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  • 1.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corporate Research, Sweden.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation of the electrical conduction of cyclohexane with TiO2 nanoparticles2014In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, IEEE , 2014, p. 6893119-Conference paper (Refereed)
    Abstract [en]

    Nanoparticles mixed with transformer oil can potentially increase the breakdown strength of the base liquid. Unfortunately, the basic physical mechanisms leading to such improvement are still not clear. This paper implements two existing theories to model the electrical conduction of cyclohexane with TiO2 nanoparticles in a needle to plane configuration. The generation and drift of carriers in the liquid are simulated by coupling the continuity equations for electrons, positive ions, negative ions, and nanoparticles with Poisson's equation for the electric field. The current-voltage characteristics are simulated and compared with the case of pure cyclohexane. The nanoparticles are modeled as either absorbers of electrons or as source of shallow traps in the fluid, according to the existing theories. The simulations show that the considered theories predict no significant effect of nanoparticles added to cyclohexane on the conduction current from a negative point electrode in steady state or under transient conditions.

  • 2. Bach, V.
    et al.
    Frohlich, J.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bogolubov-Hartree-Fock mean field theory for neutron stars and other systems with attractive interactions2009In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 50, no 10Article in journal (Refereed)
    Abstract [en]

    A simplification of the Bogolubov-Hartree-Fock theory, which is a natural generalization of the traditional Hartree-Fock theory, is derived. This simplification allows to express the pairing interaction in terms of the one-particle density matrix for systems interacting by attractive pair potentials, such as the Newtonian gravitational potential.

  • 3. Bantavis, P. I.
    et al.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Empliouk, T.
    Kyriacou, G. A.
    A Wideband Switched Beam Antenna System for 5G Femtocell Applications2017In: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 929-930Conference paper (Refereed)
    Abstract [en]

    This work introduces a wideband switched beam system for femtocell 5G base stations. The system consists of a 4 x 1 Vivaldi linear array and a 4 x 4 Butler matrix able to operate from 1.9-5.1 GHz. A soft surface is introduced along the outer edges of the vivaldi elements of the array for side lobes and back radiation suppression.

  • 4.
    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.

  • 5.
    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.

  • 6. Colombi, Davide
    et al.
    Thors, Björn
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient Whole-Body SAR Assessments by Means of Surface Scan Measurements2014In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 56, no 3, p. 539-548Article in journal (Refereed)
    Abstract [en]

    In this study, an experimental method has been investigated for efficient assessments of whole-body specific absorption rates (SAR) from radio base station antennas. Using surface amplitude measurements of the electric field components together with an integral equation technique, a method is obtained which is not biased to specific antenna designs or phantom shapes. For realistic material parameters, it has been found that only the amplitude of the tangential field components over the phantom boundary is needed to accurately assess whole-body SAR, which makes the proposed method well suited for integration with commercially available SAR measurement systems. The method has been validated with simulations and measurements. Compared with a volumetric scan, and for the cases investigated, the measurement time was reduced with a factor larger than 3 while keeping the relative error smaller than 8%.

  • 7.
    Colombi, Davide
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thors, Björn
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Experimental whole-body SAR assessments by means of surface scan with no phase information2011In: 33rd Annual Meeting of the Bioelectromagnetics Society, 2011Conference paper (Refereed)
  • 8.
    Dahlberg, Oskar
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mattsson, M.
    Silver, Gustaf
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Björkqvist, Oskar
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Novel 32 Port Cube MIMO Combining Broadside and Endfire Radiation Patterns for Full Azimuthal Coverage - A Modular Unit Approach for a Massive MIMO System2017In: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1641-1642Conference paper (Refereed)
    Abstract [en]

    In this paper we propose a novel 32 antenna port multiple-input-multiple-output (MIMO)-cube. The total volume of the cube is 320 x 320 x 120 mm(3) . On two faces, endfire radiating linear tapered slot antennas (LTSAs) are placed and on the remaining sides, a mix of both LTSAs and broadside patch antennas are placed. In total 16 LTSAs and 8 dual polarized patches are used. The LTSA is designed to operate at the GSM and 3G bands, from 1.7 to 2.3 GHz. A corrugation pattern is introduced along the edges of the LTSAs covering one face to increase directivity and decrease sidelobes. The LTSAs are placed in two different orientations in order to receive two polarisations. The patch antenna is dual band and dual polarized. It operates in the frequency bands 2.4-2.5 and 5.45-5.6 GHz where Wi-Fi communication is made. The spatial placement, with antennas on all sides of the cuboid, ensures full azimuthal coverage despite the high directivity of the antennas. Using different antennas on different faces of the cube further optimizes the volume efficiency of the cube for azimuthal coverage.

  • 9. Dejak, S. I.
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Long-time dynamics of variable coefficient modified Korteweg-de Vries solitary waves2006In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 47, no 7Article in journal (Refereed)
    Abstract [en]

    We study the long-time behavior of solutions to the Korteweg-de Vries-type equation partial derivative(t)u=-partial derivative(x)(partial derivative(2)(x)u+f(u)-b(t,x)u), with initial conditions close to a stable, b=0 solitary wave. The coefficient b is a bounded and slowly varying function, and f is a nonlinearity. For a restricted class of nonlinearities, we prove that for long time intervals, such solutions have the form of the solitary wave, whose center and scale evolve according to a certain dynamical law involving the function b(t,x), plus an H-1(R)-small fluctuation. The result is stronger than those previously obtained for general nonlinearities f.

  • 10.
    Ellgardt, Anders
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, Lars
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Resonance shift due to edge effects in finite-by-infinite monopole arrays2011In: International symposium on antennas and propagation, 2011Conference paper (Refereed)
  • 11. Fishman, Lou
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    de Hoop, Martijn
    Time Reversal Mirrors and Cross Correlation Functions in Acoustic Wave Propagation2008In: MATHEMATICAL MODELING OF WAVE PHENOMENA, 2008, p. 183-203Conference paper (Refereed)
    Abstract [en]

    In time reversal acoustics (TRA), a signal is recorded by an array of transducers, time reversed, and then retransmitted into the configuration. The retransmitted signal propagates back through the same medium and retrofocuses on the source that generated the signal. If the transducer array is a single, planar (flat) surface, then this configuration is referred to as a planar, one-sided, time reversal mirror (TRM). In signal processing, for example, in active-source seismic interferometry, the measurement of the wave field at two distinct receivers, generated by a common source, is considered. Cross correlating these two observations and integrating the result over the sources yield the cross correlation function (CCF). Adopting the TRM experiments as the basic starting point and identifying the kinematically correct correspondences, it is established that the associated CCF signal processing constructions follow in a specific, infinite recording time limit. This perspective also provides for a natural rationale for selecting the Green's function components in the TRM and CCF expressions. For a planar, one-sided, TRM experiment and the corresponding CCF signal processing construction, in a three-dimensional homogeneous medium, the exact expressions are explicitly calculated, and the connecting limiting relationship verified. Finally, the TRM and CCF results are understood in terms of the underlying, governing, two-way wave equation, its corresponding time reversal invariance (TRI) symmetry, and the absence of TRI symmetry in the associated one-way wave equations, highlighting the role played by the evanescent modal contributions.

  • 12.
    Frid, Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Holter, Henrik
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles2015In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 63, no 9, p. 4132-4138Article in journal (Refereed)
    Abstract [en]

    Calculating the mutual coupling between antennas on vehicles using full-wave simulations requires a vast amount of computer resources due to the electrical size of the structures. We therefore propose an alternative and approximate method to determine mutual coupling between antennas on vehicles for the case where there is line-of-sight (LOS) between the antennas. The proposed method is based on approximating the mutual coupling between LOS antennas on vehicles as near-field transmission between antennas in free space. We begin the analysis with a brief review of four methods for calculating the near-field free-space transmission. Of the investigated methods, we demonstrate that a nonsingular form of the near-field transmission integral originally proposed by Yaghjian (1982) is the most suitable for LOS antennas on vehicles. We introduce a modification to this method, in order to only use the antenna far-fields and geometrical separation to determine the mutual coupling. The comparison with full-wave simulations indicates that the proposed method has a good accuracy for LOS antennas. This paper ends with a full-scale mutual coupling calculation for two monopoles on an aircraft under LOS conditions, demonstrating a root mean square (rms) accuracy of 6 dB for frequencies up to 5 GHz, as compared with full-wave simulations.

  • 13. Froehlich, J.
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lenzmann, E.
    Effective dynamics for boson stars2007In: Nonlinearity, ISSN 0951-7715, E-ISSN 1361-6544, Vol. 20, no 5, p. 1031-1075Article in journal (Refereed)
    Abstract [en]

    We study solutions close to solitary waves of the pseudo-relativistic Hartree equation describing boson stars under the influence of an external gravitational field. In particular, we analyse the long-time effective dynamics of such solutions. In essence, we establish a ( long-time) stability result for solutions describing boson stars that move under the influence of an external gravitational field. The proof of our main result tackles difficulties that are absent when deriving similar results on effective solitary wave motions for nonlinear Schrodinger equations or nonlinear wave equations. This is due to the fact that the pseudo-relativisitic Hartree equation does not exhibit Galilean or Lorentz covariance.

  • 14. Froehlich, Juerg
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lenzmann, Enno
    Boson stars as solitary waves2007In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 274, no 1, p. 1-30Article in journal (Refereed)
    Abstract [en]

    We study the nonlinear equation i theta t psi = (root-Delta+m(2) - m) psi - (vertical bar x vertical bar(-1) * vertical bar psi vertical bar(2)) psi on R-3, which is known to describe the dynamics of pseudo-relativistic boson stars in the meanfield limit. For positive mass parameters, m > 0, we prove existence of travelling solitary waves, psi(t, x) = ei t mu phi(v)(x - vt), for some mu is an element of R and with speed vertical bar v vertical bar < 1, where c = 1 corresponds to the speed of light in our units. Due to the lack of Lorentz covariance, such travelling solitary waves cannot be obtained by applying a Lorentz boost to a solitary wave at rest (with v = 0). To overcome this difficulty, we introduce and study an appropriate variational problem that yields the functions phi(v) H-1/2(R-3) as minimizers, which we call boosted ground states. Our existence proof makes extensive use of concentration-compactness-type arguments. In addition to their existence, we prove orbital stability of travelling solitary waves psi(t, x) = e i t mu(v)(x - vt) and pointwise exponential decay of phi(v)(x) in x.

  • 15. Frohlich, J.
    et al.
    Gustafson, S.
    Jonsson, B. Lars G.
    KTH, Superseded Departments, Electromagnetic Theory.
    Sigal, I. M.
    Solitary wave dynamics in an external potential2004In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 250, no 3, p. 613-642Article in journal (Refereed)
    Abstract [en]

    We study the behavior of solitary-wave solutions of some generalized nonlinear Schrodinger equations with an external potential. The equations have the feature that in the absence of the external potential, they have solutions describing inertial motions of stable solitary waves. We consider solutions of the equations with a non-vanishing external potential corresponding to initial conditions close to one of these solitary wave solutions and show that, over a large interval of time, they describe a solitary wave whose center of mass motion is a solution of Newton's equations of motion for a point particle in the given external potential, up to small corrections corresponding to radiation damping.

  • 16. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    An overview of stored electromagnetic energy2014In: Proceedings - 2014 International Conference on Electromagnetics in Advanced Applications, ICEAA 2014, 2014, p. 793-795Conference paper (Refereed)
    Abstract [en]

    Although, the stored electromagnetic energy of an antenna is used to determine the antenna Q, it is difficult to define the stored energy. The stored energy can be estimated from the input impedance of the antenna, the electromagnetic fields around the antenna, and the current densities in the antenna structure. These estimates are similar but not equal for all antennas. Here, the different approaches to determine the stored energy are discussed.

  • 17. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Superseded Departments, Electromagnetic Theory.
    Iterative time reversal retrofocusing of Electromagnetic fields2004Conference paper (Refereed)
  • 18. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Superseded Departments, Electromagnetic Theory.
    Time Reversal Retrofocusing and Inverse Scattering of Acoustic Wave Fields2003Conference paper (Refereed)
  • 19. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Superseded Departments, Electromagnetic Theory.
    Time Reversal Retrofocusing and Inverse Scattering of Electromagnetic Wave Fields2003Conference paper (Refereed)
  • 20. Gustafsson, M.
    et al.
    Kristensson, G.
    Bernland, A.
    Sjöberg, D.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Physical bounds on the partial realized gain2010Conference paper (Refereed)
    Abstract [en]

    An antenna identity, derived from the forward scattering sum rule, shows that the partial realized gain of an antenna is related to the polarizability of the antenna structure. The partial realized gain contains the mismatch, directivity, efficiency, and polarization properties of the antenna. The antenna identity expresses how the performance depends on the electrical size and shape of the antenna structure. It is also the starting point for several antenna bounds. In this paper, the identity, its associated physical bounds, and computational aspects of the polarizability dyadics are discussed.

  • 21. Gustafsson, Mats
    et al.
    Cismasu, Marius
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Physical Bounds and Optimal Currents on Antennas2012In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, no 6, p. 2672-2681Article in journal (Refereed)
    Abstract [en]

    Physical bounds on the directivity Q-factor quotient and optimal current distributions are determined for antennas of arbitrary shape and size using an optimization formulation. A variational approach offers closed form solutions for small antennas expressed in the polarizability of the antenna structure. Finite sized antennas are solved using Lagrangian parameters in a method of moments formulation. It is also shown that the optimal charge density for a small antenna can be generated by several current densities. Numerical examples for small and large antennas are used to illustrate the results.

  • 22. Gustafsson, Mats
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Antenna Q and Stored Energy Expressed in the Fields, Currents, and Input Impedance2015In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 63, no 1, p. 240-249Article in journal (Refereed)
    Abstract [en]

    Although the stored energy of an antenna is instrumental in the evaluation of antenna Q and the associated physical bounds, it is difficult to strictly define stored energy. Classically, the stored energy is either determined from the input impedance of the antenna or the electromagnetic fields around the antenna. The new energy expressions proposed by Vandenbosch express the stored energy in the current densities in the antenna structure. These expressions are equal to the stored energy defined from the difference between the energy density and the far field energy for many but not all cases. Here, the different approaches to determine the stored energy are compared for dipole, loop, inverted L-antennas, and bow-tie antennas. We use Brune synthesized circuit models to determine the stored energy from the input impedance. We also compare the results with differentiation of the input impedance and the obtained bandwidth. The results indicate that the stored energy in the fields, currents, and circuit models agree well for small antennas. For higher frequencies, the stored energy expressed in the currents agrees with the stored energy determined from Brune synthesized circuit models whereas the stored energy approximated by differentiation of input impedance gives a lower value for some cases. The corresponding results for the bandwidth suggest that the inverse proportionality between the fractional bandwidth and Q-factor depends on the threshold level of the reflection coefficient.

  • 23.
    Gustafsson, Mats
    et al.
    Electrical and information technology, Lund University.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Stored electromagnetic energy and antenna Q2015In: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 150, p. 13-27Article in journal (Refereed)
    Abstract [en]

    Decomposition of the electromagnetic energy into its stored and radiated parts is instrumental in the evaluation of antenna Q and the corresponding fundamental limitations on antennas. This decomposition is not unique and there are several proposals in the literature. Here, it is shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases. This also explains the observed cases with negative stored energy and suggests a possible remedy to them. The results are compared with the classical explicit expressions for spherical regions where the results only differ by the electrical size ka that is interpreted as the far-field energy in the interior of the sphere.

  • 24.
    Gustafsson, Mats
    et al.
    Department of Electroscience, Electromagnetic Theory, Lund Institute of Technology.
    Jonsson, B. Lars G.
    Department of Mathematics, University of Toronto, Toronto, Ontario, Canada.
    Time-reversal retrofocusing and inverse scattering2002In: Proceedings General Assembly of the International Union of Radio Science, 2002Conference paper (Refereed)
    Abstract [en]

    Time-reversal retrofocusing is used together with a gradient based inverse scattering algorithm to identify the material distribution in a cavity. The time-reversal retrofocusing algorithm designs input fields such that the field energy is concentrated to the region where the material is unknown at a specific time. After this time the field energy in the cavity decays rapidly.  

  • 25.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On directivity constraints and their influence on the lower Q-factor bound for embedded small antennas2017In: Proceedings of the 2017 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1770-1773Conference paper (Refereed)
    Abstract [en]

    Constraints on the directivity reduce the available bandwidth of antennas. We develop here a formulation that determines the smallest Q-factor for an arbitrary shaped embedded antenna for a given partial or total directivity. An embedded antenna is an antenna that is located within a device often as part of a circuit board, where the main volume of the device is dedicated to non-antenna functions. We show that semi-definite relaxation can be used to predict the lowest Q-factor in an embedded antenna for a partial or a total directivity in a given direction, and that the bound is tight. The paper ends with an example.

  • 26.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On Passive RCS Reduction for Planar Scatterers in a Metallic Hull2008Conference paper (Refereed)
  • 27.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the effective dynamics of the pseudo-relativistic Hartree equation2006Conference paper (Other academic)
  • 28.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    The kernel condition of a linearized pseudo-relativistic Hartree equation, a numerical approach2009In: MATHEMATICAL MODELING OF WAVE PHENOMENA / [ed] Nilsson B; Fishman L; Karlsson A; Nordebo S, 2009, Vol. 1106, p. 173-180Conference paper (Refereed)
    Abstract [en]

    We consider the nonlinear equation i partial derivative(t)psi = (root-Delta+m(2) - m)psi - (vertical bar x vertical bar(-1) * vertical bar psi vertical bar(2))psi on R-3 describing the dynamics of pseudo-relativistic boson stars in the mean-field limit. Recently this equation, with an external potential has been used to describe the dynamics of boson stars under the influence of an external gravitational field. This analysis makes one explicit critical assumption. To the above differential equation we call associate all energy function. The assumption is on the size of the kernel of the Hessian of the energy functional when it is linearized around a soliton, In this paper we provide a numerical indicator that the assumption is satisfied. To achieve this goal. we need to numerically calculate the soliton for a range of normalized frequencies as well as and the spectrum of the linearization around a soliton of the Euler-Lagrange equations describing the minimizer.

  • 29.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    WAVE SPLITTING OF MAXWELL'S EQUATIONS WITH ANISOTROPIC HETEROGENEOUS CONSTITUTIVE RELATIONS2009Article in journal (Refereed)
    Abstract [en]

    The equations for the electromagnetic field in an anisotropic media are written in a form containing only the transverse field components relative to a half plane boundary. The operator corresponding to this formulation is the electromagnetic system's matrix. A constructive proof of the existence of directional wave-field decomposition with respect to the normal of the boundary is presented. In the process of defining the wave-field decomposition (wave-splitting), the resolvent set of the time-Laplace representation of the system's matrix is analyzed. This set is shown to contain a strip around the imaginary axis. We construct a splitting matrix as a Dunford-Taylor type integral over the resolvent of the unbounded operator defined by the electromagnetic system's matrix. The splitting matrix commutes with the system's matrix and the decomposition is obtained via a generalized eigenvalue-eigenvector procedure. The decomposition is expressed in terms of components of the splitting matrix. The constructive solution to the question of the existence of a decomposition also generates an impedance mapping solution to an algebraic Riccati operator equation. This solution is the electromagnetic generalization in an anisotropic media of a Dirichlet-to-Neumann map.

  • 30.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    de Hoop, M. V.
    Wave field decomposition in anisotropic fluids: A spectral theory approach2001In: Acta Applicandae Mathematicae - An International Survey Journal on Applying Mathematics and Mathematical Applications, ISSN 0167-8019, E-ISSN 1572-9036, Vol. 67, no 2, p. 117-171Article in journal (Refereed)
    Abstract [en]

    An extension of directional wave field decomposition in acoustics from heterogenous isotropic media to generic heterogenous anisotropic media is established. We make a connection between the Dirichlet-to-Neumann map for a level plane, the solution to an algebraic Riccati operator equation, and a projector defined via a Dunford-Taylor type integral over the resolvent of a nonnormal, noncompact matrix operator with continuous spectrum. In the course of the analysis, the spectrum of the Laplace transformed acoustic system's matrix is analyzed and shown to separate into two nontrivial parts. The existence of a projector is established and using a generalized eigenvector procedure, we find the solution to the associated algebraic Riccati operator equation. The solution generates the decomposition of the wave field and is expressed in terms of the elements of a Dunford-Taylor type integral over the resolvent.

  • 31.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Dejak, S.
    Sigal, I. M.
    On long time dynamics for KdV solitons2003Conference paper (Refereed)
  • 32.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Frohlich, J.
    Gustafson, S.
    Sigal, I. M.
    Long time motion of NLS solitary waves in a confining potential2006In: Annales de l'Institute Henri Poincare. Physique theorique, ISSN 1424-0637, E-ISSN 1424-0661, Vol. 7, no 4, p. 621-660Article in journal (Refereed)
    Abstract [en]

    We study the motion of solitary-wave solutions of a family of focusing generalized nonlinear Schrodinger equations with a confining, slowly varying external potential, V(x). A Lyapunov-Schmidt decomposition of the solution combined with energy estimates allows us to control the motion of the solitary wave over a long, but finite, time interval. We show that the center of mass of the solitary wave follows a trajectory close to that of a Newtonian point particle in the external potential V(x) over a long time interval.

  • 33.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fröhlich, J.
    On the numerical verification of a kernel assumption for the pseudo-relativistic Hartree equation2007Conference paper (Other academic)
  • 34.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On dynamics of a NLS-soliton in an external potential2003Conference paper (Refereed)
  • 35.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On dynamics of a NLS-soliton in an external potential2004Conference paper (Refereed)
  • 36.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On solitary wave dynamics in an external potential2004Conference paper (Other academic)
  • 37.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fröhlich, J.
    Lenzmann, E.
    On the effective dynamics of the pseudo-relativisitc Hartree equation2006Conference paper (Other academic)
  • 38.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fröhlich, J.
    Lenzmann, E.
    On the effective dynamics of the pseudo-relativistic Hartree equation2007Conference paper (Other academic)
  • 39.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fröhlich, Juerg
    On the numerical verication of a kernel assumption for the pseudo-relativistic Hartree equation2007In: 7:th international conference on Symmetry in Nonlinear Mathematical Physics, 2007Conference paper (Refereed)
  • 40.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Fröhlich, Juerg
    Lenzmann, Enno
    On the eective dynamics of the pseudo-relativistic Hartree equation2007In: Deutsche PhysikalischeGesellschaft e.V., Heidelberg, 2007Conference paper (Refereed)
  • 41.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, M.
    On Multi-Dimensional Systems: Properties of their Transfer Functions2016In: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS), IEEE, 2016, p. 512-514Conference paper (Refereed)
    Abstract [en]

    A range of interesting electromagnetic systems like antennas, extraordinary transmission and absorbers have been shown to have certain bandwidth limitations given by a family of sum-rules. Common for the systems are that they are passive, linear and time-translational invariant. In this paper we shortly review the extension from one-dimensional passive systems to multi-dimensional systems, aiming towards constraining the system properties. The most well-known case of system constraints follows from multi-dimensional passivity, where a Schwartz-kernel representation theorem maps Borel-measures with a growth condition to the (complexified) Fourier transform of the transfer function. A weaker form of system constraints follow from generalizations of Kramers-Kronig relations. One such approach is a generalized Cauchy-Bochner representations, under Sobolev space limitations on the transform pair. This approach is closely connected to that the support of the transfer function is within an acute cone. Another approach to system transfer constraints is the multi-dimensional Hilbert-transform, often with squareinte-grable function requirements. It is observed that the Cauchy-Bochner representation and the multi-dimensional Hilbert transform yield different representations in higher dimensions although they give the same in one dimension. We end the paper with a few explicit examples of functions that satisfy the constraints.

  • 42.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, M.
    Stored energies for electric and magnetic currents with applications to Q for small antennas2013In: 2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings, IEEE , 2013, p. 1050-1053Conference paper (Refereed)
    Abstract [en]

    Fundamental limitations restrict the bandwidth of electrically small antennas. A method to obtain such limitations is based on stored electric and magnetic energies. Vandenbosch recently proposed a set of integral expression for the stored energies. These expressions provide a method to determine optimal currents and physical bounds on antennas for maximal bandwidth and desired radiated fields. In the present paper, we generalize the expressions for the stored energies to include magnetic sources for small structures. We give an expression for the antenna Q for electrically small shapes. Examples for small spheres are tested and the results agree with the published results.

  • 43.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, M.
    Stored energies in electric and magnetic current densities for small antennas2015In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 471, no 2176, article id 20140897Article in journal (Refereed)
    Abstract [en]

    Electric andmagnetic currents are essential to describe electromagnetic-stored energy, and the associated antenna Q and the partial directivity to antenna Q-ratio, D/Q, for arbitrarily shaped structures. The upper bound of previous D/Q results for antennas modelled by electric currents is accurate enough to be predictive. This motivates us to develop the analysis required to determine upper and/or lower bounds for electromagnetic problems that include magnetic model currents. Here we derive new expressions for the stored energies, which are used to determine antenna Q bounds and D/Q bounds for the combination of electric and magnetic currents, in the limit of electrically small antennas. In this investigation, we show both new analytical results and we illustrate numerical realizations of them. We show that the lower bound of antenna Q is inversely proportional to the largest eigenvalue of certain combinations of the electric and magnetic polarizability tensors. These results are an extension of the electric only currents, which come as a special case. The proposed method to determine the minimum Q-value which is based on the new expressions for the stored energies, also yields a family of current-density minimizers for optimal electric and magnetic currents that can lend insight into antenna designs.

  • 44.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Gustafsson, M.
    Weston, V. H.
    de Hoop, M. V.
    Retrofocusing for Acoustic and Electromagnetic fields by Iterated Time reversal2003Conference paper (Refereed)
  • 45.
    Jonsson, B. Lars G.
    et al.
    KTH, Superseded Departments, Electromagnetic Theory.
    Gustafsson, M.
    Weston, V. H.
    de Hoop, M. V.
    Retrofocusing of acoustic wave fields by iterated time reversal2004In: SIAM Journal on Applied Mathematics, ISSN 0036-1399, E-ISSN 1095-712X, Vol. 64, no 6, p. 1954-1986Article in journal (Refereed)
    Abstract [en]

    In the present paper an iterative time-reversal algorithm that retrofocuses an acoustic wave field to its controllable part is established. For a fixed temporal support, i.e., transducer excitation time, the algorithm generates an optimal retrofocusing in the least-squares sense. Thus the iterative time-reversal algorithm reduces the temporal support of the excitation from the requirement of negligible remaining energy to the requirement of controllability. The time-reversal retrofocusing is analyzed from a boundary-control perspective where time reversal is used to steer the acoustic wave field towards a desired state. The wave field is controlled by transducers located at subsets of the boundary, i.e., the controllable part of the boundary. The time-reversal cavity and time-reversal mirror cases are analyzed. In the cavity case, the transducers generate a locally plane wave in the fundamental mode through a set of ducts. Numerical examples are given to illustrate the convergence of the iterative time-reversal algorithm. In the mirror case, a homogeneous half space is considered. For this case the analytic expression for the retrofocused wave field is given for finite temporal support. It is shown that the mirror case does not have the same degree of steering as the cavity case. It is also shown that the pressure can be perfectly retrofocused for infinite temporal support. Two examples are given that indicate that the influence of the evanescent part of the wave field is small.

  • 46.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, Mats
    Limitations on the effective area and bandwidth product for array antennas2010In: Symposium Digest - 20th URSI International Symposium on Electromagnetic Theory, EMTS 2010, 2010, p. 711-714Conference paper (Refereed)
    Abstract [en]

    An upper bound on the effective area and bandwidth product for linearly polarized array antennas is derived. The bound is based on the forward scattering sum rule that relates the antenna properties with the polarizability of the antenna structure. The results are illustrated for a dipole array and a capacitively loaded dipole array with numerical simulations.

  • 47.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kolitsidas, Christos I.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On methods to estimate bandwidth performance for array antennas with ground plane2014In: 2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Array antenna impedance bandwidth performance is a critical factor for antenna design, in particular for arrays in radar application and more recently for array antennas in communication systems. A priori methods to quantify bandwidth include stored energy-based estimates through the quality factor antenna Q, and sum-rule based estimates based on the antenna as a scattering object. A recently introduced, array figure of merit, uses a square window or walltype estimate on the return-loss to obtain bounds in terms of return-loss level, bandwidth, scan-range and unit-cell specific geometrical and material information, it is based on a fundamental physics result, linking bandwidth to essentially the thickness of the array. An alternative approach is based on the Bode-Fano theory, resulting in bandwidth measures in terms of one or several quality factors. Both methods apply both to single and multi-band array antennas. Here we present these methods and make a comparison between the two approaches.

  • 48.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kolitsidas, Christos I.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hussain, N.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Array Antenna Limitations2013In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 12, p. 1539-1542Article in journal (Refereed)
    Abstract [en]

    This letter defines a physical-bound-based array figure of merit for both single and multiband array antennas. It provides a measure to compare their performance with respect to return loss, bandwidth(s), thickness of the array over the ground plane, and scan range. The result is based on a sum-rule result of Rozanov-type for linear polarization. For single-band antennas, it extends an existing limit for a given fixed scan-angle to include the whole scan range of the array, as well as the unit-cell structure in the bound. The letter ends with an investigation of the array figure of merit for some wideband and/or wide-scan antennas with linear polarization. We find arrays with a figure of merit >0.6 that empirically defines high-performance antennas with respect to this measure.

  • 49.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Asymptotic wave-splitting in anisotropic linear acoustics2010In: Wave motion, ISSN 0165-2125, E-ISSN 1878-433X, Vol. 47, no 5, p. 318-326Article in journal (Refereed)
    Abstract [en]

    In the present paper, we present a simple wave-splitting procedure for instantaneously reacting anisotropic media that includes spatial variation in depth. The method includes both the traditional (approximate) and a 'true amplitude' wave-field decomposition. The results are presented in time-Laplace domain. One of the main advantages of the method presented here is that it gives an explicit asymptotic representation of the linear acoustic-admittance operator to all orders of smoothness for the smooth, positive definite anisotropic material parameters considered here. Once the admittance operator is known we obtain an explicit asymptotic wave-splitting solution. (C) 2009 Elsevier B.V. All rights reserved.

  • 50.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ovchinnikov, Yu. N.
    Sigal, I. M.
    Ting, F. S. T.
    Dynamics of breakup of multiple vortices in Gross-Pitaevskii equations of superfluids2011In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 52, no 9Article in journal (Refereed)
    Abstract [en]

    In this paper we study the Gross-Pitaevskii equation of the theory of superfluidity, i.e., the nonlinear Schroumldinger equation of the Ginzburg-Landau type. We investigate the dynamics of the breakup of the double vortex. More specifically, we prove instability of the double vortex, compute the complex eigenvalue responsible for this instability, and derive the dynamical equation of motion of (centers of) single vortices resulting from splitting of the double vortex. We expect that our analysis can be extended to vortices of higher degree and to magnetic and Chern-Simmons vortices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3629473]

12 1 - 50 of 88
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