Droplet Generation
Micro Droplet Generation （JMEMS 2002, MNF 2010, JMM 2012）
In this serials work, an innovative microinjector, featuring a bubble valve, which entails superior droplet ejection characteristics and monolithic fabrication, which allows handling of a wide range of liquids (1-1and1-2), was invented. These articles have been cited for more than 103 times (upto Jan. 2014). The related patents were licensed to BenQ Inc. in 2000, and the device was introduced into mass-production in 2005. This new microinjector uses asymmetric bubbles to reduce crosstalk, increase frequency response and eliminate satellite droplets. During a firing, i.e., droplet ejection, the “virtual valve” closes, by growing a thermal bubble in the microchannel, to isolate the microchamber from the liquid supply and neighboring chambers. Between firings, however, the virtual valve opens, by collapsing the bubble, to reduce flow restriction for fast refilling of the microchamber. The use of bubble valves brings about fast and reliable device operation without imposing the significant complication fabrication of physical microvalves would call for. In addition, through a special heater configuration and chamber designs, bubbles surrounding the nozzle cutoff the tail of the droplets being ejected and completely eliminate satellite droplets. The droplet ejection of the microinjector with 10 m diameter nozzle has been characterized at a frequency over 35 kHz, at least 3 times higher than those of commercial counterparts. The droplet volume from this device is smaller than 1 pl, 10 times smaller than those of commercial inkjets employed in the consumer market at the time of testing. Visualization results have verified that the design operates in the frequency several times higher than those of commercial products and reduces the cross talk among neighboring chambers. In addition, the reported device eliminates satellite droplets, one of the most troublesome problems among top-shooting inkjets. By employing the similar idea of virtual check vale from high speed bubbles, another type of inkjet printhead was invented and operated without the need of the chamber walls among each firing chambers (1-3). The coordination among 4-5 bubbles together dynamically help on the containing of chamber pressure during firing and larger flow passive during refilling process.