Brain-computer interfaces (BCIs), invasive or non-invasive, have projected unparalleled vision and promise for assisting patients in need to better their interaction with the surroundings. Inspired by the BCI-based rehabilitation technologies for nerve-system impairments and amputation, we propose an electromagnetic brain-computer-metasurface (EBCM) paradigm, regulated by human’s cognition by brain signals directly and non-invasively. We experimentally show that our EBCM platform can translate human’s mind from evoked potentials of P300-based electroencephalography to digital coding information in the electromagnetic domain non-invasively, which can be further processed and transported by an information metasurface in automated and wireless fashions. Directly wireless communications of the human minds are performed between two EBCM operators with accurate text transmissions. Moreover, several other proof-of-concept mind-control schemes are presented using the same EBCM platform, exhibiting flexibly-customized capabilities of information processing and synthesis like visual-beam scanning, wave modulations, and pattern encoding.

Metasurface holography has shown great potentials to reconstruct the full‐wave information of electromagnetic (EM) waves, bringing benefits of high spatial resolution and good precision of reconstructed images. To obtain higher security of the metasurface holography, orbital‐angular‐momentum (OAM) of EM waves is taken into consideration as new freedom of the metasurface holography. The use two coding information metasurfaces is proposed to achieve the OAM‐encrypted holography. One metasurface is used to generate different OAM beams with l = ±1 helical mode indices, which functions as the OAM feed; while the other is used to integrate different OAM helical‐phase wavefronts into the holograms of the transmitted images, forming the OAM‐encrypted holography. The predesigned images are accurately decoded only when the OAM‐encrypted metasurface is illuminated by the incident OAM beams with the inverse helical mode indices (l = ∓1) under the incidence of defined polarization states. Experimental results agree well with the theoretical design and numerical simulations, verifying the feasibility and security of the OAM‐encrypted holography. The proposed method will be a good candidate to enhance the secure communication systems and imaging systems.

Recent advances in digitally programmable metamaterials have accelerated the development of reconfigurable intelligent surfaces (RIS). However, the excessive use of active components (e.g., pin diodes and varactor diodes) leads to high costs, especially for those operating at millimeter-wave frequencies, impeding their large-scale deployments in RIS. Here, we introduce an entirely different approach—moiré metasurfaces—to implement dynamic beamforming through mutual twists of two closely stacked metasurfaces. The superposition of two high-spatial-frequency patterns produces a low-spatial-frequency moiré pattern through the moiré effect, which provides the surface impedance profiles to generate desired radiation patterns. We demonstrate experimentally that the direction of the radiated beams can continuously sweep over the entire reflection space along predesigned trajectories by simply adjusting the twist angle and the overall orientation. Our work opens previously unexplored directions for synthesizing far-field scattering through the direct contact of mutually twisted metallic patterns with different plane symmetry groups.

Metasurface holograms have the potential to be applied in a variety of practical fields. Here an anisotropic digital metasurface is proposed that can project polarization multiplexing patterns at the microwave frequency, in which a modified Gerchberg–Saxton algorithm is presented to calculate the phase masks. A 3‐bit coding metamaterial unit is also proposed, which is capable of independently manipulating the transmission phases of orthogonal linearly polarized electromagnetic waves. The influence of wave‐front has been analyzed by comparing two holographic results with distinct source optimization methods. A prototype of the anisotropic digital coding metasurface optimized with horn wave‐front is designed, manufactured, and tested. The experimental measurements present the expected holographic fields and have a good match with the simulation results.

scale, they are considered as alternative approaches towards the radio frequency (RF) front-end design to realize beamforming and scanning in wireless communication systems. [8][9][10] In the past decades, several major breakthroughs have boosted the research of metamaterials significantly. [11] For instance, active components were introduced to the metasurfaces to realize dynamic controls of EM waves. In 2014, Cui et al. proposed the concept of programmable digital coding metasurfaces, bridging the digital world to the EM physical world for the first time. [12][13][14] Following the footstep of information society and booming of artificial intelligence, the focus of the latest researches around the metasurfaces has shifted to autonomous perception, self-adaptation, and high-performance computing in the EM fields. [15][16][17][18][19][20] Today's data-driven society has witnessed a pressing demand for high-resolution and rapid-response imaging system. However, the traditional microwave imagers require very bulky and repetitive circuit components, restraining their applications in cost-sensitive and deployable situations. Combined with the superior manipulation of the EM wave and compact dimensions, the metasurface-based microwave imagers have been proposed in recent years and exhibited excellent performance in the image reconstruction and processing. For example, a linear EM model for the reflective-metasurface-based microwave imager with multiple measurements was presented. [21] Based on this model, a frequency-multiplexing metasurface-based microwave imager was designed for security check, where a passive metasurface was used as the EM wave reflector and the parameters at several frequency points were collected as the raw data. [22] However, the quality of reconstructed images suffers from severe deterioration when the noise level increases. Also, compressed sensing algorithm was employed to reconstruct the images from the scattered signals under random scattering pattern iteratively, which inevitably increases the complexity of system. [23,24] Other novel methods have also been proposed to solve the inverse problems in EM imaging, including artificial neural networks, convolution neural networks, which are all limited in the digital domain implemented in the postprocessing module. [25][26][27] In 2014, a terahertz compressive imaging system was proposed using metamaterial spatial light modulators. [28] With the introduction of active metasurfaces, the incident EM beam was manipulated artificially with improved signal-to-noiseIn the data-driven society, fidelity and accuracy of automatic decisions behind the scene rely fundamentally on a solid data or imaging acquisition system. However, conventional microwave imagers are inadequate relating to their resolution and noise capability, mainly due to the limited aperture size and rigid working principle. Here, a programmable metasurface imager with highresolution and anti-interference performance is proposed. By implementing the structure of multilayer perceptron n...