Acoustic holography based on composite metasurface with decoupled modulation of phase and amplitude

Abstract

Acoustic holography has extensive possibilities in acoustic sensing, acoustic illusion, contactless particle manipulation, and medical imaging. Based on coating unit cells and perforated panels, an acoustic composite metasurface is constructed with a decoupled modulation of phase and amplitude, which has been used to design acoustic holography. This proposal not only has lower complexity than conventional acoustic holography of active arrays due to the avoidance of complex structures and circuits but also provides more flexibility than acoustic holography based on the acoustic metasurface with phase-only modulation benefitting from the efficient decoupled modulation of phase and amplitude. We have further demonstrated three acoustic holographic applications, such as multi-directional transmission, multi-focal focusing, and holographic imaging. Due to the low complexity and the great flexibility, this proposal has potential to achieve the high-quality holograms with high information content, fine resolution, and large scale.

Systematic design of broadband path-coiling acoustic metamaterials

“…19 Combining Eqs. (2), (4), (6), and (7), the overall complex transmission can be obtained using Mathematica as…”

“…Acoustic metasurfaces, as a sub-category of acoustic metamaterials, have attracted much research effort in recent years due to their thin structure and outstanding ability in wavefront engineering. 2,[4][5][6][7][8] The increasing interest in acoustic metasurface calls for the search of high transmission metamaterial unit cells with strong local phase control capability. In most scenarios, the performance of the metasurface is determined by the property of the individual unit cell, of which many designs have been proposed in the past few years.…”

“…The design strategy has been used in various applications of wavefront engineering, such as beam-bending, acoustic focusing, hologram imaging, etc. [5][6][7]11,14,15 However, such resonance-based acoustic metamaterial unit cells suffer from a narrow bandwidth, as high transmission only exists near the resonant frequencies. When the frequency of the incident wave is off resonance, the impedance mismatch between the narrow channel and the surrounding background medium at the entrance leads to high reflection.…”

Acoustic metasurfaces

“…However, the impedance of a space-coiling structure or its declination, namely, a labyrinthine structure, is usually poorly matched to the impedance of air 63,65,66 . To overcome this limitation, various designs have been proposed, such as tapered labyrinthine metamaterials 83 , spatially varied coiling-slit units 79,84 and impedance-matching layers of gradient index 85 .…”

“…For example, the metasurface array can replace active arrays to focus ultrasound through the skull to ablate brain tumours or disintegrate clots in the treatment of stroke 93 . The accuracy of acoustical holography is improved if both the phase and amplitude can be modulated 84,94 .…”