Mingde Feng

Broadband polarization rotator based on multi-order plasmon resonances and high impedance surfaces

We experimentally investigate the electromagnetic (EM) responses of a broadband reflective polarization rotator under normal incidence. It is found that the rotator can generate multi-order plasmon resonances at three neighboring frequencies. At each frequency, the rotator behaves as a high impedance surface along one axis while as a metallic reflective surface along the other axis. Thus, a 180° phase difference is generated between the two orthogonal components of reflected waves. When the incident wave is polarized by 45° with respect to the symmetry axis of the rotator, the polarization of reflected waves is rotated by 90°. The designed rotator presents broadband properties. It can perform perfect 90° polarization rotation at three frequencies and maintains a polarization conversion efficiency greater than 56% in 2.0–3.5 GHz. The rotator provides a route to broadband polarization rotation and has application values in polarization control.

Spatial k -dispersion engineering of spoof surface plasmon polaritons for customized absorption

Absorption of electromagnetic waves in a medium is generally manipulated by controlling the frequency dispersion of constitutive parameters. However, it is still challenging to gain the desired constitutive parameters for customized absorption over a broad frequency range. Here, by virtue of spoof surface plasmonic polaritons (SPPs), we demonstrate capabilities of the spatial k-dispersion engineering for producing the customized broadband absorption. Incident waves can be efficiently converted to the spoof SPPs by plasmonic arrays, and their propagation and/or absorption can be controlled by engineering the spatial dispersion of k-vector. Based on this feature, we show how such concept is employed to achieve broadband as well as frequency-selective broadband absorptions as examples. It is expected that the proposed concept can be extended to other manipulations of propagating electromagnetic waves over a broad frequency range.

k-dispersion engineering of spoof surface plasmon polaritons for beam steering

In this paper, we propose to achieve beam steering by k-dispersion engineering of spoof surface plasmon polaritons (spoof SPP) at microwave frequencies. The planar plasmonic metamaterials (PPMs) are employed to couple and guide spoof SPP. High-efficiency transmission based on spoof SPP coupling is realized via matching the wave-vectors of the spoof SPP and the space wave. The transmission phase can be modulated by k-dispersion engineering of the spoof SPP with great freedom. Due to the independent phase shift produced by the spoof SPP on the PPMs, the phase gradient achieved by using the PPMs as the sub-unit cells can be altered by changing the repetition period of the sub-unit cells. Two phase gradient materials (PGMs) are achieved by using nine different PPMs as the sub-unit cells with the repetition period q = 4mm and 4.5mm. Both the simulated and measured results demonstrated the excellent performances of the PGMs on high efficiency, wideband, tunable beam steering.

Symmetry-based coding method and synthesis topology optimization design of ultra-wideband polarization conversion metasurfaces

In this letter, we propose the synthesis topology optimization method of designing ultra-wideband polarization conversion metasurface for linearly polarized waves. The general design principle of polarization conversion metasurfaces is derived theoretically. Symmetry-based coding, with shorter coding length and better optimization efficiency, is then proposed. As an example, a topological metasurface is demonstrated with an ultra-wideband polarization conversion property. The results of both simulations and experiments show that the metasurface can convert linearly polarized waves into cross-polarized waves in 8.0–30.0 GHz, obtaining the property of ultra-wideband polarization conversion based on metasurfaces, and hence validating the synthesis design method. The proposed method combines the merits of topology optimization and symmetry-based coding method, which provides an efficient tool for the design of high-performance polarization conversion metasurfaces.

A Tri-Band, Highly Selective, Bandpass FSS Using Cascaded Multilayer Loop Arrays

A highly selective tri-band bandpass frequency-selective surface (FSS) is presented by cascading three layers of periodic arrays. The middle layer is composed of double square loops (DSLs) while the two exterior layers are composed of gridded-double square loops (G-DSLs) structure. The proposed FSS can provide multitransmission zeros which lead to a wide out-of-band rejection between each two adjacent passbands and sharp rejection behavior on both sides of each passband. Furthermore, the FSS exhibits stable response over a wide range of incident angles for both TE and TM polarizations. The design procedure, simulation, and experiment of the FSS are presented. The measured results are in good agreement with the simulations.

Achieving all-dielectric metamaterial band-pass frequency selective surface via high-permittivity ceramics

In this paper, we propose the design of all-dielectric metamaterial band-pass frequency selective surfaces (FSSs) using high-permittivity ceramics based on effective medium theory and dielectric resonator theory. The band-pass response can be determined by the permittivity of the dielectric material, the periodicity, and geometrical shape of the dielectric unit cell. As an example, a band-pass FSS composed of H shaped ceramic resonators is demonstrated. Both the simulation and experiment results show that the FSS can achieve a pass band in X-band. Since such FSSs are made of low-loss high-permittivity ceramics, they are of important application values, especially in high-temperature, high-power environments. The design method can be readily extended to the design of FSSs in other frequencies.

Achromatic flat focusing lens based on dispersion engineering of spoof surface plasmon polaritons

In this letter, we first analyze the dispersion relation for achromatic focusing and obtain the achromatic focusing conditions for discretized unit cells of flat lenses. Then, we propose to engineer the dispersion of spoof surface plasmon polaritons (SSPPs) to satisfy the achromatic focusing conditions. Metallic blades structures are utilized to achieve the linear dispersion response by tailoring the weak dispersion region of SSPPs. A broadband achromatic flat focusing lens (AFFL) is implemented with delicate combinations of the blade structures. A prototype was designed, fabricated, and measured. Both the simulated and experimental results demonstrate that the proposed AFFL can achieve achromatic focusing from 7.5 to 9.0 GHz under the normal incidence.

Electromagnetic wave absorption and compressive behavior of a three-dimensional metamaterial absorber based on 3D printed honeycomb

Lightweight structures with multi-functions such as electromagnetic wave absorption and excellent mechanical properties are required in spacecraft. A three-dimensional metamaterial absorber consisting of honeycomb and resistive films was proposed and fabricated through 3D printing and silk-screen printing technology. According to simulation and experiment results, the present three-dimensional metamaterial absorber can realize an absorptivity of more than 90% in a wide band of 3.53–24.00 GHz, and improve absorbing efficiency for transverse magnetic (TM) waves of oblique incidence angle from 0° to 70°. The compression test results reveal that compressive strength of the 3D printed honeycomb can reach 10.7 MPa with density of only 254.91 kg/m3, and the energy absorption per volume Wv and per unit mass Wm are 4.37 × 103 KJ/m3 and 17.14 KJ/Kg, respectively. The peak compressive strength and energy absorption per mass are at least 2.2 and 3 times comparing to metallic lattice cores with the same density. Outstanding electromagnetic wave absorption and mechanical performance make the present three-dimensional metamaterial absorber more competitive in engineering applications.

Extraordinary transmission of electromagnetic waves through sub-wavelength slot arrays mediated by spoof surface plasmon polaritons

One-dimensional gratings consisting of sub-wavelength metallic slot arrays have been widely applied in the design of novel devices due to their polarization-selective characteristics. When the incident electric field is polarized along the slot direction, the slot arrays are opaque, behaving like a metal surface. Here we propose a scheme of making slot arrays transparent for electromagnetic (EM) waves, which is achieved by the incorporation of corrugated metal strip arrays. Incident waves are first converted into spoof surface plasmonpolaritons (SSPPs) propagating along the strips. Since SSPPs confine EM fields in sub-wavelength scales, EM waves can penetrate through the sub-wavelength slots. High transmission was thus obtained, with an efficiency as high as 95%. Moreover, position and bandwidth of the transmission band can be tailored by adjusting the groove depth and the slot width, respectively. It is expected that the design may find potential applications in the multifunctional devices with frequency- and polarization-selective features.

A novel miniaturized dual-stop-band FSS for Wi-Fi application

In this paper, we propose a new miniaturized dual band frequency selective surface (FSS) for Wi-Fi applications. The proposed FSS possesses 0.42 GHz and 0.30 GHz bandwidths with insertion loss less than -15 dB around the two central operating frequencies 2.4 GHz and 4.6 GHz, respectively. The FSS exhibits excellent miniaturization with 0.057λ₁ × 0.057λ₁ or 0.11λ₂×0.11λ₂ unit cells, where λ₁ and λ₂ represent the free-space wavelengths of two operating bands. Furthermore, the unit cell structure provides a stable performance for both TE and TM polarizations under incident angles up to ±60°. A prototype of the proposed FSS is fabricated and measured. The measured results agree well with the simulated results.