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.

In this paper, a nematic liquid crystal (NLC)-based tunable terahertz (THz) plasmonic metamaterials (MMs) with large modulation depth (MD) and low insertion loss (IL) is designed and experimentally verified at THz frequencies. The proposed structure includes two-layered MM that is immersed in LC. The metal MM is used directly as electrode. The tunable device with a 46×46 array of sub-wavelength circular air loops was fabricated on a quartz glass substrate, with 2×2 cm² area and 220 µm thickness. The obtained results show that the amplitude MD and IL for normally incident electromagnetic (EM) waves are about 96% and 1.19 dB at 421.2 GHz, respectively, when the bias voltage applied to the NLC layer varies from 0 to 16 V. Meanwhile, the transmission peak frequency gradually decreases from 421.2 to 381.8 GHz, and the frequency tunability (FT) of the proposed structure is greater than 9.35%. This study provides a potential solution for THz modulators, filters, and switches.

A metamaterial absorber and its application in liquid sensing is proposed in this paper. The unit cell of the sensor structure consists of two quartz substrates with metallic patterns and sheets printed on their surfaces. The liquid tunnel with optimal thickness is created by placing the glass micro-pearls between the quartz substrates. By incorporating dual semi-toroidal resonators, the enhanced spectral shift per refractive index unit (RIU) improves the sensitivity of the proposed design effectively, and sensitive frequency detection with 52.50 GHz/RIU is numerically demonstrated. Moreover, we experimentally demonstrate its application for determining ethanol and sucrose solutions with different concentrations and three commonly used oils. A good agreement with the experiments and simulations is obtained. In addition, the proposed sensor has the advantages such as compact size, easy fabrication, and reusability, which offers excellent potential in food industry applications.

In this article, an ultrabroadband electromagnetic wave absorber with wide angular stability is proposed. The absorber matrix is formed by multilayers of foams and resistive films with different patterns, and two dielectric matching layers are superimposed on the surface of the absorber to improve the absorption effect of the absorber in the case of oblique incidences. Simulations show that the absorptivity of the proposed design reaches more than 90% in the frequency range of 4.0–50.9 GHz, with a relative absorption bandwidth of 171%. In addition, when the incidence angle reaches 60°, the absorber absorbs more than 90% within the frequency band of 15.3–47.3 GHz and 11.3–52 GHz when transverse electric (TE-) and tra nsverse magnetic TM-polarized waves are incident, respectively. The broadband absorption mechanism of the absorber and the role of the dielectric matching layers on the stability of oblique incidence are analyzed, and samples are prepared and tested to validate the design. The ultra-broadband absorbing bandwidth and wide angular stability make the absorber potentially useful for energy absorption and radar scattering cross section reduction applications.

An electrically tuned phase shifter based on the single slot unit cell and liquid crystal for a reconfigurable reflectarray antenna was presented. The simulation and measured results obtained at the F-band were used to demonstrate that the dielectric properties of a nematic state liquid crystal could be exploited to realize a slot unit cell phase shifter for the reconfigurable reflectarrays antennas. By reducing the inhomogeneous of the external electric field in the liquid crystal layer, a lower control voltage and improved model accuracy was obtained. In the experiments test, the achieved saturation bias voltage (10 V) was smaller than the previously reported structure, and the phase shift of the reflectarray greater than 300° was achieved in the frequency range 121.5–126 GHz. The maximum phase shift of 306° occurred at 124.5 GHz.

This study presents the design and experiment of a terahertz reflective phase shifter based on liquid crystal. The proposed voltage‐tunable phase shifter takes advantage of the variable permittivity of the liquid crystal, adjusted by an external electric field, providing tunable reflective phase shift of terahertz (THz) waves. We analysed the performance of this phase shifter using a simple isotropic and homogeneous model considering the angle of incidence. The phase variation was achieved in a range greater than 360° and frequencies from 349 to 361 GHz. An array constituted of 900 patch elements was fabricated using the photolithographic process. It provided tunable phase range of 350° over the frequency range of 353.5–359.3 GHz at 40 V, where a maximum phase shift 362.6° was achieved at 357 GHz. The LC dielectric constant was obtained by fitting the computed reflectance spectrum to the measured result. We compared accurate model, considering both inhomogeneity and anisotropy of the liquid crystal, with the simplified model. In addition, the differences were analysed between the measurements, accurate and conventional model. The results show the liquid crystal phase shifter is great for beam scanning antenna array in THz.