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- Gevorgian, Spartak, 1948, et al.
(författare)
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HTS/ferroelectric devices for microwave applications
- 1997
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 7:2, s. 2458 - 2461
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Tidskriftsartikel (refereegranskat)abstract
- High Temperature Superconducting (HTS, e.g. YBCO) microwave devices based on bulk or thin film ferroelectrics (e.g. Strontium Titanate-STO) are studied theoretically and experimentally. YBCO/STO/YBCO parallel-plate resonators and based on bulk single crystal STO are for electrically tunable high power filters, phase shifters and other devices in the frequency band 0.5-2.0 GHz of advanced microwave communication systems. Thin film YBCO/STO Inter-digital Capacitors (IDC), Coplanar Waveguides (CPW) phase shifters/delay lines are also designed and studied experimentally for low microwave power applications. Modelling problems of these devices and microwave losses in ferroelectrics are also discussed
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- Gevorgian, Spartak, 1948, et al.
(författare)
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Modelling of thin-film HTS/ferroelectric interdigital capacitors
- 1996
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Ingår i: IEE Proceedings: Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1350-2417 .- 1359-706X. ; 143:5, s. 397 - 401
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Tidskriftsartikel (refereegranskat)abstract
- The model of the interdigital capacitor (IDC) has been used for monitoring and analysing the dielectric properties of thin ferroelectric films. The dielectric properties of the film are correlated to its crystalline structure using a simple model of STO. The results of the analysis may be used for optimisation of growth and annealing processes of the films and reducing the effects of the electrode ferroelectric interface. The model can be used to optimise the design of IDCs in the sense of minimum losses and maximum controllability by selecting finger width and gapwidth of the IDC. Further improvement of the model suggests a comprehensive study of all possible mechanisms affecting the dielectric constant and the losses of STO films
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- Hygge, Staffan, et al.
(författare)
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The effect of functional hearing loss and age on long- and short-term visuospatial memory: evidence from the UK Biobank resource: a longitudinal follow up
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In a recent study (Rönnberg, Hygge, Keidser & Rudner, 2014) we reported cross-sectional epidemiological data from the UK Biobank, which in total contains >500,000 individuals in the UK. The focus in that study was on the effects of functional hearing loss and age on long- and short-term visuospatial memory. Our selection of variables resulted in a sub-sample of 138,098 participants after discarding extreme values.A digit triplets functional hearing test was used to divide the participants into three groups: poor, insufficient and normal hearers. We found negative relationships between functional hearing loss and both visuospatial working memory (i.e., a card pair matching task) and visuospatial, episodic long-term memory (i.e., a prospective memory task), with the strongest association for episodic long-term memory. The use of hearing aids showed a small positive effect for working memory performance for the poor hearers, but did not have any influence on episodic long-term memory. Age also showed strong main effects for both memory tasks and interacted with gender and education for the long-term memory task.Close to 20,000 of the original (>500,000) participants recently went through the very same test battery a second time, 2-7 years after the first time. In the present study, we will scrutinize in which respects the addition of extra years in the longitudinal analysis is commensurable with extra years from our previous cross-sectional analysis, for the same sets of original moderators and mediators.
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- Jonsson, Rolf, et al.
(författare)
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Broadband RF SiC MESFET power amplifiers
- 2005
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 483, s. 857-860
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Tidskriftsartikel (refereegranskat)abstract
- We have designed and characterized preliminary versions of two wideband SiC-based RF power amplifiers using SiC MESFETs from Chalmers University and Lateral Epitaxy SiC MEESFETs fabricated at AMDS AB. When optimized transistors are available they will be used in the design of amplifiers for a 100-500 MHz multifunction EW system.
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- Jonsson, Rolf, et al.
(författare)
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Computational load pull simulations of SiC microwave power transistors
- 2003
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 47:11, s. 1921-1926
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Tidskriftsartikel (refereegranskat)abstract
- The design of power transistors for microwave applications requires a good understanding of their large signal behaviour in a real circuit context. The computational load-pull simulation technique is a powerful new way to evaluate the full time-domain voltages and currents of microwave power transistors during realistic operation. With this method it is possible to relate details in the time domain voltages and currents to corresponding variations in carrier densities, electrical field, etc. in the device. We have utilised the standard device simulator Medici, directly driven by sine voltage sources on both input and output. The resulting data from the simulations was then analysed using Matlab. Several 4H-SiC MESFET structures were evaluated by this technique and we found the p-type buffer layer doping and thickness to be crucial to obtain an optimum RF power. A 4H-SiC MESFET structure was found to have an output power of 6.2 W/mm at 1 GHz. ⌐ 2003 Elsevier Ltd. All rights reserved.
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- Jonsson, Rolf, et al.
(författare)
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DC and RF performance of insulating gate 4H-SiC depletion mode Field Effect Transistors
- 2004
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Ingår i: Materials Science Forum, Vols. 457-460. ; , s. 1225-1228
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Konferensbidrag (refereegranskat)abstract
- A depletion mode 4H-SiC MOSFET for RT applications is studied using drift-diffusion physical device simulations. The structure is basically the same as for a MESFET. A MOS gate with a 30 nm thick SiO2 layer replaces the Schottky gate. A 40% increase in the drain current was observed for a positive gate bias of 7 V compared to 0 V. The small signal AC analysis showed f(T) and f(max) to be 15.7 and 52.9 GHz respectively.
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