| 1. |
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
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| 12. |
- Jonsson, Rolf, et al.
(författare)
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Evaluation of SiC MESFET structures using large-signal time-domain simulations
- 2002
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Ingår i: Materials Science Forum Vols. 389-393. ; , s. 1395-1398
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Konferensbidrag (refereegranskat)abstract
- When designing transistors for microwave power applications a good understanding of their large signal behaviour in a real circuit context is essential. We have used the device simulator Medici in a novel way to simulate the large signal high frequency time domain properties of different SiC MESFET structures. The simulations show that even for transistors with good DC properties the exact design of the channel-buffer and the buffer-substrate regions is important when a good high power RF performance is required. Our simulations indicate that output power densities above 6W/mm are possible if heating problems are solved.
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| 13. |
- Kabir, Mohammad, 1974, et al.
(författare)
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A Test Vehicle for RF/DC Evaluation and Destructive Testing Of Vertically Grown Nanostructures (VGCNS)
- 2011
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Ingår i: Proceedings of the NT11 International Conference on the Science and Application of Nanotubes, Cambridge, UK, July 10-16, 2011.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have developed an RF test vehicle suitable for measuring DC and microwave performance of vertically grown carbon nanostructures (VGCNS) as via-interconnects. A first version of the interconnect test vehicles devices were designed, fabricated and characterized. The RF small signal (S-parameter) and large signal measurements show that carbon nanofibres can be used as interconnects in microwave circuit, even for power devices. The design of test vehicle employs a three metal layer concept, forming sequentially the ground, signal and device under test structures for characterization in a microstrip configuration. The structures as such consisted of interconnects of dimensions ranging from 50 nm to 100 µm diameter made of VGCNS. In the first version of the interconnect test vehicles, the interconnects were made of carbon nanofibers grown at 450 C. From SEM measurement we found that the resulting height was around 1.5-2 µm. Epoxy polymer SU-8 was employed by spinning on the device and a subsequent etch back process was carried out to open up the tip of the fibres to connect to consecutive interconnects with the third metallisation layer. After growing the nanofibres, it was observed, using SEM, that interconnect sizes smaller than 10 µm diameter suffered from parasitic growth and therefore the effective device dimension deviated from the initial design. We carried out small signal measurements using a vector network analyser for frequency ranging from 1 to 25 GHz, in order to characterise the transmission and reflection/absorption of the devices as function of their diameter size. The large signal evaluation was performed by measuring the gain compression of the devices. In addition destructive tests, aiming at testing the current carrying capability of the interconnect, have also been performed.The resistivity of interconnects was measured to vary varies from 0.2 µΩ·mm-1.3 mΩ·mm. Apparently, the device performance is considerably influenced by the fill factor of the interconnect with VGCNS. Small variations in fill factor (in %) provided a large variations in device resistivity. Furthermore, it was also observed that the resistance drops at higher power levels. RF conductivity of interconnects ranges from 5x10^3 S/m to 7x10^5 S/m. The average input power before interconnect destruction is larger than 25W with effective device diameter ranging from 3 µm to 100 µm interconnects. In addition, the average gain compression before interconnect destruction was found to be 0.6 dB. It was not possible to extract the conductivity value of an individual nanofiber using comparison to simulation data, since the devices might have suffered from parasitic growth as well as pinhole metal diffusion during top metal contact formation. This certainly affects the actual device dimension and properties. Nevertheless, the proof of concept of design and manufacturing a test vehicle for RF measurements of vertically grown nanostructures was achieved. We will report the findings and anomalies in the measured devices. Further improvement is expected in the coming test vehicle version.
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| 14. |
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| 15. |
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| 16. |
- Keidser, Gitte, et al.
(författare)
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On the relationship between functional hearing and depression
- 2015
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Ingår i: International Journal of Audiology. - : Informa UK Limited. - 1499-2027 .- 1708-8186. ; 54:10, s. 653-664
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To establish the effect of self-rated and measured functional hearing on depression, taking age and gender into account. Additionally, the study investigates if hearing-aid usage mitigates the effect, and if other physical health problems and social engagement confound it.DESIGN: Cross-sectional data from the UK Biobank resource, including subjective and behavioural measures of functional hearing and multifactorial measures of depressive episodes and symptoms, were accessed and analysed using multi-regression analyses.STUDY SAMPLE: Over 100 000 community-dwelling, 39-70 year-old volunteers.RESULTS: Irrespective of measurement method, poor functional hearing was significantly (p < 0.001) associated with higher levels of depressive episodes (≤ 0.16 factor scores) and depressive symptoms (≤ 0.30 factor scores) when controlling for age and gender. Associations were stronger for subjective reports, for depressive symptoms, and the younger participants. Females generally reported higher levels of depression. Hearing-aid usage did not show a mitigating effect on the associations. Other physical health problems particularly partially confounded the effects.CONCLUSION: Data support an association between functional hearing and depression that is stronger in the younger participants (40-49 years old) and for milder depression. The association was not alleviated by hearing-aid usage, but was partially confounded by other physical health problems.
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| 17. |
- Keidser, Gitte, et al.
(författare)
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The Effect of Functional Hearing and Hearing Aid Usage on Verbal Reasoning in a Large Community-Dwelling Population
- 2016
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Ingår i: Ear and Hearing. - : LIPPINCOTT WILLIAMS & WILKINS. - 0196-0202 .- 1538-4667. ; 37:1, s. e26-e36
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Verbal reasoning performance is an indicator of the ability to think constructively in everyday life and relies on both crystallized and fluid intelligence. This study aimed to determine the effect of functional hearing on verbal reasoning when controlling for age, gender, and education. In addition, the study investigated whether hearing aid usage mitigated the effect and examined different routes from hearing to verbal reasoning.Design: Cross-sectional data on 40- to 70-year-old community-dwelling participants from the UK Biobank resource were accessed. Data consisted of behavioral and subjective measures of functional hearing, assessments of numerical and linguistic verbal reasoning, measures of executive function, and demographic and lifestyle information. Data on 119,093 participants who had completed hearing and verbal reasoning tests were submitted to multiple regression analyses, and data on 61,688 of these participants, who had completed additional cognitive tests and provided relevant lifestyle information, were submitted to structural equation modeling.Results: Poorer performance on the behavioral measure of functional hearing was significantly associated with poorer verbal reasoning in both the numerical and linguistic domains (p < 0.001). There was no association between the subjective measure of functional hearing and verbal reasoning. Functional hearing significantly interacted with education (p < 0.002), showing a trend for functional hearing to have a greater impact on verbal reasoning among those with a higher level of formal education. Among those with poor hearing, hearing aid usage had a significant positive, but not necessarily causal, effect on both numerical and linguistic verbal reasoning (p < 0.005). The estimated effect of hearing aid usage was less than the effect of poor functional hearing. Structural equation modeling analyses confirmed that controlling for education reduced the effect of functional hearing on verbal reasoning and showed that controlling for executive function eliminated the effect. However, when computer usage was controlled for, the eliminating effect of executive function was weakened.Conclusions: Poor functional hearing was associated with poor verbal reasoning in a 40- to 70-year-old community-dwelling population after controlling for age, gender, and education. The effect of functional hearing on verbal reasoning was significantly reduced among hearing aid users and completely overcome by good executive function skills, which may be enhanced by playing computer games.
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| 18. |
- Keidser, Gitte, et al.
(författare)
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The relationship between functional hearing and verbal reasoning
- 2015
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Konferensbidrag (refereegranskat)abstract
- Verbal reasoning performance is an indicator of the ability to think constructively in everyday life, and relies particularly on semantic long-term memory and working memory. Using cross-sectional data from the UK Biobank resource, obtained on over 100,000 40-70 year olds, this study investigated the effect of functional hearing on numerical and linguistic verbal reasoning when controlling for age, gender, and education. The study further investigated if hearing aid usage mitigated the effect, and examined different pathways from hearing to verbal reasoning. Multiple regression analyses showed that poor functional hearing was significantly associated with reduced numerical and linguistic verbal reasoning scores, and that hearing aid usage mitigated the association among those with poor hearing. Hearing significantly interacted with education as larger negative effects of hearing were seen among those with higher levels of qualifications. Structural equation modelling showed that education partially confounded, and the central executive function completely mediated the association between hearing and verbal reasoning when controlling for age. The mediation effect by the central executive function was further partially confounded by computer usage. Findings encourage further investigations into a possible positive effect of hearing aid usage on verbal reasoning (and other cognitive tasks) and of multi-tasking computer games on the central executive function/working memory in middle-aged hearing-impaired adults.
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| 19. |
- Rudner, Mary, et al.
(författare)
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Better visuospatial working memory in adults who report profound deafness compared to those with normal or poor hearing : data from the UK Biobank resource
- 2016
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Ingår i: Ear and Hearing. - : Lippincott Williams & Wilkins. - 0196-0202 .- 1538-4667. ; 37:5, s. 620-622
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Tidskriftsartikel (refereegranskat)abstract
- Experimental work has shown better visuospatial working memory (VSWM) in profoundly deaf individuals compared to those with normal hearing. Other data, including the UK Biobank resource shows poorer VSWM in individuals with poorer hearing. Using the same database, the authors investigated VSWM in individuals who reported profound deafness. Included in this study were 112 participants who were profoundly deaf, 1310 with poor hearing and 74,635 with normal hearing. All participants performed a card-pair matching task as a test of VSWM. Although variance in VSWM performance was large among profoundly deaf participants, at group level it was superior to that of participants with both normal and poor hearing. VSWM in adults is related to hearing status but the association is not linear. Future study should investigate the mechanism behind enhanced VSWM in profoundly deaf adults.
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| 20. |
- Rönnberg, Jerker, et al.
(författare)
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Hearing loss and episodic long-term memory
- 2015
-
Konferensbidrag (refereegranskat)abstract
- The UK Biobank offers cross-sectional epidemiological data collected on >500,000 individuals in the UK between 40 and 70 years of age. Using the UK Biobank data, the aim of this study was to investigate the effects of functional hearing loss and hearing aid usage on visuospatial memory function. A sub-sample of 138,098 participants was selected. 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 (Rönnberg et al., 2014). The selectivity in effect on memory systems replicate previous results (Rönnberg et al., 2011). In addition, the collective results suggest that the selectivity is independent of encoding format in the memory task (auditory, motor or visuospatial), implying an effect of hearing loss on a multimodal episodic long-term memory system.
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| 21. |
- Rönnberg, Jerker, 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
- 2014
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Ingår i: Frontiers in Aging Neuroscience. - : Frontiers Media SA. - 1663-4365. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- The UK Biobank offers cross-sectional epidemiological data collected on > 500 000 individuals in the UK between 40 and 70 years of age. Using the UK Biobank data, the aim of this study was to investigate the effects of functional hearing loss and hearing aid usage on visuospatial memory function. This 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. Broader theoretical implications based on a memory systems approach will be discussed and compared to theoretical alternatives.
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| 22. |
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| 23. |
- Stake, Jan, 1971, et al.
(författare)
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Terahertz technology and applications
- 2008
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Ingår i: International Symposium on Terahertz between Japan and Sweden.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- THz or submillimetre-wave sensing covers the frequency range from 300 GHz to 10 THz (wavelengths from 1 mm to 30 µm). With energy levels in the 1.2-40 meV range, terahertz interactions with matter involve intermolecular, rather than atomic transitions. This gives rise to some imaging and spectroscopy applications that are unique to this particular region of the electromagnetic spectrum. Many polar molecules in the low pressure gaseous state have strong, narrow band, vibrational and rotational emission or absorption modes that peak in this regime and are used as probes for quantum chemistry, astrophysical processes and the dynamics of planetary atmospheres, including the Earth. Still, the terahertz spectral region is by far the least explored portion of the electromagnetic spectrum. A great obstacle has been the absence of robust and reasonable inexpensive receiver components that can operate at room temperature. The talk will consist of two parts: a) room temperature technology for THz applications and b) terahertz applications in biology and medicine.At Chalmers, several key technologies are explored for future THz systems such as radiometers, radars, spectrometers and communication links for frequencies from approximately 100GHz to several THz. Transistors with 50 nm gate length based on the two dimensional electron gas can at present be used for frequencies up to and above 300 GHz for circuits such as amplifiers, frequency mixers, frequency multipliers, oscillators, and modulators. For even higher frequencies, submicron low noise Schottky diodes are used for heterodyne mixers. We are currently pursuing studies of high functionality THz mixers (SSB) and in-house fabrication of monolithically integrated Schottky diode circuits. Results and progress on single side band mixers at 340 GHz aimed for future climate research satellites such as the ESA PREMIER mission. Furthermore, single chip receivers (MMIC) up to 220 GHz for imaging applications will be presented.THz imaging and spectroscopy for biomedical applications is being targeted for the very first time, including assessment of protein conformational states, molecular binding and interaction, DNA hybridization, isomer identification, skin hydration level, drug delivery, wound healing, tumour identification and margin assessment, and cell processes. The submillimeter wave advanced technology group at Caltech, in conjunction with the group at Chalmers (J.Stake was visiting Caltech under a sabbatical), set up a very flexible exposure and monitoring system to be used to systematically investigate the interaction of THz radiation with cells.The talk will cover the latest results obtained from Chalmers on MMICs and Schottky diode mixers for terahertz frequencies (sensors), as well as results from initial investigations towards thermal and non-thermal effects of THz radiation on biological systems (Caltech/JPL-Chalmers).
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| 24. |
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| 25. |
- Svedin, Jan, et al.
(författare)
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An experimental 210 GHz radar system for 3D stand-off detection
- 2010
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Ingår i: 35th International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010. - 9781424466559
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Konferensbidrag (refereegranskat)abstract
- A 210 GHz radar system for studies of personscanning at stand-off distances is presented. The radar uses amechanically scanned RX front-end based on an antennaintegratedMMIC. The TX part is based on an HBV quintupler.Image data formation is made using the FMCW and SARprinciples.
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| 26. |
- Svedin, Jan, et al.
(författare)
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Development of a 210 GHz near-field measurement radar system based on an antenna-integrated MMIC receiver front-end and an ultra-compact HBV transmitter source module
- 2008
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819473493 ; 7117, s. Art. no. 71170H-
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Konferensbidrag (refereegranskat)abstract
- The development of a 210 GHz radar system intended to study security applications such as personnel scanning is reported. The system is designed to operate with a transmit antenna floodlighting the target scene and a mechanically scanned antenna-integrated receiver module. For increased performance and potential future volume production the receiver front-end is based on highly integrated MMICs manufactured using the IAF 0.1 µm GaAs mHEMT process made available through a Swedish-German MoU. A single-chip MMIC solution is being developed containing feed antenna, LNA, mixer and an LO multiplier-chain. The transmitter part is based on a high-power HBV quintupler source-module.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Wang, Xin, et al.
(författare)
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Composition, structure, and dielectric tunability of epitaxial SrTiO3 thin films grown by radio frequency magnetron sputtering
- 1999
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 17:2, s. 564-570
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial (001) oriented SrTiO3 films have been deposited on LaAlO3(001) substrates by off-axis radio frequency magnetron sputtering in Ar:O-2 gas mixtures at substrate temperatures ranging from 650 to 850 degrees C. For the deposition conditions used, stoichiometric targets yielded 20% Sr-deficient films, whereas Sr-enriched targets (Sr1.1TiO0.9O3.0) resulted in stoichiometric films. The Sr-deficient films had a mosaic structure and a larger lattice parameter in comparison to bulk SrTiO3. The stoichiometric films on the other hand had a much higher crystalline quality in the as-deposited condition. The mosaicity of the latter films was primarily limited by the crystalline quality of the LaAlO3 substrates. The lattice parameters of the stoichiometric films were also smaller than the Sr-deficient ones and closer to the bulk value. The dielectric properties of the stoichiometric films were superior to the Sr-deficient films. For films with a thickness of similar to 300 nm, the typical dielectric constants as measured at similar to 77 K and I MHz were determined to be 820 and 500, for the stoichiometric and Sr-deficient films, respectively. Also the capacitance change, as a direct current bias voltage was applied to an interdigital capacitor, was higher for the stoichiometric film, 27.3% as compared to 8.6% when applying a bias of 300 V at 77 K. We also demonstrate the effectiveness of thermal annealing in improving both crystalline quality and dielectric properties, especially for the Sr-deficient films. (C) 1999 American Vacuum Society. [S0734-2101(99)010002-7].
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| 31. |
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| 32. |
- Winkler, Dag, 1957, et al.
(författare)
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A sub-mm wave quasiparticle receiver for 750 GHz-progress report
- 1986
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - 0277-786X. ; 598, s. 33-38
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Konferensbidrag (refereegranskat)abstract
- The authors have designed a sub-mm wave receiver using superconducting edge tunnel junctions (SIS/SIN). The mixer is subharmonically pumped at about 375 GHz, whereas the signal frequency is at twice this frequency. The local oscillator and the signal are both coupled to a constant width slot antenna, and via an exponential tapering to an array of two junctions coupled in series across a slotline. Design and preliminary results are discussed
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