Observations on the behavior of bubbles generated by laser focusing in a piezo-driven inkjet head

In recent years inkjet technology has a wide range of application such as Flat Panel Display and Semiconductors. The stability of jetting is a major requirement for industrial inkjet heads. However, air bubbles can cause jetting failures in piezo-driven inkjet heads. The piezo actuators can be used as sensors to detect the acoustic influence caused by air bubbles. In order to analyze the relationship between the air bubbles and the voltage signal from the piezo actuator, a controllable bubble generation method inside the inkjet head is strongly required. In this paper, we propose a bubble generation method by focused THG Nd:YVO4 laser and the secondary Bjerknes forces and obtain bubbles from about 5 micron to ISO micron in radius inside the inkjet head. Using the observation technique with a glass nozzle plate, some interesting bubble migration patterns in the applied pressure field are observed. We consider that the primary Bjerknes forces drive the displacement of air bubbles against buoyancy.