Subwavelength Acoustic Focusing Within Multi-Breadth Bands With A Window-Shape Metasurface

The traditional phase gradient acoustic focusing metasurfaces based on the generalized Snell law (GSL) can manipulate acoustic waves freely. However, their applications are limited largely because of their narrow bandwidth, large volume, and single function. To resolve these problems, a kind of window-shape acoustic focusing metasurface (WSAFM) is proposed, the well performed focusing can be obtained by the flexibly varied longitudinal length of two handles inside the basic structure unit (BSU). The results demonstrate that, within multi-breadth bands (5000 Hz -6500 Hz, 7100 Hz -7600 Hz, 12100 Hz -13600 Hz), the WSAFM can realize the near-zero-sidelobe (NZS) subwavelength focusing, the variation of focus position, and the breakthrough of diffraction limit at multi-frequency. More importantly, when the non-Hermitian parameters (non-Hermitian system) are introduced to the WSAFM, the focus intensity can be enhanced without varying other parameters. The WSAFM proposed in this paper shows promising potentials in biomedical ultrasound imaging and the design of acoustic devices with multi-breadth bands.