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Acoustic metasurfaces are two-dimensional materials that impart non-trivial amplitude and phase shifts on incident acoustic waves at a predetermined frequency. While acoustic metasurfaces enable extraordinary wavefront engineering capabilities, they are not developed well enough to independently control the amplitude and phase of reflected and transmitted acoustic waves simultaneously, which are governed by their geometry. We aim to solve the inverse design problem of finding a geometry to achieve a specified set of acoustic properties. The geometry is modeled by discretizing the continuous space into a finite number of elements, where each element can either be filled with air or solid material. Full wave simulations are performed to obtain the acoustic properties for a given geometry. It is computationally infeasible to simulate all geometries. To address this challenge, we develop an experimental design-based algorithm to efficiently perform the simulations. The algorithm starts with a few geometries and adaptively adds geometries to the set, such that they fill the entire space of the desired acoustic properties using a small fraction of the possible geometries. We find that the geometry needs to have at least 7 × 7 elements to obtain any given acoustic property with a tolerance of 5.4% of its maximum range. This is achieved by simulating 24 000 geometries using the proposed algorithm, which is only [Formula: see text] of the 563 × 10 12 possible geometries. The method provides a general solution to the inverse design problem that can be extended to control more acoustic properties.
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This content will become publicly available on May 1, 2026
Inflatable acoustic metasurfaces for tunable wave focusing
Acoustic metasurfaces are two-dimensional architected materials designed to enable non-trivial control of waves, with a thickness that is either thinner than or comparable to the wavelength. However, most metasurfaces today have a fixed geometry and lack the ability to tune acoustic waves on command. This limits their ability to perform multiple functions, such as beam steering and dynamic focusing. This study introduces inflatable acoustic metasurface (IAM) lenses that enable tunable focusing. The IAMs feature two-dimensional diffractive focusing patterns embedded in a membrane that can be inflated nonplanarly through hydraulic control. It is experimentally demonstrated that inflation allows continuous focal length adjustment from –2.49λ to +3.17λ. To characterize the lens performance, changes in focal characteristics, including peak pressure, full width at half-maximum, and full length at half-maximum, are tracked at different levels of inflation. Furthermore, it is shown that IAMs can correct aberrations that occur as the angle of incidence increases in conventional planar lenses. To validate this, IAMs were tested in a concave configuration at a 20° oblique incidence angle. The results of this study may be applicable to fields requiring continuous and real-time response in tunable focusing, including acoustic imaging and communication, ultrasound surgery, and neuromodulation.
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- Award ID(s):
- 2052827
- PAR ID:
- 10608464
- Publisher / Repository:
- ASA - Acoustical Society of America
- Date Published:
- Journal Name:
- The Journal of the Acoustical Society of America
- Volume:
- 157
- Issue:
- 5
- ISSN:
- 1520-8524
- Page Range / eLocation ID:
- 3286 to 3295
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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