Further improvements of the thermal efficiency of gas turbine cycle are closely coupled to the increase of turbine inlet temperature. This requires intensive and efficient cooling of the blades. In this perspective, experimental investigations of the gas temperature and heat transfer distribution around the airfoil are of primary importance. The present work aims at the development of two measurement techniques based on applications of the thin film sensors: the two-layer gauge for the wall heat transfer determination and the dual thin film probe for flow temperature measurements. Both techniques are used in short duration tunnels of the von Karman Institute (VKI) under engine representative conditions and are able to resolve both time-averaged component and time-resolved component i.e. periodic blade passing events at ~5-7 kHz with harmonics up to 50 kHz. In order to derive the wall heat flux with the two-layer gauge, the unsteady conduction equation is solved in the two-layer substrate using the measured value of the wall temperature as a boundary condition. The gauges are extensively calibrated and the data reduction method is validated on a blade of the second stator of the VKI turbine. A very good repeatability is achieved. Measurements are also performed on the complex geometry of a blade tip in a cascade configuration revealing the high three dimensionality of the flow. The dual thin film probe combines the operation of two thin films and determines the flow temperature from two independent heat flux measurements. The probe is calibrated and then validated with measurements downstream a cascade. The robustness and the reliability of the probe are also demonstrated by measurements downstream of the rotor and the second stator of the VKI turbine.

It is customary to obtain ac power from batteries through a power converter, where mains ac power is not readily available. Such a power converter is also needed in several mobile/ airborne/ space applications. Till recently this application is served by a H bridge inverter followed by a low frequency transformer and a passive low pass filter. The H bridge inverter employs high frequency pulse width modulation. The transformer is made of standard silicon steel. The filter is made of L and C elements. In such a converter the magnetics account for about 30% of cost and 50% of weight. Moreover the dc input current in such converters is discontinuous, leading to poor efficiency. There is need for an input filter as well. This thesis presents the development of an inverter with high frequency (hf) link. The power converter employs a boost front end resulting in continuous input current. The H bridge inverter employs phase modulation technique with soft switching features. The boost converter and the H bridge share power devices. The isolation transformer handles high frequency ac power and is compact. It is shown that the transformer size can be reduced by more than one order of magnitude. There is a rear end cycloconverter to reconvert the high frequency ac power into 50 Hz output power. Innovative pulse sequencing in the cycloconverter ensures loss-less switching. The pulse width modulation shifts the dominant harmonic frequency to double the switching frequency. The output LC filter is light. The converter can handle bidirectional power. The controller is digital. The overall concept was demonstrated through the 500 W prototype design. The proposed topology offers small size, low losses and continous input current. The controller is digital and offers totally software based compensation and settings. It is expected that on account of the small size and cost, this topology is likely to become more popular in the near future. The applications of such power converters will bring down the size and cost of UPS, solar inverters, wind mill inverters etc.

ORMOCERR®s are organic-inorganic hybrid polymers. Since their material properties can be tailored precisely during synthesis, they are suitable for a wide range of applications in dielectric and optical microelectronics. This thesis reports on process development of ORMOCERR®s for Sequentially Build-Up (SBU) test vehicles, suitable for both electrical and optical interconnect. Furthermore, this work includes materials characterization, such as refractive index studies (system B59:V32), optical loss measurements (systems B59:V32 and B59:B66), and surface characterization through contact angle measurement and surface energy estimation (systems B59:V32 and B59:B66). Process development for a high-frequency test vehicle was performed applying a newly developed dielectric material of the ORMOCER® class. Dielectric layers in a total thickness of 80 μm were build-up on a common FR4 substrate, applying photolithographic processes and moderate process temperatures of below 433 K. The loss tangent and the permittivity of the material were measured to be 0.024 (loss tangent) and 3.05 (permittivity) over the entire frequency range 10 GHz to 40 GHz. The compatibility of the material to standard processes of the PCB industry was proven. Furthermore, a possibility for cost reduction in high-frequency MCM applications was shown, through the possibility of using low-cost substrates. The concept of a “flexible manufacture approach” for large-area panel optical backplane interconnects was introduced. Here, a 101.6 mm x 101.6 mm photolithographic mask is to be stepped-out over a large-area panel substrate (up to 609.6 mm x 609.6 mm). The goal is to be able to create a large amount of continuous and unique waveguide patterns over the whole area with a small portfolio of masks, thus being able to minimize excess costs. In practice continuous waveguide patterns were created over an area of 204.8 mm x 204.8 mm on a large-are panel (609.6 mm x 609.6 mm), using a large-are mask aligner and a 101.6 mm x 101.6 mm waveguide mask. The optical loss of the waveguides was measured to be 0.6 dB/cm (B59:V32 material system, λ =850 nm). In connection to the large-area panel project a re-evaluation on the optical power budget needed for high bit rate optical interconnects was performed. This work was mainly based on literature surveys of optical waveguide materials, planar optical amplifiers, light coupling structures, and planar light-routing structures. It was shown that optical amplification is necessary at certain places on realistically routed optical backplanes to boost the optical signal. Therefore, the concept of a flip-chip mountable optical amplifier (FOWA) device, based on planar optical waveguide amplifiers and Semiconductor Optical Amplifiers, was developed. The device’s design allows an independent manufacturing to the rest of the board and a mounting at key-positions using standard pick and place technology. Additionally, it was observed that most of the amplifier research is focused on the wavelength of 1310 nm and 1550 nm, whereas optical backplane applications are targeting the 830 nm range. During SBU processing of waveguide structures was discovered a de-wetting phenomenon of B59 resin on a cured B59:B66 and B59:V32 surface, respectively. Good wetting behavior could be achieved by adding small amounts of B66 or V32, respectively, to the B59. Surface tension estimations on various compositions of the systems B59:B66 and B59:V32 could not directly be correlated to the de-wetting phenomenon. Furthermore, the optical loss properties of B59 were only affected to a minor degree by adding B66 or V32. The process route proposed is an efficient alternative to processes including surface activations steps, thus opening possibilities for large-area processing in PCB industry, where surface activation steps, such as plasma activation or silanization, are not available. The process development, materials characterization, and reviews presented provide a basis for further research on processes for high-performance electro/optical backplane interconnects with focus on Large-Area Panel processing.

High-frequency dc-dc converters are nowadays widely used in a diversity of power electronic applications. High operating frequencies entail a reduction in size of the passive components, such as inductors, capacitors and power transformers. By operating the converter at higher frequencies with conventional hard-switching topologies, the transistor switching losses increase at both turn-on and turn-off. High-voltage converters in the power range of 1-10MW will therefore have excessive switching losses if the switching frequency is higher than 4 kHz. In order to achieve a high-frequency operation with moderate switching losses a number of soft-switched topologies have been studied in [Dem1]. The favourable DC-DC converter was found to be the Dual-Active Bridge when a bi-directional power flow is demanded. Additionally, the Single-Active Bridge (SAB) topology was introduced for the first time. In this thesis the two topologies are thoroughly studied. The dynamic small-signal models are presented and the dynamic behaviour of the converters is discussed in deep. Different control strategies are presented concerning the two converters and the advantages and the disadvantages of the different control strategies are stated. Critical issues as efficiency and stability are presented separately for the two converters. / QC 20101005

In high frequency computational electromagnetics, rigorous numerical methods be come unrealistic tools due to computational demand increasing with the frequency. Instead approximations to the solutions of the Maxwell equations can be employed to evaluate th electromagnetic fields. In this thesis, we present the implementations of three high frequency approximat methods. The first two, namely the Geometrical Theory of Diffraction (GTD) and th Physical Optics (PO), are commonly used approximations. The third is a new invention that will be referred to as the Surface Current Extraction-Extrapolation (SCEE). Specifically, the GTD solver is a flexible and modular software package which use Non-Uniform Rational B-spline (NURBS) surfaces to model complex geometries. The PO solver is based on a triangular description of the surfaces and includes fas shadowing by ray tracing as well as contribution from edges to the scattered fields. GTD ray tracing was combined with the PO solver by a well thought-out software architecture Both implementations are now part of the GEMS software suite, the General ElectroMag netic Solvers, which incorporates state-of-the-art numerical methods. During validations both GTD and PO techniques turned out not to be accurate enough to meet the indus trial standards, thus creating the need for a new fast approximate method providing bette control of the approximations. In the SCEE approach, we construct high frequency approximate surface currents ex trapolated from rigourous Method of Moments (MoM) models at lower frequency. T do so, the low frequency currents are projected onto special basis vectors defined on th surface relative to the direction of the incident magnetic field. In such configuration, w observe that each component displays systematic spatial patterns evolving over frequenc in close correlation with the incident magnetic field, thus allowing us to formulate a fre quency model for each component. This new approach is fast, provides good control of th error and represents a platform for future development of high frequency approximations. As an application, we have used these tools to analyse the radar detectability of a new marine distress signaling device. The device, called "Rescue-Wing", works as an inflatabl radar reflector designed to provide a strong radar echo useful for detection and positionin during rescue operations of persons missing at sea. / QC 20101004

Pre-eclampsia is associated with increased risk of cardiovascular disease (CVD) later in life. The ‘gold standard’ for estimating cardiovascular risk - ultrasound assessment of the common carotid artery intima-media thickness (CCA-IMT) - does not convincingly demonstrate this increased risk. The aim of this thesis was to examine whether high-frequency (22 MHz) ultrasound assessment of the individual CCA intima and media layers and calculation of the intima/media (I/M) ratio - can indicate the increased cardiovascular risk after pre-eclampsia. After validation of the method in premenopausal women with systemic lupus erythematosus (SLE) who have a recognized increased risk of CVD, women during and after normal and preeclamptic pregnancies were investigated. Assessment of the individual artery wall layers reliably demonstrated the increased cardiovascular risk in premenopausal women with SLE, while CCA-IMT did not. The artery wall layer dimensions in women with SLE were comparable to those of postmenopausal women without SLE and were 30 years older. Among the women with normal pregnancies negative changes to the artery wall later on in the pregnancy were seen in those with lower serum estradiol, older age, higher body mass index or higher blood pressure early in the pregnancy. About one year postpartum, both the mean intima thickness and the I/M ratio had improved, compared to values during pregnancy. These findings support the theory that normal pregnancy is a stress on the vascular system. Women who developed pre-eclampsia (mean age 31 years) had thicker intima layers, thinner media layers and higher I/M ratios, both at diagnosis and one year postpartum, than women with normal pregnancies, indicating increased cardiovascular risk. Women with a history of severe pre-eclampsia (mean age 44 years; mean 11 years since the last delivery) had thicker intima layers and higher I/M ratios than women with a history of normal pregnancies, indicating long-standing negative vascular effects. Assessment of individual CCA wall layers, but not of CCA-IMT, provided clear evidence of the well-known increased cardiovascular risk in women with SLE or pre-eclampsia. The method has the potential to become an important tool in reducing cardiovascular morbidity and mortality in these women through early diagnosis and intervention.

High-power voltage sourced converters(VSC’s) are becoming increasingly prevalent in modern transmission systems. These systems primarily use switching schemes generating kHz range harmonics, which may be magnified by one or more system resonances. Despite the high frequency harmonics, VSC systems widely use insulated equipment designed for operation at power frequencies; this includes critical substation components such as medium voltage polymeric cables and terminations. The stress grading systems of non-geometric (compact) cable terminations are susceptible to insulation degradation and eventual flashover failure, under high frequency harmonic stresses. As such, the present work studies high frequency voltage effects in cross-linked polyethylene cable terminations, and their relationship to stress grading (SG) design and material properties. Finite element modeling (FEM) has been used to analyze electric field and resistive heating in termination designs, in response to parametric variations in SG material properties. Experimental studies investigate thermal behaviour in a variety of commercial termination designs, using a high voltage, high frequency test setup developed to replicate conditions of high frequency harmonic resonance in a VSC system. The study results show that high frequency voltage application increases the electric field, resistive heating, and surface temperature rise, in non-geometric (compact) termination designs using field-dependant stress grading materials. Geometric (stress cone) designs are insensitive to high frequency harmonics; however, they have disadvantages compared to compact designs, making them a less practical long-term solution for high frequency applications. Among non-geometric designs, the field-dependent electrical conductivity σ (E), the permittivity ε, and the temperature dependencies of σ (E) and ε strongly influence the termination electrical and thermal behaviour under high frequency stress. Since thermal hotspots in cable termination SG areas may lead to material degradation and eventual failure, recommendations are made for an optimal non-geometric stress grading design, for terminations operating in environments where high frequency harmonics may be present.

Concerns exist regarding the ability of HFOV to provide the needed lung protective ventilation for adult patients with ARDS. HFOV is increasingly being used as a lung protecting ventilation mode even if some of its protective attributes may be lost as the airway resistance (Raw) increases or decreases. In fact, in cases of shifting air resistance, HFOV may have caused lung injury. PURPOSE: The purpose of this study was to investigate the effect of airway resistance on tidal volume (Vt) delivered by HFOV to adult patients. Also, the study intended to determine direction for volume change when resistance increases or decreases. METHODS: An in vitro model was used to simulate an adult passive patient with ARDS using a breathing simulator (Active Servo Lung 5000, Ingmar Medical, Pittsburgh, PA, USA). Adjustable resistance and compliance for each lung was used. The resistance levels of 15, 30, 45 (cm H2O/L/sec) were used for upper and lower Raw and CL was fixed at 40 mL/cm H2O. The ventilator (Sensormedics 3100B) was set to MAP = 35 cm H2O, to insp-time of 33%, to bias flow =30 L/min, to delta-P of 80, and to 50% oxygen. Vt was recorded (n=3) for each Raw, and the data was collected on the host computer. Approximately 200-250 breaths of data for each Raw were captured via the ASL software and then converted to Excel for analysis. An average of 80 breathes (following the steady Vt level) was used in each analysis. DATA ANALYSIS: The data analysis was performed with one way ANOVA and with a post hoc Bonferroni test in order to determine the statistical significance of the delivered Vt with each Raw. A probability of (p < 0.05) was accepted as statistically significant. RESULTS: The descriptive statistics of the average delivered Vt with regard to each Raw (15, 30, 45 cm H2O/L/sec) were the number of experiments (n=3), mean Vt (93.52, 89.09, 85.99 mL), and standard deviations (SD) (1.38, 1.11, 1.10) respectively. There was an inverse relationship between tidal volume and airway resistance during HFOV. With all other variables kept constant, higher resistance caused less volume, whereas lower resistance caused more volume. The one-way ANOVA test showed that there were significant differences between the delivered tidal volumes. When the post hoc Bonferroni test was used, the data showed significant differences between airway resistances of 15 cm H2O/L/sec and 30 cm H2O/L/sec and between 15 cm H2O/L/sec and 45 cm H2O/L/sec. In contrast, no significant differences were found between airway resistances of 30 cm H2O/L/sec and 45 cm H2O/L/sec. CONCLUSION: Vt is not constant during HFOV. Airway resistance is one of the determinants of delivered tidal volume in adults with ARDS during HFOV. Airway resistance should be an important factor in ventilator management and in clinical experiments of patients on HFOV. Without a proper Vt measurement device HFOV should not be used as lung protective ventilation for adult patients with ARDS.

The goal of this thesis work is to enable an existing UHF radar to operate in the VHF band instead. In order to achieve this, new coherent local oscillators are required. Different options are suggested and one of them is implemented and analyzed.

High-power voltage sourced converters(VSC’s) are becoming increasingly prevalent in modern transmission systems. These systems primarily use switching schemes generating kHz range harmonics, which may be magnified by one or more system resonances. Despite the high frequency harmonics, VSC systems widely use insulated equipment designed for operation at power frequencies; this includes critical substation components such as medium voltage polymeric cables and terminations. The stress grading systems of non-geometric (compact) cable terminations are susceptible to insulation degradation and eventual flashover failure, under high frequency harmonic stresses. As such, the present work studies high frequency voltage effects in cross-linked polyethylene cable terminations, and their relationship to stress grading (SG) design and material properties. Finite element modeling (FEM) has been used to analyze electric field and resistive heating in termination designs, in response to parametric variations in SG material properties. Experimental studies investigate thermal behaviour in a variety of commercial termination designs, using a high voltage, high frequency test setup developed to replicate conditions of high frequency harmonic resonance in a VSC system. The study results show that high frequency voltage application increases the electric field, resistive heating, and surface temperature rise, in non-geometric (compact) termination designs using field-dependant stress grading materials. Geometric (stress cone) designs are insensitive to high frequency harmonics; however, they have disadvantages compared to compact designs, making them a less practical long-term solution for high frequency applications. Among non-geometric designs, the field-dependent electrical conductivity σ (E), the permittivity ε, and the temperature dependencies of σ (E) and ε strongly influence the termination electrical and thermal behaviour under high frequency stress. Since thermal hotspots in cable termination SG areas may lead to material degradation and eventual failure, recommendations are made for an optimal non-geometric stress grading design, for terminations operating in environments where high frequency harmonics may be present.