Sound‐Speed Modifying Acoustic Metasurfaces for Acoustic Holography

Abstract

Acoustic metasurfaces offer unique capabilities to steer and direct acoustic fields, though these are generally composed of complex 3D structures, complicating their fabrication and applicability to higher frequencies. Here, an ultrathin metasurface approach is demonstrated, wherein planarized micropillars in a discretized phase array are utilized. This subwavelength metasurface is easily produced via a single‐step etching process and is suitable for megahertz‐scale applications. The flexibility of this approach is further demonstrated in the production of complex acoustic patterns via acoustic holography. This metasurface approach, with models used to predict their behavior, has broad potential in applications where robust, high‐frequency acoustic manipulation is required, including microfluidics, cell/tissue engineering, and medical ultrasound.

Microscale actuation using acoustofluidics for rapid micromanipulation and 3D printing

“…Accordingly, acoustic holography seeks to manipulate the phase and/or amplitude of propagating wavefronts to reconstruct a desired acoustic field at a target plane [16]. In our work, we expand on the methodology via which acoustic holography can be applied, including via a unique acoustic metamaterial to form the phase plate [17], form acoustic fields in microchannels [8], and create multiple acoustic fields at the same target plane using the same holographic phase plate [18].…”

Enhanced acoustic streaming effects via sharp-edged 3D microstructures

“…21,22 Whereas much of acoustofluidic work has exploited simple periodic patterns using standing waves, 23,24 recent efforts have demonstrated that the interaction between acoustic field and complex structures has the potential to further enhance the spatial selectivity and complexity of acoustic manipulation. [25][26][27] Acoustofluidic effects around oscillating sharp edges, for example, have been used to induce fluid mixing, pumping, and particle manipulation. [28][29][30] Sharp-edge microstructures are typically fabricated as a component of a microfluidic channel wall, protruding into the fluid domain and presenting a single line-shaped edge at the apex.…”

“…21,22 Whereas much of acoustofluidic work has exploited simple periodic patterns using standing waves, 23,24 recent efforts have demonstrated that the interaction between acoustic field and complex structures has the potential to further enhance the spatial selectivity and complexity of acoustic manipulation. 25–27…”

Programmable Acoustic Holography using Medium‐Sound‐Speed Modulation

“…[30][31][32] Additionally, while select acoustic approaches can generate nonperiodic patterns, [33][34][35][36][37] acoustic holograms have the advantage of decoupling structures that modify the acoustic field from the region they are utilized, making them more widely applicable beyond microfluidic devices. A limitation of most static metasurface-based holograms [29,38,39] is that only a single and static acoustic field can be generated at a target plane for a given hologram, limiting the range of activities that can be performed, whereas applications in tissue engineering and 3D printing benefit from the incorporation of designed heterogeneity. [40,41] Flexible and reconfigurable acoustic fields can be generated using phased array transducers (PATs), [17,[42][43][44][45][46] in which many ultrasonic devices are individually actuated with varying phase/amplitude.…”