Search

Harmonic generation and utilization are significant topics in nonlinear science. Although the progress in the microwave region has been expedited by the development of time‐modulated metasurfaces, one major issue of these devices is the strong entanglement of multiple harmonics, leading to criticism of their use in frequency‐division multiplexing (FDM) applications. Previous studies have attempted to overcome this limitation, but they suffer from designing complexity or insufficient controlling capability. Here a new space‐time‐coding metasurface (STCM) is proposed to independently and precisely synthesize not only the phases but also the amplitudes of various harmonics. This promising feature is successfully demonstrated in wireless space‐ and frequency‐division multiplexing experiments, where modulated and unmodulated signals are simultaneously transmitted via different harmonics using a shared STCM. To illustrate the advantages, binary frequency shift keying (BFSK) and quadrature phase shift keying (QPSK) modulation schemes are respectively implemented. Behind the intriguing functionality, the mechanism of the space‐time coding strategy and the analytical designing method are elaborated, which are validated numerically and experimentally. It is believed that the achievements can potentially propel the time‐vary metasurfaces in the next‐generation wireless applications. [ABSTRACT FROM AUTHOR]

Hand gesture plays an important role in many circumstances, which is one of the most common interactive methods in daily life, especially for disabled people. Human–machine interaction is another popular research topic to realize direct and efficient control, making machines intelligent and maneuverable. Here, a special human–machine interaction system is proposed and namedas computer‐vision (CV) based gesture‐metasurface interaction (GMI) system, which can be used for both direct beam manipulations and real‐time wireless communications. The GMI system first needs to select its working mode according to the gesture command to determine whether to perform beam manipulations or wireless communications, and then validate the permission for further operation by recognizing unlocking gesture to ensure security. Both beam manipulation and wireless communication functions are validated experimentally, which show that the GMI system can not only realize real‐time switching and remote control of different beams through gesture command, but also communicate with a remote computer in real time by translating the gesture language to text message. The proposed non‐contact GMI system has the advantages of good interactivity, high flexibility, and multiple functions, which can find potential applications in community security, gesture‐command smart home, barrier‐free communications, and so on. [ABSTRACT FROM AUTHOR]

Metasurfaces with spin‐selective reflection or transmission functions for circularly‐polarized (CP) incident waves have aroused researchers' great attention. However, current spin‐selective metasurface designs have yet to mature into a practical method due to the limitations of single operating band or inefficient phase modulation. Herein, a novel chiral meta‐atom is proposed, exhibiting spin‐selective absorption/reflection functions for dual‐orthogonal CP incident waves at three different operating bands. More significantly, the Pancharatnam–Berry phase theory is introduced at all working frequencies to generate a full 2π reflection phase modulation by rotating the chiral resonator, and the three distinct absorption bands remain almost constant with the rotation. Theoretical results indicate that high absorption can separately act on left‐handed or right‐handed CP incident waves at triple bands, and meanwhile, the other incident wave with different handedness is efficiently reflected without changing the handedness. As a proof of concept, two tri‐band meta‐devices with spin‐selective anomalous reflection and spin‐selective orbital angular momentum generating functions are designed and experimentally characterized, both of which exhibit excellent spin‐dependent bi‐functional performances at three different operating bands. The research results provide a promising route to realize spin‐selective meta‐devices with multi‐band operating modes in wireless communication systems and multispectral imaging and information encryption fields. [ABSTRACT FROM AUTHOR]

In recent years, frequency‐multiplexed metasurfaces have received extensive attention due to the increasing demands for device integration and communication capacity. However, most of previously reported works can only manipulate either surface waves (SW) or spatially propagating waves (SPW). In this paper, a frequency‐multiplexed holographic‐reflective‐integration (HRI) coding metasurface is proposed, which can independently manipulate SW and SPW at different frequencies with a shared aperture. To be specific, the metasurface can act as a holographic metasurface to manipulate SW at low frequency and a reflective metasurface to manipulate SPW at high frequency. The performance of the frequency‐multiplexed HRI coding metasurface is validated by matched simulation and measurement results of versatile wavefront and polarization manipulations. Due to the advantages of low profile, high aperture usage, and multifunction integration, the proposed frequency‐multiplexed HRI coding metasurface is promising to be applied in wireless communications, radar detections, and holographic technology. [ABSTRACT FROM AUTHOR]

Programmable and information metasurfaces have shown great potentials in wireless communications, but there are few reports on encrypted communications. In this paper, a programmable polarization‐modulated (PoM) information metasurface is proposed, which can not only customize arbitrarily linearly polarized reflected waves, but also modulate their amplitudes in real time. Based on this feature, a physical‐level wireless communication encryption scheme is presented and experimentally demonstrated by introducing a meta‐key, which can be encrypted and sent by the programmable PoM information metasurface. To be specific, the key is encoded and concealed into different linear polarization channels, and then modulated and transmitted by the information metasurface at the transmitting end. At the receiving end, the modulated signal can be received and decoded by using a pair of polarization discrimination antennas. A wireless transceiver system is established to verify the feasibility of the scheme. It is shown that, once the meta‐key is obtained, the corresponding encrypted target information that has been sent to the user in advance can be recovered. [ABSTRACT FROM AUTHOR]

In order to enhance channel capacity in modern wireless communications, diverse multiplexing techniques, such as polarization, frequency, and spatial multiplexing, are proposed and implemented. Here, a non‐interleaved polarization‐frequency multiplexing metasurface is proposed, which can realize independent controls of orthogonal linearly polarized or circularly polarized waves in two frequency bands to achieve four independent information channels. As a proof of concept, the metasurfaces that can independently realize four different polarized holographic images in two frequency bands are designed, simulated, and measured. The results show that two orthogonally polarized holographic images are achieved in each frequency band, respectively, which can be either linear or circular polarization. Benefitting from the advantages of non‐interleaved design, the proposed metasurfaces can reach not only high information capacity but also high information density by taking full use of the metasurface apertures. [ABSTRACT FROM AUTHOR]