Dissertations / Theses on the topic 'Traveling wave'

Thesis (M.S.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Applied Mathematics and Scientific Computation Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Thesis (M.S.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Dept. of Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

This thesis addresses research on the design and modeling of GaAs traveling wave electro-optic modulators with a highly doped layer. These modulators are in the form of a waveguide integrated with Planar Microstrip electrodes (PMS), and of a Mach-Zehnder interferometer integrated with capacitively loaded Coplanar Strips (CPS) electrodes. In both, the use of a thin highly doped layer ensures a good overlap between the applied electric field and optical mode. The design space of both PMS and loaded CPS electrodes are fully characterized. Waveguides of low propagation loss are designed. Wide bandwidth traveling wave modulators require low optical and microwave insertion loss, impedance matching, velocity matching and low half wave voltage. The simulation results predict that modulators with PMS electrodes have a limited frequency response while the modulators with CPS loaded electrodes have an electrical 3 dB bandwidth up to 70 GHz for 1cm device and Vpi of 9.4 V·cm.

TAs the millimeterwave and sub-millimeterwave portions of the electromagnetic spectrum are increasingly utilized, the need for greater power at those frequencies also increases. Unfortunately, as frequency is increased, the power available from a single solid-state device decreases. Thus, in many applications, the combining of power from several solid-state devices becomes necessary to have usable signal power levels. This thesis presents two such power combining approaches, whose designs are compatible with existing microfabrication techniques that may be used to produce devices operating at 300 GHz and beyond. Additionally, this thesis describes a mathematical modeling procedure that incorporates signal flow and transmission line concepts, and aids in the efficient design of one of these topologies, the Planar-Probe Traveling-Wave Divider- Combiner. Such a modeling approach could be readily applied to traveling wave structures of different topologies. The complete design, simulation, and experimental validation of a conventionally-machined two-way traveling-wave dividing-combining module is demonstrated at X-band frequencies. The demonstrated 15 dB return loss fractional bandwidth was almost 21%, and the insertion loss was found to be better than 0.5 dB throughout most of the operational band. The promising performance of this structure shows that further investigation is merited.

We prove the existence of a one-parameter family of solutions of the porous medium equation, a nonlinear heat equation. In our work, with space dimension 3, the interface is a half line whose end point advances at constant speed. We prove, by using maximum principle, that the solutions are stable under a suitable class of perturbations. We discuss the relevance of our solutions, when restricted to two dimensions, to gravity driven flows of thin films. Here we extend the results of J. Iaia and S. Betelu in the paper "Solutions of the porous medium equation with degenerate interfaces" to a higher dimension.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.
Includes bibliographical references (p. 209-214).
by William Libbey Menninger.
Ph.D.

The overall goal of the current thesis addresses the configuration of the waveguide used in Traveling-wave Optical Modulators. In general, our concerns affiliate mostly with achievement of high confinement factor, improved coupling efficiencies and finally single-mode propagation. In principle, waveguides for optical modulators are quite difficult to design entirely, and the usual, and perhaps the most fruitful, approach is to incorporate or slightly modify one of the existing designs. In this sense, we base our structure on the available waveguide, which was already realized in the department, and introduce two etched channels in either side of the mesa structure. From technological point of view, the mentioned fact guarantees the robustness of the novel waveguide for implementation purposes. Meanwhile, we restrict our modifications in a way not to violate the plausible properties of the available guides rather to enhance them more to meet our further expectations. We show that both confinement factor and coupling efficiency can enhance considerably by virtue of these etched channels. Also, it is shown that the novel design renders single-mode propagation structure.

The large signal model for electro-absorption modulators is studied and simulated. In the previous model, the effect of frequency chirp has not been included and also there is no phase information of the optical carrier. This thesis focuses on introducing the phase information of the optical carrier by representing it as a time varying sinusoidal voltage as well as modeling frequency chirp in traveling wave electro-absorption modulators by using a voltage dependent transmission line delay. The transmission line is designed as periodic LC section, where all the capacitance values were modeled to have a quadratic dependence on the microwave voltage using the CBREAK model in PSPICE. This means that the transmission line delay will have a linear dependence on the voltage. The whole modified model for the modulator is then simulated and the frequency chirp effect on the modulator performance was studied. It is shown that the frequency chirp broadens the modulator spectrum but it has no pronounced effect on the eye diagram. This means that long distance transmission will be mutilated due to dispersion. By choosing a small absorption and large change in delay, the phase modulator is simulated and can be fabricated by using a three step quantum well because it has a large change in refractive index and small change in absorption. On the other hand, to fabricate an electro-absorption modulator a rectangular quantum well should be used.

Electro-Absorption Modulators (EAMs) have been instrumental in achieving ultrafast modulation speeds of over 100 Gb/s, and in particular, segmented Travelling-Wave (TWEAMs) designs offer excellent compatibility with standardmicrowave technology due to their characteristic impedance being closer to 50. The TWEAM device fabricated as part of the European Project HECTO, has been succesful is field trials at 112 Gb/s using On-Off Keying (OOK). Achieving phase modulation using a TWEAM offers not only significant improvements over OOK in terms of higher bit rate, but also a great advantage against other phase modulators that use electro-optic effects which need much stronger drive signals and also present issues with chip-integration. The existing model for the TWEAM has been modified to incorporate a variable delay line to simulate enhanced electro-optic effects in the active quantum well layer. Simulations were performed for Binary and Quadrature Phase Shift Keying, and 8-Quadrature Amplitude Modulation. Clear constellation diagrams are obtained at 10 Gb/s with Error Vector Magnitude of around -19 dB at 10 Gb/s and -10 dB at 50 Gb/s. Results from this thesis emphasize the need for further optimization of the model and fabricating a TWEAM that is capable of advanced modulation formats.

Determining the composition of solid materials is of high interest in areas such as material research or quality assurance. There are several modalities at disposal with which various parameters of the material can be observed, but of those only magnetic resonance imaging (MRI) or computer tomography (CT) offer anon-destructive determination of material distribution in 3D. A novel non-destructive imaging method is Magnetic Particle Imaging (MPI), which uses dynamic magnetic fields for a direct determination of the distribution of magnetic materials in 3D. With this approach, it is possible to determine and differentiate magnetic and non-magnetic behaviour. In this paper, the first proof-of-principle measurements of magnetic properties in solid environments are presented using a home-built traveling wave magnetic particle imaging scanner.

JIANG, XIN. Two new Ka-band traveling wave power divider/combiner designs. (Under the direction of Dr. Amir Mortazawi).The purpose of this thesis is to develop a traveling wave power dividing/combining technique for a Ka-band 32-device high power amplifier system. Based on this technique, two main components of the power amplifier system have been designed. One component is a back-to-back connected 4-way waveguide-to-waveguide power divider/combiner and the other one is a back-to-back connected 8-way waveguide-to-microstrip power divider/combiner. Of the two components, the former has exhibited a 4 GHz (~12.5%) 0.5 dB bandwidth with 0.15 dB insertion loss at 32 GHz in simulation. The later utilizes a novel power coupling structure, which has the advantages of low profile, ease of fabrication and efficient heat sinking for the solid-state amplifiers. It was fabricated and experiments on this passive structure have demonstrated a minimum overall insertion loss of 1.8 dB at 32.5 GHz with a 3 dB bandwidth of 15%. The power amplifier composed of these two traveling-wave designs offers a potential broadband solution for solid-state amplifiers applied in high power millimeter-wave systems.

High-speed guided-wave $LiNbO sb3$ electrooptical modulators are important components for future broadband optical fiber communications. Various types of high speed modulators have been reported; among them the Mach-Zehnder interferometric modulators using Y-branches is one of the most widely used structures for broadband modulation because of its simplicity and easy fabrication. Traveling-wave integrated optical modulators fabricated in substrate materials for which the optical and microwave velocities are equal offer the potential of very broad modulation bandwidth. In order to achieve broadband electrooptic intensity modulators, design optimization is very important. A thorough understanding of the characteristics of the electrode structure permits parameter optimization in the design of electrooptic modulators. In this thesis, calculations of the electric field distribution, impedance, and the effective index for microwaves are presented using the Fourier-series method for a quasi-static analysis of coplanar waveguide (CPW). Using this approach, the design optimization will also be discussed.

In this thesis a single-ended traveling wave fault location algorithm is developed for autonomously locating short circuit faults on a radial distribution line using the high frequency traveling wave transients. The traveling wave pattern observed at the sub-station is correlated with the traveling wave pattern predicted using time tree analysis for different fault locations and fault resistance. Genetic search techniques are used to evolve an initial population of possible fault locations to determine the most likely fault location. It is shown through extensive EMTP simulations that the scheme is capable of finding the location of three phase faults, inter-phase faults and single-phase faults for fault resistances ranging from 0 - 1000 ohm on a radial distribution line with five sub-feeders. A new high speed FPGA based data acquisition system is developed suitable for capturing traveling wave fault data from a radial distribution line with the necessary fidelity for the proposed fault location algorithm. The data acquisition system is deployed on a Medium Voltage distribution line in the Santa Caterina region of Brazil. A branched communication network is constructed out of RG-58 coaxial cable and a Time Domain Reflectometry device is used to capture the reflection pattern under different fault conditions. The fault location algorithm is adapted to work with TDR a opposed to fault generated traveling waves. The location algorithm is capable of locating faults with resistance between 0 and 75 ohm up to three zones away from the injection point.

Recent studies have utilized spanwise traveling waves to alter the turbulent boundary layer with the aim of reducing skin friction drag. Spanwise traveling waves are a promising active drag reduction technique; however, the wave generation methods used in previous studies are bulky and could not be practically implemented. This research has developed an implementable traveling wave generation method and then fundamentally demonstrated how it changes the turbulent boundary layer, which is in a manner consistent with skin friction/shear stress reduction. Traveling waves were generated on a two-dimensional surface using low-profile piezoelectric actuators, in an open-loop fashion, and with minimal frequency limitations. The wave generation method was developed to generate tailored traveling wave patterns; thus, yielding control over the propagation direction, number of wave-fronts, and regions of the surface containing traveling waves. These tailored traveling waves have the capacity not just for affecting the boundary layer, but also for other applications such as propulsion. The implementable traveling wave generation method was then tested in a low-speed wind tunnel and shown to alter the structure of the turbulent boundary layer. The boundary layer is pushed off the wall, and the viscous sublayer is thickened, indicating a reduction in shear stress. Analysis of the boundary layer at positions phase-locked to the wave oscillation suggests that the traveling waves induce a phase-lag effect in the flow. This phase-lag produces a stretching of the viscous sublayer and may contribute to the skin friction reduction. The effects of standing waves on the turbulent boundary layer were also investigated and compared with traveling waves. The results indicate that both wave types alter the boundary layer in the same manner. Standing waves are simpler to generate than traveling waves, suggesting that standing waves may be an effective skin friction reduction method. Before traveling or standing waves can be implemented, further research is necessary to investigate the interaction between the wave pattern and the turbulent phenomena and also to quantify the skin friction reduction and overall net energy usage.
Ph. D.

In power transmission systems, locating faults is an essential technology. When a fault occurs on a transmission line, it will affect the whole power system. To find the fault location accurately and promptly is required to ensure the power supply. In this paper, the study of traveling wave theory, fault location method, Karrenbauer transform, and Wavelet transform is presented. This thesis focuses on single ended fault location method. The signal processing technique and evaluation study are presented. The MATLAB SimPowerSystem is used to test and simulate fault scenarios for evaluation studies.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1989.
Includes bibliographical references (leaves 182-184).
by Andrew Patrick Washabaugh.
M.S.

The need for potable water is increasing with the ever-increasing world population. Further development of fast, portable, and cost effective analytical tools is necessary in order to create diagnostic techniques capable of supporting the water needs of the world’s population. Within the last decade microfluidics and Lab-on-a-Chip (LOC) technologies have increased the portability and speed of detection for aqueous samples. Photolithography techniques serve as a cost effective fabrication tool to create LOC electrodes on the micron scale. An in-depth look at the fabrication process is undertaken in this paper in order to further the development of micro-scale detection techniques. An electrode array capable of detecting multiple targets within one aqueous sample was designed and fabricated. The electrode array was assessed for performance characteristics to determine if reproducibility is possible. The fabrication process was also detailed for a new chemical separation technique, traveling-wave electrophoresis (TWE). TWE could serve as a separation tool capable of separating out specific charged molecules for biological and chemical samples. The TWE device was assessed on the capabilities to move charged molecules.

External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well.

This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload.

An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450μm long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250μm device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration.

Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50Ω­ impedance a bandwidth in the90GHz region was indicated.

Magnetic Particle Imaging (MPI) ist eine noch sehr junge Technologie unter den nicht-invasiven tomographischen Verfahren. Seit der ersten Veröffentlichung 2005 wurden einige Scannertypen und Konzepte vorgestellt, welche durch die Messung des Antwortsignals von superparamagnetischen Eisennanopartikeln (SPIOs) auf wechselnde Magnetfelder ein dreidi-mensionales Bild ihrer Verteilung berechnen können. Durch die direkte Messung des Tracers handelt es sich beim MPI um eine sehr sensitive und hochspezifische bildgebende Methode. Zu Beginn dieser Forschungsarbeit gab es nur wenige bekannte MPI-Scanner, die jedoch alle ein nur kleines Field-of-View (FOV) vorweisen konnten. Der Grund dafür liegt in der Ver-wendung von Permanentmagneten. Das Ziel war es nun, ein neues Konzept auszuarbeiten und einen 3D-MPI-Scanner zu entwer-fen, der in der Lage ist, ein mausgroßes Objekt zu messen. In dieser Arbeit wird ein alternatives Scannerkonzept für die dreidimensionale Bildge-bung superparamagnetischer Eisennanopartikel vorgestellt. Der Traveling Wave MPI-Scanner (TWMPI) basiert auf einem neu entwickelten Hauptspulensystem, welches aus mehreren Elektromagneten besteht. Dadurch ist die Hardware bereits in der Lage, eine Linie entlang der Symmetrieachse über einen großen Bereich dynamisch zu kodieren. Mit Hilfe weiterer Ab-lenkspulen kann schließlich ein FOV von 65 x 25 x 25 Millimetern dreidimensional abgetastet werden. Dazu stehen mehrere Scanverfahren zur Verfügung, welche das Probenvolumen li-nienweise oder ebenenweise abtasten und mit einer Auflösung von ca. 2 Millimetern die Ver-teilung der SPIOs in wenigen Millisekunden abbilden können. Mit diesem neuen Hardwareansatz konnte erstmals ein MPI-Scanner mit einem MR-Tomographen (MRT) kombiniert werden. Das MPI/MRT-Hybridsystem liefert tomographi-sche Bilder des Gewebes (MRT) und zeigt die Verteilung des eisenhaltigen Kontrastmittels (MPI), ohne die Probe bewegen zu müssen. In einer in-vivo Echtzeitmessung konnte der TWMPI-Scanner mit 20 Bildern pro Se-kunde die dynamische Verteilung eines eisenhaltigen Kontrastmittels im Körper und speziell im schlagenden Herzen eines Tieres darstellen. Diese Echtzeitfähigkeit eröffnet in der kardi-ovaskuläre Bildgebung neue Möglichkeiten. Erste Messungen mit funktionalisierten Eisenpartikeln zeigen die spezifische Bildge-bung verschiedener Zelltypen und stellen einen interessanten Aspekt für die molekulare Bild-gebung dar. Die Sensitivität des Scanners liegt dabei im Bereich von wenigen Mikrogramm Eisen pro Milliliter, was für den Nachweis von wenigen 10.000 mit Eisen markierten Zellen ausreicht. Neben Messungen an diversen Ferrofluiden und eisenhaltigen Kontrastmitteln konnte der Einfluss von massiven Materialen, wie Eisenstückchen oder Eisenspänen, auf die rekon-struierten Bilder untersucht werden. Erste Messungen an Gestein zeigen die Verteilung von Eiseneinschlüssen und bieten die Möglichkeit einer weiteren zerstörungsfreien Untersuchungsmethode für Materialwissen-schaftler und Geologen. Weiterführende Testmessungen mit einer unabhängigen μMPI-Anlage zeigen erste Ergebnisse mit Auflösungen im Mikrometerbereich und liefern Erkennt-nisse für den Umgang und Messung mit starken Gradientenfeldern. Eine Modifizierung der Messanlage erlaubt es, in gerade einmal 500 μs ein komplettes Bild aufzunehmen, womit die Bewegung eines Ferrofluidtropfens in Wasser sichtbar gemacht werden konnte. Damit ist diese TWMPI-Anlage das schnellste MPI-System und eröffnet die Möglichkeit grundlegende Erfahrungen in der Partikeldynamik zu erlangen. Der vorgestellte Traveling Wave MPI-Scanner ist ein alternativer Scannertyp, welcher sich von anderen MPI-Scannern abhebt. Mit neuen Ansätzen ist in der Lage ein mausgroßes Objekt auf dynamische Weise sehr schnell abzutasten. Dabei konnten in verschiedenen Mes-sungen die Funktionalität und Leistungsfähigkeit des TWMPI-Konzeptes demonstriert wer-den, welche die gesteckten Ziele deutlich übertreffen
Magnetic particle imaging (MPI) is still a very young technology among the non-invasive tomographic modalities. Since its first publication in 2005, several types of scanners and concepts were presented, which can reconstruct a three-dimensional image of the distri-bution of superparamagnetic iron-oxide nanoparticles (SPIOs) by measuring their magnetiza-tion response to varying magnetic fields. Due to the direct measurement of the tracer MPI is a very sensitive and highly specific imaging modality. At the beginning of this project only a few MPI-scanners were known, but all of them are limited to a small field-of-view (FOV). The reason for this is the use of permanent mag-nets. The aim of this work was to develop a new concept and design for a 3D-MPI-scanner, which is able to measure a mouse sized object. In this thesis an alternative scanner concept for three-dimensional imaging of super-paramagnetic iron nanoparticles is presented. The Traveling Wave-MPI-scanner (TWMPI) is based on a newly developed main coil system, which consists of a series of electromagnets. This coil array is by itself able to dynamically encode a line along the symmetry axis over an extended length. With additional offset coils the system is able to scan a FOV of 65 x 25 x 25 millimeters in three dimensions. For scanning the whole volume several tech-niques are available, which map the data line-by-line or slice-by-slice in a few milliseconds and yield the distribution of SPIOs with a resolution of about 2 millimeters. Using this new hardware approach a MPI-scanner was successfully combined with an MRI-scanner for the first time. The MPI/MRI-hybrid-system provides tomographic images of the tissue (MRI) and detects the distribution of iron-containing contrast agent (MPI), without the need to move the sample. In an in-vivo real-time measurement using the TWMPI-scanner the dynamic distribu-tion of an iron-containing contrast agent was visualized in the body and especially in the beat-ing heart of an animal with a temporal resolution of 20 frames per second. This real-time ca-pability opens up new possibilities in cardio-vascular imaging. First measurements using functionalized iron-oxide nanoparticles specifically detect different cell types and thereby provide an interesting aspect for molecular imaging. The sensi-tivity of the scanner is in the range of a few micrograms of iron per milliliter, which is suffi-cient to detect about 50,000 iron-labeled cells. In several studies the influence of various ferrofluids, iron-containing contrast agents and solid materials, such as pieces of iron or iron filings, were examined on the reconstructed images. First measurements on ferrous rock show the location of iron-inclusions and offer an-other non-destructive imaging technique for material scientists and geologists. Additional tests with an independent μMPI-system were performed to explore resolutions in the micrometer range and provide insights for handling and measuring with a high gradient strength. A modification of the setup allows to acquire a full slice in just 500 microseconds, which enable the visualization of the motion of a droplet of ferrofluid in water. With this TWMPI is the fastest MPI-system available and gives access to fundamental studies of particle dynamics. The presented Traveling Wave MPI-system is an alternative scanner concept, which sets itself apart from other MPI-scanners. Mouse-sized objects can be imaged in a dynamic way in very short times. The feasibility and performance of the TWMPI-concept were suc-cessfully demonstrated in various measurements considerably exceeding the original aims

Vacuum microwave tubes, such as klystron, traveling-wave tube, gyrotron are high efficiency devices, where the RF interaction structure facilitates efficient energy transfer from the kinetic energy of the high energy electron beam to the electromagnetic wave. Traveling-wave Tube is the most versatile microwave power amplifier widely used for terrestrial communication, radar and aerospace applications. The waveguide based slow-wave structures like Millman, Karp, inter digital, grated waveguide, ring-plane, ring-bar, millitron and folded-waveguide structure gathered importance for application in millimeter-wave traveling-wave tubes. Among these millimeter-wave interaction structures, the folded-waveguide slow-wave structure became the most popular due to its robust structure, high power capability, low RF loss, simpler coupling, reasonably wide bandwidth and ease of fabrication for millimeter-wave to terahertz frequencies. Hence this thesis aims to analyse the folded-waveguide slow-wave structure for broad-banding and efficiency enhancement. The existing approaches for the analysis of cold circuit parameters (dispersion and interaction impedance characteristics) of folded-waveguide slow-wave structure are reinvestigated and found that these have limitation, as the effects of E-plane bend and beam-hole discontinuities are ignored in the parametric analysis. A cascaded matrix equivalent circuit model includes the effect of E-plane and beam-hole discontinuities for the analysis, but reported only for the serpentine folded-waveguide slow-wave structure. The cold test measurement technique was reported only for the dispersion characteristics. Hence the measurement technique has to be extended for the measurement of interaction impedance. The author proposes to orient the present doctoral work to (i) extend the proposed cascaded transmission matrix equivalent model for the analysis of rectangular folded-waveguide slow-wave structure, (ii) develop a non-resonant perturbation technique for the measurement of interaction impedance characteristics of the folded-waveguide slow-wave structure and also to (iii) establish new analysis models for the folded-waveguide slow-wave structure. The effect of E-plane bend and beam-hole discontinuities on the RF characteristics have been considered and simple, yet accurate closed form expressions for the computation of dispersion and interaction impedance characteristics have been established by three different approaches namely: transmission line equivalent circuit model, conformal mapping equivalent circuit model and quasi-TEM approach. The analysis results are benchmarked against 3-D electromagnetic modeling. The non-resonant perturbation theory is developed for the interaction impedance measurement. Typical Ka-band structures are fabricated by wire-EDM process and cold test measurements are carried out to benchmark the analysis approaches. The equivalent circuit models based on lumped circuit model are simpler than the cascaded matrix equivalent circuit model and can give closed form expressions for the prediction of dispersion and interaction impedance characteristics. The quasi-TEM approach can be extended for the complicated structure like ridge-loaded FWG-SWS. Broad-banding of the conventional folded-waveguide slow-wave structure is attempted by ridge-loading on the broad wall of the structure. The ridge-loaded folded-waveguide slow-wave structure is analyzed by parametric approach, cascaded transmission matrix equivalent circuit model and quasi-TEM approach and validated against numerical simulation. The analysis is extended for exploring the efficacy of the ridge-loading on broad-banding of the traveling-wave tube. Finally efficiency enhancement of the folded-waveguide slow-wave structure is attempted by introducing grating on the broad wall of the structure. The analysis is carried out by numerical simulation for exploring the efficacy of the grating on efficiency enhancement of the traveling-wave tube.

碩士
國立中央大學
電機工程研究所
97
In a wireless communication system, a high performance switch is an important building block of RF front-end system. In order to achieve a broadband switch, a traveling-wave topology is applied to the circuit design. Also, the improvement and applications of the traveling-wave switch are included in the thesis. Introduction is given in chapter 1.The switch involved in the thesis are mainly based on the traveling-wave topology. The topology is described by two circuit designs with different processes and specifications in chapter 2: one traveling-wave T/R switch with a 50-Ω, λ/4 impedance transformer is designed using CMOS process, and the operating frequency is from 30 to 70 GHz. The other switch with a series transistor is designed using PHEMT process, and the operating frequency is from DC to 44 GHz. Furthermore, a technique of negative body bias is proposed to improve ciucuit performance in chapter 3. Based on the theory calculation and the experimental results, the insertion loss and power handling capability of the swiches are improved. In addition, a double-pole double-throw (DPDT) traveling-wave switch using a ring structurce is presented in chapter 4, and the operating frequency is from DC to 20 GHz. Finally, the conclusion is given in chapter 5.

碩士
南台科技大學
電機工程系
94
ABSTRACT A gyrotron traveling wave amplifier (gyro-TWT) is a high-power, broadband, millimeter-wave amplifier, applied in communication, military radar and satellite. Harmonic Multiplying gyro-TWT drives a fundamental TE11 wave in the input section and a second harmonic TE21 wave in the output section. This operation has two advantages. First, the magnetic field requirement can alleviate efficiently. Second, tuning the output waveguide radius achieves the multiplying frequency, relative to the input frequency. However, operating of the high current, the output power, gain, and efficiency of gyro-TWT will be degraded where the absolute instability oscillation occur to cause mode competition. Stability issues comprise the key factors limiting the performance of the gyro-TWT. The structure with distributed interaction wall losses, the length of interaction section and attenuation servers was shown to be effective in suppressing instability oscillation in the event. Therefore, the interaction structures with distributed wall losses and attenuating severs were more stability for instability oscillation. A harmonic multiplying gyro-TWT design with distributed-loss and severed structures is proposed to stabilize the amplification. This study presents a nonlinear analysis of typical oscillations, including analysis of instability oscillation. The lossy and severed sections of the harmonic multiplying gyro-TWT seem to increase effectively the start-oscillation currents of the instability oscillation. The harmonic multiplying gyro-TWT is predicted to yield a peak output power of 213 kW at 33.67 GHz with an efficiency of 27.3 %, a saturated gain of 47.8 dB and a bandwidth of 0.4 GHz for a 60 kV, 13 A electron beam with an axial velocity spread ∆νz/νz=8 %.

博士
國立臺灣大學
光電工程學研究所
90
ABSTRACT Metal-Semiconductor-Metal Traveling-Wave Photodetectors by Jin-Wei Shi The maximum available power of photodetector decreases as electrical bandwidth increases, and Power-Bandwidth (PB) product is an important figure of merit in the performances of ultra-high speed photodetectors (PDs). PDs with high PB products afford the applications in fiber radio communication system, photoreceiver circuit without electrical amplifier, and the sub-millimeter wave signals generation. Traveling wave photodetectors (TWPDs) is an attractive option for increasing the PB product over the intrinsic limit of vertically illuminated PDs. By properly guiding the launched optical wave signals and photo-excited microwave signals, the inherent tradeoff between maximum available power and electrical bandwidth limitation is diminished. In this dissertation, we proposed and demonstrated a novel type of TWPD: low temperature grown GaAs based metal-semiconductor-metal traveling wave photodetectors (LTG-GaAs based MSMTWPDs). We simulated this demonstrated device with the traditional LTG-GaAs based p-i-n TWPDs for comparison purpose by the photo-distributed current model. According to our simulation, MSMTWPD has better microwave guiding properties than p-i-n TWPD, such as lower high-frequency microwave loss, higher microwave velocity, and better impedance matching between external loads and TWPDs. The superior microwave performances and short carrier trapping time of LTG-GaAs in this novel device imply its excellent performance in high PB products. The theory, fabrication, and measurement of MSMTWPD comprise this thesis work. We established two electro-optic sampling systems to characterize the ultra-high speed performances of MSMTWPD in ~800nm and ~1300nm wavelengths regime. The MSMTWPD displays record high electrical bandwidth (570GHz) and record PB products as large as 5.7 THz-V, which is larger than the previous best-published results (432GHz-V) of Uni-Traveling-Carrier PD (UTC-PD) over ten times. Different nonlinear behaviors of MSMTWPD have also been observed and analyzed in these two wavelength regimes, which are originated from the internal material propriety of LTG-GaAs. By using the LTG-GaAs based MSMTWPD, we also demonstrated a novel THz photonic transmitter, which can radiate the signals at THz frequency regime by the integration of the MSMTWPD with a slot antenna and proper optical excitation. Record high E/O (electrical power/optical power) conversion efficiency has been demonstrated in the 1.6THz. The obtained conversion efficiency ( ) is larger than the previous best-published results of photomixer at the same operation frequency regime (1.6THz) over ten times ( .

碩士
國立中央大學
數學研究所
100
The purpose of this thesis is to investigate the existence of monotonic traveling wave solutions for some epidemic models. Using the monotone iteration method, combining with a pair of upper solution and lower solution, we show that there exist a minimal wave speed c* such that if the wave speed is greater than c* , then there exist monotone traveling wave solutions.

碩士
南台科技大學
電機工程系
91
High power and broad bandwidth capability of the gyrotron traveling wave amplifier (gyro-TWT) makes it an attractive source of coherent radiation in the millimeter wavelength range. The mode exhibits the lowest ohmic dissipation in previous gyro-TWT experiment. Moreover, it’s field peaks at a radial position of half the waveguide radius, so the quality of electron beam isn’t degraded. However, operating of the high current, the output power, gain, and efficiency of gyro-TWT will be degraded where the absolute instability, gyrotron backward oscillation (gyro-BWO) and reflective oscillation occur to cause mode competition. Stability issues comprise the key factors limiting the performance of the gyro-TWT, therefore physical origins of spontaneous oscillations in the gyro-TWT are analyzed and characterized. The structure with distributed interaction wall losses was shown to be effective in suppressing absolute instability in the event. Moreover, the attenuation severs to decrease interaction length of gyrotron backward oscillations in effect. Therefore, the interaction structures with distributed wall losses and attenuating severs were more stability for absolute instability and gyrotron backward oscillations. The improved gyro-TWT (type I) is predicted to yield a peak output power of 155 kW at 32.9 GHz with an efficiency of 15 %, a saturated gain of 45 dB and a bandwidth of 2.2 GHz for a 100 kV, 10 A electron beam with an axial velocity spread . Besides, is the improved gyro-TWT (type II) predicted to yield a peak output power of 418 kW at 33 GHz with an efficiency of 20.9 %, a saturated gain of 77 dB and a bandwidth of 2.6 GHz.

碩士
國立澎湖科技大學
電資研究所
103
Gyrotron travelling-wave tube (gyro-TWT) amplifier is a source of coherent electromagnetic wave and has the capability of high power, high gain, and broad bandwidth in the millimeter and submillimeter wave range. In this research, the gyro-TWT operates at a center frequency of 0.2 THz, beam voltage of 20 kV, beam current of 3 A, beam velocity ratio of 1.0 and beam velocity spread of 5%. To increase the transverse size of the interaction waveguide for high power operation, the gyro-TWT operates at a higher order mode 〖TE〗_(-8,2)^((1)). Because of the mode selective properties of the coaxial structure, a coaxial interaction waveguide is adopted to avoid the mode competition problem. Firstly, we analyze the dispersion relation and the beam-wave coupling strength to find the possible oscillating modes. Then, the distributed losses on the outer cylinder and the inner cylinder are used to suppress the oscillating modes. Finally, under stable operating conditions, the gyro-TWT amplifier achieves an output power of 11 kW, an efficiency of 18 %, a saturated gain of 38 dB, and a bandwidth of 1.5%. Furthermore, we tapered the radius of the inner cylinder to suppress the oscillations. For the interaction structure with a tapered inner cylinder, the gyro-TWT amplifier achieves an output power of 12 kW, an efficiency of 20 %, a saturated` gain of 41 dB, and a bandwidth of 3.85 GHz (1.9 %). Compared with the interaction structure with a uniform cross section, the tapered structure uses fewer losses and has a broader bandwidth.

碩士
國立臺灣大學
應用力學研究所
96
This thesis studies experimentally the traveling wave dielectrophoretic pump for delivering two-phase suspension medium, using human blood as an example. The pump is essentially a rectangular straight micro channel with a crosstie type electrode array built on one wall and operated under ac voltage with phase shift at neighboring electrodes. Both the conventional and traveling wave dielectrophoresis are generated. The negative conventional dielectrophoretic force repels the red blood cells from the electrode surface and the traveling wave dielectrophoretic force drives the cells along the direction of increasing phase. As the cells move, they drag their neighboring fluid (plasma), and the whole blood is delivered, after some sophisticated interaction of dielectrophoresis and fluid mechanics. The pump was fabricated using MEMS techniques and tested with different parameters of experiment, including the applied voltage, the operating frequency, the phase shift between neighboring electrodes, the number of electrodes, the dimensions of the channel, and the type of enhanced electrodes. It is found that the pump can attain a maximum pumping velocity at an intermediate frequency (about 20 MHz) and channel height (about 40 μm) with four phase signals. The steady average cell velocity can attain 15 μm/s for a pump with 1mm length and 24 electrodes, and operated with a four phase signal at 5 volts and 20 MHz. The pumping performance can be enhanced 2.4 times if two additional electrodes with appropriate applied voltages are added before the regular twDEP array.

碩士
國立臺灣大學
應用力學研究所
95
The traveling wave dielectrophoretic pump studied in this thesis is essentially a straight micro channel with electrode array(s) built on one or two of its walls. A traveling wave electric field is generated inside the channel when an ac field is applied to the electrodes with suitable phase shift between neighboring electrodes. A generalized dielectrophoretic force, including both the traditional and traveling wave dielectrophoretic force, is imparted on the suspended dielectric particles in fluid (such as our cells in blood) inside the channel. Under suitable conditions, the particles move along the channel. As the particles move, they drag their neighboring fluid, and thus the whole medium is delivered (the two phase suspension medium is being pumped). This goal of this thesis is to study such a pump, and several works were completed. (1) The electric fields for different electrode arrangements have been solved via analytical and numerical method. (2) When the pump is operated at frequency shifted from its optimized design frequency (when the real part of the Clausius-Mossotti factor equals zero), the traditional dielectrophoretic force will exert a force to the particles, which is opposite to the driving traveling dielectrophoretic force, when they entered the region above the electrode region. Such opposite force slows down the particles which degrade the pumping efficiency, or even blocks the particles which make the pump fails. In order to overcome such a drawback, a remedy is proposed, which is to add two assistant electrodes before the electrode array. When the assistant electrodes are operated at phase 90 and 270 or 180 and 270 (0 for the first electrode of the array) at a suitable voltage less than that of the electrode array, the opposite traditional dielectrophoretic force can be reduced. Also the pumping efficiency is enhanced with the assistant electrodes. At optimized design frequency, the average velocities of particles at the pump exit are 100 micron/s and 160 micron/s, respectively, for a typical case without and with assistant electrodes. (3) Calculation of two-phase suspension flow under the electric field is required for studying the pumping efficiency. We have updated an existing computer program by modifying the boundary conditions for particle impact and including variable electric properties and of the fluid, which are crucial for a correct simulation. For a typical case with assistant electrode, the numerical average velocity of the particles at exit accounting for the variable electric properties is 13.46 micron/s, which is about 10% less than the corresponding experimental result, 15 micron/s.

碩士
國立臺灣大學
應用力學研究所
95
This thesis studies experimentally the traveling wave dielectrophoretic pump, which is a micropump suitable for delivering two-phase suspension medium, such as our blood. The pump is essentially a straight microchannel with square cross section with array of electrodes built on one of its walls. Ac voltage is applied to the electrodes with a certain phase shift on neighboring electrodes. Both conventional and traveling wave dielectrophorsis are generated and drive the suspended particles (or cells) in motion. When the traveling wave dielectrophoretic force dominates the particle motion, the particles move along the direction of increasing phase if the imaginary part of the Clausius factor is positive (or vice versa), drag their surrounding fluid, and thus the whole medium is transported. We first manufactured the pump via MEMS techniques and demonstrate the feasibility of the above idea for pumping using human blood. Then we studied the performance of the pump for different parameters, including applied electric voltage, electric frequency, phase shift for neighboring electrodes, number of electrodes, concentration of suspended particles (by varying blood/saline ratio), different particles (blood cells of wister and human), without and with assistant electrodes before the normal electrode array, and different driving sources (functional generator or small IC chip). It is found that we have larger cell velocity for larger voltage, more electrodes, 90o phase shift (in comparing with 120o), larger cells, and with assistant electrodes. Typical cell velocity of human blood reaches 28.4 μm/s for 6 volts, 10 MHz, 90 phase shift and 24 electrodes with assistant electrodes. The pump also works when it is integrated with a IC chip, which shows the possibilities of building a small portable device. The result may find application in biomedical area.

碩士
中原大學
機械工程研究所
94
By use of a pair of Langevin vibrators and by use of associated rail and slide, a linear actuator is developed. One of the Langevin vibrators performs as a vibrator and the other one performs as an absorber. Besides the Langevin vibrator, design of the waveguide and the slider are included in this article. Also, the generated traveling wave and the transmission loss due to friction and contact pressure and so on are studied. The vibration wave generated by the vibrators is simulated by ANSYS and measured in experiment. Experimental data shows that both are approximate and with error of about 3%. Similarly, the slider output of the developed linear actuator system by use of Langevin vibrators is tested that can reach the speed of about 466 mm/sec. Since the transmission loss is significant, except the manufacturing and assembly errors, the cause and effect as well as how to increase the efficiency to transfer more energy into the slider is investigated. Modeling of transmission loss is derived including the factors of friction and contact pressure and material property. It is seen that by adjusting these parameters, the transmission loss can be reduced; in other words, the speed and force output of the slider can be increased. It is believed the model of transmission is useful for understanding the energy transfer of the traveling wave to the driven mechanism, and it provides a design index for similar actuator design by use of traveling wave.

碩士
南臺科技大學
光電工程系
105
In recent years,the use of terahertz-frequency gyrotrons has been increased with the rapid growth in nuclear magnetic resonance (NMR), electron spin resonance, outer space research and military radar and other related applications. The harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWA) suffer from the drawback of having small waveduide radii; this significantly increases their ohmic loasses. However, the harmonic multiplying gyro-TWA can improve the stability and permits magnetic field reduction and frequency multiplication. Ina ddition, produce high power and broad bandwidth of source in sub-terahertz frequency. Thus the importance of operating at high-order-mode harmonic multiplying gyro-TWA. However operating of the high current, the output power, gain and efficiency of gyro-TWAs will be degraded where the absolute instability oscillation occurs to cause mode competition. This study presents a comparative three schemes analysis of fourth-harmonic multiplying gyro-TWA, M=1, M=2 and M=4, respectively. Absolute instabilities in the gyro-TWA are suppressed by distributed-wall losses and a mode selective circuit. Regardless of the scheme, the mode-selective can provide an attenuation of more than 20dB to suppress the competing modes that from fundamental-harmonic TE_11^((1)) mode. The amplification of the waves in a gyro-TWA depends on the lengths of the sections, and the simulated results show that the gain increases for all schemes, as the length of the lossy section or the length of the copper section increases. The fourth- harmonic multiplying gyro-TWA, regardless of the scheme is exhibit nearly the same saturated output powers (~15kW) and bandwidths (~0.9GHz), where the saturated gain of the scheme at a high frequency multiplication ratio is smaller than that of the scheme at a low frequency multiplication ratio at an interaction efficiency of 5% for a 100kV, 3A electron beam with an axial velocity spread =5%.

Magnetic Particle Imaging (MPI) ist ein neuartiges tomographisches Bildgebungsverfahren, welches in der Lage ist, dreidimensional die Verteilung von superparamagnetischen Nanopartikeln zu detektieren. Aufgrund des direkten Nachweises des Tracers ist MPI ein sehr schnelles und sensitives Verfahren [12] und benötigt für eine Einordnung des Tracers (z.B. im Gewebe) eine weitere bildgebende Modalität wie die Magnetresonanztomographie (MRI) oder die Computertomographie. Die strukturelle Einordnung wird häufig mit dem Fusion-Imaging-Verfahren durchgeführt, bei dem die Proben separat in den Geräten vermessen und die Datensätze retrospektiv korreliert werden [75][76]. In einem ersten Experiment wurde bereits ein Traveling-Wave-MPI-Scanner (TWMPI) [17] mit einem Niederfeld-MRI-Scanner kombiniert und die ersten Hybridmessung durchgeführt [15]. Der technische Aufwand, zwei separate Geräte aufzubauen sowie die Tatsache, dass ein MRI-Gerät bei 30mT sehr lange benötigt, diente als Motivation für ein integriertes TWMPIMRI- Hybridsystem, bei dem das dynamische lineare Gradientenarray (dLGA) eines TWMPI-Scanners intrinsisch das B0-Feld für ein MRI-Gerät erzeugen sollte. Das Ziel dieser Arbeit war es, die Grundlagen für einen integrierten TWMPI-MRIHybridscanner zu schaffen. Die Geometrie des dLGAs sollte dabei nicht verändert werden, damit TWMPI-Messungen weiterhin ohne Einschränkungen möglich sind. Zusammenfassend werden hier noch mal die wichtigsten Schritte und Ergebnisse dieser Arbeit aufgezeigt. Zu Beginn dieser Arbeit wurde mittels Magnetfeldsimulationen nach einer geeigneten Stromverteilung gesucht, um allein mit dem dLGA ein ausreichend homogenes Magnetfeld erzeugen zu können. Die Ergebnisse der Simulationen zeigten, dass bereits zwei unterschiedliche Ströme in 14 der 20 Einzelspulen des dLGAs genügten, um ein Field of View (FOV) mit der Größe 36mm x 12mm mit ausreichender Homogenität zu erreichen. Die Homogenität innerhalb des FOVs betrug dabei 3000 ppm. Für die angestrebte Feldstärke von 235mT waren Stromstärken von 129A und 124A nötig. Die hohen Ströme des dLGAs erforderten die Entwicklung eines dafür angepassten Verstärkers. Das ursprüngliche Konzept, welches auf einem linear angesteuerten Leistungstransistors aufbaute, wurde in zahlreichen Schritten so weit verbessert, dass die nötigen Stromstärken stabil an- und ausgeschaltet werden konnten. Mithilfe eines Ganzkörper-MRIs konnte erstmals das B0-Feld des dLGAs, welches durch den selbstgebauten Verstärker erzeugt wurde, gemessen und mit der Simulation verglichen werden. Zwischen den beiden Verläufen zeigte sich eine qualitativ gute Übereinstimmung. Das Finden des NMR-Signals stellte wegen des selbstgebauten Verstärkers eine Herausforderung dar, da zu diesem Zeitpunkt die nötige Präzision noch nicht erreicht wurde und der wichtigste Parameter, die Magnetfeldstärke im dLGA, nicht gemessen werden konnte. Dagegen konnte die Länge der Pulse für die Spin-Echo- Sequenz sehr gut gemessen werden, jedoch war der optimale Wert noch nicht bekannt. Durch iterative Messungen wurden die richtigen Einstellungen gefunden, die nach Änderungen an der Hardware jeweils angepasst wurden. Die Performanz des Verstärkers konnte anhand wiederholter Messungen des NMRSignals genauer untersucht werden. Es zeigte sich, dass die Präzision weiter verbessert werden musste, um reproduzierbare Ergebnisse zu erhalten. Mithilfe des NMR-Signals konnten auch das B0-Feld ausgemessen werden. Es zeigte eine gute Übereinstimmung zur Simulation. Mithilfe von vier Segmentspulen des dLGAs war es möglich einen linearen Gradienten entlang der z-Achse zu erzeugen. Ein Gradient wurde zusätzlich zum B0-Feld geschaltet und ebenfalls ausgemessen. Auch dieser Verlauf zeigte eine gute Übereinstimmung zur Simulation. Mithilfe des Gradienten wurde erfolgreich die Frequenzkodierung und die Phasenkodierung implementiert, durch die bei beiden Messungen zwei Proben anhand des Ortes unterschieden werden konnten. Damit war die Entwicklung des MRIScanners abgeschlossen. Der Aufbau des TWMPI-Scanners benötigte neben dem Bau des dLGAs die Anfertigung von Sattelspulen. Für die MPI-Messungen konnte der fehlende Teil der Sendekette sowie die gesamte Empfangskette von einer früheren Version benutzt werden. Auch für das MPI wurde die Funktionalität mithilfe einer Punktprobe und eines Phantoms überprüft, allerdings hier in zwei Dimensionen. Die Erweiterung zu einem Hybridscanner erforderte weitere Modifikationen gegenüber einem reinen TWMPI- bzw. MRI-Scanner. Es musste ein Weg gefunden werden, die Beschaltung des dLGAs für die jeweilige Modalität zügig anzupassen. Dafür wurde ein Steckbrett gebaut, das es erlaubt, die Verkabelung des dLGAs in kurzer Zeit zu ändern. Außerdem mussten innerhalb des dLGAs die Sattelspulen und die Empfangsspule des TWMPIs sowie die Empfangsspule des MRIs untergebracht werden. Ein modulares System erlaubte die gleichzeitige Anordnung aller Komponenten innerhalb des dLGAs. Das messbare FOV des MRIs ist der Homogenität des B0-Feldes angepasst, das FOV des TWMPI ist ausgedehnter. Zum Ende dieser Arbeit wurde erfolgreich eine Hybridmessung durchgeführt. Das Phantom bestand aus je zwei Kugeln gefüllt mit Öl und mit einem MPI-Tracer (Resovist). Mit TWMPI war die räumliche Abbildung der Resovistkugeln möglich, während mit MRI die der Ölkugeln möglich war. Diese in situ Messung zeigte die erfolgreiche Umsetzung des Konzeptes für den TWMPI-MRI-Hybridscanner. Zusammenfassend wurden in dieser Arbeit die Grundlagen für einen TWMPIMRI- Hybridscanner gelegt. Die größte Schwierigkeit bestand darin, ein ausreichend homogenes B0-Feld für das MRI zu erzeugen, mit dem man ein gutes NMRSignal aufnehmen konnte. Mit einer einfachen Stromverteilung, bestehend aus zwei unterschiedlichen Strömen, konnte ein ausreichend homogenes B0-Feld erzeugt werden. Durch komplexere Stromverteilungen lässt sich die Homogenität noch verbessern und somit das FOV vergrößern. Die MRI-Bildgebung wurde in dieser Arbeit für eine Dimension implementiert und soll in fortführenden Arbeiten auf 2D und 3D ausgedehnt werden. Letztendlich soll anhand eines MRI-Bildes die Partikelverteilung des MPI-Tracers in Lebewesen deren Anatomie zugeordnet werden. In [76][77][78] sind die ersten präklinischen Anwendungen mit dem TWMPI-Scanner durchgeführt worden. Diese Anwendungen erlangen eine höhere Aussagekraft durch die zusätzlichen Informationen eines TWMPI-MRI-Hybridscanners. In weiteren Arbeiten sollte zusätzlich die Größe des FOVs für das MRI erweitert werden. Außerdem macht es Sinn, einen elektronischen Schalter zum Umschalten des dLGAs zwischen MRI und MPI zu realisieren. Die nächste Version des Hybridscanners könnte beispielsweise ein komplett neu gestaltetes dLGA enthalten, in dem jede Segmentspule in radialer Richtung einmal geteilt wird und dadurch in eine innere und eine äußere Spule zerlegt wird. Für das MRI werden die beiden Spulenteile gegen geschaltet, um ein homogenes Feld in radialer Richtung zu erhalten. Für das TWMPI werden die Spulenteile gleichgeschaltet, um einen möglichst starken Feldgradienten zu erreichen. In dieser Arbeit wurde für die nächste Version eines TWMPI-MRI-Hybridscanners viel Wissen generiert, das äußerst hilfreich für das neue Design sein wird. Anhand der Vermessung des B0-Feldes hat sich gezeigt, dass die simulierten Magnetfelder gut mit den gemessenen Magnetfeldern übereinstimmen. Außerdem wurde viel gelernt über die Kombination von TWMPI mit MRI
Magnetic Particle Imaging (MPI) is a novel tomographic imaging technique, which can detect the distribution of superparamagnetic iron oxides in three dimensions. MPI is a fast and sensitive technique due to its immediate tracer detection [12] but needs another imaging modality like magnetic resonance imaging (MRI) or computed tomography for tracer classification (e.g. to tissue). The classification is often done with the fusion imaging technology where the sample is measured in different systems and the data are correlated afterwards [75][76]. In a first experiment a traveling-wave-MPI-scanner (TWMPI) [17] was combined with a low-field-MRIscanner and first hybrid measurements were acquired [15]. The motivation for an integrated TWMPI-MRI-hybrid system, in which the dynamic linear gradient array (dLGA) generates the main magnetic field B0 intrinsically, was such that an MRI-system at 30mT needs a long time for data acquisition as well as the higher technical effort for assembling two separate systems. The aim of this work was to establish the basic principles of an integrated TWMPIMRI- hybrid scanner. The geometry of the dLGA should not be altered in this process so that TWMPI-measurements are still possible without limitations. All important steps and measurements of this work are presented here in summary. At the beginning of this work it was necessary to find a suitable current configuration by the use of magnetic field simulations. The aim was to generate a magnetic field that is homogenous enough for NMR measurements only with the dLGA coils. The results of the simulations showed that only two different currents in 14 of the 20 dLGA coils are necessary to obtain a field of view (FOV) with a sufficiently homogeneity of 3000ppm and a size of 36mm x 12 mm. For the target field strength of 235mT currents of 129A and 124A are required. The high currents in the dLGA made it necessary to develop a custom amplifier. The original concept, which is based on a linear controlled power transistor, was improved in numerous steps so that the high currents could be turned on and off in a stable way. The magnetic field B0 of the dLGA, which was generated by the custom amplifier, could firstly be measured with the aid of a full-body MRI. Its comparison to the simulation showed a qualitative good agreement. A challenge was to find the NMR-signal because of the custom amplifier which did not have the necessary precision at this particular time and also the most important parameter, the magnetic field strength inside the dLGA, could not be measured. In contrast the length of the pulses for the spin-echo-sequence could be measured accurately, but the ideal value was not known. Iterative measurements were used to find the right adjustments, which had to be adapted after each change in the hardware. The amplifier performance could be analyzed more in detail by repeated measurements of the NMR-signal. They indicated that the precision had to be improved further to achieve reproducible results. The B0-field could be measured by means of the NMR-signal. It showed good agreement to the simulation. By means of four segment coils of the dLGA it was possible to create a linear gradient along the z-axis. as well as the gradient along the z-axis By means of the gradient frequency encoding and phase encoding were successfully implemented. Two samples could be differentiated by its location for both encoding methods. That completes the development of the MRI-scanner. The design of the TWMPI-scanner required the construction of the saddle coils besides the production of the dLGA. The missing parts of the transmit chain and the whole receive chain could be used from an earlier version for MPI-measurements. The functionality of the MPI was tested with a point sample and a phantom, but this time in two dimensions. The extension to a hybrid scanner required additional modifications compared to a pure TWMPI- or MRI-scanner. An efficient way had to be found to change the connections of the dLGA for the particular modality. A pinboard was built which made a rapid change of the connections of the dLGA possible. Furthermore the saddle coils and the receive coil of the TWMPI-system as well as the receive coil of the MRI had to be placed inside the dLGA. This problem was solved with a modular system which made it possible to simultaneously place all components inside the dLGA. The measurable FOV of the MRI is adapted to the homogeneity of the B0-field, the FOV of the TWMPI is larger. At the end of this work a hybrid measurement was successfully performed. The phantom consisted of two spheres filled with oil and another two spheres filled with an MPI-tracer (Resovist). With TWMPI the spatial resolution of the Resovist spheres was possible, while with MRI it was possible for the oil spheres. This in situ measurement showed the successful implementation of the TWMPI-MRIhybrid scanner concept. In summary the basic principles for a TWMPI-MRI-hybrid scanner were established in this work. The highest obstacle was the generation of a homogenous magnetic field B0 for MRI, which lead to a good NMR-signal. A simple current configuration, consisting of two different currents, generated a sufficient homogenous magnetic field. With more complex current configurations a more homogenous field and thereby a larger FOV is possible. MRI-imaging was implemented in this work in one dimension and should be extended to 2D and 3D in further projects. Eventually an MRI-image should be used to display a relation between particle distribution of the MPI-tracer in living creatures and their anatomy. The first preclinical applications were implemented with the TWMPI-scanner [76][77][78]. These applications would reach a higher information value with the use of a TWMPI-MRI-hybrid scanner. The size of the FOV for the MRI should be extended in further projects. Furthermore it is reasonable to realize an electric switch for changing the connections of the dLGA between MRI and MPI. The next version of the hybrid scanner could contain for example a completely newly designed dLGA in which every segment coil is divided radially. The segment coils would consist of an inner and an outer part. For MRI-measurements both magnetic fields work against each other to create a radially homogenous magnetic field. For TWMPI both magnetic fields work together to create a high magnetic field gradient. For the next version of a TWMPI-MRI-hybrid scanner a lot of know-how was created which will be helpful for the new design. By means of the B0 measurements it was shown that the simulated magnetic fields fit well to the measured ones. Furthermore plenty was learned for the combination of TWMPI and MRI