (CPA)-laser point in the electromagnetic PT symmetry, which has recently gained attention owing to its singular characteristics for the PT-symmetric
We show that bidirectional negative refraction can be obtained independent of the direction of incidence, by using a PT-symmetric system involving both local and global PT-symmetries
Summary
Negative refraction plays an important role in acoustic wave manipulation and imaging. The globally PT-symmetric system, which is composed of two identical locally PT-symmetric metasurfaces that can simultaneously behave as a perfect absorber and an amplifier, amazingly realizes the exceptional behavior of bidirectional acoustic negative refraction.
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