A low‐cost, precise piezoelectric droplet‐on‐demand generator

repeatable experiments require a reliable and precise droplet generation technique. Repeatable droplet generation is also required for a number of diverse applications ranging from inkjet printing to liquid crystal display manufacturing (Fan et al. 2008). A variety of droplet-on-demand (DOD) generators are described in the literature, but most existing designs are complex, costly, and difficult to adopt for use in other studies. Many systems are designed for the generation of droplets smaller than 500 μm in diameter (Bransky et al. 2009; Reis et al. 2005; Meacham et al. 2005; Perçin and KhuriYakub 2003; Cheng and Chandra 2003; Goghari and Chandra 2008; Chen and Basaran 2002; Dong et al. 2006; Switzer 1991), below the desired range for the walking droplet experiments. We here describe a simple, repeatable DOD system designed specifically for this range, 0.5–1.3 mm (Protiere et al. 2006; Moláček and Bush 2013). The present device is inspired by the design of Yang et al. (1997) which ejects a droplet from a nozzle at the base of a fluid chamber by contracting a piezoelectric disk sealed to the top of the chamber. They used a fixed fluid reservoir and custom-fabricated glass nozzles. For a range of nozzles 125–250 μm in diameter, they found an overall variability in size of <10 % of the measured droplet diameters (<500 μm). Their device has since been adopted for relatively large-scale drop (diameters >500 μm) generation (Mehdizadeh et al. 2004; Hawke 2006). Castrejón-Pita et al. (2008) used a loudspeaker to actuate their DOD generator and fabricated interchangeable nozzle plates ranging from 0.15 to 3.00 mm in diameter. A fluid reservoir of adjustable height allowed for control of the pressure at the nozzle outlet. For fixed control parameters, the device was stated to have an overall variability of droplet size of <5 %. Terwagne (2011) successfully designed and employed a DOD generator to produce droplets for their own bouncing Abstract We present the design of a piezoelectric droplet-on-demand generator capable of producing droplets of highly repeatable size ranging from 0.5 to 1.4 mm in diameter. The generator is low cost and simple to fabricate. We demonstrate the manner in which droplet diameter can be controlled through variation of the piezoelectric driving waveform parameters, outlet pressure, and nozzle diameter.