No description available.

No description available.

No description available.

Plasma actuators are devices that with two electrodesand a dielectric material can ionize the air around itand thus control the airflow. They have considerable potentialfor a multitude of reasons, one of which being that they haveno moving parts, making them easy to produce and hard tobreak. Using this technology on the front of vehicles like truckscould be revolutionary in increasing fuel efficiency and thusreducing emissions. A model of a plasma actuator in COMSOLMultiphysics was used to simulate the effect it has on the airaround it. The focus of the project has been to optimize thedesign of an actuator for increased velocity in the air around it.This has been done with regards to properties of the appliedvoltage, the distance between the electrodes and material ofthe dielectric. Parametric analyses of all the above propertieswas performed. Close-to-optimal values of some of the abovementioned parameters were successfully calculated. However,other parameters, such as the horizontal distance between theelectrodes, were beyond the model’s capability to determine usingthe described method. / Plasmaställdon är anordningar som medtvå elektroder och ett dielektriskt material kan jonisera luftenrunt sig och på detta sätt styra luftflödet. De har betydandepotential av en mängd anledningar, varav en är att de inte har några rörliga delar, vilket gör dem lätta att producera och ochsvåra att förstöra. Användande av denna teknologi på fronterav fordon som lastbilar skulle kunna vara revolutionerande förökad bränsleeffektivitet och därmed minska utsläpp. En modellav ett plasmaställdon i COMSOL Multiphysics användes för attsimulera effekterna den har på luften runt sig. Projektets fokushar varit på att optimera ett ställdons design för ökad hastigheti luften runt den. Detta har gjorts med avseende på egenskaperhos den tillförda spänningen, avståndet mellan elektroderna ochdielektrikumets material. Parametriska analyser för alla dessaegenskaper har genomförts. Nästintill optimala värden för någraav de ovan nämnda parametrarna beräknades med framgång.Andra parametrar, som det horisontella avståndet mellan elektroderna,var bortom modellens förmåga att bestämma vidanvändande av den beskrivna metoden. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

<p>Accurate knowledge of the frequency- and temperature-dependent dielectric properties of biological tissues is crucial in the development of ultra-wideband diagnostic and therapeutic technologies such as microwave breast cancer detection and hyperthermia treatments. This work examines the temperature dependence of the dielectric properties of the five tissue phantom-types developed by our group as well as porcine fat, muscle and liver tissues for the frequency range from 3 GHz to 10 GHz and for the temperature range from 5 °C to 45 °C. A systematic and simple measurement procedure is developed to measure the continuous temperature dependence of the dielectric properties of the various phantom and tissue types. The temperature trends of the dielectric properties of the different phantoms and tissues are investigated.</p> <p>Linear temperature coefficients at discrete frequencies are impractical and insufficient in ultra-wideband applications when realistic, non-linear numerical models of the dielectric properties are required. Therefore, a compact one-pole Cole-Cole model is used to model the frequency dependence of the dielectric properties of the measured samples at every temperature point. A second- or third-order polynomial is used to model the temperature dependence of the Cole-Cole parameters. The final model is a one-pole Cole-Cole model whose parameters are polynomial functions of temperature. This model enables the estimation of the relative permittivity and the conductivity of the measured phantom and tissue types at any temperature and frequency.</p> / Master of Applied Science (MASc)

Composite materials, constructed from a combination of fibre and resin, have rapidly emerged as a high performance alternative to conventional materials for new constructions as well as strengthening and repair of existing structures. However, the use of such materials may be accompanied by various types of damages and failure modes, including delamination, debonding, fibre rupture, and matrix cracking. This thesis presents a new nondestructive evaluation (NDE) technique for damage detection in composite structures. The concept, based on detecting local dielectric permittivity variations, was employed to design capacitance sensors with high sensitivity to detect such damages. An analytical and 2D finite element models were used to assess the influence of the sensor geometrical parameters on the output signals and to optimize the sensor design. Concrete and wood specimens wrapped with glass-fibre composites containing pre-induced defects with different types and sizes were constructed and inspected. The sensors were also used to detect the delaminations and water intrusion defects in pultruded composite members. The principles behind the sensor operation were also applied to detect other damages in other structures; the capacitance sensors were designed and used to locate ungrouted cells in a concrete masonry wall. The proposed sensors, coupled with a commercially available portable capacitance meter, facilitate employing this technique in the field for rapid inspection of composite structures without the need for sophisticated data analyses that are usually required by other more expensive and time consuming NDE techniques. / Thesis / Master of Applied Science (MASc)

<p> Novel scalar and full-vectorial mode solvers based on quadratic spline collocation (QSC) method have been developed in MATLAB for optical dielectric waveguide with arbitrary two-dimensional cross-section and refractive index profile.</p> <p> Compared with the conventional finite difference mode solver in the literature and a commercial mode solver, the QSC mode solvers are simple and easy to implement in MATLAB without losing the accuracy of the mode solutions. The scalar mode solver is fast for solving weakly guiding waveguides. Three typical rib waveguides are calculated by the QSC scalar mode solver and compared with the numerical results of a finite difference scalar mode solver in the literature. The full-vectorial mode solver is capable of solving both weakly and strongly guiding waveguides. Typical numerical examples are calculated by the full-vectorial QSC mode solver and the solver is verified by comparing the results to a commercial mode solver.</p> <p> At the end of the thesis, methods of calculating leaky and radiation modes of general dielectric waveguides and possible methods of increasing the accuracy of the QSC mode solvers are proposed.</p> / Thesis / Master of Applied Science (MASc)

<p> The modeling, design and simulation of optical waveguides and integrated optical triplexer filters are presented. The work includes two subjects. One is application of improved three-point fourth-order finite-difference method and the other is design of triplexer optical filter for fiber-to-the-home passive optical network.</p> <p> The improved three-point fourth-order finite-difference method utilizes special format of one dimensional Helmholtz Equation and adopts generalized Douglas scheme and boundary conditions matching at interface. The modal analysis of dielectric slab waveguides and metal slab waveguides that support Surface Plasmon Plaritons by using this improved fourth-order finite-difference method is compared by using traditional first-order central difference method. The application of using improved three-point fourth-order finite-difference method in modal analysis of optical fiber waveguide is also provided.</p> <p> The modeling, design and simulation of monolithically integrated triplexer optical filter based on silicon wire waveguide are presented in detail. The design of this device facilitates multi-mode interference device (MMI) and arrayed waveguide grating (AWG) device to function as coarse wavelength division multiplexing and dense wavelength division multiplexing respectively. The MMI is used to separate downstream signs for upstream signal and AWG is used to further separate two down-stream signals with different bandwidths required. This design is validated by simulation that shows excellent performance in terms of spectral response as well as insertion loss.</p> / Thesis / Master of Applied Science (MASc)

Electrohydrodynamics in convective boiling heat exchangers has been studied since the early 1990’s and has been shown to result in a large variation in the average performance enhancement of these systems. The behaviour of EHD assisted convective boiling heat exchangers, is still largely unpredictable owing to a number of conflicting parameters which are rarely kept constant in empirical studies, i.e. flow pattern and heat flux. In this thesis, it is hypothesised that by reducing the number of confounding variables in the experimental test conditions, and understanding the behaviour of EHD in convective boiling systems from a flow pattern dependent point of view, this can allow for the development of flow pattern dependent experimental correlations & numerical models to develop a methodology for performance prediction, control strategies and system integration for an EHD assisted convective boiling heat exchange device. A 30 cm long, smooth, concentric, annular test section is used to analyse the effect of EHD on convective boiling performance under constant flow pattern, constant, low heat flux, and negligible free charge conditions. Saturated boiling conditions for flow-rates between 60 kg/m2s and 180 kg/m2s and thermodynamic quality range of 0.25 - 0.55 were tested. Heat transfer enhancement ranged from 0.95 to 2.3 fold and pressure drop penalty varied from 1.4-3 fold over these test conditions. The local EHD behaviour was found to be more consistent along the axial length of the test section compared to empirical data in the literature, which uses much longer test section lengths, where flow pattern can vary. An experimental database of EHD convective boiling data for horizontal annular electrode geometries was compiled to be used for analysis purposes. The performance of the heat exchanger in both free-field and high voltage conditions could be explained by looking at the flow patterns in each case. Electrostatic modelling was used to determine electric field strength distributions and interfacial stress due to the dielectrophoretic and electrostriction forces on the liquid vapour interface, which induce liquid extraction based flow pattern re-distribution in two phase dielectric flows. A fully coupled 2D, adiabatic numerical model for the effect of the electric body force on two phase flow pattern distribution was developed. Charge was neglected in this model. Two different models for the interface migration were used and compared; a moving mesh (MM) interface tracking model and a volume of fluid (VOF) interface tracking mode. Both were verified against published experimental data. For the liquid extraction verification case, the VOF model suffers interface stretching up to 300% resulting in a 42% slower extraction time and underestimated forces. However, it is useful to use the VOF model when simulating complex flow patterns which are subject to topological changes like bubble detachment or droplet coalescence as these cannot be simulated with the moving mesh model. The moving mesh model can be used to determine the error in forces and phase velocities when using the VOF model. A methodology for generating two-phase EHD flow pattern maps was developed by incorporating the electric Froude number into each of the flow pattern transition equations. A semi-analytical model was developed to determine the maximum interfacial stress due to EHD for stratified flows to reduce the requirement of numerical modeling, and thus the flow pattern map generation methodology is fully equation based. Although transition equations developed by multiple researchers were used and compared, it is recommended that the Steiner transitions equations be used for EHD two-phase flow pattern mapping, until more fundamental experimental data can be gathered to modify the semi-empirical transition equations used in more state-of-the-art maps. EHD was found to significantly affect the “stratified-stratified wavy (SSW)” and “stratified wavy – intermittent/annular (SWIA)” transitions for concentric horizontal geometries, with minimal effect on the transition to dryout and no effect on the “intermittent dispersed bubbly (IB)” transition. The EHD flow pattern maps were generated and compared against data from the present study and a database of experimental EHD convective boiling studies. The regions where maximum enhancement were seen in the literature correlate well with those regions predicted by the maps. Performance correlations for the EHD convective boiling heat transfer and pressure drop were developed. They are based on the free-field Kandlikar correlation [1] for two-phase heat transfer and the Chisholm-Laird [2] correlations for two-phase pressure drop, respectively. The EHD flow pattern map is used to determine what the flow pattern for a given applied voltage will be, and flow pattern based enhancement linear multipliers are then used to determine the EHD performance above the free-field case. EHD is a form of active enhancement, i.e. it requires power. Thus, it would be used in systems that require performance control or regulation, in addition to some niche applications like space where it can be used instead of gravity. A method for EHD controller design was established and an EHD control algorithm was designed and implemented on the test section for the flow pattern and applied waveforms that were determined to be optimal to maximize enhancement in this geometry. System identification was performed empirically to determine the transfer function between EHD voltage and heat load to be controlled for. This resulted in a 1st order plus dead-time model to which proportional-integral controller constants were tuned. Two controllers were developed; a PID control system and a Smith model predictive control system and these were compared based on their ability to regulate the output quality of the heat exchanger when subject to dynamic heat loading. Regulation was achieved for a dynamic heat load within ±25% bound from the designed steady state load. These controllers operate on one flow pattern as the test section is 30 cm long. Flow pattern dependent controller design would be required for a full length convective boiling heat exchanger. / Thesis / Doctor of Philosophy (PhD) / Control of boiling heat transfer using electric fields is hard to predict. This thesis presents a set a design guidelines based on how the electric field enhances the flow pattern.

No / A heterogeneous hybrid computational electromagnetics method is presented, which enables different parts of an antenna simulation problem to be treated by different methods, thus enabling the most appropriate method to be used for each part. The method uses a standard frequency-domain moment-method program and a finite-difference time-domain program to compute the fields in two regions. The two regions are interfaced by surfaces on which effective sources are defined by application of the Equivalence Principle. An extension to this permits conduction currents to cross the boundary between the different computational domains. Several validation cases are examined and the results compared with available data. The method is particularly suitable for simulation of the behavior of an antenna that is partially buried, or closely coupled with lossy dielectric volumes such as soil, building structures or the human body.