Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-12-22T12:14:15Z No. of bitstreams: 0 / Made available in DSpace on 2016-12-22T12:14:15Z (GMT). No. of bitstreams: 0 / A irradiação de alimentos é um meio de preservação de alimentos onde se utiliza uma técnica de processamento que expõe os alimentos a uma radiação ionizante controlada de alta energia. O tratamento realizado com o uso das radiações ionizantes em alimentos tem muitas aplicações tecnologicamente e tecnicamente viáveis incluindo a capacidade de melhorar a segurança microbiológica, reduzir os níveis de bactérias patogénicas, inibir a germinação de tubérculos, aplicação fitossanitária, conservar alimentos armazenados ou a estabilidade de armazenamento e também é utilizada para aumentar a vida de prateleira de determinados produtos devido à redução da contaminação por microrganismos. Em função do aumento do comércio internacional de alimentos e das crescentes exigências regulatórias dos mercados consumidores, cada vez mais países importadores e exportadores têm demonstrando interesse na irradiação de alimentos e desenvolvido pesquisas na aplicação prática desta tecnologia e de métodos de detecção do tratamento. Inúmeras pesquisas foram realizadas mundialmente, resultando em eficientes protocolos para identificar quais alimentos foram ou não irradiados. Até então, o \"mito\" que alimentos irradiados não poderiam ser detectados e que não eram formados quaisquer produtos únicos da radiação foi substituído pelo conhecimento que muitas mudanças podem ocorrer nos alimentos irradiados e essas mudanças poderiam ser utilizadas como ferramentas para identificar essa tecnologia. O processamento por radiação resulta em formações de padrões característicos de hidrocarbonetos saturados, aldeídos, metil e etil ésteres e 2-alcilciclobutanonas, dependendo da composição do ácido graxo do lipídio que compõe o alimento. Com isso a proposta do trabalho foi levantar dados para comparar os efeitos das diferentes doses de radiação gama e de elétrons em alimentos que possuem gordura para verificar as possíveis alterações decorrentes do uso da irradiação, como a presença de 2-Alcilciclobutanonas e também, mostrar os principais equipamentos utilizados para a irradiação de alimentos e suas categorias, com o objetivo de informar o publico em geral. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

The finite element method (FEM) is a widely-used numerical tool in the fields of structural dynamics, acoustics and electromagnetics. In this work, our goal is to develop robust FEM strategies for solving problems in the areas of acoustics, structures and electromagnetics, and then extend these strategies to solve multi-physics problems such as magnetohydrodynamics and structural acoustics. We now briefly describe the finite element strategies developed in each of the above domains. In the structural domain, we show that the trapezoidal rule, which is a special case of the Newmark family of algorithms, conserves linear and angular momenta and energy in the case of undamped linear elastodynamics problems, and an ‘energy-like measure’ in the case of undamped acoustic problems. These conservation properties, thus, provide a rational basis for using this algorithm. In linear elastodynamics variants of the trapezoidal rule that incorporate ‘high-frequency’ dissipation are often used, since the higher frequencies, which are not approximated properly by the standard displacement-based approach, often result in unphysical behavior. Instead of modifying the trapezoidal algorithm, we propose using a hybrid FEM framework for constructing the stiffness matrix. Hybrid finite elements, which are based on a two-field variational formulation involving displacement and stresses, are known to approximate the eigenvalues much more accurately than the standard displacement-based approach, thereby either bypassing or reducing the need for high-frequency dissipation. We show this by means of several examples, where we compare the numerical solutions obtained using the displacementbased and hybrid approaches against analytical solutions. We also present a monolithic formulation for the solution of structural acoustic problems based on the hybrid finite element approach. In the area of electromagnetics, since our goal is to ultimately couple the electromagnetic analysis with structural or fluid variables in a ‘monolithic’ framework, we focus on developing nodal finite elements rather than using ‘edge elements’. It is well-known that conventional nodal finite elements can give rise to spurious solutions, and that they cannot capture singularities when the domains are nonconvex and have sharp corners. The commonly used remedies of either adding a penalty term or using a potential formulation are unable to address these problems satisfactorily. In order to overcome this problem, we first develop several mixed finite elements in two and three dimensions which predict the eigenfrequencies (including their multiplicities) accurately, even for non-convex domains. In this proposed formulation, no ad-hoc terms are added as in the penalty formulation, and the improvement is achieved purely by an appropriate choice of the finite element spaces for the different variables. For inhomogeneous domains, ‘double noding’ is used to enforce the appropriate continuity conditions at an interface. Although the developed mixed FEM works very accurately for all 2D geometries and regular Cartesian 3D geometries, it has so far not yielded success for curved 3D geometries. Therefore, for 3D harmonic and transient analysis problems, we propose and use a modified form of the potential formulation that overcomes the disadvantages of the standard potential method, especially on non-convex domains. Electromagnetic radiation and scattering in an exterior domain traditionally involved imposing a suitable absorbing boundary condition (ABC) on the truncation boundary of the numerical domain to inhibit reflection from it. In this work, based on the Wilcox asymptotic expansion of the electric far-field, we propose an amplitude formulation within the framework of the nodal FEM, whereby the highly oscillatory radial part of the field is separated out a-priori so that the standard Lagrange interpolation functions have to capture a relatively gently varying function. Since these elements can be used in the immediate vicinity of the radiator or scatterer (with few exceptions which we enumerate), it is more effective compared to methods of imposing ABCs, especially for high-frequency problems. We show the effectiveness of the proposed formulation on a wide variety of radiation and scattering problems involving both conducting and dielectric bodies, and involving both convex and non-convex domains with sharp corners. The Time Domain Finite Element Method (TDFEM) has been used extensively to solve transient electromagnetic radiation and scattering problems. Although conservation of energy in electromagnetics is well-known, we show in this work that there are additional quantities that are also conserved in the absence of loading. We then show that the developed time-stepping strategy (which is closely related to the trapezoidal rule) mimics these continuum conservation properties either exactly or to a very good approximation. Thus, the developed numerical strategy can be said to be ‘unconditionally stable’ (from an energy perspective) allowing the use of arbitrarily large time-steps. We demonstrate the high accuracy and robustness of the developed method for solving both interior and exterior domain radiation problems, and for finding the scattered field from conducting and dielectric bodies. In the field of magneto-hydrodynamics, we develop a monolithic strategy based on a continuous velocity-pressure formulation that is known to satisfy the Babuska-Brezzi (BB) conditions. The magnetic field is interpolated in the same way as the velocity field, and the entire formulation is within a nodal finite element framework. Both transient and steady-state formulations are developed for two- and three-dimensional geometries. An exact linearization of the monolithic strategy ensures that rapid (quadratic) convergence is achieved within each time (or load) step, while the stable nature of the interpolations used ensure that no instabilities arise in the solution. Good agreement with analytical solutions, even with the use of very coarse meshes, shows the efficacy of the developed formulation.

Abstract The aims of the present study were to clarify the antenna function and radio frequency radiation (RFR) sensitivity of human subjects using theoretical calculations and field tests. The weak very high frequency (VHF) electromagnetic fields and spontaneous hand movements were recorded. Groups of university students, other volunteers and as a very interesting group, experienced well finders, were used as test subjects. The VHF field was studied using a spectrum analyser and tuneable narrow-band or broad-band meter with a dipole antenna. The hand movements were registered by potentiometric systems and electromyography (EMG). The test subjects (altogether n = 140) in different tests were walking, sitting in a cart being pulled slowly forward, or sitting in a moving car. The responses were observed and hand movements were recorded and analysed by personal computers. By visual inspection and using the Pearson's correlation, the results of different individuals have been compared with the measured intensity of far fields of a radio mast. Reaction spots and graphs defined by different individuals in the same experiment areas have been compared to each other. Hand movement correlated with the reactions of the forearm and shoulder muscles, e.g., pronator teres and trapezius, by EMG measurements. The reactions of some persons correlated with each other. Experiments in a slow moving wagon and in a moving car showed a correlation between the test subjects’ hand movements and the intensity of below 1 mV/m radio and TV signals measured in the vicinity of the test subject. In open field tests different persons usually reacted in widely different ways. The most evident results were recorded near the buildings, where the radio waves reflected from the wall and patterns of standing waves were clear. Many VHF frequency modulated (FM) broadcasting signals were summed at these places at the same time. It is concluded that the spontaneous hand movement reactions occurred as a response of the human body to the gradients of the VHF field intensity. The reaction generally occurred in interference patterns of multipath propagation or standing waves originating from the radiation of FM radio and TV broadcasting transmitters and radiation reflected from the walls of buildings or from other objects. This non-thermal reaction was clearly observable as spontaneous arm movements by 39 percent of the 85 tested students. / Tiivistelmä Tässä tutkimuksessa selvitettiin ihmisen herkkyyttä radiotaajuiselle säteilylle. Ihmisen toimimista radioaaltojen antennina tarkasteltiin teoreettisesti ja kenttäkokein. Heikkojen VHF-alueen radioaaltojen voimakkuutta ja tahattomia käsien liikkeitä rekisteröitiin valituilla koepoluilla. Koehenkilöinä on ollut yliopiston opiskelijoita ja muita vapaaehtoisten ryhmiä. Kiinnostavin ryhmä oli kokeneet kaivonkatsojat, joiden käsienliikereaktioihin radioaaltojen vaikutuksista löytyy viitteitä kirjallisuudesta. Radioaaltojen voimakkuuden vaihteluja mitattiin spektrianalysaattorilla ja laajakaistaisella VHF-alueen integroivalla mittarilla. Käsien liikkeitä rekisteröitiin potentiometriin perustuvilla liikeantureilla. Lihasten sähköimpulsseja rekisteröitiin elektromyografia- eli EMG-laitteella. Eri koesarjoissa koehenkilöt (yhteensä 140) kävelivät, istuivat hitaasti vedettävässä vaunussa tai istuivat liikkuvassa autossa. Reaktioita tarkkailtiin ja käsien liikkeet ja mitatut kentänvoimakkuudet rekisteröitiin ja analysoitiin tietokoneella. Eri koehenkilöiden tuloksia, reagointipaikkoja ja rekisteröityjä käyriä 5–35 km:n etäisyydellä mastoista tarkasteltiin silmämääräisesti. Pearsonin korrelaatiolaskentaa apuna käyttäen tuloksia verrattiin radiomastojen säteilyn voimakkuuteen. Eri ihmisten reagointikohtia ja käyriä samoilta koealueilta vertailtiin keskenään. Koeasetelmassa käsienliikkeiden todettiin korreloivan joidenkin kyynärvarren ja hartialihasten (mm. pronator teres ja trapezius) EMG-signaaleihin. Joidenkin koehenkilöiden tulokset korreloivat keskenään. Hitaasti vedettävässä vaunussa ja liikkuvassa autossa tehdyissä kokeissa tuli esille korrelaatio vartalon edessä olevien käsien loittonemis-lähestymis-liikkeiden ja koehenkilön välittömässä läheisyydessä mitattujen 1 mV/m -tasoisten radio- ja TV-signaalien voimakkuusvaihtelujen välillä. Avoimella kentällä henkilöt reagoivat hyvin eri tavoin. Parhaiten yhteys tuli esille rakennusten lähellä sijaitsevilla koealueilla, joissa radioaallot heijastuivat rakennuksen seinästä muodostaen selkeitä seisovan aallon kuvioita. Useat taajuusmoduloidut VHF-alueen radiosignaalit summautuivat näissä paikoissa samanaikaisesti. Johtopäätöksenä on, että tahattomat käsienliikkeet tapahtuvat kehon vasteena VHF-kentän voimakkuuden muutoksille. Reaktio tapahtui yleensä interferenssi-kuvioissa tai seisovissa aalloissa, jotka muodostuvat FM-radio- ja TV-lähetysten monitie-etenemisestä radioaaltojen heijastuessa rakennusten seinistä tai muista kohteista. Tämä ei-lämpövaikutustason reaktio oli selvästi havaittavissa olkapään tasalle koukistetun käden tahattomana ojennus-koukistus-liikkeenä 39 prosentilla testatuista 85 opiskelijasta.

Graduation thesis describes basic data about Sun, suns constant, solar radiation thoroughfare by the earth's atmosphere. Thesis describes effects of components of optical radiation and physical character of solar radiation. Thesis also describes character of day lighting in nature, spectral distribution of natural lighting, average time of sunshine. The next point of thesis is description of measuring equipment Konica Minolta. In chapter measuring procedure is described measuring process of the sky radiance. Measurement analysis is mentioned in conclusion.

The paper describes a theoretical base and realization of realistic volumetric clouds visualization in an environment of real-time simulator. The first part is concerned with a meteorological background of this problem. I show international classification of ten basic cloud types including a short description and cases of occurence. The following part is concerned with an interaction between cloudiness and simulation core, which is based on the fact, that each cloud acts as a mechanical or an electromagnetic obstacle. This should be considered on some way in simulation. The next part describes technologies and practical implementations of visualization and evaluates their characteristics. Finally, the last chapter describes my implementation and tries to outline project advancement.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Introduction: Elimination of bacteria and active infection within an infected root canal system is one of the primary objectives of nonsurgical root canal treatment. One of the measures of successful root canal treatment is subsequent bone healing of periapical lesions caused by previous infection. A previous study by Yumoto et al. showed that electromagnetic wave stimulation can increase proliferation of osteoblastic cells with no cytotoxicity, and it can also up-regulate growth factors such as vascular endothelial growth factor and platelet-derived growth factor.18 They also showed increased proliferation of an immortalized osteoblastic MC3T3-E1 cell line 3 days following electromagnetic stimulation (EMS).18 Previously, Pauly et al. found increased alkaline phosphatase (ALP) activity with 10 mA EMS application to primary murine calvaria-derived osteoblastic cells with 5 pulses at 1 second per pulse, but no significant differences were found for MTS proliferation nor mineral deposition compared to a negative control group.82 Optimization of the different variables including post-treatment incubation time, current delivery, and number of pulses per treatment may be necessary to improve osteogenic activity. The use of mesenchymal stem cells from murine bone marrow may also offer a physiologically relevant model for osteoblastic regeneration of periapical lesions. Objectives: The goal of this study was to investigate and optimize the effects of electromagnetic wave stimulation (EMS) on murine bone marrow mesenchymal stem cells (MSCs) by evaluating the proliferation and differentiation of the cells after exposure to different EMS treatment regimens. Materials and Methods: 5 x104 stromal osteoblasts (SOBs) were cultured in 24-well plates in α-MEM containing 10% fetal bovine serum. Cells were then subjected to pulsed EMS treatments of 1 mA, 10 mA, and 50 mA. EMS was generated using an electromagnetic apical treatment (EMAT) device created by J. Morita MFG Corp. Proliferation was assessed via MTS assay 1 days after treatment. For osteogenic differentiation, ascorbic acid and β-glycerol phosphate were added to the culture media, and SOBs were cultured for 14 days. Afterwards, alkaline phosphatase (ALP) activity and Alizarin-red S mineral deposition were quantified as measures of osteoblast activity. Cells grown in osteogenic media without EMS treatment served as the negative control. Results: Although MSC proliferation was unaffected by different EMS treatment regimens, 50 mA EMS resulted in a decrease in ALP activity and mineral deposition by osteoblasts. Conclusions: Our findings suggest bone healing by EMS may involve a different cellular mechanism, that is not reproduced in vitro in our studies. Utilizing different amperage and EMS regimens may improve osteogenic differentiation.

The advent and proliferation of planar technologies for power converters are driven in part by the overall trends in analog and digital electronics. These trends coupled with the demands for increasingly higher power quality and tighter regulations raise various design challenges. Because inductors and transformers constitute a rather large part of the overall converter volume, size and performance improvement of these structures can subsequently enhance the capability of power converters to meet these application-driven demands. Increasing the switching frequency has been the traditional approach in reducing converter size and improving performance. However, the increase in switching frequency leads to increased power loss density in windings and core, with subsequent increase in device temperature, parasitics and electromagnetic radiation. An accurate set of reduced-order modeling methodologies is presented in this work in order to predict the high-frequency behavior of inductors and transformers. Analytical frequency-dependent expressions to predict losses in planar, foil windings and cores are given. The losses in the core and windings raise the temperature of the structure. In order to ensure temperature limitation of the structure is not exceeded, 1-D thermal modeling is undertaken. Based on the losses and temperature limitation, a methodology to optimize performance of magnetics is outlined. Both numerical and analytical means are employed in the extraction of transformer parasitics and cross-coupling. The results are compared against experimental measurements and are found to be in good accord. A simple near-field electromagnetic shield design is presented in order to mitigate the amount of radiation. Due to inadequacy of existing winding technology in forming suitable planar windings for PCB application, an alternate winding scheme is proposed which relies on depositing windings directly onto the core. / Master of Science

Η υπερθερμία αποτελεί μια επικουρική μέθοδο θεραπείας του καρκίνου και η βιοϊατρική έρευνα τις τελευταίες δεκαετίες, με σκοπό την εκμετάλλευση και την ανάδειξη των ιδιοτήτων της μεθόδου, στοχεύει στην εφαρμογή της στην κλινική πράξη. Μία προσπάθεια με παρόμοιο σκοπό γίνεται τα τελευταία χρόνια στο Εργαστήριο Μικροκυμάτων και Οπτικών Ινών (ΕΜΟΙ) της σχολής Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών (ΗΜΜΥ) του Εθνικού Μετσόβιου Πολυτεχνείου, όπου έχει σχεδιαστεί και κατασκευαστεί ένα σύστημα υπερθερμίας. Το προτεινόμενο σύστημα ενσωματώθηκε σε ένα τρισδιάστατο σύστημα παθητικής μικροκυματικής ραδιομετρικής απεικόνισης (ΜiRaIS) για διαγνωστικές εφαρμογές εγκεφάλου, το οποίο μελετήθηκε και κατασκευάστηκε στα πλαίσια διδακτορικής διατριβής στο ίδιο εργαστήριο της σχολής ΗΜΜΥ. Στην παρούσα διπλωματική εργασία γίνεται η θεωρητική και πειραματική μελέτη του προτεινόμενου συστήματος της υπερθερμίας. Η αρχή λειτουργίας του είναι όμοια με αυτή του MiRaIS και βασίζεται στη χρήση μια ελλειψοειδούς αγώγιμης κοιλότητας για εστίαση της ακτινοβολίας επιλεκτικά στους ιστούς που χρήζουν θεραπείας. Ο ανακλαστήρας για εστίαση, που κατασκευάστηκε και χρησιμοποιήθηκε στην πειραματική διαδικασία, βελτιώνει την εργονομία του συστήματος, διατηρώντας παράλληλα της ιδιότητες εστίασης του πρωτότυπου ελλειψοειδούς. Στα πλαίσια της παρούσας διπλωματικής εργασίας πραγματοποιήθηκε θεωρητική μελέτη και μοντελοποίηση της διάταξης με σκοπό τη βελτίωση των ιδιοτήτων εστίασής της, καθώς και πειραματικές μετρήσεις του συνολικού συστήματος υπερθερμίας-μικροκυματικής ραδιομετρίας. Στη θεωρητική μελέτη, με χρήση του λογισμικού xFDTD που βασίζεται στη μέθοδο των πεπερασμένων διαφορών στο πεδίο του χρόνου, ερευνώνται δυο μέθοδοι για τη βελτίωση των ιδιοτήτων εστίασης του συστήματος (βάθος διείσδυσης της ακτινοβολίας, χωρική διακριτική ικανότητα) με τη χρήση διηλεκτρικών υλικών. Τα υλικά αυτά τοποθετούνται στο εσωτερικό του ελλειψοειδούς καθώς και γύρω από το μοντέλο κεφαλιού ως στρώματα προσαρμογής για την επίτευξη βηματικής αλλαγής της διηλεκτρικής σταθεράς στη διεπιφάνεια αέρα-μοντέλο ανθρώπινου κεφαλιού. Στην πρώτη προσέγγιση, το εσωτερικό του ελλειψοειδούς ανακλαστήρα γεμίζει με διηλεκτρικό υλικό χαμηλών απωλειών, με τα αποτελέσματα να δείχνουν σημαντική βελτίωση της χωρικής διακριτικής ικανότητας του συστήματος. Στη δεύτερη προσέγγιση του προβλήματος, χρησιμοποιείται ένα ημισφαίριο από διηλεκτρικό γύρω από το μοντέλο κεφαλιού, με τα αποτελέσματα να δείχνουν την αντίστοιχη βελτίωση της χωρικής διακριτικής ικανότητας και παράλληλα σημαντική μείωση των ανεπιθύμητων περιοχών εστίασης της ενέργειας. Η πειραματική διάταξη τοποθετήθηκε σε ανηχοϊκό θάλαμο, όπου και πραγματοποιήθηκαν όλες οι μετρήσεις. Παράλληλα με τα πειράματα υπερθερμίας, μελετήθηκε η δυνατότητα εφαρμογής της μεθόδου της μικροκυματικής ραδιομετρίας με τη γεωμετρία του προτεινόμενου συστήματος. Η μέθοδος της μικροκυματικής ραδιομετρίας θα μπορούσε να παρέχει τον έλεγχο της θερμοκρασίας της ακτινοβολούμενης περιοχής κατά τη διάρκεια των συνεδριών της υπερθερμίας. Στις πειραματικές διαδικασίες που ακολουθήθηκαν, χρησιμοποιήθηκαν ομοιώματα νερού, τα οποία στη φάση της υπερθερμίας υπέδειξαν τις περιοχές εστίασης της ενέργειας για τη συχνότητα ακτινοβολίας, ενώ στη φάση της μικροκυματικής ραδιομετρίας βοήθησαν στη μελέτη της θερμοκρασιακής διακριτικής ικανότητας του συστήματος. Επίσης, διενεργήθηκαν μετρήσεις με στρώματα προσαρμογής από διηλεκτρικά υλικά, τα οποία τοποθετούνταν γύρω από το αντικείμενο ενδιαφέροντος, για την πληρέστερη κατανόηση της επίδρασης των υλικών αυτών στις ιδιότητες εστίασης του συστήματος και για την επιβεβαίωση των αντίστοιχων θεωρητικών αποτελεσμάτων. / The application of hyperthermia process has been widely used in clinical research and efforts are being made for its implementation in clinical practice, as many researchers have used this method as an adjunct treatment procedure for cancer. During the past two decades, a great deal of research has been carried out, with the aim of developing effective techniques for hyperthermia treatment, primarily using RF, microwave, and ultrasound energy. A similar effort is carried out in the Laboratory of Microwaves and Fiber Optics (MFOL), School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), where a proposed hyperthermia system has been designed and constructed. A system for deep brain hyperthermia treatment, designed to also provide passive measurements of temperature and/or conductivity variations inside the human body, is presented in this paper. The proposed system comprises both therapeutic and diagnostic modules, operating in a totally contactless way, based on the use of an ellipsoidal beamformer to achieve focusing on the areas under treatment and monitoring. The radiometry monitoring module, the Three Dimensional Passive Microwave Radiometry Imaging System (MiRaIS), has been studied, designed and constructed in the framework of a PhD thesis in the same laboratory of MFOL. In the present thesis, the proposed system is theoretically and experimentally studied. The operation principal is based on the use of an ellipsoidal conductive wall cavity for focusing the emitted radiation on the tissues that should accept treatment. The ellipsoidal cavity, which was constructed and used in the experimentation procedure, is newly developed and improves the system’s ergonomy retaining at the same time the focusing properties of the prototype system. In the framework of the present study, theoretical modelling and experimentation of the proposed system was carried out in order to examine and improve its focusing attributes. In the theoretical study, two methods for the improvement of the system’s focusing properties (e.g. penetration depth of the electromagnetic field, spatial sensitivity) using dielectric materials are tested with the use of a commercially available software tool, xFDTD (x-Finite Difference Time Domain). The materials are placed inside the ellipsoidal or used as matching layers around the head model for the achievement of a stepped change of the refraction index on the air-human head model interface. In the first approach, the ellipsoidal volume is filled with a low loss dielectric material in order to improve the system’s spatial sensitivity. In the second approach, a hemi-sphere also filled with a dielectric material is placed around the human head model and the results revealed the improvement of the system’s spatial sensitivity and the reduction of the undesirable auxiliary energy-absorbing areas. The experiments were performed inside an anechoic chamber providing maximum accuracy by avoiding any external interference. Along with the hyperthermia experiments, the implementation of the microwave radiometry process was also tested with the proposed system. Microwave radiometry could provide the temperature monitoring of the radiated area during the hyperthermia sessions. In the experimental procedures water phantoms were used, which during hyperthermia indicated the energy-absorbing areas at the irradiation frequency, and during microwave radiometry revealed the system’s temperature sensitivity. Also, measurements were conducted using dielectric matching layers, placed around the medium of interest, in order to fully understand the effect of those materials on the system’s focusing properties as well as to confirm the respective theoretical results. Taking into consideration the present study and the advantage of the non invasive character of the proposed brain hyperthermia system, it is concluded that further research is required in order to explore its potentials at becoming a part of the standard treatment protocol of brain malignancy in the future.

Η υπερθερμία αποτελεί μια επικουρική μέθοδο θεραπείας του καρκίνου και η βιοϊατρική έρευνα τις τελευταίες δεκαετίες, με σκοπό την εκμετάλλευση και την ανάδειξη των ιδιοτήτων της μεθόδου, στοχεύει στην εφαρμογή της στην κλινική πράξη. Μια προσπάθεια με παρόμοιο σκοπό γίνεται τα τελευταία χρόνια στο Εργαστήριο Μικροκυμάτων και Οπτικών Ινών (ΕΜΟΙ) της σχολής Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών (ΗΜΜΥ) του Εθνικού Μετσόβιου Πολυτεχνείου, όπου έχει σχεδιαστεί και κατασκευαστεί ένα μικροκυματικό σύστημα υπερθερμίας. Το προτεινόμενο σύστημα ενσωματώθηκε σε ένα τρισδιάστατο σύστημα παθητικής μικροκυματικής ραδιομετρικής απεικόνισης (ΜiRaIS), το οποίο παρέχει τη δυνατότητα παρακολούθησης των μεταβολών της θερμοκρασίας και της αγωγιμότητας της υπό εξέταση περιοχής σε πραγματικό χρόνο και μελετήθηκε και κατασκευάστηκε στα πλαίσια παλαιότερης διδακτορικής διατριβής στο ίδιο εργαστήριο της σχολής ΗΜΜΥ. Στην παρούσα διδακτορική διατριβή γίνεται η θεωρητική και πειραματική μελέτη του προτεινόμενου συστήματος υπερθερμίας. Η αρχή λειτουργίας του συστήματος είναι όμοια με εκείνη του MiRaIS και βασίζεται στη χρήση μιας ελλειψοειδούς αγώγιμης κοιλότητας για εστίαση της ακτινοβολίας επιλεκτικά στους ιστούς που χρήζουν θεραπείας. Ο ανακλαστήρας για εστίαση που κατασκευάστηκε και χρησιμοποιήθηκε στην πειραματική διαδικασία, βελτιώνει την εργονομία του συστήματος, διατηρώντας παράλληλα της ιδιότητες εστίασης του πρωτότυπου ελλειψοειδούς. Στα πλαίσια της παρούσας διατριβής πραγματοποιήθηκε αρχικά η θεωρητική μελέτη και μοντελοποίηση της διάταξης με σκοπό την εξακρίβωση των ιδιοτήτων εστίασης του συστήματος και στη συνέχεια επιχειρήθηκε η βελτίωση των ιδιοτήτων αυτών με χρήση διατάξεων διηελκτρικών υλικών, καθώς και πειραματικές μετρήσεις του συνολικού συστήματος υπερθερμίας-μικροκυματικής ραδιομετρίας. Η θεωρητική ηλεκτρομαγνητική μελέτη του συστήματος έγινε με τη χρήση ενός εμπορικά διαθέσιμου υπολογιστικού πακέτου προσομοίωσης (XFdtd, Remcom Inc.), το οποίο χρησιμοποιεί τη μέθοδο των πεπερασμένων διαφορών στο πεδίο του χρόνου για την επίλυση ηλεκτρομαγνητικών προβλημάτων. Ερευνώνται τρεις διατάξεις διηλεκτρικών υλικών με σκοπό τη βελτίωση των ιδιοτήτων εστίασης του συστήματος, οι οποίες επικεντρώνονται στη μελέτη του βάθους διείσδυσης της ακτινοβολίας και της χωρικής διακριτικής ικανότητας. Τα υλικά τοποθετούνται είτε στο εσωτερικό του ελλειψοειδούς είτε γύρω από το μοντέλο κεφαλιού ως στρώματα προσαρμογής, με σκοπό την επίτευξη βηματικής αλλαγής της διηλεκτρικής σταθεράς στη διεπιφάνεια αέρα-μοντέλο ανθρώπινου κεφαλιού. Τα αποτελέσματα καταδεικνύουν τα πλεονεκτήματα από τη χρήση των διηλεκτρικών υλικών, καθώς παρουσιάζεται βελτίωση και στις δυο παραμέτρους των ιδιοτήτων εστίασης, ανάλογα με τη διάταξη που χρησιμοποιείται, τη θέση του μοντέλου κεφαλιού στο εσωτερικό του συστήματος και τη συχνότητα λειτουργίας. Για τη διενέργεια των πειραμάτων, η πειραματική διάταξη τοποθετήθηκε σε ανηχοϊκό θάλαμο, ο οποίος εξασφαλίζει την απομόνωσή της από τον περιβάλλοντα χώρο. Στις πειραματικές διαδικασίες που ακολουθήθηκαν, χρησιμοποιήθηκαν ομοιώματα, τα οποία στη φάση της υπερθερμίας υπέδειξαν τις περιοχές εστίασης της ενέργειας για την εκάστοτε συχνότητα ακτινοβολίας, ενώ στη φάση της μικροκυματικής ραδιομετρίας βοήθησαν στη μελέτη της θερμοκρασιακής διακριτικής ικανότητας του συστήματος. Η μέθοδος της μικροκυματικής ραδιομετρίας χρησιμοποιήθηκε για την παρακολούθηση των μεταβολών της θερμοκρασίας της ακτινοβολούμενης περιοχής κατά τη διάρκεια των συνεδριών της υπερθερμίας. Επίσης, κατά τη διάρκεια των πειραμάτων πραγματοποιήθηκαν μετρήσεις με στρώματα προσαρμογής από διηλεκτρικά υλικά, τα οποία τοποθετήθηκαν γύρω από το αντικείμενο ενδιαφέροντος και βοήθησαν στην πληρέστερη κατανόηση της επίδρασης της παρουσίας τους στις ιδιότητες εστίασης του συστήματος και στην επιβεβαίωση των αντίστοιχων θεωρητικών αποτελεσμάτων. / The application of hyperthermia process has been widely used in clinical research and efforts are being made for its implementation in clinical practice, as many researchers have used this method as an adjunct treatment procedure for cancer. During the past two decades, a great deal of research has been carried out, with the aim of developing effective techniques for hyperthermia treatment, primarily using RF, microwave and ultrasound energy. A similar effort is carried out in the Laboratory of Microwaves and Fiber Optics (MFOL), School of Electrical and Computer Engineering, National Technical University of Athens (NTUA), where a proposed hyperthermia system has been designed and constructed. A system for deep brain hyperthermia treatment, designed to also provide passive measurements of temperature and/or conductivity variations inside the human body, is presented in the present PhD thesis. The proposed system comprises both therapeutic and diagnostic modules, operating in a totally contactless way, based on the use of an ellipsoidal beamformer to achieve focusing on the areas under treatment and monitoring. The radiometry monitoring module, the Three Dimensional Passive Microwave Radiometry Imaging System (MiRaIS), has been studied, designed and constructed in the framework of a previous PhD thesis in the same laboratory of MFOL. In the present thesis, the proposed system is theoretically and experimentally studied. The operation principal is based on the use of an ellipsoidal conductive wall cavity for focusing the emitted radiation on the tissues that should accept treatment. The ellipsoidal cavity, which was constructed and used in the experimentation procedure, is newly developed and improves the system’s ergonomics retaining at the same time the focusing properties of the prototype system. In the framework of the present work, theoretical modeling and experimentation of the proposed system is carried out in order to examine and improve its focusing attributes. In the theoretical study, three setups are investigated for the improvement of the system’s focusing properties (e.g. penetration depth of the electromagnetic field, spatial sensitivity) using dielectric materials. The research is carried out with the use of a commercially available software tool, XFdtd (Remcom Inc.). The materials are placed inside the ellipsoidal or used as matching layers around the head model for the achievement of a stepped change of the refraction index on the air-human head model interface. The results revealed the possible advantages of using matching dielectric materials, as improvement on the focusing properties of the system is clearly observed, depending on the setup used, the position of the head model inside the system and the operating frequency. The experiments were performed inside an anechoic chamber providing maximum accuracy by avoiding all possible EMC/EMI issues. Along with the hyperthermia experiments, the implementation of the microwave radiometry process was also tested with the proposed system. Microwave radiometry could provide the temperature monitoring of the radiated area during the hyperthermia sessions. In the experimental procedures water phantoms were used, which during hyperthermia indicated the energy absorbing areas at the irradiation frequency, while during microwave radiometry revealed the system’s temperature sensitivity. Also, measurements were conducted using dielectric matching layers, placed around the medium of interest, in order to fully understand the effect of those materials on the system’s focusing properties as well as to confirm the respective theoretical results. Taking into consideration the present study and the advantage of the non invasive character of the proposed brain hyperthermia system, it is concluded that further research is required in order to explore its potentials at becoming a part of the standard treatment protocol of brain malignancy in the future.