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3 pages, 189 KiB

Open AccessEditorial

Editorial for the Special Issue on Recent Advances in Inkjet Technology

by Dong Kee Sohn

Micromachines 2023, 14(3), 681; https://doi.org/10.3390/mi14030681 - 19 Mar 2023

Viewed by 1356

Abstract

Inkjet is a well-established technology that has been applied in various applications ranging from graphical printing to functional material printing [...] Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

Research

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19 pages, 7745 KiB

Open AccessArticle

High-Frequency Rheological and Piezo-Voltage Waveform Characterization of Inkjet-Printed Polymer-Based Dopant-Source Inks

by Zulkifl Hussain, Zohreh Kiaee, Milad Nazarzadeh, Christian Reichel, Sebastian Tepner, Tri Tuladhar, Mike Jahn and Roman Keding

Micromachines 2023, 14(1), 80; https://doi.org/10.3390/mi14010080 - 28 Dec 2022

Cited by 3 | Viewed by 4349

Abstract

This work focuses on developing an understanding of the rheological properties of polymer-based dopant-source inks at the timescales relevant to inkjet printing and their corresponding roles in determining the production of defect-free droplets. Ink-specific optimization of printing processes for phosphorus and boron dopant-source [...] Read more.

This work focuses on developing an understanding of the rheological properties of polymer-based dopant-source inks at the timescales relevant to inkjet printing and their corresponding roles in determining the production of defect-free droplets. Ink-specific optimization of printing processes for phosphorus and boron dopant-source inks with different compositions is demonstrated. Rheological flow curves measured by a piezo axial vibrator (PAV) were used to study the changes in complex viscosity (η*) and in the elastic (G′) and viscous (G″) components of the shear modulus (G*) with respect to changes in frequency (from f_min = 1 kHz to f_max = 10 kHz) to obtain an insight into the high-frequency behaviour of inks, as well as the effects of temperature (25 °C and 45 °C) and the natural aging time of the inks. Inks demonstrating complex viscosity η*_min ≥ 2 mPas to η*_max ≤ 20 mPas and an elastic modulus G′ ≤ 20 Pa, produced droplets with negligible defects. Of the three rheological parameters (η*, G′ and G″), the elastic component (G′) of the shear modulus was observed to have the greatest significance in determining the stability and homogeneity of ink droplets, thus dictating the quality of the printed structures. The reliability and stability of droplet formation were further investigated through voltage waveform simulation using an oscilloscope. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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15 pages, 4604 KiB

Open AccessArticle

Development of an Inkjet Setup for Printing and Monitoring Microdroplets

by Beatriz Cavaleiro de Ferreira, Tiago Coutinho, Miguel Ayala Botto and Susana Cardoso

Micromachines 2022, 13(11), 1878; https://doi.org/10.3390/mi13111878 - 31 Oct 2022

Cited by 5 | Viewed by 1990

Abstract

Inkjet printing is a digitally controlled additive technology that allows the precise deposition of droplets. Because it is additive, it enables geometries usually unattainable by other technologies. Because it is digitally controlled, its output is easily modulated, even during operation. Combined with the [...] Read more.

Inkjet printing is a digitally controlled additive technology that allows the precise deposition of droplets. Because it is additive, it enables geometries usually unattainable by other technologies. Because it is digitally controlled, its output is easily modulated, even during operation. Combined with the development of functional materials and their micrometer precision, it can be applicable in a wide range of fields beyond the traditional graphic industry, such as medical diagnosis, electronics manufacturing, and the fabrication of microlenses. In this work, a solution based on open-source hardware and software was implemented instead of choosing a commercial alternative, making the most of inkjet flexibility in terms of inks, substrates, and actuation signal. First, a piezoelectric printhead from MicroFab, driven by an ArduinoDue, was mounted in a 3D printer adapted to ensure precise movement in three dimensions. Then, a monitoring system using a USB digital microscope and a computational algorithm was integrated. Both systems combined allow the printing and measurement of microdroplets by digital regulation of a unipolar signal. Finally, based on a theoretical model and a set of experimentally collected samples, the curve that relates the unipolar signal amplitude to the size of the microdroplets was estimated with an acceptable range of prediction uncertainty. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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14 pages, 63853 KiB

Open AccessArticle

Wound-Dressing-Based Antenna Inkjet-Printed Using Nanosilver Ink for Wireless Medical Monitoring

by Chun-Bing Chen, Hsuan-Ling Kao, Li-Chun Chang, Yi-Chen Lin, Yung-Yu Chen, Wen-Hung Chung and Hsien-Chin Chiu

Micromachines 2022, 13(9), 1510; https://doi.org/10.3390/mi13091510 - 12 Sep 2022

Cited by 6 | Viewed by 1950

Abstract

In this paper, we present a wound-dressing-based antenna fabricated via screen-printed and inkjet-printed technologies. To inkjet print a conductive film on wound dressing, it must be screen-printed, UV-curable-pasted, and hard-baked to provide appropriate surface wettability. Two passes were UV-curable-pasted and hard-baked at 100 [...] Read more.

In this paper, we present a wound-dressing-based antenna fabricated via screen-printed and inkjet-printed technologies. To inkjet print a conductive film on wound dressing, it must be screen-printed, UV-curable-pasted, and hard-baked to provide appropriate surface wettability. Two passes were UV-curable-pasted and hard-baked at 100 °C for 2 h on the wound dressing to obtain 65° WCA for silver printing. The silver film was printed onto the wound dressing at room-tempature with 23 μm droplet spacing for three passes, then sintered at 120 °C for 1 h. By optimizing the inkjet printing conditions by modifying the surface morphologies and electrical properties, three-pass printed silver films with 3.15 μm thickness and 1.05 × 10⁷ S/m conductivity were obtained. The insertion losses at the resonant frequency (17 and 8.85 GHz) were −2.9 and −2.1 dB for the 5000 and 10,000 μm microstrip transmission lines, respectively. The material properties of wound dressing with the relative permittivity and loss-tangent of 3.15–3.25 and 0.04–0.05, respectively, were determined by two transmission line methods and used for antenna design. A quasi-Yagi antenna was designed and implemented on the wound-dressing with an antenna bandwidth of 3.2–4.6 GHz, maximal gain of 0.67 dBi, and 42% radiation efficiency. The bending effects parallel and perpendicular to the dipole direction of three fixtures were also examined. The gain decreased from 0.67 to −1.22 dBi and −0.44 dBi for a flat to curvature radius of 5 cm fixture after parallel and perpendicular bending, respectively. Although the maximal gain was reduced with the bending radius, the directivity of the radiation pattern remained unchanged. The feasibility of a wound-dressing antenna demonstrates that inkjet-printed technology enables fast fabrication with low cost and environmental friendliness. Additionally, inkjet-printed technology can be combined with sensing technology to realize remote medical monitoring, such as with smart bandages, for assessment of chronic wound status or basic physical conditions. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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14 pages, 2633 KiB

Open AccessArticle

The Effect of Ink Supply Pressure on Piezoelectric Inkjet

by San Kim, Jun Hyeok Choi, Dong Kee Sohn and Han Seo Ko

Micromachines 2022, 13(4), 615; https://doi.org/10.3390/mi13040615 - 14 Apr 2022

Cited by 13 | Viewed by 3825

Abstract

Experimental and numerical analysis of the drop-on-demand inkjet was conducted to determine the jetting characteristics and meniscus motion under the control of the ink supply pressure. A single transparent nozzle inkjet head driven by a piezoelectric actuator was used to eject droplets. To [...] Read more.

Experimental and numerical analysis of the drop-on-demand inkjet was conducted to determine the jetting characteristics and meniscus motion under the control of the ink supply pressure. A single transparent nozzle inkjet head driven by a piezoelectric actuator was used to eject droplets. To control ink supply pressure, the pressure of the air in the reservoir was regulated by a dual valve pressure controller. The inkjet performance and the motion of the meniscus were evaluated by visualization and numerical simulation. A two-dimensional axisymmetric numerical simulation with the dynamic mesh method was performed to simulate the inkjet dynamics, including the actual deformation of the piezoelectric actuator. Numerical simulation showed good agreement with the experimental results of droplet velocity and volume with an accuracy of 87.1%. Both the experimental and simulation results showed that the drop volume and velocity were linearly proportional to the voltage change. For the specific voltages, an analysis of the effect of the ink supply pressure control was conducted. At the maximum negative pressure, −3 kPa, the average velocity reductions were 0.558 and 0.392 m/s in the experiment and simulation, respectively, which were 18.7 and 11.6% less than those of the uncontrolled case of 0 kPa. Therefore, the simulation environment capable of simulating the entire inkjet dynamics, including meniscus movement regarded to be successfully established. The average volume reductions were 18.7 and 6.97 pL for the experiment and simulation, respectively, which were 21.7 and 9.17% less than those of the uncontrolled case. In the results of the meniscus motion simulation, the damping of the residual vibration agreed well with the experimental results according to the ink supply pressure change. Reducing the ink supply pressure reduced the speed and volume, improved the damping of residual vibrations, and suppressed satellite drops. Decreasing ink supply pressure can be expected to improve the stability and productivity of inkjet printing. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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18 pages, 3854 KiB

Open AccessArticle

Integrated Fabrication of Novel Inkjet-Printed Silver Nanoparticle Sensors on Carbon Fiber Reinforced Nylon Composites

by Büşra Karaş, Vimanyu Beedasy, Zhaoyuan Leong, Nicola A. Morley, Kamran Mumtaz and Patrick J. Smith

Micromachines 2021, 12(10), 1185; https://doi.org/10.3390/mi12101185 - 29 Sep 2021

Cited by 6 | Viewed by 3026

Abstract

Inkjet-printing technology enables the contactless deposition of functional materials such as conductive inks on surfaces, hence reducing contamination and the risk of substrate damage. In printed electronics, inkjet technology offers the significant advantage of controlling the volume of material deposited, and therefore the [...] Read more.

Inkjet-printing technology enables the contactless deposition of functional materials such as conductive inks on surfaces, hence reducing contamination and the risk of substrate damage. In printed electronics, inkjet technology offers the significant advantage of controlling the volume of material deposited, and therefore the fine-tuning of the printed geometry, which is crucial for the performance of the final printed electronics. Inkjet printing of functional inks can be used to produce sensors to detect failure of mechanical structures such as carbon fiber reinforced composite (CFRC) components, instead of using attached sensors, which are subject to delamination. Here, silver nanoparticle-based strain sensors were embedded directly in an insulated carbon-fiber laminate by using inkjet printing to achieve an optimized conductive and adhesive geometry, forming a piezoresistive strain sensor. Following the inkjet-printing optimization process, the sensor conductivity and adhesion performance were evaluated. Finally, the sensor was quantified by using a bending rig which applied a pre-determined strain, with the response indicating an accurate sensitivity as the resistance increased with an increased strain. The ability to embed the sensor directly on the CFRC prevents the use of interfacial adhesives which is the main source of failure due to delamination. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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Graphical abstract

20 pages, 3856 KiB

Open AccessArticle

Formulation of a Ceramic Ink for 3D Inkjet Printing

by Dennis Graf, Judith Jung and Thomas Hanemann

Micromachines 2021, 12(9), 1136; https://doi.org/10.3390/mi12091136 - 21 Sep 2021

Cited by 7 | Viewed by 3923

Abstract

Due to its multi-material capabilities, 3D inkjet printing allows for the fabrication of components with functional elements which may significantly reduce the production steps. The potential to print electronics requires jettable polymer-ceramic composites for thermal management. In this study, a respective material was [...] Read more.

Due to its multi-material capabilities, 3D inkjet printing allows for the fabrication of components with functional elements which may significantly reduce the production steps. The potential to print electronics requires jettable polymer-ceramic composites for thermal management. In this study, a respective material was formulated by functionalizing submicron alumina particles by 3-(trimethoxysilyl)propylmethacrylate (MPS) and suspending them in a mixture of the oligourethane Genomer 4247 with two acrylate functionalities and a volatile solvent. Ink jetting tests were performed, as well as thermal conductance and mechanical property measurements. The material met the strict requirements of the printing technology, showing viscosities of around 16 mPa·s as a liquid. After solidification, it exhibited a ceramic content of 50 vol%, with a thermal conductance of 1 W/(m·K). The resulting values reflect the physical possibilities within the frame of the allowed tolerances set by the production method. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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12 pages, 9435 KiB

Open AccessArticle

Enhancement of High-Resolution 3D Inkjet-Printing of Optical Freeform Surfaces Using Digital Twins

by Ingo Sieber, Richard Thelen and Ulrich Gengenbach

Micromachines 2021, 12(1), 35; https://doi.org/10.3390/mi12010035 - 30 Dec 2020

Cited by 20 | Viewed by 3954

Abstract

3D-inkjet-printing is just beginning to take off in the optical field. Advantages of this technique include its fast and cost-efficient fabrication without tooling costs. However, there are still obstacles preventing 3D inkjet-printing from a broad usage in optics, e.g., insufficient form fidelity. In [...] Read more.

3D-inkjet-printing is just beginning to take off in the optical field. Advantages of this technique include its fast and cost-efficient fabrication without tooling costs. However, there are still obstacles preventing 3D inkjet-printing from a broad usage in optics, e.g., insufficient form fidelity. In this article, we present the formulation of a digital twin by the enhancement of an optical model by integrating geometrical measurement data. This approach strengthens the high-precision 3D printing process to fulfil optical precision requirements. A process flow between the design of freeform components, fabrication by inkjet printing, the geometrical measurement of the fabricated optical surface, and the feedback of the measurement data into the simulation model was developed, and its interfaces were defined. The evaluation of the measurements allowed for the adaptation of the printing process to compensate for process errors and tolerances. Furthermore, the performance of the manufactured component was simulated and compared with the nominal performance, and the enhanced model could be used for sensitivity analysis. The method was applied to a highly complex helical surface that allowed for the adjustment of the optical power by rotation. We show that sensitivity analysis could be used to define acceptable tolerance budgets of the process. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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Review

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35 pages, 4492 KiB

Open AccessReview

Monitoring Symptoms of Infectious Diseases: Perspectives for Printed Wearable Sensors

by Ala’aldeen Al-Halhouli, Ahmed Albagdady, Ja’far Alawadi and Mahmoud Abu Abeeleh

Micromachines 2021, 12(6), 620; https://doi.org/10.3390/mi12060620 - 27 May 2021

Cited by 18 | Viewed by 6329

Abstract

Infectious diseases possess a serious threat to the world’s population, economies, and healthcare systems. In this review, we cover the infectious diseases that are most likely to cause a pandemic according to the WHO (World Health Organization). The list includes COVID-19, Crimean-Congo Hemorrhagic [...] Read more.

Infectious diseases possess a serious threat to the world’s population, economies, and healthcare systems. In this review, we cover the infectious diseases that are most likely to cause a pandemic according to the WHO (World Health Organization). The list includes COVID-19, Crimean-Congo Hemorrhagic Fever (CCHF), Ebola Virus Disease (EBOV), Marburg Virus Disease (MARV), Lassa Hemorrhagic Fever (LHF), Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory Syndrome (SARS), Nipah Virus diseases (NiV), and Rift Valley fever (RVF). This review also investigates research trends in infectious diseases by analyzing published research history on each disease from 2000–2020 in PubMed. A comprehensive review of sensor printing methods including flexographic printing, gravure printing, inkjet printing, and screen printing is conducted to provide guidelines for the best method depending on the printing scale, resolution, design modification ability, and other requirements. Printed sensors for respiratory rate, heart rate, oxygen saturation, body temperature, and blood pressure are reviewed for the possibility of being used for disease symptom monitoring. Printed wearable sensors are of great potential for continuous monitoring of vital signs in patients and the quarantined as tools for epidemiological screening. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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