Search

The rapid development of modern electronic technology has provided high efficiency for social production, but it also brings serious electromagnetic interference (EMI). Although traditional metals and their alloys can serve as good electromagnetic shielding materials, their heavy weight, high cost as well as poor corrosion resistance limit their application in EMI shielding. Therefore, electromagnetic shielding materials with lightweight are gradually attracting more and more attention to meet the trend of lightweight and highly integrated electronic equipment. Polymers are widely used in EMI shielding materials because of their unique characteristics, such as lightweight, high flexibility and excellent corrosion resistance. This review is focused on the well-studied polymer-based lightweight composites, with the aim of providing a comprehensive review of the existing EMI shielding mechanism, preparation and application of polymer-based lightweight composites, along with retrieving new general insights into the advantages and limitations associated with the different measurement and prediction techniques, as well as the EMI shielding effectiveness of polymer-based lightweight composites including metal-containing composites, intrinsic conductive polymers, filler-containing polymers and newly discovered materials. These lightweight materials with fine EMI shielding performance will find more and more potential applications in communications, electronics, aerospace, military, environmental protection, etc.

In this article, the problem of receiver autonomous integrity monitoring (RAIM) is transformed into a modeling problem using dynamic data and an artificial neural network. A new RAIM method based on a probabilistic neural network (P-RAIM) is presented to improve integrity monitoring performance. Compared with existing RAIM methods, P-RAIM has a greater ability to meet the monitoring requirements for localizer performance with vertical guidance down to altitudes of 250 feet (LPV-250) in a single global navigation satellite system. First, by projecting the pseudorange error model from the measurement domain into the positioning domain through multiconvolution, patterns including a satellite fault pattern and a fault-free pattern are obtained based on variance inflation theory. Second, the P-RAIM model is proposed as a modified dynamic-data-driven probabilistic neural network with five layers; moreover, unique methods for training sample collection and integrity support are presented. Then, particle swarm optimization is applied to optimize a fitness function based on the false alarm probability and missed detection probability thereby improving the ability of P-RAIM to meet the LPV-250 requirements, including the false alarm probability, missed detection probability, vertical alarm limit and alarm time. Finally, utilizing real satellite data from a receiver located in Beijing to verify the effectiveness and universality of P-RAIM, evaluation experiments show that both the false alarm probability and missed detection probability can be effectively reduced to meet the LPV-250 requirements when the positioning bias is no less than 40 m. Compared with least-squares-residuals RAIM, P-RAIM can more easily detect potential faulty satellites in a single constellation.

A cross-layer non-vertical transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurred in a quarantine hotel in Guangzhou, Guangdong Province, China in June 2021. To explore the cross-layer transmission path and influencing factors of viral aerosol, we set up different scenarios to carry out simulation experiments. The results showed that the air in the polluted room can enter the corridor by opening the door to take food and move out the garbage, then mix with the fresh air taken from the outside as part of the air supply of the central air conditioning system and re-enter into different rooms on the same floor leading to the same-layer transmission. In addition, flushing the toilet after defecation and urination will produce viral aerosol that pollutes rooms on different floors through the exhaust system and the vertical drainage pipe in the bathroom, resulting in cross-layer vertical transmission, also aggravating the transmission in different rooms on the same floor after mixing with the air of the room and entering the corridor to become part of the air supply, and meanwhile, continuing to increase the cross-layer transmission through the vertical drainage pipe. Therefore, the air conditioning and ventilation system of the quarantine hotel should be operated in full fresh air mode and close the return air; the exhaust volume of the bathroom should be greater than the fresh air volume. The exhaust pipe of the bathroom should be independently set and cannot be interconnected or connected in series. The riser of the sewage and drainage pipeline of the bathroom should maintain vertical to exhaust independently and cannot be arbitrarily changed to horizontal pipe assembly.

Sulfur-free expanded graphite (EG) was prepared by chemical oxidation, then EG-based cobalt-nickel alloy hybrid (EG@CoNi) was obtained via hydrothermal method in this work. CoNi particles with the diameter of 0.1–0.5 µm were tightly attached to the surface of the layered EG. The incorporation of CoNi was conducive to the absorption of electromagnetic waves due to the increase in Ms and Hc, which enhanced the soft magnetization of EG@CoNi hybrids. The resulting EG@CoNi hybrids exhibited better dielectric loss than CoNi particles, and the optimal value of reflection loss (RL) reached − 50 dB, while the optimal bandwidth less than − 10 dB was 4 GHz, indicating enhanced microwave absorption characteristics. The well impedance matching and electromagnetic wave attenuation of EG@CoNi hybrids benefited from the synergy and double-loss mechanism between CoNi nanoparticles and EG. The dielectric loss in the double-loss mechanism was mainly dipole polarization and interface polarization, while the magnetic loss was mainly the natural ferromagnetic resonance and eddy current loss of CoNi nanoparticles. These multi-layer EG@CoNi hybrids with light weight and high dielectric characteristics would show good application prospects in high-efficiency electromagnetic wave absorbers.

The thermal behavior and decomposition kinetics of CL-20-based plastic-bonded explosives (PBXs) composed of main explosive CL-20 and additives were first time explored by means of DSC, TG and ARC techniques. The DSC study at different heating rates was performed and showed the effect of the additives on the exothermic peaks of CL-20-based PBXs. The thermal stability of CL-20-based PBXs was evaluated by DSC, TG and ARC, indicating that the largest influence on lowering the activation energy is the presence of plasticizer. The kinetic parameters after addition of additives were compared with those of raw CL-20 by means of Kissinger and Ozawa methods. Moreover, the mechanical sensitivities of investigated CL-20-based PBXs were supported, which was well consistent with the data from DSC and ARC measurements.

The enthalpies of dissolution for 5,5′-Bistetrazole-1, 1′-dihydroxy ((H2O)2BTO) and disodium 5,5′-Bistetrazole-1,1′-diolate ([Na2(H2O)4]BTO) in dimethyl sulfoxide (DMSO) at 298.15 K were studied by using a C-80 Calvet microcalorimeter. Empirical formulae for the calculation of the molar enthalpies of dissolution (Δdiss H), relative partial molar enthalpies (Δdiss H partial), and relative apparent molar enthalpies (Δdiss H apparent) were deduced by the experimental results of the dissolution processes of (H2O)2BTO and [Na2(H2O)4]BTO in DMSO. Finally, the corresponding kinetic equations describing the dissolution processes were dα/dt = 10−2.60(1−α)0.61 for the dissolution of (H2O)2BTO in DMSO, and dα/dt = 10−2.69(1−α)0.62 for the dissolution of [Na2(H2O)4]BTO in DMSO.

Graphene/polyurethane (PU) porous composites combined the advantages of graphene and PU with high flexibility, electromagnetic shielding as well as fine flame retardant properties were prepared by a simple one-pot process. Graphene/PU composites with the density of 29.5 kg/m3 exhibited polygonal cell structure, which facilitated the multiple reflection attenuation of electromagnetic waves. The transmittance of the resulting composites to near infrared and mid-infrared bands was close to 0%, while the electromagnetic interference (EMI) shielding effectiveness (SE) reached 30 dB at low frequency band. The addition of flexible graphene sheets improved the flame retardancy and the flexibility of polyurethane. The peak heat release rate (PHRR) reduced from 518 to 395 kW/m2, and the elongation at break reached 300%, which was recoverable. The introduction of graphene increased the thermal degradation temperature of PU and played a positive role in the thermal stability of graphene/PU composites. These ultra-light porous composites with high flexibility, EMI shielding and fine flame retardancy showed potential in the fields of flexible electronics and stealth materials.

In this research, the rolling of Mg-9Li-1Zn alloy at different temperatures was simulated, and it was found that the temperature control had an effect on the grain size and temperature field of the sheet. Combined with the experimental analysis, the results showed that the alloy with proper rolling temperature control had fine microstructure and plasticity. Under the conditions of 300 °C for the first pass and 275 °C for the second pass, the β-Li phase was recrystallized dynamically and most of the α-Mg phase was spheroidized. The tensile strength was 233 MPa, and a large number of dimples were produced on the tensile fracture, which was ductile fracture with an elongation of 45%. In addition, according to Gibbs-Thomson theorem and metallographic analysis, the mechanism of α-Mg spheroidization was explained.