Asymmetric Transmission in a Mie-Based Dielectric Metamaterial with Fano Resonance

Ultra-broadband and high-efficiency polarization conversion metamaterial based on a metal combination water structure

A linear-to-linear polarization conversion metamaterial is proposed with a water-metal structure. The simulation results show that the proposed metamaterial design can achieve ultra-broadband and high-efficiency polarization conversion within the frequency range from 7.46 GHz to 14.84 GHz with a polarization conversion ratio over 90%. This metamaterial exhibits sensitivity to the incidence angle but not to and temperature. The physical mechanism of polarization conversion is analyzed based on the distributions of the surface current and the magnetic field. An experimental sample of the designed metamaterial is fabricated, assembled, and measured in such a way as to realize reflective polarization conversion. This work provides a significant stepping stone for water-based metamaterial design and polarization control.

Microwave and Terahertz Properties of Spark-Plasma-Sintered Zr0.8Sn0.2TiO4 Ceramics

Zr_0.8Sn_0.2TiO₃ (ZST) powders synthesized by solid-state reaction were subject to processing by spark plasma sintering (SPS). A single-phase ceramic with a high relative density of 95.7% and 99.6% was obtained for sintering temperatures of 1150 °C and 1200 °C, respectively, and for a dwell time of 3 min. In order to reduce the oxygen vacancies, as-sintered discs were annealed in air at 1000 °C. The dielectric loss of the annealed samples, expressed by the Q × f product, measured in the microwave (MW) domain, varied between 35 THz and 50 THz. The intrinsic losses (Q × f ~ 60 THz) were derived by using terahertz time-domain spectroscopy (THz-TDS).

Single-layer metasurface for ultra-wideband polarization conversion: bandwidth extension via Fano resonance

In this paper, we propose a method of designing ultra-wideband single-layer metasurfaces for cross-polarization conversion, via the introduction of Fano resonances. By adding sub-branches onto the unit cell structure, the induced surface currents are disturbed, leading to coexistence of both bright and dark modes at higher frequencies. Due to the strong interaction between the two modes, Fano resonance can be produced. In this way, five resonances in all are produced by the single-layer metasurface. The first four are conventional and are generated by electric and magnetic resonances, whereas the fifth one is caused by Fano resonance, which further extends the bandwidth. A prototype was designed, fabricated and measured to verify this method. Both the simulated and measured results show that a 1:4.4 bandwidth can be achieved for both x- and y-polarized waves, with almost all polarization conversion ratio (PCR) above 90%. This method provides an effective alternative to metasurface bandwidth extension and can also be extended to higher bands such as THz and infrared frequencies.

Intrinsic Dielectric Loss in Zr0.8Sn0.2TiO4 Ceramics Investigated by Terahertz Time Domain Spectroscopy

Terahertz time-domain spectroscopy (THz-TDS) was employed for estimation of intrinsic dielectric loss of Zr_0.8Sn_0.2TiO₄ (ZST) ceramics. Single-phase ZST dielectric resonators (DRs) with various synthesis parameters and, consequently, different extrinsic losses, were prepared by conventional ceramic technology. Even though the DRs exhibit a similar microstructure, their quality factor (Q is the inverse of dielectric loss tangent) measured in microwave (MW) domain at 6 GHz varies between 2500 and 8400. On the other hand, it was found that the THz dielectric loss is less sensitive to the sample preparation. The intrinsic losses (Q × f ~60 THz) of the ZST ceramics have been derived from THz data.

Asymmetric transmission of linearly polarized waves based on Mie resonance in all-dielectric terahertz metamaterials

Interest in asymmetric transmission (AT) at terahertz frequencies has increased dramatically in recent years. We present an all-silicon metamaterial to achieve the AT effect for linearly polarized electromagnetic waves in the terahertz regime. The metamaterial is constructed by rectangular silicon pillars and a thick silicon substrate. The magnetic Mie resonance excited by the incident polarized terahertz wave contributes to the AT effect, which is verified by the field distributions. In addition, the rotation angle and dimensions of the silicon pillars are shown to have a great influence on the AT efficiency. The proposed metamaterial with straightforward design has promising applications in polarization control scenarios.