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Metasurfaces based on the Pancharatnam–Berry (PB) phase have attracted significant attention in the domains of subwavelength optics and electromagnetics. Conventional theory predicts that the PB phase is exactly twice the rotation angle of the anisotropic meta-atoms. Differently, a recent advance has demonstrated that the generalized PB phase representing multiple times of the rotation angle could be obtained with high-fold rotational symmetry meta-atoms, but it suffers from the low cross-polarization conversion efficiency (the theoretical upper limit of 25%) that impedes its further applications, especially for meta-atoms with rotational symmetry ≥3. Here, we verify that the chiral meta-atoms with high-fold rotational symmetries could produce the generalized PB phase. Besides, the all-metallic configuration is utilized to design C2, C3, and C5 chiral catenary meta-atoms to improve their efficiency and bandwidth. The equivalent air waveguide with low loss between two adjacent meta-atoms is formed to analyse the higher performances of the all-metallic scheme for the realization of the generalized PB phase compared with the metal–insulator–metal and all-dielectric C3 meta-atoms. As a proof of concept, four metadevices including two spin-Hall metadevices and two holograms are experimentally demonstrated and their maximum efficiency could exceed 83% in simulation. This work could provide a high-efficiency platform for the study of the generalized PB phase in linear and nonlinear optics.

Terahertz (THz) absorbers have attracted considerable attention due to their potential applications in high-resolution imaging systems, sensing, and imaging. However, the limited bandwidth of THz absorbers limits their further applications. Recently, the dispersion management of metasurfaces has become a simple strategy for the bandwidth extension of THz devices. In this paper, we used the capability of dispersion management to extend the bandwidth of THz absorbers. As a proof-of-concept, a dual metasurface-based reflective device was proposed for broadband near-unity THz absorber, which was composed of two polarization-independent metasurfaces separated from a metallic ground by dielectric layers with different thickness. Benefiting from the fully released dispersion management ability in adjusting the dimensions of the metasurfaces, we obtained an absorbance above 90% in the frequency range from 0.52 to 4.4 THz and the total thickness for the bandwidth approaching the theoretical Rozanov limit. The experimental results verified the ability of dispersion management in designing broadband absorbers and the performance of the designed absorber. The underlying physical mechanism of dispersion management was interpreted in the general equivalent circuit theory and transmission line model. In addition, the catenary optical model was used to further interpret the physics behind this dual metasurface. Moreover, we found that the alignment deviations between the dual metasurface had little impact on the performance of the designed absorber, which indicates that the dual-metasurface does not require center alignment and is easy to be fabricated. The results of this work could broaden the application areas of THz absorbers.

Structural colors emerge when a particular wavelength range is filtered out from a broadband light source. It is regarded as a valuable platform for color display and digital imaging due to the benefits of environmental friendliness, higher visibility, and durability. However, current devices capable of generating colors are all based on direct transmission or reflection. Material loss, thick configuration, and the lack of tunability hinder their transition to practical applications. In this paper, a novel mechanism that generates high-purity colors by photon spin restoration on ultrashallow plasmonic grating is proposed. We fabricated the sample by interference lithography and experimentally observed full color display, tunable color logo imaging, and chromatic sensing. The unique combination of high efficiency, high-purity colors, tunable chromatic display, ultrathin structure, and friendliness for fabrication makes this design an easy way to bridge the gap between theoretical investigations and daily-life applications.

Nickel cobalt sulfide is a promising electrode material for high-performance energy storage devices but it still suffers from inferior electrical conductivity. Here highly graphitized carbon dots (GCDs, diameter is 10–20 nm) were synthesized by propane pyrolysis via the chemical vapor deposition method. The GCDs are applied to improve the electrical conductivity of Ni2CoS4 and also make Ni2CoS4 nanoparticles smaller, and then a Ni2CoS4/GCD composite was prepared through microwave assisted heating followed by solvothermal methods. The Ni2CoS4/GCD composite exhibits an extremely high specific capacitance of 2450 F g−1 at a current density of 5 A g−1, an outstanding rate performance of 90% when the current density increases from 5 A g−1 to 30 A g−1, and an exceptional cycling stability of 96.3% at a current density of 30 A g−1 after 2000 cycles. Furthermore, an asymmetric supercapacitor assembled using the Ni2CoS4/GCD cathode and the activated carbon anode provides a promising energy density of 57.3 W h kg−1 at a power density of 491.0 W kg−1. Meanwhile, after 8000 cycles at a current density of 10 A g−1, 90% of its initial specific capacitance can be maintained and excellent stability is achieved. The ultra-high specific capacitance, excellent ratio capability, and outstanding cycling stability of the Ni2CoS4/GCD composite are due to the high intrinsic theory capacitance of Ni2CoS4 as well as the unique properties of small particles and excellent conductivity of GCDs. Therefore, this composite delivers great prospects for applications in the energy storage field. [ABSTRACT FROM AUTHOR]

The corrosion of rebars will change the mechanical properties of the reinforced concrete structure, leading to the decline in the structural strength, which seriously threatens the safety and stability of buildings and power equipment foundations. Hence, it is of great significance to detect the internal corrosion of reinforced concrete structures. In this paper, a nondestructive detection method for detecting the corrosion in reinforced concrete structures based on microwave was proposed, and the corrosion state of rebar can be evaluated by the change of microwave information. Compared with other detection methods, microwave nondestructive detection has the advantages of low energy consumption, strong penetration, no contact, and small equipment volume and weight. In order to verify the effectiveness of the method, a microwave nondestructive detection simulation test platform was built and reinforced concrete test models with different corrosion lengths and depths were made. The influences of concrete parameters, the microwave frequency, and the lifting distance of the waveguide were analyzed. The frequency sweeping and moving scanning detection methods of the waveguide were carried out for the test models with different corrosion defects, and the changes of microwave S-parameters under different corrosion defects were obtained. The results show that when the waveguide is placed horizontally by the frequency sweeping detection method, the corrosion length detection effect of rebar is better. When the waveguide is placed vertically by the frequency sweeping detection method, the corrosion depth can be identified and the amplitude of transmission coefficient increases with the increase in the corrosion depth. The corrosion length of rebars can be identified quantitatively by the moving scanning detection method of the waveguide. [ABSTRACT FROM AUTHOR]