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.
针对羰基铁粉吸收剂在温度较高时易被氧化的问题,采用水热法制备了氧化锌包覆羰基铁粉核壳结构复合粒子,并分别将羰基铁粉和氧化锌/羰基铁粉核壳粒子与石蜡混合,制备复合材料。结果表明,氧化锌纳米棒致密的包覆在羰基铁粉颗粒表面形成海胆状核壳结构复合粒子,正是这种结构将羰基铁粉颗粒与空气隔绝,使得复合粒子的抗氧化性能得到显著改善。与羰基铁粉复合吸波材料相比,氧化锌/羰基铁粉核壳粒子的复合材料吸收峰稍向低频移动,反射损耗小于-5 d B的带宽几乎保持不变,在不改变电磁吸波性能的前提下,提高了羰基铁粉粒子的使用温度。
