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  • 1.
    Aljure, Mauricio
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. ABB Corporate Research, Sweden.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Simulation of the electrical conduction of cyclohexane with TiO2 nanoparticles2014Ingår i: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, IEEE , 2014, s. 6893119-Konferensbidrag (Refereegranskat)
    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, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bogolubov-Hartree-Fock mean field theory for neutron stars and other systems with attractive interactions2009Ingår i: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 50, nr 10Artikel i tidskrift (Refereegranskat)
    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, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Empliouk, T.
    Le Roy, M.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Kyriacou, G. A.
    A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station2018Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 66, nr 12, s. 6851-6861, artikel-id 8485638Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A wideband switched beam antenna array system operating from 2 to 5 GHz is presented. It is comprised of a 4 × 1 Vivaldi antenna elements and a 4 × 4 Butler matrix beamformer driven by a digitally controlled double-pole four-throw RF switch. The Butler matrix is implemented on a multilayer structure, using 90° hybrid couplers and 45° phase shifters. For the design of the coupler and phase shifter, we propose a unified methodology applied, but not limited, to elliptically shaped geometries. The multilayer realization enables us to avoid microstrip crossing and supports wideband operation of the beamforming network. To realize the Butler matrix, we introduce a step-by-step and stage-by-stage design methodology that enables accurate balance of the output weights at the antenna ports to achieve a stable beamforming performance. In this paper, we use a Vivaldi antenna element in a linear four-element array, since such element supports wideband and wide-scan angle operation. A soft condition in the form of corrugations is implemented around the periphery of the array, in order to reduce the edge effects. This technique improved the gain, the sidelobes, and helped to obtain back radiation suppression. Finally, impedance loading was also utilized in the two edge elements of the array to improve the active impedance. The proposed system of the Butler matrix in conjunction with the constructed array can be utilized as a common RF front end in a wideband air interface for a small cell 5G application and beyond as it is capable to simultaneously cover all the commercial bands from 2 to 5 GHz.

  • 4. Bantavis, P. I.
    et al.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Empliouk, T.
    Kyriacou, G. A.
    A Wideband Switched Beam Antenna System for 5G Femtocell Applications2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 929-930Konferensbidrag (Refereegranskat)
    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.

  • 5.
    Björkqvist, Oskar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Silver, Gustaf
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mattsson, M.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Novel Efficient Multiple Input Single Output RF Energy Harvesting Rectification Scheme2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1605-1606Konferensbidrag (Refereegranskat)
    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.

  • 6.
    Bukhsh, Waqquas Ahmed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Persson, P.
    Element position perturbation for a narrow spot beam with applications to satellite communication antennas2010Ingår i: PROGRESS IN ELECTROMAGNETICS RESEARCH-PIER, ISSN 1559-8985, Vol. 104, s. 283-295Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Capek, Miloslav
    et al.
    Czech Tech Univ, Prague, Czech Republic..
    Jelinek, Lukas
    Czech Tech Univ, Prague, Czech Republic..
    Schab, Kurt
    Santa Clara Univ, Santa Clara, CA 95053 USA..
    Gustafsson, Mats
    Lund Univ, Lund, Sweden..
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Ferrero, Fabien
    Univ Cote Azur, Nice, France..
    Ehrenborg, Casimir
    Lund Univ, Dept Elect & Informat Technol, Lund, Sweden..
    Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.2019Ingår i: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 61, nr 4, s. 19-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here, we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on the radiation quality factor (Q-factor) (maximizing single-resonance fractional bandwidth) but are far from reaching the associated physical bounds for efficiency. The relative performance of other canonical antenna designs is comparable in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.

  • 8. Colombi, Davide
    et al.
    Thors, Björn
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Efficient Whole-Body SAR Assessments by Means of Surface Scan Measurements2014Ingår i: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 56, nr 3, s. 539-548Artikel i tidskrift (Refereegranskat)
    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%.

  • 9.
    Colombi, Davide
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Thors, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Experimental whole-body SAR assessments by means of surface scan with no phase information2011Ingår i: 33rd Annual Meeting of the Bioelectromagnetics Society, 2011Konferensbidrag (Refereegranskat)
  • 10.
    Dahlberg, Oskar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mattsson, M.
    Silver, Gustaf
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Björkqvist, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Novel 32 Port Cube MIMO Combining Broadside and Endfire Radiation Patterns for Full Azimuthal Coverage - A Modular Unit Approach for a Massive MIMO System2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1641-1642Konferensbidrag (Refereegranskat)
    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.

  • 11. Dejak, S. I.
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Long-time dynamics of variable coefficient modified Korteweg-de Vries solitary waves2006Ingår i: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 47, nr 7Artikel i tidskrift (Refereegranskat)
    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.

  • 12.
    Ellgardt, Anders
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Resonance shift due to edge effects in finite-by-infinite monopole arrays2011Ingår i: International symposium on antennas and propagation, 2011Konferensbidrag (Refereegranskat)
  • 13. Fishman, Lou
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    de Hoop, Martijn
    Time Reversal Mirrors and Cross Correlation Functions in Acoustic Wave Propagation2008Ingår i: MATHEMATICAL MODELING OF WAVE PHENOMENA, 2008, s. 183-203Konferensbidrag (Refereegranskat)
    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.

  • 14.
    Frid, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Holter, Henrik
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles2015Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 63, nr 9, s. 4132-4138Artikel i tidskrift (Refereegranskat)
    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.

  • 15. Frid, Henrik
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Compensation of radome effects in small airborne monopulse arrays by convex optimization2018Ingår i: IET Conference Publications, Institution of Engineering and Technology , 2018, nr CP741Konferensbidrag (Refereegranskat)
    Abstract [en]

    The quality of small array antennas in airborne monopulse systems can be significantly reduced by the radome. We therefore present a convex optimization approach to minimize radome effects in monopulse arrays. This is achieved by using active element patterns in the optimization to determine the excitation weights. Simulation results for a BoR array with 48 elements and an extended hemispherical radome are presented. We demonstrate that it is possible to reduce the side-lobe level by 3.5 dB by taking radome effects into account in the optimization. This approach also results in an increased gain, particularly at large scan angles. Furthermore, the presented approach allows the monopulse slope to be indirectly specified as a design parameter. It is shown that the trade-off between the monopulse slope coefficient and the side-lobe level is approximately linear.

  • 16.
    Frid, Henrik
    et al.
    Saab Surveillance, Stockholm, Sweden.;KTH Royal Inst Technol, Osquldas Vag 10, SE-10044 Stockholm, Sweden..
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Determining Installation Errors for DOA Estimation with Four-Quadrant Monopulse Arrays by using Installed Element Patterns2018Ingår i: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, artikel-id 8471377Konferensbidrag (Refereegranskat)
    Abstract [en]

    The four-quadrant monopulse array is widely used for direction of arrival (DOA) estimation. Errors in the angle estimate are introduced when installing the array on a platform, due to unwanted reflections in the platform, as well as reflection and refraction in the radome. These installation effects are captured in the installed element patterns, which can be computed using a number of computational electromagnetics methods. In this paper, we demonstrate that the error introduced in the DOA estimate can be determined from the installed element patterns. To illustrate how the method is used, we present results for two cases: (a) BoR-array without radome and (b) BoR-array with an extended hemispherical radome. The presented method can be applied for any installation configuration, as long as the installed element patterns can be computed.

  • 17. Froehlich, J.
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lenzmann, E.
    Effective dynamics for boson stars2007Ingår i: Nonlinearity, ISSN 0951-7715, E-ISSN 1361-6544, Vol. 20, nr 5, s. 1031-1075Artikel i tidskrift (Refereegranskat)
    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.

  • 18. Froehlich, Juerg
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Lenzmann, Enno
    Boson stars as solitary waves2007Ingår i: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 274, nr 1, s. 1-30Artikel i tidskrift (Refereegranskat)
    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.

  • 19. Frohlich, J.
    et al.
    Gustafson, S.
    Jonsson, B. Lars G.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Sigal, I. M.
    Solitary wave dynamics in an external potential2004Ingår i: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 250, nr 3, s. 613-642Artikel i tidskrift (Refereegranskat)
    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.

  • 20. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An overview of stored electromagnetic energy2014Ingår i: Proceedings - 2014 International Conference on Electromagnetics in Advanced Applications, ICEAA 2014, 2014, s. 793-795Konferensbidrag (Refereegranskat)
    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.

  • 21. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Iterative time reversal retrofocusing of Electromagnetic fields2004Konferensbidrag (Refereegranskat)
  • 22. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Time Reversal Retrofocusing and Inverse Scattering of Acoustic Wave Fields2003Konferensbidrag (Refereegranskat)
  • 23. Gustafsson, M.
    et al.
    Jonsson, B. Lars G.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Time Reversal Retrofocusing and Inverse Scattering of Electromagnetic Wave Fields2003Konferensbidrag (Refereegranskat)
  • 24. Gustafsson, M.
    et al.
    Kristensson, G.
    Bernland, A.
    Sjöberg, D.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Physical bounds on the partial realized gain2010Konferensbidrag (Refereegranskat)
    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.

  • 25. Gustafsson, Mats
    et al.
    Cismasu, Marius
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Physical Bounds and Optimal Currents on Antennas2012Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, nr 6, s. 2672-2681Artikel i tidskrift (Refereegranskat)
    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.

  • 26. Gustafsson, Mats
    et al.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Antenna Q and Stored Energy Expressed in the Fields, Currents, and Input Impedance2015Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 63, nr 1, s. 240-249Artikel i tidskrift (Refereegranskat)
    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.

  • 27.
    Gustafsson, Mats
    et al.
    Electrical and information technology, Lund University.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Stored electromagnetic energy and antenna Q2015Ingår i: Progress In Electromagnetics Research, ISSN 1070-4698, E-ISSN 1559-8985, Vol. 150, s. 13-27Artikel i tidskrift (Refereegranskat)
    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.

  • 28.
    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 scattering2002Ingår i: Proceedings General Assembly of the International Union of Radio Science, 2002Konferensbidrag (Refereegranskat)
    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.  

  • 29.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    A Comparison Between QCQP-relaxation Methods to Determine a Lower Bound on a Small Antenna Q-factor2019Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, artikel-id 8739996Konferensbidrag (Refereegranskat)
    Abstract [en]

    Quadratically constrained quadratic programming (QCQP) can be used to determine the best Q-factor for small antennas with constraints on the antenna efficiency. Constraints on the total directivity and a given front-to-back ratio can also be expressed as QCQP. Such problems are non-convex and hence challenging to solve. Their solution gives the best Q-factor available for any antenna within the considered volume. Thus, solutions to this type of problems provide a tool, which before the design can predict the best possible antenna performance within a given volume of a device. It is hence important to investigate methods to solve this class of QCQP problems. In this paper we compare and investigate two relaxation methods, the Lagrangian dual and semidefinite relaxation, to estimate lower bounds on the Q-factor. The former method is here reduced to solving a generalized eigenvalue-problem. Properties of the different relaxation methods are illustrated and compared. We focus in this paper on the Q-factor and its relation to efficiency, as expressed by the dissipation factor. However, these tools also apply to a larger class of problems including constraints on the directivity and other far-field conditions.

  • 30.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On directivity constraints and their influence on the lower Q-factor bound for embedded small antennas2017Ingår i: Proceedings of the 2017 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1770-1773Konferensbidrag (Refereegranskat)
    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.

  • 31.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On Passive RCS Reduction for Planar Scatterers in a Metallic Hull2008Konferensbidrag (Refereegranskat)
  • 32.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On the effective dynamics of the pseudo-relativistic Hartree equation2006Konferensbidrag (Övrigt vetenskapligt)
  • 33.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    The kernel condition of a linearized pseudo-relativistic Hartree equation, a numerical approach2009Ingår i: MATHEMATICAL MODELING OF WAVE PHENOMENA / [ed] Nilsson B; Fishman L; Karlsson A; Nordebo S, 2009, Vol. 1106, s. 173-180Konferensbidrag (Refereegranskat)
    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.

  • 34.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    WAVE SPLITTING OF MAXWELL'S EQUATIONS WITH ANISOTROPIC HETEROGENEOUS CONSTITUTIVE RELATIONS2009Artikel i tidskrift (Refereegranskat)
    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.

  • 35.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner                               , Teoretisk elektroteknik.
    de Hoop, M. V.
    Wave field decomposition in anisotropic fluids: A spectral theory approach2001Ingår i: Acta Applicandae Mathematicae - An International Survey Journal on Applying Mathematics and Mathematical Applications, ISSN 0167-8019, E-ISSN 1572-9036, Vol. 67, nr 2, s. 117-171Artikel i tidskrift (Refereegranskat)
    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.

  • 36.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Dejak, S.
    Sigal, I. M.
    On long time dynamics for KdV solitons2003Konferensbidrag (Refereegranskat)
  • 37.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Ferrero, Fabien
    Univ Cote Azur, CNRS, LEAT, Sophia Antipolis, France..
    On Q-factor Bounds for Lossy Embedded Antennas in Electrically Small Devices2019Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019, IEEE, 2019, artikel-id 8739833Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we investigate a method to determine the best available bandwidth for small embedded antennas. The available bandwidth depend both on the size and the position within a device, but also on the ohmic losses in the structure. Here we use that solutions to a non-convex optimization problem to predict the available bandwidth for a range of surface resistances. The optimization problem utilizes stored energies, and it is phrased as a current optimization problem. We illustrate the method by comparing the results with embedded antennas in a small IoT terminal. We show that an optimized embedded come rather close to the bounds.

  • 38.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Frohlich, J.
    Gustafson, S.
    Sigal, I. M.
    Long time motion of NLS solitary waves in a confining potential2006Ingår i: Annales de l'Institute Henri Poincare. Physique theorique, ISSN 1424-0637, E-ISSN 1424-0661, Vol. 7, nr 4, s. 621-660Artikel i tidskrift (Refereegranskat)
    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.

  • 39.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fröhlich, J.
    On the numerical verification of a kernel assumption for the pseudo-relativistic Hartree equation2007Konferensbidrag (Övrigt vetenskapligt)
  • 40.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On dynamics of a NLS-soliton in an external potential2003Konferensbidrag (Refereegranskat)
  • 41.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On dynamics of a NLS-soliton in an external potential2004Konferensbidrag (Refereegranskat)
  • 42.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Fröhlich, J.
    Gustafson, S.
    Sigal, I. M.
    On solitary wave dynamics in an external potential2004Konferensbidrag (Övrigt vetenskapligt)
  • 43.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fröhlich, J.
    Lenzmann, E.
    On the effective dynamics of the pseudo-relativisitc Hartree equation2006Konferensbidrag (Övrigt vetenskapligt)
  • 44.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fröhlich, J.
    Lenzmann, E.
    On the effective dynamics of the pseudo-relativistic Hartree equation2007Konferensbidrag (Övrigt vetenskapligt)
  • 45.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fröhlich, Juerg
    On the numerical verication of a kernel assumption for the pseudo-relativistic Hartree equation2007Ingår i: 7:th international conference on Symmetry in Nonlinear Mathematical Physics, 2007Konferensbidrag (Refereegranskat)
  • 46.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Fröhlich, Juerg
    Lenzmann, Enno
    On the eective dynamics of the pseudo-relativistic Hartree equation2007Ingår i: Deutsche PhysikalischeGesellschaft e.V., Heidelberg, 2007Konferensbidrag (Refereegranskat)
  • 47.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gustafsson, M.
    On Multi-Dimensional Systems: Properties of their Transfer Functions2016Ingår i: 2016 URSI INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC THEORY (EMTS), IEEE, 2016, s. 512-514Konferensbidrag (Refereegranskat)
    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.

  • 48.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gustafsson, M.
    Stored energies for electric and magnetic currents with applications to Q for small antennas2013Ingår i: 2013 International Symposium on Electromagnetic Theory, EMTS 2013 - Proceedings, IEEE , 2013, s. 1050-1053Konferensbidrag (Refereegranskat)
    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.

  • 49.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gustafsson, M.
    Stored energies in electric and magnetic current densities for small antennas2015Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 471, nr 2176, artikel-id 20140897Artikel i tidskrift (Refereegranskat)
    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.

  • 50.
    Jonsson, B. Lars G.
    et al.
    KTH, Tidigare Institutioner, Teoretisk elektroteknik.
    Gustafsson, M.
    Weston, V. H.
    de Hoop, M. V.
    Retrofocusing for Acoustic and Electromagnetic fields by Iterated Time reversal2003Konferensbidrag (Refereegranskat)
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