In order to verify the feasibility of three-dimensional (3D) printing technology in preparing the metamaterial absorbers with complex structure, a three-layer broadband absorbing metamaterial is designed and fabricated by 3D printing technology. The surface layer and middle layer of the metamaterial are composed of periodic arrays with different unit dimensions and the bottom layer of a slab structure. The optimized thickness of the metamaterial is 4.7 mm. A composite absorbent which consists of carbonyl iron powder and nylon is used to fabricate the absorber. In experiment, the obtained absorber is vertically irradiated by an electromagnetic (EM) wave. Two strong absorption peaks at 5.3 GHz and 14.1 GHz are achieved, with the reflection losses of -15.1 dB and -12.5 dB, respectively. The superposition of the two absorption peaks results in a reflection loss below -10 dB in a range from 4 to 18 GHz. The effective EM parameters of the surface layer and the middle layer are calculated by the S parameter inversion method. An effective model of the three-layer structure absorber is proposed and its reflectivity is calculated by using a multilayer structure reflectivity formula. The calculated reflectivity agrees well with the measured one. The absorbing and resonance mechanisms of the two absorption peaks are investigated by analyzing the dynamic distributions of power density loss, electric field and magnetic field. It can be clearly confirmed that the reflection losses at 5.3 GHz and 14.1 GHz are primarily concentrated on the bottom layer and surface layer, and the broadband absorption performance can be derived from the superposition of broadband absorptions of the three absorbing layers. Meanwhile, the strong electric coupling effect between the adjacent units in the surface layer is demonstrated by analyzing the electric-field distributions, which indicates that the strong reflection loss at 14.1 GHz is mainly caused by the electric response. The multiple scattering effects among the three layers are also considered according to the magnetic field distributions at two resonance frequencies. It is shown that there are two magnetic responses at 5.3 GHz and 14.1 GHz, respectively, and the multiple scattering contributes to increasing the EM wave propagation distance and enhancing the power loss. The designed absorbing metamaterials in this paper achieve good broadband absorption performances, particularly in the low frequency band. Combined with 3D printing rapid technology, a promising route to constructing 3D absorbing metamaterials with complex structures is proposed, which would be of great significance and broad practical prospect.

Single crystals of two hybrid organic-inorganic molecular solids, benzyl pyridinium tetra(isothiocyanate)cobalt ([BzPy]₂[Co(NCS)₄]) (1) and benzyl quinolinium tetra(isothiocyanate)cobalt ([BzQl]₂[Co(NCS)₄]) (2), were grown using a slow evaporation growth technique at room temperature and their IR, UV-Vis, X-ray crystal structures, luminescence, and magnetism were reported. The crystal structural analysis revealed that two molecular solids crystallize in the monoclinic space group P2₁/c of 1 and P2₁/n of 2. The cations form a dimer through weak C–H···π/π···π interactions in 1 and 2, and the adjacent cation (containing N(6) atom) in 2 forms a columnar structure through π···π weak interactions between the quinoline and benzene rings, while the anions in 1 form a layer structure via short S···Co interactions. The anions (A) and cations (C) are arranged alternatively into a column in the sequence of ···A–CC–A–CC–A··· for 1, while the two anions and cationic dimer in 2 form an alliance by the C–H···π, C–H···S and C–H···N hydrogen bonds. A weak S···π interaction was found in 1 and 2. The two molecular solids show a broad fluorescence emission around 400 nm in the solid state at room temperature, and weak antiferromagnetic coupling behavior when the temperature is lowered.

Hot compressive deformation behaviors of a powder metallurgy Ti-45Al-5Nb-0.4W/2Nb (at. %) were investigated at strain rates from 0.001 s⁻¹ to 1 s⁻¹ and temperatures from 1050 °C to 1200 °C. The Zener-Hollomon (Z) parameter can affect the hot deformation mechanism significantly. At a high Z condition, Nb particles played an important role in coordinating the deformation. At a low Z condition, deformation of Nb particles accompanied by dynamic recrystallization (DRX) can act as a dominant softening mechanism. The as-forged pancake exhibits a short rod-like particle-toughened equiaxed matrix. For notched three-point bending (3PB) tests, the fracture toughness of an Nb-particles-toughened high-Nb-containing duplex phase γ-TiAl alloy was hardly affected by the loading rate, presenting a peak fracture toughness of about 12.9 MPa·m^1/2. The toughness of the present alloy can be improved by ductile Nb particles. A model based on the Griffith-Orowan-Irwin relation was constructed, which is quite accurate to predict the facture toughness of the present specimen using tensile properties.