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We demonstrate that a defect unit in periodic textured closed surfaces is able to trap spoof surface plasmons (SPs) into a deep subwavelength scale. The resonant frequency of a trapped spoof SP can be tuned freely by properly tailoring the dimension of the defect unit. By introducing multiple defect units with different dimensions at different positions of the textured closed surfaces, the spoof SPs with different frequencies trapped effectively at desired places are also demonstrated. In addition, we further design a graded defect structure with continuously variable dimensions to trap the spoof SPs over an ultrawide spectral band. The interval between the trapped waves on the closed surfaces can be tuned conveniently by changing the grade of the defect dimensions. The designer structures may indicate potential applications in the optical switch and storage in the microwave and terahertz frequencies.

Previous reflectionless metasurfaces based on balanced electric and magnetic responses in engineered resonant meta-atoms become ineffective at oblique incident angles and usually have strong reflection at grazing incidence, where the impedance becomes near-zero or divergent. Here, by introducing the concept of anomalous generalized Brewster effect to metasurfaces, we demonstrate an exceptional resonance-free Brewster metasurface that exhibits ultrabroadband zero reflection at grazing incidence. The anomalous generalized Brewster effect is obtained via combining the mechanisms of the generalized Brewster effect and the anomalous Brewster effect, which are both resonance-free and thus enable ultrabroadband functionalities. As a practical application, Brewster metasurfaces exhibiting ultrabroadband reflectionless perfect absorption at grazing incident angles are constructed and demonstrated by full-wave simulations and microwave experiments. Our work could enable reflectionless wave manipulation at grazing incidence with an ultrawide working bandwidth.

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Dynamically switchable light transmission/absorption functionality is highly desirable in sensing and functional devices. However, the operating bandwidth of the newly emerging schemes using resonant meta-structures is inherently limited. In this work, we design and numerically demonstrate a non-resonant tilted anisotropic metamaterial consisting of phase-change materials. When the phase transition of the phase-change material from amorphous phase to crystalline phase occurs, the functionality of the metamaterial can be switched from perfect transparency to perfect absorption for transverse-magnetic polarization under oblique incidence over a broad spectrum. Such a remarkable phenomenon originates in the anomalous Brewster effect, which enables broadband reflectionless transmission/absorption of light under the anomalous Brewster’s angle. Moreover, gradient metamaterials exhibiting dynamically controllable functionality for incident light with an almost arbitrary wavefront are demonstrated. The proposed metamaterials are simple but highly efficient, which may find applications in sensing and advanced and intelligent optical devices.