We present a broadband and polarization-insensitive metamaterial absorber (MA) composed of a dielectric substrate sandwiched with double-circle rings (DCRs) and welded with lumped resistances and continuous metal film. The structure is designed with thickness of 3 mm and investigated by simulation, fabrication, and experiment. The results show that the composite MA loaded with lumped resistances has wider absorptivity compared with a structure with only DCRs. The simulation results indicate that the proposed absorber achieves 7.60-GHz-wide absorption from 8.87 GHz to 16.47 GHz with absorptivity greater than 90%, in excellent agreement with experimental results. Further simulations indicate that there exist optimal values for the lumped resistances for which the absorptivity is the highest and the bandwidth widest. Additionally, the proposed MA is polarization insensitive at normal incidence. Simulation results for wide angles of incidence of both transverse electric and transverse magnetic waves are also investigated.

A new relaxor ferroelectric ceramics, Sr 4 CaBiTi 3 Nb 7 O 30, were prepared. The microstructure, morphology, dielectric, and ferroelectric properties were studied. The ceramics were found that growing in some directions preferentially. Two dielectric relaxations were observed below the Burns temperature T B = 460 K and relaxation-I can be described by the VogelFulcher law. The Curie-Weiss constant (C) of 1.33 3 10 5 K confirms the displacive-type ferroelectric phase transition. The ceramics exhibit the first-order diffuse ferroelectric phase transition feature. The diffusion exponent varies from 1.99 to 1.92 with different applied frequencies. Room-temperature (RT) polarization was evaluated, and P r = 2.6 lC/cm 2, E c = 15.2 kV/cm values were obtained. The high breakdown voltage (≥80 kV/cm) and low leakage current confirmed the high quality of Sr 4 CaBiTi 3 Nb 7 O 30 ceramics. All of these features suggest that Sr 4 CaBiTi 3 Nb 7 O 30 may be used to substitute lead-based relaxor ferroelectric materials for environmental friendly. Raman spectra and polarization measured at different temperatures attribute the high-and low-temperature dielectric relaxation to flipping and breathing of polar nanoregions, respectively.

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Polycrystalline Ni(Cr1−xMnx)2O4 (0.1 ≤ x ≤ 0.325) ceramic samples were studied through different protocols of dc magnetization measurements. The samples exhibit 2 kinds of magnetic compensation effects below the ferrimagnetic transition temperature TC. Remarkable magnetization reversal is observed between the 2 compensation temperatures Tcomp1 and Tcomp2, which is regarded as arising from the negative exchange coupling between the 2 magnetic sublattices at different crystallographic sites. The magnetization is reversed at TSR due to spin‐reorientation caused by magnetostructural coupling. The spin‐reorientation is supported by Mn substitution and TSR is increased to 96 K when x reaches 0.325. However, it is suppressed due to the strong ionic site preference and thus the magnetization is slightly increased in the negative direction of the magnetic field. Near the 2 compensation temperatures, tunable magnetic switching effects can be obtained just by changing the magnitude of the applied magnetic field. Moreover, both normal and inverse magnetocaloric effects were also demonstrated.