Inkjet printing devices are useful tools in many applications. They can be classified into two main categories: thermal jet and piezoelectric microjet devices. Thermal jet devices (TJD) are mostly used in conventional graphics printing due to their simple design and low cost. Here, jetting the droplets involve forming the vapor bubbles in the liquid with the aid of a resistive film. On the other hand, piezoelectric micro-jet device (PMJD) operation does not require liquid thermal stress. Instead, a voltage signal applied to the piezoelectric actuator not only jets the droplets but also helps control the droplet volume, flow rate and velocity. Generally, the piezoelectric working principle is advantageous as it allows for anti-electromagnetic interference, high dynamic response, high precision and easy controlling of the droplet parameters. As such, PMJD has become the center of current research, which seeks to advance them further.
To date, several PMJDs capable of distributing viscosity liquids have been developed. Notably, these devices work with different liquids at different viscosity and flow rates. However, most of the existing research concentrated on the distribution of low-viscosity fluids. But with the rapid advancement and application of precision distribution, efficient distribution of high-viscosity liquids is necessary. To this note, some needle-collision PMJDs have been used for high-viscosity liquid distribution. Their limited jetting frequency and reduced efficiency are a barrier to their operation. Therefore, high-speed jetting of high-viscosity fluids is highly desirable.
On this account, a team of researchers at Harbin Institute of Technology: Mr. Hengyu Li, Prof. Junkao Liu, Prof. Yingxiang Liu, Dr. Kai Li and Mr. Yuming Feng developed a resonant piezoelectric micro-jet (RPMJ) comprising of micro-jet element (MJE) and longitudinal transducer for realizing high-speed jetting of high-viscosity liquids. In particular, an RPMJ prototype was successfully fabricated and tested. Their research work is currently published in the journal, Mechanical Systems and Signal Processing.
In their approach, the research team first explored the configuration and the operating principle of the RPMJ. The resonant frequencies of the longitudinal transducer under liquid-loading and unloading conditions were 19.7 and 19.8 kHz, respectively. The high-frequency vibration of the longitudinal transducer generated a pressure change of the MJE to produce continuous droplets. The RPMJ design was discussed in detail and simulated to obtain the change in pressure and the jetting status. The resonant frequency of the longitudinal transducer was obtained via modal and harmonic response analysis. Lastly, by optimizing the MJE parameters through transient and two-phase coupling analysis, the authors evaluated and tested the jetting performances of the RPMJ system.
The proposed RPMJ could realize a high-speed jetting of high-viscosity liquids than most of the existing designs. Results demonstrated the successful jetting of silicone oil with a viscosity of 150 cps at an average flow rate of 0.07 ml/s, voltage of 300 Vp-p and frequency of 19.4 kHz. Moreover, a maximum average flow rate of 0.51 ml/s could be attained at a viscosity of 2 cps. Under liquid-loading and unloading conditions, the tested amplitudes were 3.59 µm and 14.39 µm, while the obtained frequencies were 19.4 kHz and 19.7 kHz, respectively. Furthermore, the voltages and input powers exhibited a linear relationship with the silicon oils’ viscosities and average flow rates, respectively.
In summary, an RPMJ comprising of a micro-jet element and a longitudinal transducer was reported in the study to achieve high-viscosity liquid distribution. Based on the results, the proposed RPMJ broadened the viscosity range of the operable liquid, allowing for high-speed jetting of high-viscosity fluids. From the simulation, the errors in the frequency and amplitude were 0.5%, 1.5%, 3.9% and 3.5% for unloading and liquid-loading conditions, respectively. This indicated a superior performance than most of the existing system designs. In a statement to Advances in Engineering, Professor Yingxiang Liu explained their new study would facilitate further advancement of precision liquid distribution by enhancing the droplet stability and microscopic jetting performance.
Li, H., Liu, J., Liu, Y., Li, K., & Feng, Y. (2021). Development of a resonant piezoelectric micro-jet for high-viscosity liquid using a longitudinal transducer. Mechanical Systems and Signal Processing, 146, 107012.