scholarly journals Investigation of Microwave Absorption Mechanisms in Microcellular Foamed Conductive Composites

Micro ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 86-101
Author(s):  
Isabelle Huynen
Keyword(s):  
Microwave Absorption ◽  
Parametric Analysis ◽  
Multiple Reflections ◽  
Microcellular Foam ◽  
Foam Structure ◽  
One Dimensional ◽  
Conductive Composites ◽  
Enhanced Absorption ◽  
Composite Foams ◽  
1D Model

The paper investigates the mechanisms of microwave absorption in microcellular foamed conductive composites dedicated to protection against electromagnetic interferences (EMI). A multi-layered electromagnetic one-dimensional (1D) model mimicking the microcellular foam structure is built and validated using previous measurements carried out on various fabricated composite foams. Our model enables us to perform a parametric analysis of the absorption behaviour in a foamed composite, using as parameters the size of the hollow cell, the thickness of the cell’s walls and its conductivity, as well as the overall thickness of the composite and the frequency. Our investigations demonstrate that multiple reflections of the microwave signal between the cellular walls are not the main mechanism responsible for absorption, although they are often reported as a cause of enhanced absorption in the literature. On the contrary, our work demonstrates that the enhancement of the absorption observed in foamed conductive composite compared to unfoamed composite is mainly due to the presence of air in the microcells of the composite.

scholarly journals Interface Engineered Microcellular Magnetic Conductive Polyurethane Nanocomposite Foams for Electromagnetic Interference Shielding

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Guolong Sang ◽  
Pei Xu ◽  
Tong Yan ◽  
Vignesh Murugadoss ◽  
Nithesh Naik ◽  
...  
Keyword(s):  
Electromagnetic Interference ◽  
Magnetic Loss ◽  
Interfacial Polarization ◽  
Conductive Network ◽  
Shielding Effectiveness ◽  
Electromagnetic Interference Shielding ◽  
Multiple Reflections ◽  
Conduction Loss ◽  
Composite Foams ◽  
Emi Se

Abstract Lightweight microcellular polyurethane (TPU)/carbon nanotubes (CNTs)/ nickel-coated CNTs (Ni@CNTs)/polymerizable ionic liquid copolymer (PIL) composite foams are prepared by non-solvent induced phase separation (NIPS). CNTs and Ni@CNTs modified by PIL provide more heterogeneous nucleation sites and inhibit the aggregation and combination of microcellular structure. Compared with TPU/CNTs, the TPU/CNTs/PIL and TPU/CNTs/Ni@CNTs/PIL composite foams with smaller microcellular structures have a high electromagnetic interference shielding effectiveness (EMI SE). The evaporate time regulates the microcellular structure, improves the conductive network of composite foams and reduces the microcellular size, which strengthens the multiple reflections of electromagnetic wave. The TPU/10CNTs/10Ni@CNTs/PIL foam exhibits slightly higher SE values (69.9 dB) compared with TPU/20CNTs/PIL foam (53.3 dB). The highest specific EMI SE of TPU/20CNTs/PIL and TPU/10CNTs/10Ni@CNTs/PIL reaches up to 187.2 and 211.5 dB/(g cm−3), respectively. The polarization losses caused by interfacial polarization between TPU substrates and conductive fillers, conduction loss caused by conductive network of fillers and magnetic loss caused by Ni@CNT synergistically attenuate the microwave energy.

Effect of the crystallinity and morphology on the microcellular foam structure of semicrystalline polymers

1996 ◽  
Vol 36 (21) ◽  
pp. 2645-2662 ◽  
Author(s):  
Saeed Doroudiani ◽  
Chul B. Park ◽  
Mark T. Kortschot
Keyword(s):  
Semicrystalline Polymers ◽  
Microcellular Foam ◽  
Foam Structure

In situ growth of one-dimensional nanowires on porous PDC-SiC/Si3N4 ceramics with excellent microwave absorption properties

2017 ◽  
Vol 43 (16) ◽  
pp. 14301-14308 ◽  
Author(s):  
Wenhu Hong ◽  
Shun Dong ◽  
Ping Hu ◽  
Xiaoguang Luo ◽  
Shanyi Du
Keyword(s):  
Microwave Absorption ◽  
In Situ Growth ◽  
Absorption Properties ◽  
Microwave Absorption Properties ◽  
One Dimensional ◽  
Si3n4 Ceramics

Enhanced absorption of graphene with one-dimensional photonic crystal

2012 ◽  
Vol 101 (5) ◽  
pp. 052104 ◽  
Author(s):  
Jiang-Tao Liu ◽  
Nian-Hua Liu ◽  
Jun Li ◽  
Xiao Jing Li ◽  
Jie-Hui Huang
Keyword(s):  
Photonic Crystal ◽  
One Dimensional ◽  
Dimensional Photonic Crystal ◽  
Enhanced Absorption

scholarly journals Facile fabrication of ultra-light and highly resilient PU/RGO foams for microwave absorption

RSC Advances ◽  
2017 ◽  
Vol 7 (66) ◽  
pp. 41321-41329 ◽  
Author(s):  
Chunmei Zhang ◽  
Hua Li ◽  
Zhangzhi Zhuo ◽  
Roberto Dugnani ◽  
Chongyang Sun ◽  
...  
Keyword(s):  
Microwave Absorption ◽  
Dip Coating ◽  
Composite Foams ◽  
Coating Method ◽  
Facile Fabrication ◽  
Absorption Performance ◽  
Microwave Absorbing ◽  
Dip Coating Method ◽  
Microwave Absorption Performance

Ultra-light and highly resilient PU/RGO foams are fabricated by a simple dip-coating method. The composite foams exhibit excellent microwave absorption performance and can be used as good microwave absorbing commercial cladding materials.

scholarly journals Enhanced Microwave Absorption and Electromagnetic Properties of Si-Modified rGO@Fe3O4/PVDF-co-HFP Composites

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 933 ◽  
Author(s):  
Yuexuan Li ◽  
Yugang Duan ◽  
Chengmeng Wang
Keyword(s):  
Microwave Absorption ◽  
Reflection Loss ◽  
High Efficiency ◽  
Vinylidene Fluoride ◽  
Synergistic Effects ◽  
Electromagnetic Properties ◽  
Absorption Mechanism ◽  
Simple Method ◽  
Absorption Frequency ◽  
Enhanced Absorption

Graphene has been regarded as one of the most promising two-dimensional nanomaterials. Even so, graphene was still faced with several key issues such as impedance mismatching and narrow bandwidth, which have hindered the practical applications of graphene-based nanocomposites in the field of microwave absorption materials. Herein, a series of Si-modified rGO@Fe3O4 composites were investigated and fabricated by a simple method. On one hand, the degree of defects in graphene carbon could be tuned by different silane coupling reagents, which were beneficial to enhancing the dielectric loss. On the other hand, the spherical Fe3O4 nanoparticles provided the magnetic loss resonance, which contributed to controlling the impedance matching. Subsequently, the electromagnetic absorption (EMA) properties of Si-modified rGO@Fe3O4 composites with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) were investigated in this work. As a result, the Si(2)-rGO@Fe3O4/PVDF-co-HFP composite exhibited the excellent EMA performance in the range of 2–18 GHz. The maximum reflection loss (RLmax) reached −32.1 dB at 3.68 GHz at the thickness of 7 mm and the effective absorption frequency bandwidth for reflection loss (RL) below −10 dB was 4.8 GHz at the thickness of 2 mm. Furthermore, the enhanced absorption mechanism revealed that the high-efficiency absorption performance of Si(2)-rGO@Fe3O4/PVDF-co-HFP composite was attributed to the interference absorption (quarter-wave matching model) and the synergistic effects between Si(2)-rGO@Fe3O4 and PVDF-co-HFP. This work provides a potential strategy for the fabrication of the high-performance EMA materials.

An Improved 1D Model for Liquid Slugs Travelling in Pipelines

2014 ◽  
Author(s):  
Arris S. Tijsseling ◽  
Qingzhi Hou ◽  
Zafer Bozkuş
Keyword(s):  
Experimental Data ◽  
Flow Separation ◽  
Parameter Variation ◽  
Numerical Results ◽  
Liquid Slug ◽  
Straight Pipe ◽  
One Dimensional ◽  
1D Model

An improved one-dimensional (1D) model — compared to previous work by the authors — is proposed which is able to predict the acceleration and shortening of a single liquid slug propagating in a straight pipe with a downstream bend. The model includes holdup at the slug’s tail and flow separation at the bend. The obtained analytical and numerical results are validated against experimental data. The effects of the improvement and of holdup are examined in a parameter variation study.

Temperature-Dependent Luminescence Quenching in Random Nano Porous Media

2004 ◽  
Author(s):  
Xiulin Ruan ◽  
Massoud Kaviany
Keyword(s):  
Porous Media ◽  
Thermal Emission ◽  
Luminescence Quenching ◽  
Photon Absorption ◽  
Temperature Dependent ◽  
One Dimensional ◽  
Irradiation Intensity ◽  
Enhanced Absorption ◽  
Coherent Wave ◽  
Transport Transition

The luminescence quenching of a random, crystalline one-dimensional model porous medium doped with rare-earth elements, is analyzed by considering the transport, transition, and interaction of the fundamental energy carriers. The quenching in nano porous media is enhanced compared to a single crystal, due to multiple scattering, enhanced absorption, and low thermal conductivity. The coherent wave treatment is used to calculate the photon absorption, in order to allow for field interference and enhancement. The luminescent and thermal emission is considered as incoherent. The luminescence quenching and non-linear thermal emission, occurring with increasing irradiation intensity, are predicted.

Hypergravity and Multiple Reflections in Wave Propagation in the Aorta

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
J. M. B. Kroot ◽  
C. G. Giannopapa
Keyword(s):  
Blood Flow ◽  
Wave Propagation ◽  
Cerebral Blood Flow ◽  
Total Pressure ◽  
Loss Of Consciousness ◽  
Pressure Waves ◽  
Multiple Reflections ◽  
One Dimensional ◽  
Gravity Changes ◽  
Pressure Part

Hypergravity and gravity changes encountered in, e.g., airplanes, rollercoasters, and spaceflight can result in headaches or loss of consciousness due to decreased cerebral blood flow. This paper describes the effect of hypergravity and gravity changes on the pressure in the aorta and the distension of its wall. The model presented consists of a pressure part caused by gravity and a part representing pressure waves propagating through the vessel. The total pressure is described by a one-dimensional formulation in the frequency domain. To accommodate for geometrical and material variations, the vessel is modeled as a series of sections in which multiple reflections can occur. Results are presented for constant and varying gravity in straight and tapered flexible vessels.

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