Daniel Sjoberg

Lund University, Lund, Skåne, Sweden

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Publications (32)17.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: An experimental approach to investigate the forward scattering sum rule for periodic structures is presented. This approach allows an upper bound on the total cross section integrated over a bandwidth from a simple static problem to be found. Based on energy conservation, the optical theorem is used to construct a relation between the total cross section and the forward scattering of periodic structures as well as single scatterers inside a parallel-plate waveguide. Dynamic measurements are performed using a parallel-plate waveguide and a parallel-plate capacitor is utilized to find the static polarizability. Convex optimization is introduced to identify the total cross section in the dynamic measurements and estimate an optimal lower bound on the polarizability for objects. The results show that the interactions between the electromagnetic field and an object over all wavelengths are given by the static polarizability of the object.
    IEEE Transactions on Microwave Theory and Techniques 09/2014; 62(99):1-9. DOI:10.1109/TMTT.2014.2354592 · 2.94 Impact Factor
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    ABSTRACT: An integrated millimeter-wave wavelet transmitter has been fabricated and characterized. It consists of a generator core on a co-designed compact monolithically-integrated antenna. The peak output equivalent isotropic radiated power has been measured to 11 dBm, in 80, 160, and 320 ps wavelets centred at 63.5 GHz. This corresponds to a power of 5 dBm radiated from the 6 dBi antenna. At a dc-supply of 1.45 V, the on-state power dissipation was estimated to 37 mW. The radiated wavelet-power over dc-dissipation conversion-efficiency is 9%.
    IEEE Microwave and Wireless Components Letters 09/2014; 24(9):625-627. DOI:10.1109/LMWC.2014.2330699 · 2.24 Impact Factor
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    ABSTRACT: This paper presents a convex optimization approach to study optimal realizations of passive electromagnetic structures. The optimization approach complements recently developed theory and techniques to derive sum rules and physical limitations for passive systems operating over a given bandwidth. The sum rules are based solely on the analytical properties of the corresponding Herglotz functions. However, the application of sum rules is limited by certain assumptions regarding the low- and high-frequency asymptotic behavior of the system, and the sum rules typically do not give much information towards an optimal realization of the passive system at hand. In contrast, the corresponding convex optimization problem is formulated to explicitly generate a Herglotz function as an optimal realization of the passive structure. The procedure does not require any additional assumptions on the low- and high frequency asymptotic behavior, but additional convex constraints can straightforwardly be incorporated in the formulation. Typical application areas are concerned with antennas, periodic structures, material responses, scattering, absorption, reflection, and extinction. In this paper, we consider three concrete examples regarding dispersion compensation for waveguides, passive metamaterials and passive radar absorbers.
    IEEE Transactions on Antennas and Propagation 09/2014; 62(9):4686-4694. DOI:10.1109/TAP.2014.2336694 · 2.46 Impact Factor
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    ABSTRACT: A readily mass-producible, flip-chip assembled, and slot-coupled III-V compound semiconductor dielectric resonator antenna operating in the millimeter-wave spectrum has been fabricated and characterized. The antenna has a 6.1% relative bandwidth, deduced from its 10 dB return loss over 58.8-62.5 GHz, located around the resonance at 60.5 GHz. Gating in the delay-domain alleviated the analysis of the complex response from the measured structure. The radiation efficiency is better than -0.1 dB in simulations fed from the on-chip coupling-structure, but reduced by 3.7 dB insertion loss through the measurement assembly feed. Antenna gain measurements show distortion in relation to the simulated pattern, which has a maximum gain of 6 dBi, mainly caused by interference from the electrically large connector used in the assembly. Mode degeneration in the utilized quadratic-footprint resonator was not seen to influence the performance of the antenna. The antenna is intended for on-chip integration and the fabrication technology allows scaling of the operation frequency over the complete millimeter-wave spectrum.
    IEEE Transactions on Antennas and Propagation 04/2013; 61(4):1599-1607. DOI:10.1109/TAP.2012.2237005 · 2.46 Impact Factor
  • D. Sjoberg, C. Larsson
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    ABSTRACT: We present a method aimed at reducing uncertainties and instabilities when characterizing materials in waveguide setups. The S-parameters for a rectangular waveguide loaded with a rectangular sample block are measured for three different sample orientations, and the corresponding geometries are modeled in a finite element program, taking any material parameters as input. The material parameters of the sample are found by minimizing the squared distance between measured and calculated S-parameters.
    Electromagnetic Theory (EMTS), Proceedings of 2013 URSI International Symposium on; 01/2013
  • D. Sjoberg, M. Gustafsson, R. Seviour
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    ABSTRACT: We give a physical bound on the product of bandwidth and attenuation per unit length for general electromagnetic band gap structures. The analysis is based on the Kramers-Kronig relations for the Bloch refractive index for a fixed direction of propagation through the crystal. The bound is given in terms of the low- and high-frequency asymptotes of the refractive index, which can be given simple estimates in terms of the volume fractions of the component materials and their static permittivities.
    Electromagnetics in Advanced Applications (ICEAA), 2013 International Conference on; 01/2013
  • D. Sjoberg
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    ABSTRACT: We investigate the scattering of plane waves from singly curved multilayer structures. It is shown by several examples that by normalizing the monostatic echo width by the corresponding echo width of a PEC cylinder with the same outer radius, a number close to the reflection coefficient for a planar design is obtained if the radius of curvature is about a wavelength or more. It is also shown that the polarization with the electric field parallel to the cylinder axis is less sensitive to curvature than the polarization with the magnetic field along the axis.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
  • Source
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    ABSTRACT: Based on energy conservation, an optical theorem is constructed for a slab having an arbitrary periodic microstructure in a plane. A sum rule for low pass structures is derived using analytic properties of Herglotz functions based on causality and passivity. The sum rule relates the total cross section to the static polarizability per unit cell, and quantifies the interaction between the slab and electromagnetic fields possible over all wavelengths. The results are illustrated with several numerical and experimental examples.
    IEEE Transactions on Antennas and Propagation 08/2012; 60(8):3818-3826. DOI:10.1109/TAP.2012.2201113 · 2.46 Impact Factor
  • I. Vakili, M. Gustafsson, D. Sjoberg
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    ABSTRACT: Forward scattering measurements of periodic meta-materials are investigated. A sum rule for forward scattering is derived using the optical theorem and analytic properties of Herglotz functions. It shows that the absorbed and scattered power over all wavelengths from a periodic metamaterial is related to the static polarizability per unit cell. The theoretical results are verified by a parallel plate waveguide measurement setup.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • Daniel Sjoberg, Christer Larsson
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    ABSTRACT: We compute the Cramér-Rao lower bounds for determination of isotropic permittivity and permeability in slabs using reflection and transmission data. The results apply to three common measurement situations: free space, rectangular waveguides, and coaxial waveguides. The bounds depend only on the available data and not on the actual inversion method used, making them suitable to evaluate a particular experimental setup. The results are illustrated with several measurements in a rectangular waveguide setting.
    IEEE Transactions on Microwave Theory and Techniques 11/2011; 59(11):2970-2977. DOI:10.1109/TMTT.2011.2166085 · 2.94 Impact Factor
  • Mats Gustafsson, Daniel Sjoberg
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    ABSTRACT: High-impedance surfaces are artificial surfaces synthesized from periodic structures. The high impedance is useful as it does not short circuit electric currents and reflects electric fields without phase shift. Here, a sum rule is presented that relates frequency intervals having high impedance with the thickness of the structure. The sum rule is used to derive physical bounds on the bandwidth for high-impedance surfaces composed by periodic structures above a perfectly conducting ground plane. Numerical examples are used to illustrate the result, and show that the physical bounds are tight.
    IEEE Transactions on Antennas and Propagation 07/2011; 59(6-59):2196 - 2204. DOI:10.1109/TAP.2011.2143688 · 2.46 Impact Factor
  • Christer Larsson, Daniel Sjoberg, Lisa Elmkvist
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    ABSTRACT: This paper describes a method to measure the per- mittivity and permeability at temperatures from room temper- ature up to 1000 ◦ C using a single rectangular waveguide. The hardware design of the setup that can handle these tempera- tures, and the procedure that is required to correct the thermal expansion is developed. This includes the sample displacement, the displacement of the calibration reference planes, the thermal expansion of the waveguide, and the gap between the sample and the waveguide wall. Measurements on Macor and NiZn ferrite samples are performed in order to evaluate the performance of the setup and the procedure that is used to determine the permittivity and permeability from the measured S-parameters.
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    ABSTRACT: This paper describes a parallel plate waveguide designed for scattering and material measurements. The experimental setup can for certain scatterers be considered as a two dimensional radar cross section range. Measurements on metallic circular cylinders of finite length are performed, and the forward radar cross section and the extinction cross section are determined. Two different calibration methods are used, and it is found that the method employing a calibration object is the most accurate. It is concluded that the two dimensional radar cross section in the forward direction can be measured with 1 dB accuracy at the level of 10 cm and the accuracy at the level of 1 cm is estimated to 3 dB.
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    Mats Gustafsson, Daniel Sjoberg
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    ABSTRACT: Metamaterial applications such as cloaking, perfect lenses, and articial permeability are restricted by the frequency dependence of the permittivity, permeability, and index of refraction. Here, causality and passivity together with integral identities for Herglotz functions are used to construct sum rules. The sum rules relate the frequency dependence of the material parameters with their high- and low-frequency values. The corresponding physical bounds determine the minimum variations of the material parameters over a frequency interval. The results are illustrated with a numerical example for articial permeability.
  • Christer Larsson, Daniel Sjoberg, Lisa Elmkvist
  • Johan C.-E. Sten, Daniel Sjoberg
    Progress In Electromagnetics Research B 01/2011; 35:187-212. DOI:10.2528/PIERB11090606
  • M. Gustafsson, D. Sjoberg
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    ABSTRACT: A relation between the radiation resistance and the quasi-static polarizability, input capacitance, and input induc- tance for small electric dipole antennas is investigated. The relation follows from the forward scattering sum rule and sum rules for the input impedance together with resonance models for the partial realized gain and the reflection coefficient. I. INTRODUCTION The antenna sum rules and associated physical bounds based on forward scattering (1, 2) and transmission line scattering (3) are here combined to construct a simple estimate of the radiation resistance at the resonance frequency. The relation is based on the assumption that the antenna has a dominating first resonance and acts as an open circuit in the low-frequency limit. Resonance models are used for the partial realized gain (1, 2) and the reflection coefficient (or equivalently the input impedance) (3). Assuming a narrow banded first resonance with negligible variation of the directivity lets us compare the Q-factors of the two cases. Both Q-factors are dominated by a cubic dependence on the resonance wavenumber, k0. Setting the two Q-factors equal cancels the dependence of k0 and re- veals an approximate relation between the radiation resistance evaluated at the resonance with the static polarizability, static capacity, and quasi-static inductance. The relation also contains the directivity,D, and the general- ized (all spectrum) absorption efficiency, . It is observed that these factors can be accurately approximated with D 3=2 and 1=2 for many small antennas (4). Although these estimates are valid for the antennas considered in this paper, it is important to realize that there exists antennas with other properties.
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    M. Gustafsson, D. Sjoberg, I. Vakili
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    ABSTRACT: Extraordinary transmission of electromagnetic power through sub-wavelength apertures is usually observed in a narrow bandwidth range and the transmission outside this range is low. In this paper, it is shown that the transmission through periodic apertures in an otherwise perfectly electric conducting sheet satis- fies a sum rule that relates wavelength regions with transmission above a threshold with the polarizability of the complementary structure. The theoretical results are illustrated with a numerical example for split ring apertures.
  • D. Sjoberg, Mats Gustafsson
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    ABSTRACT: A high surface impedance can be achieved in a limited frequency band by using composite structures. Based on the principles of causality, passivity, linearity, and time translational invariance we demonstrate that this bandwidth is bounded by the thickness and magnetic polarizability per unit area of the structure at normal incidence.
  • M. Gustafsson, D. Sjoberg
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    ABSTRACT: The frequency dependence of the permittivity, permeability, and index of refraction restrict metamaterial applications such as cloaking and perfect lenses. Here, the principles of causality and passivity together with identities for Herglotz functions are used to construct various sum rules. The sum rules relate the frequency dependence of the material parameters with their high- and low-frequency values. The corresponding physical bounds determine minimum variations of the material parameters over a frequency interval.