| 1. |
- Sonderby, Ida E., et al.
(författare)
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Dose response of the 16p11.2 distal copy number variant on intracranial volume and basal ganglia
- 2020
-
Ingår i: Molecular Psychiatry. - : Nature Publishing Group. - 1359-4184 .- 1476-5578. ; 25:3, s. 584-602
-
Tidskriftsartikel (refereegranskat)abstract
- Carriers of large recurrent copy number variants (CNVs) have a higher risk of developing neurodevelopmental disorders. The 16p11.2 distal CNV predisposes carriers to e.g., autism spectrum disorder and schizophrenia. We compared subcortical brain volumes of 12 16p11.2 distal deletion and 12 duplication carriers to 6882 non-carriers from the large-scale brain Magnetic Resonance Imaging collaboration, ENIGMA-CNV. After stringent CNV calling procedures, and standardized FreeSurfer image analysis, we found negative dose-response associations with copy number on intracranial volume and on regional caudate, pallidum and putamen volumes (β = −0.71 to −1.37; P < 0.0005). In an independent sample, consistent results were obtained, with significant effects in the pallidum (β = −0.95, P = 0.0042). The two data sets combined showed significant negative dose-response for the accumbens, caudate, pallidum, putamen and ICV (P = 0.0032, 8.9 × 10−6, 1.7 × 10−9, 3.5 × 10−12 and 1.0 × 10−4, respectively). Full scale IQ was lower in both deletion and duplication carriers compared to non-carriers. This is the first brain MRI study of the impact of the 16p11.2 distal CNV, and we demonstrate a specific effect on subcortical brain structures, suggesting a neuropathological pattern underlying the neurodevelopmental syndromes.
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| 2. |
- Chani Cahuana, Jessica, 1988, et al.
(författare)
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Linearization of dual-input Doherty power amplifiers
- 2014
-
Ingår i: International Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, INMMiC 2014. ; , s. Art. no. 6815085-
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Konferensbidrag (refereegranskat)abstract
- This paper studies the linearity of dual-input Doherty power amplifiers. We propose a linearization scheme that uses a combination of an efficiency-optimized static splitter and a vector-switched digital predistorter. The performance of the proposed linearization scheme is evaluated on a dual-input Doherty power amplifier operating at 2.0 GHz with 42 dBm peak output power. Experimental results show that the proposed linearization scheme achieves a normalized mean square error of-43.7 dB and an adjacent channel power ratio of-55.8 dBc with a power added efficiency of 42.4%.
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| 3. |
- Leidermark, Daniel, 1980-, et al.
(författare)
-
The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
- 2012
-
Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 51:1, s. 273-280
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Tidskriftsartikel (refereegranskat)abstract
- Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.
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| 4. |
- Andersson, Christer, 1982, et al.
(författare)
-
A 1-3-GHz Digitally Controlled Dual-RF Input Power-Amplifier Design Based on a Doherty-Outphasing Continuum Analysis
- 2013
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 61:10, s. 3743-3752
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a linear multi-harmonic analysis method to evaluate the performance of digitally controlled dual RF-input power amplifiers (PAs). The method enables, due to its low computational cost, optimization of PA efficiency and bandwidth in a complex design space involving two independent inputs. Under the idealized assumption of short-circuited higher harmonics, the analysis is used to prove the existence of a Doherty-outphasing continuum, featuring high average efficiency over 100% fractional bandwidth. With this result as a foundation, a combiner incorporating microwave transistor parasitics is analyzed without assuming short-circuited higher harmonics, showing that high average efficiencies are also achievable under more realistic conditions. A PA is straightforwardly designed from these calculation results using two 15-W GaN HEMTs. The simulated layout-ready (large-signal transistor model) PA average drain efficiency exceeds 50% over 1.1-3.7 GHz for a 6.7-dB peak-to-average power-ratio WCDMA signal. The measured PA has a maximum output power of 44 +/- 0.9 dBm and a 6-dB output power back-off (OPBO) power-added efficiency (PAE) of 45% over 1-3 GHz. After applying digital pre-distortion, excellent linearity is demonstrated when transmitting the WCDMA signal, resulting in an adjacent channel leakage power ratio lower than -57 dBc with corresponding average PAE of 50% and 40% at 1.2 and 2.3 GHz, respectively. This is, to the authors' knowledge, the most wideband OPBO efficiency enhanced PA reported to date, proving the effectiveness of employing linear multi-harmonic analysis in dual-input PA design.
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| 5. |
- Andersson, Christer, 1982, et al.
(författare)
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A packaged 86 W GaN transmitter with SiC varactor-based dynamic load modulation
- 2013
-
Ingår i: 43rd European Microwave Conference, EuMC 2013 - Held as Part of the 16th European Microwave Week, EuMW 2013, Nuremberg, Germany, 7-10 October 2013. - 9782874870316 ; , s. 283-286
-
Konferensbidrag (refereegranskat)abstract
- Output power scaling based on class-J dynamic load modulation (DLM) theory is used to design an unprecedentedly high power microwave transmitter with varactor-based DLM functionality. Matching networks are realized on high dielectric constant substrates in order to reduce the form factor. The fully matched DLM PA incorporates a 24-mm GaN HEMT powerbar and a stack of four SiC varactors, all fit into a CuW package (40 mm × 20 mm). Peak output power is reconfigurable by changing the drain voltage, while retaining the DLMeffect. Under pulsed conditions at 40 V the PA delivers a peak power of 86 W at 2.14 GHz. Efficiency enhancement by DLM is 10-15 percentage-units at 6 dB output power back-off (OPBO). Employing digital predistortion (DPD) with a vector switched generalized memory polynomial (VS-GMP) the ACLR is -46 dBc at an average output power of 17 W and a drain efficiency of 34%. These results prove the potential for high output power levels in varactor-based DLM transmitters.
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| 6. |
- Andersson, Christer, 1982, et al.
(författare)
-
Theory and Design of Class-J Power Amplifiers With Dynamic Load Modulation
- 2012
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:12, s. 3778-3786
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Tidskriftsartikel (refereegranskat)abstract
- A theory for class-J microwave amplifier operation as a function of drive level and fundamental load impedance is derived. Calculations show that, under appropriate operating conditions, it is sufficient to modulate the transistor load reactance to enable high-efficiency operation (>70%) over a large output power dynamic range (>10 dB) with high transistor power utilization. Such dynamic load modulation (DLM) networks are an ideal application of continuously tunable varactor technologies. Multiharmonic load–pull measurements are performed on a GaN HEMT and experimentally verify the theory of operation. A demonstrator amplifier using an SiC varactor technology is then designed and characterized by static measurements. The amplifier has a peak power of 38 dBm at 2.08 GHz and maintains efficiencies above 45% over 8 dB of power dynamic range. An analysis of the load network losses is performed to show the potential of the class-J DLM transmitter concept.
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| 7. |
- Busse, Christian, 1989-
(författare)
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Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys.The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures.This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.
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| 8. |
- Chen, Z., et al.
(författare)
-
Plastic Deformation and Residual Stress in High Speed Turning of AD730™ Nickel-based Superalloy with PCBN and WC Tools
- 2018
-
Ingår i: Procedia CIRP. - AMSTERDAM, NETHERLANDS : Elsevier BV. - 2212-8271. ; 71, s. 440-445, s. 440-445
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Konferensbidrag (refereegranskat)abstract
- A higher gas turbine efficiency can be achieved by increasing the operating temperature in hot sections. AD730™ is a recently-developed wrought/cast nickel-based superalloy which can maintain excellent mechanical properties above 700. However, machining of AD730™ could be a difficult task like other nickel-based superalloys. Therefore, studies are needed with respect to the machinability of this new alloy. In this paper, high-speed turning was performed on AD730™ using polycrystalline cubic boron nitride (PCBN) tools and coated tungsten carbide (WC) tools at varied cutting speeds. The surface integrity was assessed in two important aspects, i.e., surface and sub-surface plastic deformation and residual stresses. The PCBN tools generally showed better performance compared with the WC tools since it led to reduced machining time without largely compromising the surface integrity achieved. The optimal cutting speed was identified in the range of 200-250 m/min when using the PCBN tools, which gives rise to a good combination of machining efficiency and surface integrity. The further increase of the cutting speed to 300 m/min resulted in severe and deep plastic deformation. Meanwhile, a continuous white layer was formed at the machined surface. When turning with the WC tools, the increased cutting speed from 80 m/min to 100 m/min showed very little effect with respect to the plastic deformation on the machined surface. It was found that tensile residual stresses were developed on all machined surfaces no matter when the PCBN or WC tools were used, and the surface tension was generally increased with increasing cutting speed. The tensile layer might need to be modified by e.g., post-machining surface treatments such as shot peening, if taking good fatigue performance into consideration.
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| 9. |
- Fager, Christian, 1974, et al.
(författare)
-
Analysis of nonlinear distortion in phased array transmitters
- 2017
-
Ingår i: Proceedings of the 2017 International Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, INMMiC 2017. - 9781509058624
-
Konferensbidrag (refereegranskat)abstract
- This paper investigates nonlinear distortion effects in active antenna phased array transmitters. Using a nonlinear modeling technique, the joint interactions between power amplifiers and antennas are investigated in detail. Numerical simulations based on a 28 GHz GaN MMIC PA and a 64-element antenna array are used to exemplify the use of the proposed technique in a typical 5G application. The results show that the antenna mutual coupling will cause the individual PA compression characteristics and hence the far field distortion to depend significantly on beam steer angle.
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| 10. |
- Fager, Christian, 1974, et al.
(författare)
-
Design of linear and efficient power amplifiers by generalization of the Doherty theory
- 2017
-
Ingår i: Proceedings of the 2017 IEEE Topical Conference on Power Amplifiers for Wireless and Radio Applications. - 9781509034574 ; , s. 29-32
-
Konferensbidrag (refereegranskat)abstract
- The Doherty power amplifier (PA) is now established as one the most widely adopted architectures for enhancement of energy efficiency in wireless communication transmitters. More than 80 years after its invention, most of today's implementations still rely on the original circuit topology. This paper describes a new Doherty solution continuum that is revealed when the original λ/4 combiner is replaced by a generic, analytically derived, lossless combiner network. As a result, novel Doherty PA solutions that in practice are both more efficient and more linear are enabled. A variety of practical design examples are included to illustrate how the presented techniques can enable enhanced performance in both traditional and emerging mm-wave 5G wireless communication transmitter applications.
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| 11. |
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| 12. |
- Gustafsson, David, 1983, et al.
(författare)
-
A GaN MMIC Modified Doherty PA With Large Bandwidth and Reconfigurable Efficiency
- 2014
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 62:12, s. 3006-3016
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we further develop the concept of a wideband Doherty power-amplifier topology with reconfigurable efficiency. This is done by presenting new theory that-in contrast to previous work-makes it possible to analyze how the performance of the amplifier depends on the input network properties and the choice of gate bias voltages. The utility of the presented theory is demonstrated by the design and characterization of a gallium-nitride monolithic-microwave integrated-circuit amplifier designed in close agreement with the theoretical findings. Continuous-wave (CW) measurements show that the fabricated amplifier provides more than 31% power-added efficiency (PAE) at 9-dB output power back-off over a 5.8-8.8-GHz frequency range, and that the efficiency can be reconfigured as predicted by the presented theory. Modulated measurements-employing digital pre-distortion (DPD) and a 20-MHz signal with 8.5-dB peak-to-average power ratio-show more than 32% average PAE across the same 5.8-8.8-GHz frequency range. Both the CW and the modulated measurements thereby verify the wideband performance predicted by the theory. In addition, modulated measurements at 7.0 GHz without DPD show that the amplifier can provide excellent raw linearity by demonstrating -41.0-dBc adjacent channel power ratio and -34.2-dB normalized mean square error.
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| 13. |
- Gustafsson, David, 1983, et al.
(författare)
-
A Modified Doherty Power Amplifier With Extended Bandwidth and Reconfigurable Efficiency
- 2013
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 61:1, s. 533-542
-
Tidskriftsartikel (refereegranskat)abstract
- This paper derives the theory and presents measurements of a new power amplifier based on the Doherty power amplifier topology. It is theoretically shown that the proposed amplifier can simultaneously provide high efficiency at both full output power and at output power back-off, over a much improved bandwidth compared to the conventional Doherty power amplifier. It is also shown that the proposed amplifier allows reconfiguration of the efficiency in power back-off without the need of tunable elements.A demonstrator circuit with individually controlled main and auxiliary amplifier input signals is designed to validate the theoretical findings. Measurements show state-of-the-art efficiency bandwidth with more than 49% drain efficiency at both full output power (42 dBm) and at 6 dB output power back-off (36 dBm) over a 1.5-2.4 GHz frequency range. The measurements also demonstrate that the efficiency in back-off can be conveniently reconfigured. The measurements thereby validate the presented theory and demonstrate the potential of the proposed amplifier for use in future wireless transmitter applications.
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| 14. |
- Gustafsson, David, 1983, et al.
(författare)
-
A novel wideband and reconfigurable high average efficiency power amplifier
- 2012
-
Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871
-
Konferensbidrag (refereegranskat)abstract
- This work presents theory and measurements of a new power amplifier based on the Doherty topology. It is theoretically shown that, by using a new set of design parameters with a Doherty power amplifier topology, the proposed amplifier can provide high efficiency, both at full output power and at power back-off, over a much improved bandwidth compared to the conventional Doherty power amplifier configuration. It is also shown that the proposed amplifier allows for simple reconfiguration of the efficiency in power back-off. A demonstrator circuit using individually controlled main and peak amplifier input signals is designed to validate the theoretical findings. Measurements show state-of-the art efficiency bandwidth at both full output power and at power back-off, as well as reconfigurable efficiency, thus validating the theory and demonstrating the potential of the proposed PA for use in future wireless transmitter applications.
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| 15. |
- Gustafsson, David, 1983, et al.
(författare)
-
A Wideband and Compact GaN MMIC Doherty Amplifier for Microwave Link Applications
- 2013
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 61:2, s. 922-930
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the limitations and difficulties, in terms of DC-current density restrictions, and process limitations, associated with implementing impedance inverters with high characteristic impedance for monolithic microwave integrated circuit (MMIC) Doherty power amplifiers (DPAs). It is theoretically shown that impedance inverters with high characteristic impedance can be realized by utilizing the output capacitance of the active devices, together with a compact Tee-network of transmission lines with feasible linewidths. The utility of the impedance inverter is proven by design and fabrication of a GaN MMIC-DPA for microwave link applications. Continuous wave (CW) measurements demonstrate a maximum output power of 35 +/- 0.5 dBm over a frequency range of 6.6-8.5 GHz. The power added efficiency (PAE) in 9 dB output power back-off (OPBO) is better than 30% in a frequency range of 6.7-7.8 GHz. Moreover, linearized modulated measurements, employing a 10 MHz 256-QAM signal with 7.8 dB peak to average power ratio (PAPR), demonstrate higher than 35% average PAE, with 27.5 +/- 0.2 dBm average output power, and an adjacent channel power ratio (ACPR) less than -45 dBc, across a 6.8-8.5 GHz frequency range. The fabricated chip-size measures 2.1 mm x 1.5 mm.
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| 16. |
- Gustafsson, David, 1983, et al.
(författare)
-
An analysis of the suitability of using CW-theory when designing Doherty PAs for wideband or concurrent multi-band operation
- 2013
-
Ingår i: 43rd European Microwave Conference, EuMC 2013 - Held as Part of the 16th European Microwave Week, EuMW 2013, Nuremberg, Germany, 7-10 October 2013. - 9782874870316 ; , s. 287-290
-
Konferensbidrag (refereegranskat)abstract
- In this paper it is analyzed whether the commonly used continuous-wave (CW) based theory can properly describe and predict the behavior of the Doherty power amplifier (DPA) under wideband or concurrent multi-band operation. The analysis shows that the CW-theory in fact fails to do so and that the functionality of the DPA is strongly dependent on how intermodulation frequencies are terminated. In particular, it is shown that the network connecting the main and auxiliary amplifiers needs to function as an impedance inverter at specific odd order intermodulation frequencies, such as the cross-carrier intermodulation in the multi-band case. The theoretical analysis is verified by simulations, demonstrating how the functionality of a concurrent dual-band DPA is distorted despite CW-theory predicting ideal performance in each band. The findings in this paper are an important contribution to the understanding of how to further improve the performance of wideband or concurrent multi-band DPAs.
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| 17. |
- Gustafsson, David, 1983-
(författare)
-
Constitutive and fatigue crack propagation behaviour of Inconel 718
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this licentiate thesis the work done in the TURBO POWER project Influence of high temperature hold times on the fatigue life of nickel-based superalloys will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. Firstly, the constitutive behaviour of the material has been been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures. Secondly, the fatigue crack propagation behaviour under high temperature hold times has been studied. Focus has here been placed on investigating the main fatigue crack propagation phenomena with the aim of setting up a basis for fatigue crack propagation modelling.This thesis is divided into two parts. The first part describes the general framework, including basic constitutive and fatigue crack propagation behaviour as well as a theoretical background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the four included papers.
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| 18. |
- Gustafsson, David, 1983
(författare)
-
Extending the Bandwidth of the Doherty Power Amplifier
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Doherty power amplifier (DPA) is one of the most popular power amplifier (PA) architectures used to obtain high efficiency for modern communication signals having high peak-to-average power ratios. Its often narrowband performance does, however, make it difficult for the DPA to meet the increasing demands of frequency agility in modern wireless communication systems. This thesis examines the theoretical and practical bandwidth limitations of the DPA and presents new methods to overcome them.A new type of output network topology that serves to reduce the influence of device output parasitics and to overcome manufacturing limitations, thereby extending the bandwidth, is proposed. The utility of the network is demonstrated by implementation in a gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) DPA. Measurements show that by doing so, a power added efficiency (PAE) higher than 30% at 9 dB output power back-off (OPBO) is obtained across a 6.7–7.8 GHz frequency range. To overcome the inherent bandwidth limitations imposed by the impedance inverter, a modified DPA is proposed. A comprehensive theoretical analysis is presented which shows that the modified DPA has a significantly larger bandwidth compared to the standard DPA, as well as reconfigurable efficiency. The theoretical findings are validated by the design and characterization of two demonstrator circuits. The first circuit, having dual RF-inputs and using baredie GaN devices, has a drain efficiency higher than 48 % at both full output power and at 6 dB OPBO across a 1.5–2.4 GHz frequency range. The second circuit is a single RF-input GaN MMIC DPA that delivers a PAE higher than 30% at 9 dB OPBO from 5.8 to 8.8 GHz, constituting a fractional bandwidth of 41%.To achieve bandwidths greater than one octave, a linear multi-harmonic analysis method based on a Doherty-outphasing continuum is proposed. By using this method a dual RF-input amplifier is designed. Measurements showthat the amplifier provides more than 45% PAE at 6 dB OPBO over a 1.0–3.0 GHz frequency range, corresponding to a 100% fractional bandwidth. In summary, the results presented in this thesis shows that the DPA no longer needs be considered as a necessarily narrowband amplifier. This thesis is therefore an important contribution in the pursuit of high efficiency and frequency agile power amplifiers targeting the needs in future mobile communicationsystems.
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| 19. |
- Gustafsson, David, 1983, et al.
(författare)
-
Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
- 2010
-
Ingår i: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 2:1, s. 1095-1104
-
Konferensbidrag (refereegranskat)abstract
- In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 °C, 550 °C and 650 °C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates. © 2010 Published by Elsevier Ltd.
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| 20. |
- Gustafsson, David, 1983-
(författare)
-
High temperature fatigue crack propagation behaviour of Inconel 718
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall objective of this work has been to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. The fatigue crack propagation behaviour under high temperature hold times has been studied. Firstly, the main fatigue crack propagation phenomena have been investigated with the aim of setting up a basis for fatigue crack propagation modelling. Secondly, modelling of the observed behaviour has been performed. Finally, the constitutive behaviour of the material has been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures.This thesis is divided into two parts. The first part describes the general framework, including basic observed fatigue crack propagation behaviour of the material when subjected to hold times at high temperature as well as a background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the seven included papers.
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| 21. |
- Gustafsson, David, 1983-, et al.
(författare)
-
Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures
- 2011
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Ingår i: Journal of engineering for gas turbines and power. - : ASME. - 0742-4795 .- 1528-8919. ; 133, s. 094501-1-094501-4
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Tidskriftsartikel (refereegranskat)abstract
- Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiation, the work generally starts with a rigorous analysis of thefirst few cycles, during which an important stress redistributionwill always take place in an inelastic structure. In this work, thenonlinear kinematic hardening law by Ohno and Wang (1998,“Constitutive Modeling of Cyclic Plasticity With Emphasis onRatchetting,” Int. J. Mech. Sci., 40, pp. 251–261) has been used incombination with an isotropic softening law for describing theinitial stress-strain distribution for strain controlled uniaxial testsof the material Inconel 718. Focus has been placed on finding asimple model with few material parameters and to describe theinitial softening and the comparatively small mean stress relaxationobserved during the material testing. The simulation resultsobtained by using the model fit the experimental resultswell.
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| 22. |
- Gustafsson, David, 1983
(författare)
-
Theory and Design of Wideband Doherty Power Amplifiers
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Doherty power amplifier (DPA) is one of the most popular power amplifier architectures for obtaining high average efficiency for modern communication signals with high peak-to-average power ratios (PAPR). However, the DPA suffers from often having narrowband performance which limits its capabilities in wideband and/or multi-standard microwave and radio frequency applications. In this thesis, the theoretical and practical bandwidth limitations of the DPA are examined and it is demonstrated, by theory and measurements, how to design high performance and wideband DPAs. A Tee-line network of transmission lines is presented that enables simple design of Doherty combining networks in many situations where traditional approaches would fail. The utility of the Tee-line network is demonstrated by implementation in a 7-8 GHz gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) DPA. Continuous wave measurements showed a power added efficiency (PAE) larger than 30 % at 9 dB output power back-off across a 6.7-7.8 GHz frequency range. The maximum output power was maintained within 35 ± 0.5 dBm from 6.6 to 8.5 GHz. Linearized modulated measurements, employing a signal with 7.8 dB (PAPR), reported average PAE larger than 35 %, with an average output power of 27.5 ± 0.2 dBm and an adjacent channel power ratio (ACPR) less than -45 dBc, across a 6.8-8.5 GHz frequency range. The results demonstrates state-of-the art performance both in terms of PAE and bandwidth.To extend the inherent bandwidth of the DPAs a new type of power amplifier, based on the DPA topology, is presented. It is theoretically shown that the proposed amplifier can simultaneously provide high efficiency at full output power and at power back-off, as well as reconfiguration of the efficiency in power back-off without the need of tunable elements. The theoretical findings were confirmed by the fabrication and measurements of a demonstratorcircuit. Measurements reported higher than 48 % drain efficiency at both full output power and at power back-off from 1.5-2.4 GHz, thereby demonstrating a unique combination of high fractional bandwidth and high back-off efficiency. The reported fractional bandwidth that was simultaneously achieved at full output power and at 6 dB output power back-off is to the author’s knowledge larger than what has been reported for any power amplifier architecture
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| 23. |
- Hallberg, William, 1988, et al.
(författare)
-
A class-J power amplifier with varactor-based dynamic load modulation across a large bandwidth
- 2015
-
Ingår i: 2015 IEEE MTT-S International Microwave Symposium, IMS 2015. - 9781479982752
-
Konferensbidrag (refereegranskat)abstract
- A novel class-J operated power amplifier (PA) utilizing varactor-based dynamic load modulation is presented. It is theoretically shown that the proposed PA can maintain high average efficiency across more than 35% RF bandwidth by means of a purely reactive load modulation after the transistor output capacitance. The theory is experimentally verified by a 15 W GaN HEMT PA operating from 1.80 to 2.20 GHz, using SiC varactors as dynamically tunable load elements. In the band, the PA presents a power added efficiency (PAE) higher than 39% at 6 dB output power back-off. For a 3.84 MHz W-CDMA signal with 6.7 dB peak to average power ratio, an average PAE higher than 39% and an adjacent channel leakage ratio below -45.8 dBc are obtained across the entire band after linearization.
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| 24. |
- Hallberg, William, 1988, et al.
(författare)
-
A Doherty Power Amplifier Design Method for Improved Efficiency and Linearity
- 2016
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 64:12, s. 4491-4504
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Tidskriftsartikel (refereegranskat)abstract
- A novel Doherty power amplifier (PA) design method enabling high efficiency and high linearity simultaneously is proposed. The output combiner network is treated as a black box, and its parameters, together with the input phase delay, are solved based on given transistor characteristics and design requirements. This opens for new PA solutions with nonconventional Doherty behavior. The increased design space enables new tradeoffs in Doherty PA designs, including solutions with both high efficiency and high linearity simultaneously. A method utilizing the new design space is developed. For verification, a 20-W 2.14-GHz symmetrical gallium nitride high electron mobility transistors Doherty PA is fabricated and measured. The PA obtains an average power added efficiency of 40% and an adjacent power leakage ratio of -41 dBc without any linearization for an 8.6-dB peak to average power ratio 10-MHz-long term evolution signal, at an average output power of 35.5 dBm.
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| 25. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(författare)
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High temperature fatigue crack growth in Alloy 718 - Effect of tensile hold times
- 2011
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Ingår i: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 10, s. 147-152
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Konferensbidrag (refereegranskat)abstract
- The present investigation aims to clarify the mechanisms behind hold-time fatigue crack growth in Alloy 718 by using well designed tests where the crack length is carefully monitored. The results indicate that there is a significant embrittlement in a zone ahead of the crack tip during the hold-time, which is cracked open on the next load reversal. This leads to a very large cyclic contribution to the total crack length increment during a cycle, orders of magnitude larger than expected from purely cyclic tests at higher frequencies. During the hold-time follows the growth determined from pure sustained load tests, with the exception of an initial transient after the opening of the embrittled zone. An attempt to model the crack growth rate was made using a superposition model where the crack growth increments from high frequency da/dN testing and sustained load tests were added. The predictions of the total crack growth rate are generally adequate, but when the predictions of the individual contributions are scrutinized, it is obvious that the simple model does not correlate with the physical reality. Therefore both inter- and extrapolations from such a model are uncertain. Further, the test results show a decreased sustained load crack growth immediately after unloading/reloading of the crack. This transient behavior can potentially explain the reduction in crack growth rates previously explained by overload effects. © 2011 Published by Elsevier Ltd.
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| 26. |
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Kommunerna och hållbar utveckling : Demokrati, välfärd och lokal utveckling
- 2022
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- I 25 år har Centrum för kommunstrategisk forskning, CKS, varit ett nav för forskning och samverkan kring kommunal och regional utveckling. Den här boken är en del i uppmärksammandet av 25-årsjubiléet.Boken är en antologi som belyser frågor om hållbar utveckling utifrån kommunernas olika roller och ansvar för samhällsstrukturer och samhällsprocesser. Författarna till de olika kapitlen är forskare vid CKS och forskare som ingår i CKS samarbetsnätverk. I de olika kapitlen sammanfattas i flera fall forskning som har sträckt sig över många år. På så sätt visar vi genom den här boken hur kontinuiteten genom vår centrumbildning har bidragit till en livskraftig struktur för fördjupad kommunstrategisk och regionstrategisk forskning som tagit stöd i dialoger med miljöer utanför och innanför forskarsamhället.Redaktör för boken är Brita Hermelin, professor i kulturgeografi vid CKS. Övriga författare är Magnus Dahlstedt, David Ekholm, Gissur Ó Erlingsson, Ida Grundel, Sara Gustafsson, Robert Jonsson, Martin Klinthäll, Dick Magnusson, Kristina Trygg, Susanne Wallman Lundåsen, Emanuel Wittberg, Johan Wänström och Richard Öhrvall.
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| 27. |
- Loureiro, Jordi, 1985-, et al.
(författare)
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Accounting for crack closure effects in TMF crack growth tests with extended hold times in gas turbine blade alloys
- 2021
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 142
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Tidskriftsartikel (refereegranskat)abstract
- Crack closure effects are known to have a large impact on crack growth behaviour. In this work, tests were performed on Inconel 792 specimens under TMF loading conditions at 100–850 °C with extended hold times at tensile stress. The effective stress-intensity range was estimated experimentally using a compliance-based method leading to the conclusion that crack closure appears to have a primary impact on the crack growth behaviour for this material under the conditions studied. The crack closure behaviour for the tests was successfully modelled using numerical simulations, including creep.
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| 28. |
- Palmert, Frans, 1986-
(författare)
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Crack growth in single crystal gas turbine blade alloys under service-like conditions
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes, and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Crack growth testing has been performed, both using conventional isothermal testing methods and using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance-based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance for the understanding of the crack driving force under different testing conditions. The influence of hold time on crack growth behaviour was analysed, both in terms of creep crack growth and in terms of creep effects on the crack opening force. The transition between non-crystallographic and crystallographic crack growth was studied in detail and a criterion was developed to enable accurate predictions of this transition under a wide range of loading conditions representative for gas turbine blades.
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| 29. |
- Palmert, Frans, 1986-
(författare)
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Crack growth in single crystal nickel base superalloys under isothermal and thermomechanical fatigue
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and also to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close-packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Fatigue crack growth testing has been performed, both using conventional isothermal testing methods and also using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are however only presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, in order to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance in the understanding of the crack driving force under different testing conditions.
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| 30. |
- Palmert, Frans, 1986-, et al.
(författare)
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Modelling of the transition from mode I to crystallographic crack growth in a single crystal gas turbine blade alloy under service-like loading conditions
- 2022
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- In fatigue life prediction of single crystal gas turbine blades, the risk of rapid crystallographic crack growth along the close-packed planes poses a large uncertainty. A criterion is proposed to predict the transition from mode I to crystallographic crack growth, which is necessary for reliable prediction of the number of cycles from crack initiation to the onset of crystallographic crack growth. The proposed criterion is calibrated against tests performed under a wide range of conditions representative for a gas turbine blade, including isothermal fatigue crack growth tests and thermomechanical fatigue crack growth tests, some including hold times and pre-test aging.
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| 31. |
- Palmert, Frans, 1986-, et al.
(författare)
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Thermomechanical fatigue crack growth in a single crystal nickel base superalloy
- 2019
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 122, s. 184-198
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Tidskriftsartikel (refereegranskat)abstract
- Thermomechanical fatigue crack growth in a single crystal nickel base superalloy was studied. Tests were performed on single edge notched specimens, using in phase and out of phase thermomechanical fatigue cycling with temperature ranges of 100-750°C and 100-850°C and hold times at maximum temperature ranging from 10s to 6h. Isothermal testing at 100°C, 750°C and 850°C was also performed using the same test setup. A compliance-based method is proposed to experimentally evaluate the crack opening stress and thereby estimate the effective stress intensity factor range ΔKeff for both isothermal and nonisothermal conditions. For in phase thermomechanical fatigue, the crack growth rate is increased if a hold time is applied at the maximum temperature. By using the compliance-based crack opening evaluation, this increase in crack growth rate was explained by an increase in the effective stress intensity factor range which accelerated the cycle dependent crack growth. No significant difference in crack growth rate vs ΔKeff was observed between in phase thermomechanical fatigue tests and isothermal tests at the maximum temperature. For out of phase thermomechanical fatigue, the crack growth rate was insensitive to the maximum temperature and also to the length of hold time at maximum temperature. The crack growth rate vs ΔKeff during out of phase thermomechanical fatigue was significantly higher than during isothermal fatigue at the minimum temperature, even though the advancement of the crack presumably occurs at the same temperature. Dissolution of γ′ precipitates and recrystallization at the crack tip during out of phase thermomechanical fatigue is suggested as a likely explanation for this difference in crack growth rate.
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