We design an ultra-thin multi-band polarization-insensitive metamaterial absorber (MMA) using a single circular sector resonator (CSR) structure in the microwave region. Simulated results show that the proposed MMA has three distinctive absorption peaks at 3.35 GHz, 8.65 GHz, and 12.44 GHz, with absorbance of 98.8%, 99.7%, and 98.3%, respectively, which agree well with an experiment. Simulated surface current distributions of the unit-cell structure reveal that the triple-band absorption mainly originates from multiple-harmonic magnetic resonance. The proposed triple-band MMA can remain at a high absorption level for all polarization of both transverse-electric (TE) and transverse-magnetic (TM) modes under normal incidence. Moreover, by further optimizing the geometric parameters of the CSRs, four-band and five-band MMAs can also be obtained. Thus, our design will have potential application in detection, sensing, and stealth technology.

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Abstract-In this paper, a bi-layer twisted split-ring structure asymmetric chiral metamaterial was proposed, which could achieve circularly polarized (giant circular dichroism effect) wave with dual bands and linear polarization transformation (giant optical activity) with asymmetric transmission wave emissions simultaneously from linearly polarized incident wave at microwave frequencies. Experiment and simulation calculations are in good agreement, indicating that the dual-band circular polarizer features high conversion efficiency around 5.32 GHz and 6.6 GHz in addition to large polarization extinction ratio of more than 16 dB, while cross linear polarization transformation with asymmetric transmission is observed around 10.52 GHz. The transformation behavior for both circular and linear polarizations could be further illustrated by simulated surface current and electric field distributions. The proposed asymmetric chiral metamaterial structure could be useful in designing novel EM or optical devices, as well as polarization control devices.

In this paper, a chiral metamaterial (CMM) with triple-layer twisted split-ring resonators structure was proposed, which could exhibit a linear polarization conversion as well as asymmetric transmission only for forward and backward propagating linearly polarized waves in a broadband frequency range. The polarization of broadband linearly polarized electromagnetic waves can be rotated in a specific direction by passing it through such a CMM slab with a thickness of about one-twelfth the operational center wavelength. Experiment and simulation calculations are in good agreement, and the polarization conversion rate is above 90% in the frequency range of 5.5-11.1 GHz. The physical mechanism of the broadband linear polarization conversion effect could be further illustrated by simulated electrical field and surface current distributions.

We present a simple design for a broadband tunable terahertz (THz) metamaterial absorber (MMA) consisting of a complementary cross-oval-shaped graphene (CCOSG) structure and dielectric substrate placed on a continuous metal film. Both numerical simulation and theoretical calculation results indicate that the absorbance is greater than 80% from 1.2 to 1.8 THz, and the corresponding relative bandwidth is up to 40%. Simulated electric field and power loss density distributions reveal that the broadband absorption mainly originates from the excitation of continuous surface plasmon resonance (SPR) on the CCOSG. In addition, the MMA is polarization-insensitive for both transverse-electric (TE) and transverse-magnetic (TM) modes due to the geometry rotational symmetry of the unit-cell structure. Furthermore, the broadband absorption properties of the designed MMA can be effectively tunable by varying the geometric parameters of the unit-cell and chemical potential of graphene. Our results may find promising applications in sensing, detecting, and optoelectronic-related devices.