lnu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 125) Show all publications
Nordebo, S., Kristensson, G., Mirmoosa, M. & Tretyakov, S. (2019). Optimal plasmonic multipole resonances of a sphere in lossy media. Physical Review B, 99(5), Article ID 054301.
Open this publication in new window or tab >>Optimal plasmonic multipole resonances of a sphere in lossy media
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 5, article id 054301Article in journal (Refereed) Published
Abstract [en]

Fundamental upper bounds are given for the plasmonic multipole absorption and scattering of a rotationally invariant dielectric sphere embedded in a lossy surrounding medium. A specialized Mie theory is developed for this purpose and when combined with the corresponding generalized optical theorem, an optimization problem is obtained which is explicitly solved by straightforward analysis. In particular, the absorption cross section is a concave quadratic form in the related Mie (scattering) parameters and the convex scattering cross section can be maximized by using a Lagrange multiplier constraining the absorption to be non-negative. For the homogeneous sphere, the Weierstrass preparation theorem is used to establish the existence and the uniqueness of the plasmonic singularities and explicit asymptotic expressions are given for the dipole and the quadrupole. It is shown that the optimal passive material for multipole absorption and scattering of a small homogeneous dielectric sphere embedded in a dispersive medium is given approximately as the complex conjugate and the real part of the corresponding pole positions, respectively. Numerical examples are given to illustrate the theory, including a comparison with the plasmonic dipole and quadrupole resonances obtained in gold, silver, and aluminum nanospheres based on some specific Brendel-Bormann (BB) dielectric models for these metals. Based on these BB models, it is interesting to note that the metal spheres can be tuned to optimal absorption at a particular size at a particular frequency.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Condensed Matter Physics
Research subject
Physics, Condensed Matter Physics
Identifiers
urn:nbn:se:lnu:diva-80776 (URN)10.1103/PhysRevB.99.054301 (DOI)000457729700001 ()
Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-02-22Bibliographically approved
Nordebo, S., Dalarsson, M., Khodadad, D., Müller, B., Waldermann, A. D., Becher, T., . . . Bayford, R. (2018). A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing. Journal of Physics D: Applied Physics, 51(20), Article ID 205401.
Open this publication in new window or tab >>A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing
Show others...
2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 20, article id 205401Article in journal (Refereed) Published
Abstract [en]

Classical homogenization theory based on the Hashin–Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples based on realistic parameter values and frequency ranges used with electrical impedance tomography (EIT). The theory may be potentially useful for imaging and clinical evaluations in connection with lung EIT for respiratory management and control.

National Category
Medical Image Processing
Research subject
Natural Science, Medicine
Identifiers
urn:nbn:se:lnu:diva-74401 (URN)10.1088/1361-6463/aabc04 (DOI)
Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-09-10Bibliographically approved
Nordebo, S., Gustafsson, M., Ivanenko, Y., Nilsson, B. & Sjöberg, D. (2018). Cylindrical multipole expansion for periodic sources with applications for three-phase power cables. Mathematical methods in the applied sciences, 41(3), 959-965
Open this publication in new window or tab >>Cylindrical multipole expansion for periodic sources with applications for three-phase power cables
Show others...
2018 (English)In: Mathematical methods in the applied sciences, ISSN 0170-4214, E-ISSN 1099-1476, Vol. 41, no 3, p. 959-965Article in journal (Refereed) Published
Abstract [en]

This paper presents a c ylindrical multipole expansion for periodic sources with applications for three-phase power cables.It is the aim of the contribution to provide some analytical solutions and techniques that can be useful in the calculation ofcable losses. Explicit analytical results are given for the fields generated by a three-phase helical current distribution andwhich can be computed efficiently as an input to other numerical methods such as, for example , the Method of Moments.It is shown that the field computations are numerically stable at low frequencies (such as 50 Hz) as well as in the quasi-magnetostatic limit provided that sources are divergence-free. The cylindrical multipole expansion is fur thermore usedto derive an efficient analytical model of a measurement coil to measure and estimate the complex valued permeability ofmagnetic steel armour in the presence of a strong skin-effect.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Signal Processing
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-59497 (URN)10.1002/mma.3992 (DOI)000425834700011 ()
Available from: 2016-12-23 Created: 2016-12-23 Last updated: 2018-03-09Bibliographically approved
Khodadad, D., Nordebo, S., Mueller, B., Waldmann, A. D., Yerworth, R., Becher, T., . . . Bayford, R. H. (2018). Optimized breath detection algorithm in electrical impedance tomography. Physiological Measurement, 39(9), Article ID 094001.
Open this publication in new window or tab >>Optimized breath detection algorithm in electrical impedance tomography
Show others...
2018 (English)In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 39, no 9, article id 094001Article in journal (Refereed) Published
Abstract [en]

Objective: This paper defines a method for optimizing the breath delineation algorithms used in Electrical Impedance Tomography (EIT). In lung EIT the identification of the breath phases is central for generating tidal impedance variation images, subsequent data analysis and clinical evaluation. The optimisation of these algorithms is particularly important in neonatal care since the existing breath detectors developed for adults may give insufficient reliability in neonates due to their very irregular breathing pattern. Approach: Our approach is generic in the sense that it relies on the definition of a gold standard and the associated definition of detector sensitivity and specificity, an optimisation criterion and a set of detector parameters to be investigated. The gold standard has been defined by 11 clinicians with previous experience with EIT and the performance of our approach is described and validated using a neonatal EIT dataset acquired within the EU-funded CRADL project. Main results: Three different algorithms are proposed that are improving the breath detector performance by adding conditions on 1) maximum tidal breath rate obtained from zero-crossings of the EIT breathing signal, 2) minimum tidal impedance amplitude and 3) minimum tidal breath rate obtained from Time-Frequency (TF) analysis. As a baseline the zero crossing algorithm has been used with some default parameters based on the Swisstom EIT device. Significance: Based on the gold standard, the most crucial parameters of the proposed algorithms are optimised by using a simple exhaustive search and a weighted metric defined in connection with the Receiver Operating Characterics (ROC). This provides a practical way to achieve any desirable trade-off between the sensitivity and the specificity of the detectors.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
National Category
Medical Engineering Medical Equipment Engineering
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-77552 (URN)10.1088/1361-6579/aad7e6 (DOI)000444050400001 ()30074906 (PubMedID)
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2018-09-20Bibliographically approved
Ivanenko, Y., Nedic, M., Gustafsson, M., Jonsson, B. L., Luger, A. & Nordebo, S. (2018). Quasi-Herglotz functions and convex optimization.
Open this publication in new window or tab >>Quasi-Herglotz functions and convex optimization
Show others...
2018 (English)Report (Other academic)
Abstract [en]

We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modeling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions, and we show that several of the important properties and modeling perspectives of Herglotz functions are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modeling of a non-passive gain media formulated as a convex optimization problem,where the generating measure is modeled by using a finite expansion of B-splines and point masses.

Publisher
p. 24
Keywords
Quasi-Herglotz functions, non-passive systems, approximation, convex optimization, sum rules
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Mathematics
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-78933 (URN)
Funder
Swedish Foundation for Strategic Research , AM13-0011
Available from: 2018-11-22 Created: 2018-11-22 Last updated: 2018-11-26Bibliographically approved
Khodadad, D., Nordebo, S., Seifnaraghi, N., Yerworth, R., Waldmann, A. D., Muller, B., . . . Bayford, R. (2018). The Value of Phase Angle in Electrical Impedance Tomography Breath Detection. In: Progress In Electromagnetics Research Symposium 2018: . Paper presented at Progress In Electromagnetics Research Symposium (PIERS), 1-4 August, 2018, Toyama, Japan (pp. 1040-1043). IEEE
Open this publication in new window or tab >>The Value of Phase Angle in Electrical Impedance Tomography Breath Detection
Show others...
2018 (English)In: Progress In Electromagnetics Research Symposium 2018, IEEE, 2018, p. 1040-1043Conference paper, Published paper (Refereed)
Abstract [en]

The objective of this paper is to report our investigation demonstrating that the phase angle information of complex impedance could be a simple indicator of a breath cycle in chest Electrical Impedance Tomography (EIT). The study used clinical neonatal EIT data. The results show that measurement of the phase angle from complex EIT data can be used as a complementary information for improving the conventional breath detection algorithms.

Place, publisher, year, edition, pages
IEEE, 2018
Series
Progress in Electromagnetics Research Symposium, ISSN 1559-9450
National Category
Medical Equipment Engineering
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-77556 (URN)10.23919/PIERS.2018.8597702 (DOI)000458673700183 ()978-4-8855-2316-8 (ISBN)978-1-5386-5455-2 (ISBN)
Conference
Progress In Electromagnetics Research Symposium (PIERS), 1-4 August, 2018, Toyama, Japan
Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2019-03-15Bibliographically approved
de Gelidi, S., Seifnaraghi, N., Bardill, A., Tizzard, A., Wu, Y., Sorantin, E., . . . Bayford, R. (2018). Torso shape detection to improve lung monitoring. Physiological Measurement, 39(7), Article ID 074001.
Open this publication in new window or tab >>Torso shape detection to improve lung monitoring
Show others...
2018 (English)In: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 39, no 7, article id 074001Article in journal (Refereed) Published
Abstract [en]

Objective: Newborns with lung immaturity often require continuous monitoring and treatment of their lung ventilation in intensive care units, especially if born preterm. Recent studies indicate that electrical impedance tomography (EIT) is feasible in newborn infants and children, and can quantitatively identify changes in regional lung aeration and ventilation following alterations to respiratory conditions. Information on the patient-specific shape of the torso and its role in minimizing the artefacts in the reconstructed images can improve the accuracy of the clinical parameters obtained from EIT. Currently, only idealized models or those segmented from CT scans are usually adopted. Approach: This study presents and compares two methodologies that can detect the patient-specific torso shape by means of wearable devices based on (1) previously reported bend sensor technology, and (2) a novel approach based on the use of accelerometers. Main results: The reconstruction of different phantoms, taking into account anatomical asymmetries and different sizes, are produced for comparison. Significance: As a result, the accelerometers are more versatile than bend sensors, which cannot be used on bigger cross-sections. The computational study estimates the optimal number of accelerometers required in order to generate an image reconstruction comparable to the use of a CT scan as the forward model. Furthermore, since the patient position is crucial to monitoring lung ventilation, the orientation of the phantoms is automatically detected by the accelerometer-based method.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
shape detection, accelerometers, EIT, reconstruction, orientation
National Category
Biomedical Laboratory Science/Technology
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-77008 (URN)10.1088/1361-6579/aacc1c (DOI)000437841700001 ()29894309 (PubMedID)
Available from: 2018-07-27 Created: 2018-07-27 Last updated: 2018-07-27Bibliographically approved
Dalarsson, M., Nordebo, S., Sjöberg, D. & Bayford, R. (2017). Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media. Journal of Physics D: Applied Physics, 50(34), Article ID 345401.
Open this publication in new window or tab >>Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media
2017 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 34, article id 345401Article in journal (Refereed) Published
Abstract [en]

A new simplified formula is derived for the absorption cross section of small dielectric ellipsoidal particles embedded in lossy media. The new expression leads directly to a closed form solution for the optimal conjugate match with respect to the surrounding medium, i.e. the optimal permittivity of the ellipsoidal particle that maximizes the absorption at any given frequency. This defines the optimal plasmonic resonance for the ellipsoid. The optimal conjugate match represents a metamaterial in the sense that the corresponding optimal permittivity function may have negative real part (inductive properties), and can not in general be implemented as a passive material over a given bandwidth. A necessary and sufficient condition is derived for the feasibility of tuning the Drude model to the optimal conjugate match at a single frequency, and it is found that all the prolate spheroids and some of the (not too flat) oblate spheroids can be tuned into optimal plasmonic resonance at any desired center frequency. Numerical examples are given to illustrate the analysis. Except for the general understanding of plasmonic resonances in lossy media, it is also anticipated that the new results can be useful for feasibility studies with e.g. the radiotherapeutic hyperthermia based methods to treat cancer based on electrophoretic heating in gold nanoparticle suspensions using microwave radiation.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2017
Keywords
particle absorption, plasmonic resonances, absorption cross section
National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:lnu:diva-67496 (URN)10.1088/1361-6463/aa7c8a (DOI)000406527200001 ()
Available from: 2017-08-29 Created: 2017-08-29 Last updated: 2017-08-29Bibliographically approved
Khodadad, D., Nordebo, S., Seifnaraghi, N., Waldmann, A. D., Müller, B. & Bayford, R. (2017). Breath detection using short-time Fourier transform analysis in electrical impedance tomography. In: 2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017: . Paper presented at General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017 XXXIInd, Montreal; Canada; 19 - 26 August 2017 (pp. 1-3). IEEE
Open this publication in new window or tab >>Breath detection using short-time Fourier transform analysis in electrical impedance tomography
Show others...
2017 (English)In: 2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017, IEEE, 2017, , p. 3p. 1-3Conference paper, Published paper (Refereed)
Abstract [en]

Spectral analysis based on short-time Fourier transform (STFT) using Kaiser window is proposed to examine the frequency components of neonates EIT data. In this way, a simultaneous spatial-time-frequency analysis is achieved.

Place, publisher, year, edition, pages
IEEE, 2017. p. 3
Keywords
Tomography, Impedance, Lungs, Pediatrics, Monitoring, Ventilation
National Category
Medical Image Processing
Research subject
Computer Science, Information and software visualization
Identifiers
urn:nbn:se:lnu:diva-74403 (URN)10.23919/URSIGASS.2017.8105231 (DOI)9789082598704 (ISBN)
Conference
General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017 XXXIInd, Montreal; Canada; 19 - 26 August 2017
Funder
EU, Horizon 2020, 668259
Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-09-10Bibliographically approved
Seifnaraghi, N., Tizzard, A., de Gelidi, S., Khodadad, D., Nordebo, S., Van Kaam, A., . . . Bayford, R. (2017). Estimation of thorax shape for forward modelling in lungs EIT. In: Alistair Boyle, Ryan Halter, Ethan Murphy & Andy Adler (Ed.), Proceedings of the 18th International Conference on Biomedical Applications of Electrical Impedance Tomography: . Paper presented at 18th International Conference on Biomedical Applications of Electrical Impedance Tomography (EIT2017), Hanover, New Hampshire, USA, June 21-24, 2017 (pp. 58-58). Hanover, New Hampshire, USA: Thayer School of Engineering at Dartmouth
Open this publication in new window or tab >>Estimation of thorax shape for forward modelling in lungs EIT
Show others...
2017 (English)In: Proceedings of the 18th International Conference on Biomedical Applications of Electrical Impedance Tomography / [ed] Alistair Boyle, Ryan Halter, Ethan Murphy & Andy Adler, Hanover, New Hampshire, USA: Thayer School of Engineering at Dartmouth , 2017, p. 58-58Conference paper, Published paper (Refereed)
Abstract [en]

The thorax models for pre-term babies are developed based on the CT scans from new-borns and their effect on image reconstruction is evaluated in comparison with other available models.

Place, publisher, year, edition, pages
Hanover, New Hampshire, USA: Thayer School of Engineering at Dartmouth, 2017
Series
Proceedings of the International Conferences on Biomedical Applications of Electrical Impedance Tomography
National Category
Medical Engineering
Identifiers
urn:nbn:se:lnu:diva-75361 (URN)
Conference
18th International Conference on Biomedical Applications of Electrical Impedance Tomography (EIT2017), Hanover, New Hampshire, USA, June 21-24, 2017
Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-09-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7018-6248

Search in DiVA

Show all publications