A broadband metamaterial absorber with a single layer of tantalum nitride (${\mathrm{Ta}}_2{\mathrm{N}}_3$) frequency selective surface layer, printed on a foam substrate, is presented. The proposed design has been numerically examined at the terahertz region. The results have shown that a wideband absorption with absorptivity greater than 90% was achieved in the frequency range 1.17–2.99 THz, and the relative absorption bandwidth was up to 112.97%, which is significantly better than previously reported results. Moreover, the absorber was independent of wave polarization, and a high absorption for a wide range of oblique incidence was achieved. The surface current distribution, the electric field distributions, and the power loss analyses were used to explain the physical mechanism of a wideband absorption. However, the tantalum nitride layer has an important role in the energy absorption. According to the obtained results, the proposed absorber, which is compact and simple to design, has a potential application in evolving broadband terahertz absorbers and sensors.

A liquid crystal based dual-band tunable metamaterial absorber with frequency tunability of 2.45% and 3.65% is realized in the terahertz region.

In this work, an ultra-broadband and polarization-insensitive metamaterial absorber (MA) with high optical transparency is presented. Indium-tin-oxide (ITO) films are used as frequency selective surfaces in multiple conductive layers and also as the reflective backplane. Numerical simulation analysis demonstrates that the absorptivity of the proposed absorber exceeds 90% in the frequency range from 10 to 75.5 GHz, corresponding to a relative absorption bandwidth of 153%. The proposed structure has a total thickness of 2.9 mm, which is approximately 1/10 of the free space wavelength of its lowest operating frequency. The absorber also has good polarization insensitivity due to its symmetric geometry. Moreover, for TE-polarized waves, the proposed absorber can maintain an absorptivity greater than 70% for frequencies ranging from 10 to 80 GHz as the incident angle is increased to 45°. For TM-polarized waves, it provides absorptivity of more than 80% at incident angles up to 60°. Surface current distribution on each conductive ITO layer was simulated to analyze the absorption mechanism of the MA. A prototype composed of 16 × 16 unit cells was fabricated and the experimental results show a good agreement with the numerical simulations. Due to its ultra-wideband absorption and wide-incident-angle stability, the proposed MA has potential value in electromagnetic applications such as optically transparent EM shielding and microwave radiation protection.

An ultrathin and flexible metamaterial absorber (MA) with triple absorption peaks is presented in this paper. The proposed absorber has been designed in such a way that three absorption peaks are located at 8.5, 13.5, and 17 GHz (X and Ku bands) with absorption of 99.9%, 99.5%, and 99.9%, respectively. The proposed structure is only 0.4 mm thick, which is approximately 1/88, 1/55, and 1/44 for the respective free space wavelengths of absorption frequency in various bands. The MA is also insensitive due to its symmetric geometry. In addition, the proposed structure exhibits minimum 86% absorption (TE incidence) within 60° angle of incidence. For TM incidence, the proposed absorber exhibits more than 99% absorptivity up to 60° incidence. Surface current and electric field distributions were investigated to analyze the mechanism governing absorption. Parameter analyses were performed for absorption optimization. Moreover, the performance of the MA was experimentally demonstrated in free space on a sample under test with 20 × 30 unit cells fabricated on a flexible dielectric. Under normal incidence, the fabricated MA exhibits near perfect absorption at each absorption peak for all polarization angles, and the experimental results were found to be consistent with simulation results. Due to its advantages of high-efficiency absorption over a broad range of incidence angles, the proposed absorber can be used in energy harvesting and electromagnetic shielding.

A novel approach for dual-polarized Liquid Crystal (LC) unit cell design is introduced, allowing significant thickness reduction of a LC layer without compromising its loss and phase shift. For each unit cell, LC is used for a tunable superstrate between a cross patch above and a square patch below. The square and cross patches are coupled through two slots for each polarization. By changing the voltage applied to the square and cross patches, the LC in-between varies the resonant frequency and phase of the unit cell to realize 2D beam steering. 10×10 dual-polarized reflectarray (RA) with 30 μm (0.0028 λ) and 4 μm (3.73×10 ^-4 λ) thick LC layers are simulated in the 28 GHz band, where the aperture efficiencies (AE) are 25.3% and 22.5%, respectively. As a proof of concept, the dual-polarized RA with 30 μm thick LC is fabricated manually and measured at 28.5 GHz. A measurement technique is proposed to obtain the phase curves of the RA and reduce the effect of fabrication errors. With the imperfect manual fabrication, the RA still achieves the measured realized gain of 14.6 dBi corresponding to 12.5% AE. Besides, ±45° beam steering is demonstrated in the 2D plane for both polarizations.

A tunable metamaterial absorber based on the liquid crystal intended for F frequency band is presented. The proposed absorber was analyzed both numerically and experimentally. The conducted analysis has shown that the bias voltage affects the orientation of the nematic liquid crystal embedded in the mesh voids and causes the resonant frequency shift from 110.9 to 103.8 GHz with the frequency tunability of 6.4%. The absorptivity of the proposed absorber was measured, and it was higher than 90% for all bias voltages. Therefore, the proposed absorber provides a new opportunity in development of tunable sensors and absorbers.