Dual-Function Metasurface for Tunable Selective Absorption

Metamaterials have become a powerful technique in interdisciplinary research, especially in the field of designing terahertz devices. In this paper, two pairs of different structural units of aluminum–polymer composite metamaterials (APCM) for tunable selectivity are designed. One is designed to achieve high-contrast near-field imaging of linear polarized waves, the other is designed to achieve high-contrast near-field imaging of circularly polarized waves, which means the structural units have very large circular dichroisms. After theoretical design and simulation optimization, it can be found that the contrast of near-field imaging can be effectively controlled by using vanadium oxide (VO2) to fill the open gap of the structure. When the conductivity of VO2 is 200 S/m, both the reflection difference under linear polarization excitation and the reflection difference under the excitation of the circularly polarized wave are at the maximum. The former has a modulation depth of 0.8, and the latter has a modulation depth of 0.55. This work shows excellent tunable selective absorption ability, which will promote the application of metamaterials in terahertz absorber, such as biomedical, non-destructive testing, security inspection, wireless communication and so on

Flame-Retardant and Sound-Absorption Properties of Composites Based on Kapok Fiber

In order to improve the utilization rate of kapok fiber, flame-retardant and sound-absorption composites were prepared by the hot pressing method with kapok fiber as the reinforced material, polyε-caprolactone as the matrix material, and magnesium hydroxide as the flame retardant. Then, the effects of hot pressing temperature, hot pressing time, density of composites, mass fraction of kapok fiber, thickness of composites, and air layer thickness on the sound-absorption properties of composites were analyzed, with the average sound absorption coefficient as the index. Under the optimal process parameters, the maximum sound absorption coefficient reached 0.830, the average sound absorption coefficient was 0.520, and the sound-absorption band was wide. Thus, the composites belonged to high-efficiency sound-absorbing material. The flame-retardant effect of magnesium hydroxide on the composites was investigated, and the limiting oxygen index could reach 31.5%. Finally, multifunctional composites based on kapok fiber with flame retardant properties, and sound-absorption properties were obtained

Bending Properties of Zigzag-Shaped 3D Woven Spacer Composites: Experiment and FEM Simulation

Conventionally laminated spacer composites are extensively applied in many fields owing to their light weight. However, their impact resistance, interlaminar strength, and integrity are poor. In order to overcome these flaws, the zigzag-shaped 3D woven spacer composites were rationally designed. The zigzag-shaped 3D woven spacer fabrics with the basalt fiber filaments tows 400 tex (metric count of yarn) used as warp and weft yarns were fabricated on a common loom with low-cost processing. The zigzag-shaped 3D woven spacer composites were obtained using the VARTM (vacuum-assisted resin transfer molding) process. The three-point bending deformation and effects of damage in zigzag-shaped 3D woven spacer composites were studied both in experiment and using the finite element method (FEM). The bending properties of zigzag-shaped 3D woven spacer composites with different direction, different numbers of weaving cycle, and different heights were tested in experiments. In FEM simulation, the geometrical model was established to analyze the deformation and damage based on the 3D woven composite structure. Compared with data obtained from the experiments and FEM simulation, the results show good agreement and also prove the validity of the model. Based on the FEM results, the deformation, damage, and propagation of stress obtained from the model are very helpful in analyzing the failure mechanism of zigzag-shaped 3D woven composites. Furthermore, the results can significantly guide the fabrication process of real composite materials

<tex>Lp\mathrm{L}_p</tex> Quasi Norm State Estimator for Power Systems

This paper proposes an Lp (0&#x003C;p&#x003C;1) quasi norm state estimator for power system static state estimation. Compared with the existing L, and L2 norm estimators, the proposed estimator can suppress the bad data more effectively. The robustness of the proposed estimator is discussed, and an analysis shows that its ability to suppress bad data increases as $p$ decreases. Moreover, an algorithm is suggested to solve the non-convex state estimation problem. By introducing a relaxation factor in the mathematical model of the proposed estimator, the algorithm can prevent the solution from converging to a local optimum as much as possible. Finally, simulations on a 3-bus DC system, the IEEE 14-bus and IEEE 300-bus systems as well as a 1204-bus provincial system verify the high computation efficiency and robustness of the proposed estimator

Structure of Waste Hemp Stalks and Their Sound Absorbing Properties

To broaden the application fields of waste hemp stalks, the macromolecular, supramolecular, and morphological structures of waste hemp stalks were analyzed, and the relationship between these properties and the sound absorption properties of the hemp stalks was explored. Then, waste hemp stalk/polycaprolactone sound-absorbing composite materials were prepared by the hot pressing method. The influence of hemp stalk length and mass fraction, and the density and thickness of the composite materials on the sound absorption properties of composites prepared with the hot pressing temperature set to 140 &deg;C, the pressure set to 8 MPa, and the pressing time set to 30 min was investigated. The results showed that, when the sound energy acts on the hemp stalk, the force between the chain segments, the unique hollow structure, and the large specific surface, act together to attenuate the sound energy and convert it into heat and mechanical energy in the process of propagation, to produce a good sound absorption effect. When the hemp stalk length and mass fraction were set to 6 mm and 50%, respectively, and the density and thickness of the material were set to 0.30 g/cm3 and 1.5 cm, respectively, the average sound absorption coefficient of the waste hemp stalk/polycaprolactone sound-absorbing composite material was 0.44, the noise reduction coefficient was 0.42, the maximum sound absorption coefficient was 1.00, and the sound-absorbing band was wide. The study provided an experimental and theoretical basis for the development of waste hemp stalk/polycaprolactone sound-absorbing composite materials, and provided a new idea for the recycling of the waste hemp stalk

Explicit Analytical Solutions for a Complete Set of the Eshelby Tensors of an Ellipsoidal Inclusion

The celebrated solution of the Eshelby ellipsoidal inclusion has laid the cornerstone for many fundamental aspects of micromechanics. A well-known difficulty of this classical solution is to determine the elastic field outside the ellipsoidal inclusion. In this paper, we first analytically present the full displacement field of an ellipsoidal inclusion subjected to uniform eigenstrain. It is demonstrated that the displacements inside inclusion are linearly related to the coordinates and continuous across the interface of inclusion and matrix. The exterior displacement, which is less detailed in existing literatures, may be expressed in a more compact, explicit, and simpler form through utilizing the outward unit normal vector of an auxiliary confocal ellipsoid. Other than many practical applications in geological engineering, the displacement solution can be a convenient starting point to derive the deformation gradient, and subsequently in a straightforward manner to accomplish the full-field solutions of the strain and stress. Following Eshelby&apos;s definition, a complete set of the Eshelby tensors corresponding to the displacement, deformation gradient, strain, and stress are expressed in explicit analytical form. Furthermore, the jump conditions to quantify the discontinuities across the interface are discussed and a benchmark problem is provided to validate the present formulation