Electrohydrodynamic Inkjet Printing Research Articles

A review on multi nozzle electrohydrodynamic inkjet printing system for MEMS applications

New microproducts require to utilize the variety of materials. Their complex three-dimensional microstructures have big aspect ratios. This ability to fabricate geometrically complicated 3D microstructures provides some additional profits to the additive manufacturing systems over traditional methods. Among the enormous variety of micro-products, depending on the mixtures of usefulness of the product and fundamentals of operation, the foremost types are micro-opto-electro-mechanical systems, micro electromechanical systems, micro-optical electronics systems and microelectronic products. Electrohydrodynamic inkjet printing is an innovative high-resolution technology of inkjet printing which has the benefits of being a non-contact, maskless, additive and direct-write methods. The resolution of printing of EHD surpasses by approx. two orders of magnitude compared to the general inkjet printing methods. It has been used mostly in cases of nano or micro manufacturing of very small objects for modelling of a big range of constituents on different substrates having the alternatives of either Drop-On-Demand mode or continuous mode. It is considered to be a capable substitute to thermal and piezoelectric based inkjet printing methods since it has a unique quality of producing small jet or droplets in comparison to the nozzle orifice. Several advantages in fine patterning are presented by EHD inkjet printing processes, but the little manufacturing speed of EHD inkjet printing is an unadorned disadvantage that has been hindering its probable extensive uses in the industry of electronics. To overcome this restriction, the direct printing of colloidal solutions with the help of multiple nozzle EHD inkjet printing method is used. This review offers a short account of multiple-nozzle electrohydrodynamic inkjet printing of colloidal solutions for its application in MEMS.

CFD-based numerical modeling to predict the dimensions of printed droplets in electrohydrodynamic inkjet printing

Electrohydrodynamic (EHD) inkjet printing is a type of potential non-contact micro/nanoscale manufacturing technology. The printed droplet dimension plays an important role in EHD inkjet printing due to its significant influence on printing quality and the resolution of patterns. The complexity of the mechanism and the limited process optimization techniques present a challenge in obtaining the desired printing resolution, eventually becoming an expensive and time-consuming endeavor. In this study, a CFD model is proposed to investigate the mechanism of the cone-jet printing process in EHD inkjet printing. The complete cone-jet printing process is successfully simulated. A further analysis predicts the jetting diameter and printed droplet diameter with different operating parameters and substrates. The simulation has a satisfactory agreement with experiments in predicting the printing behavior and printing quality (jetting diameter, printed droplet diameter). Such advancement in modeling can be utilized to guide the quick determination of operation parameters for the desired printing resolution when given a new ink. • Electrohydrodynamic inkjet printing is a non-contact micro/nano manufacturing technique that utilizes electric force to generate droplets. • A computational fluid dynamics (CFD) model is proposed to investigate the cone-jet printing mechanism in EHD printing. • A complete cone-jet printing cycle with four phases is simulated: cone formation, jet generation, jet break and droplet expansion. • A further analysis predicts the jetting diameter and printed droplet diameter using different operating parameters and substrates. • The modeling advancement can guide the quick determination of operation parameters for desired printing resolution given a new ink. Electrohydrodynamic (EHD) inkjet printing is a type of potential non-contact micro/nanoscale manufacturing technology. The printed droplet dimension plays an important role in EHD inkjet printing due to its significant influence on printing quality and the resolution of patterns. The complexity of the mechanism and the limited process optimization techniques present a challenge in obtaining the desired printing resolution, eventually becoming an expensive and time consuming endeavor. Recent developments in computational fluid dynamics (CFD) bring an effective alternative to alleviate the aforementioned challenges. In this study, a CFD model is proposed to investigate the mechanism of the cone-jet printing process in EHD inkjet printing. The complete cone-jet printing process is successfully simulated with four phases: Taylor cone formation, cone-jet generation, jet break and droplet expansion. A further analysis predicts the jetting diameter and printed droplet diameter with different operating parameters and substrates. The simulation has a satisfactory agreement with experiments in predicting the printing behavior and printing quality (jetting diameter, printed droplet diameter). Such advancement in modeling can be utilized to guide the quick determination of operation parameters for the desired printing resolution when given a new ink.

Fabrication of circuits by multi-nozzle electrohydrodynamic inkjet printing for soft wearable electronics

Wearable electronic devices are evolving from current rigid configurations to flexible and ultimately stretchable structures. These emerging systems require soft circuits for connecting the various working units of the overall system. This paper presents fabrication of soft circuits by electrohydrodynamic (EHD) inkjet-printing technique. Multi-nozzle EHD printing head is employed for rapid fabrication of electric circuits on a wide set of materials, including glass substrate (rigid), flexible polyethylene terephthalate (PET) films, and stretchable thermoplastic polyurethane (TPU) films. To avoid the effects of substrate materials on the jettability, the proposed multi-nozzle head is equipped with integrated individual counter electrodes (electrodes are placed above the printing substrate). High-resolution circuits (50 ± 5 µm) with high electrical conductivity (0.6 Ω □−1) on soft substrate materials validate our well-controlled multi-nozzle EHD printing approach. The produced circuits showed excellent flexibility (bending radius ≈ 5 mm radius), high stretchability (strain ≈ 100%), and long-term mechanical stability (500 cycles at 30% strain). The concept is further demonstrated with a soft strain sensor based on a multi-nozzle EHD-printed circuit, employed for monitoring the human motion (finger bending), indicating the potential applications of these circuits in soft wearable electronic devices.Graphic

Fabrication of microvascular constructs using high resolution electrohydrodynamic inkjet printing

Fabrication of the intricate anatomy of vasculature within engineered tissue remains one of the key challenges facing the field of tissue engineering. We report the use of electrohydrodynamic (EHD) inkjet printing to create hydrogel-based microvascular tissues with hierarchical and branching channels, whose minimum feature size of 30 μm approaches the physical scale of native capillary blood vessels. The principle relies on the use of complementary thermoreversible gelling properties of Pluronic F127 (PF-127) and gelatin methacryloyl, which served as sacrificial templates and permanent matrices respectively. Human dermal fibroblasts and human umbilical vein endothelial cells were successfully co-cultured within the engineered microvascular tissue constructs for up to 21 days, and attained high cell viability. Tissue specific morphology was maintained on perfusion. The ability to create cellularised, vascularised proto-tissues with high spatial resolution using EHD inkjet printing, provides a new strategy for developing advanced vascular models with the potential to impact upon an extensive range of biomedical applications.

Fabrication of silver microstructures via electrohydrodynamic inkjet printing as customizable X-ray marker in bio-structure for biomedical diagnostic imaging

X-ray markers have been applied for diagnostic purposes in the medical imaging field. However, they were not flexible enough to accommodate the fast evolution of biomedical applications leading to a considerable performance gap. EHD-inkjet printing technique as a high-resolution, low-cost, and flexible approach was used to fabricate a silver X-ray marker to fill the gap in the biomedical field. Even though X-ray characterization of bulk silver had been studied, silver nanoink has presented a different X-ray absorption response. To understand the X-ray characterization of silver microstructures, multiple samples were fabricated. The EHD-inkjet printing system was applied to fabricate silver microstructures under optimized printing parameters, including voltage amplitude, pulse width, frequency, and printing speed. To understand X-ray characteristic differences between bulk silver and nanoink silver, experiments were designed to print a single layer and multiple layers of silver nanoink lines. Microstructures, which were e-jet printed by silver nanoink, presented different X-ray absorption rate to the bulk silver under the same radiation condition and thickness. Sub-30 μm microstructures of silver nanoink were achieved by e-jet printing; part of them will serve as the X-ray marker in bio-scaffold. This research proposed a method to bridge the e-jet printing technique with a customizable X-ray marker in bio-scaffold, which could effectively resolve the problem of flexibility, improve the resolution, and reduce the cost of manufacturing. Moreover, it supported the development of biomedical products that were fabricated by silver nanoink material, such as in vivo embedded biosensors in computed tomography applications.

Flexible Structural Color Films Based on Electro-Hydrodynamic Inkjet Printing

Structural coloration based on nanostructures is one of the alternatives that can prevent environmental pollution compared to the use of chemically synthesized materials. This technique has attracted considerable attention for various applications, including displays and sensors. In this study, a photonic crystal structure based on spherical silica was formed to provide structural color using an electro-hydrodynamic (EHD) equipment, a printed electronic system attracting considerable interest. The EHD inkjet printing equipment could print micro- and nanostructures using the voltage applied between the nozzle and substrate. Silica-based ink samples were prepared for use in the EHD equipment. Appropriate printing parameters for the EHD inkjet printing were set using the prepared sample. Spherical silica was printed on a polyimide (PI) film layer. The spherical silica nanoparticles discharged during the EHD inkjet printing were not deformed by the EHD process. A photonic crystal structure was formed on a polydimethylsiloxane (PDMS) layer by EHD printing by covering the PDMS layer on the PI film. The spherical-silica-based photonic crystal structure formed on the PDMS layer with elasticity and flexibility exhibited a color change with bending loads.

Geometry Control of Source/Drain Electrodes in Organic Field-Effect Transistors by Electrohydrodynamic Inkjet Printing.

In this work we study the influence of dielectric surface and process parameters on the geometry and electrical properties of silver electrodes obtained by electrohydrodynamic inkjet printing. The cross-section and thickness of printed silver tracks are optimized to achieve a high conductivity. Silver overprints with cross-section larger than 4 μm2 and thickness larger than 90 nm exhibit the lowest resistivity. To fabricate electrodes in the desired geometry, a sufficient volume of ink is distributed on the surface by applying appropriate voltage amplitude. Single and multilayer overprints are incorporated as bottom contacts in bottom gate organic field-effect transistors (OFETs) with a semiconducting polymer as active layer. The multilayer electrodes result in significantly higher electrical parameters than single layer contacts, confirming the importance of a careful design of the printed tracks for reliable device performance. The results provide important design guidelines for precise fabrication of electrodes in electronic devices by electrohydrodynamic inkjet printing.

Grid-type sensors using resistance change ratio for micro-crack detection

A new sensing technique for detecting micro-cracks is proposed using the grid-type circuit. The location of micro damage can be estimated based on the tendency of resistance change ratio. The construction of a well-defined grid circuit is important to reliably measure the resistances for micro-scale crack detection. Therefore, the electrohydrodynamic (EHD) inkjet printing technology is applied to build the uniform grid-type circuit. A comparison analysis with respect to the resolution of the grid pattern is conducted to estimate more accurately the location of cracks on the grid-type sensor constructed by the EHD technique. In this work, the 10⨯10 and 20⨯20 grid circuits are considered on an identical surface. By measuring the resistance variations between the two endpoints on every grid with respect to each direction, the location of cracks is estimated by a simple algorithm. Finally, the micro-crack point can be detected using the proposed sensing approach. The proposed mechanism shows the ability to accurately detect the location of cracks.

Optimization of drop ejection frequency in EHD inkjet printing system using an improved Firefly Algorithm

Swarm intelligence approaches have been used to solve various optimization real-world applications in recent years. Firefly Algorithm (FA) is one of the popular stochastic swarm intelligence paradigms developed in the recent past. In order to solve the slow convergence speed of the standard FA, a new improved Firefly Algorithm (iFA) is proposed in this research. Instead of keeping a constant initial brightness coefficient, a new rule has been proposed for updating the brightness of the fireflies based on a selection probability during generations which leads to a better balance between exploration and exploitation. The efficiency of the iFA has been tested by solving benchmark mathematical functions as well as in a real-world engineering problems. In order to comprehensively compare the performance of the iFA, several other metaheuristic algorithms were used for solving the same benchmark functions and the real-world problems. The iFA shows its superiority in almost all the cases for finding better optima in terms of the objective function value. The droplet ejection speed of an electrohydrodynamic inkjet printing system has been significantly improved by the iFA, which hence fully demonstrates its potential to solve real-world problems. Additionally, the iFA proves its efficiency in solving some challenging, classic engineering design problems with unknown search space. The source codes of the iFA are publiclyavailable at https://www.amitball.com/projects/iFA.

Nanomaterial Coating on Micro-Hotplate By EHD Inkjet Printing with in-Site Infrared Laser Heating

Introduction EHD inkjet printing was applied in the fabrication of micro gas sensors recently [1-3]. In most cases, the evaporation of the ink solvent is slow, which makes thickness and uniformity of the film difficult to control. This work introduces an IR laser heating source to the EHD printing system of previous work [2], which accelerates the evaporation of the as-deposited ink solvent on the MHP, so that thick films and even columnar structures can be deposited without the use of special ink solvent.This paper reports a novel in-situ infrared (IR) laser aided electrohydrodynamic (EHD) inkjet printing technique which can deposit hierarchical micro/nano-structured gas-sensitive materials on micro-hotplate (MHP) for micro gas sensor fabrication. Gas-sensitive materials can be deposited quickly on an MHP to form flatten thin film, thick film, and 3D columnar structures. Method The diagram of the printing system is shown in Figure 1. An 808 nm IR laser source with adjustable output power is mounted on the EHD inkjet printing system, focusing at the printing spot with a diameter of about 1 mm. The freestanding MHP with metal electrodes embedded in SiO2 membrane can be heated up to 200oC in seconds by adsorption of the IR power. After EHD printing of the ink onto the 100 µm * 100 µm area of the MHP, the IR laser is turned on with optimized output power and time interval to heat the MHP to a temperature that the solvent evaporated rapidly and the dry gas-sensitive materials are uniformly covered on the surface of the MHP. By repeating the EHD printing and IR heating process, thickness of the film increases regularly and thick film can be prepared. In the preparation of columnar structure, by shrinking the amount of ink droplet and accelerating the IR heating, a tip appears on the surface of the deposited materials. The electric field intensity is larger at the tip since it shortened the distance to the needle, therefore, the electric force drives the ink droplet to deposit on the tip and the tip continues to grow, forming a 3D columnar structure. Results and Conclusions The temperature of the MHP changes with the power of the IR laser in a linear relationship (Figure 2). The flower-like tin oxide powder doped with 3 at% palladium was prepared as the hierarchical-structured gas-sensitive material with a hydrothermal method (Figure 3). The ink was prepared by mixing the powder, DI water and surfactant in a proper proportion, and it was EHD printed on the surface of the MHP (Figure 4). Without IR heating, the solvent did not evaporate completely even after 600 s at room temperature, making it not suitable to print again. By turning on the IR laser with 450 mW for 5 s, the ink was dried and uniform thin film with thickness dfilm<1 µm was coated on the MHP as shown in figure 5 (b). Repeat the printing-heating cycle for 4 times only took 100 s, and thick film of dfilm ≈ 40 µm was obtained as shown in Figure 5 (c). Figure 6 compares the power consumption of the MHP before and after printing, which shows that the MHP with thick gas sensitive film remains good thermal isolation property. The printed 3D columnar structure with height of about 120 µm is shown in figure 5 (d). Increasing the power of the laser can accelerate the evaporation. However, when the IR laser power is more than 500 mW, the droplet on the MHP boil violently and nanomaterials splashes all around.For the first time, the IR aided EHD printing allows the printing of flatten thick gas sensitive film composed of hierarchical-structured nanomaterial on MHP. Also, the technique can further be applied in fabrication of other MEMS devices.This work is supported by the Nature Science Foundation of China (61874018 and 61274076), the Fundamental Research Funds for the Central Universities, and the Nature Science Foundation of Liaoning (20180550923).

Study effects of particle size in metal nanoink for electrohydrodynamic inkjet printing through analysis of droplet impact behaviors

Abstract Ink properties play a critical role in different printing techniques. However, it is not straightforward to correlate ink properties to the printing results. In this study, several parameters were identified and analyzed to evaluate the droplet behavior in electrohydrodynamic inkjet printing. More specifically, the effects of metallic nanoparticle sizes in the ink formulation were explored through the analysis of droplet impact behaviors. These parameters include droplet wetting diameter, height, initial impact velocity, and contact angle. With the assistance of machine vision, a high-speed camera captured a sequence of images, which were analyzed to extract the aforementioned parameters. Under fields of gravitational force with/without electric force, four phases of ink droplet behaviors were identified. Our data suggest that with an electric force field, particle size dominates the droplet behavior in respect to contact angle and wetting diameter. The increase of particle size decreased the droplet wetting diameter with an electric field, while increased the droplet wetting diameter without the electric field applied. Larger droplet size resulted in higher bouncing frequency and lower droplet height. Furthermore, under both gravitational and electrical fields, the droplet with medium particle size (average diameter of 276 nm) had a higher impact velocity than that with small (average diameter of 140 nm) and big (average diameter of 1517 nm) particle sizes. This study contributes to fundamental understanding of particle size effects. The results will help optimize ink formulations when designing new ink materials for electrohydrodynamic inkjet printing.

Fabrication of paper-based microfluidic channels by electrohydrodynamic inkjet printing technology for analytical biochemistry applications

Paper-based microchannels are important components in paper-based microfluidic devices. Paper-based microchannels are usually manufactured by creating lines with hydrophobic patterns enclosing an area of hydrophilic paper inside. Among the many techniques for making hydrophobic lines, the printing method in general and inkjet printing in particular have become more common because of their advantages in terms of material saving, high precision, low-cost, etc. In this paper, the electrohydrodynamic (EHD) inkjet printing method, which has been studied and developed in recent years, has been used to drop glycol ether solvent-based ink onto a nitrocellulose paper. The results of the field emission scanning electron microscope (FE-SEM) show that the solvent based ink could dissolve through membrane and form a transparent hydrophobic layer on the created space. The width of the barrier lines can be controlled from about 200 μm to 260 μm, which is quite small when compared to other manufacturing methods. Based on this fabrication process, paper-based microfluidic analytical devices have been designed and fabricated for use in analytical biochemistry assays. Human chorionic gonadotropin (hCG) was selected as the biological target for this assay. Initial results have shown that the target for hCG can be quantitatively determined by these devices with a coefficient of determination (R2) of approximately 0.99. Therefore, EHD inkjet printing technology can be used for the manufacture of paper-based microfluidic analytical devices (μPADs) that may be applied in the future for analytical biochemistry assays.

Electrohydrodynamic inkjet printing of Polydimethylsiloxane (PDMS)

The current fabrication methods for micro and nano scale Polydimethylsiloxane (PDMS) devices either require high environmental conditions or sophisticated procedures at high cost. Electrohydrodynamic inkjet (EHD) printing is a potential method to effectively fabricate micro scale PDMS devices because EHD printing is environment-friendly, low-cost, compatible to various inks, and most importantly, high resolution. However, little research has been conducted to study EHD printing of PDMS-based ink. In this paper, EHD printing of PDMS has been investigated. The effects of several critical parameters on the printing process were studied. The dimension of the printed patterns and the printing frequency were preciously controlled by the voltage parameters. The patterns with a network structure was demonstrated. The results indicated that the voltage amplitude and the pulse frequency could both control the dimensions of droplets and the printing frequency. As future work, we plan to develop a simulation tool to predict printing quality of PDMS and optimize printing process to fabricated 3D PDMS structures in micro scale.

High-resolution organic field-effect transistors manufactured by electrohydrodynamic inkjet printing of doped electrodes

A top-contact, sub-5 μm resolution OFET is realized using inkjet printed electrodes with different F4-TCNQ doping concentrations.

Electrical evaluations of anisotropic conductive film manufactured by electrohydrodynamic ink jet printing technology

Generally, anisotropic conductive films (ACFs) used for bonding in communication devices and displays are manufactured by applying pressure to conductive particles at desired positions. The conventional production process has serious disadvantages that waste of conductive particles and the non-uniform number of particles captured, etc. In order to overcome these disadvantages, the film production using electrohydrodynamic (EHD) ink jet printing technique is proposed in this work. The EHD printing results are greatly affected by the ink properties and printing conditions. Therefore, polymer inks suitable for EHD ink jet printing are developed, and then the variation of the meniscus according to the intensity of the voltage was evaluated. As a main material of ACFs, conductive particles are added to the polymer inks to assess the feasibility of generating the ACFs using EHD technology. The results show that the electrical conductivity of the manufactured ink with conductive particles shows good performance.

Printed 3D Electrode Arrays with Micrometer‐Scale Lateral Resolution for Extracellular Recording of Action Potentials

AbstractCurrent investigations on neuronal or cardiac tissues call for systems that can electrically monitor cellular activity in three dimensions as opposed to classical planar approaches. Typically the fabrication of such 3D microelectrode arrays (3D MEAs) relies on advanced cleanroom fabrication techniques. However, additive manufacturing is becoming an ever versatile alternative for rapid prototyping of novel sensor designs due to its low cost and material expense. Here, the possibility of fabricating high‐resolution 3D MEAs is demonstrated by using electrohydrodynamic inkjet printing. The height and aspect ratio of the 3D electrodes can be readily tuned by adjusting the printing conditions and number of deposited ink droplets per electrode. The fabrication of pillar electrode arrays with electrode diameters of sintered structures below 3 µm is shown. The functionality of the array is confirmed using impedance spectroscopy and extracellular recordings of action potentials from HL‐1 cells.

In-situ monitoring of electrohydrodynamic inkjet printing via scalar diffraction for printed droplets

Electrohydrodynamic inkjet (e-jet) printing is a technique which utilizes electrical forces to generate droplets in micro/nano scale using conductive inks. Currently, there is no procedure in place to measure the printed patterns without taking the sample away from the printer setup. Removal of the substrate from the printing stage during the e-jet printing process prevents any additional work from being performed on the sample. We investigated the application of scalar diffraction for the in-situ measurement and digital reconstruction of opaque material printed on transparent substrates. Measurement and characterization of the printed material can be achieved in-situ to alter printing condition in process for quality assurance. In order to accomplish the sample reconstruction, a digital recording of a scalar diffraction pattern in the image plane was employed in this paper with a magnification of 5× with the help of a combination of lenses. The reconstructed images were then compared to images captured by an offline high-resolution microscope. The results indicated a submicron accuracy of the feature radii and the locations of feature centers. In addition to the quantitative measurements, this method also allows for the operator to view the overall form of the printed patterns. Our findings demonstrate an effective approach for in-situ monitoring of e-jet printing and printed patterns, which could pave the way for the industrial application in printing testing field.

Fabrication of micro-scale radiation shielding structures using tungsten nanoink through electrohydrodynamic inkjet printing

Electronics components used in space and strategic missions are exposed to harsh radiation environments, which could cause operational malfunction of the system through lattice displacement or ionization effects. One potential solution is to use tungsten as radiation shielding. Tungsten is a very effective material in shielding electronic components and manufacturing gratings for x-ray imaging. However, intrinsic properties of tungsten (e.g. density, chemical/thermal inertness and hardness) post a significant challenge of fabricating the material into micro-scale and delicate structures, especially in electronic device fabrication. To address the problem, we designed a new tungsten nanoink and developed a straightforward approach to create tungsten micro-structures by 3D printing. Various microstructures down to 10 µm resolution have been patterned and fabricated by electrohydrodynamic inkjet (e-jet) printing using tungsten nanoink. By optimizing process parameters (voltage modality) and materials properties (ink formulation), the dimension and morphology of the structures can be precisely controlled. An AC-modulated voltage was employed during the e-jet printing process to make the patterns much more controllable and stable. Multi-layer tungsten lines were characterized by x-ray imaging and exhibited excellent absorption of x-ray radiation. With the same thickness, printed lines showed nearly 1/3 absorptivity of x-ray radiation of bulk tungsten, leading to significant radiation attenuation effectiveness. Tungsten nanoink is a new material used in e-jet printing that has not been reported in the literature to the best of authors’ knowledge. The study establishes a new methodology of manufacturing micro-nano scale shielding components for electronic devices and rapid prototyping of gratings and collimators in radiography for medical and inspection applications. The research also provides practical guidance to fabricate high melting-point metals via nanoink and micro/nano scale 3D printing.

Modeling of EHD inkjet printing performance using soft computing-based approaches

Nature-inspired heuristic and/or metaheuristic algorithms have been used for solving complex real-world problems in recent years. Electrohydrodynamic (EHD) inkjet printing is a microadditive manufacturing process in which high-resolution jets of polarizable functional materials were deposited on the defined spot of a substrate at the appointed time. The quality of the printed features is derived by the complex physics of the system. Parameter modeling of this process was carried out by using regression analysis, a feed-forward neural network trained with backpropagation (BPNN) and a neural network trained with a genetic algorithm (GA-NN) separately. This study emphasizes the droplet diameter prediction of an EHD inkjet printing system and explores the applicability of the soft computing-based methods for this new emerging technology. Soft computing-based approaches have been developed for the first time in this area to model the EHD inkjet process. Five hundred data were produced through the conventional regression analysis to train the neural network-based models. Output droplet diameter was predicted for different combinations of input parameters such as standoff height (SH), applied voltage (AV) and ink flow rate (FR) using the above three approaches, and their performances were analyzed through some randomly created real experimental test cases. All three models gave good prediction accuracy with less than 10% error in the prediction of the droplet diameter. Furthermore, it had been observed that the performance of GA-NN surpasses both the regression- and BPNN-based approaches in most of the test cases. It achieved quite satisfactory average absolute percentage deviation value of 2.51% between the target and predicted output using GA-NN model, which also showed an improvement over the regression or BPNN model.

Experimentation modelling and optimization of electrohydrodynamic inkjet microfabrication approach: a Taguchi regression analysis

Electrohydrodynamic (EHD) inkjet is a modern non-contact printing approach, which uses a direct writing technology of functional materials to achieve micro/nanoscale of printing resolution. As an alternative to conventional inkjet technology, the goal of the EHD inkjet printing is to generate uniformly minimized droplets on a substrate. In this study, the effects of applied voltage, standoff height and ink flow rate on droplet diameter formation in EHD inkjet printing process were analysed using Taguchi methodology and regression analysis. Several experiments were carried out using an L27 (313) orthogonal array. Based on signal to noise (S/N) ratio and mean response, optimal droplet diameter was achieved. The analysis of variance (ANOVA) was used to find the significance and percentage of contribution of each input parameter along with their interaction on the output droplet diameter. Analysis of the results revealed that the ink flow rate was the dominant factor that affected the droplet diameter mostly. The effect of the applied voltage is significant until regular ejection starts. It helps reduce droplet diameter more than five times compared with its initial droplet diameter in the absence of the electric field. A confirmation test was carried out with a 90% confidence level to illustrate the effectiveness of the Taguchi optimization method. Both linear and quadratic regression analysis were applied to predict the output droplet diameter. The predicted result from the model and actual test results are very close to each other, justifying the significance of the models.