1,721,002 research outputs found
Flash photography vision system for inkjet drop formation characterization
No full textOp het Instituut voor Materiaalonderzoek (IMO) van de UHasselt ontwikkelt men functionele inkten voor het inkjet printen van bijvoorbeeld RFID antennes. Printen binnen zeer kleine toleranties eist echter kennis van het exact materiaalgedrag tijdens elk van volgende afzettingsfasen: het uitstoten van de inkt, haar val naar het substraat en haar interactie met het oppervlak. In deze masterproef wordt een systeem ontwikkeld om inkjet druppels over de volledige afstand van printkop tot substraat optisch te inspecteren.
Om de vallende druppels zeer scherp in beeld te brengen, wordt gekozen voor flash photography. Hierbij is niet de mechanische sluitertijd van de camera maar de duur van de gepulste belichting bepalend voor de effectieve belichtingstijd van de druppel. Verder levert het gebruik van bi-telecentrische lenzen meer accurate beelden op door randeffecten en vervorming te beperken. Een tijdkritische hardware schakeling garandeert vervolgens betrouwbaar getimede vastlegging van beelden voor verdere verwerking in LabView.
Het resultaat bestaat uit twee delen. Enerzijds werd een zorgvuldig samengesteld visiesysteem opgebouwd dat, met gekarakteriseerde nauwkeurigheid, geschikt is om de druppels te observeren. Anderzijds zijn metingen uitgevoerd op de resulterende camerabeelden bij één vaste instelling van de printkop. Hieruit werden een straal van ongeveer 24µm, snelheid van gemiddeld 1.08m/s en volume van naar schatting 62 picoliter afgeleid als eigenschappen van de hoofddruppel
Electronic devices which stretch like rubber bands: a holistic approach to materials and fabrication methods for stretchable electronics
No full textThis thesis revolves around a vision of electronic circuits which are mechanically soft and can be stretched and bent to certain degrees. These stretchable (soft) electronics first of all offer great advantages over the traditional, rigid devices with which we are surrounded in terms of integration: circuits and sensors that can stretch and bend can now be indiscernibly integrated on for instance textiles or the human skin. In general any conformable surface or soft object really. Furthermore these circuits exhibit unseen reliability due to their ability to withstand unconventional mechanical deformations. As the technology behind them matures
rapidly from lab-based workflows to industrially applicable production principles, stretchable electronics have become increasingly relevant. A first and more traditional approach to achieve stretchable electronic circuits is the one of composite materials. Either by accommodating stretch within a conductive material through inclusion of elastomeric fillers, or by rendering a stretchable base material conductive through the addition of conductive fillers. Both approaches are explored
within this thesis whereby results emphasize a characteristic trade-off: an increase in stretchability is coupled to a decrease in conductivity and vice versa. Percolation
theory in this context is used as a tool to clarify the mechanism by which a composite blend transitions into conductive behavior. Aside from the characteristic trade-off between conductivity and stretchability, extreme viscosities reached at
elevated filler weight fractions pose a main practical impediment to the pursuit of blends which display both satisfactory conductivity and stretchability. A novel
approach, then, to achieve stretchable electronic circuits is by exchanging first traditional copper circuit traces for liquid metal and second the rigid board which holds components for a silicone elastomer. The result contains commercially
available off-the-shelf components: the very same as in traditional rigid circuits, however integrated into a soft and stretchable entity since at its core is a sheet of silicone elastomer. One of the contributions of this thesis entails an approach to chemically bond off-the-shelf components to their silicone encapsulant. Without this Abstract xii
chemical bond, components delaminate from their silicone cover layer which causes their liquid metal interconnects to short circuit. As the interconnections are composed of a liquid metal they do not break under deformation, instead the metal
just flows inside its silicone container and ensures proper electrical conductivity. In its current state, the Silicone Devices fabrication workflow can be used to convert any arbitrarily complex rigid circuit design into a soft circuit implementation. These circuits can span multiple layers which are interconnected by VIA’s. The workflow excels in its proportionality between the ease of creating a soft circuit and the corresponding performance exhibited this circuit. All precision steps are thereby outsourced to a computer controlled laser cutter, reducing the possibility of human error. As a Do-It-Yourself (DIY) research tool, Silicone Devices serves anyone who wants to explore the (application) possibilities of stretchable electronic circuits.
Significant emphasis was therefore placed on exclusively resorting to accessible materials and processes. Due to the disruptive nature, performance of early proofof-concepts, and interest shown from industry, an opportunity to commercialization was concluded. In sequence, the Silicone Devices fabrication approach’s Technology Readiness Level (TRL), System Readiness Level (SRL) and Demand Readiness Level
(DRL) are established. By further tailoring the underlying materials system and developing this DIY approach to industrially viable fabrication steps, the process
behind Silicone Devices can be further refined to match the production quality of conventional rigid circuits
Flash photography vision system for inkjet drop formation characterization
No full textOp het Instituut voor Materiaalonderzoek (IMO) van de UHasselt ontwikkelt men functionele inkten voor het inkjet printen van bijvoorbeeld RFID antennes. Printen binnen zeer kleine toleranties eist echter kennis van het exact materiaalgedrag tijdens elk van volgende afzettingsfasen: het uitstoten van de inkt, haar val naar het substraat en haar interactie met het oppervlak. In deze masterproef wordt een systeem ontwikkeld om inkjet druppels over de volledige afstand van printkop tot substraat optisch te inspecteren.
Om de vallende druppels zeer scherp in beeld te brengen, wordt gekozen voor flash photography. Hierbij is niet de mechanische sluitertijd van de camera maar de duur van de gepulste belichting bepalend voor de effectieve belichtingstijd van de druppel. Verder levert het gebruik van bi-telecentrische lenzen meer accurate beelden op door randeffecten en vervorming te beperken. Een tijdkritische hardware schakeling garandeert vervolgens betrouwbaar getimede vastlegging van beelden voor verdere verwerking in LabView.
Het resultaat bestaat uit twee delen. Enerzijds werd een zorgvuldig samengesteld visiesysteem opgebouwd dat, met gekarakteriseerde nauwkeurigheid, geschikt is om de druppels te observeren. Anderzijds zijn metingen uitgevoerd op de resulterende camerabeelden bij één vaste instelling van de printkop. Hieruit werden een straal van ongeveer 24µm, snelheid van gemiddeld 1.08m/s en volume van naar schatting 62 picoliter afgeleid als eigenschappen van de hoofddruppel
Electronic devices which stretch like rubber bands: a holistic approach to materials and fabrication methods for stretchable electronics
No full textThis thesis revolves around a vision of electronic circuits which are mechanically soft and can be stretched and bent to certain degrees. These stretchable (soft) electronics first of all offer great advantages over the traditional, rigid devices with which we are surrounded in terms of integration: circuits and sensors that can stretch and bend can now be indiscernibly integrated on for instance textiles or the human skin. In general any conformable surface or soft object really. Furthermore these circuits exhibit unseen reliability due to their ability to withstand unconventional mechanical deformations. As the technology behind them matures
rapidly from lab-based workflows to industrially applicable production principles, stretchable electronics have become increasingly relevant. A first and more traditional approach to achieve stretchable electronic circuits is the one of composite materials. Either by accommodating stretch within a conductive material through inclusion of elastomeric fillers, or by rendering a stretchable base material conductive through the addition of conductive fillers. Both approaches are explored
within this thesis whereby results emphasize a characteristic trade-off: an increase in stretchability is coupled to a decrease in conductivity and vice versa. Percolation
theory in this context is used as a tool to clarify the mechanism by which a composite blend transitions into conductive behavior. Aside from the characteristic trade-off between conductivity and stretchability, extreme viscosities reached at
elevated filler weight fractions pose a main practical impediment to the pursuit of blends which display both satisfactory conductivity and stretchability. A novel
approach, then, to achieve stretchable electronic circuits is by exchanging first traditional copper circuit traces for liquid metal and second the rigid board which holds components for a silicone elastomer. The result contains commercially
available off-the-shelf components: the very same as in traditional rigid circuits, however integrated into a soft and stretchable entity since at its core is a sheet of silicone elastomer. One of the contributions of this thesis entails an approach to chemically bond off-the-shelf components to their silicone encapsulant. Without this Abstract xii
chemical bond, components delaminate from their silicone cover layer which causes their liquid metal interconnects to short circuit. As the interconnections are composed of a liquid metal they do not break under deformation, instead the metal
just flows inside its silicone container and ensures proper electrical conductivity. In its current state, the Silicone Devices fabrication workflow can be used to convert any arbitrarily complex rigid circuit design into a soft circuit implementation. These circuits can span multiple layers which are interconnected by VIA’s. The workflow excels in its proportionality between the ease of creating a soft circuit and the corresponding performance exhibited this circuit. All precision steps are thereby outsourced to a computer controlled laser cutter, reducing the possibility of human error. As a Do-It-Yourself (DIY) research tool, Silicone Devices serves anyone who wants to explore the (application) possibilities of stretchable electronic circuits.
Significant emphasis was therefore placed on exclusively resorting to accessible materials and processes. Due to the disruptive nature, performance of early proofof-concepts, and interest shown from industry, an opportunity to commercialization was concluded. In sequence, the Silicone Devices fabrication approach’s Technology Readiness Level (TRL), System Readiness Level (SRL) and Demand Readiness Level
(DRL) are established. By further tailoring the underlying materials system and developing this DIY approach to industrially viable fabrication steps, the process
behind Silicone Devices can be further refined to match the production quality of conventional rigid circuits
Silver nanowire networks: prospects towards printed energy applications
No full textSeveral applications related to energy harvesting (e.g. photovoltaics) or energy efficient lighting (EL, OLEDs, …) strongly rely on effective transparent electrodes. Recently, metal nanowire networks are put forward as a promising concept for replacing transparent conducting oxides, such as Indium Tin Oxide (ITO). In such networks, the nanowires conduct charge carriers, while the open areas allow the transmission of light. Metal nanowires are both printable and achieve a performance equivalent to ITO upon thermal processing at moderate temperatures below 150°C, making them ideal for printing (flexible) transparent electrodes on plastic substrates.
Various formulations containing Ag NWs were prepared and their rheological behavior was assessed in view of screen printing on PET. The opto-electrical properties of the printed features are characterized by a Van der Pauw method and UV-Vis spectroscopy and analyzed by a semi-empirical model, relating the transparency and conductivity of the electrodes. Depending on the concentration and dimensions of the nanowires, the features have a transparency ranging from 50% up to 90% and a sheet resistance down to
20 Ohm/sq, fulfilling the requirements for a wide range of optoelectronic devices.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864
Screen-printing of flexible transparent electrodes and devices based on silver nanowire networks
No full textSilver nanowire networks have demonstrated significant potential as semi-transparent electrodes for various applications. However, for their widespread utilisation in devices, upscaled coating technologies such as screen-printing need to be explored and related to this, the formulation of suitable inks is indispensable. This work contributes to this effort by the synthesis of Ag-NW based formulations. The rheological characteristics that are essential for screen-printing are obtained by the addition of hydrophobically modified cellulose. The electrical and optical characteristics of screen-printed features on PET are compared by a Van der Pauw method and UV–vis spectroscopy. Despite the presence of the cellulose additive, the screen-printed electrodes exhibit a transmittance from 92.8% to 57.3% and a sheet resistance down to 27 Ohm sq−1. Based on the percolation theory in composites, a mathematical expression is presented, which allows the in-depth analysis of the resulting opto-electrical properties. The application potential of the nanowire-containing formulations is finally demonstrated by screen-printing functional, flexible electroluminescent devices.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864
Silver nanowire networks: prospects towards printed energy applications
No full textSeveral applications related to energy harvesting (e.g. photovoltaics) or energy efficient lighting (EL, OLEDs, …) strongly rely on effective transparent electrodes. Recently, metal nanowire networks are put forward as a promising concept for replacing transparent conducting oxides, such as Indium Tin Oxide (ITO). In such networks, the nanowires conduct charge carriers, while the open areas allow the transmission of light. Metal nanowires are both printable and achieve a performance equivalent to ITO upon thermal processing at moderate temperatures below 150°C, making them ideal for printing (flexible) transparent electrodes on plastic substrates.
Various formulations containing Ag NWs were prepared and their rheological behavior was assessed in view of screen printing on PET. The opto-electrical properties of the printed features are characterized by a Van der Pauw method and UV-Vis spectroscopy and analyzed by a semi-empirical model, relating the transparency and conductivity of the electrodes. Depending on the concentration and dimensions of the nanowires, the features have a transparency ranging from 50% up to 90% and a sheet resistance down to
20 Ohm/sq, fulfilling the requirements for a wide range of optoelectronic devices.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864
Biocompatibility Testing of Liquid Metal as an Interconnection Material for Flexible Implant Technology
Full text linkGalinstan, a liquid metal at room temperature, is a promising material for use in flexible electronics. Since it has been successfully integrated in devices for external use, e.g., as stretchable electronic skin in tactile sensation, the possibility of using galinstan for flexible implant technology comes to mind. Usage of liquid metals in a flexible implant would reduce the risk of broken conductive pathways in the implants and therefore reduce the possibility of implant failure. However, the biocompatibility of the liquid metal under study, i.e., galinstan, has not been proven in state-of-the-art literature. Therefore, in this paper, a material combination of galinstan and silicone rubber is under investigation regarding the success of sterilization methods and to establish biocompatibility testing for an in vivo application. First cell biocompatibility tests (WST-1 assays) and cell toxicity tests (LDH assays) show promising results regarding biocompatibility. This work paves the way towards the successful integration of stretchable devices using liquid metals embedded in a silicone rubber encapsulant for flexible surface electro-cortical grid arrays and other flexible implants
ESA–BEXUS project: OSCAR - Zonne-Energie Voor De Planeet Aarde En Verder
No full textZonne–energie is ontegensprekelijk één van de belangrijkste en duurzaamste oplossingen voor de globale energie– en klimaatuitdagingen waar onze planeet voor staat. Nieuwe generatie printbare, plooibare en ultra–dunnen zonnecellen kunnen bovendien leiden tot tal van nieuwe toepassingen, gaande van energie–bevoorrading voor draag bare elektronica (smartphones, tablets, …) tot grensverleggende toepassingen voor toekomstige ruimtereizen. Printbare organische en perovskiet–zonnecellen zijn namelijk de wereldkampioenen qua verhouding energie–opbrengst versus gewicht. Voor toekomstige ruimtevaartmissies hebben deze zonnecellen dus de bijzondere voordelen dat ze een ultra–licht gewicht hebben, plooibaar en uitvouwbaar zijn en bovendien ter plaatse (in ruimteschepen of in ruimtestations op bijvoorbeeld de Maan of op Mars) kunnen geprint worden.
Door deelname aan het BEXUS–programma (Balloon Experiments for University Students) van de Europese ruimtevaartorganisatie ESA, hebben een team van negen UHasselt–doctoraatstudenten en studenten Fysica (Miguel–Angel Beynaerts, Ilaria Cardinaletti, Rob Cornelissen, Jaroslav Hruby, Steven Nagels, Dieter Schreurs, Jelle Vodnik, Tim Vangerven & Koen Wouters) een wereldrecord gebroken qua gebruik van printbare zonnecellen op grote hoogte. Met het OSCAR–project (Optical Sensors based on CARbon Materials) hebben ze voor het eerste de prestaties van printbare zonnecellen en van een nieuwe magnetische–veldsensor bestudeerd in echte ruimtevaartcondities. Vanuit het lanceerstation Kiruna in Zweden werd een onderzoeksballon in de stratosfeer gebracht — op 32 kilometer hoogte (3x hoogte van vliegtuigtrajecten) — waarbij extreme condities heersen zoals lage luchtdruk, lage temperaturen (tot wel –60 graden Celsius) en een pak meer straling van de zon
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