Electromagnetic Scattering From Two-Scatterers Using the Extended Propagation-Inside-Layer Expansion Method

In this paper, the electromagnetic scattering from two scatterers is analyzed from a rigorous integral formulation solved by the method of moments (MoM). G. Kubick´e has recently developed the E-PILE (Extended Propagation-Inside-Layer Expansion) method to calculate the scattering from an object above a rough surface for a two-dimensional problem. This method allows us to calculate separately and exactly the interactions between the object and the rough surface. The purpose of this paper is to extend the E-PILE method to a three-dimensional problem

Approches tomographiques structurelles pour l'analyse du milieu urbain par tomographie SAR THR : TomoSAR

SAR tomography consists in exploiting multiple images from the same area acquired from a slightly different angle to retrieve the 3-D distribution of the complex reflectivity on the ground. As the transmitted waves are coherent, the desired spatial information (along with the vertical axis) is coded in the phase of the pixels. Many methods have been proposed to retrieve this information in the past years. However, the natural redundancies of the scene are generally not exploited to improve the tomographic estimation step. This Ph.D. presents new approaches to regularize the estimated reflectivity density obtained through SAR tomography by exploiting the urban geometrical structures.La tomographie SAR exploite plusieurs acquisitions d'une même zone acquises d'un point de vue légerement différent pour reconstruire la densité complexe de réflectivité au sol. Cette technique d'imagerie s'appuyant sur l'émission et la réception d'ondes électromagnétiques cohérentes, les données analysées sont complexes et l'information spatiale manquante (selon la verticale) est codée dans la phase. De nombreuse méthodes ont pu être proposées pour retrouver cette information. L'utilisation des redondances naturelles à certains milieux n'est toutefois généralement pas exploitée pour améliorer l'estimation tomographique. Cette thèse propose d'utiliser l'information structurelle propre aux structures urbaines pour régulariser les densités de réflecteurs obtenues par cette technique

Nuclear methods for real-time range verification in proton therapy based on prompt gamma-ray imaging

Accelerated protons are excellent candidates for treating several types of tumours. Such charged particles stop at a defined depth, where their ionisation density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nonetheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of proton over photon therapy and limits its ultimate aspirations. Prompt gamma rays, a by-product of the irradiation that is correlated to the dose deposition, are reliable signatures for the detection of range deviations and even for three-dimensional in vivo dosimetry. In this work, two methods for Prompt Gamma-ray Imaging (PGI) are investigated: the Compton camera (Cc) and the Prompt Gamma-ray Timing (PGT). Their applicability in a clinical scenario is discussed and compared. The first method aspires to reconstruct the prompt gamma ray emission density map based on an iterative imaging algorithm and multiple position sensitive gamma ray detectors. These are arranged in scatterer and absorber plane. The second method has been recently proposed as an alternative to collimated PGI systems and relies on timing spectroscopy with a single monolithic detector. The detection times of prompt gamma rays encode essential information about the depth-dose profile as a consequence of the measurable transit time of ions through matter. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and OncoRay, detector components are characterised in realistic radiation environments as a step towards a clinical Cc. Conventional block detectors deployed in commercial Positron Emission Tomography (PET) scanners, made of Cerium-doped lutetium oxyorthosilicate - Lu2SiO5:Ce (LSO) or Bismuth Germanium Oxide - Bi4Ge3O12 (BGO) scintillators, are suitable candidates for the absorber of a Cc due to their high density and absorption efficiency with respect to the prompt gamma ray energy range (several MeV). LSO and BGO block detectors are compared experimentally in clinically relevant radiation fields in terms of energy, spatial and time resolution. On a different note, two BGO block detectors (from PET scanners), arranged as the BGO block Compton camera (BbCc), are deployed for simple imaging tests with high energy prompt gamma rays produced in homogeneous Plexiglas targets by a proton pencil beam. The rationale is to maximise the detection efficiency in the scatterer plane despite a moderate energy resolution. Target shifts, increase of the target thickness and beam energy variation experiments are conducted. Concerning the PGT concept, in a collaboration among OncoRay, HZDR and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with several detectors and heterogeneous phantoms is performed. The sensitivity of the method to range shifts is investigated, the robustness against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterised for different proton energies. With respect to the material choice for the absorber of the Cc, the BGO scintillator closes the gap with respect to the brighter LSO. The reason behind is the high energies of prompt gamma rays compared to the PET scenario, which increase significantly the energy, spatial and time resolution of BGO. Regarding the BbCc, shifts of a point-like radioactive source are correctly detected, line sources are reconstructed, and one centimetre proton range deviations are identified based on the evident changes of the back projection images. Concerning the PGT experiments, for clinically relevant doses, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. Experimental data are well reproduced by analytical modelling. The Cc and the PGT are ambitious approaches for range verification in proton therapy based on PGI. Intensive detector characterisation and tests in clinical facilities are mandatory for developing robust prototypes, since the energy range of prompt gamma rays spans over the MeV region, not used traditionally in medical applications. Regarding the material choice for the Cc: notwithstanding the overall superiority of LSO, BGO catches up in the field of PGI. It can be considered as a competitive alternative to LSO for the absorber plane due to its lower price, higher photoabsorption efficiency, and the lack of intrinsic radioactivity. The results concerning the BbCc, obtained with relatively simple means, highlight the potential application of Compton cameras for high energy prompt gamma ray imaging. Nevertheless, technical constraints like the low statistics collected per pencil beam spot (if clinical currents are used) question their applicability as a real-time and in vivo range verification method in proton therapy. The PGT is an alternative approach, which may have faster translation into clinical practice due to its lower price and higher efficiency. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype, that may detect significant range deviations for the strongest beam spots. The experimental results emphasise the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.:1 Introduction 1.1 Proton therapy 1.1.1 The beginnings 1.1.2 Essential features 1.1.3 Advantages and drawbacks 1.2 Range uncertainties and their consequences 1.3 Range verification methods 1.4 Prompt gamma-ray imaging 1.4.1 Passive collimation 1.4.2 Active collimation 1.4.3 Correlation to dose 1.5 Aim of this work 2 Compton camera 2.1 Theoretical background 2.1.1 Compton formula and Klein-Nishina cross section 2.1.2 Detection principle 2.1.3 Intersection of cone surface and plane 2.1.4 Practical considerations 2.2 Motivation 2.3 Goals 2.4 Materials 2.4.1 Scintillator properties 2.4.2 Block detector properties 2.4.3 Electronics and data acquisition 2.4.4 High efficiency Compton camera setup 2.5 Experimental setup 2.5.1 Accelerators 2.5.2 Detector setup 2.5.3 Trigger regime 2.6 Methods 2.6.1 Energy calibration 2.6.2 Spatial calibration 2.6.3 Time calibration 2.6.4 Error analysis 2.6.5 Systematic measurement program 2.7 Results – absorber choice 2.7.1 Energy resolution 2.7.2 Spatial resolution 2.7.3 Time resolution 2.8 Discussion – absorber choice 2.9 Results – BbCc setup 2.10 Discussion – BbCc setup 3 Prompt gamma-ray timing 3.1 Theoretical background 3.1.1 Detection principle 3.1.2 Kinematics 3.1.3 Detector model 3.1.4 Quantitative assessment 3.2 Goals 3.3 Materials 3.3.1 Detectors 3.3.2 Electronics 3.3.3 Accelerators 3.4 Methods 3.4.1 Detector and module settings 3.4.2 Proton bunch phase stability 3.4.3 Proton bunch time structure 3.4.4 Systematic measurement program 3.4.5 Data acquisition rate 3.4.6 Data analysis 3.4.7 Modelling of PGT spectra 3.5 Results 3.5.1 Intrinsic detector time resolution 3.5.2 Illustrative energy over time spectra 3.5.3 Proton bunch phase stability 3.5.4 Proton bunch time structure 3.5.5 Systematic measurement program 3.6 Discussion 3.7 Conclusions 4 Discussion 4.1 Detector load, event throughput and spot duration 4.2 Comparison of PGI systems 4.3 Summary 4.4 Zusammenfassung BibliographyBeschleunigte Protonen sind ausgezeichnete Kandidaten für die Behandlung von diversen Tumorarten. Diese geladenen Teilchen stoppen in einer bestimmten Tiefe, bei der die Ionisierungsdichte maximal ist. Da die deponierte Dosis hinter der distalen Kante sehr klein ist, minimiert die Protonentherapie den Schaden an normalem Gewebe verglichen mit der Photonentherapie. Inhärente Reichweitenunsicherheiten stellen jedoch die Bestrahlung von Tumoren in der Nähe von Risikoorganen in Frage und führen zur Anwendung von konservativen Sicherheitssäumen. Dadurch werden die potentiellen Vorteile der Protonen- gegenüber der Photonentherapie sowie ihre letzten Ziele eingeschränkt. Prompte Gammastrahlung, ein Nebenprodukt der Bestrahlung, welche mit der Dosisdeposition korreliert, ist eine zuverlässige Signatur um Reichweitenunterschiede zu detektieren und könnte sogar für eine dreidimensionale in vivo Dosimetrie genutzt werden. In dieser Arbeit werden zwei Methoden für Prompt Gamma-ray Imaging (PGI) erforscht: die Compton-Kamera (CK) und das Prompt Gamma-ray Timing (PGT)-Konzept. Des Weiteren soll deren Anwendbarkeit im klinischen Szenario diskutiert und verglichen werden. Die erste Methode strebt nach der Rekonstruktion der Emissionsdichtenverteilung der prompten Gammastrahlung und basiert auf einem iterativen Bildgebungsalgorithmus sowie auf mehreren positionsempfindlichen Detektoren. Diese werden in eine Streuer- und Absorberebene eingeteilt. Die zweite Methode ist vor Kurzem als eine Alternative zu kollimierten PGI Systemen vorgeschlagen worden, und beruht auf dem Prinzip der Zeitspektroskopie mit einem einzelnen monolithischen Detektor. Die Detektionszeiten der prompten Gammastrahlen beinhalten entscheidende Informationen über das Tiefendosisprofil aufgrund der messbaren Durchgangszeit von Ionen durch Materie. Am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) und OncoRay werden Detektorkomponenten in realistischen Strahlungsumgebungen als ein Schritt zur klinischen CK charakterisiert. Konventionelle Blockdetektoren, welche in kommerziellen Positronen-Emissions-Tomographie (PET)-Scannern zum Einsatz kommen und auf Cer dotiertem Lutetiumoxyorthosilikat - Lu2SiO5:Ce (LSO) oder Bismutgermanat - Bi4Ge3O12 (BGO) Szintillatoren basieren, sind geeignete Kandidaten für den Absorber einer CK wegen der hohen Dichte und Absorptionseffizienz im Energiebereich von prompten Gammastrahlen (mehrere MeV). LSO- und BGO-Blockdetektoren werden in klinisch relevanten Strahlungsfeldern in Bezug auf Energie-, Orts- und Zeitauflösung verglichen. Weiterhin werden zwei BGO-Blockdetektoren (von PET-Scannern), angeordnet als BGO Block Compton-Kamera (BBCK), benutzt, um die Bildgebung von hochenergetischen prompten Gammastrahlen zu untersuchen, die in homogenen Plexiglas-Targets durch einen Protonen-Bleistiftstrahl emittiert werden. Die Motivation hierfür ist, die Detektionseffizienz der Streuerebene zu maximieren, wobei jedoch die Energieauflösung vernachlässigt wird. Targetverschiebungen, sowie Änderungen der Targetdicke und der Teilchenenergie werden untersucht. In einer Kollaboration zwischen OncoRay, HZDR and IBA, wird der erste Test des PGT-Konzepts an einem klinischen Protonenbeschleuniger (Westdeutsches Protonentherapiezentrum Essen) mit mehreren Detektoren und heterogenen Phantomen durchgeführt. Die Sensitivität der Methode hinsichtlich Reichweitenveränderungen wird erforscht. Des Weiteren wird der Einfluss von Untergrund und Stabilität des Zeitprofils des Strahlenbündels untersucht, sowie die Zeitverschmierung des Bündels für verschiedene Protonenenergien charakterisiert. Für die Materialauswahl für den Absorber der CK ergibt sich, dass sich BGO dem lichtstärkeren LSO Szintillator angleicht. Der Grund dafür sind die höheren Energien der prompten Gammastrahlung im Vergleich zum PET Szenario, welche die Energie-, Orts- und Zeitauflösung von BGO stark verbessern. Anhand von offensichtlichen Änderungen der Rückprojektionsbilder zeigt sich, dass mit der BBCK Verschiebungen einer punktförmigen radioaktiven Quelle erfolgreich detektiert, Linienquellen rekonstruiert und Verschiebungen der Protonenreichweite um einen Zentimeter identifiziert werden. Für die PGT-Experimente können mit einem einzigen Detektor Reichweitenunterschiede von fünf Millimetern für definierte heterogene Targets bei klinisch relevanten Dosen detektiert werden. Dies wird durch den numerischen Vergleich der Spektrumform ermöglicht. Bei größerer Ereigniszahl können Reichweitenunterschiede von bis zu zwei Millimetern detektiert werden. Die experimentellen Daten werden durch analytische Modellierung wiedergegeben. Die CK und das PGT-Konzept sind ambitionierte Ansätze zur Verifizierung der Reichweite in der Protonentherapie basierend auf PGI. Intensive Detektorcharakterisierung und Tests an klinischen Einrichtungen sind Pflicht für die Entwicklung geeigneter Prototypen, da der Energiebereich prompter Gammastrahlung sich über mehrere MeV erstreckt, was nicht dem Normbereich der traditionellen medizinischen Anwendungen entspricht. Im Bezug auf die Materialauswahl der CK wird ersichtlich, dass BGO trotz der allgemeinen Überlegenheit von LSO für die Anwendung im Bereich PGI aufholt. Wegen des niedrigeren Preises, der höheren Photoabsorptionseffizienz und der nicht vorhandenen Eigenaktivität erscheint BGO als eine konkurrenzfähige Alternative für die Absorberebene der CK im Vergleich zu LSO. Die Ergebnisse der BBCK, welche mit relativ einfachen Mitteln gewonnen werden, heben die potentielle Anwendung von Compton-Kameras für die Bildgebung prompter hochenergetischer Gammastrahlen hervor. Trotzdem stellen technische Beschränkungen wie die mangelnde Anzahl von Messereignissen pro Bestrahlungspunkt (falls klinische Ströme genutzt werden) die Anwendbarkeit der CK als Echtzeit- und in vivo Reichweitenverifikationsmethode in der Protonentherapie in Frage. Die PGT-Methode ist ein alternativer Ansatz, welcher aufgrund der geringeren Kosten und der höheren Effizienz eine schnellere Umsetzung in die klinische Praxis haben könnte. Ein Protonenbunchmonitor, höherer Detektordurchsatz und eine quantitative Reichweitenrekonstruktion sind die weiteren Schritte in Richtung eines klinisch anwendbaren Prototyps, der signifikante Reichweitenunterschiede für die stärksten Bestrahlungspunkte detektieren könnte. Die experimentellen Ergebnisse unterstreichen das Potential dieser Reichweitenverifikationsmethode an einem klinischen Bleistiftstrahl und lassen diesen neuartigen Ansatz als eine vielversprechende Alternative auf dem Gebiet der in vivo Dosimetrie erscheinen.:1 Introduction 1.1 Proton therapy 1.1.1 The beginnings 1.1.2 Essential features 1.1.3 Advantages and drawbacks 1.2 Range uncertainties and their consequences 1.3 Range verification methods 1.4 Prompt gamma-ray imaging 1.4.1 Passive collimation 1.4.2 Active collimation 1.4.3 Correlation to dose 1.5 Aim of this work 2 Compton camera 2.1 Theoretical background 2.1.1 Compton formula and Klein-Nishina cross section 2.1.2 Detection principle 2.1.3 Intersection of cone surface and plane 2.1.4 Practical considerations 2.2 Motivation 2.3 Goals 2.4 Materials 2.4.1 Scintillator properties 2.4.2 Block detector properties 2.4.3 Electronics and data acquisition 2.4.4 High efficiency Compton camera setup 2.5 Experimental setup 2.5.1 Accelerators 2.5.2 Detector setup 2.5.3 Trigger regime 2.6 Methods 2.6.1 Energy calibration 2.6.2 Spatial calibration 2.6.3 Time calibration 2.6.4 Error analysis 2.6.5 Systematic measurement program 2.7 Results – absorber choice 2.7.1 Energy resolution 2.7.2 Spatial resolution 2.7.3 Time resolution 2.8 Discussion – absorber choice 2.9 Results – BbCc setup 2.10 Discussion – BbCc setup 3 Prompt gamma-ray timing 3.1 Theoretical background 3.1.1 Detection principle 3.1.2 Kinematics 3.1.3 Detector model 3.1.4 Quantitative assessment 3.2 Goals 3.3 Materials 3.3.1 Detectors 3.3.2 Electronics 3.3.3 Accelerators 3.4 Methods 3.4.1 Detector and module settings 3.4.2 Proton bunch phase stability 3.4.3 Proton bunch time structure 3.4.4 Systematic measurement program 3.4.5 Data acquisition rate 3.4.6 Data analysis 3.4.7 Modelling of PGT spectra 3.5 Results 3.5.1 Intrinsic detector time resolution 3.5.2 Illustrative energy over time spectra 3.5.3 Proton bunch phase stability 3.5.4 Proton bunch time structure 3.5.5 Systematic measurement program 3.6 Discussion 3.7 Conclusions 4 Discussion 4.1 Detector load, event throughput and spot duration 4.2 Comparison of PGI systems 4.3 Summary 4.4 Zusammenfassung Bibliograph

Seismic evidence for Earth’s crusty deep mantle

Seismic tomography resolves anomalies interpreted as oceanic lithosphere subducted deep into Earth’s lower mantle. However, the fate of the compositionally distinct oceanic crust that is part of the lithosphere is poorly constrained but provides important constraints on mixing processes and the recycling process in the deep Earth. We present high-resolution seismic array analyses of anomalous P-waves sampling the deep mantle, and deterministically locate heterogeneities in the lowermost 300 km of the mantle. Spectral analysis indicates that the dominant scale length of the heterogeneity is 4 to 7 km. The heterogeneity distribution varies laterally and radially and heterogeneities are more abundant near the margins of the lowermost mantle Large Low Velocity Provinces (LLVPs), consistent with mantle convection simulations that show elevated accumulations of deeply advected crustal material near the boundaries of thermo-chemical piles. The size and distribution of the observed heterogeneities is consistent with that expected for subducted oceanic crust. These results thus suggest the deep mantle contains an imprint of continued subduction of oceanic crust, stirred by mantle convection and modulated by long lasting thermo-chemical structures. The preferred location of the heterogeneity in the lowermost mantle is consistent with a thermo-chemical origin of the LLVPs. Our observations relate to the mixing behaviour of small length-scale heterogeneity in the deep Earth and indicate that compositional heterogeneities from the subduction process can survive for extended times in the lowermost mantle

Single scattering from nonspherical Chebyshev particles: A compendium of calculations

A large set of exact calculations of the scattering from a class of nonspherical particles known as Chebyshev particles' has been performed. Phase function and degree of polarization in random orientation, and parallel and perpendicular intensities in fixed orientations, are plotted for a variety of particles shapes and sizes. The intention is to furnish a data base against which both experimental data, and the predictions of approximate methods, can be tested. The calculations are performed with the widely-used Extended Boundary Condition Method. An extensive discussion of this method is given, including much material that is not easily available elsewhere (especially the analysis of its convergence properties). An extensive review is also given of all extant methods for nonspherical scattering calculations, as well as of the available pool of experimental data

Cavity quantum electrodynamics with three-dimensional photonic bandgap crystals

This paper gives an overview of recent work on three-dimensional (3D) photonic crystals with a "full and complete" 3D photonic band gap. We review five main aspects: 1) spontaneous emission inhibition, 2) spatial localization of light within a tiny nanoscale volume (aka "a nanobox for light"), 3) the introduction of a gain medium leading to thresholdless lasers, 4) breaking of the weak-coupling approximation of cavity QED, both in the frequency and in the time-domain, 5) decoherence, in particular the shielding of vacuum fluctuations by a 3D photonic bandgap. In addition, we list and evaluate all known photonic crystal structures with a demonstrated 3D band gap.Comment: 21 pages, 6 figures, 2 tables, Chapter 8 in "Light Localisation and Lasing: Random and Pseudorandom Photonic Structures", Eds. M. Ghulinyan and L. Pavesi (Cambridge University Press, Cambridge, 2015, ISBN 978-1-107-03877-6

CHANNEL MODELING FOR FIFTH GENERATION CELLULAR NETWORKS AND WIRELESS SENSOR NETWORKS

In view of exponential growth in data traffic demand, the wireless communications industry has aimed to increase the capacity of existing networks by 1000 times over the next 20 years. A combination of extreme cell densification, more bandwidth, and higher spectral efficiency is needed to support the data traffic requirements for fifth generation (5G) cellular communications. In this research, the potential improvements achieved by using three major 5G enabling technologies (i.e., small cells, millimeter-wave spectrum, and massive MIMO) in rural and urban environments are investigated. This work develops SPM and KA-based ray models to investigate the impact of geometrical parameters on terrain-based multiuser MIMO channel characteristic. Moreover, a new directional 3D channel model is developed for urban millimeter-wave (mmW) small cells. Path-loss, spatial correlation, coverage distance, and coherence length are studied in urban areas. Exploiting physical optics (PO) and geometric optics (GO) solutions, closed form expressions are derived for spatial correlation. Achievable spatial diversity is evaluated using horizontal and vertical linear arrays as well as planar 2D arrays. In another study, a versatile near-ground field prediction model is proposed to facilitate accurate wireless sensor network (WSN) simulations. Monte Carlo simulations are used to investigate the effects of antenna height, frequency of operation, polarization, and terrain dielectric and roughness properties on WSNs performance

Polarimetric Synthetic Aperture Radar

This open access book focuses on the practical application of electromagnetic polarimetry principles in Earth remote sensing with an educational purpose. In the last decade, the operations from fully polarimetric synthetic aperture radar such as the Japanese ALOS/PalSAR, the Canadian Radarsat-2 and the German TerraSAR-X and their easy data access for scientific use have developed further the research and data applications at L,C and X band. As a consequence, the wider distribution of polarimetric data sets across the remote sensing community boosted activity and development in polarimetric SAR applications, also in view of future missions. Numerous experiments with real data from spaceborne platforms are shown, with the aim of giving an up-to-date and complete treatment of the unique benefits of fully polarimetric synthetic aperture radar data in five different domains: forest, agriculture, cryosphere, urban and oceans

Nanoplasmonic surface structures for integrated photonics

Nanoplasmonic surfaces are known to be able to alter the localisation and propagation characteristics of light owing to the subwavelength interactions with the metallic elements. The recent improvements of nanolithography and self-assembly techniques have enabled the design of ever smaller and intricate structures with a high precision, allowing for research into more complex nanoplasmonic structures that control light on the nano-scale. Up until now, plasmonic surfaces are mostly operated with out-of-plane excitation which, although well-established and experimentally convenient to perform, has limited potential for on-chip applications. The integration of surface plasmonic structures with photonic waveguides allows for light to be confined to a guiding layer while being kept in interaction along the surface structure without inducing uncontrolled scattering or excessive dissipative loss. In this work, plasmonic surface structures such as plasmonic antennas and array structures that are integrated with a CMOS compatible platform are explored. In particular, a new class of plasmonic surfaces, plasmonic nanogap tilings, are introduced. Remarkably, these simple periodic structures provide a rich physics characterised by many different regimes of operation, including subwavelength surface enhancement, hybrid plasmonic-photonic resonances, transmission stop-bands, resonant back scattering, coupling to out-of-plane radiation and asymmetric transmission. The ability of the nanogap tiling to concentrate the field on the surface is studied in detail as it allows for sensing changes in the dielectric medium on the accessible surface or the inclusion of nonlinear or gain materials to functionalise the device in an integrated setup.Open Acces