In this paper,we propose a novel transmit/reflect switchable frequency selective surface(FSS)in millimeter wave band based on the effective medium theory under quasi-static limit,which is designed with square-hole elements cut from continuum dielectric plates.The building elements of the surface are composed of all dielectric metamaterial rather than metal material.With proper structural design and parameters tuning,the resonance frequencies can be tuned appropriately.The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface 90°,which means under different incident polarizations.The reflective response can be realized due to the effect of electric and magnetic resonances.Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances.And the transmitting response is the left-handed passband,arises from the coupling of the electric and magnetic resonances.In addition,effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses.The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.
A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band. Near-unity absorptions around 9.785 GHz, 11.525 GHz, and 12.37 GHz are observed for this metamaterial absorber. The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss. The mechanism for the near-unity absorption is investigated via the dielectric resonator theory. It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator. In addition, the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers. Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes.
We propose to achieve a high-efficiency wideband flat focusing reflector using metasurfaces. To obtain the wide band,the polarization conversion mechanism is introduced into the reflector design, based on the fact that the reflection phases of cross-polarized waves are linear in quite a wide band. This facilitates the design of wideband parabolic reflection phase profile. As an example, we design two reflective focusing metasurfaces with one- and two-dimensional in-plane parabolic reflection phase profiles based on elliptical split ring resonators（ESRRs）. Both the simulation and experiment verify the wideband focusing performance in 10.0–22.0 GHz of the flat reflectors. Due to the wide operating band, such reflectors have important application values in communication, detection, measurement, imaging, etc.
Deep sub-wavelength metamaterials are the key to the further development of practical metamaterials with small volumes and broadband properties. We propose to reduce the electrical sizes of metamaterials down to more sub-wavelength scales by lowering the plasma frequencies of metallic wires. The theoretical model is firstly established by analyzing the plasma frequency of continuous thin wires. By introducing more inductance elements, the effective electron mass can be enhanced drastically, leading to significantly lowered plasma frequencies. Based on this theory, we demonstrate that both the electric and the magnetic plasma frequencies of metamaterials can be lowered significantly and thus the electrical sizes of metamaterials can be reduced to more sub-wavelength scales. This provides an efficient route to deep sub-wavelength metamaterials and will give rigorous impetus for the further development of practical metamaterials.
