Tunable Double-Band Perfect Absorbers via Acoustic Metasurfaces with Nesting Helical Tracks

We propose a design of tunable double-band perfect absorbers based on the resonance absorption in acoustic metasurfaces with nesting helical tracks and deep-subwavelength thicknesses(<λ/30 withλbeing the operation wavelength).By rotating the cover cap with an open aperture on the nesting helical tracks,we can tailor the effective lengths of resonant tubular cavities in the absorber at will,while the absorption peak frequency is flexibly shifted in spectrum and the acoustic impedance is roughly matched with air.The simulated particle velocity fields at different configurations reveal that sound absorption mainly occurs at the open aperture.Our experiment measurements agree well with the theoretical analysis and simulation,demonstrating the wide-spectrum and tunable absorption performance of the designed flat acoustic device.

Acoustic topological adiabatic passage via a level crossing

Stimulated adiabatic passage has been extensively studied to achieve robust and selective population transfer in quantum systems. Recently, the quantum-classic analogy has been rapidly developing and can be considered responsible for the implementation of the adiabatic transfer of sound energy in cavity chain systems. In this article, we investigate the adiabatic transfer of sound energy between two topological end states in the Su-Schrieffer-Heeger(SSH) cavity chain, which can be considered to be the acoustic analog of the quantum chirped-pulse excitation. The topological adiabatic passage in SSH cavity chain has two categories. When the single-cavity resonance frequencies on the sublattices A and B in the SSH cavity chain do not switch their spectrum positions, the topologically protected adiabatic evolution results in the returning passage of the sound excited in one end cavity. When a level crossing with single-cavity resonance frequencies on the sublattices A and B exhibits switch in the frequency spectrum, acoustic energy is observed to be topologically pumped between the two end cavities of the SSH chain.

Super-resolution acoustic image montage via a biaxial metamaterial lens

Ever since the Victorian era, montage, the process of pictorial composition made by juxtaposing or superimposing photographs, has been a very popular post-editing imaging technique. Despite showing a strong power in demonstrating complex wave field effects, this technique has neither been fully explored in acoustic imaging nor been realized in real-time systems with the capability beyond diffraction limits.On the other hand, the recent prospect of metamaterials has shown their great potentials in superresolution acoustic imaging. However, the miracle jigsaw of more advanced functional modulation of acoustic wave fields at deep subwavelength scale still remains elusive. Here we report the experimental implementation of super-resolution acoustic image montage through a judiciously designed biaxial metamaterial lens. Based on the non-diffraction birefringence in the biaxial metamaterials, we realized various montage functionalities such as duplication, composition, and decomposition of sound images with distinctive deep subwavelength features. Our work represents an important step in developing versatile functional acoustic metamaterial devices for imaging purposes, as it provides on-demand editing of sound field patterns beyond diffraction limits.