Piezoelectric Inkjet Printhead Research Articles

Squeeze-Type Piezoelectric Inkjet Printhead Actuating Waveform Design Method Based on Numerical Simulation and Experiment.

The piezoelectric inkjet printing technique has been commonly used to produce conductive graphics. In this paper, a trapezoidal waveform design method for squeeze-type piezoelectric inkjet printhead is presented to provide a modified steady ejection and optimal droplet shape, in which a coupled multi-physics model of a piezoelectric inkjet printhead is developed. This research describes the effects of parameters, including rising time tr, falling time tf, and dwelling time td, of the trapezoidal waveform on the pressure at the nozzle through numerical simulations. These parameters are initially optimized based on numerical simulations and further optimized based on experimental results. When the printhead is actuated by the optimized waveform with the tr = 5 µs, td = 10 µs, and tf = 2 µs, the droplets are in optimal shape, and their size is about half the diameter of the nozzle. The experimental results validate the efficacy of this waveform design method, which combines numerical simulation and experiment, as well as demonstrating that ink droplet formation can be studied from the point of pressure variation at the nozzle.

Numerical Analysis and Optimal CFD Model Verification of Piezoelectric Inkjet Printhead

Flow dynamics accurate prediction is critical for the early-stage design and performance optimization of the piezoelectric (PZT) printhead. To achieve this, the Computational Fluid Dynamics (CFD) method has been widely used. However, for accurate fluid simulation of the PZT printhead, the optimal parameters settings still need to be clarified, which will be discussed in full in this paper. The modelling work is divided into two sub-parts, namely, a three-dimensional (3-D) modelling for the ink chamber and a two-dimensional (2-D) modelling for the nozzle-air domain. Simulations of the 3-D ink chamber were carried out firstly, thereby the transient mass flow rate of the ink outflow from the chamber could be obtained, which will be set as the inlet boundary condition of the 2-D nozzle-air simulations. To ensure accuracy and convergence of 2-D simulations, independence tests of the mesh grid and time step were performed, where the Fine level mesh density and 1e-8 s time step were identified as the optimal choice. And this combination was adopted in the transient simulations of the droplet ejection process. For the model validation purpose, an experimental test rig was developed, and comparisons between the simulations and experimental tests show a good agreement, verifying the accuracy of the developed model. In addition, to validate the feasibility of the developed model, the effect of the ink viscosity on the droplet ejection process was tested, and the results were consistent with those produced by published literature, confirming the feasibility of the CFD model developed in this paper.

Modelling of Power-Law Fluid Flow Inside a Piezoelectric Inkjet Printhead.

Piezoelectric three-dimensional inkjet printing has been used to manufacture heterogeneous objects due to its high level of flexibility. The materials used are non-Newtonian inks with complex rheological properties, and their behavior in the context of inkjet printing has not been fully understood: for example, the fact that the shear-thinning viscosity affects the droplet generation. Therefore, a control strategy coping with shear-thinning behaviors is needed to ensure printing consistency. In this paper, a novel model-based approach is presented to describe the shear-thinning ink dynamics inside the piezoelectric inkjet printhead, which provides the basis to design the excitation parameters in a systematic way. The dynamic equation is simplified into a quasi-one-dimensional equation through the combination of the boundary layer theory and the constitutive equation of the power-law fluid, of which the viscosity is shear-thinning. Based on this, a nonlinear time-varying equivalent circuit model is presented to simulate the power-law fluid flow rate inside the tube. The feasibility and effectiveness of this model can be evaluated by comparing the results of computational fluid dynamics and the experimental results.

Actuating Voltage Waveform Optimization of Piezoelectric Inkjet Printhead for Suppression of Residual Vibrations.

After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time ( ), dwell time (), rising time (), falling time (), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, , and and were finalized as the optimal parameters; in the case of another waveform, the optimal parameters of , , and were found to be , , and , respectively. The optimal voltage amplitude of the second pulse was found to be 1/3 the amplitude of the first pulse. On the basis of our analysis, the tuning time in Waveform 01 is the most sensitive parameter, and the performance yielded is even poorer than that yielded by standard waveform, if not optimized. Therefore, the other waveform is recommended for the suppression of residual vibrations.

Analysis of drop-on-demand piezo inkjet performance

For a particular printing ink and drop-on-demand piezoelectric inkjet printhead, piezoelectric voltage and temperature of the ink were varied to change the inkjet performance, and the jetting velocity of the inkjet was analyzed under various conditions. The ink was cooled by using a Peltier module, which was attached to the nozzle plate as a heat sink. The inkjet drops were captured by the shadowgraphic method using a high-speed camera. The positions and velocities of these drops were then estimated after image processing. The drop state was distinguished by dimensionless numbers, such as the Weber and Z numbers, to decide whether it was stable for ejection and printing. Increasing the piezoelectric voltage increased the ejection velocity but with an associated generation of satellite drops. Cooling the ink increased the viscosity, which in turn decreased the drop velocity while diminishing the satellite drops. Therefore, it was shown that the cooled ink enabled stabilized inkjet ejection.

Design and fabrication of composite vibrating plate used for piezoelectric inkjet print head

A piezoelectric vibrating plate is an important component of the piezoelectric inkjet print head, it determines the ejection performance of the piezoelectric inkjet print head. Based on the design model of the vibrating plate and the lead zirconate titanate piezoelectric film in the inkjet print head, the approximate expression of the equivalent load and deflection of the vibrating plate were established. The Cu/SiO2 vibration plate structure of the piezoelectric inkjet print head was fabricated based on MEMS process. The laser Doppler test was performed on the vibrating plate to obtain the amplitude of the Cu/SiO2 vibrating plate. The test results are in good agreement with the theoretical predictions based on the mechanical analysis.

Study on the dynamic characteristics of piezoelectric inkjet print head with basic excitation methods

In this paper, the dynamic characteristics of piezoelectric inkjet print head were studied by analyzing vibration mode and resonant frequency. The modal analysis was carried out by using the multiphysics simulation software COMSOL. The vibration characteristics of print head were measured. The piezoelectric actuator and print head were excited by two basic excitation methods: fast sine sweep and white noise, respectively. The speed response was measured by the laser Doppler vibrometer and the power spectrum was obtained by using MATLAB software to obtain the first-order resonant frequency. The results show that the first-order mode is most suitable for droplet formation and ejection, and the print head in the working state is indeed under the first-order mode. The fluid–solid coupling effect has great influence on the shape and amplitude of the vibration curve. The presence of liquid lower the peak of the resonant frequency and the severe liquid motion affect the number of peaks of the resonant frequency.

Characterization of a Piezoelectric Inkjet Aerosol Generator for the Study of Bioaerosol Survivability

ABSTRACT In laboratory-based bioaerosol researches, the ability to reliably generate bioaerosols with minimal damage to the microorganisms is critical. In this work, a thermally consistent inkjet-based aerosol generation technique was adopted to generate bioaerosols, and its ability to preserve microbial survivability was assessed. The performance of the piezoelectric inkjet aerosol generator was evaluated using a potassium sodium tartrate solution and an aqueous suspension of 3-µm polystyrene latex spheres. An Aerodynamic Particle Sizer was employed to measure the aerosol number concentration and the size distribution. The main operating parameters of the inkjet print head for generating viable aerosols were the driving voltage, pulse duration, dispersion air flow, pulse frequency, and volume fraction of the solids in the nebulizing liquid. In the bioaerosol survivability experiments, yeast was used as the test microorganism. The nebulized yeast cells were sampled at different distances from the outlet of the inkjet aerosol generator and thus exposed to varying degrees of relative humidity for different residence times. Three bioaerosol samplers, namely, a BioSampler, a gelatin filter cassette, and a Marple cascade impactor with Mylar film, were used to collect the airborne yeast samples. Yeast survivability was determined by methylene blue viability staining. This study successfully demonstrated the feasibility and the advantages of using a piezoelectric inkjet print head to generate viable aerosols. Applying a square wave with appropriate combinations of voltage and pulse duration enabled the inkjet system to produce a liquid with rheological properties similar to those of water, and the particle generation rate was manipulated by adjusting the pulse frequency. Moreover, dispersion air was required to reduce coagulation. Although the number of droplets containing PSL spheres increased with the volume fraction of the spheres (Fv), a high Fv also reduced the probability of singlets forming.

Optimization of the driving waveform of a piezoelectric inkjet printhead based on a system dynamics model

PurposeThis paper aims to present an optimization method of the input driving signal of a piezoelectric inkjet printhead to improve droplet consistency and increase jetting frequency.Design/methodology/approachThe optimization target is the transient pressure in the nozzle caused by the input driving signal, which directly generates the droplets. After demonstrating the linearity of the driving input and system pressure, an analytic model as a transfer function was developed, allowing calculation of the pressure vibration in the nozzle for an arbitrary input. Different patterns of input signal were parameterized and applied into the optimizing function, which represents the difference between the ideal and the actual pressure vibration. By determining the function minimum, the optimized parameters of the input signal were estimated.FindingsOptimization results of different input patterns were compared and verified by the numerical model of the printhead, and it was revealed that the optimization method that combined the quenching pulse and an increased falling time interval was more effective than use of a single method.Originality/valueAfter the process of optimization, a new type of input signal to the piezoelectric inkjet printhead was showed. By this method, the frequency of the printhead could be increased without losing consistency of droplets.

Droplet property optimization in printable electronics fabrication using root system growth algorithm

For printable electronics fabrication, the printing quality delivered by a Drop-on-Demand (DoD) Piezoelectric Inkjet (PIJ) Printhead is limited due to the residual vibration problem in the ink channel. The residual vibration after jetting the ink drop influences the droplet velocity and volume consistency, and limits the maximum jetting frequency of the printhead. In order to meet the challenging requirements of printable electronics fabrication, this work proposes a novel Optimization framework for optimal parameter setting of the high-frequency driving waveform. A novel Root System Growth Algorithm (RSGA), based on principles from plant root growth and foraging behaviors, is chosen as the core optimization algorithm of the framework. The proposed RSGA is benchmarked against other four state-of-the-art bio-inspired algorithms using CEC2005 test function suite. Then several groups of experiment results for various targets are presented to demonstrate the universality of the proposed optimization-based search system for the improvement of printing quality. Simulation results show that the RSGA has an outstanding performance in searching the driving waveform parameters for specified droplet properties.

A waveform design method for piezoelectric inkjet printhead with Doppler vibration test and numerical simulation

Piezoelectric inkjet printing technology has been widely used in recent years. A new method for driving waveform design was presented to overcome the limitations in traditional waveform design methods. In this paper, the Doppler vibration test was used to determine the time of voltage rising and falling section. According to the superposition principle of velocity wave, the time of voltage dwelling section was determined by the numerical simulation. The optimal parameters with trise = 5 μs, tdwell = 16 μs and tfall = 3 μs of unipolar trapezoidal driving waveform was obtained. By using this method, the number of experiments can be significantly reduced in the initial stage of the printhead development process. The experimental results proved the feasibility of this method.

Effects of the ‘spring structure’ on the performance of a vibrating plate of the piezoelectric inkjet print-head

One of the core components of piezoelectric inkjet print-head is the piezoelectric vibrating plate which directly affects the jet performance of a print-head. In the present paper, a simplified coupling model theory of the composite vibrating plate was studied in combination with the actual manufacturing process of the piezoelectric vibrating plate. The ‘spring structure’ is formed by releasing the long edge of Lead Zirconate Titanate (PZT) thin films to enhance the amplitude of the piezoelectric vibrating plate. The laser Doppler measurement was carried out on the piezoelectric vibrating plate, and the results were verified by using numerical simulation. The results show that the ‘spring structure’ can effectively improve the amplitude and average deformation rate of the piezoelectric vibration plate in the air while does not affect the deformation time. The amplitude of the vibrating plate with spring structure increased continuously in the dwelling stage of the drive signal when the ink was inspired. Moreover, the magnitude of residual vibration also increased.

Fabricating method of SU-8 photoresist conical nozzle for inkjet printhead

ABSTRACTA novel conical nozzle fabrication method for piezoelectric inkjet printhead is proposed based on the microelectromechanical system technology. By optimizing the exposure gap, exposure dose, postexposure bake (PEB), and development time, the SU-8 conical nozzle was fabricated. After thermal bonding with an open chamber, the piezoelectric inkjet printhead chamber was formed. The results show that the optimum SU-8 conical nozzle can be fabricated by applying exposure dose of 105 mJ/cm2, exposure gap of 50 µm, PEB temperature of 65°C, PEB time of 10 min, and development time of 210 s. The final size of optimum conical nozzle is the large aperture of 30.46 ± 1.17 µm, small aperture of 20.34 ± 1.42 µm, and nozzle height of 45.38 ± 1.02 µm.

Process for fabricating microactuator membranes of piezoelectric inkjet print head using multi‐step deep reactive ion etching process

As part of an effort to develop piezoelectric inkjet print head (PIPH), a process for fabricating its Si-cups and actuator membranes of multi-layered structures was investigated. The manufacture of this device was enabled by the use of deep reactive ion etching (DRIE). Based on that, multi-step DRIE process was proposed to etch the multi-layered actuator membranes on silicon on insulator wafers. Due to the appropriate parameters of the etching process, undesirable effects, such as Si grasses, notching effect of Si-cups and the bowing formation on the sidewalls, were also avoided. The way to eliminate the over-etching of SiO2 membranes by controlling the appropriate platen power and process duration simultaneously was also presented. High quality PIPH actuator membranes were finally obtained, making great contributes to the successful inkjet test.

A waveform design method for high DPI piezoelectric inkjet print-head based on numerical simulation

In order to increase the Dots Per Inch (DPI) of the piezoelectric inkjet print-head, the width and length of the pressure chamber have become much smaller. This makes some previous waveform design methods no longer suitable for the design of high DPI piezoelectric inkjet print-head. In this paper, a new waveform design method based on numerical simulation for high DPI print-head is proposed. Different parameters of the unipolar trapezoidal waveform were optimized using the multi-physics simulation software COMSOL to acquire the optimal waveform for good quality jetting. And meniscus motion at the nozzle exit was measured to predict the jetting behavior of print-head and verify the simulation results. When the high DPI print-head was actuated by the optimized waveform with the rising time tr = 3 µs, dwelling time td = 16 µs, and falling time tf = 3 µs, the high DPI piezoelectric inkjet print-head was continuous injection.

산업용 잉크젯 압전프린트 헤드의 특성해석 및 잉크 망점제어에 의한 PCB 전기회로패턴 공정개선

This paper was analyzed the characteristics of piezoelectric inkjet print head using finite element method(FEM). It showed the bending node driving of piezoelectric and relation theory principle consider piezoelectric material characteristics and ink characteristics. From such result we were had the piezoelectric head design and manufacture. It got a this head characteristics through experiment, we confirmed that proper voltage control is possible to through ink drop control experiment of piezoelectric print head. This paper was obtained the suitable ink jetting characteristics that manufacture the control circuit and piezoelectric inkjet print head. This practice product was applied to improvement of PCB electric circuit pattern by etching resist ink that PCB manufactured to complex process over traditional 6 stages can be simpled to 1 stage by inkjet printing technology.

The production of monodisperse explosive particles with piezo-electric inkjet printing technology.

We have developed a method to produce discrete microparticles from compounds dissolved in nonpolar or polar solvents using drop-on-demand inkjet printer technology. A piezoelectric inkjet printhead located atop a drying tube produces precise droplets containing defined quantities of analyte. Droplets solidify into microparticles with known composition and size as they traverse down the drying tube. Because this is a drop-on-demand printing process, a known number of droplets are produced providing quantitative particle delivery to a variety of substrates. Particular emphasis is placed on the development and characterization of the drying tube in this work. The drying tube was modeled using computational fluid dynamics and experimentally evaluated using laser-based flow visualization techniques. A notable design feature of the drying tube is the ability to push heated air through the tube rather than the need to pull air from the exit. This provides the ability to place a known number of well-defined particles onto almost any substrate of interest, rather than having to collect particles onto a filter first and then transfer them to another surface. Several types of particles have been produced by this system, examples of which are pure particles of cyclotrimethylenetrinitramine ranging from 10 μm to 30 μm in diameter, and ammonium nitrate particles of 40 μm diameter. The final particle size is directly related to the solute concentration of the printing solution and the size of the initial jetted droplet.

Modeling and Optimizing Industrial Inkjet Printhead for Printable Electronics Fabrication

The most significant issues in printable electronics fabrication are the printing quality and efficiency delivered by drop-on-demand (DOD) industrial inkjet printhead. Aiming to characterize the nonlinear behaviors of piezoelectric inkjet printhead, the dynamic lumped element model (DLEM) is proposed to cast the original LEM into a time-varying and nonlinear fashion. At the same time , the PSO-based optimization for paramenters is incorporated in DLEM. Due to new characteristics, DLEM can accurately simulate the inkjet-printed nanosilver droplet formation process and effectively predicate optimal combinations of high-frequency driving waveform with high printing quality. From extensive experimental studies, the effectiveness and efficiency of the proposed DLEM is validated.

Design and Validation of an Open-Hardware Print-Head for Bioprinting Application

In the last decades drop-on-demand inkjet technology played an increasing role in industrial and medical applications. This is due to the ability to deposit a small amount of material in precisely defined position. In the field of Biofabrication, inkjet printers are used to build 2D and 3D scaffolds and gels with biological molecules, including living cells. Several works, including seminal papers on inkjet bioprinting, were carried out with modified office printers. These printers have fixed structural characteristics and operating size, especially on the print-head, limiting the range of materials that can be dispensed. The aim of the present work is the design and fabrication of an open-source piezoelectric inkjet print-head, optimized for the bioprinting field. This low-cost, reproducible, reliable, versatile and biocompatible device will enable various research laboratories to work with a shared device; the open source allowing for parts to be modified to suit specific needs. The design was carried out by Finite Element (FE) modelling of the piezoelectric, mechanical, fluid dynamics and their coupling. The design was optimized for shear rate, which we minimized in order to be able to print cells. The mechanical frame of the printer was designed and built using a low-cost 3D printer. The nozzle plate was fabricated from a polycarbonate disc coated with biocompatible silicone, to increase the hydrophobicity of the outer surface of the disc, preventing ink adhesion on the edge of the nozzle; the refilling system, and the electronic control were also part of the project and will be freely available to download. The FE models were validated with ad-hoc experiments, printing water, gelatin solution, and cell culture media, by modulating the wave power in amplitude, frequency and duty cycle. The tests showed a large working window both respect to viscosity and to surface tension. Finally Human Skin Fibroblasts (ATCC-CRL- 2522, Teddington UK), suspended in culture media, were printed. Cell viability, assessed by CellTiter-Blue and LIVE / DEAD tests, resulted comparable with the control, demonstrating the validity of the first open source piezoelectric inkjet print-head for biofabrication.

Numerical Analysis of Droplet Formation and Effect of Ink Properties in Shear-Type Piezoelectric Inkjet Printhead

Numerical Analysis of Droplet Formation and Effect of Ink Properties in Shear-Type Piezoelectric Inkjet Printhead