Acoustical and optical characterization of air entrapment in piezo-driven inkjet printheads

Air bubbles can cause nozzle failures in piezo-driven inkjet printheads [1]. The time development of the entrapped air bubbles has experimentally been studied [2]. It was found that the air bubble has a radius of 5µm just after the entrapment. The bubble then grows by rectified diffusion due to the applied pressure field, used for jetting droplets. Bjerknes forces drive the displacement of the air bubble. First, the bubble is pushed into the channel. After reaching the resonance size, given by the characteristic printhead frequency, the Bjerknes force reverses sign, pushing the air bubble towards the nozzle. At this time the air bubble has grown so large that it is not possible to jet it out, resulting in a nozzle failure