Добірка наукової літератури з теми "Electromagnetic (EM) scattering"

Computational Electromagnetic (CEM) techniques have become an indispensable tool in efficient EM modeling, analysis and design process. EM subsurface scattering is a broad field of research with varying degree of complexity. Due level of the obscurity involved in the subsurface scattering investigation, it is therefore considered imperative to explore this problem area of EM for better insight through CEM-based study and models. In this paper, frequency domain CEM techniques are studied which have been tested to provide solution for subsurface scattering problems in terrestrial environments. The development of CEM methods for comparatively more complex problems of scattering from embedded non-metallic inhomogeneity in lossy, rough and layered media remains the focus of this article. The objective here is to provide an overview of CEM development by selecting few examples from the wide area of subsurface EM scattering.

The characterization of targets by electromagnetic (EM) scattering and underwater acoustic scattering is an important object of research in these two related fields. However, there are some difficulties in the simulation and measurement of the scattering by large targets. Consequently, a similarity study between acoustic and EM scattering may help to share results between one domain and the other and even provide a general reference method for the simulation of scattering characteristics in both fields. Based on the method of physical optics, the similarity between the EM scattering of conductors and the acoustic scattering of soft/hard targets and the similarity between the EM scattering of dielectrics and the acoustic scattering of elastics are studied. In particular, we derive how to transfer quantities from one domain into another so that similar scattering patterns arise. Then, according to these transfer rules, the EM scattering and acoustic scattering of three typical targets with different types of boundaries were simulated and measured, and the simulated EM scattering and acoustic scattering curves were found to be in perfect agreement, with correlation coefficients above 0.93. The correlation coefficients between the electromagnetic and acoustic scattering patterns were above 0.98, 0.91, and 0.65 for three typical targets. The simulated and measured scattering results verify the proposed similarity theory of EM and acoustic scattering, including the transfer from one domain into the other and the conditions of EM and acoustic scattering, and illustrate that the acoustic scattering characteristic of the target can be simulated using the EM scattering based on the derived conditions and vice versa.

The Geant4 electromagnetic (EM) physics sub-packages are a component of LHC experiment simulations. During long shutdown 2 for LHC, these packages are under intensive development and we report progress of EM physics in Geant4 versions 10.5 and 10.6, which includes faster computation, more accurate EM models, and extensions to the validation suite. New approaches are developed to simulate radiation damage for silicon vertex detectors and for configuration of multiple scattering per detector region. Improvements in user interfaces developed for low-energy and the Geant4-DNA project are used also for LHC simulation optimisation.

A new electromagnetic (EM) scattering model of the sea surface with single breaking waves is proposed based on the high-frequency method in this paper. At first, realistic breaking wave sequences are obtained by solving the fluid equations which are simplified. Then, the rough sea surface is established using the linear filtering method. A new wave model is obtained by combining breaking waves with rough sea surface using a 3D coordinate transformation. Finally, the EM scattering features of the sea surface with breaking waves are studied by using shooting and bouncing rays and the physical theory of diffraction (SBR-PTD). It is found that the structure that is similar to a dihedral corner reflector between the breaking wave and rough sea surface exhibits multiple scattering, which leads to the sea-spike phenomenon that the scattering result of horizontal (HH) polarization is larger than that of vertical (VV) polarization, especially at low-grazing-angle (LGA) incidents with upwind. The sea-spike phenomenon is also closely related to the location of strong scattering.

In this paper, the detection of the lunar surface soil permittivity with megahertz electromagnetic (EM) waves by spaceborne radar is studied based on the EM scattering theory, the Boltzmann–Shukla equations, and the improved scattering matrix method (ISMM). The reflection characteristics of the lunar surface soil subject to megahertz waves are analyzed through the EM scattering theory and expressed by the lunar surface soil permittivity. Then, the lunar ionosphere is assumed to be composed of dusty plasma, and its EM characteristics are described with the Boltzmann–Shukla equations. Finally, the transmission and reflection characteristics of the propagation of EM waves in the lunar ionosphere are numerically calculated with ISMM. Thus, the complex permittivity of lunar surface soil is obtained. In addition, the effects of detection environment situations, such as the lunar illumination intensity, characteristics of the lunar dust and dust charging process in the lunar ionosphere, on the amplitude and phase of EM waves are also investigated in this study. The simulation results show that an EM wave at a high frequency induces a strong effective wave with a stable phase shift and a significantly small interferential wave. Moreover, the lunar illumination is more effective under EM waves in low frequency bands; the characteristics of the lunar dust have a notable influence on the transmission and absorption coefficients of the effective waves. These conclusions help in real applications involving the detection of the lunar surface soil permittivity by spaceborne radar in various lunar environments.

As an integral part of the electromagnetic system, antennas are becoming more advanced and versatile than ever before, thus making it necessary to adopt new techniques to enhance their performance. Machine Learning (ML), a branch of artificial intelligence, is a method of data analysis that automates analytical model building with minimal human intervention. The potential for ML to solve unpredictable and non-linear complex challenges is attracting researchers in the field of electromagnetics (EM), especially in antenna and antenna-based systems. Numerous antenna simulations, synthesis, and pattern recognition of radiations as well as non-linear inverse scattering-based object identifications are now leveraging ML techniques. Although the accuracy of ML algorithms depends on the availability of sufficient data and expert handling of the model and hyperparameters, it is gradually becoming the desired solution when researchers are aiming for a cost-effective solution without excessive time consumption. In this context, this paper aims to present an overview of machine learning, and its applications in Electromagnetics, including communication, radar, and sensing. It extensively discusses recent research progress in the development and use of intelligent algorithms for antenna design, synthesis and analysis, electromagnetic inverse scattering, synthetic aperture radar target recognition, and fault detection systems. It also provides limitations of this emerging field of study. The unique aspect of this work is that it surveys the state-of the art and recent advances in ML techniques as applied to EM.

The electromagnetic (EM) scattering characteristics of the rough sea surface is very important for target surveying and detection in a sea environment. This work proposes a scaled sea surface designing method based on a rough thin-film medium. For the prototype sea surface, the permittivity is calculated with the seawater temperature, salinity, and EM wave frequency according to the Debye model. The scale film material is mixed with carbon black and epoxy, whose volume ratio is optimized with the genetic algorithm through the existing electromagnetic parameter library. This method can overcome the previous difficulties of adjusting the same permittivity of the prototype sea water. According to the EM scaled theory, the scaled geometric sample is numerically generated with the D-V spectrum for the given wind speed, and is fabricated using 3D printing to keep the similar seawater shape. Then, the sample is sprayed with a layer of film material for EM scattering measurement. The simulated and measured radar cross-section (RCS) results show good consistency for the prototype seawater and scaled materials, which indicates the proposed scaled method is a more efficient method to get the seawater scattering characteristics.

Time-domain physical optics (TDPO) method is extended to investigate electromagnetic (EM) scattering from two-dimensional (2D) perfectly electrically conducting (PEC) rough surface in both time domain and frequency domain. The scheme requires relatively small amounts of computer memory and CPU time, and has advantage over the Kirchhoff Approximation (KA) method in obtaining transient response of rough surface by a program run. The 2D Gaussian randomly rough surface is generated by Monte Carlo method and then is partitioned into small triangle facets through the meshing preprocess. The accuracy of TDPO is validated by comparing the numerical results with those obtained by the KA method in both backward and specular directions. The transient response and its frequency distribution of radar cross section (RCS) from rough surface is shown, respectively. The scattering results from rough surface with different size in the specular direction are given. The influence of the root mean square height (σ) and correlation length (l) on electromagnetic scattering from PEC rough surface is discussed in detail. Finally, the comparisons of backscattering results at different incident angles are presented and analyzed.

This paper presents a FEM-BEM coupling method suitable for the numerical simulation of the electromagnetic scattering of objects composed of dielectric materials and perfect electric conduc- tors. The originality of the approach lies in part in the use of the newly proposed Sparse Cardinal Sine Decomposition SCSD) method for the BEM part of the computation and the fact that the simulation software is almost entirely written in MATLAB. The performance of the method is illustrated by the computation of the electromagnetic scattering by an UAV-like object with two RAM regions proposed in the workshop ISAE EM 2016.

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Neste trabalho serão apresentados novos métodos baseados na geração e controle de comprimento de onda em lasers aleatórios e lasers de diodo. Na primeira parte do trabalho será demonstrado um laser aleatório com realimentação localizada em filmes em biopolímeros dopado com corante. O filme é constituído por um ácido desoxirribonucleico e cloreto de cetiltrimetilamônio (DNA-CTMA) dopado com DCM. No dispositivo proposto, a realimentação óptica para o laser aleatório é dada por centros de dispersão posicionados aleatoriamente ao longo das bordas da área ativa. Os elementos de dispersão são nanopartículas de dióxido de titânio (TiO2) ou defeitos aleatórios na interface entre o polímero ativo e ar. Diferentes espectros de emissão são observados, dependendo da geometria da área excitada. Um único ressonador aleatório com dimensões de 2.6 x 0.65 mm2 foi fabricado com emissão aleatória com realimentação obtida pela excitação do dispositivo por completo. A segunda parte deste trabalho apresenta um novo método para a geração e manipulação de franjas de contorno por meio de interferometria speckle com comprimento de onda sintética, usando um único laser de diodo com cavidade externa. A cavidade externa permite sintonizar duas emissões simultaneamente, o que por sua vez muda o intervalo entre as franjas de contorno do interferômetro, além de aumentar a estabilidade do laser. Uma análise de Fourier é proposta como alternativa para medir o comprimento de onda sintético resultante das duas emissões do laser.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Tissue healing is in general a complex process, which involves both local and systemic responses, and bone regeneration in particular is much slower than repair in any other human tissue. Thus, it exhibits a great challenge in clinical practice and in the field of research. Bone regeneration is comprised of a series of biological events, involving a number of cell types and intracellular and extracellular molecular- signaling pathways, with a definable temporal and spatial sequence, in an effort to optimize the skeletal repair and restore its functionality. Photobiomodulation (PBM) therapy has been shown to be effective in modulating both local and systemic responses, by enhancing cellular activities resulting in an increase in function, especially in injured tissues, leading to optimization of tissue repair and regeneration. In bone tissue, application of the photonic energy leads to bone healing by the activation of osteoblasts, leading to proliferation and differentiation, as well as osteoclast inhibition and, consequently, neoformation of bone matrix. The process of the in vitro pre-osteoblasts maturation, mimicking their in vivo behavior, passes through three distinct stages of development: proliferation, early differentiation (maturation) and late differentiation (mineralization). Despite the extensive research on the effects of photobiomodulation (PBM) light on bone regeneration, the current outcomes ranging from positive to negative effect remain controversial. These contradictory data are thought to be due to; incomplete knowledge and understanding of the mechanistic effects of laser light on cells, lack of standardized laser dosimetry, inefficient laser beam profile, improper study design and varied methods of investigation. The literature is hindered by a considerable heterogeneity of the irradiation parameters of PBM, as well as, the methods utilized to evaluate the results and the type of osteoblast-like cells irradiated. This has led to a need of standardization. Moreover, heterogeneity of the current studies and their limitations could be due to study designs and inefficient beam profile, resulting in undesirable effects and accounting for negative and inconclusive outcomes. Ultimately, lack of intimate knowledge and understanding of the PBM light behavior impinging on the target tissue, as well as the optical tissue properties, can compromise optimization of the therapeutic outcomes. Thus, an evidence-based decision for definite therapeutic application of PBM in bone regeneration is required. In this thesis, we addressed the above issues and challenges via two elements, the electromagnetic (EM) modeling experiments and the molecular and cellular impact of PBM on bone regeneration (In vitro studies). The Electromagnetic models In my PhD proposal, I intended to both create an EM model, for the first time, and examine the mechanism of interaction of the electromagnetic fields (EMFs) with cells/tissues and establish the link that can be utilized in my cellular experiments. As the project evolved, it became clear this work was breaking new grounds and was significantly more complex than initially envisaged. As it is a small part of a much larger exciting project undertaken by University of Genoa, it has meant that I need to coordinate my work with the overall timetable of this larger project. As a result, I decided to defer, the interaction of the EMF with cells of interest part, to my Post doctorate study. We developed, for the first time, a set of simple models to examine the behavior of the local electromagnetic field (EMF), determining the PBM effects on mitochondria. This set of models was tested and crosschecked for its validity by evaluating various variables in terms of, polarization, absorption and scattering coefficient, dissipated energy density and irradiance, as well as the refractive index. Ultimately, our model and preliminary data are the first stepping-stone for further experiments, in order to understand the mechanism of interaction between electromagnetic fields and cells or tissues. Our conclusions showed that when these set of models are utilized, for the phenomenon of interest, the incident field polarization had small effects on the electromagnetic field and negligible consequences on the average energy, as well as, on the dissipated power densities. The same was shown to hold true for different orientations that the mitochondria can assume. The analogous conclusions were obtained by taking into account the possible changes in the dimensions or of the real part of the refractive index of the considered organelles. The variations of the absorption coefficient were shown to have significant effects on the average dissipated power density in the mitochondria but these effects can be predicted in a surprisingly simple way. It was proved that the numerical analysis, of the problems of interest, could be computed by using three-dimensional models, involving only a few mitochondria in the plane, which was transverse to the direction of propagation of the illuminating light that generated a uniform distribution of the energy over 1cm2 area. The one- dimensional models provided significant information on the EMF, utilized to stimulate the mitochondria. Mitochondria behaved like weak scatterers. Therefore, it was not necessary to analyze large extension of such organelles to understand what happen inside one of them. The molecular and cellular impact of 980nm PBM on osteoblast maturation: in vitro studies Our pilot study data, on the bone marrow stromal cells (BMSCs), strongly suggested that the high fluence concept (over 60J/cm2 in continuous emission mode (CW)) delivered by flattop beam profile device (FT) can promote BMSCs differentiation towards osteogenesis. Moreover, the results showed an increase in cytokines synthesis with potent anti-inflammatory properties and a decrease in the release of proinflammatory mediators. This provided me with a platform, demonstrating the validity of high fluence in facilitating osteoblasts differentiation through BMSCs. Based on this; I formulated three PBM protocols for 980nm to be tested on pre- osteoblast cell line in my definitive in vitro studies. The first phase of in vitro studies aimed to evaluate the 980nm bio-stimulatory effects on osteoblasts maturation, optimise the PBM effects on bone healing with various beam profiles delivery devices, and establish protocol/protocols of 980nm PBM in bone regeneration. The primary objective was to determine the optimal 980nm dosimetry, which exerts bio- stimulatory effects to accelerate and enhance the bone regenerative process. The secondary objective was to evaluate the intra-cellular pathways of the photon-cell interaction across the metabolic proliferative and differentiation changes, which ultimately lead to bone healing and repair. The results of this study validated the contribution of PBM in bone regeneration and elucidated the biochemical effects at a cellular level. Moreover, the role of different dosages of 980nm PBM irradiation delivered by FT; in comparison to the Gaussian beam profiles (Standard (ST)) on bone regeneration were highlighted. The setup of the power outputs on the laser device was 1.1Watt (W) for the ST and 1W for the FT. However, the real (the threshold) power output reaching the target, measured by power meter, was as ∼0.9 W, (Irradiance ∼ 0.9W/cm2, Exposure time 60 seconds, energy ∼55 J (Joule), fluence ∼55 J/cm2) delivered with the FT beam profile in CW in comparison to the ST, on MC3T3-E1 pre-osteoblast maturation. The protocol was based on 60 seconds exposure time for two consecutive weeks, which employed for all the groups. The laser grouping and their associated irriadtied energies were as follows: Group 1- Irradiation once per week (Total enrgy 110J). Group 2- Irradiation three times per week (Alternate day) (Total energy 330J). Group 3 - irradiation five- times per week (Total energy 550 J). The control cultures were processed in identical conditions except that the laser device was kept off all the time. The total energy was 0J.
The metabolic activity and the osteoblasts maturation were analyzed by alkaline phosphatase assay, alizarin red S histological staining, immunoblot and/or double immunolabeling analysis for Bcl2, Bax, Runx-2, Osx, Dlx5, osteocalcin, and collagen Type 1. Our data, for the first time, prove that laser irradiation of 980 nm wavelength with flattop beam profile delivery system, compared to standard-Gaussian profile, has improved photobiomodulatory efficacy on pre-osteoblastic cells differentiation. Mechanistically, the irradiation enhances the pre-osteoblast differentiation through activation of Wnt signaling as well as the Smads 2/3-βcatenin pathway. Our results indicated and valued the intra-cellular pathways of the photon-cell interaction across the metabolic, proliferative and differentiation changes in the cells. Additionally, our data showed that the cells irradiated THREE times a week (Total energy of 330 J) and ONCE a week (Total energy of 110 J) for two consecutive weeks protocols have increased the proliferation and differentiation of the osteoblasts in both ST & FT hand-pieces but the data showed increasingly statistical significant in the FT group. The only Runx2 was detected when the cells were irradiated with the ST hand-piece. Therefore, total energy of 110 J when either of the hand-pieces utilized, has influenced early differentiation markers. Interestingly, when the process was carried out, until the mineralization and maturation (Late osteogenesis), the ST hand-piece irradiation failed to induce an effective process, and did not lead to matrix deposition, while the FT profile showed a significant effect. In conclusion, our data, for the first time, prove that laser irradiation of 980 nm wavelength with the FT beam profile delivery system in comparison to the ST profile has a great photobiomodulatory efficacy on pre-osteoblastic cells differentiation, which would assist in accelerating bone regeneration, due to its homogeneous energy distribution at each point of its cross-section. Moreover, the irradiation protocols of three times a week and once a week for two consecutive weeks were able to increase the pre-osteoblasts and osteoblasts transcription factors, which were strongly and statistically significantly increased when the FT hand-piece was utilized. Therefore, the 980 nm laser irradiation protocol was able to promote the MC3T3-E1 cell differentiation. Researchers have demonstrated that the major barrier for an effective biological healing is insufficient laser photonic energy delivered to the injured site. PBM can modify the cell metabolism by increasing the mitochondria's ATP production. Currently, the challenge is to understand the target tissues optical properties and its cellular pathway when irradiated with laser phonic energy. In this way, modification of various energy exposure values can influence clinical outcomes predictability. Therefore, in the second phase of my in vitro study, we evaluated the effect of 980nm irradiation delivered with ST and FT beam profile hand-pieces on monolayer cell, at various power outputs; 0.8W, 0.5W and 0.25W. However, the exact power output values reaching the target, measured by power meter, were as follows: 0.75W, 0.45W, and 0.20W respectively. The MC3T3-E1 cells irradiated for two consecutive weeks, according to the following protocols: once a week (Total energy 90, 54, 24 J), respectively); three times a week (total energy 270, 162, 72J, respectively); five times a week (total energy 450, 270, 120 J, respectively). Metabolic activity of viable cells evaluated as follows: Hoechst staining; Western blotting for Runx-2, Bcl2, Bax, Osx, Dlx5, β-catenin, Smads 2/3, TGFβ, p.PI3K, PI3K, p.AKt, AKt, and p.ERK. Our data, for the first time, prove that the 980 nm irradiation at power output setting at 0.75W (0.75W/cm2) for 60 seconds in CW stimulated the MC3T3-E1 pre- osteoblasts viability, by affecting the critical pre-survival markers such as p.PI3K, p.Akt, Bcl2 and Bclxl. Moreover, we concluded that 980nm PBM delivered with FT at 0.75W power output was comparable to results with the ST. However, 0.45W and 0.20W did not modulate the cell metabolic features. Additionally, none of the laser protocols delivered with FT or ST had any influence on the cell differentiation process. In summary, our in vitro studies data, for the first time, have demonstrated the potential of utilizing the FT beam profile with our established protocols in bone regeneration, as a therapeutic tool for future pre-clinical and clinical applications. Moreover, these studies have shown the mechanistic effects of the PBM light on intracellular pathway across the metabolic and differentiation of the osteoblasts towards bone regeneration.

Le travail réalisé dans cette thèse s'intègre globalement dans le cadre de I'observation et la surveillance maritime.Afin d'améliorer la reconnaissance et I'identification automatique de cibles noyées dans un environnement perturbé, nous avons opté à la fusion de différentes connaissances et informations concernant une scène observée à distance par des capteurs micro-ondes. En effet, plusieurs phénomènes physiques co-existent et perturbent la propagation des ondes électromagnétiques au-dessus d'une surface et notamment au-dessus d'une surface maritime hétérogène (la réfraction due aux gradients d'indice, la rugosité de la surface de mer, les effets hydrodynamiques non linéaires du type vagues déferlantes, la présence d'objets, les polluants, sillage de navires, zones côtières, ...). Dans ce contexte, le travail présenté dans cette thèse porte sur l'étude de la signature électromagnétique (coefficients de diffusion) d'une surface maritime hétérogène avec la prise en compte des phénomènes hydrodynamiques (linéaires : vagues de capillarité et de gravité, non linéaires : vagues déferlantes). Cette estimation de la signature électromagnétique est effectuée en configuration bistatique (monostatique et propagation avant) et en bande X. L'étude complète de cette problématique est difficile. En effet, le déferlement est un processus dissipatif de l'énergie qui correspond à la dernière étape de la vie d'une vague et qui a donc le plus souvent lieu à I'approche du rivage. Ce phénomène non linéaire produit un pic de mer qui est une augmentation rapide des coefficients de diffusion et qui peut dépasser 10 dB dans une période de 100 ms. Ce pic peut conduire à des échos parasites, qui peuvent être identifiés comme des cibles virtuelles, et par la suite elles peuvent perturber le système de détection radar (fausses alarmes). Par conséquent, pour améliorer le processus de détection et pour réduire le taux de fausses alarmes, il est important de distinguer entre les cibles et les pics de mer générés par des vagues déferlantes. Ceci constitue I’une des motivations et aussi I'intérêt d'étudier la signature électromagnétique des vagues déferlantes dans différentes configurations d'observation de sorte que nous puissions facilement indiquer la présence voir I'identification des pics de mer. Pour contribuer à cette problématique, nous avons proposé une méthodologie basée sur un modèle électromagnétique hybride basé sur une combinaison d'une part de méthodes asymptotiques(SPMI utilisée dans le cadre de ce travail) pour simuler la réponse radar des vagues linéaire (vagues de capillarité et de gravité décrites via le spectre de mer d'Elfouhaily), et d'autre part de méthodes exactes (MoM, FB < Forward-Backward ) retenue dans le travail présenté dans ce manuscrit) pour calculer la réponse électromagnétique des vagues non-linéaires (profils considérés sont issus des résultats du code LONGTANK). Afìn de compléter l'étude théorique et les simulations réalisées, nous avons effectué une phase d'évaluation et de validation par des mesures de signature radar réalisées dans la chambre anéchoïque de I'Ensta Bretagne
The work done in this thesis fits generally under the observation and maritime surveillance. To improve the detection and automatic identification of targets embedded in a noisy environment targets, we opted for the fusion of different knowledge and information regarding a remotely observed scene by microwave sensors. Indeed, several physical phenomena co-exist and interfere with the propagation of electromagnetic waves over a heterogeneous sea surface (the refraction due to the index gradients, the roughness of the sea surface, nonlinear hydrodynamic effects like waves breaking, the presence of objects, pollutants, ship wake, coastal areas,..). In this context, the work presented in this thesis focuses on the study of electromagnetic signature (diffusion coefficients) of a heterogeneous sea surface with consideration of hydrodynamic phenomena (linear: capillary and gravity waves, nonlinear: breaking waves). The electromagnetic signature is performed in bistatic configuration (monostatic and forward propagating) and in X-band. The complete study of this problem is difficult.Indeed, the breaking wave is a dissipative process of energy that corresponds to the last stage of the life of a wave and therefore has most often held in the shore. This nonlinear phenomenon produces a sea peak which is a rapid increase of the diffusion coefficients and can exceed l0 dB in a 100 ms period. This peak can lead to clutter, which can be identified as virtual targets, and then they can disrupt the detection radar system (false alarms). Therefore, to improve the detection process and reduce the false alarm rate, it is important to distinguish between targets and sea peaks generated by breaking waves. This represents one of the motivations and also the interest to study the electromagnetic signature of breaking waves in different observation configurations so that we can easily detect and identify the sea peaks. To solve this problem, we proposed a methodology based on a hybrid electromagnetic model which is on a combination of asymptotic methods (SPMI used in this work) to simulate the radar response of linear waves (capillary and gravity waves described via the Elfouhaily sea spectrum) and an exact methods, the method of moment (the FB "Forward-Backward" method is used in this work), to calculate the electromagnetic response of nonlinear waves (profiles are produced by the LONGTANK code). To complement the theoretical study and simulations, we carried out an evaluation and validation phase by measuring the radar signature of breaking wave profiles in the ENSTA Bretagne anechoic chamber

Las exigentes tolerancias de alineación en los componentes de los futuros colisionadores lineales de partículas requieren el desarrollo de nuevas técnicas de alineación más precisas que las existentes. Este es el caso del Colisionador Lineal Compacto (Compact Linear Collider, CLIC), cuyos objetivos altamente restrictivos de alineamiento alcanzan los 10 um. Para poder lograr el máximo rendimiento del acelerador, es necesario que el posicionamiento de las estructuras que aceleran las partículas y de los campos que las guían cumplan las tolerancias de alineación para dirigir el haz a lo largo de la trayectoria diseñada. Dicho procedimiento consiste en relacionar la posición de los ejes de referencia de cada componente con respecto a objetos externos, o fiduciales, lo cual resulta muy tedioso y económicamente costoso. Los errores sistemáticos y aleatorios se van acumulando en cada paso del proceso y, en consecuencia, la precisión final de alineamiento es todo un desafío. En este contexto, nace el proyecto PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometre scale), subvencionado por la Unión Europea en el programa FP7 de financiación para la investigación e innovación. El objetivo principal de PACMAN es investigar, desarrollar e implementar una solución integrada alternativa que incorpore todos los pasos de alineación en una misma ubicación, con el objetivo de mejorar la precisión de alineación de los componentes de los aceleradores, en concreto: las estructuras aceleradoras, los cuadrupolos y los monitores de posición de haz. La viabilidad de las soluciones desarrolladas y la precisión de alineamiento alcanzada deben de demostrarse en un banco de pruebas utilizando componentes de CLIC. La estrategia de PACMAN para alcanzar el objetivo técnico se divide en tres pasos. El primero consiste en la fiducialización de los componentes y sus soportes. El segundo paso es el ensamblaje de los componentes en dos tipos de soporte, uno compuesto por un monitor de posición de haz y un cuadrupolo, y otro con cuatro estructuras aceleradoras, tomando como referencia su centro electromagnético. Finalmente, ambos soportes se transportan al túnel para su alineación final utilizando técnicas de hilos tensados. En esta tesis doctoral, se describe el desarrollo de una nueva técnica no destructiva para localizar los ejes electromagnéticos de estructuras aceleradoras y su validación experimental. Para ello, se ha utilizado una estructura aceleradora de CLIC conocida como TD24. Debido a la complejidad mecánica de la TD24, su difícil acceso y su diámetro medio de iris de 5.5 mm, se desarrolla una nueva técnica denominada en esta tesis como 'el método perturbativo' y se realiza una propuesta experimental de validación. El estudio de viabilidad de este método, cumpliendo con los requisitos impuestos de precisión en la medida de 10 um, ha sido realizado con una campaña extensa de simulaciones de campos electromagnéticos en tres dimensiones utilizando la herramienta de software conocida como HFSS. Los resultados de simulación han permitido el desarrollo de un algoritmo muy completo de medidas y han proporcionado las especificaciones técnicas para el diseño conceptual de un banco de pruebas para la medida de los ejes electromagnéticos de la TD24. El preciso ensamblaje del banco de pruebas y sus correspondientes calibraciones, la incorporación de nuevos tratamientos de las medidas en el algoritmo final y la caracterización de fuentes de error en la medida, favorecieron la localización del centro electromagnético en la TD24 con una precisión menor a 1 um con un error estimado menor que 8.5 um, cumplimiendo con los objetivos de precisión establecidos.
In the next generation of linear particle accelerators, challenging alignment tolerances are required in the positioning of the components focusing, accelerating and detecting the beam over the accelerator length in order to achieve the maximum machine performance. In the case of the Compact Linear Collider (CLIC), accelerating structures, beam position monitors and quadrupole magnets need to be aligned in their support with respect to their reference axes with an accuracy of 10 um. To reach such objective, the PACMAN (Particle Accelerator Components Metrology and Alignment to the Nanometer Scale) project strives for the improvement of the current alignment accuracy by developing new methods and tools, whose feasibility should be validated using the major CLIC components. This Ph.D. thesis concerns the investigation, development and implementation of a new non-destructive intracavity technique, referenced here as 'the perturbative method', to determine the electromagnetic axes of accelerating structures by means of a stretched wire, acting as a reference of alignment. Of particular importance is the experimental validation of the method through the 5.5 mm iris-mean aperture CLIC prototype known as TD24, with complex mechanical features and difficult accessibility, in a dedicated test bench. In the first chapter of this thesis, the alignment techniques in particle accelerators and the novel proposals to be implemented in the future linear colliders are introduced, and a detailed description of the PACMAN project is provided. The feasibility study of the method, carried out with extensive electromagnetic fields simulations, is described in chapter 2, giving as a result, the knowledge of the theoretical accuracy expected in the measurement of the electromagnetic axes and facilitating the development of a measurement algorithm. The conceptual design, manufacturing and calibration of the automated experimental set-up, integrating the solution developed to measure the electromagnetic axes of the TD24, are covered in chapter 3. The future lines of research and developments of the perturbative method are also explored. In chapter 4, the most significant results obtained from an extensive experimental work are presented, analysed and compared with simulations. The proof-of-principle is completed, the measurement algorithm is optimised and the electromagnetic centre is measured in the TD24 with a precision less than 1 um and an estimated error less than 8.5 um. Finally, in chapter 5, the developments undertaken along this research work are summarised, the innovative achievements accomplished within the PACMAN project are listed and its impact is analysed.
En la generació pròxima d'acceleradors de partícules lineals, desafiant toleràncies d'alineament és requerit en el posicionament dels components que enfoquen, accelerant i detectant la biga sobre la longitud d'accelerador per tal d'aconseguir l'actuació de màquina màxima. En el cas del Colisionador Compacte Lineal (CLIC), accelerant estructures, monitors de posició de fes i imants necessiten ser alineats en el seu suport amb respectar a les seves destrals de referència amb una precisió de 10 um. Per assolir tal objectiu, el PACMAN (Metrologia de Components de l'Accelerador de partícules i Alineament al Nanometer Escala) projecte s'esforça per la millora de l'actual precisió d'alineament per mètodes nous en desenvolupament i eines, la viabilitat dels quals hauria de ser validada utilitzant els components de CLIC importants. Aquesta tesi concerneix la investigació, desenvolupament i implementació d'un nou no-destructiu tècnica interna, va referenciar ací mentre 'el mètode de pertorbació' per determinar les destrals electromagnètiques d'accelerar estructures mitjançant un cable estès, actuant com a referència d'alineament. De la importància particular és la validació experimental del mètode a través del 5.5 mm iris-roí obertura prototipus de CLIC sabut com TD24, amb característiques mecàniques complexes i accessibilitat difícil, en un banc de prova dedicat. En el primer capítol d'aquesta tesi, les tècniques d'alineament en acceleradors de partícules i les propostes novelles per ser implementades en el futur colisionador lineal és introduït, i una descripció detallada del projecte PACMAN és proporcionat. L'estudi de viabilitat el mètode de pertorbació, va dur a terme amb simulacres de camps electromagnètics extensos, és descrit dins capitol 2, donant com a resultat, el coneixement de la precisió teòrica esperada en la mida de les destrals electromagnètiques i facilitant el desenvolupament d'un algoritme de mida. El disseny conceptual, fabricació i calibratge del conjunt experimental automatitzat-amunt, integrant la solució desenvolupada per mesurar les destrals electromagnètiques del TD24, és cobert dins capitol 3. Les línies futures de recerca i desenvolupaments del mètode és també va explorar. Dins capitol 4, la majoria de resultats significatius van obtenir d'una faena experimental extensa és presentada, analitzat i comparat amb simulacres. La prova-de-el principi és completat, l'algoritme de mida és optimitzat i el centre electromagnètic és mesurat en el TD24 amb una precisió menys d'1 um i un error calculat menys de 8.5 um. Finalment, dins capitol 5, els desenvolupaments empresos al llarg d'aquesta faena de recerca és resumit, les consecucions innovadores van acomplir dins del projecte PACMAN és llistat i el seu impacte és analitzat.
Galindo Muñoz, N. (2018). Development of direct measurement techniques for the in-situ internal alignment of accelerating structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100488
TESIS

Electromagnetic imaging is the problem of determining material properties from scattered fields measured away from the domain under investigation. Solving this inverse problem is a challenging task because (i) it is ill-posed due to the presence of (smoothing) integral operators used in the representation of scattered fields in terms of material properties, and scattered fields are obtained at a finite set of points through noisy measurements; and (ii) it is nonlinear simply due the fact that scattered fields are nonlinear functions of the material properties. The work described in this thesis tackles the ill-posedness of the electromagnetic imaging problem using sparsity-based regularization techniques, which assume that the scatterer(s) occupy only a small fraction of the investigation domain. More specifically, four novel imaging methods are formulated and implemented. (i) Sparsity-regularized Born iterative method iteratively linearizes the nonlinear inverse scattering problem and each linear problem is regularized using an improved iterative shrinkage algorithm enforcing the sparsity constraint. (ii) Sparsity-regularized nonlinear inexact Newton method calls for the solution of a linear system involving the Frechet derivative matrix of the forward scattering operator at every iteration step. For faster convergence, the solution of this matrix system is regularized under the sparsity constraint and preconditioned by leveling the matrix singular values. (iii) Sparsity-regularized nonlinear Tikhonov method directly solves the nonlinear minimization problem using Landweber iterations, where a thresholding function is applied at every iteration step to enforce the sparsity constraint. (iv) This last scheme is accelerated using a projected steepest descent method when it is applied to three-dimensional investigation domains. Projection replaces the thresholding operation and enforces the sparsity constraint. Numerical experiments, which are carried out using synthetically generated or actually measured scattered fields, show that the images recovered by these sparsity-regularized methods are sharper and more accurate than those produced by existing methods. The methods developed in this work have potential application areas ranging from oil/gas reservoir engineering to biological imaging where sparse domains naturally exist.

碩士
國立中央大學
電機工程研究所
87
In the last two decades, many experimental and theoretical studi-es on propagation characteristics of UHF radio signals have been car-ried out, especially in the radio wave propagation in urban and subur-ban area. As a result, several empirical and theoretical radio wave propagation models for these service areas were developed. Most of these studies concentrate on the effects of wave reflection and dif-fraction phenomena, while the effect of electromagnetic wave scat-tering from rough surface is often ignored. But there can be signifi-cant fluctuations of signal level due to scattering in wireless commu-nications. However, no methodology exists to model those fluctua-tions. In this discussion, the received signals in wireless communica-tion systems that are impacted by the scattering mechanism of the sur-face with different roughness are analyzed. The relative importance of the coherent and incoherent scattering mechanism is related to the surface state. The coherent scattering component is dominant for a plain surface, while the incoherent component is dominant for a rough surface. Both carrier to multipath ( C/M ) and carrier to specular ( C/S ) ratios are evaluated and compared each other for differently rough surfaces.

A two-Dimensional Finite Element Method of electromagnetic (EM) wave propagation through the soil is presented in this chapter. The chapter employs a boundary value problem (BVP) to solve the Helmholtz time-harmonic electromagnetic model. An infinitely large dielectric object of an arbitrary cross-section is considered for scattering from a dielectric medium and illuminated by an incident wave. Since the domain extends to infinity, an artificial boundary, a perfectly matched layer (PML) is used to truncate the computational domain. The incident field, the scattered field, and the total field in terms of the z-component are expressed for the transverse magnetic (TM) and transverse electric (TE) modes. The radar cross-section (RCS), as a function of several other parameters, such as operating frequency, polarization, illumination angle, observation angle, geometry, and material properties of the medium, is computed to describe how a scatterer reflects an electromagnetic wave in a given direction. Simulation results obtained from MATLAB for the scattered field, the total field, and the radar cross-section are presented for three soil types – sand, loam, and clay.