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  • 101.
    Bertling, Lina
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Larsson, Mats B-O
    MML Åhus.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Review of the Swedish Network Performance Assessment Model2008Report (Other academic)
    Abstract [en]

    The Swedish energy agency (STEM), has developed a new regulatory model to supervise the revenues of the Distribution System Operators (DSO), referred to as the Network Performance Assessment Model (NPAM). The fundamental idea of the NPAM is that the electrical distribution system provides customer values, and the DSO is allowed to collect revenue corresponding to these values. The NPAM calculates customer values for a fictive electrical distribution system, with a total cost referred to as the Network Performance Assessment (NPA). The allowed debiting rate for a DSO is defined by the quotient of the revenue and the NPA. If the debiting rate is higher than a certain value, defined by the Energy Market Inspection (EMI) at STEM, the DSO is placed under review and could be forced to pay back revenue to customers. A lawsuit is currently in progress on this use of the NPAM, which has highlighted drawbacks in the model. This paper provides a comprehensive presentation of the NPAM. It describes in detail the different input data for the model, the steps in the calculations and the resulting cost factors. The paper also presents for the first time details on the theory underlying the calculations.

  • 102.
    Bertling, Lina M.
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Allan, R.
    Eriksson, Roland
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A reliability-centered asset maintenance method for assessing the impact of maintenance in power distribution systems2005In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 20, no 1, p. 75-82Article in journal (Refereed)
    Abstract [en]

    This paper proposes a method for comparing the effect of different maintenance strategies on system reliability and cost. This method relates reliability theory with the experience gained from statistics and practical knowledge of component failures and maintenance measures. The approach has been applied to rural and urban distribution systems. In particular, a functional relationship between failure rate and maintenance measures has been developed for a cable component. The results show the value of using a systematic quantitative approach for investigating the effect of different maintenance strategies.

  • 103.
    Bertling, Lina
    et al.
    Chalmers.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Excercises on reliability assessment of electric power systems2007Other (Other (popular science, discussion, etc.))
    Abstract [en]

    This compendium is collection of exercises for the course on reliability assessment of electric power systems. The course has been developed within the RCAM group at KTH School of Electrical Engineering.

    The first version of the compendium was prepared in 2005, with examples made by master theses students Carl Johan Wallnerström and Otto Wilhelmsson, in co-operation with Lina Bertling. This updated version has been translated to English by Ph.D. student Andrea Lang.

  • 104.
    Bertling, Lina
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallnerström, Carl Johan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Nätnyttomodellens tillförlitlighet med avseende på små förändringar i indata2006Report (Other academic)
  • 105.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    The Smart Grid Experience in Europe2014Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The development of a Smart Grid in Europe has a strong link to the climate goals for sustainable energy systems. Europe has been at the forefront of smart grid deployments, especially in the areas of managing large penetrations of renewable sources of energy, advanced metering infrastructure (AMI) and on advanced information technology. 

  • 106.
    Besnard, Francois
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On Optimal Maintenance Management for Wind Power Systems2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sound maintenance strategies and planning are of crucial importance for wind power systems, and especially for offshore locations. In the last decades, an increased awareness of the impact of human living on the environment has emerged in the world. The importance of developing renewable energy is today highly recognized and energy policies have been adopted towards this development. Wind energy has been the strongest growing renewable source of energy this last decade. Wind power is now developing offshore where sites are available and benefits from strong and steady wind. However, the initial investments are larger than onshore, and operation and maintenance costs may be substantially higher due to transportation costs for maintenance and accessibility constrained by the weather.

    Operational costs can be significantly reduced by optimizing decisions for maintenance strategies and maintenance planning. This is especially important for offshore wind power systems to reduce the high economic risks related to the uncertainties on the accessibility and reliability of wind turbines.

    This thesis proposes decision models for cost efficient maintenance planning and maintenance strategies for wind power systems. One model is proposed on the maintenance planning of service maintenance activities. Two models investigate the benefits of condition based maintenance strategies for the drive train and for the blades of wind turbines, respectively. Moreover, a model is proposed to optimize the inspection interval for the blade. Maintenance strategies for small components are also presented with simple models for component redundancy and age replacement.

    The models are tested in case studies and sensitivity analyses are performed for parameters of interests. The results show that maintenance costs can be significantly reduced through optimizing the maintenance strategies and the maintenance planning.

  • 107.
    Besnard, Francois
    et al.
    KTH, School of Electrical Engineering (EES).
    Nilsson, Julia
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bertling, Lina
    On the economic benefits of using condition monitoring systems for maintenance management of wind power systems2010In: 2010 IEEE 11th International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2010, 2010, p. 160-165Conference paper (Refereed)
    Abstract [en]

    The large growth in the wind power industry in the past years mainly focuses on a growing market and the development of large turbines and offshore farms. The high technical availability of wind turbines comes with a high need for frequent maintenance. Current maintenance planning is generally not optimized, and it is possible to make maintenance more efficient. Condition Monitoring Systems (CMS) are commonly used in other industries and can reduce the consequential damage at failure and provides advantages for the planning of the maintenance. It is of interest to determine if the wind industry would benefit of the use of CMS. This paper shows results from Life-Cycle-Cost (LCC) evaluated with probabilistic methods and sensitivity analysis to identify the benefit of using CMS. The results highlight that there is a high economic benefit of using CMS, as well as benefits on the risk. The benefit is highly influenced by the reliability of the gearbox.

  • 108.
    Bhowmik, Shreyasi
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Investigation of Wide Band mm-Wave Radome2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    “Radome” is a necessary shield for any type of antenna. Itsshape, thickness, mechanical and electrical properties defineits application. This thesis mainly revolves around thetechniques, used for radome analysis in W-band with thehelp of electromagnetic solvers of High Frequency StructureSimulator (HFSS) and CST Microwave Studio. Measurementof permittivity of many materials is not made atsuch high frequencies and hence one is not sure about itsmaterial characteristics. This thesis includes a survey onmaterials which are applicable in W-band regime and givea sturdy performance with single type of material or commonlyknown as ‘Style A’ radomes. The thesis further describes,the shape and thickness modification of the radome.It contemplates on the the choice of solver involved and thedifferent advantages and disadvantages of the electromagneticsolvers with respect to this particular case. Severaltrials have been done on each of these platforms and onlythe relevant results have been presented. The antenna studiedis a “Travelling Wave Microstrip Patch Antenna” whichis subjected to different sizes of ground plane in order toobtain the realistic environment for it to be simulated in.It was observed that as the thickness of radome increased,the gain through the radome enclosed antennas decreasedbut the side lobe level performances improved. The simulationsdone in HFSS have a closer resemblance to theoryof radome performance.From the perspective of measurement, the return lossand insertion loss has been recorded for the radome in theW-band. A radome piece having different thicknesses hasalso been measured using the Rhode & Shwarz VNA. Asa step further, to study the radome pattern characteristic,Fabry perot periodic resonating dipoles are simulated ona radome of desired thickness. The height of the radomefrom the ground plane is optimized in order to get a 3-dB gain at the region of interest. After implementationit was observed that, around 76.5 GHz the setup which isdescribed later on acquired a gain of 20.33 dB. Althoughit is a high gain and low profile solution, it comes witha cost of narrow beam-width. Thus one has to optimizethe number of periodic elements along with phase taperingin order to achieve the desirable beam characteristics. Inshort, the thesis outlines the theory and thinking behinddesigning a radome, its effect on the antenna and how onecan resolve the issues.

  • 109.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling and Verification of Ultra-Fast Electro-Mechanical Actuators for HVDC Breakers2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The continuously increasing demand for clean renewable energy has rekindled interest in multi-terminal high voltage direct current (HVDC) grids. Although such grids have several advantages and a great potential, their materialization has been thwarted due to the absence of HVDC breakers. In comparison with traditional alternating current (AC) breakers, they should operate and interrupt fault currents in a time frame of a few milliseconds. The aim of this thesis is focused on the design of ultra-fast electro-mechanical actuator systems suitable for such HVDC breakers.Initially, holistic multi-physics and hybrid models with different levels of complexity and computation time were developed to simulate the entire switch. These models were validated by laboratory experiments. Following a generalized analysis, in depth investigations involving simulations complemented with experiments were carried out on two of the sub-components of the switch: the ultra-fast actuator and the damper. The actuator efficiency, final speed, peak current, and maximum force were explored for different design data.The results show that models with different levels of complexity should be used to model the entire switch based on the magnitude of the impulsive forces. Deformations in the form of bending or elongation may deteriorate the efficiency of the actuator losing as much as 35%. If that cannot be avoided, then the developed first order hybrid model should be used since it can simulate the behavior of the mechanical switch with a very good accuracy. Otherwise, a model comprising of an electric circuit coupled to an electromagnetic FEM model with a simple mechanics model, is sufficient.It has been shown that using a housing made of magnetic material such as Permedyn, can boost the efficiency of an actuator by as much as 80%. In light of further optimizing the ultra-fast actuator, a robust optimization algorithm was developed and parallelized. In total, 20520 FEM models were computed successfully for a total simulation time of 7 weeks. One output from this optimization was that a capacitance of 2 mF, a charging voltage of 1100 V and 40 turns yields the highest efficiency (15%) if the desired velocity is between 10 m/s and 12 m/s.The performed studies on the passive magnetic damper showed that the Halbach arrangement gives a damping force that is two and a half times larger than oppositely oriented axially magnetized magnets. Furthermore, the 2D optimization model showed that a copper thickness of 1.5 mm and an iron tube that is 2 mm thick is the optimum damper configuration.

  • 110.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Design of Ultra-fast Electro-Mechanical Actuators2013Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The continuously increasing demand for connecting electric grids with remote renewable energy sources such as wind power and photovoltaic cells has rekindled interest in high voltage direct current (HVDC) multi-terminal networks. Although HVDC networks have numerous benefits, their adoption relies entirely on the availability of HVDC circuit breakers which, compared to traditional alternating current circuit breakers, have to operate in a time frame of milliseconds.

    This thesis deals with the design of ultra-fast electro-mechanical actuators based on the so-called Thomson coil (TC) actuator. The simulation of a (TC) actuator constitutes a multi-physical problem where electromagnetic, thermal, and mechanical aspects must be considered. Moreover, it is complex since all those variables are co-dependent and have to be solved for simultaneously. As a result, a multi-physics simulation model that can predict the behavior and performance of such actuators with a high degree of accuracy was developed.

    Furthermore, other actuator concepts were also investigated and modeled in light of searching for a drive with a superior efficiency. The theory behind the force generation principles of two different types of ultra-fast electromechanical actuators, the TC and the double sided coil (DSC), were compared by the use of static, frequency, and comprehensive transient multi-physics finite element simulation models.

    Although, simulation models serve as a powerful tool for modeling and designing such state of the art actuators, without validation, they are weak and prone to errors since they rely on approximations and simplifications that might not always hold. Therefore, a prototype was built in the laboratory and the model was validated experimentally.

    Finally, it is important to note that the drives in this thesis are intended to actuate metallic contacts. As such, their behavior and performance upon mechanical loading was studied. Furthermore, some scaling techniques were applied to boost their performance and efficiency.

  • 111.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Comparison of two Ultra-fast actuator concepts2012In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 48, no 11, p. 3315-3318Article in journal (Refereed)
    Abstract [en]

    In this paper, two different types of ultra-fast electromechanical actuators are compared using a multi-physical finite element simulation model that has been experimentally validated. They are equipped with a single-sided Thomson coil (TC) and a double-sided drive coil (DSC), respectively. The former consists of a spirally-wound flat coil with a copper armature on top, while the latter consists of two mirrored spiral coils that are connected in series. Initially, the geometry and construction of each of the actuating schemes are discussed. Subsequently, the theory behind the two force generation principles are described. Furthermore, the current, magnetic flux densities, accelerations, and induced stresses are analyzed. Moreover, mechanical loadability simulations are performed to study the impact on the requirements of the charging unit, the sensitivity of the parameters, and evaluate the degree of influence on the performance of both drives. Finally, it is confirmed that although the DSC is mechanically more complex, it has a greater efficiency than that of the TC.

  • 112.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electric to Mechanical Energy Conversion of Linear Ultra-Fast Electro-Mechanical Actuators Based on Stroke Requirements2014In: Electrical Machines (ICEM), 2014 International Conference on, IEEE conference proceedings, 2014, p. -515Conference paper (Refereed)
    Abstract [en]

    The operational efficiency of ultra fast actuators usedas drives in high voltage direct current breakers are at best5 %. To boost their efficiency, the design of the energizing circuitis crucial. A multi-physics finite element method (FEM) modelcoupled with a SPICE circuit model that is able to predict theperformance of the actuator with an accuracy of at least 95 % hasbeen developed and verified experimentally. Several variants ofprototypes and models have been simulated, built, and tested.It was shown that one of the main problems leading to lowefficiencies is the stroke of the drive. However, there is a possibilityto increase the efficiency of the electric to mechanical energyconversion process of the studied Thomson (TC) and double sidedcoils (DSC) to a maximum of 54 % and 88 % respectively iftheir stroke is minimized. This can be done at the expense ofincreasing the complexity and the cost of the contact system bydesigning a switch with several series connected contacts that isencapsulated in a medium with a high dielectric strength. Anotherproposed solution is to design a current pulse with a rise timethat is considerably shorter than the mechanical response time ofthe system. Parametric variations of capacitances and chargingvoltages show that the TC and the DSC can achieve efficienciesup to 15 % and 23 % respectively. Regardless of the chosenmethod, the DSC has a superior efficiency compared to a TC.

  • 113.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electric to Mechanical Energy Conversion of Linear Ultrafast Electromechanical Actuators Based on Stroke Requirements2015In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 51, no 4, p. 3059-3067Article in journal (Refereed)
    Abstract [en]

    The operational efficiency of ultrafast actuators used as drives in high-voltage direct-current breakers is at best 5%. To boost their efficiency, the design of the energizing circuit is crucial. A multiphysics finite-element method model coupled with a SPICE circuit model that is able to predict the performance of the actuator with an accuracy of at least 95% has been developed and verified experimentally. Several variants of prototypes and models have been simulated, built, and tested. It was shown that one of the main problems leading to low efficiencies is the stroke of the drive. However, there is a possibility to increase the efficiency of the electric to mechanical energy conversion process of the studied Thomson coil (TC) and double-sided coil (DSC) to a maximum of 54% and 88%, respectively, if their stroke is minimized. These efficiencies are idealistic, and these were obtained with clamped armature studies. The efficiency of the actuator can be increased at the expense of increasing the complexity and the cost of the contact system by designing a switch with several series-connected contacts that is encapsulated in a medium with a high dielectric strength. Another proposed solution is to design a current pulse with a rise time that is considerably shorter than the mechanical response time of the system. Parametric variations of capacitances and charging voltages show that the TC and the DSC can achieve efficiencies up to 15% and 23%, respectively. Regardless of the chosen method, the DSC has a superior efficiency compared to a TC.

  • 114.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optimal Energizing Source Design for Ultra-Fast Actuators2013Conference paper (Refereed)
    Abstract [en]

    One of the key enabling technologies for multi-terminal HVDCgrids is the existence of a breaker that can operate withina few milliseconds. A lot of research has been done to builddifferent ultra-fast drives to actuate the electric contacts ofthese breakers. What they all have in common is an operationalefficiency of at best 5 %. Capacitor banks are discharged throughspirally shaped flat coils to generate ultra-fast repulsive forces. Tooptimize the efficiency of the drive, the design of the energizingcircuit is crucial. The aim of this paper is to optimize theenergizing source and provide a deep explanation of the effectof the chosen capacitance and charging voltage for two actuatorconcepts, the Thomson coil (TC) and the double sided coil (DSC)for different stroke requirements. An experimentally validatedmulti-physics finite element method (FEM) simulation model is applied.

  • 115.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Salinas, Ener
    ABB AB Corporate Research, Sweden.
    Loadability and scaling aspects of Thomson based ultra-fast actuators2012In: Actuator 2012, 2012Conference paper (Refereed)
    Abstract [en]

    In this paper, an ultra-fast single-sided Thomson based actuator is studied. The actuator is comprised of a flat spiral-shaped coil with a conductive armature in its proximity. This armature is mechanically loaded with a uniform mass distribution over its cross section. The energizing source consists of a capacitor bank that is discharged through the actuator coil resulting in a high magnetic pressure within fractions of a millisecond. The coil is dimensioned to withstand the temperature rise.

    An experimentally validated multi-physical finite element model is used to perform simulations by varying the mechanical load to explore the performance of the actuator topology. The obtained currents, induced forces, stresses, and accelerations of the armature are then analyzed in an attempt to develop scaling techniques that can predict for example velocity and efficiency. Finally, the results of the scaling techniques are presented and compared to each other.

  • 116.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB AB Corporate Research, Sweden.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB AB Corporate Research, Sweden.
    Salinas, Ener
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multiphysics modeling and experimental verification of ultra-fast electro-mechanical actuators2015In: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800, Vol. 49, no 1, p. 51-59Article in journal (Refereed)
    Abstract [en]

    In this paper, a multi-physics computational tool has been developed to accurately model and build high performance ultra-fast actuators. The research methodology is based on a finite element method model coupled with a circuit model. Electromagnetic, thermal, mechanical, and algebraic equations are implemented in Comsol Multiphysics and verified with laboratory experiments of a built prototype. A simplified model is preferred as long as its underlying assumptions hold. However, in the presence of large current and force densities, nonlinearities such as deformations may occur. Such phenomena can only be captured by the use of the developed comprehensive multi-physics simulation model. Although this model is computationally demanding, it was shown to have an accuracy of at least 95% when compared with experiments.

  • 117.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Salinas, Ener
    ABB AB Corporate Research, Sweden.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    On the Design of Ultra-Fast Electromechanical Actuators: A Comprehensive Multi-Physical Simulation Model2012In: Sixth International Conference on Electromagnetic Field Problems and Applications (ICEF), 2012, IEEE conference proceedings, 2012, p. 1-4Conference paper (Refereed)
    Abstract [en]

    In this paper, a simulation of an ultra-fast electromechanical drive was performed by using a two-dimensional axi-symmetric multi-physical finite element model. The aim of this paper is to primarily show that the following model can be used to simulate and design those actuators with good accuracy, secondly, to study the behavior and sensitivity of the system and thirdly, to demonstrate the potential of the model for industrial applications. The simulation model is coupled to a circuit and solves for the electro-magnetic, thermal, and mechanical dynamics utilizing a moving mesh. The actuator under study is composed of a spiral-shaped coil and a disk-shaped 3mm thick copper armature on top. Two numerical studies of such an actuator powered by 2640 J capacitor banks were performed. It is shown that forces up to 38 kN can be achieved in the range of 200 μs. To add credibility, a benchmark prototype was built to validate this experimentally with the use of a high speed camera and image motion analysis.

  • 118.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corporate Research.
    Salinas, E.
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the design of a linear composite magnetic damper2015In: 2015 IEEE International Magnetics Conference, INTERMAG 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    In recent years, ultra-fast actuators have become key elements in the development of high voltage direct current (HVDC) breakers for multiterminal grids which represent a huge progress in modern power transmission [1]. After fulfilling their operation these actuators need to be decelerated using controllable forces to avoid deforming vital components incorporated in the system. In this paper, a dedicated damper is proposed based on a magnet array that induces eddy currents in a composite metal tube resulting in an efficient braking response. Several topologies are investigated by simulations and experiments. The theory behind eddy current damping is explained in [2]. The main requirements for such dampers are reliability, robustness, and ease of construction. The expected durability of these kind of dampers is longer than the breaker itself which guarantees extremely good reliability within HVDC systems.

  • 119.
    Bissal, Ara
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Salinas, Ener
    Magnusson, Jesper
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Design of a Linear Composite Magnetic Damper2015In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 11, article id 8003305Article in journal (Refereed)
    Abstract [en]

    High-voltage direct current (HVdc) breakers are the key components in the realization of multiterminal HVdc grids. In the presence of fault current, these breakers should be able to deliver impulsive forces to swiftly open the metallic contacts. After the acceleration phase, the moving armature should be decelerated using controllable forces to avoid plastically deforming fragile components integrated in the system. In this paper, finite-element method-based simulation models, complimented with small-scale and large-scale experimental prototypes, were utilized to benchmark different damping topologies. It was found that a Halbach-based configuration can deliver a damping force that is almost two and a half times larger than its sequel. Its sequel, composed of vertically stacked oppositely oriented magnets, is easier to assemble and is also capable of generating a considerable damping force. Finally, it has been shown that both these schemes, inserted in a composite tube, have a potential to be used as dampers in HVdc breakers.

  • 120. Bjurman, Ulf
    et al.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Separation of high and low frequency behavior in non linear circuit simulation excited with modulated signals1999In: Proc of the 12:th Conference on Computation of Electromagnetic Fields, Sapporo Japan, 1999, p. 260-61Conference paper (Refereed)
  • 121.
    Björkqvist, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dahlberg, Oskar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Silver, Gustaf
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mattsson, M.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Novel Efficient Multiple Input Single Output RF Energy Harvesting Rectification Scheme2017In: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1605-1606Conference paper (Refereed)
    Abstract [en]

    In this work an implementation of an ambient radio frequency harvesting system utilizing multiple input single output approach is demonstrated. Measurements of typical ambient radiation have been conducted with respect to power levels and frequency to determine which communication signals are suitable for harvesting. The measurement campaign showed that the WiFi frequency band at 2.45 GHz is a good candidate for indoors applications. A Greinacher voltage doubler is used for the rectification. A multiple input single output - MISO scalable scheme approach is implemented that is able to provide a DC differential output voltage. Simulated and experimental results proved the MISO rectenna to be an efficient scheme for RF harvesting.

  • 122.
    Bormann, Dierk
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Tavakoli, Hanif
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Reluctance Network Treatment of Skin and Proximity Effects in Multi-Conductor Transmission Lines2012In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 48, no 2, p. 735-738Article in journal (Refereed)
    Abstract [en]

    A novel method is developed to easily compute the complex series impedance matrix of amulti-conductor transmissionline in a wide frequency range. It is based on a network of complex reluctances describing flux paths around the conductors. The network parameters are derived from the geometry of the conductor-insulator arrangement and from its material parameters. The method is best suited for situations where the typical gap width between conductors is much smaller than their thicknesses, where it provides an accurate treatment of both skin and proximity effects. Especially the proximity effect is hard to treat by other means in that limit. The method is demonstrated for an idealized example geometry, where its accuracy is verified with harmonic FEM field calculations.

  • 123. Bosiljevac, M.
    et al.
    Persson, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Sipus, Z.
    Hybrid spectral domain - UTD method applied to conformal antenna analysis2006In: Eur Space Agency Spec Publ ESA SP, 2006Conference paper (Refereed)
    Abstract [en]

    A hybrid spectral domain - UTD method (Uniform Theory of Diffraction) developed for the analysis of conformal antennas is presented in this paper. The basic idea behind the hybrid method is to combine different analysis methods for conformal antennas and, at the same time, preserve the advantages of the considered methods. More specifically, the considered hybrid SD - UTD method joins the possibility of analyzing multilayer structures (spectral domain method) and the possibility of analyzing electrically large structures (UTD method). Hence, using the developed method it is possible to analyze large multilayered conformal antennas with high accuracy and speed. This work has been made possible by the ACE program for structuring the research on conformal antennas in Europe. The developed method is a result of joining research activities of University of Zagreb, Croatia and the Royal Institute of Technology, Sweden.

  • 124. Bosiljevac, Marko
    et al.
    Persson, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Sipus, Zvonimir
    Efficient Analysis of Aperture Antennas on Generally Shaped Convex Multilayered Surfaces Using a Hybrid SD-UTD Method2009In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 57, no 5, p. 1420-1431Article in journal (Refereed)
    Abstract [en]

    A novel hybrid method is described for analyzing convex multilayered conformal array antennas. The hybrid method is based on the spectral domain approach in combination with the ray-based uniform theory of diffraction (UTD) method. The analysis is divided in two parts. First, the spectral domain approach is accelerated by using an asymptotic extraction technique where the extracted term of the Green's function is calculated using UTD. It is shown that this new approach results in significant acceleration of the existing spectral domain algorithm without losing accuracy. The modified spectral domain method is then used in the second part where generally shaped convex multilayered surfaces are analyzed by using sets of canonically shaped surfaces (spheres and/or circular cylinders). Their radii are obtained using the UTD formulation, which contains important information such as distance and curvature of the generally shaped surface along each geodesic. The results obtained using the new algorithm are compared to the available results (calculated and measured) for different conformal antennas, showing very good agreement.

  • 125. Brazalez, Astrid Algaba
    et al.
    Manholm, Lars
    Johansson, Martin
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Miao, Jingwei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Investigation of a Ka-band Luneburg Lens Made of a Glide-Symmetric Holey Structure2017In: 2017 International Symposium on Antennas and Propagation (ISAP 2017), Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    A Ka-hand 2D flat-profiled Luneburg lens antenna implemented with a glide-symmetric holey structure is presented. The required refractive index for the lens design has been investigated via an analysis of the hole depth and the gap between the two metallic layers constituting the lens. The final unit cell is described and applied to create the complete metasurface Luneburg lens showing that a plane wave is obtained when feeding at an opposite arbitrary point with a discrete source.

  • 126.
    Bukhsh, Waqquas Ahmed
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Persson, P.
    Element position perturbation for a narrow spot beam with applications to satellite communication antennas2010In: PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER, ISSN 1559-8985, Vol. 104, p. 283-295Article in journal (Refereed)
    Abstract [en]

    Design of array antennas for satellite applications is always a trade-off between physical constrains and pattern requirements. In this paper, the focus is on the design of a large array antenna for earth coverage applications using spot beams. The array antenna has a diameter of 1 m and consists of circular polarized horn antennas positioned in a non-uniform grid. By using a binary coded genetic algorithm (BCGA) the desired element positions and their excitations are optimized to fulfill the pattern requirements. In addition thinning has been used to study the possibility of maintaining good antenna performance when reducing the number of elements. The proposed antenna design has robust side lobe level, beam width and gain; all remain virtually unchanged under a change of operating frequency +/- 7% and under lobe steering over earth +/- 8.8 degrees.

  • 127.
    Burger, Pierre
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ampacity calculation for low voltage cables2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The overall goal of my project was to make an update of ampacities for distribution cables. Ampacityis the maximum current that can flow permanently in a cable without exceeding the maximaltemperature of the cable. These ampacities are useful for network operators because they need toknow the power they can transport with their cables.In order to make a good study, I had to study several types of configurations for a lot of different cables.The first configuration was cables directly in the ground . Ampacity was calculated for all the cables inthese configurations, but with several conditions. The temperature and the thermal resistivity of thesoil are varied, to study the effects of season, the geographic region and the type of soil.Then I studied the case of a cable in a duct. I used the same types of conditions as the one just before,but this time the cable is inside a duct, with air between it and the duct.Finally, I studied cables in air. This configuration was done for several temperatures, and severalconfigurations of cables.The second part of the study included the cable’s thermal dynamics, about temperature increase inthe cable when the current varies. Real load curves were used to determine the current flow in thecable. One was used for summer, and another one for winter.The idea of the study was to compare two types of calculation. The types of calculations used are theanalytical method and numerical method. The idea of the analytical method is to create a model, andthen to use this model to compute directly the ampacity. It is complicated to create the model, andtypically depends on more simplifying assumptions than the numerical model, but then computationis easy. The numerical method using a finite-element solver is simpler because the cable just has tobe drawn in a software, and then the software will do all the computation in order to find the ampacity.But the computer has to do lots of simple calculations, so it can take significant time.If these two types of calculation give similar results, this gives more credibility to the result and impliesthat the assumptions made for the analytic calculation can be assumed adequate for this type ofmodelling.Nevertheless, these two methods have drawbacks. The analytical method considered here is limited,for example by being unable to make calculations for cables with a peripheral neutral conductor. Thenumerical method is also limited, since unless one uses assumptions similar to those of the analyticalmethod it is not possible to make computation for cables in air, as this is too complicated for thecomputer.Finally these two methods gave good similarity of results. The differences between the analyticalcalculation and the numerical calculation are very small.To give a better comprehension of the results, specific examples were done. They allow theunderstanding of the impact of a heat wave on cables, or the impact of a duct on ampacity. Theseexamples will be useful for the users of cables in order to understand the meaning of the study’sresults.

  • 128.
    Butt, Bilal
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electric and electromagnetic modelling for railway traction system applications2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The railway traction industry is a field that is under constant development. As the technology

    moves forward, so does the demands from customers and requirements that are needed to be

    fulfilled. A traction system consists of a number of components where traction system

    suppliers need to rely on sub-suppliers to achieve a certain performance.

    This thesis report shows with three different case studies how finite element modelling can be

    used for railway traction system applications using COMSOL Multiphysics.

    The first case presents how to model electromagnetic fields produced by an inductor used for

    filtering and see how the generated fields contributes to the heating of the component. The

    investigation also shows how to calculate the inductance of the inductor.

    The second case shows how to predict the heating effect as a result of impurities inside a

    brazing joint when brazing two stator cables in a motor. Three different impurity-levels was

    investigated and the results showed that out of a thermal point of view, the level of

    imperfections inside the brazing joint has no influence.

    The third case presents an investigation regarding what type of inductor should be used for a

    specific filtering application. The result was three different configurations where each one has

    its advantages and drawbacks. From these results, a recommendation is given based on what a

    system designer might have to take into consideration when selecting an appropriate setup.

    The conclusions drawn in this thesis is that the modelling of electric and electromagnetic

    components can be used to predict electromagnetic fields, inductance, shielding and high

    frequency behaviour of inductors and temperature distribution as a result of induction and

    resistive heating.

  • 129.
    Böös, Claes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Göransson, Richard
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Reliability centered asset management tool: The development of RACalc2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electrical distribution with high delivery quality is crucial for the society. The need for high quality power supply grows as people put more trust in electrical devices. However there are no perfect electrical distribution systems and interruptions occur randomly. To reduce the risk of outage, actions can be taken by the distribution system operator in the form of preventive maintenance. This report presents some of the methods for analysis that are available for the asset manager. The methods are all connected to the area of reliability centered asset management and have been implemented in RACalc, a software tool. RACalc is able to analyze the provided electrical distribution system and point out on which components maintenance should be placed to enhance the total system performance. Depending on what properties the distribution system operator wants to enhance, different components need to be maintained. RACalc provides the answer in relation to the system performance indices SAIFI, SAIDI, CAIDI, ASAI and AENS. The calculations have been validated by building small scale systems in RACalc and comparing results with hand made calculations.

     

    As illustrated in this report a significant theoretical improvement of the overall reliability can be achieved. By using RACalc to categorize the importance of the components in the electrical distribution system a better placement of the assets can be achieved. In the report, the results of the component importance calculation have been restricted to the twenty most significant components of the analyzed distribution systems. Furthermore, an investigation of the theoretical improvement of the overall system availability is conducted. It is shown that by reducing the failure rate on the twenty most important components found by RACalc with ten percent, the total system performance is improved by almost eight percent in average.

  • 130. Cai, F.
    et al.
    Yu, J.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Vectorial electric field Monte Caro simulations for focused laser beams (800 nm-2220 nm) in a biological sample2013In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 142, p. 667-681Article in journal (Refereed)
    Abstract [en]

    Here we develop a method that combines vectorial electric field Monte Carlo simulation with Huygens-Fresnel principle theory to determine the intensity distribution of a focused laser beam in a biological sample. The proper wavelengths for deep tissue imaging can be determined by utilizing our method. Furthermore, effects of anisotropic factor, scattering and absorption coeffcients on the focal spots are analyzed. Finally, the focal beams formed by objective lenses with different values of numerical aperture are also simulated to study the focal intensity in the biological sample.

  • 131. Cai, Fuhong
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Electric field Monte Carlo simulation of focused stimulated emission depletion beam, radially and azimuthally polarized beams for in vivo deep bioimaging2014In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 19, no 1, p. 011022-Article in journal (Refereed)
    Abstract [en]

    An electric field Monte Carlo method is used to study the focal spot of a stimulated emission depletion (STED) beam, radially and azimuthally polarized beams in a turbid medium as a function of the scattering coefficient. To consider the diffraction of light of the wave nature, the wavefront is decomposed into a set of secondary spherical subwaves according to the Huygens principle. From the simulation results, we can find that the STED beam can still form a doughnut focal spot inside the turbid medium. These simulation results are important for the feasibility study of STED microscopy for in vivo deep bioimaging. Similarly, the focal spot for an azimuthally polarized beam can also keep a doughnut spot at the focal plane in a turbid medium.

  • 132. Cai, Fuhong
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Using graphics processing units to accelerate perturbation Monte Carlo simulation in a turbid medium2012In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 17, no 4, p. 040502-Article in journal (Refereed)
    Abstract [en]

    We report a fast perturbation Monte Carlo (PMC) algorithm accelerated by graphics processing units (CPU). The two-step PMC simulation [Opt. Lett. 36, 2095 (2011)] is performed by storing the seeds instead of the photon's trajectory, and thus the requirement in computer random-access memory (RAM) becomes minimal. The two-step PMC is extremely suitable for implementation onto CPU. In a standard simulation of spatially-resolved photon migration in the turbid media, the acceleration ratio between using GPU and using conventional CPU is about 1000. Furthermore, since in the two-step PMC algorithm one records the effective seeds, which is associated to the photon that reaches a region of interest in this letter, and then re-run the MC simulation based on the recorded effective seeds, radiative transfer equation (RTE) can be solved by two-step PMC not only with an arbitrary change in the absorption coefficient, but also with large change in the scattering coefficient.

  • 133. Cai, Fuhong
    et al.
    Qian, Jun
    Jiang, Li
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Multifunctional optical imaging using dye-coated gold nanorods in a turbid medium2011In: Journal of Biomedical Optics, ISSN 1083-3668, E-ISSN 1560-2281, Vol. 16, no 1, p. 016002-Article in journal (Refereed)
    Abstract [en]

    We report multifunctional optical imaging using dye-coated gold nanorods. Three types of useful information, namely, Raman, fluorescence signals, and absorption contrast, can be obtained from a phantom experiment. These three kinds of information are detected in a nanoparticle-doped-phantom using diffuse optical imaging. Our novel nanoparticle could be used as a multimodality marker for future bioimaging applications.

  • 134. Cai, Fuhong
    et al.
    Yu, Jiaxin
    Qian, Jun
    Wang, Ye
    Chen, Zhong
    Huang, Jingyun
    Ye, Zhizhen
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Use of tunable second-harmonic signal from KNbO3 nanoneedles to find optimal wavelength for deep-tissue imaging2014In: Laser & Photonics reviews, ISSN 1863-8880, E-ISSN 1863-8899, Vol. 8, no 6, p. 865-874Article in journal (Refereed)
    Abstract [en]

    Nonlinear optical (NLO) responses of perovskite-type nanostructures have a variety of potential applications owing to the highly efficient frequency conversion guaranteed by both the material itself and the nanometer-scale configuration. KNbO3 (KN) nanoneedles have been identified as a promising NLO material because of the superior broadband frequency conversion efficiency, and if incident light is propagating in a direction perpendicular to the axis of a nanoneedle, then the phase-matching constraint can be relaxed. Here, the second-harmonic generation (SHG) and third-harmonic generation (THG) responses of both individual and clustered KN nanoneedles are reported. Based on these results, a novel method is proposed for determining the optimal excitation wavelength for NLO imaging of several biological samples, with KN nanoneedles acting as NLO agents. The method is shown to provide the optical features in the focal plane and a more reliable estimation of the optimal excitation wavelength for deep-tissue imaging.

  • 135. Cai, Tao
    et al.
    Liu, Qingkun
    Shi, Yaocheng
    Chen, Pengxin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    An efficiently tunable microring resonator using a liquid crystal-cladded polymer waveguide2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, no 12, p. 121109-Article in journal (Refereed)
    Abstract [en]

    An electrically tunable polymer microring resonator of large tunability and low applied voltage is demonstrated using active liquid crystal (LC) cladding. A large tuning range of 0.73 nm is achieved due to more homogenous LC molecular alignment and enhanced interaction of the light with the LC cladding in the simplified polymer waveguide structure. The operating voltage decreases to 10 V with a threshold of only 3 V by the utilization of interdigital electrodes.

  • 136. Cai, Tingting
    et al.
    Zhu, Huilin
    Xu, Jie
    Wu, Shijing
    Li, Xinge
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Human cortical neural correlates of visual fatigue during binocular depth perception: An fNIRS study2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 2, article id e0172426Article in journal (Refereed)
    Abstract [en]

    Functional near-infrared spectroscopy (fNIRS) was adopted to investigate the cortical neural correlates of visual fatigue during binocular depth perception for different disparities (from 0.1 degrees to 1.5 degrees). By using a slow event-related paradigm, the oxyhaemoglobin (HbO) responses to fused binocular stimuli presented by the random-dot stereogram (RDS) were recorded over the whole visual dorsal area. To extract from an HbO curve the characteristics that are correlated with subjective experiences of stereopsis and visual fatigue, we proposed a novel method to fit the time-course HbO curve with various response functions which could reflect various processes of binocular depth perception. Our results indicate that the parietal-occipital cortices are spatially correlated with binocular depth perception and that the process of depth perception includes two steps, associated with generating and sustaining stereovision. Visual fatigue is caused mainly by generating stereovision, while the amplitude of the haemodynamic response corresponding to sustaining stereovision is correlated with stereopsis. Combining statistical parameter analysis and the fitted time-course analysis, fNIRS could be a promising method to study visual fatigue and possibly other multi-process neural bases.

  • 137. Cai, Y.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of a Laguerre-Gaussian beam through a slightly misaligned paraxial optical system2006In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 84, no 3, p. 493-500Article in journal (Refereed)
  • 138.
    Cai, Yangjian
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of some coherent and partially coherent laser beams2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis, we investigate the propagation of some coherent and partially coherent laser beams, including a dark hollow beam (DHB), an elliptical Gaussian beam (EGB), a flat-topped beam and a twisted anisotropic Gaussian Schell-model (TAGSM) beam, through a paraxial optical system or a turbulent atmosphere. Several theoretical models are proposed to describe a DHB of circular or non-circular symmetry. Approximate analytical formulas for a DHB and a partially coherent TAGSM beam propagating through an apertured paraxial optical system are derived based on the generalized Collins formula. Analytical formulas for a DHB, an EGB, a flat-topped beam and a partially coherent TAGSM beam propagating in a turbulent atmosphere are derived in a tensor form based on the extended Huygens-Fresnel integral formula. It is found that after a long propagation distance these beams become circular Gaussian beams in a turbulent atmosphere, and this is quite different from their propagation properties in free space. The conversion of any of these beams to a circular Gaussian beam becomes quicker and the beam spot in the far field spreads more rapidly for a larger structure constant of the turbulent atmosphere, a shorter wavelength and a smaller waist size of the initial beam. Lower coherence and larger twist have a stronger effect of anti-circularization of the beam spot. Our analytical formulas provide a convenient way for studying the propagation of various laser beams through a paraxial optical system or a turbulent atmosphere. The concept of coincidence fractional Fourier transform (FRT) with an incoherent or partially coherent beam is introduced, and the optical system for its implementation is designed. The coincidence FRT is demonstrated experimentally with a partially coherent beam, and the experimental results are consistent with the theoretical results.

  • 139.
    Cai, Yangjian
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of various flat-topped beams in a turbulent atmosphere2006In: Journal of Optics. A, Pure and applied optics, ISSN 1464-4258, E-ISSN 1741-3567, Vol. 8, no 6, p. 537-545Article in journal (Refereed)
    Abstract [en]

    The propagation of flat-topped beams with circular, elliptical and rectangular symmetries in a turbulent atmosphere is investigated. Analytical formulae for the average intensity of various flat-topped beams propagating in a turbulent atmosphere are derived in a tensor form. The formulae derived can easily be reduced to those for flat-topped beams propagating in free space (in the absence of turbulence). The propagation properties of flat-topped beams are studied in detail. We find that a flat-topped beam with circular or non-circular symmetry will evolve into a circular Gaussian beam in the far field under the influence of atmospheric turbulence, which is quite different to its properties in free space. Our method provides an effective and convenient way to analyse the propagation of various flat-topped beams in a turbulent atmosphere.

  • 140.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ge, Di
    Analytical formula for a decentered elliptical Gaussian beam propagating in a turbulent atmosphere2007In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 271, no 2, p. 509-516Article in journal (Refereed)
    Abstract [en]

    Analytical formulas for the average intensity and decentered parameter of a decentered elliptical Gaussian beam (DEGB) propagating in a turbulent atmosphere are derived in a tensor form. The propagation properties of a DEGB in a turbulent atmosphere are investigated in detail, and found to be different from that in free space. Furthermore, as an application example, we investigate the propagation of a decentered elliptical flat-topped beam (DEFB) by expressing its electric field as a finite sum of DEGBs in a turbulent atmosphere. The properties of a DEGB or a DEFB in a turbulent atmosphere are closely related with the beam's parameters and the structure constant of the turbulent atmosphere.

  • 141.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ge, Di
    Propagation of various dark hollow beams through an apertured paraxial ABCD optical system2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 357, no 1, p. 72-80Article in journal (Refereed)
    Abstract [en]

    Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry through an apertured paraxial ABCD optical system is investigated. Approximate analytical formulas for various DHBs propagating through an apertured paraxial optical system are derived by expanding the hard-aperture function into a finite sum of complex Gaussian functions in terms of a tensor method. Some numerical results are given. Our formulas provide a convenient way for studying the propagation of various DHBs through an apertured paraxial optical system.

  • 142.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Average intensity and spreading of an elliptical Gaussian beam propagating in a turbulent atmosphere2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 5, p. 568-570Article in journal (Refereed)
    Abstract [en]

    An analytical formula for the average intensity of an elliptical Gaussian beam (EGB) propagating in a turbulent atmosphere is derived. The spreading properties of an EGB in a turbulent atmosphere are studied. It is found that an EGB will eventually become a circular Gaussian beam in a turbulent atmosphere. This interesting phenomenon is quite different from the propagation of an EGB in free space. The evolution properties are closely related to the parameters of the beam and the turbulent atmosphere

  • 143. Cai, Yangjian
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Partially coherent flattened Gaussian beam and its paraxial propagation properties2006In: Journal of the Optical Society of America a-Optics Image Science and Vision, ISSN 1084-7529, Vol. 23, no 10, p. 2623-2628Article in journal (Refereed)
  • 144.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of a partially coherent twisted anisotropic Gaussian Schell-model beam in a turbulent atmosphere2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 4Article in journal (Refereed)
    Abstract [en]

    Analytical formulas are derived for the propagation of a partially coherent twisted anisotropic Gaussian Schell-model (TAGSM) beam in a turbulent atmosphere. Propagation properties of a TAGSM beam in a turbulent atmosphere are investigated in detail. It is found that a TAGSM beam will become a circular beam in a turbulent atmosphere, and low coherence and larger twist have an effect of anticircularization of the beam spot. The beam spot spreads more rapidly for lower coherence, larger twist, or stronger turbulence.

  • 145.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of hollow Gaussian beams through apertured paraxial optical systems2006In: Journal of the Optical Society of America a-Optics Image Science and Vision, ISSN 1084-7529, Vol. 23, no 6, p. 1410-1418Article in journal (Refereed)
    Abstract [en]

    On the basis of the generalized Collins formula and the expansion of the hard-aperture function into a finite sum of complex Gaussian functions, an approximate analytical formula for a hollow Gaussian beam propagating through an apertured paraxial stigmatic (ST) ABCD optical system is derived. Some numerical examples are given. Furthermore, by using a tensor method, we derive approximate analytical formulas for a hollow elliptical Gaussian beam propagating through an apertured paraxial general astigmatic ABCD optical system and an apertured paraxial misaligned ST ABCD optical system. Our results provide a convenient way for studying the propagation and transformation of a hollow Gaussian beam and a hollow elliptical Gaussian beam through an apertured general optical system.

  • 146.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Propagation of various dark hollow beams in a turbulent atmosphere2006In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 14, no 4, p. 1353-1367Article in journal (Refereed)
    Abstract [en]

    Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry in a turbulent atmosphere is investigated. Analytical formulas for the average intensity of various DHBs propagating in a turbulent atmosphere are derived in a tensor form based on the extended Huygens-Fresnel integral. The intensity and spreading properties of the DHBs in a turbulent atmosphere are studied numerically. It is found that after a long propagation distance a dark hollow beam of circular or non-circular eventually becomes a circular Gaussian beam (without dark hollow) in a turbulent atmosphere, which is much different from its propagation properties in free space. The conversion from a DHB to a circular Gaussian beam becomes quicker and the beam spot in the far field spreads more rapidly for a larger structure constant, a shorter wavelength, a lower beam order and a smaller waist size of the initial beam.

  • 147.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hu, Li
    Propagation of partially coherent twisted anisotropic Gaussian Schell-model beams through an apertured astigmatic optical system2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 6, p. 685-687Article in journal (Refereed)
    Abstract [en]

    By expanding the hard-aperture function into a finite sum of complex Gaussian functions, we derived an approximate analytical formula for a partially coherent twisted anisotropic Gaussian Schell-model (AGSM) beam propagating through an apertured paraxial general astigmatic (GA) optical system by use of a tenser method. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. Our formulas avoid time-consuming numerical integration and provide a convenient and effective way for studying the propagation and transformation of a partially coherent twisted AGSM beam through an apertured paraxial GA optical system. (c) 2006 Optical Society of America.

  • 148.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lin, Q.
    Zhu, S. Y.
    Coincidence subwavelength fractional Fourier transform2006In: Optical Society of America. Journal A: Optics, Image Science, and Vision, ISSN 1084-7529, E-ISSN 1520-8532, Vol. 23, no 4, p. 835-841Article in journal (Refereed)
    Abstract [en]

    The coincidence subwavelength fractional Fourier transforms (FRTs) with entangled photon pairs and incoherent light radiation are introduced as an extension of the recently introduced coincidence FRT. Optical systems for implementing the coincidence subwavelength FRTs are designed. The width of the coincidence subwavelength FRT pattern is two times narrower than the width of the coincidence FRT. The coincidence subwavelength FRT with partially coherent light radiation is also studied numerically. Differences between the coincidence subwavelength FRT with entangled photon pairs and that with incoherent light radiation are discussed.

  • 149.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Fei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lensless imaging with partially coherent light2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 3, p. 205-207Article in journal (Refereed)
    Abstract [en]

    Based on the fourth-order correlation of light, lensless imaging with incoherent or partially coherent light is investigated theoretically by use of classical optical coherence theory. A novel lensless optical system for implementing imaging is proposed. The visibility and quality of the image are influenced by the coherence and transverse size of the light source. The results suggest useful imaging applications in x-ray, gamma-ray, or other wavelengths where no effective lens is available, and they have potential applications in optical metrology and holography.

  • 150.
    Cai, Yangjian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Fei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lensless optical implementation of the coincidence fractional Fourier transform2006In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 31, no 15, p. 2278-2280Article in journal (Refereed)
    Abstract [en]

    A lensless optical system for implementing the coincidence fractional Fourier transform (FRT) is proposed. The conditions for the lensless optical system to implement the coincidence FRT with incoherent light and entangled photon pairs are discussed. The results offer a novel scheme for FRTs and thus suggest useful applications.

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