| 1. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
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Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive
- 2020
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 453
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Tidskriftsartikel (refereegranskat)abstract
- Self-discharge is being recognized as one of the main obstacles to implementing the supercapacitor (SC) in standalone self-powered systems. Strategies for addressing this issue include the modification of electrodes, electrolytes, separators, and diverse device configurations. However, an improved self-discharge behavior is often achieved with a large compromise on other prominent figures of merit such as capacitance, energy density, or cycle life of the device. In this work, a thorough comparative electrochemical investigation of SCs containing a neutral aqueous electrolyte, 1 M Li2SO4, and with a liquid crystal (LC) additive, 2% 4-n-pentyl-4′-cyanobiphenyl (5CB) in 1 M Li2SO4, has been carried out at different states of charge. The results demonstrate that the device containing the LC additive 5CB exhibits a reduced self-discharge and leakage current without compromising the capacitive performance at different nominal voltages compared to the behavior of the device without 5CB. We suggest an explanation of the difference of the self-discharge behavior between the devices through tunability of the effective conductivity of the electrolyte composite upon applied voltages. As a result, in an open circuit condition, the device containing LC shows a slower diffusion of ions that facilitates a decreased self-discharge and leakage current.
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| 2. |
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| 3. |
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| 4. |
- Köhler, Elof, 1980, et al.
(författare)
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Impact of designed asymmetries on the effective bandwidth of a backfolded piezoelectric energy harvester
- 2019
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Ingår i: Sensors and Actuators, A: Physical. - : Elsevier BV. - 0924-4247. ; 292, s. 77-89
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Tidskriftsartikel (refereegranskat)abstract
- For the successful realization of autonomous wireless sensors, they will have to be able to harvest energy from their surroundings. Vibrational energy harvesting is one possible power source for wireless sensors, since vibrations are abundant in many environments. In order to make vibrational energy harvesters more useful, a broad bandwidth is desirable since many vibrations are stochastic in nature. In this paper we implement asymmetry to a backfolded piezoelectric energy harvester to achieve broader effective bandwidth with maintained power output. The optimized harvester achieves a minimum of 2.75 V in the frequency range 92–162 Hz with peak power output of 1.80 mW. Asymmetry based on different lengths of the conjoined cantilevers is experimentally and numerically shown to have the largest impact on the bandwidth, compared to the impact of modified mass loadings.
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| 5. |
- Naboka, Olga, 1981, et al.
(författare)
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Carbon Nanofibers Synthesized from Electrospun Cellulose for Advanced Materials Applications
- 2013
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Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 730-732, s. 903-908
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Konferensbidrag (refereegranskat)abstract
- Carbon nanofibrous sheets (conductivity 1.9 to 35.5 S×cm-1, water contact angle up to 137°) consisting of amorphous fibers with diameter of 20 - 150 nm (C:O atomic ratio 25.4 - 86.0) were synthesized by carbonization of cellulose regenerated from electrospun cellulose acetate mats with three methods of alkaline deacetylation. It was established that C:O atomic ratio, conductivity and hydrophobicity depended on the regeneration method and on the temperature of carbonization. The highest flexibility, lowest conductivity and lowest water contact angle was observed for carbon synthesized from cellulose regenerated with NaOH in ethanol (0.05 mol/l) for 24 hours at room temperature. The highest conductivity, highest water contact angle and lowest flexibility was observed for carbon synthesized from cellulose regenerated with water solution of NaOH/NaCl (3.75 M NaOH, 2.1 M NaCl) during 15 minutes at 65°C.
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| 7. |
- Ragnarsson, Lars-Åke, 1968, et al.
(författare)
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Surface potential influence on defect passivation kinetics probed by chromium gated metal-oxide-silicon devices
- 1999
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Ingår i: Microelectronic Engineering. - 0167-9317. ; 48:1-4, s. 219-222
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Tidskriftsartikel (refereegranskat)abstract
- In this study we present a new scheme for obtaining information on the passivation mechanisms of as-grown Si-SiO2 interface defects by resolving the effects of bias on the defect passivation reaction. This is possible when using chromium gated metal-oxide-silicon devices for which the effect of non-biased passivation is very small compared to devices with for example aluminum gates. It is shown that a negative surface potential promotes the passivation of interface states while a positive surface potential reduces it.
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| 8. |
- Rahiminejad, Sofia, 1987, et al.
(författare)
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Design of micromachined ridge gap waveguides for millimeter-wave applications
- 2011
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Ingår i: Procedia Eng.. - : Elsevier BV. ; 25, s. 519-522
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Konferensbidrag (refereegranskat)abstract
- The ridge gap waveguide is a new transmission line for millimeter-wave applications. Traditionally, rectangular waveguides are used for those applications due to their low loss. However their fabrication requires precision machining, very good electrical contact and alignment between two joining mechanical parts. Ridge gap waveguides can obtain similar performance without requiring conductive sidewalls and this provides more freedom during the fabrication and assembly process as the structure is no longer sensitive to small gaps between the side walls and the upper lid. The ridge gap waveguide has already been validated for 10-20 GHz using conventional fabrication methods. The ridge gap waveguide prototypes presented in this paper are designed to work in the frequency region between 210 and 340 GHz, and fabricated using MEMS technology. MEMS technology provides fabrication precision of the structures and thus opens the path for high-frequency components.
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| 9. |
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| 10. |
- Rahiminejad, Sofia, 1987, et al.
(författare)
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Micromachined Ridge Gap Waveguide and Resonator for Millimeter-Wave Applications
- 2012
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Ingår i: Sensors and Actuators, A: Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 186, s. 264-269
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Tidskriftsartikel (refereegranskat)abstract
- The ridge gap waveguide is a fundamentally new high-frequency waveguide. It does not need any electrical contact between the split blocks which gives it an advantage compared to the rectangular waveguide which is the standard today. These waveguides are conventionally fabricated by milling, although above 100 GHz milling is not adequate anymore. MEMS technology on the other hand, can offer high-precision fabrication and thus opens the path for new types of high-frequency components. In this paper both a ridge gap waveguide and a ridge gap resonator have been fabricated for the frequencies 220–325 GHz using MEMS technology. Support packages have been designed to enable device measurements. Simulations show that the reflection coefficient for the ridge gap waveguide is below −15 dB between 240 and 340 GHz. Two resonance peaks were measured at the frequencies 234 GHz and 284 GHz for the ridge gap resonator with unloaded Q-values of 336 and 527 respectively. Both the waveguide and resonator have the potential to obtain similar performances as the rectangular waveguide without strict requirement on electrical contact, allowing simplified fabrication and assembly technique.
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