Ink Jetting with Piezoelectric Vibrating-Membrane Ejectors

While piezoelectric vibrating-mesh atomizers are widely utilized for nebulization, their application in inkjet printing and fluid dispensing is hindered by spreading ejection, satellite deposits formation, and restricted working distances. In this study, we found that piezoelectric vibrating-membrane ejectors (PVMEs) featuring a single micro-orifice switch their ejection states between two distinct modes, namely, aligned and spreading, depending on the orifice size and actuation-voltage amplitude. This feature offers a new opportunity for using these vibrating membrane-based devices to perform precise inkjet printing or fluid dispensing at working distances of ≥1 mm. Mechanism analysis attributes the change in ejection mode to air bubble generation via cavitation and/or air intrusion, where partial blockage and/or asymmetric collapse induces off-axis jetting. The water ejection flow rate in the aligned mode was fitted and evaluated with a physical model that suggests the ejected liquid volume is proportional to the volume change in the liquid chamber caused by membrane vibration. Uniform and non-uniform droplet sizes were observed for the aligned and spreading ejection modes, respectively. The 22 and 11 µm orifice PVMEs exhibited aligned ejection of aqueous glycerol solutions with viscosities up to 22.5 mPa · s, indicating their suitability for ejecting water- or solvent-based liquids. The printability of the PVME-based printheads was validated at different working distances through the printing of dots, lines, interdigitated electrodes, and ink dots for die inking. As a result of the different ejection modes, clean dots and lines with feature sizes of several hundred micrometers can be printed with the 22 and 11 µm orifice PVMEs at relatively long working distances (≥1 mm), whereas for smaller feature sizes, i.e., as small as approximately 50 µm, a 6 or 3 µm orifice PVME has to be used at a short working distance (≤1 mm). These findings establish the PVME method as a structurally simple, power-efficient, and cost-effective alternative for precise inkjet-printing and fluid-dispensing applications.