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Considering the extraordinary wavefront modulation properties, acoustic metasurfaces have been extensively utilized to achieve powerful wave-manipulation functionalities. The next-generation acoustic metasurfaces are urgently required to encode more information capacity and process an increasing number of signal channels in a compact device, which needs more degrees of freedom for multifunctional wavefront modulation. In this study, subwavelength monolayer transmission–reflection-integrated metasurfaces (TRIMs) are systemically designed through a gradient-free topology optimization method to simultaneously realize diverse acoustic functions, such as beam steering, focusing, splitting, and diffusion, in reflection mode and transmission mode. Both numerical and experimental results demonstrate the desired wave-manipulation performance of the metasurfaces. In addition, a dual-frequency multiplexed TRIM is also numerically achieved for exploring the integration of multiple degrees of freedom and tunable function switching, which promise many unprecedented applications in integrated medical imaging, underwater wireless telecommunications, on-chip signal processing, etc.
Cheng et al. (Mon,) studied this question.