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This paper proposes a dual-band linear polarization converter based on multi-mode metasurface. The converter consists of square-patch-resonator-based metasurface etched with cross-slot, which is beneficial to separate the degenerate modes of the patch resonator in the first band, as well as to generate additional resonant modes for the second conversion band. Different from the traditional method of using multiple resonators for dual-band polarization converters, the proposed one only utilizes one multi-mode resonator. Additionally, the two bands can be tuned relatively independently by appropriately changing the physical parameters of the resonator. To verify the design method, one sample is fabricated and measured. The proposed linear polarization converter works in the two frequency ranges of 3.16–3.52 GHz and 7.19–8.61 GHz with a polarization conversion rate (PCR) ≥ 90 %.

Magnetic nitrogen-doped carbon nanotubes have been recognized as promising microstructures for electromagnetic wave absorption, benefiting from the internal hollow structure, excellent electrical conductivity and easy functionalization. Herein, a new composite composed of the thin-wall carbon nanotubes coated with the cobalt nanoparticles (hereafter labelled as: Co@NCNTs) on the tip was designed and synthesized through high temperature pyrolysis process. Revealed by scanning electron microscopy and X-ray photoelectron spectroscopy, the geometric and electronic structures of product were susceptible to the carbonization temperature. With the multiple dielectric polarization relaxations, higher magnetism and good impedance matching, the flammulina velutipes-like Co@NCNTs-700 exhibited the strongest dielectric loss, magnetic loss and electromagnetic wave absorption performance. The minimum reflection loss value and effective absorption bandwidth was determined to be −21.0 dB at 4.96 GHz and 5.28 GHz, respectively, superior to the previous reports. Furthermore, the thickness is at 2 mm and the filler mass loading is only 10%. Therefore, our present Co@NCNTs materials will be an ultralight material as potential high-efficiency EMW absorber.

Laminated Ti3C2Tx MXene has been considered as a promising absorbing material. However, microwave absorption (MA) performance of single Ti3C2Tx MXene is always limited. The introduction of magnetic components has been proven to improve impedance matching and MA performance effectively. In this paper, a novel CoNi@Ti3C2Tx composites with various CoNi loading were in-situ fabricated via a simple and low-temperature hydrothermal method. By introducing different contents of CoNi nanoparticles, the electromagnetic (EM) parameters of CoNi@Ti3C2Tx composites are regulated to enhance magnetic loss and improve impedance matching. The CoNi@Ti3C2Tx composites with 40 wt% CoNi nanoparticles showed a strong reflection loss of −58.18 dB at 13.20 GHz as the thickness is only 1.55 mm and a broad effective absorption bandwidth of 5.68 GHz can be achieved. The superior MA performance can be attributed to natural resonance, multiple scattering and reflection of the laminated structure, dipole polarization and interfacial polarization. This low-cost, energy-saving and simple method is significative for microwave absorption applications of MXene-based composite materials.

The cost-effective copper (Cu) nanoparticles and core/shell derived architectures with novel physicochemical properties have received tremendous attention in recent years. Herein, the effect of nanoparticle geometry (including diameter and core/shell ratio) on optical scattering and absorption of Cu@C core/shell nanoparticles has been investigated through a combination of DDA-based simulation and experimental validation. Simulated results have shown that the localized surface plasmon resonance (LSPR) peaks of Cu@C core-shell nanoparticles present slightly blue-shift with the increase of core/shell ratio, the core/shell ratio play the dominant role in the shift of the LSPR peak. Moreover, scattering efficiencies factors are inclined to be increasing faster with particle size and core/shell ratio increase, corresponding to enhanced surface electric field intensity which originated from excessive electron concentration on the interface between Cu core and C shell. Finally, experimental optical absorption performance has been performed with the aim at confirmation of size-sensitive light scattering behaviors of Cu@C core-shell nanoparticles via metal organic chemical vapor deposition technology. Results have found that the light absorption coefficient of up to 99.4% could be achieved for nanoparticles with an average particle diameter of 10 nm, while 98.9% for 23 nm. Further decrease in diameter on the nanometer scale is demonstrated to promote optical absorption to a certain extent, which agrees well with simulated results. All these findings have demonstrated ultra-small Cu@C core-shell nanoparticle to be a promising candidate for efficient optical absorption, and are beneficial for design and development of Cu@C core-shell nanoparticles enabled optical-based devices.

A cross-shaped metamaterial absorber (CSMMA) has been introduced to integrate with two-layered polyurethane foam absorbers (PUFAs). By incorporating with CSMMA, microwave absorptive performance of the proposed PUFAs in 8–18 GHz has been remarkably improved for various oblique incident angles under the transverse electric (TE) and transverse magnetic (TM) waves. For the TE wave, the effective bandwidths of −10 dB reflection loss for the PUFAs incorporated with CSMMA increase by 0.85 GHz, 1.15 GHz, 1.25 GHz, 1.50 GHz and 1.70 GHz for 0°, 15°, 30°, 45° and 60°, respectively. As for the TM wave, the effective bandwidths of −10 dB reflection loss for the modified PUFAs by CSMMA rise by 0.85 GHz, 1.10 GHz, 1.20 GHz, 2.85 GHz and 2.90 GHz for 0°, 15°, 30°, 45° and 60°, respectively. The proposed PUFAs optimized by CSMMA could operate well at incident angles ranging from 0° to 60° for both TE and TM waves. In addition, the different variation rules of absorption peak intensity of CSMMA have been revealed through the magnetic field distributions under TE and TM waves. Results indicate that PUFAs combined with CSMMA can be utilized for microwave absorbers adapting to both TE and TM waves at various oblique incident angles. Keywords: Wide-angle absorption, Polyurethane foam, Metamaterial absorber, Electromagnetic field distribution

Incorporation of magnetic loss component is more favorable to high-performance microwave absorbing materials. In this paper, the NiFe2O4-decorated Ti3C2Tx MXene composites were synthesized by the in-situ chemical co-precipitation method. The magnetic NiFe2O4 nanoparticles were attached on the surfaces or inserted into the interlayers of Ti3C2Tx MXene. Interestingly, we reduced effectively complex permittivity and enhanced magnetic loss by increasing the NiFe2O4 content on Ti3C2Tx MXene. Stronger electromagnetic attenuation ability and preferable impedance matching property were achieved and considered to be responsible mainly for improving absorbing peaks as well as bandwidth of the NiFe2O4-Ti3C2Tx MXene composite. In particular, the NiFe2O4-Ti3C2Tx-20 sample exhibited an optimal effective absorption bandwidth (RL