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29. Topological Lattice Metamaterials -- A Platform For Novel Electromagnetic Material Design Based On An Artificial Topological 'Atom'

Author

Zhang, Wenjin, Meng, Ziyuan, Zhang, Zidong, Bi, Ke, Fan, Runhua, Du, Yi, and Hao, Weichang

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

In nature, most materials are composed of atoms with periodic structures. Hence, it's impossible to introduce topological structures into their lattice compose, because the atoms as basic blocks cannot be modulated. However, the lattice compose of metamaterials can be designed conveniently. In our work, we propose to introduce topological non-trivial structures, Mobius unknots, as the basic block (the artificial chiral "atoms") to design metamaterials. A 5.95 GHz intrinsic peak, in addition to the electrical resonance peak near 11 GHz on the transmission coefficient spectrum was confirmed by theoretical calculations, finite-difference time-domain (FDTD) simulations and experiments when electromagnetic waves transfer to a chiral Mobius unknot. Theoretical analysis indicates that this intrinsic peak originates from the phase transition caused by the electromagnetic waves propagate along the Mobius unknot non-trivial structure. It is similar to the state of spin-splitting of electron levels. Take the artificial chiral "atoms" - Mobius unknots as the basic block, we can construct two-dimensional and even three-dimensional ordered metamaterials. The simulation and experimental results showed that the response to electromagnetic wave in the GHz band can be modulated by the coupling between the periodic potential and the spin-like of energy levels., Comment: 9 pages, 5 figures

Published
2019

46. Epsilon‐negative materials with lower percolation threshold derived from segregated structures.

Author

Yuan, Yuan, Yang, Pengtao, Wang, Zongxiang, He, Qifa, Sun, Kai, and Fan, Runhua

Subjects
PLASMA oscillations, ELECTRON transport, ELECTRON distribution, COMPOSITE structures, RADIO frequency
Abstract

Epsilon‐negative materials (ENM) at radio frequency, usually designed based on percolation theory, recently drew much attention because of their potential applications in capacitors, transistors, and antennas. However, randomly distributed conductive functional materials cannot achieve directional long‐range electron transportation within the material, resulting in decreased utilization efficiency. The morphology design of the substrate material can change the distribution state and electron transfer pathway of conductive fillers. By controlling the size of the polystyrene (PS) and the content of multi‐walled carbon nanotubes (MWCNTs), PS/MWCNTs composites with random structures and segregated structures were designed, both of which exhibited negative permittivity with increasing MWCNTs content. Further investigation revealed that negative permittivity behavior is due to the establishment of the conductive network and the plasma oscillation of free electrons. Moreover, components with segregated structures have lower percolation thresholds, as directional electron transport is achieved and conductive fillers are efficiently utilized. This work provides a new method for guiding the electron transport pathway and effectively changing the distribution state of conductive fillers in ENM. Highlights: Negative permittivity is achieved by plasma oscillation at radio frequency.The segregated structure leads to a decrease in the percolation threshold.Epsilon‐negative materials have good prospects in inductive components. [ABSTRACT FROM AUTHOR]

Published
2024
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48. The energy consumption characteristics of a new type of energy dissipating vibration-damping fastener.

Author

Liu, Yan, Zhu, Jiansen, Yuan, Xianpu, Fan, Runhua, and Yuan, Yuan

Subjects
PRONY analysis, VIBRATION isolation, DYNAMIC stiffness, ENERGY dissipation, SIMULATION software
Abstract

To address the issue of inadequate energy dissipation capacity in current vibration-damping fasteners, this study examined the impact of stiffness and damping factor of vibration-damping fasteners on the vibration attenuation rate of rails, based on the theoretical model of a periodic double-layer support system. An intrinsic manganese–copper (Mn–Cu) damping alloy model was established, and the parameters for the Prony analysis and PRF model were determined to accurately define the hyperelastic and linear viscoelastic properties of the damping alloy in the finite element simulation software. A new type of energy dissipating vibration-damping fastener (NEDF) was designed based on these criteria and practical operational conditions. Static and dynamic stiffness simulation calculations were performed to examine the vibration isolation ability of NEDF, which was then installed in a rail system to conduct hammering tests, aiming to investigate its energy dissipation characteristics. The results indicated that NEDF exhibited a high damping factor and maintained significant vibration isolation capacity, notably enhancing the vibration attenuation rate of the rails and improving energy dissipation capacity. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Enhanced dielectric properties of Sr2+ and Zr4+ doped BaTiO3 colossal permittivity metamaterials

Author

Tang Qingyang, Shi Zhicheng, Xia Shuimiao, Bie Xiaohan, Yang Yujie, Bian Dedong, Xu Daofeng, and Fan Runhua

Subjects
metamaterial, dielectric property, breakdown strength, barium titanate, simulation, Electrical engineering. Electronics. Nuclear engineering, TK1-9971, Physics, QC1-999
Abstract

BaTiO3, as one of the most important functional materials of perovskite structure, is widely used in the electronic industry. However, the dielectric permittivity of BaTiO3 remains relatively low, which greatly limits its practical application in metamaterials with colossal dielectric permittivity. In this work, (Ba100−xSrx)(Ti100−yZry)O3 composite ceramics are fabricated via the solid sintering method. Surprisingly, the dielectric properties of (Ba100−xSrx)(Ti100−yZry)O3 composite ceramic materials are strongly dependent on the occupancy of Sr2+ and Zr4+ at the A-sites and B-sites, respectively. Consequently, via adjusting the doping amount of SrTiO3 and BaZrO3, a greatly enhanced dielectric permittivity of 28287 (65 °C, 1 kHz), along with a high breakdown strength of 84.47 kV/cm is achieved in (Ba90Sr10)(Ti90Zr10)O3 composite ceramics, which are 2144% and 13 % higher than those of (Ba99Sr1)(Ti99Zr1)O3 composite ceramics, respectively. Moreover, the reasons for the significant increase in dielectric permittivity are identified through finite element simulations, and the breakdown mechanism of composite ceramic materials is explored. This work provides a facile approach to constructing high dielectric permittivity composite ceramics, the (Ba100−xSrx)(Ti100−yZry)O3 composite ceramics have broad application prospects in electronics and electrostatic energy storage capacitors.

Published
2024
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