Programmable metasurfaces allow real-time electromagnetic (EM) manipulation in a digital manner, showing great potential to construct advanced multifunctional EM devices. However, the current programmable metasurfaces typically need human participation to achieve various EM functions. In this Letter, we propose, design, and construct a self-adaptive metasurface platform that can achieve beam control automatically based on image recognition. Such a platform is composed of a metasurface with
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active units, a single-board computer, and two independent cameras that can detect the position of the objects. The single-board computer, Raspberry Pi, is used to calculate the information of the objects and generate the coding sequences to control the digital metasurface based on a low complexity binocular localization algorithm. Such a smart metasurface platform can generate different beams according to the location of the receiver and can be used as intelligent antennas in future communications and radars.
This letter presents the design and experimental demonstration of a gradient metasurface guiding spoof surface acoustic waves (SSAWs) in the manner of a Luneburg lens for sound. By correlating the propagation characteristics of SSAWs with the effective surface acoustic impedance, a straightforward concentric surface structure design is proposed to realize the required refractive index distribution. The results from both simulation and measurement show that grazing incident sound is converted into SSAWs propagating along the metasurface and focusing on the edge of the opposite side of the lens, which may find applications in direction detection and acoustic sensing.
Space-time and time-varying metastructures have attracted a lot of research interest in recent years. On the other hand, digital programmable metasurfaces have also gained great attention owing to their powerful capabilities in controlling electromagnetic (EM) fields and waves in real time, which is very suitable for implementing spatiotemporal modulations in a digital manner. Accordingly, space-time-coding (STC) digital metasurfaces have recently been proposed to realize advanced manipulations of EM wavefronts and digital information, allowing simultaneous control of propagation directions in the space domain and harmonic distributions in the frequency domain. However, their instantaneous responses and the connection between the time- and frequency-domain characteristics have not yet been fully revealed. Here, we present a joint time-frequency analysis method to revisit STC digital metasurfaces, in which the time-domain instantaneous scattering patterns and frequency-domain equivalent excitations are investigated to analyze the spatial-spectral distributions of the modulated waves. This joint time-frequency analysis method helps to better explain the basic working principle of STC digital metasurfaces and is expected to facilitate more applications in wireless communications, radar, imaging, and beamforming.
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