Application Cases

Research Direction：

Inkjet printing, electrophoretic printing,Multifield numerical simulation.

Experimental objective：

The experimental purpose of this paper is to verify the feasibility and superiority of a new electro-hydrodynamic (EHD) jetting method based on the high-frequency vibration of a piezoelectric-driven concave surface.

The aim is to break through the bottleneck of the low printing frequency (only at the level of hundreds of Hz) of traditional EHD printing, by exciting the resonance of the liquid column in the capillary to generate a pulsating flow field, enabling the concave surface to sharpen the tip in sub-microsecond time, thereby increasing the continuous jetting frequency to nearly MHz level (956.9 kHz), the drip frequency as per demand reaching above 10 kHz, and significantly reducing the volume of a single jet to the level of femtoliters or even picoliters.

Ultimately, it aims to achieve high-resolution and high-throughput micro-nano scale printing, and provide theoretical basis and technical support for industrial applications in fields such as biomedicine, printed electronics, and micro-nano manufacturing.

Testing equipment：

Signal generator,ATA-7030 high-voltage amplifier, High-voltage direct current power supply, High-speed camera and stroboscopic lighting system, Precision injection pump and displacement platform, etc.

Experimental process：

The developed ionic fluid printing mode requires applying a continuous high-frequency excitation signal to the piezoelectric ceramic, keeping the curved liquid surface in a high-frequency oscillation state.

Then, applying a continuous high-voltage pulse electric field to the high-frequency oscillating curved liquid surface for a specific period of time can achieve synchronous ejection with the pulse electric field.

In this group of experiments, a square wave with an excitation frequency of 108.9 kHz and a peak-to-peak voltage of 3 V was applied to the piezoelectric ceramic. Using the ATA-7030, the low-voltage high-frequency signal (10 kHz) of the signal generator was amplified to an 800V pulse electric field as the induced electric field. The experimental device diagram is shown in Figure 1.

Figure1 Live photo of the experimental platform. 

Figure2 Schematic diagram of the experimental apparatus and observation setup.

Experimental results：

In the experiment, the high-frequency pulsed electric field generated by ATA-7030 played a crucial role. After the curved liquid surface entered a stable oscillation state, by accurately applying the high-voltage pulsed electric field produced by the signal generator and ATA-7030 during the liquid surface retraction process, a fine EHD jet could be generated. The experimental results obtained are shown in the attached figure. The oscillation and jet behavior of the curved liquid surface and the functional patterns printed using this method are respectively shown in the following figures. The jet behavior captured by the high-speed camera and the simulation results of Comsol are shown in the following figure.

Figure3 . (a) The driving method of MVEHD DOD-jetting mode. The red square wave is the driving single (fd = 108.9 kHz) applied to the PZT plate, and the pictures from 0 to 9.2 us show the meniscus vibration state at a driving voltage of Vpp = 3 V. The blue box shows jetting behavior of the MVEHD under an 800 V pulse voltage. (b) Patterns printed by MVEHD DOD-jetting mode, the nozzle diameter is 15 um, and the dots' size is 4 um. Multimedia available online.

Figure4 The one-to-one comparison of the experimental observed creep behavior of MVEHD liquid surface during withdrawal process (a) with the numerical simulation (b) at exact time. Where the blue curve above the nozzle represents the velocity profile of the pulsating flow field. The one-to-one comparison of the experimental observed liquid accumulation and jetting behavior of traditional EHD jet (c) with the numerical simulation (d) at exact time.

The effectiveness of the amplifier in this experiment：

1.High-voltage electric field drive: The low-voltage pulse signal output by the signal generator is linearly amplified to a 800 V high-voltage pulse, which is applied between the nozzle and the substrate, thereby generating sufficient static electric force at the concave surface to induce the jet to be ejected from the micrometer-sized nozzle.

2.Timing control for on-demand jetting (DOD): While the continuous driving of the PZT keeps the concave surface vibrating at a high frequency (108.9 kHz), the pulsed electric field generated by the power amplifier is synchronized with the vibration period. Only during the pulse duration is the trigger current activated, thereby achieving controllable on-demand droplet jetting with a frequency up to 10 kHz, and ensuring that each pulse corresponds one-to-one with the jetting behavior.

3.Flexible adjustment of jet volume and resolution: By changing the pulse voltage amplitude (used in the experiment as 800 V) and pulse width of the power amplifier output, the volume of the droplets in a single jet and the duration of the jet can be controlled, thereby optimizing the print point diameter (minimum approximately 4 μm) and the pattern accuracy.

Application fields：

Printed Electronics and Flexible Devices、Display manufacturing、Biomedicine and Pharmacy、Micro-nano manufacturing and additive manufacturing、Advanced packaging and interconnection technologies.