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Hjelm, Mats
Publications (10 of 38) Show all publications
Geterud, E., Hjelm, M., Ciamulski, T. & Sypniewski, M. (2009). Simulation of a lens antenna using a parallelized version of an FDTD simulator. In: European Conference on Antennas and Propagation, EuCAP 2009, Proceedings. Paper presented at 3rd European Conference on Antennas and Propagation, EuCAP 2009; Berlin; 23 March 2009 through 27 March 2009 (pp. 3457-3461). IEEE conference proceedings
Open this publication in new window or tab >>Simulation of a lens antenna using a parallelized version of an FDTD simulator
2009 (English)In: European Conference on Antennas and Propagation, EuCAP 2009, Proceedings, IEEE conference proceedings, 2009, p. 3457-3461Conference paper, Published paper (Refereed)
Abstract [en]

This article is evaluating parallel processing in electromagnetic simulations for computationally demanding application, using developed FDTD code. A waveguide lens antenna which is complex and large in terms of wavelengths has been simulated and a prototype has been fabricated and measured. Simulated and measured radiation patterns are compared and showing good agreement. The approach of using parallel version of QuickWave-3D software on a popular multi-CPU shared-memory computer has been found suitable for demanding simulations of complex structures.

 

 

Place, publisher, year, edition, pages
IEEE conference proceedings, 2009
Keywords
Electromagnetic analysis; FDTD methods; Lens antennas; Parallel processing; Simulation; Waveguide arrays
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-11832 (URN)2-s2.0-70349852695 (Scopus ID)978-300024573-2 (ISBN)
Conference
3rd European Conference on Antennas and Propagation, EuCAP 2009; Berlin; 23 March 2009 through 27 March 2009
Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2013-03-22Bibliographically approved
Rahmani, R., Åhlund, C. & Hjelm, M. (2008). Active Queue Management for TCP Friendly Rate Control Traffic in Heterogeneous Networks. In: 2008 International Conference on Telecommunications, ICT: . Paper presented at 2008 International Conference on Telecommunications, ICT; St. Petersburg; Russian Federation; 16 June 2008 through 19 June 2008; Category number08EX2191; Code 77440. New York: IEEE conference proceedings, Article ID 4652662.
Open this publication in new window or tab >>Active Queue Management for TCP Friendly Rate Control Traffic in Heterogeneous Networks
2008 (English)In: 2008 International Conference on Telecommunications, ICT, New York: IEEE conference proceedings, 2008, article id 4652662Conference paper, Published paper (Refereed)
Abstract [en]

This paper studied the performance of the small-packet variant of the TCP Friendly Rate Control protocol in heterogeneous networks. The objective is to maximize system utilization, often called goodput, while maintaining fairness between the nodes. We show that by selecting the right queue size policy, it can be ensured that the bandwidth is fully utilized at a steady state. Additionally, we show that the judicious use of such a policy is beneficial for heterogeneous networks with high packet drop rates.

Place, publisher, year, edition, pages
New York: IEEE conference proceedings, 2008
Keywords
AQM, TFRC & DCCP
National Category
Computer Sciences
Identifiers
urn:nbn:se:miun:diva-4033 (URN)10.1109/ICTEL.2008.4652662 (DOI)000262437800052 ()2-s2.0-67650218233 (Scopus ID)4961 (Local ID)978-1-4244-2035-3 (ISBN)4961 (Archive number)4961 (OAI)
Conference
2008 International Conference on Telecommunications, ICT; St. Petersburg; Russian Federation; 16 June 2008 through 19 June 2008; Category number08EX2191; Code 77440
Available from: 2008-09-30 Created: 2009-07-24 Last updated: 2018-01-12Bibliographically approved
Olsson, T., Hjelm, M., Sidén, J. & Nilsson, H.-E. (2007). Comparative robustness study of planar antennas. IET Microwaves, Antennas & Propagation, 1(3), 674-680
Open this publication in new window or tab >>Comparative robustness study of planar antennas
2007 (English)In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 1, no 3, p. 674-680Article in journal (Refereed) Published
Abstract [en]

Is it possible to produce a planar dipole-like antenna with a reduced conductive area without any loss in either robustness or performance? The objective is to reduce the amount of expensive conductor to be used when applying a meshing technique to the printing of antennas. In this context, robustness means that the characteristics are maintained when the antenna is damaged, for example if it is scratched. This is particularly important for radio frequency identification tags in logistic systems. A general antenna robustness evaluation methodology, based on numerical simulations of a large number of randomly damaged antennas, is used for the antenna comparisons. The antenna performance degradation, based on the return loss (S11) at 868MHz, is monitored for some basic planar antennas. Finally, we show that it is possible to produce robust low-cost antennas using wire replacements for the solid planar antennas and thus, provided that the robustness requirement is moderate, replace the solid antenna with a thin conductor analogue.

Keywords
Antennas, robustness, RFID
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3630 (URN)10.1049/iet-map:20060155 (DOI)000247853300021 ()2-s2.0-34249880500 (Scopus ID)4191 (Local ID)4191 (Archive number)4191 (OAI)
Projects
STC - Sensible Things that Communicate
Note

VR-

Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
Hjelm, M., Martinez, A., Nilsson, H.-E. & Lindefelt, U. (2007). Interband tunneling description of holes in Wurtzite GaN at high electric fields. Journal of Computational Electronics, 6(1-3), 163-166
Open this publication in new window or tab >>Interband tunneling description of holes in Wurtzite GaN at high electric fields
2007 (English)In: Journal of Computational Electronics, ISSN 1569-8025, E-ISSN 1572-8137, Vol. 6, no 1-3, p. 163-166Article in journal (Refereed) Published
Abstract [en]

We have studied the time evolution of an ensemble of holes in Wurtzite GaN under the effect of a high electric field. The density matrix equation used as a foundation in the study includes band-to-band tunneling, but disregards collisions. In the description of the ensemble dynamics the full band structure is used. The average energy and group velocity for the ensemble is calculated, as well as velocity components corresponding to the non-diagonal elements of the velocity operator (interference). The calculations have been carried out for the electric field strengths 0.4 and 4 MV/cm. A comparison is presented of the results with and without inclusion of band tunneling in the ensemble dynamics. There is also a comparison of the velocity with and without the non-diagonal elements of the velocity operator terms. A conclusion is that Monte Carlo simulations considering band tunneling, but not interference, can give accurate results.

Keywords
band-to-band tunneling, density matrix, GaN, high-field simulation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-4224 (URN)10.1007/s10825-006-0081-y (DOI)000208473600039 ()2-s2.0-34247381937 (Scopus ID)4956 (Local ID)4956 (Archive number)4956 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
Ciamulski, T., Hjelm, M. & Sypniewski, M. (2007). Parallel FDTD calculation efficiency on computers with shared memory architecture. In: 2007 WORKSHOP ON COMPUTATIONAL ELECTROMAGNETICS IN TIME-DOMAIN: . Paper presented at Workshop on Computational Electromagnetics in Time-Domain, oct 15-17, 2007, Perugia, Italy (pp. 33-36). New York: IEEE conference proceedings
Open this publication in new window or tab >>Parallel FDTD calculation efficiency on computers with shared memory architecture
2007 (English)In: 2007 WORKSHOP ON COMPUTATIONAL ELECTROMAGNETICS IN TIME-DOMAIN, New York: IEEE conference proceedings, 2007, p. 33-36Conference paper, Published paper (Refereed)
Abstract [en]

Fast parallel processing of the FDTD method is becoming very important, and its efficiency on different multiprocessor computer architectures should be carefully examined. Is it possible to have the same versatile parallel FDTD simulator working efficiently on a set of very different computer architectures? In contrast to distributed memory systems, shared memory systems can be built with a variety of memory configuration types (and subtypes) as well as combined with distributed memory systems. The paper focuses on viability of different shared memory architectures for parallel FDTD processing. Our analysis concerns the processing method suitable for both shared and distributed memory systems. The results of experiments comparing parallel processing efficiency on different shared memory machines are presented.

Place, publisher, year, edition, pages
New York: IEEE conference proceedings, 2007
Keywords
electromagnetic analysis; FDTD methods; parallel algorithms; parallel processing; shared memory systems; distributed memory systems
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-11851 (URN)000253089600009 ()2-s2.0-50249120597 (Scopus ID)978-1-4244-1169-6 (ISBN)
Conference
Workshop on Computational Electromagnetics in Time-Domain, oct 15-17, 2007, Perugia, Italy
Available from: 2010-07-14 Created: 2010-07-14 Last updated: 2017-10-18Bibliographically approved
Ciamulski, T., Sypniewski, M., Wieckowski, A., Hjelm, M. & Nilsson, H.-E. (2007). Parallel FDTD Processing on Shared Memory Computers. In: The 23rd annual review of Progress in Applied computational electromagnetics: March 19-23, 2007 Verona, Italy.
Open this publication in new window or tab >>Parallel FDTD Processing on Shared Memory Computers
Show others...
2007 (English)In: The 23rd annual review of Progress in Applied computational electromagnetics: March 19-23, 2007 Verona, Italy, 2007Conference paper, Published paper (Other academic)
Abstract [en]

An ongoing European project on customization of electromagnetic simulation tool is ready to present significantly improved performance of parallel version of a professional FDTD simulator. The first stage of the work is concentrated on solution for computers with the shared memory architecture. The relevance and feasibility study of the solution for contemporary computers is shown. Possible ways to reach further performance improvements as well as solutions for distributed memory machines are discussed.

Keywords
Parallell computing, FDTD, EM simulation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-4097 (URN)4671 (Local ID)4671 (Archive number)4671 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2016-10-05Bibliographically approved
Olsson, T., Sidén, J., Hjelm, M. & Nilsson, H.-E. (2007). Robustness of printed patch antenna. IEEE Transactions on Antennas and Propagation, 55(10), 2709-2717
Open this publication in new window or tab >>Robustness of printed patch antenna
2007 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 55, no 10, p. 2709-2717Article in journal (Refereed) Published
Abstract [en]

We address the question of robustness of damaged microstrip antennas, the damage being either penetrating, caused by fragment impact, or floating, caused by manufacturing imperfections. A simple analytic expression is derived to facilitate the prediction of robustness. To verify this expression a Monte Carlo method, based on a general 3D electromagnetic solver, is used to evaluate the robustness of the antennas. The simulations are verified by measurements and supplementary simulations in an alternative electromagnetic solver, using the finite difference time domain method (FDTD). The agreement between the simulated results and the analytic expression is found to be good in a qualitative comparison.

Keywords
Antennas
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-3631 (URN)10.1109/TAP.2007.905950 (DOI)000250178500009 ()2-s2.0-35348842141 (Scopus ID)4192 (Local ID)4192 (Archive number)4192 (OAI)
Projects
STC - Sensible Things that Communicate
Note

VR-Materials Science

Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
Ciamulski, T., Hjelm, M. & Sypniewski, M. (2006). Custumisation of FDTD simulator kernel for parallel computing in advanced applications. In: ICSES'06 - International Conference on Signals and Electronic Systems, Proceedings: . Paper presented at International Conference on Signals and Electronic Systems, ICSES'06; Lodz; Poland; 17 September 2006 through 20 September 2006; Code 74996 (pp. 649-652).
Open this publication in new window or tab >>Custumisation of FDTD simulator kernel for parallel computing in advanced applications
2006 (English)In: ICSES'06 - International Conference on Signals and Electronic Systems, Proceedings, 2006, p. 649-652Conference paper, Published paper (Other academic)
Abstract [en]

A commercial FDTD simulation software is the basis of an ongoing parallelization project. In the first phase of the project the work is aiming at optimization of the program on shared memory computers. In this paper we present the initial methods of parallelization with the achieved performance on a Sun Fire 15K NUMA computer. The achieved results are discussed, together with the possible paths to improve the speedup.

Keywords
FDTD
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-4222 (URN)2-s2.0-58449112985 (Scopus ID)4954 (Local ID)8392117263 (ISBN)978-839211726-1 (ISBN)4954 (Archive number)4954 (OAI)
Conference
International Conference on Signals and Electronic Systems, ICSES'06; Lodz; Poland; 17 September 2006 through 20 September 2006; Code 74996
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2016-09-26Bibliographically approved
Hjelm, M., Nilsson, H.-E. & Martinez, A. (2005). Critical evaluation of scattering models within the full band Monte Carlo simulation framework. In: Recent Advances in Multidisciplinary Applied Physics: . Paper presented at APHYS 2003 (pp. 305-311).
Open this publication in new window or tab >>Critical evaluation of scattering models within the full band Monte Carlo simulation framework
2005 (English)In: Recent Advances in Multidisciplinary Applied Physics, 2005, p. 305-311Conference paper, Published paper (Other academic)
Abstract [en]

The full band Monte Carlo (MC) simulation framework is regarded as the most accurate method available to study high-field carrier transport in semiconductors. Its potential has been demonstrated in a large number of studies over the years. In this work we focus on how the quantum mechanical uncertainty at high scattering rates affects the validity Fermi's Golden Rule, which traditionally is the basis for the scattering handling in the MC method. Considering the uncertainty is important in for instance silicon carbide, which at moderate energies exhibits a scattering rate exceeding 1014 s-1. The expression for time-dependent scattering rate is presented together with calculated rates for some initial states with acoustic as well as polar-optical phonon interaction. A first-order time-dependent algorithm for handling of scattering events in MC simulators is proposed.

Keywords
Monte Carlo simulation, Fermi's Golden rule, time-dependent scattering rate
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Natural Sciences
Identifiers
urn:nbn:se:miun:diva-2886 (URN)10.1016/B978-008044648-6.50051-3 (DOI)2-s2.0-84884828254 (Scopus ID)2540 (Local ID)978-008044648-6 (ISBN)2540 (Archive number)2540 (OAI)
Conference
APHYS 2003
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2016-10-05Bibliographically approved
Lindefelt, U., Nilsson, H.-E. & Hjelm, M. (2004). Choice of wavefunction phases in the equations for electric-field-induced interband transitions. Semiconductor Science and Technology, 19(8), 1061-1066
Open this publication in new window or tab >>Choice of wavefunction phases in the equations for electric-field-induced interband transitions
2004 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 19, no 8, p. 1061-1066Article in journal (Refereed) Published
Abstract [en]

A set of equations for calculating the probability for electric-field-induced interband transitions in periodic crystals (Krieger and Iafrate 1986 Phys. Rev. B 33 5494) can be used in combination with the full band Monte Carlo method to study high-field electronic transport properties in semiconductors. However, when the equations are applied to realistic cases in which the underlying band structure is obtained from numerical band structure programmes, the equations are not directly solvable because of the indeterminacy of the phases of the band structure Bloch wavefunctions. Here we discuss this problem and present a method for choosing the phases of the Bloch functions in such a way that the equations yield physically correct interband transition probabilities.

Keywords
High-field transport
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-2836 (URN)10.1088/0268-1242/19/8/018 (DOI)000224975600021 ()2-s2.0-4043098243 (Scopus ID)2505 (Local ID)2505 (Archive number)2505 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2017-12-12Bibliographically approved
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