A systematic study of a robust angular tolerance ultra-broadband metasurface for arbitrary rotation of linear polarization is demonstrated. The proposed method combines the spin-dependent Pancharatnam-Berry phase and the generalized Snell’s law to achieve an arbitrary angle linear polarization rotator and beam splitter. Numerical results of one terahertz example show that a 90° polarization rotator has a polarization conversion ratio of more than 90% from 1.3 to 2.3 THz in the ultra-broadband range. This method represents a significant advance in versatile, flexible design and performance compared to previously reported birefringent material wave plates, grating structures, and multi-resonance-based polarization rotators.

The Luneburg lens is widely applied in both the optical and microwave regimes because it offers high gain and a wide beam-scanning range. However, Luneburg lens typically suffer from low efficiency which is caused by the dielectric loss of medium employed. To address this issue, we propose herein a general method for discretization of two-dimensional Luneburg lens based on correctional effective-medium theory. In discrete Luneburg, the efficiency is not dependent on the employed medium roughly because that the main component in the lens is air, resulting into a significant improvement of efficiency. Subsequently, a systemic study of lens discretization is presented, which is validated by a discrete Luneburg lens easily fabricated by using 3D printing. In addition, a novel wave-patch reduction feature allows the discrete lens to function as well. This work presents a fundamental theory for lens discretization, which is valid not only for the Luneburg lens but also for other types of lenses. It can be applied in imaging, antennas, or phase manipulation in both the optical and microwave bands.

Herein, we propose an approach for sensitivity improvement of dual-axis strain sensing using the property of a metasurface (MS) that the phase response shifts sharply with the MS deformation. A feasible approach for phase measurement is first demonstrated by calculating multi-polarized reception when the incident electromagnetic (EM) wave has anisotropic phase values. A flexible MS consisting of periodically arranged lantern-shaped elements is designed and fabricated for dual-axis strain sensing and evaluation based on the proposed method. The simulation and measurement results demonstrated a high sensitivity of the proposed MS for strain sensing in the microwave band. The method can be used potentially in both pressure and tensile sensing. Moreover, the operational frequency can be extended to the THz range and even to the optical band.

Frequency-selective surfaces (FSSs) have attracted great attention owing to their unique feature to manipulate transmission performance over the frequency domain. In this work, a filtering antenna-filtering antenna (FA-FA) FSS with a wide passband and double-side sharp roll-off characteristics is presented by inter-using the filtering antenna and receiving–transmitting metasurface methods. First, a dual-polarized filtering antenna element was designed by employing a parasitic band-stop structure with an L-probe feed. Then, the FA-FA-based FSS unit was constructed by placing two such filtering antennas back to back, with their feedings connected through metallic vias. Finally, the FSS with a wide passband and high selectivity was realized by arraying the FA-FA units periodically. The full-wave simulation results demonstrated that the designed FA-FA-based FSS had a wide passband from 13.06 GHz to 14.46 GHz with a flat in-band frequency response. The lower and upper roll-off bandwidths were sharp, reaching 1% and 1.2% of the center frequency. The proposed FA-FA-based FSS was fabricated and measured, achieving the coincident performance according to the theoretical prediction. The wideband band-pass FSS obtained a sharp double-side roll-off feature, which can be applied in various studies such as an antenna array, metasurface, communication, etc.

Metasurfaces (MSs) have been an effective method for the manipulation of electromagnetic (EM) radiation. However, this research mainly focused on controlling single-directional radiation. In this paper, a Fabry–Perot cavity (FPC) antenna based on the MSs technique is proposed, which obtains a bi-directional radiation with independent control of the forward and backward radiation patterns. The antenna is located in an FPC with two MSs forming the top and bottom surfaces. The MSs can partially reflect the x-polarized incident wave, i.e., it is a partially reflective metasurface (PRMS). Meanwhile, it can transform a specific incident component from x-polarization into y-polarization with a transmittance around −9.2 dB. In addition, the phase of the x-polarized reflection and y-polarized transmission can be controlled independently. So, a bi-directional radiation, of which the forward and backward radiation can be independently controlled, is obtained by the FPC antenna by manipulating the transmission phase distribution of the two PRMSs. As validation, two bi-directional radiation FPC antennas are designed based on the proposed method. Antenna 1 achieved a bi-directional single-beam radiation, of which the forward and backward radiation radiate to 2° and 177° with a gain of 13.4 dBi and 12.3 dBi, respectively. Antenna 2 achieved a bi-directional multibeam radiation, which radiates dual beams forward and a single beam backward. The two beams forward fire to 37° and 322° with a gain of 9.53 dBi and 9.3 dBi, while the beam backward fires to 178° with a gain of 7.8 dBi. At last, the first antenna is fabricated and measured for experimental validation, achieving the coincident results as simulation. This research can be potentially applied in research on antennas, communication, and wireless sensors in several practical scenarios, such as multibeam electromagnetic radiation, multi-user communication, multi-target monitoring, and sensor–communication system integration.

A broadband metamaterial (MM) absorber based on water droplets is proposed and investigated in this paper. The proposed MM absorber is composed of a periodic array of holes drilled in the dielectric substrate which are then filled with water droplets. The absorption property of such water absorber can be tuned by manipulating the volume of the water droplets. Through optimized design, a broadband water electromagnetic (EM) wave absorber is achieved in microwaves regime, which obtains 90% absorption efficiency across the frequency band from 7.63 to 14.94 GHz. The physical mechanism of the proposed MM absorber is investigated. The absorption performance of such MM absorber is verified through both full-wave simulation and experimental measurement which coincide with each other.