Electromagnetic Composites: from Effective Medium Theories to Metamaterials

Electromagnetic (EM) composites have stimulated tremendous fundamental and practical interests owing to their flexible electromagnetic properties and extensive potential engineering applications. Hence, it is necessary to systematically understand the physical mechanisms and design principles controlling EM composites. In this tutorial, we first provide an overview of the basic theory of electromagnetism about electromagnetic constitutive parameters that can represent the electromagnetic properties of materials. We show how this corpus allows a consistent construction of effective medium theories and allows for numerical simulation of EM composites to deal with structure-property relationships. We then discuss the influence of spatial dispersion of shaped inclusions in the material medium on the EM properties of composites, which has not been systematically illustrated in the context of this interdisciplinary topic. Next, artificial composites or metamaterials with peculiar properties not readily available in nature are highlighted with particular emphasis on the control of the EM interaction with composites. We conclude by discussing appropriate methods of electromagnetic measurement and practical aspects for implementing composites for specific applications are described. Overall, this tutorial will serve the purpose of introducing the basics and applications of electromagnetic composites to newcomers in this field. It is also anticipated that researchers from different backgrounds including materials science, optics, and electrical engineering can communicate to each other with the same language when dealing with this interdisciplinary subject and further push forward this advancement from fundamental science to technological applications.Comment: 63 pages, 20 figure

DYNAMIC MAGNETIC EFFECTS IN AMORPHOUS MICROWIRES FOR SENSORS AND CODING APPLICATIONS

This work is devoted to the study of the dynamic properties of magnetic amorphous wires, in particular, glass-coated microwires, which have small diameters (5-30 microns), outstanding soft magnetic behaviour with a high permeability and low coercivity, yet, possess a well-defined magnetic structure. First part of my PhD research has been devoted to the investigation of a bi-stable magnetisation reversal in glass-coated amorphous microwires. In contrast to traditional approaches, where characteristics of the magnetisation reversal are analysed as a consequence of the eddy current effect, l have applied stochastic methods for modelling the remagnetisation reversal in the microwires with axial anisotropy. While the eddy current approach, widely discussed in literature, was based on the single domain model, proposed stochastic approach takes into account a multi-domain state of studied samples. A modified stochastic Neel-Brown model of the magnetisation reversal has been proposed enabling the explanation of number of characteristic parameters of the microwires with axial magnetisation. Such important parameters of Barkhausen discontinuity as a mean switching field and a standard deviation of the switching field distribution have been investigated experimentally for understanding the influence of extrinsic factors such as a slew rate of the alternating magnetic field on applications operation. A deep understanding of the remagnetisation process in amorphous the microwires with axial anisotropy was successfully applied in development of a new type of the remote magnetic interrogation system. My reading system allows the large Barkhausen jump to be detected without actual contact between the magnetic microwire and the magnetic field detector. Experiments show that the detection will be possible at a distance of approximately 100-150 mm from the detecting sensor. A very low cost and easily repetitive amorphous microwires with axial anisotropy are . incontrovertibly best materials for Electronic Article Surveillance (EAS) applications. During the study of the microwires with axial anisotropy and development of the application based on them, I took part in the investigation of unusual coding methods of the amorphous microwires using a localised laser annealing treatment. This treatment produces a multi-pulse code within the wire and therefore adds to the information contained within the wire, improving reliability and security. I developed and used a magnetic interrogation system allowing an accurate and reliable test and analysis of the studied samples. The second part of my PhD research has included investigations of microwires with circumferential and helical anisotropies. The main interest in these materials is due to their applications for high-performance magnetic and stress sensors. Within this research project, the microwires with circumferential/helical anisotropy have been studied in a broad range of frequencies. A number of dynamic effects have been experimentally obtained and analysed. In particular, a detailed investigation of dynamic circular hysteresis (10kHz-300kHz) has been carried out allowing explanation of different behaviour of the materials with circumferential/helical anisotropy at different frequencies. The experimental curves are proposed to be analysed in terms of field dependence of characteristic permeabilities: domain wall displacements (reversible and irreversible) and magnetisation rotation. It was established that these permeabilities have different field behaviour. That explains different MI patterns at relatively low frequencies (less than a few MHz) and relatively high frequencies (more than 10 MHz). Further, some special features of the Magneto-Impedance effect in the microwires with a circumferential anisotropy such as off-diagonal impedance and microwave impedance have been considered. In this research, the former presents a considerable interest for development of linear magnetic sensors and the latter can find application in tuneable microwave materials and devices. As a result of this study several types of linear, bi-directional MI sensors were developed. I also developed new MI sensing approaches (such as off-diagonal response) and a new high performance detection technique allowing us to improve sensitivity, bandwidth, and linearity at low cost and simple construction .. The last part of the PhD research has been devoted to an investigation of the stress-impedance in the ultra high-frequency (UHF) band (300MHz-3 GHz). Based on the experimental investigation, a new type of a stress-sensitive composite material is proposed. The microwave effective permittivity of such material depends on mechanical stresses. These composite materials opens up new possibilities for remote monitoring of stress with the use of microwave "free-space" techniques. This kind of composite material can be characterised as a "sensing medium", which images the mechanical stress distribution inside construction or on its surface

Development of Novel Analytical Methods with the Aim of Forensic Analyte Detection using Ultra-Thin Layer Chromatography, Surface Enhanced Raman Spectroscopy, and Magneto-Elastic Wire Sensing

The purpose of this dissertation is to develop analytical methods that aid in the detection of forensic analytes. Forensic analytes require methods with increased sensitivity and low limit of detection capabilities. Improvements in separation techniques, surface enhanced Raman spectroscopic techniques, and wire-less gas sensing can each assist in the detection of trace evidence. When surface enhanced Raman is coupled with thin-layer chromatography a mixture of compounds can be separated and transferred to a metal substrate to be detected using Raman spectroscopy. Surface enhanced Raman scattering enhances the Raman signal intensity by placing a metal substrate in close proximity to an analyte. The new method gives a chemically specific intensified signal along with a chromatographic separation. A traditional separation is performed on a TLC plate, allowed to dry, wetted with a solvent, placed in contact with a metal substrate, and detected using Raman. More efficient chromatographic platforms can be implemented with this method. New efficient chromatographic platforms are also beneficial to the detection of forensic analytes. Recently, photolithographically nanofabricated open system pillar arrays have proved to be more efficient separation platforms when compared to traditional TLC. These platforms are a form of ultra-thin layer chromatography. This dissertation describes the effects of manipulation on the inter-pillar gap distances with respect to band dispersion. The studies herein manipulate the pillar arrays in order to optimize the separation platform. The third method developed involved gas sensing of volatile organic compounds. An amorphous ferromagnetic micro-wire was coated with a polymer, where the polymer swelled in response to the gas introduced. When the gas caused the polymer to swell a differential stress response was applied on the micro-wire. The fabricated sensor was tested on simple organic gases but has capabilities to detect low concentrations of low vapor pressure forensic analytes. All three projects were significant advancements in analytical method development. The analytes used were either fluorescent dyes or volatile organic compounds to test feasibility of each method. More efficient chromatographic platforms were fabricated, surface enhanced Raman was coupled to TLC, and a micro-wire gas sensor was calibrated for the studies performed in this dissertation

Optimization of magnetic composites properties for low and high frequency applications by advanced mechanical alloying techniques of amorphus materials

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 07-03-2017La presente tesis doctoral se centra en el desarrollo de materiales magnéticos como son las ferritas y los materiales magnéticamente blandos amorfos y nanocristalinos, en forma de cintas y microhilos. La estructura y propiedades magnéticas de estos materiales han sido optimizadas mediante el empleo de diferentes técnicas de molienda mecánica. Esto ha permitido la fabricación de materiales compuestos para aplicaciones de apantallamiento electromagnético e imanes permanentes isótropos libres de tierras raras. Las aleaciones nanocristalinas basadas en Fe y FeCo son bien conocidas por presentar unas adecuadas propiedades magnéticas como material blando, que las hacen adecuadas para aplicaciones específicas. En este trabajo, se han utilizado diferentes técnicas de molienda mecánica de bolas de alta energía (en medio seco y húmedo) y criomolienda, para obtener polvo de tamaño submicrométrico de cintas nanocristalinas y microhilos amorfos. Se ha estudiado la influencia de las técnicas de molienda seleccionadas sobre la microestructura y las propiedades magnéticas blandas del producto final. Se han empleado microhilos amorfos para fabricar materiales compuestos de matriz polimérica destinados a aplicaciones de atenuación de microondas, cuyas propiedades dependen de la relación de aspecto y longitud final de los microcrohilos. Así mismo, se han caracterizado a alta frecuencia láminas de material compuesto con diferentes espesores y con un contenido variable de polvo de microhilo y de microhilos de 2 mm de longitud, considerando además la naturaleza conductora o no conductora de la matriz. Así, se han obtenido valores de atenuación y de ancho de banda superiores a los que presentan otros tipos de materiales compuestos de matriz polimérica reforzados con microhilos. Los datos experimentales obtenidos se han validado mediante el empleo de la aproximación de medio efectivo de Maxwell Garnett. Por otro lado, la creciente demanda de imanes permanentes ha impulsado la investigación para reducir el uso de tierras raras en su proceso de fabricación. En este trabajo, se han combinado ferritas de Sr tipo M como fase dura con polvo nanocristalino de Fe y FeCo como fase blanda, con objeto de alcanzar un acoplamiento efectivo entre las fases que permita obtener un elevado producto máximo de energía. Así pues, se ha desarrollado un procedimiento de molienda mecánica de bolas de alta energía para obtener una dispersión homogénea de ambas fases y preservar las propiedades estructurales de las fases individuales. De este modo, se ha conseguido obtener un material compuesto que presenta un producto máximo de energía superior en un 30% al que presentan las ferritas comerciales y cuyo proceso de obtención presenta adecuadas características para ser industrializado. Así mismo, se han realizado medidas de retroceso de histéresis, de imanación IRM y de desimanación DC, así como curvas Henkel para analizar la naturaleza de las interacciones magnéticas entre las fases duras y blandas. Por otro lado, el comportamiento del material como una sola fase ha sido observado a partir de ciclos de histéresis medidos a 5 K, sin embargo, el análisis de la distribución de los campos de inversión ha mostrado procesos de desimanación independientes para dichas fases...Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEunpu

Designing a Giant Stress Impedance (GSI) Strain Sensor for Monitoring Intermediate Level Nuclear Waste (ILW) Packages

In this thesis the practicality and viability of a giant stress impedance (GSI) sensor was studied on three amorphous magnetic ribbons. The GMI effect between the three amorphous magnetic ribbons was investigated, initially, to understand the influence of the GMI behaviour between materials of varying magnetic properties, especially the different chemical structure and, their respective, magnetostriction coefficients (a variable that describes a magnetic material's magnetoelastic properties) (λS); Co66Si15B14Fe4Ni1 (λS = < 1x10^-6), Fe81Si13.5B13C2 (λS = 30x10^-6) and Ni40Fe40Si+B19Mo1-2 (λS = 8x10^-6). Initial characterisation of the GMI effect was difficult due to the dimensions of the samples being larger compared to previous studies investigating the GMI effect of their studied samples. It used a trial-and-error approach to improve the characterisation technique to the point it could repeatably measure a consistent GMI response of the samples. The characterisation technique for measuring the GSI effect followed a similar procedure but with little time remaining it was incomplete to achieve the desired reliability. The influence of the geometry, λS and fabrication process of the samples on their GMI behaviour was explored. It was observed that the Co-rich sample had a higher GMI response compared to Fe- and Ni-rich ribbon samples. This was related to the difference in domain structures where a negative (near zero) λS domain structure promotes transverse permeability (µT), thus having a higher GMI response. A critical aspect ratio (l/w = 20) was observed for all three samples where at the critical aspect ratio all samples exhibited their highest GMI response. In addition, it was observed the GMI response of the three samples would be impeded by the presence of permanent damages (such as plastic deformation) caused by the fabrication process. The varying GMI behaviour between the ribbon samples was discussed using the competing effects between the shape anisotropy and demagnetisation factors, influencing the ribbon sample’s transverse permeability (µT). The suitability of using the GSI effect to detect the expansion of intermediate-level nuclear waste (ILW) packages was investigated by applying stress/strain on the sensing material directly. The influence of the magnetostriction coefficients (λS) to the GSI effect of the three samples displayed similar responses to their GMI behaviours; where the Co-rich ribbon sample exhibited the highest magnitude in GSI ratio compared to the Fe- and Ni-rich ribbon samples. This implies the lower the magnetoelastic effects the higher GSI response. Although, the data suggests a more complicated interaction between the transverse permeability (µT) to the shape and stress anisotropies (magnetoelastic effects). The GSI performance between all three samples was explored at stresses/ strains up to 400 MPa/ 10x10^-3 at frequencies between 0.1 – 10 MHz. Finally, the demonstration of the feasibility of the selected material (Co-rich) as a strain sensor on monitoring globally expanding ILW nuclear waste packages was investigated. Simulating the strains that were comparable to a globally expanding ILW waste package (referenced from Sellafield Ltd) the strain sensor observed a clear noticeable trend when undergoing strain at 0.4 Ω decrease at 0.25% strain. This demonstrated a proof-of-concept of using a GSI strain sensor to monitor the expansion of a nuclear waste package using the change in the stress impedance of the sensor – where high and low impedance values signify the early and late stages of the waste package expansion. This is under the assumption the sensor will be used to monitor the waste package within an approximate time period of a decade. The experimental results and the existing literature on using the GSI effect for strain sensing applications suggest the technology is applicable for structural health monitoring for detecting very small changes of strain that are not (typically) noticeable by the naked eye. This is possible from their high sensitivity to detecting minor external changes in the material, which includes minor changes of strain. In addition, it is possible to adjust the strain-sensing capability of the material by either adjusting its magnetic or mechanical properties, such as heat treatments or Young’s modulus. As a result, this is considered a viable solution for the current application of monitoring the expansion of intermediate-level nuclear waste (ILW) packages since it has been reported by the staff at Sellafield, the expansion becomes noticeable after decades of observation [1]