Lead-free self-focused piezoelectric transducers for viscous liquid ejection

Self-focused piezoelectric transducers using lead-free (K0.48Na0.48Li0.04)(Nb0.90Sb0.06Ta0.04)O3 piezoelectric ceramic have been fabricated for ejecting viscous liquids in the drop-on-demand mode. The lead-free piezoelectric ceramics, with a dense structure and good piezoelectric properties (d33 = 230 pC/N and kt = 0.56) are prepared by an ordinary sintering technique, and are used to fabricate the driving and focusing elements (Fresnel zone plates) for the transducers. The Fresnel zone plate is a piezoelectric plate patterned with a series of annular electrodes on its surfaces, and the generated acoustic waves are focused by constructive interference. Our results show that the acoustic waves are effectively self-focused in glycerin (with a viscosity of 1400 mPa s), giving a high pressure at the liquid surface to eject droplets without a nozzle. Driven by a simple wave train comprising a series of sinusoidal voltages with an amplitude of 35 V, a frequency of 4.20 MHz and a duration of 1 ms, the transducer can eject glycerin droplets in the drop-on-demand mode.