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Sökning: LAR1:lu > Sjöberg Daniel > Lunds universitet > Kungliga Tekniska Högskolan

  • Resultat 1-10 av 12
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1.
  • Ericsson, Andreas, et al. (författare)
  • A combined electromagnetic and acoustic analysis of a triaxial carbon fiber weave for reflector antenna applications
  • 2016
  • Ingår i: Aerospace Science and Technology. - : Elsevier. - 1270-9638 .- 1626-3219. ; 58, s. 401-417
  • Tidskriftsartikel (refereegranskat)abstract
    • Fiber composites are widely used for space applications such as antennas, solar panels and spacecraft support structures. This paper presents a combined electromagnetic and acoustic analysis of a triaxial carbon fiber weave structure, designed for ultra lightweight reflector antennas in satellite communication systems. The electromagnetic and acoustic performance of the structure are analyzed over a wide range of parametric studies, both at a microscopic and mesoscopic length scale. The electromagnetic study indicates that the main parameter governing the electromagnetic reflection performance of the weave is the electric conductivity of the carbon fibers, given that the weave structure is significantly smaller than the wavelength of the incident signals. The acoustic study identifies a critical threshold in the mesoscale geometry in order to avoid a critically high resistive behavior of the weave structure, driven by viscous effects. Design guidelines are drawn from these analyses in order to achieve a trade-off between the electromagnetic reflection properties and the resistance to acoustic loading of such composite materials. These combined analyses allow to deepen the understanding from both an electromagnetic and acoustic perspective in order to open for some new design possibilities.
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2.
  • Gustafsson, Mats, et al. (författare)
  • Physical bounds on the partial realized gain
  • 2010
  • Ingår i: [Host publication title missing]. ; , s. 1-6
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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3.
  • Helander, Jakob, et al. (författare)
  • Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
  • 2016
  • Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225 .- 1548-5757. ; 15, s. 504-507
  • Tidskriftsartikel (refereegranskat)abstract
    • This letter discusses the usage of high-gain steerable antenna arrays operating at millimeter-wave (mmWave) frequencies for future cellular networks (5G). Based on the probable outline of the 5G networks, a method for characterizing phased array antennas in cellular handsets has been introduced. For analyzing the performance, the total scan pattern of the array configuration together with its respective coverage efficiency are essential to consider in order to compare different antenna designs and topology approaches with each other. Two design approaches and subarray schemes of these have been considered in order to illustrate the relevance of such a characterization method. The results show the importance of evaluating potential array antennas in such manners. The method can be applied to much more complex system models, where polarization diversity, hand and body effect, and statistical modeling of the channel may be included.
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4.
  • Ramprecht, Jörgen, et al. (författare)
  • Biased magnetic materials in RAM applications
  • 2007
  • Ingår i: Progress in Electromagnetics Research. - 1559-8985 .- 1070-4698. ; 75, s. 85-117
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetization of a ferro- or ferri-magnetic material has been modeled with the Landau-Lifshitz-Gilbert (LLG) equation. In this model demagnetization effects are included. By applying a linearized small signal model of the LLG equation, it was found that the material can be described by an effective permeability and with the aid of a static external biasing field, the material can be switched between a Lorentz-like material and a material that exhibits a magnetic conductivity. Furthermore, the reflection coefficient for normally impinging waves on a PEC covered with a ferro/ferri-magnetic material, biased in the normal direction, is calculated. When the material is switched into the resonance mode, two distinct resonance frequencies in the reflection coefficient were found, one associated with the precession frequency of the magnetization and the other associated with the thickness of the layer. The former of these resonance frequencies can be controlled by the bias field and for a bias field strength close to the saturation magnetization, where the material starts to exhibit a magnetic conductivity, low reflection ( around - 20 dB) for a quite large bandwidth ( more than two decades) can be achieved.
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5.
  • Ramprecht, Jörgen, et al. (författare)
  • Magnetic Losses in Composite Materials
  • 2008
  • Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 41:13, s. 135005-
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss some of the problems involved in homogenization of a composite material built from ferromagnetic inclusions in a nonmagnetic background material. The small signal permeability for a ferromagnetic spherical particle is combined with a homogenization formula to give an effective permeability for the composite material. The composite material inherits the gyrotropic structure and resonant behaviour of the single particle. The resonance frequency of the composite material is found to be independent of the volume fraction, unlike dielectric composite materials. The magnetic losses are described by a magnetic conductivity which can be made independent of frequency and proportional to the volume fraction by choosing a certain bias. Finally, some concerns regarding particles of small size, i.e. nanoparticles, are treated and the possibility of exciting exchange modes are discussed. These exchange modes may be an interesting way to increase losses in composite materials.
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6.
  • Ramprecht, Jörgen, et al. (författare)
  • On the amount of magnetic material necessary in broadband magnetic absorbers
  • 2008
  • Ingår i: 2008 IEEE International Symposium on Antennas and Propagation (AP-S 2008). - 9781424420414 ; , s. 1412-1415
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we have examined the use of ferromagnetic particles for thin broadband RAMs. The permeability of the composite material was obtained from a well tested model for ferromagnetic materials and a result from homogenization theory. It was found that the resonance frequency of the composite is independent of the volume fraction of the particles and that a magnetic conductivity proportional to the volume fraction exists. Furthermore, we showed that a certain amount of magnetic material is required in order to maintain a low reflection and that there exists a lower bound on how thin we could expect the absorber to be. Numerical calculations show that, though thin, the RAM tends to be quite heavy, which might prevent the use of ferromagnetic material in RAM applications. These results may serve as guidelines when designing thin broadband RAMs.
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7.
  • Ramprecht, Jörgen, et al. (författare)
  • On the feasibility of using ferromagnetic materials for thin em absorbers
  • 2007
  • Ingår i: 2007 International Conference on Electromagnetics in Advanced Applications, ICEAA'07. - 1424407672 - 9781424407675 ; , s. 324-327
  • Konferensbidrag (refereegranskat)abstract
    • In this paper the magnetization of a ferro- or ferri-magnetic material has been modeled with the Landau-Lifshitz-Gilbert (LLG) equation. We show that with the aid of a static magnetic bias field the material can be switched between a Lorentz-like material with a resonance frequency and a material exhibiting a magnetic conductivity. The reflection from a magnetic material backed by a perfect electrical conductor (PEC) is then analyzed. It is found that one can achieve low reflection (around -20 dB) for a quite large bandwidth (more than two decades).
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8.
  • Ramprecht, Jörgen, et al. (författare)
  • Scattering from a thin magnetic layer with a periodic lateral magnetization : application to electromagnetic absorbers
  • 2008
  • Ingår i: Progress in Electromagnetics Research. - 1559-8985. ; 83, s. 199-224
  • Tidskriftsartikel (refereegranskat)abstract
    • A magnetized thin layer mounted on a PEC surface is considered as an alternative for an absorbing layer. The magnetic material is modeled with the Landau-Lifshitz-Gilbert equation, with a lateral static magnetization having a periodic variation along one lateral direction. The scattering problem is solved by means of an expansion into Floquet-modes, a propagator formalism and wave-splitting. Numerical results are presented, and for parameter values close to the typical values for ferro- or ferrimagnetic media, reflection coefficients below -20 dB can be achieved for the fundamental mode over the frequency range 1-4 GHz, for both polarizations. It is found that the periodicity of the medium makes the reflection properties for the fundamental mode almost independent of the azimuthal direction of incidence, for both normally and obliquely incident waves.
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9.
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10.
  • Xu, Bo, et al. (författare)
  • Investigation of Planar Near-Field Measurement of Millimeter-Wave Antenna for 5G Application
  • 2016
  • Ingår i: 2016 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP). - : IEEE. - 9784885523137 ; , s. 600-601
  • Konferensbidrag (refereegranskat)abstract
    • The requirement of higher data rates and the emergence of new wireless device demands in future 5G communication put millimeter-wave frequencies in focus. To investigate electromagnetic-filed exposure at such frequencies for 5G cellular phone application, a planar near-field antenna measurement system is established. A tapered open-ended rectangular waveguide was used as the probe antenna, and a patch array antenna operating at 28 GHz was used as antenna under test. The distribution of power density above the antenna surface was calculated based on the measured data and the plane wave expansion method.
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