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This paper investigates the characteristics of a piezoelectric micro-injector for drop-on-demand (DOD) applications. The micro-injector is designed with an inner block inside the chamber to enhance the instability energy for the production of mono-size droplet. The micro-nozzle was fabricated by MEMS processes. The upper chip is a silicon chip with two holes as the inlet and outlet of the liquid matter. A diaphragm is mounted on the center of the upper chip. The lower chip has an orifice of 50µm in diameter. The flow through the chamber is used to promote the refilling mechanism for droplet generation. A piezoelectric actuator operated in push mode (D₃₃) was mounted on the upper chip to drive the liquid through the nozzle. An inner block is designed on the inner side of the upper chip. Results show that the micro-injector with inner block could generate mono-size droplet under the driving voltage ranging from 62.5 to 150 volt at frequency of 3.2 kHz. The droplets size was 60µm with velocity ranging from 3.3 to 4.7 m/s which is higher than the case without inner block. As a comparison, the injection of the micro-injector without inner block needs a much higher driving voltage of 112.5 volt at driving frequency of 9.7kHz. It is concluded that the micro-injector with the inner block performs better than the one without the inner block.

Hydroxyapatite (HA) and titanium oxide (TiO₂) suspensions were utilized to fabricate the functionally graded coating via the Drop-on-Demand (DOD) micro-dispensing technique. A three-layered structure was formed, with a bottom 100% TiO₂ layer, an intermediate layer consisting of 50% TiO₂ and 50% HA, and a top 100% HA layer. The coating was then subjected to various characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), fourier transform infrared spectroscopy (FTIR), contact angle measurement, and adhesion test. The SEM, XRD, and FTIR techniques revealed that the DOD technique did not change the morphology, phase, and chemical composition of the coating materials. In addition, EDS results demonstrated the graded elemental distribution within the layer which confirmed the versatility of the DOD technique. A coating thickness of 20 μm was achieved, with a critical load to failure at 59 mN.