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Full-space metasurfaces demonstrate powerful abilities in manipulating electromagnetic (EM) waves, but most of them are usually single band. Here, a multiband bidirectional digital coding metasurface is proposed for multiple tasks, which can achieve completely different functions in up to six frequency bands when the EM waves are incident from the front and back of the metasurface. As a proof-of-concept, we design and fabricate a dual-band full-space metasurface with integrated functions of reflection, transmission, holographic imaging, and vortex-beam forming, and a six-band full-space metasurface with completely independent holographic imaging functions at different frequency bands. Simulated and measured results are in good agreements with the theoretical predictions, verifying the good performance of the proposed multitask bidirectional digital coding metasurface.

Vectorial structured beam, which possesses diverse inhomogeneous spatial field distributions, has been developed into an advanced technology for particle trapping, optical communication, and quantum information. However, most of the related studies are based on static devices that can only generate structured light with fixed field distributions. To break through this restriction, the study proposes and experimentally demonstrates a reflection‐type spin‐independent programmable metasurface (SIPM) that can generate arbitrary vector vortex beams (VVBs) dynamically in microwave frequencies. By controlling the working states of loaded positive‐intrinsic‐negative (PIN) diodes, the metasurface can realize real‐time and spin‐independent manipulations of amplitude and phase of the reflected waves. Therefore, any desired VVBs can be achieved by dynamically controlling the superimposition of left‐ and right‐handed reflected circularly polarized vortexes. The proposed SIPM exhibits powerful abilities in modulating the vectorial structured beams in the microwave band, and may bring potential technological innovations for the future spintronics, imaging display, optical computing, and wireless communications. [ABSTRACT FROM AUTHOR]

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]

In this paper, an ultrabroadband linear array in which horn‐reflector antennas are used as radiating elements by adding a central ridge to the rectangular waveguide, leading to an increased bandwidth of 3:1. With a reflector embedded in the H‐plane sectoral ridged horn, a desired narrow beam can be easily achieved. Moreover, due to the compact enclosed structure, the proposed reflector array can not only eliminate the illumination loss but also significantly reduce size compared with those of conventional array‐fed parabolic cylinder antennas. Good agreement between the calculated and measured results is obtained, showing that the proposed antenna array has a high aperture efficiency of about 80%, a ±45° scanning range in the E‐plane and 5° beam coverage with low side lobes in the H‐plane within the frequency range of 6–18 GHz. [ABSTRACT FROM AUTHOR]

In recent years, manipulations of amplitudes and phases of circularly polarized (CP) waves using metasurfaces have attracted significant attention. However, most of the current works are limited to operating in reflection or transmission space, and the amplitude manipulations are mainly achieved through polarization conversion or resistive loss, which will inevitably lead to cross‐polarization pollution and energy waste. Here, a transmission–reflection‐integrated metasurface that can manipulate the amplitudes and phases of the CP waves simultaneously in full space, which can not only realize arbitrary amplitude allocation of transmitted and reflected CP waves but also independently manipulate their phase responses is proposed. As proofs of concept, two integrated metasurfaces are designed and demonstrated, including a CP reflectarray antenna with simultaneously low side‐lobe level and low cross‐polarization level, and a meta‐grating that can arbitrarily control the intensity of transmitted diffraction wave while focusing the reflected wave. Both simulated and measured results agree very well with the theoretical predictions, demonstrating the powerful ability of the proposed metasurface to control the CP waves in full space, which is promising to be applied in future satellite communications, photonic meta‐devices, and so on. [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]

A simple guided-mode resonance filter composed of a single layer of molybdenum disulfide (MoS 2), a dielectric grating, and a dielectric substrate is designed to enhance light absorption in the visible range. The absorption characteristics of the system are investigated and analyzed by using the rigorous coupled-wave analysis method and the slab waveguide theory. The results reveal that the high absorption over 65% can be obtained for TE polarization and over 53% for TM polarization. Intriguingly, the structure exhibits an ultranarrow absorption bandwidth under TM polarization, the full width at half maximum is only 0.51 nm, and the quality factor can be more than 1200. In addition, multichannel absorption can be realized by increasing the thickness of the grating layer. The resonant wavelength can be dynamically selected by merely tuning the incident angle. The proposed device with its simple design can be applied to enhance the absorption of other two-dimensional materials. [ABSTRACT FROM AUTHOR]

Spin‐decoupled metasurfaces can realize independent phase controls of two orthogonally circularly polarized (CP) waves, and hence have attracted much attention in recent years. However, all previously reported metasurfaces capable of simultaneously manipulating the transmission and reflection of CP waves can only achieve two decoupled polarization conversion channels. In this work, a spin‐ and space‐multiplexing metasurface is proposed, that can achieve independent phase controls of four different CP conversion channels, including two cross‐polarized transmission channels and two co‐polarized reflection channels. The performance of the metasurface is experimentally validated by multi‐channel independent holographic imaging. The results show that four independent holograms are realized in four CP conversion channels by only using a single metasurface, which can greatly improve the information capacity of the metasurfaces and make full use of polarization and space resources. [ABSTRACT FROM AUTHOR]

This paper presents a novel compact meta-structure, which is characterized by left-handed properties. In the novel structure, two linear arrays of metallic vias and short-stub inductors are used to generate shunt inductors besides the series interdigital capacitors. Compared with conventional composite right/left-handed transmission-line structures, the new structure has weaker coupling to other components and is easily controlled by adjusting the shunt inductance and series capacitance to produce different left-handed properties. Due to the isolation of two via arrays, the proposed structure can also be transplanted directly from the microstrip system to the coplanar-waveguide system. We have proposed an efficient procedure to retrieve the equivalent propagating modes for both forward and backward waves based on the matrix pencil method, which provides an easy way to study the propagation characteristics. Using such a meta-structure, a series of super-wide bandpass filters are designed and fabricated at different frequency bands. Good agreements between simulation and experiment results have been achieved, and good performance in passbands and stopbands has been observed with a relative 3-dB bandwidth larger than 70%. For easy design of such super-wide bandpass filters, an experienced formula is given between the physical size and the center frequency of the 3-dB passband, which can be used to redesign any filters at other frequency bands. Index Terms--Composite right/left-handed (CRLH) transmission line (TL), matrix pencil method, meta-structure, propagating mode, super-wide bandpass filter.