| 1. |
- Avolio, G., et al.
(författare)
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A procedure for the extraction of a nonlinear microwave GaN FET model
- 2017
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Ingår i: International Journal of Numerical Modelling: Electronic Networks, Devices and Fields. - : Wiley. - 0894-3370 .- 1099-1204. ; 30:1, s. UNSP e2151-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we describe an extraction procedure of nonlinear models for microwave field-effect transistor (FET). We use a nonlinear model available in commercial CAD tools, and we extract the parameters by combining direct extraction and numerical optimization. We determine a first estimate of the model parameters by few DC and S-parameter measurements. Next, we refine the parameters by optimization against low-frequency and high-frequency vector-calibrated large-signal measurements gathered with a Large-Signal-Network Analyzer (LSNA). As case study we consider a 0.25x200 mu m(2) GaN FET on SiC for power amplifier applications. Ultimately, we want to show that a good accuracy level can be achieved while minimizing the extraction effort and that an accurate model can be built and suitably tailored depending on the final application.
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| 2. |
- Biello, Elia, et al.
(författare)
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A delay‐rational model of electromagnetic interference on multiconductor transmission lines
- 2018
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Ingår i: International journal of numerical modelling. - : John Wiley & Sons. - 0894-3370 .- 1099-1204. ; 31:4
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Tidskriftsartikel (refereegranskat)abstract
- Multiconductor transmission lines have found a wide range of applications, as power lines, as high‐speed interconnects, and as on‐chip interconnects. Electromagnetic interference (EMI) can be described in terms of plane waves that couple to these lines, leading to unwanted disturbance. This paper presents a delayed spectral formulation for the analysis of plane‐wave coupling to multiconductor transmission lines in both the frequency and time domains, called the DeRaG‐EMI model (short for “delay‐rational model based on Green's functions for electromagnetic interference”). The model is based on Green's functions and is described in terms of delayed differential equations in the time domain. The model is suitable for studying the EMI on multiconductor transmission lines in the case of incident fields. The coupling of a plane wave to a line is described in terms of equivalent sources that account for both the delay of the line and the delays of the incoming plane wave. The delay is explicitly extracted and incorporated into the model with hyperbolic functions. The DeRaG‐EMI model does not require any segmentation of the line. Numerical results confirm its accuracy and its improved performance compared with the previous spectral model and with the inverse fast Fourier transform technique.
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| 3. |
- Botha, Matthys M, et al.
(författare)
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Analysis and estimation of quadrature errors in weakly singular source integrals of the method of moments
- 2018
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Ingår i: International Journal of Numerical Modelling: Electronic Networks, Devices and Fields. - : Wiley. - 0894-3370 .- 1099-1204. ; 31:1
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Tidskriftsartikel (refereegranskat)abstract
- The method of moments (MoM) is used for the numerical solution of electromagnetic field integral equations. Weakly singular integrals over surfaces in 3 dimensions (3D) are routinely evaluated for the impedance matrix setup and for post-processing. Available numerical integration schemes range from direct application of Gauss-Legendre product-rule quadrature, to singularity and near-singularity cancellation, coordinate transformation schemes. This paper presents a general, explicit, pole-based, a priori procedure to estimate quadrature errors in the numerical evaluation of weakly singular and near-singular, 3D surface integrals in the MoM. It is based on an error theorem for linear Gaussian quadrature, which involves the analytic extension of the integrand into the complex plane. Errors are linked to poles in the complex plane. New closed-form estimates are presented for direct Gaussian product-rule integration, polar-coordinate integration, and the Radial-Angular-R 1 -Sqrt singularity cancellation scheme, for triangle integration domains. This work can serve as a foundation/template for further, 3D MoM-related work to identify appropriate quadrature schemes according to their error characteristics; for automatic selection of optimal schemes and quadrature orders in a computer implementation of the MoM; and for local and global estimation of MoM quadrature errors. This work can be specialized to the MoM for surfaces in 2D.
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| 4. |
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| 5. |
- Ferber, M., et al.
(författare)
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Efficient worst-case analysis of electronic networks in intervals of frequency
- 2018
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Ingår i: International journal of numerical modelling. - : WILEY. - 0894-3370 .- 1099-1204. ; 31:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new method to compute upper and lower bounds of any voltage or current of an arbitrary linear electric circuit model with uncertain parameters. The bounds are in the frequency domain, and when compared to a previously proposed method, this novel approach provides a higher level of guarantee. The reason is that the bounds are not only computed for a set of fixed frequencies but also computed to a set of intervals of frequencies. The details of the proposed approach, especially the equivalent uncertain element models, are given. Additionally, tests are performed on problems with low and high number of uncertain parameters. Contrary to the classical method of Monte Carlo, the results are not based on a random choice of parameters and do not depend on the number of iterations. It is shown on an example that the classical method of Monte Carlo needs a high number of iterations to reach results in agreement with the proposed method. Then, it leads to higher computation times of several orders of magnitude.
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| 6. |
- Kaufmann, Thomas, et al.
(författare)
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High-order absorbing boundary conditions for the meshless radial point interpolation method in the frequency domain
- 2013
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Ingår i: International journal of numerical modelling. - : Wiley-Blackwell. - 0894-3370 .- 1099-1204. ; 26:5, s. 478-492
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Tidskriftsartikel (refereegranskat)abstract
- The meshless radial point interpolation method (RPIM) in frequency domain for electromagnetic scattering problems is presented. This method promises high accuracy in a simple collocation approach using radial basis functions. The treatment of high-order non-reflecting boundary conditions for open waveguides is discussed and implemented up to fourth-order. RPIM allows the direct calculation of high-order spatial derivatives without the introduction of auxiliary variables. High-order absorbing boundary conditions offer a choice of absorbing angles for each degree of spatial derivatives. For general applications, a set of these absorbing angles is calculated using global optimization. Numerical experiments show that at the same computational cost, the numerical reflections of the absorbing boundary conditions are much lower than conventional perfectly matched layers, especially at high angles of incidence.
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| 7. |
- Kaufmann, Thomas, et al.
(författare)
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Recent developments of the meshless radial point interpolation method for time-domain electromagnetics
- 2012
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Ingår i: International Journal of Numerical Modelling: Electronic Networks, Devices and Fields. - : Wiley. - 0894-3370 .- 1099-1204. ; 25:5-6, s. 468-489
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Forskningsöversikt (refereegranskat)abstract
- Meshless methods are a promising new field in computational electromagnetics. Instead of relying on an explicit mesh topology, a numerical solution is computed on an unstructured set of collocation nodes. This allows to model fine geometrical details with high accuracy and facilitates the adaptation of node distributions for optimization or refinement purposes. The radial point interpolation method (RPIM) is a meshless method based on radial basis functions. In this paper, the current state of the RPIM in electromagnetics is reviewed. The localized RPIM scheme is summarized, and the interpolation accuracy is discussed in dependence of important parameters. A time-domain implementation is presented, and important time iteration aspects are reviewed. New formulations for perfectly matched layers and waveguide ports are introduced. An unconditionally stable RPIM scheme is summarized, and its advantages for hybridization with the classical RPIM scheme are discussed in a practical example. The capabilities of an adaptive time-domain refinement strategy based on the experiences on a frequency-domain solver are discussed.
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| 8. |
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| 9. |
- Kjellström, Anna, 1970-
(författare)
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Possible Cases of Leprosy and Tuberculosis in Medieval Sigtuna, Sweden
- 2012
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Ingår i: International journal of osteoarchaeology. - : Wiley. - 1047-482X .- 1099-1212. ; 22:3, s. 261-283
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Forskningsöversikt (refereegranskat)abstract
- In Sigtuna, Sweden, a medieval cemetery, including 227 skeletons, was analysed in 2006. On the outskirts of the churchyard, six skeletons with bone changes indicating systemic inflammatory disease were observed. Two out of three individuals with well‐preserved facial bone regions displayed signs of rhinomaxillary remodelling. Four of the afflicted exhibit severe bilateral alterations of the lower legs and phalanges of the feet and concentric atrophy of the metatarsals. In addition, one of the individuals exhibited a kyphosis in the lumbar vertebrae. In a discussion about alternative diagnoses, lepromatous leprosy and tuberculosis were identified as the causes of the destructive lesions in two individuals. Though the skeletal changes of the lower legs and feet in four cases demonstrate a close resemblance to secondary lesions of leprosy, the disease could not be confirmed. The skeletal changes of the last individual were unspecific and the possible causes several, rendering diagnosis difficult.The burial locations imply that the afflicted persons belonged to a lower social stratum. Due to the significantly higher frequency of pathological changes in the cemetery compared to other cemeteries in the town, the individuals could be regarded as fellow sufferers among others with various medical conditions. The bioarchaeological identification of systemic infectious diseases of a group of individuals of this size is unique to north of Scania in Sweden, where only a few cases of leprosy and tuberculosis have previously been diagnosed. The significance of the present study is emphasised by the interconnection between the afflicted, the archaeological context and the knowledge of the medieval society in Sigtuna.
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