Elaboration and Characterization of Cu Based Nanocomposites for Electromagnetic Interferences Shielding

An electromagnetic interferences (EMI) shielding is a material that attenuates radiated electromagnetic energy. Polymer nanocomposites is a class of materials that combine electrical, thermal, dielectric, magnetic and/ or mechanical properties, which are useful for the suppression of electromagnetic interferences. In this work, we looked over the effectiveness of the electromagnetic interferences shielding of polymer-based nanocomposites. These are thin samples of epoxy resin strengthened with nanostructured Cu powders. Nanostructured Cu powders were obtained by mechanical milling using the high-energy RETSCH PM400 ball mill (200 rpm). A powder sampling was conducted after 3h, 6h, 12h, 24h, 33h, 46h and 58h milling for characterization requirements. XRD analysis via the Williamson-Hall method shows that the mean crystallites size decreases from 151.6 nm (pure Cu phase) to 13.8 nm (58 h milling). Simultaneously, the lattice strain increases from 0.1% (pure Cu phase) to 0.59% (58 h milling). The elaboration of thin samples was performed by mixing a vol./3 fractions of nanostructured Cu powder, epoxy resin and hardener. Thin slabs of 1 mm thickness were moulded for use in a rectangular wave-guide. The EMI shielding experimental involved a two ports S parameters cell measurement made of R120 metallic wave-guides of rectangular section (19.05x9.525 mm2) and operational over the frequency band of 9.84 to 15 GHz associated to a network analyser. Obtained results show moderate EMI shielding effectiveness for the milled Cu-based slabs.

Creating synthetic spaces for higher-order topological sound transport

Modern technological advances allow for the study of systems with additional synthetic dimensions. Higher-order topological insulators in topological states of matters have been pursued in lower physical dimensions by exploiting synthetic dimensions with phase transitions. While synthetic dimensions can be rendered in the photonics and cold atomic gases, little to no work has been succeeded in acoustics because acoustic wave-guides cannot be weakly coupled in a continuous fashion. Here, we formulate the theoretical principles and manufacture acoustic crystals composed of arrays of acoustic cavities strongly coupled through modulated channels to evidence one-dimensional (1D) and two-dimensional (2D) dynamic topological pumpings. In particular, the higher-order topological edge-bulk-edge and corner-bulk-corner transport are physically illustrated in finite-sized acoustic structures. We delineate the generated 2D and four-dimensional (4D) quantum Hall effects by calculating first and second Chern numbers and physically demonstrate robustness against the geometrical imperfections. Synthetic dimensions could provide a powerful way for acoustic topological wave steering and open up a platform to explore any continuous orbit in higher-order topological matter in dimensions four and higher.

Bio-inspired origami metamaterials with metastable phases through mechanical phase transitions

Structural instability, once a catastrophic phenomenon to be avoided in engineering applications, is being harnessed to improve functionality of structures and materials, and has catalyzed a substantial research in the field. One important application is to create functional metamaterials that deform their internal structure to adjust performance, resembling phase transformations in natural materials. In this paper, we propose a novel origami pattern, named the Shrimp pattern, with application to multi-phase architected metamaterials whose phase transition is achieve mechanically by snap-through. The Shrimp pattern consists of units that can be easily tessellated in two dimensions, either periodically with homogeneous local geometry, or non-periodically with heterogeneous local geometries. We can use a few design parameters to program the unit cell to become either monostable or bistable, and tune the energy barrier between the bistable states. By tessellating these unit cells into an architected metamaterial, we can create complex yet navigable energy landscape, leading to multiple metastable phases of the material. As each phase has different geometry, the metamaterial can switch between different mechanical properties and shapes. The geometric origin of the multi-stable behavior implies that our designs are scale-independent, making them candidates for a variety of innovative applications, including reprogrammable materials, reconfigurable acoustic wave guides, and microelectronic mechanical systems and energy storage systems.

Investigation of the Microwave Absorption Properties of Fe Based Nanocomposites

The objective of this work was to provide information about the behaviour of Fe-based nanocomposites when exposed to microwaves. It is about rectangular bulk samples of epoxy resin reinforced by nanocrystalline Fe powders and shaped in accordance to the internal section of the R100 metallic waveguide (8.2 to 12.4 GHz) at a fixed thickness of 7 mm. The nanocrystalline Fe powders were obtained by high-energy mechanical milling process using a planetary Retsch PM 400-ball mill. The milling speed was fixed at 200 rpm for three durations and the milling process were performed under Argon atmosphere. The bulk nanocomposites were obtained by dispersion of 30% vol. of the nanocrystalline Fe powders in the resin matrix. Electromagnetic parameters as complex relative dielectric permittivity and magnetic permeability, electric and magnetic loss tangent and reflection loss were calculated using reordered S parameters. The scattering parameters were characterized using a measure cell made off two metallic R100 wave-guides associated to an Agilent 8719 network analyser according to the reflection-transmission technique. The obtained spectra inform on the new electromagnetic properties as well as the absorption characteristic acquired by the bulk nanocomposites due to the presence of the nanocrystalline Fe powders.

On the effect of oscillatory phenomena on Stokes inversion results

Stokes inversion codes are crucial in returning properties of the solar atmosphere, such as temperature and magnetic field strength. However, the success of such algorithms to return reliable values can be hindered by the presence of oscillatory phenomena within magnetic wave guides. Returning accurate parameters is crucial to both magnetohydrodynamics (MHD) studies and solar physics in general. Here, we employ a simulation featuring propagating MHD waves within a flux tube with a known driver and atmospheric parameters. We invert the Stokes profiles for the 6301 Å and 6302 Å line pair emergent from the simulations using the well-known Stokes Inversions from Response functions code to see if the atmospheric parameters can be returned for typical spatial resolutions at ground-based observatories. The inversions return synthetic spectra comparable to the original input spectra, even with asymmetries introduced in the spectra from wave propagation in the atmosphere. The output models from the inversions match closely to the simulations in temperature, line-of-sight magnetic field and line-of-sight velocity within typical formation heights of the inverted lines. Deviations from the simulations are seen away from these height regions. The inversions results are less accurate during passage of the waves within the line formation region. The original wave period could be recovered from the atmosphere output by the inversions, with empirical mode decomposition performing better than the wavelet approach in this task. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

Experimental Investigation of Optimal Relay Position for Magneto-Inductive Wireless Sensor Networks

Magneto-inductive (MI) waveguide technology is often proposed to increase the MI communication distance without adding significant cost and power consumption to the wireless sensor network. The idea is to add intermediate relaying nodes between transmitter (Tx) and receiver (Rx) to relay the information from Tx to Rx. Our study of MI wave-guides has realized that adding a relay node improves the communication distance, however, the performance is greatly dependent on the position of the relaying node in the network. We therefore, in this work have investigated the effect of placement of a relay node and have determined the optimal relay position. We have performed various sets of experiments to thoroughly understand the behavior and identified three main regions: (a) for region 1, when the distance between Tx and Rx is equal or less than the diameter of the coils ( d ≤ 2 r ), the optimal relay position is close to Tx, (b) for region 2, when the distance between Tx and Rx is greater than diameter of the coils but less than twice the diameter ( 2 r < d < 4 r ), the optimal relay position lies in the center of Tx and Rx, and (c) for region 3, when the distance between the Tx and Rx is equal or greater than twice the diameter of the coils ( d ≥ 4 r ), the optimal relay position is close to Rx.

Characteristics of Surface Plasmon Polaritons in Magnetized Plasma Film Walled by Two Graphene Layers

The theoretical analysis of surface plasmon polaritons in magnetized plasma film walled by two graphene layers is presented in this manuscript. The conductivity of graphene is calculated from the Kubo's formula. By tailoring the graphene conductivity, the propagation of Surface Plasmon Polariton wave can be controlled. Under the certain boundary conditions Maxwell's Equations in differential form are used to solve the problem. For using these wave guides we also investigate factor of confinement and comparatively length of shorter propagation for parallel plate waveguide. The effects of chemical potential (μ), plasma frequency (ωp), cyclotron frequency (ωc), relaxation time (τ), and number of layers of graphene (N) on the dispersion curve are investigated. The present work may have potential applications in nano-waveguide designing and plasma optics technology in the gigahertz frequency range.