SwePub - sökning: WFRF:(Smith Anderson David 198...

Numrering	Referens	Omslagsbild	Hitta
1.	Clementini, G., et al. (författare) Testing parallaxes with local Cepheids and RR Lyrae stars 2017 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 605 Tidskriftsartikel (refereegranskat)abstract Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the HIPPARCOS and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims. In order to test these first parallax measurements of the primary standard candles of the cosmological distance ladder, which involve astrometry collected by Gaia during the initial 14 months of science operation, we compared them with literature estimates and derived new period-luminosity (PL), period-Wesenheit (PW) relations for classical and Type II Cepheids and infrared PL, PL-metallicity (PLZ), and optical luminosity-metallicity (MV-[Fe/H]) relations for the RR Lyrae stars, with zero points based on TGAS.Methods. Classical Cepheids were carefully selected in order to discard known or suspected binary systems. The final sample comprises 102 fundamental mode pulsators with periods ranging from 1.68 to 51.66 days (of which 33 with sigma(omega)/omega < 0 : 5). The Type II Cepheids include a total of 26 W Virginis and BL Herculis stars spanning the period range from 1.16 to 30.00 days (of which only 7 with sigma(omega)/omega 0 : 5). The RR Lyrae stars include 200 sources with pulsation period ranging from 0.27 to 0.80 days (of which 112 with sigma(omega)/omega < 0 : 5). The new relations were computed using multi- band (V; I; J; K-s) photometry and spectroscopic metal abundances available in the literature, and by applying three alternative approaches: (i) linear least-squares fitting of the absolute magnitudes inferred from direct transformation of the TGAS parallaxes; (ii) adopting astrometry-based luminosities; and (iii) using a Bayesian fitting approach. The last two methods work in parallax space where parallaxes are used directly, thus maintaining symmetrical errors and allowing negative parallaxes to be used. The TGAS-based PL; PW; PLZ, and MV [Fe/H] relations are discussed by comparing the distance to the Large Magellanic Cloud provided by different types of pulsating stars and alternative fitting methods.Results. Good agreement is found from direct comparison of the parallaxes of RR Lyrae stars for which both TGAS and HST measurements are available. Similarly, very good agreement is found between the TGAS values and the parallaxes inferred from the absolute magnitudes of Cepheids and RR Lyrae stars analysed with the Baade-Wesselink method. TGAS values also compare favourably with the parallaxes inferred by theoretical model fitting of the multi-band light curves for two of the three classical Cepheids and one RR Lyrae star, which were analysed with this technique in our samples. The K-band PL relations show the significant improvement of the TGAS parallaxes for Cepheids and RR Lyrae stars with respect to the HIPPARCOS measurements. This is particularly true for the RR Lyrae stars for which improvement in quality and statistics is impressive.Conclusions. TGAS parallaxes bring a significant added value to the previous HIPPARCOS estimates. The relations presented in this paper represent the first Gaia-calibrated relations and form a work-in-progress milestone report in the wait for Gaia-only parallaxes of which a first solution will become available with Gaia Data Release 2 (DR2) in 2018.
2.	van Leeuwen, F., et al. (författare) Gaia Data Release 1 : Open cluster astrometry: Performance, limitations, and future prospects 2017 Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601 Tidskriftsartikel (refereegranskat)abstract Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.
3.	Li, Qi, 1990, et al. (författare) Finger Number and Device Performance: A Case Study of Reduced Graphene Oxide Microsupercapacitors 2021 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2 Tidskriftsartikel (refereegranskat)abstract Microsupercapacitors (MSCs) are recognized as suitable energy storage devices for the internet of things (IoTs) applications. Herein is described the work conducted to assess the areal energy and power densities of MSCs with 2, 10, 20, and 40 interdigital finger electrodes on a fixed device footprint area (the finger interspacing is fixed at 40 μm, and the finger width and length are allowed to vary to fit the footprint area). The MSCs are based on reduced graphene oxide (rGO) materials and fabricated with a spin-coating and etch method. The performance evaluation indicates a strong dependency of areal capacitance and energy density on the number of fingers, and the maximum (impedance match) power density is also influenced to a relatively large extent, whereas the average power density is not sensitive to the configuration parameters in the present evaluation settings (scan rate 20–200 mV s−1 and current density of 100 μA cm−2). For the rGO-based devices, the equivalent distributed resistance may play an important role in determining the device resistance and power-related performance.
4.	Smith, Anderson David, 1985, et al. (författare) Toward CMOS compatible wafer-scale fabrication of carbon-based microsupercapacitors for IoT 2018 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1052:1 Konferensbidrag (refereegranskat)abstract This work presents a wafer-scale method of microsupercapacitor (MSC) fabrication. Deposition of the electrode precursor, i.e. graphene oxide, is accomplished through spin-coating which allows for potential application in CMOS compatible processes for future integrated on-chip energy storage systems. Our MSCs have an areal capacitance of 0.4 mF/cm2at 10 μA, which is a very promising result. Further, the MSC has good rate capability as its capacitance decreases by only 0.03 mF/cm2when the current increases to 50 μA. The MSCs have a maximum energy density of 0.04 μWh/cm2and a maximum power density as high as 96 μW/cm2. Additionally, the wafer-scale process demonstrates industrial viability.
5.	Vyas, Agin, 1992, et al. (författare) Enhanced Electrode Deposition for On-Chip Integrated Micro-Supercapacitors by Controlled Surface Roughening 2020 Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 5219-5228 Tidskriftsartikel (refereegranskat)abstract On-chip micro-supercapacitors (MSCs), integrated with energy harvesters, hold substantial promise for developing self-powered wireless sensor systems. However, MSCs have conventionally been manufactured through techniques incompatible with semiconductor fabrication technology, the most significant bottleneck being the electrode deposition technique. Utilization of spin-coating for electrode deposition has shown potential to deliver several complementary metal-oxide-semiconductor (CMOS)-compatible MSCs on a silicon substrate. Yet, their limited electrochemical performance and yield over the substrate have remained challenges obstructing their subsequent integration. We report a facile surface roughening technique for improving the wafer yield and the electrochemical performance of CMOS-compatible MSCs, specifically for reduced graphene oxide as an electrode material. A 4 nm iron layer is deposited and annealed on the wafer substrate to increase the roughness of the surface. In comparison to standard nonroughened MSCs, the increase in surface roughness leads to a 78% increased electrode thickness, 21% improvement in mass retention, 57% improvement in the uniformity of the spin-coated electrodes, and a high yield of 87% working devices on a 2″ silicon substrate. Furthermore, these improvements directly translate to higher capacitive performance with enhanced rate capability, energy, and power density. This technique brings us one step closer to fully integrable CMOS-compatible MSCs in self-powered systems for on-chip wireless sensor electronics. ©
6.	Vyas, Agin, 1992, et al. (författare) Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes 2019 Ingår i: MRS Advances. - : Springer Science and Business Media LLC. - 2059-8521. ; 4:23, s. 1335-1340 Konferensbidrag (refereegranskat)abstract Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things' sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO 2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
7.	Fan, Xuge, 1985-, et al. (författare) Manufacturing of Graphene Membranes with Suspended Silicon Proof Masses forMEMS and NEMS Tidskriftsartikel (refereegranskat)
8.	Hansson, Josef, 1991, et al. (författare) Bipolar electrochemical capacitors using double-sided carbon nanotubes on graphite electrodes 2020 Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 451 Tidskriftsartikel (refereegranskat)abstract The electrochemical capacitor (EC) is a key enabler for the miniaturized self-powered systems expected to become ubiquitous with the advent of the internet-of-things (IoT). Vertically aligned carbon nanotubes (VACNTs) on graphite holds promise as electrodes for compact and low-loss ECs. However, as with all ECs, the operating voltage is low, and miniaturization of higher voltage devices necessitates a bipolar design. In this paper, we demonstrate a bipolar EC using graphite/VACNTs electrodes fabricated using a joule heating chemical vapor deposition (CVD) setup. The constructed EC contains one layer of double-sided VACNTs on graphite as bipolar electrode. Compared to a series connection of two individual devices, the bipolar EC has 22% boost in volumetric energy density. More significant boost is envisaged for stacking more bipolar electrode layers. The energy enhancement is achieved without aggravating self-discharge (71.2% retention after 1 h), and at no sacrifice of cycling stability (96.7% over 50000 cycles) owing to uniform growth of VACNTs and thus eliminating cell imbalance problems.
9.	Haque, Mohammad Mazharul, 1984, et al. (författare) Identification of self-discharge mechanisms of ionic liquid electrolyte based supercapacitor under high-temperature operation 2021 Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 485 Tidskriftsartikel (refereegranskat)abstract Ionic liquids (ILs) are promising electrolytes for supercapacitors (SCs) aimed for high-temperature applications, where increased ionic conductivity results in superior capacitive performance compared to room temperature (RT) performance. However, an increased temperature also accelerates the self-discharge rate that adversely affects energy retention and restricts the usage of SCs in standalone applications. In this study, a detailed electrochemical investigation on the self-discharge behaviour of carbon-based SCs containing an IL, 1-Ethyl-3-methylimidazolium acetate (EMIM Ac), has been carried out in the temperature range RT - 60 °C, and the underlying self-discharge mechanisms are identified. The results reveal that at a high voltage of 1.5 V, the self-discharge is characterized by a combination of charge redistribution and diffusion at both RT and 60 °C. At 60 °C, the diffusion-controlled mechanism dominates at lower voltages over the charge redistribution effect, while at RT both mechanisms contribute to a similar extent. The observed difference in the self-discharge mechanism between RT and 60 °C is explained in terms of a decreased RC time constant (τRC) at elevated temperature, and the same conclusions are potentially applicable to other IL-containing SCs as well.
10.	Haque, Mohammad Mazharul, 1984, et al. (författare) Ionic liquid electrolyte for supercapacitor with high temperature compatibility 2017 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1 Konferensbidrag (refereegranskat)abstract This work describes the electrochemical investigation of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate (EMIM Ac) and 1-butyl-3-methylimidazolium chloride (BMIM Cl), as electrolytes in supercapacitors (SC). A comprehensive study on high temperature (HT) endurance that is required for system integration in microelectronics has also been carried out. It has been found that EMIM Ac containing SC performs better than a BMIM Cl containing SC, and HT treatment improves the capacitive performance.
11.	Haque, Mohammad Mazharul, 1984, et al. (författare) Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive 2020 Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 453 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.
12.	Haque, Mohammad Mazharul, 1984, et al. (författare) Thermal influence on the electrochemical behavior of a supercapacitor containing an ionic liquid electrolyte 2018 Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 263, s. 249-260 Tidskriftsartikel (refereegranskat)abstract Emerging demands on heat-durable electronics have accelerated the need for high temperature supercapacitors as well as for understanding the influence of elevated temperatures on the capacitive behavior. In this work, we present a comprehensive study of the thermal influence on a supercapacitor containing 1-ethyl-3-methylimidazolium acetate (EMIM Ac) electrolyte and activated carbon (AC) electrodes. The performance variation as a function of temperature in a range from 21 °C to 150 °C reveals that a high specific capacitance of 142 F g−1 can be achieved at 150 °C at a current density of 2 A g−1 with a rate capability of 87% at 15 A g−1 (relative to 2 A g−1). At 150 °C, equivalent series resistance (ESR) is only 0.37 Ω cm2, which is a result of improved ionic conductivity of the electrolyte at elevated temperature. The ESR value of 2.5 Ω cm2 at room temperature reflects a good compatibility between EMIM Ac and AC. In addition, a capacitance retention of more than 95% (in the end of 1000 cycles) is maintained up to120 °C followed by 85% at 150 °C. These results confirm EMIM Ac as a suitable candidate for carbon-based high temperature supercapacitors, and the observations regarding the thermal influence on performance metrics e.g. usable operation voltage could be applicable to other energy storage devices.
13.	Köhler, Elof, 1980, et al. (författare) Impact of designed asymmetries on the effective bandwidth of a backfolded piezoelectric energy harvester 2019 Ingår i: Sensors and Actuators, A: Physical. - : Elsevier BV. - 0924-4247. ; 292, s. 77-89 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.
14.	Li, Qi, 1990, et al. (författare) Carbon hybrid and its derived materials for electrochemical capacitors 2018 Konferensbidrag (övrigt vetenskapligt/konstnärligt)
15.	Li, Qi, 1990, et al. (författare) Compact and low loss electrochemical capacitors using a graphite / carbon nanotube hybrid material for miniaturized systems 2019 Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 412, s. 374-383 Tidskriftsartikel (refereegranskat)abstract With the establishment of the internet of things (IoT) and the rapid development of advanced microsystems, there is a growing demand to develop electrochemical capacitors (ECs) to replace bulky electrolytic capacitors on circuit boards for AC line filtering, and as a storage unit in energy autonomous systems. For this purpose, ECs must be capable of handling sufficiently high signal frequencies, display minimum energy loss through self-discharge and leakage current as well as maintaining an adequate capacitance. Here, we demonstrate ECs based on mechanically flexible, covalently bonded graphite/vertically aligned carbon nanotubes (graphite/VACNTs) hybrid materials. The ECs employing a KOH electrolyte exhibit a phase angle of −84.8°, an areal capacitance of 1.38 mF cm−2 and a volumetric capacitance (device level) of 345 mF cm−3 at 120 Hz, which is among the highest values for carbon based high frequency ECs. Additionally, the performance as a storage EC for miniaturized systems is evaluated. We demonstrate capacitive charging/discharging at μA current with a gel electrolyte, and sub-μA leakage current reached within 50 s, and 100 nA level equilibrium leakage within 100 s at 2.0 V floating with an ionic liquid electrolyte.
16.	Li, Qi, 1990, et al. (författare) Explanation of anomalous rate capability enhancement by manganese oxide incorporation in carbon nanoﬁber electrodes for electrochemical capacitors 2020 Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 340 Tidskriftsartikel (refereegranskat)abstract Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, characteristics which most battery technologies lack. Making composites out of carbon and pseudocapacitive materials is a popular strategy directed on narrowing the gap in energy density with regard to batteries. Usually, the incorporation of pseudocapacitive materials leads to a decrease in power performance compared to a pure carbon matrix, due to inferior electrical conductivity. This work, however, presents signiﬁcant improvement in rate capability demonstrated by a composite electrode containing carbon nanoﬁbers (NCNF) and manganese oxides (MnO2). The NCNF/MnO2 is prepared with a common method through the reaction with permanganate. The material has excellent performance metrics, especially a 78.2% rate capability (capacitance retention at 15 A g−1 relative to 0.5 A g−1), more than 10 times that for the NCNF carbon matrix. The exceptional enhancement can be explained by the development of micropores and surface area of NCNF, thus alleviating the “pore starvation” issue, and surface functional groups variation that enhances capacitive performance. This work highlights the importance of paying attention to the modiﬁcation of carbon substrate when investigating carbon composite electrodes e.g. carbon/MnO2 networks.
17.	Li, Qi, 1990, et al. (författare) Graphite paper / carbon nanotube composite: A potential supercapacitor electrode for powering microsystem technology 2017 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1 Konferensbidrag (refereegranskat)abstract This work describes fabrication of a flexible supercapacitor electrode. The fabrication starts with graphite paper (GP). Carbon nanotubes (CNTs) are then grown directly to the carbon surface by chemical vapor deposition (CVD), forming a heterogeneous structure of GP/CNT. The integration of CNT enhances capacitive performance while maintaining the flexibility of GP, thus making GP/CNT a promising supercapacitor electrode material for potentially powering microsystem technology.
18.	Li, Qi, 1990, et al. (författare) Redox enhanced energy storage in an aqueous high-voltage electrochemical capacitor with a potassium bromide electrolyte 2017 Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 348, s. 219-228 Tidskriftsartikel (refereegranskat)abstract This paper reports a detailed electrochemical investigation of a symmetric carbon-carbon electrochemical device with a potassium bromide (KBr) electrolyte. Below 1.6 V, KBr gives electrochemical double layer behavior. At higher voltages the Br-/Br-3 redox reaction comes into effect and enhances the energy storage. The redox-enhanced device has a high energy density, excellent stability, as well as high coulombic and energy efficiencies even at 1.9 V. More importantly, the redox contribution can be “triggered” by pre-cycling at 1.9 V, and remains beneficial after switching to 1.6 V. The triggering operation leads to a 22% increase in stored energy with negligible sacrifice of power. The intriguing behavior is accompanied by a series of complex variations including the shifts of electrode potential limits and the shift of potential of zero voltage. The electro-oxidation of the positive electrode and kinetics of the Br-/Br-3 electrode reactions are proposed to be the main causes for the triggering phenomenon. These findings provide means to improve the design and operation of devices that contain bromine, or other redox species with a comparably high electrode potential.
19.	Moreno-Garcia, D., et al. (författare) A Resonant Graphene NEMS Vibrometer 2022 Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 18:28 Tidskriftsartikel (refereegranskat)abstract Measuring vibrations is essential to ensuring building structural safety and machine stability. Predictive maintenance is a central internet of things (IoT) application within the new industrial revolution, where sustainability and performance increase over time are going to be paramount. To reduce the footprint and cost of vibration sensors while improving their performance, new sensor concepts are needed. Here, double-layer graphene membranes are utilized with a suspended silicon proof demonstrating their operation as resonant vibration sensors that show outstanding performance for a given footprint and proof mass. The unveiled sensing effect is based on resonant transduction and has important implications for experimental studies involving thin nano and micro mechanical resonators that are excited by an external shaker.
20.	Rajendra Babu Kalai Arasi, Azega, 1995, et al. (författare) Durable Activated Carbon Electrodes with a Green Binder 2022 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2 Tidskriftsartikel (refereegranskat)abstract Herein, the fabrication and electrochemical performance of thick (180−280 μm) activated carbon (AC) electrodes with carbonized lignin-derived carbon fiber (LCF) inclusions are reported. Efforts are taken in fabricating robust free-standing electrodes from an environmentally friendly binder, microfibrillated cellulose (MFC), considering the biologically hazardous nature of other commonly used binders like polytetrafluoroethylene (PTFE), n-methyl-2-pyrrolidone (NMP), and polyvinylidene fluoride (PVDF). Generally, electrodes composed of MFC binder are prone to cracking upon drying, especially with higher mass loadings, which leads to nonflexibility and poor device stability. The LCF inclusions into the AC electrode with MFC binders not only increase flexibility but also contribute to better conductivity in the electrodes. The LCFs act as an intermediate layer among AC particles and serve as conductive pathways, facilitating exposure of more active surfaces to the electrolyte. A thick electrode with high mass loading of 10 mg cm−2 is achieved. The results show that by incorporating 2 wt% LCF to the AC material, the best device with 5 mg cm−2 delivers a specific capacitance of 97 F g−1, while the specific capacitance of the reference AC device without LCF is 85 F g−1.
21.	Smith, Anderson David, 1985, et al. (författare) Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks : Present and Future Development 2019 Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 19:19 Tidskriftsartikel (refereegranskat)abstract There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering.
22.	Staaf, Henrik, 1976, et al. (författare) Achieving increased bandwidth for 4 degree of freedom self-tuning energy harvester 2018 Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 420, s. 165-173 Tidskriftsartikel (refereegranskat)abstract The frequency response of a self-tuning energy harvester composed of two piezoelectric cantilevers connected by a middle beam with a sliding mass is investigated. Measurements show that incorporation of a free-sliding mass increases the bandwidth. Using an analytical model, the system is explained through close investigation of the resonance modes. Resonance mode behavior further suggests that, by breaking the symmetry of the system, even broader bandwidths are achievable.
23.	Staaf, Henrik, 1976, et al. (författare) Effective piezoelectric energy harvesting with bandwidth enhancement by assymetry augmented self-tuning of conjoined cantilevers 2019 Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403. ; 150, s. 1-11 Tidskriftsartikel (refereegranskat)abstract Vibrational energy harvesting offers a potential power supply for future intelligent wireless sensors. 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 use a piezoelectric self-tuning energy harvester to demonstrate the importance of designing for asymmetry in a system of conjoined cantilevers. Asymmetry is achieved by varying the piezoelectric cantilever lengths as well as the proof mass weights. In addition to bandwidth broadening, a self-tuning effect is experimentally demonstrated by a sliding mass. The measurement results confirm previous model predictions.
24.	Staaf, Henrik, 1976, et al. (författare) Verification of Self-Tuning 4DOF Piezoelectric Energy Harvester with Enhanced Bandwidth 2018 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. Konferensbidrag (refereegranskat)abstract In this paper, we present an analytical model to predict enhanced bandwidth for a piezoelectric energy harvester with self-tuning, accomplished by a sliding mass. The model predicts that by implementing asymmetry of different piezoelectric cantilever lengths , the bandwidth can theoretically approach 60 Hz. Validation measurements demonstrate an increased 3dB bandwidth up to 21 Hz with 150 mW, by configuration 23/17 mm in open length – providing sufficient power for a ZigBee to continually transmit.
25.	Velasco, Andres, et al. (författare) Investigation of vertical carbon nanosheet growth and its potential for microsupercapacitors 2021 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1837:1 Konferensbidrag (refereegranskat)abstract One of the biggest applications that are coming with the Internet of Things (IoT) are miniaturized sensor networks that connect wirelessly to each other and the internet. Microsupercapacitors (MSCs) are ideal to power these devices, with large cyclability and lifetime. Porous carbons are the material of choice for these devices, but their morphology and manufacturing are far from optimized. Vertically oriented graphene MSCs have shown great promise due to their high specific surface areas and conductivity. In this work, the growth of vertically aligned carbon nanosheets (CNS) on 2-inch wafers has been studied, and it has been used as active material to manufacture MSC and transmission line model (TLM) wafers. The fabricated CNS MSC devices show a capacitance of 7.4 ?F (50.7 ?F/cm2, normalized to the area of the electrodes), a five-times increase from previous results obtained by the group.
26.	Vyas, Agin, 1992, et al. (författare) A micromachined coupled-cantilever for piezoelectric energy harvesters 2018 Ingår i: Micromachines. - : MDPI AG. - 2072-666X. ; 9:5 Tidskriftsartikel (refereegranskat)abstract This paper presents a demonstration of the feasibility of fabricating micro-cantilever harvesters with extended stress distribution and enhanced bandwidth by exploiting an M-shaped two-degrees-of-freedom design. The measured mechanical response of the fabricated device displays the predicted dual resonance peak behavior with the fundamental peak at the intended frequency. This design has the features of high energy conversion efficiency in a miniaturized environment where the available vibrational energy varies in frequency. It makes such a design suitable for future large volume production of integrated self powered sensors nodes for the Internet-of-Things
27.	Vyas, Agin, 1992, et al. (författare) Alkyl-Amino Functionalized Reduced-Graphene-Oxide–heptadecan-9-amine-Based Spin-Coated Microsupercapacitors for On-Chip Low Power Electronics 2022 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2 Tidskriftsartikel (refereegranskat)abstract With the miniaturization of microelectronics, integrated circuits can benefit from an on-chip solid-state power supply. Microsupercapacitors (MSCs), owing to their long lifetimes and complementary metal-oxide-semiconductor (CMOS) compatible fabrication, can be a potential on-chip energy storage unit. MSCs fabricated through spin coating graphene-oxide (GrO) often suffer from insufficient electrode thicknesses that lead to low energy densities. It, therefore, requires functionalizations for GrO that can improve the MSC electrode thickness and, thereby, the performance of the MSC. Thus, herein, the MSCs fabricated of alkyl-amino functionalized reduced-graphene-oxide–heptadecan-9-amine (rGO) are reported for enhanced electrode thickness, high capacitance, and lower series resistance compared with functionalized GrO-based MSCs (GO-MSCs). The functionalized rGO solves a significant issue of inadequate electrode thickness in wafer-scale MSC fabrication while achieving higher energy densities in fewer spin coatings. The rGO-MSC displays an areal capacitance of 108 μF cm−2 compared with 24 μF cm−2 for the GO-MSC while also demonstrating more than twice its power density in an integration compatible ionic liquid electrolyte 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI).
28.	Vyas, Agin, 1992, et al. (författare) Comparison of Thermally Grown Carbon Nanofiber-Based and Reduced Graphene Oxide-Based CMOS-Compatible Microsupercapacitors 2021 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2 Tidskriftsartikel (refereegranskat)abstract Microsupercapacitors as miniature energy storage devices require complementary metal-oxide-semiconductor (CMOS) compatible techniques for electrode deposition to be integrated in wireless sensor network sensor systems. Among several processing techniques, chemical vapor deposition (CVD) and spin coating, present in CMOS manufacturing facilities, are the two most viable processes for electrode growth and deposition, respectively. To make an argument for choosing either of these techniques to fabricate MSCs utilizable for an on-chip power supply, we need a comparative assessment of their electrochemical performance. Herein, the evaluation of MSCs with CVD-grown carbon nanofiber (CNF)-based and spin-coated reduced graphene oxide (rGO)-based electrodes is reported. The devices are compared for their capacitance, energy and power density, charge retention, characteristic frequencies, and ease of fabrication over a large sweep of scan rates, current densities, and frequencies. The rGO-based MSCs demonstrate 112 mu F cm(-2) at 100 mV s(-1) and a power density of 12.8 mW cm(-2). The CNF-based MSCs show 269.7 mu F cm(-2) and 30.8 mW cm(-2). CVD-grown CNF outperforms spin-coated rGO in capacitive storage at low frequencies, whereas the latter is better in terms of charge retention and high-frequency capacitance response.
29.	Vyas, Agin, 1992, et al. (författare) Impact of electrode geometry and thickness on planar on-chip microsupercapacitors 2020 Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:52, s. 31435-31441 Tidskriftsartikel (refereegranskat)abstract We report an assessment of the influence of both finger geometry and vertically-oriented carbon nanofiber lengths in planar micro-supercapacitors. Increasing the finger number leads to an up-scaling in areal power densities, which increases with scan rate. Growing the nanofibers longer, however, does not lead to a proportional growth in capacitance, proposedly related to limited ion penetration of the electrode.
30.	Vyas, Agin, 1992, et al. (författare) Investigation of palladium current collectors for vertical graphene-based microsupercapacitors 2019 Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1319:1 Konferensbidrag (refereegranskat)abstract As microsystems are reduced in size and become integrated in the Internet of Things (IoT), they require an adequate power supply which can be integrated at the same size scale. Microsupercapacitors (MSCs), if coupled with on-chip harvesters, can offer solutions for a self-sustaining, on-chip power supply. However, the implementation of reliable MSC wafer-scale production compatible with CMOS technology remains a challenge. Palladium (Pd) is known as a CMOS compatible metal and, in this paper, we investigate the use of Pd as a contact material for vertical graphene (VG) electrodes in wafer-scale MSC fabrication. We show that a Ti diffusion barrier is required to prevent short-circuiting for the successful employment of Pd contacts. The fabricated MSCs demonstrate a capacitance of 1.3 μF/cm2 with an energy density of 0.42 μJ/cm2. Thus, utilization of a Ti diffusion barrier with a CMOS compatible Pd metal electrode is a step towards integrating MSCs in semiconductor microsystems.
31.	Vyas, Agin, 1992, et al. (författare) Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors 2022 Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:4, s. 4221-4231 Tidskriftsartikel (refereegranskat)abstract Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF/cm^2 at 20 mV/s^1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF/cm^2 at 20 mV/s^1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.
32.	Vyas, Agin, 1992, et al. (författare) Towards Integrated Flexible Energy Harvester and Supercapacitor for Self-powered Wearable Sensors 2020 Ingår i: 2019 19TH INTERNATIONAL CONFERENCE ON MICRO AND NANOTECHNOLOGY FOR POWER GENERATION AND ENERGY CONVERSION APPLICATIONS (POWERMEMS). Konferensbidrag (refereegranskat)abstract We present the first results of a flexible energy harvester and a foldable supercapacitor to power wearable and flexible sensors. The flexible energy harvester is fabricated by using 38 mu m piezoelectric polyvinylidene difluoride (PVDF) sandwiched between carbon electrodes. Both the design and process excel in simplicity and cost-effectiveness. The flexible harvester demonstrates a power output of 2.6 mu W cm(-3) at a resonant frequency of 50 Hz with a 3dB bandwidth of about 11 Hz, which is higher than devices previously reported and similar to a commercial PZT harvester film of same size. A flexible energy storage supercapacitor (GP-SC) was fabricated using a graphite/VACNTs (vertically aligned carbon nanotubes) material as electrodes. A prototype GP-SCs has an areal capacitance of about 1.2 mF cm(-2). Finally, an integrated scheme is proposed for future work.

Skapa referenser, mejla, bekava och länka

Länka till träfflistan

Träfflista för sökning "WFRF:(Smith Anderson David 1985) "

Avgränsa träffmängd

År