Light scattering is a fundamental property that can be exploited to create essential devices such as particle analysers. The most common particle size analyser relies on measuring the angle-dependent diffracted light from a sample illuminated by a laser beam. Compared to other non-light-based counterparts, such a laser diffraction scheme offers precision, but it does so at the expense of size, complexity and cost. In this paper, we introduce the concept of a new particle size analyser in a collimated beam configuration using a consumer electronic camera and machine learning. The key novelty is a small form factor angular spatial filter that allows for the collection of light scattered by the particles up to predefined discrete angles. The filter is combined with a light-emitting diode and a complementary metal-oxide-semiconductor image sensor array to acquire angularly resolved scattering images. From these images, a machine learning model predicts the volume median diameter of the particles. To validate the proposed device, glass beads with diameters ranging from 13 to 125 µm were measured in suspension at several concentrations. We were able to correct for multiple scattering effects and predict the particle size with mean absolute percentage errors of 5.09% and 2.5% for the cases without and with concentration as an input parameter, respectively. When only spherical particles were analysed, the former error was significantly reduced (0.72%). Given that it is compact (on the order of ten cm) and built with low-cost consumer electronics, the newly designed particle size analyser has significant potential for use outside a standard laboratory, for example, in online and in-line industrial process monitoring.
MULTIFILE
With a market demand for low cost, easy to produce, flexible and portable applications in healthcare, energy, biomedical or electronics markets, large research programs are initiated to develop new technologies to provide this demand with new innovative ideas. One of these fast developing technologies is organic printed electronics. As the term printed electronics implies, functional materials are printed via, e.g. inkjet, flexo or gravure printing techniques, on to a substrate material. Applications are, among others, organic light emitting diodes (OLED), sensors and Lab-on-a-chip devices. For all these applications, in some way, the interaction of fluids with the substrate is of great importance. The most used substrate materials for these low-cost devices are (coated) paper or plastic. Plastic substrates have a relatively low surface energy which frequently leads to poor wetting and/or poor adhesion of the fluids on the substrates during printing and/ or post-processing. Plasma technology has had a long history in treating materials in order to improve wetting or promote adhesion. The µPlasma patterning tool described in this thesis combines a digital inkjet printing platform with an atmospheric dielectric barrier discharge plasma tool. Thus enabling selective and local plasma treatment, at atmospheric pressure, of substrates without the use of any masking materials. In this thesis, we show that dependent on the gas composition the substrate surface can either be functionalized, thus increasing its surface energy, or material can be deposited on the surface, lowering its surface energy. Through XPS and ATR-FTIR analysis of the treated (polymer) substrate surfaces, chemical modification of the surface structure was confirmed. The chemical modification and wetting properties of the treated substrates remained present for at least one month after storage. Localized changes in wettability through µPlasma patterning were obtained with a resolution of 300µm. Next to the control of wettability of an ink on a substrate in printed electronics is the interaction of ink droplets with themselves of importance. In printing applications, coalescence of droplets is standard practice as consecutive droplets are printed onto, or close to each other. Understanding the behaviour of these droplets upon coalescence is therefore important, especially when the ink droplets are of different composition and/or volume. For droplets of equal volume, it was found that dye transport across the coalescence bridge could be fully described by diffusion only. This is as expected, as due to the droplet symmetry on either side of the bridge, the convective flows towards the bridge are of equal size but opposite in direction. For droplets of unequal volume, the symmetry across the bridge is no longer present. Experimental analysis of these merging droplets show that in the early stages of coalescence a convective flow from the small to large droplet is present. Also, a smaller convective flow of shorter duration from the large into the small droplet was identified. The origin of this flow might be due to the presence of vortices along the interface of the bridge, due to the strong transverse flow to open the bridge. To conclude, three potential applications were showcased. In the first application we used µPlasma patterning to create hydrophilic patterns on hydrophobic dodecyl-trichlorosilane (DTS) covered glass. Capillaries for a Lab-on-a-chip device were successfully created by placing two µPlasma patterned glass slides on top of each other separated by scotch tape. In the second application we showcased the production of a RFID tag via inkjet printing. Functional RFID-tags on paper were created via inkjet printing of silver nanoparticle ink connected to an integrated circuit. The optimal operating frequency of the produced tags is in the range of 860-865 MHz, making them usable for the European market, although the small working range of 1 m needs further improvement. Lastly, we showed the production of a chemresistor based gas sensor. In house synthesised polyemeraldine salt (PANi) was coated by hand on top of inkjet printed silver electrodes. The sensor proved to be equally sensitive to ethanol and water vapour, reducing its selectivity in detecting changes in gas composition.
DOCUMENT
The transmission of constant-envelope orthogonal frequency division multiplexing (CE-OFDM) signals, based on electrical phase modulation, was shown to improve the tolerance to noise and the nonlinearity introduced by light-emitting diodes (LEDs) in visible light communication (VLC) systems. This allows the application of larger signal amplitudes despite the LED-nonlinearities and, thus, data transmission over larger distances. The performance of a 9.51 Mb/s CE-OFDM based system, with 16-QAM subcarrier mapping in a bandwidth of 5 MHz, was compared to the efficiency of a conventional OFDM system. The error vector magnitude (EVM) was reduced from 17.5% to 10% (which is below the FEC limit), an improvement around 43%, when the CE-OFDM scheme was applied in the VLC link of 6 m. A good performance was achieved by the CE-OFDM based VLC system in a link of 8 m, when 4-QAM was used as subcarrier mapping.
DOCUMENT
Despite Dutch Hospitality industry’s significant economic value, employers struggle to attract and retain early career professionals at a time when tourism is forecasted to grow exponentially (Ruël, 2018). Universally, hospitality management graduates are shunning hospitality careers preferring other career paths; stimulating the Dutch Hospitality to find innovative ways of attracting and retaining early career professionals. Following calls from the Human Resource Management (HRM) community (Ehnert, 2009), we attribute this trend to personnel being depicted as rentable resources, driving profit’’ often at personal expense. For example, hotels primarily employ immigrants and students for a minimum wage suppressing salaries of local talent (Kusluvan, et al 2010, O’Relly and Pfeffer, 2010). Similarly, flattening organizational structures have eliminated management positions, placing responsibility on inexperienced shoulders, with vacancies commonly filled by pressured employees accepting unpaid overtime jeopardizing their work life balance (Davidson, et al 2010,). These HRM practices fuel attrition by exposing early career professionals to burnout (Baum et al, 2016, Goh et al, 2015, Deery and Jog, 2009). Collectively this has eroded the industry’s employer brand, now characterized by unsocial working hours, poor compensation, limited career opportunities, low professional standing, high turnover and substance abuse (Mooney et al, 2016, Gehrels and de Looij, 2011). In contrast, Sustainable HRM “enables an organizational goal achievement while simultaneously reproducing the human resource base over a long-lasting calendar time (Ehnert, 2009, p. 74).” Hence, to overcome this barrier we suggest embracing the ROC framework (Prins et al, 2014), which (R)espects internal stakeholders, embraces an (O)pen HRM approach while ensuring (C)ontinuity of economic and societal sustainability which could overcome this barrier. Accordingly, we will employ field research, narrative discourse, survey analysis and quarterly workshops with industry partners, employees, union representatives, hotel school students to develop sustainable HRM practices attracting and retaining career professionals to pursue Dutch hospitality careers.
Consumenten wensen light-emitting diodes (LEDs) die energie-efficiënt zijn, maar tegelijkertijd de gewenste kleuren licht uitzenden. Binnenverlichting moet bijvoorbeeld voldoende rood bevatten om een warme sfeer te creëren, terwijl beeldschermen mooie pure kleuren moeten produceren. De Universiteit Utrecht en het bedrijf Seaborough B.V. gaan samenwerken aan nieuwe manieren om efficiënt licht te genereren met nanokristallen. Nanokristallen hebben als voordeel dat het uitgezonden lichtspectrum nauwkeurig kan worden gestuurd en dat hun fabricage minder schaarse materialen gebruikt dan bestaande technologieën. Om ze licht te laten uitzenden, moet er echter energie worden toegevoerd. De onderzoekers gaan een strategie uittesten om energie zo snel en efficiënt mogelijk door een dunne film van nanokristallen te laten reizen. De beoogde strategie berust op het gebruik van golfgeleiders, die elektromagnetische straling in een gewenst richting sturen. Succes in dit project zal bijdragen aan het efficiënter en mooier maken van kunstmatige lichtbronnen, terwijl er minder materialen gebruikt hoeven te worden.
Light-emitting diodes (LEDs) vervangen andere typen kunstmatige verlichting in rap tempo, omdat ze zuiniger en robuuster zijn. LEDs vormen dan ook een alsmaar groeiende markt van vele tientallen miljarden. De meest voorkomende technologie maakt gebruik van InGaN om blauw licht te maken onder elektrische aandrijving. “Fosforen” zetten vervolgens een deel van dit blauwe licht om in de andere kleuren van de regenboog. Helaas werken bestaande fosforen vooral goed in toepassingen waarbij lage lichtintensiteit voldoende is. Bij hogere lichtintensiteit treedt “verzadiging” op: de efficiëntie van kleuromzetting wordt minder. Dit leidt tot energieverliezen. Daarnaast kan verzadiging de kleurbeleving van een LED-lamp ongewenst blauwig oftewel “koel” maken, aangezien vooral “warme” rode fosforen last hebben van dit probleem. De onderzoekers willen innovatieve fosformaterialen ontwerpen die efficiënt blijven ook bij hoge lichtintensiteit. Ze gaan samengestelde nanomaterialen maken met twee componenten, waarbij blauw licht wordt geabsorbeerd door de ene component en rood licht uitgezonden door de andere. Via het ontwerp van de samengestelde fosfor kan de snelheid van energieoverdracht van de ene naar de andere component worden gecontroleerd. Berekeningen wijzen uit dat slim gebruik van energieoverdracht verzadiging van de kleuromzetting kan verminderen. Dit project zal deze berekeningen toetsen en de praktische mogelijkheden verkennen om dit concept te gebruiken. Het kan daarmee de basis leggen voor vervolgonderzoek waar de beste ontwerpen verder worden ontwikkeld tot heldere rode fosforen. Deze zijn nodig voor de realisatie van zuinigere verlichting met een prettigere kleurbeleving voor de consument.
