The measurement of the volumes of small (10–100 μm) liquid drops is important in a number of fields including inkjet printing, liquid dispensing and spraying. This article explores the use of synthetic, constructed images, representing shapes with precisely known volumes, and real photographic images of inkjet drops to compare a number of image processing methods designed to estimate drop volume. The synthetic images were generated with a range of sizes, background gray levels and degrees of blur and noise. The image processing methods were chosen to represent a range of approaches, some very simple and some more complex. A comparison of the results from these methods shows that they responded differently to various image features. The process described in this article could be used to compare other existing or new processing methods, and the results should be valuable in the development of standard methods for drop measurement.
Wireless reliability tests of lightweight composite materials by electromagnetic waves have become more and more interesting in the aerospace and automotive fields. The embedding of conductive printed patterns as electromagnetic resonators seems to be one of the useful techniques. The printing technology is a resource as well as time and cost efficient fabrication method to manufacture electronic devices. In particular, contactless and digital technologies like inkjet printing have great potential to be combined with integration processes like resin infusion technology. The combination of these manufacturing processes enables fast and efficient production of smart lightweight applications. The main focus of this work is the manufacture of a passive high frequency resonator on flexible substrates using inkjet printing. The conductive patterns are integrated into a composite material by resin infusion, enabling sensor applications in the field of clean energy, particularly for wireless ice detection on wind rotor blades.
The development of novel manufacturing methods for flexible, light weight and cost-efficient electronics has attracted great interest in recent years. The inkjet printing technology is an attractive fabrication process due to its additive, high precision and up-scalable deposition process.
One of the key components of printed electronic devices is the conductive track. A major requirement is a desired and device dependent electrical performance induced by an appropriate post treatment process. Here, the novel method of using intense pulsed light (IPL) to convert printed liquid films into solid and functionalized metallic layers has great potential when it comes to fabrication of electronics on thin, flexible and even stretchable polymeric foils.
Within this research, the IPL sintering and its dependence on the spectral absorption and reflection of various materials is investigated. A nanoparticle silver ink is inkjet printed on a transparent PET foil. Afterwards, the printed samples are placed at a defined distance from the background inside the photonic sintering equipment and flashed on one hand with various flashing parameters and on the other with changing background materials and colors. Changing the background color influences the reflection and absorption properties of the flashlight; the electrical performance of the IPL processed conductive layers can be drastically changed when such a phenomenon occurs. Highly conductive silver tracks or electrodes can be manufactured on thin and flexible polymeric substrates without damage.
Resonant oscillations set up internal fluid waves within a piezo-drop-on-demand (DoD) print-head channel as a result of actuation drive pulses. Such waves will persist for some time after droplet ejection from the nozzle, and the residual wave amplitude can interfere (constructively or destructively) with all succeeding actuation drive pulses, potentially altering the speed and volume of successive droplets. As uncontrolled interference would worsen printing quality, residual waves are usually reduced by a combination of print-head design and waveform optimization for better performance at continuous (steady state) printing frequencies. However, the residual waves following any changes of printing frequency can influence “first” drops and short bursts of drops. Exact analytic expressions are provided here for the N-pulse burst DoD print-head response function with fixed printing frequency. This article explains the purpose and application of the model predictions to published piezo-driven DoD data. An examination of the effect of fluid properties, the identification of unexpected jetting behavior and some issues with manufacturing prototype quality, tests of assumptions made in the simple model and extensions to the prediction of print-head performance using realistic complex waveforms are also discussed. An earlier shorter article, mainly introducing the multi pulse train modeling approach and some applications within Xaar, was first presented at NIP31/DF2015 [S. D. Hoath, A simple model for DoD inkjet frequency response, Proc. IS&Ts 31st Int’l. Conf. on Digital Printing Technologies (IS&T, Springfield, VA 2015), 8–12].
MoS2 is a layered material which is abundant and non-toxic and has been increasingly studied during the last few years as a semiconducting alternative to graphene. While most studies have been performed on single MoS2 nanosheets, for example to demonstrate high-performance electronic transistors, more work is needed to explore the use of MoS2 in printed electronics. The importance of using MoS2 as a printed electronic material could be understood by considering the several orders higher electron mobility in MoS2, even in several nanometer thick layers, compared to the organic and other materials used today. In the few studies performed so far on printing MoS2, the developed dispersions used mainly organic solvents that might be detrimental for the environment. Here, we show an environmentally friendly liquid-based exfoliation method in water where the solution was stabilized by sodium dodecyl sulfate (SDS) surfactant. The dispersions consisted of very thin MoS2 nanosheets with average lateral size of about 150 nm, surface tension of 28 mN m−1, and a shelf life of a year. Although both the concentration and viscosity was less than optimal, we were able to inkjet print the MoS2 solution on paper and on PET films, using multiple printing passes. By tuning the concentration/viscosity, this approach might lead to an environmentally friendly MoS2 ink suitable for printed electronics.
Thermal inkjet technology has long been used in the printing industry, but little has been studied on the benefits that it can provide to the drug-screening field. The objective of the work reported here was a proof of concept of using a modified inkjet printer to have a more accessible and miniature cellomic anticancer drug-screening platform. The authors’ previous findings have shown that inkjet-based screening can reliably create isolated arrays of spots of living cells and antibiotics at low volume (180 pl) and high throughput (213 spots/sec) [J. I. Rodríguez-Dévora, B. Zhang, D. Reyna, Z. D. Shi, and T. Xu, “High throughput miniature drug-screening platform using bioprinting technology,” Biofabrication 4, 035001 (2012)]. The methodology of the work reported here included using a modified office inkjet printing device; the authors studied the inhibitory effects of dichloroacetate sodium (DCA) over hepatocellular carcinoma (HepG2) and epithelial cells (EpC). A DCA drug concentration gradient was printed over cell cultures to evaluate the drug’s cytotoxic effect. Half maximal and ninety percent inhibitory concentrations (IC50, IC90) were obtained from the dose–response curves and compared with concentrations obtained using the traditional micropipetting technique. The resulting inhibitory concentration values obtained by both dispensing techniques fall within the millimolar range. The significance of these finding is that the proposed screening platform closely mimics the traditional screening outcome at a miniaturized volume rate, thus downsizing the screening process from traditional sub-microliter to nano- or even picoliter range. Inkjet technology shows promise in miniaturizing and expediting the drug-screening process. This platform can be used to asses a preliminary dose–response curve in order to improve the treatment modalities using the patient’s limited supply of biopsied cells toward personalized medicine.
Exposure fusion is the process of generating a pseudo-HDR (high dynamic range) image by directly fusing the images in a multi-exposure sequence. The main weakness of exposure fusion is the appearance of ghost artifacts caused by moving objects while shooting the sequence. Therefore, this article presents an improved temporal consistency assessment based on intensity and hue consistency maps for ghost-free exposure fusion. An intensity consistency map is generated by multiplying a multi-level threshold binary map and an intensity binary map, while a hue consistency map is generated by the difference of hue angle. The two maps are then multiplied to obtain a temporal weight map. A spatial weight map is generated by multiplying three image quality measures. Finally, the temporal and spatial weight maps are multiplied together, resulting in the final weights needed to produce the pseudo-HDR. Experiments show a reduction of ghost artifacts in the pseudo-HDR images produced by the proposed method when compared with the images produced by other conventional methods.
In drop-on-demand (DOD) inkjet printing microdroplets are ejected from the nozzle as a result of the internal acoustics set in motion by a pressure pulse from an expanding bubble or a piezoelement. The acoustic response, both in the frequency domain and in the time domain, and the resulting droplet formation processes are well-modeled and characterized by various experimental techniques. However, the behavior of the liquid meniscus in the nozzle is a critical mediator between these regimes and poorly accessible in experiment. The meniscus shape and motion vary between different print head designs, electrical pulse shapes and wetting conditions. In the last decade several novel approaches have been proposed and implemented to study experimentally the meniscus motion within inkjet nozzles. These experimental methods are reviewed here and compared in terms of accuracy and applicability.
With the advance of information technology, digitization has revolutionized workflows in the printing industry, resulting in the explosive growth of the digital production inkjet printer, which is distinguished by its high-speed printing. The further possibility of accelerating the operation is investigated by studying satellite behavior driven by the double-pulse waveform with changing ink properties. A satellite-free condition is achieved when the satellite becomes faster and then merges with the preceding main drop by adjusting the waveform. The satellite speed is correlated with the timing of the filament separation of the jet which is also affected by the ink properties. For high-speed printing, faster jetting is required, although an increase of drop speed and a satellite-free condition are not compatible. Therefore, improvements in both structural design and fabrication technology of the printhead are considered to be required breakthroughs for future advance of the production inkjet.