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Publications (10 of 63) Show all publications
Hassan, E., Berggren, M., Scheiner, B., Michler, F., Weigel, R. & Lurz, F. (2019). Design of Planar Microstrip-to-Waveguide Transitions Using Topology Optimization. In: 2019 IEEE Radio and Wireless Symposium (RWS), Orlando, USA, January 20-23, 2019: . Paper presented at 2019 IEEE Radio and Wireless Symposium (RWS). IEEE
Open this publication in new window or tab >>Design of Planar Microstrip-to-Waveguide Transitions Using Topology Optimization
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2019 (English)In: 2019 IEEE Radio and Wireless Symposium (RWS), Orlando, USA, January 20-23, 2019, IEEE, 2019, p. -3Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a topology optimization approach to design planar transitions between a microstrip line (MSL) and a rectangular waveguide (RWG) in the K-band. The transition comprises two sub-transitions: one from the MSL to a substrate integrated waveguide (SIW) and the second from the SIW to the RWG. Both are on the same substrate and can be manufactured with a standard printed circuit board process. This leads to a very costeffective solution compared with other approaches. A WR-42 waveguide can easily be surface mounted to the transitions using a standard flange. The transitions have been fabricated, and their measured performance shows good agreement with the simulations. The MSL-SIW transition has a broadband behavior and the SIW-RWG transition still reaches a relative bandwidth of 10%.

Place, publisher, year, edition, pages
IEEE, 2019
National Category
Communication Systems
Identifiers
urn:nbn:se:umu:diva-159568 (URN)10.1109/RWS.2019.8714566 (DOI)000470822000077 ()
Conference
2019 IEEE Radio and Wireless Symposium (RWS)
Funder
eSSENCE - An eScience Collaboration, 570015103
Available from: 2019-06-02 Created: 2019-06-02 Last updated: 2019-07-09Bibliographically approved
Bernland, A., Wadbro, E. & Berggren, M. (2019). SHAPE OPTIMIZATION OF A COMPRESSION DRIVER PHASE PLUG. SIAM Journal on Scientific Computing, 41(1), B181-B204
Open this publication in new window or tab >>SHAPE OPTIMIZATION OF A COMPRESSION DRIVER PHASE PLUG
2019 (English)In: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 41, no 1, p. B181-B204Article in journal (Refereed) Published
Abstract [en]

A compression driver is an electro-acoustic transducer with considerably higher efficiency than direct radiating loudspeakers, thanks to the increased radiation resistance caused by a large vibrating diaphragm placed in a compression chamber with small openings. The transition section between compression chamber and output waveguide, the phase plug, must be carefully designed to avoid irregularities in the output sound pressure level (SPL) as a function of frequency. Here we present a shape optimization method based on an implicit level-set description and adjoint sensitivity analysis, which enables a large number of design parameters and vast design freedom. The CutFEM approach, a fictitious domain finite element method, removes the need for mesh updates and makes the method robust and computationally inexpensive. Numerical experiments for a generic annular diaphragm compression driver are presented, with optimized designs showing only minor frequency irregularities. Two different objective functions are considered: one for maximum SPL and one where the SPL is fitted to that of a hypothetical ideal design; the latter approach is found to be more effective in reducing irregularities. Visco-thermal boundary-layer losses are included in a post-processing step, and, though the influence of losses is clearly noticeable, the overall performance is similar and the optimized designs still outperform the original design.

Place, publisher, year, edition, pages
SIAM PUBLICATIONS, 2019
Keywords
shape optimization; level set, CutFEM, Helmholtz equation, electro-acoustic transducer
National Category
Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-157539 (URN)10.1137/18M1175768 (DOI)000460118500035 ()
Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-03-26Bibliographically approved
Berggren, M., Bernland, A. & Noreland, D. (2018). Acoustic boundary layers as boundary conditions. Journal of Computational Physics, 371, 633-650
Open this publication in new window or tab >>Acoustic boundary layers as boundary conditions
2018 (English)In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 371, p. 633-650Article in journal (Refereed) Published
Abstract [en]

The linearized, compressible Navier-Stokes equations can be used to model acoustic wave propagation in the presence of viscous and thermal boundary layers. However, acoustic boundary layers are notorious for invoking prohibitively high resolution requirements on numerical solutions of the equations. We derive and present a strategy for how viscous and thermal boundary-layer effects can be represented as a boundary condition on the standard Helmholtz equation for the acoustic pressure. This boundary condition constitutes an O (delta) perturbation, where delta is the boundary-layer thickness, of the vanishing Neumann condition for the acoustic pressure associated with a lossless sound-hard wall. The approximate model is valid when the wavelength and the minimum radius of curvature of the wall is much larger than the boundary layer thickness. In the special case of sound propagation in a cylindrical duct, the model collapses to the classical Kirchhoff solution. We assess the model in the case of sound propagation through a compression driver, a kind of transducer that is commonly used to feed horn loudspeakers. Due to the presence of shallow chambers and thin slits in the device, it is crucial to include modeling of visco-thermal losses in the acoustic analysis. The transmitted power spectrum through the device calculated numerically using our model agrees well with computations using a hybrid model, where the full linearized, compressible Navier-Stokes equations are solved in the narrow regions of the device and the inviscid Helmholtz equations elsewhere. However, our model needs about two orders of magnitude less memory and computational time than the more complete model. 

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Acoustics, Visco-thermal boundary layers, Helmholtz equation, Wentzell boundary condition, Compression driver
National Category
Fluid Mechanics and Acoustics Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-150643 (URN)10.1016/j.jcp.2018.06.005 (DOI)000438393900031 ()2-s2.0-85048401964 (Scopus ID)
Funder
Swedish Research Council, 621-2013-3706Swedish Foundation for Strategic Research , AM13-0029
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2018-08-31Bibliographically approved
Bernland, A., Wadbro, E. & Berggren, M. (2018). Acoustic shape optimization using cut finite elements. International Journal for Numerical Methods in Engineering, 113(3), 432-449
Open this publication in new window or tab >>Acoustic shape optimization using cut finite elements
2018 (English)In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 113, no 3, p. 432-449Article in journal (Refereed) Published
Abstract [en]

Fictitious domain methods are attractive for shape optimization applications, since they do not require deformed or regenerated meshes. A recently developed such method is the CutFEM approach, which allows crisp boundary representations and for which uniformly well-conditioned system matrices can be guaranteed. Here, we investigate the use of the CutFEM approach for acoustic shape optimization, using as test problem the design of an acoustic horn for favorable impedance-matching properties. The CutFEM approach is used to solve the Helmholtz equation, and the geometry of the horn is implicitly described by a level-set function. To promote smooth algorithmic updates of the geometry, we propose to use the nodal values of the Laplacian of the level-set function as design variables. This strategy also improves the algorithm's convergence rate, counteracts mesh dependence, and, in combination with Tikhonov regularization, controls small details in the optimized designs. An advantage with the proposed method is that the exact derivatives of the discrete objective function can be expressed as boundary integrals, as opposed to when using a traditional method that uses mesh deformations. The resulting horns possess excellent impedance-matching properties and exhibit surprising subwavelength structures, not previously seen, which are possible to capture due to the fixed mesh approach.

Place, publisher, year, edition, pages
Hoboken: John Wiley & Sons, 2018
Keywords
shape optimization, level set, CutFEM, sensitivity analysis, acoustic horn, Helmholtz equation
National Category
Computational Mathematics Computer Sciences
Identifiers
urn:nbn:se:umu:diva-143623 (URN)10.1002/nme.5621 (DOI)000418346200004 ()
Funder
Swedish Research Council, 621-2013-3706Swedish Foundation for Strategic Research , AM13-0029
Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-06-09Bibliographically approved
Badariah Asan, N., Hassan, E., Velander, J., Redzwan Mohd Shah, S., Noreland, D., Blokhuis, T. J., . . . Augustine, R. (2018). Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies. Sensors, 18(9), Article ID 2752.
Open this publication in new window or tab >>Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies
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2018 (English)In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 18, no 9, article id 2752Article in journal (Refereed) Published
Abstract [en]

In this paper, we investigate the use of fat tissue as a communication channel between in-body, implanted devices at R-band frequencies (1.7–2.6 GHz). The proposed fat channel is based on an anatomical model of the human body. We propose a novel probe that is optimized to efficiently radiate the R-band frequencies into the fat tissue. We use our probe to evaluate the path loss of the fat channel by studying the channel transmission coefficient over the R-band frequencies. We conduct extensive simulation studies and validate our results by experimentation on phantom and ex-vivo porcine tissue, with good agreement between simulations and experiments. We demonstrate a performance comparison between the fat channel and similar waveguide structures. Our characterization of the fat channel reveals propagation path loss of ∼0.7 dB and ∼1.9 dB per cm for phantom and ex-vivo porcine tissue, respectively. These results demonstrate that fat tissue can be used as a communication channel for high data rate intra-body networks.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
intra-body communication, path loss, microwave probes, channel characterization, fat tissue, ex-vivo, phantom, dielectric properties, topology optimization
National Category
Communication Systems Computer Sciences Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:umu:diva-150977 (URN)10.3390/s18092752 (DOI)000446940600011 ()30134629 (PubMedID)2-s2.0-85052218591 (Scopus ID)
Funder
eSSENCE - An eScience Collaboration, 5700-15103VINNOVA, 2015-04159Swedish Foundation for Strategic Research , RIT17-0020
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-12-13Bibliographically approved
Hassan, E., Wadbro, E., Hägg, L. & Berggren, M. (2018). Topology optimization of compact wideband coaxial-to-waveguide transitions with minimum-size control. Structural and multidisciplinary optimization (Print), 57(4), 1765-1777
Open this publication in new window or tab >>Topology optimization of compact wideband coaxial-to-waveguide transitions with minimum-size control
2018 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 57, no 4, p. 1765-1777Article in journal (Refereed) Published
Abstract [en]

This paper presents a density-based topology optimization approach to design compact wideband coaxial-to-waveguide transitions. The underlying optimization problem shows a strong self penalization towards binary solutions, which entails mesh-dependent designs that generally exhibit poor performance. To address the self penalization issue, we develop a filtering approach that consists of two phases. The first phase aims to relax the self penalization by using a sequence of linear filters. The second phase relies on nonlinear filters and aims to obtain binary solutions and to impose minimum-size control on the final design. We present results for optimizing compact transitions between a 50-Ohm coaxial cable and a standard WR90 waveguide operating in the X-band (8-12 GHz).

Place, publisher, year, edition, pages
New York: Springer, 2018
Keywords
Maxwell's equations, sensitivity analysis, optimization, waveguide
National Category
Communication Systems Computer Sciences
Identifiers
urn:nbn:se:umu:diva-146663 (URN)10.1007/s00158-017-1844-8 (DOI)000430101600022 ()
Available from: 2018-04-16 Created: 2018-04-16 Last updated: 2018-06-09Bibliographically approved
Saglietti, C., Schlatter, P., Wadbro, E., Berggren, M. & Henningson, D. (2018). Topology optimization of heat sinks in a square differentially heated cavity. International Journal of Heat and Fluid Flow, 74, 36-52
Open this publication in new window or tab >>Topology optimization of heat sinks in a square differentially heated cavity
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2018 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 74, p. 36-52Article in journal (Refereed) Published
Abstract [en]

Innovative designs of heat sinks are generated in the present paper through numerical optimization, by applying a material distribution topology optimization approach. The potential of the method is demonstrated in a two-dimensional differentially heated cavity, in which the heat transfer is increased by means of introducing a solid structure that acts as a heat sink. We simulate the heat transfer in the whole system by performing direct numerical simulations of the conjugated problem, i.e. temperature diffusion and convection in the entire domain and momentum conservation in the fluid surrounding the solid. The flow is driven by the buoyancy force, under the Boussinesq approximation, and we describe the presence of solid material as the action of a Brinkman friction force in the Navier–Stokes equations. To obtain a design with a given length scale, we apply regularization techniques by filtering the material distribution. Two different types of filters are applied and compared for obtaining the most realistic solution. Given the large scale of the problem, the optimization is solved with a gradient based method that relies on adjoint sensitivity analysis. The results show the applicability of the method by presenting innovative geometries that are increasing the heat flux. Moreover, the effect of various factors is studied: We investigate the impact of boundary conditions, initial designs, and Rayleigh number. Complex tree-like structures are favored when a horizontal temperature gradient is imposed on the boundary and when we limit the amount of solid volume in the cavity. The choice of the initial design affects the final topology of the generated solid structures, but not their performance for the studied cases. Additionally, when the Rayleigh number increases, the topology of the heat exchanger is able to substantially enhance the convection contribution to the heat transfer.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Topology optimization, Natural convection, Heat sink, Conjugate heat transfer, Differentially heated cavity, Direct numerical simulations
National Category
Fluid Mechanics and Acoustics Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-152105 (URN)10.1016/j.ijheatfluidflow.2018.08.004 (DOI)000454372000004 ()
Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2019-01-14Bibliographically approved
Yedeg, E. L., Wadbro, E. & Berggren, M. (2017). Layout optimization of thin sound-hard material to improve the far-field directivity properties of an acoustic horn. Structural and multidisciplinary optimization (Print), 55(3), 795-808
Open this publication in new window or tab >>Layout optimization of thin sound-hard material to improve the far-field directivity properties of an acoustic horn
2017 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, no 3, p. 795-808Article in journal (Refereed) Published
Abstract [en]

To improve the far-field directivity properties of a given mid-range acoustic horn, previously designed by shape optimization to exhibit almost ideal transmission properties in the frequency range 1.6–9.05 kHz, we apply layout optimization of thin sound-hard material in the interior of the horn. The purpose of the optimization is to place scattering material to prevent the sound intensity to increasingly be concentrated, with increasing frequency, along the horn axis. Absence or presence of thin sound-hard material is modeled by an equivalent surface transmission impedance, and the optimization algorithm determines the distribution of air or sound-hard material along a “ground structure” in the form of a grid inside the horn. The surface impedance is numerically handled using a newly developed finite-element formulation that allows exact enforcement of a vanishing impedance, corresponding to air, which would not be possible using a standard formulation. Horns provided with the optimized scatterers show a much improved angular coverage, compared to the initial configuration, with beam widths that exceed 60 ∘ uniformly over the operational frequency range, without destroying the good transmission properties of the initial horn.

Keywords
Layout optimization, Helmholtz equation, Thin structures, Interface problem, Acoustic impedance
National Category
Computer Systems
Identifiers
urn:nbn:se:umu:diva-119973 (URN)10.1007/s00158-016-1536-9 (DOI)000398114200004 ()
Funder
Swedish Research Council, 621-2013-3706
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2018-06-07Bibliographically approved
Hassan, E., Noreland, D., Wadbro, E. & Berggren, M. (2017). Topology Optimisation of Wideband Coaxial-to-Waveguide Transitions. Scientific Reports, 7, Article ID 45110.
Open this publication in new window or tab >>Topology Optimisation of Wideband Coaxial-to-Waveguide Transitions
2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 45110Article in journal (Refereed) Published
Abstract [en]

To maximize the matching between a coaxial cable and rectangular waveguides, we present a computational topology optimisation approach that decides for each point in a given domain whether to hold a good conductor or a good dielectric. The conductivity is determined by a gradient-based optimisation method that relies on finite-difference time-domain solutions to the 3D Maxwell’s equations. Unlike previously reported results in the literature for this kind of problems, our design algorithm can efficiently handle tens of thousands of design variables that can allow novel conceptual waveguide designs. We demonstrate the effectiveness of the approach by presenting optimised transitions with reflection coefficients lower than −15dB over more than a 60% bandwidth, both for right-angle and end-launcher configurations. The performance of the proposed transitions is crossverified with a commercial software, and one design case is validated experimentally.

Keywords
topology optimization, finite-difference time- domain (FDTD), adjoint-field problem, waveguides, coaxial cable, transitions design, end-launcher.
National Category
Computer Sciences
Identifiers
urn:nbn:se:umu:diva-102577 (URN)10.1038/srep45110 (DOI)000397137700001 ()
Funder
Swedish Research Council, 621-2013-3706
Available from: 2015-04-28 Created: 2015-04-28 Last updated: 2018-06-07Bibliographically approved
Yedeg, E. L., Wadbro, E., Hansbo, P., Larson, M. G. & Berggren, M. (2016). A Nitsche-type Method for Helmholtz Equation with an Embedded Acoustically Permeable Interface. Computer Methods in Applied Mechanics and Engineering, 304, 479-500
Open this publication in new window or tab >>A Nitsche-type Method for Helmholtz Equation with an Embedded Acoustically Permeable Interface
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2016 (English)In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 304, p. 479-500Article in journal (Refereed) Published
Abstract [en]

We propose a new finite element method for Helmholtz equation in the situation where an acoustically permeable interface is embedded in the computational domain. A variant of Nitsche's method, different from the standard one, weakly enforces the impedance conditions for transmission through the interface. As opposed to a standard finite-element discretization of the problem, our method seamlessly handles a complex-valued impedance function Z that is allowed to vanish. In the case of a vanishing impedance, the proposed method reduces to the classic Nitsche method to weakly enforce continuity over the interface. We show stability of the method, in terms of a discrete Gårding inequality, for a quite general class of surface impedance functions, provided that possible surface waves are sufficiently resolved by the mesh. Moreover, we prove an a priori error estimate under the assumption that the absolute value of the impedance is bounded away from zero almost everywhere. Numerical experiments illustrate the performance of the method for a number of test cases in 2D and 3D with different interface conditions. 

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Helmholtz equation, Finite Element method, Nitsche's method, interface problem, surface wave, Gårding inequality
National Category
Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-119977 (URN)10.1016/j.cma.2016.02.032 (DOI)000374506600020 ()
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2018-06-07Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0473-3263

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