Metasurfaces have been extensively investigated due to their ability to tailor the amplitude, phase, and polarization of electromagnetic waves at subwavelength scales. However, most of the research has focused on planar metasurfaces. This has limited their applicability since curved geometries are required in numerous applications. In this article, wave propagation in the radial direction of cascaded, cylindrical structures is studied. The intent is to develop a synthesis method that enables designers to realize arbitrary scattering matrices with cascaded, azimuthally invariant metasurfaces (subwavelength patterned metallic claddings) and dielectric spacers. The proposed method exploits a wave matrix formulation, which relates the incident and scattered fields on one side of a scatterer to those on the other side. It combines the merits of the scattering matrix and ABCD matrix. Design examples are demonstrated using the proposed wave matrix design approach and verified through a commercial electromagnetic solver. The cascaded cylindrical metasurfaces studied in this article are expected to find use in various applications involving antenna beam steering, polarization manipulation, and hologram generation.

Lossless, reciprocal bianisotropic metasurfaces have the ability to control the amplitude, phase, and polarization of electromagnetic wavefronts. However, producing the responses that are necessary for achieving this control with physically realizable surfaces is a challenging task. Here, several design approaches for bianisotropic metasurfaces are reviewed that produce physically realizable metasurfaces using cascaded impedance sheets. In practice, three or four impedance sheets are often used to realize bianisotropic responses, which can result in narrowband designs that require the unit cells to be optimized in order to improve the performance of the metasurface. The notion of a metasurface quality factor is introduced for three-sheet metasurfaces to address these issues in a systematic manner. It is shown that the quality factor can be used to predict the bandwidth of a homogeneous metasurface, and it can also be used to locate problematic unit cells when designing inhomogeneous metasurfaces. Several design examples are provided to demonstrate the utility of the quality factor, including an impedance matching layer with maximal bandwidth and a gradient metasurface for plane wave refraction. In addition to these examples, several metasurfaces for polarization control are also reported, including an isotropic polarization rotator and an asymmetric circular polarizer.

A miniaturized absorptive frequency-selective surface (AFSS) allowing power transmission in other specific band is proposed in this paper. The via-based structure is adopted to make unit-cell size only 0.109λ₀ x 0.109λ₀, where λ₀ is the wavelength in free space at operating frequency. The maximum absorption rate of 99.3% locates at 5.45 GHz and half-power absorption ranges from 5.198 to 5.882 GHz, covering the whole 5-GHz Wi-Fi band. It also allows half-power transmission below 1.016 GHz. Furthermore, the absorption characteristic of the proposed AFSS is relatively stable under different backside materials, incident angles, and polarizations of incoming electromagnetic field. In addition, air vents, which are created to provide heat dissipation, make the proposed miniaturized AFSS a multifunction candidate for advanced packaging.

In recent years, there has been extensive research on planar metasurfaces capable of arbitrarily controlling scattered fields. However, rigorous studies on conformal metasurfaces, such as those that are cylindrical, have been few in number likely due to their more complex geometry and corresponding analysis. Here, wave propagation in cascaded cylindrical structures consisting of layers of dielectric spacers and azimuthally-varying metasurfaces (subwavelength patterned metallic claddings) is investigated. A wave matrix approach, which incorporates the advantages of both ABCD (transmission) matrices and scattering matrices (S matrices), is adopted. Wave matrices are used to model the higher-order coupling between metasurface layers, overcoming the fabrication difficulties associated with previous works. The proposed framework provides an efficient approach to synthesize the inhomogeneous sheet admittances that realize desired cylindrical field transformations. Design examples are reported to illustrate the power and potential applications of the proposed method in antenna design and stealth technology.

In this letter, a realistic coaxial feed is integrated into the design of cascaded cylindrical metasurfaces. This is in contrast to the fictitious current source that is often reported in literature. The $S$ -matrix of the coaxial feed is obtained by way of the mode-matching technique, which is subsequently combined with the $S$ -matrix of the cascaded cylindrical metasurfaces to account for the interaction between the feed and metasurfaces. The integration of a realistic feed into the design process enables practical cylindrical-metasurface-based devices.