Effective heater-size and droplet-volume adjustable microinjectors using the digital combination of multiple current paths in a dingle heater

Abstract

The thesis presents a single-heater microinjector, whose ejected fluid droplet volume is adjusted by changing current paths in a single microheater. The previous droplet volume adjustable methods have used multiple heaters or multiple signals, while the novel aspect of the present method includes the use of single heater with an identical signal for multiple current paths to achieve multi-level droplet volume adjustment. We design two types of the microinjectors including rectangular heater type and circular heater type microinjector using $ANSYS^{®}5.7$ thermal simulation and fabricate the microinjectors by micromachining. Each microinjector has a single microheater with eight electric lines to control the current path. In the experimental study, we measure the size of the generated bubble and the volume, velocity of the ejected droplet as the current path changing. In bubble generation test, we use the 1kHz 15.0V 3 μ sec$ pulse-width electrical signal and DI water at room temperature. The maximum bubble sizes are obtained at 3~5 μ sec$ after the supply of electrical signal. The projected area of the generated bubble is changed from $440 ㎛^{2}$ to $1360 ㎛^{2}$ for rectangular type microinjector and from $800 ㎛^{2}$ to $3300 ㎛^{2}$ for circular type at 6 levels. Under the same experimental condition, we measure the ejected droplet volume and velocity. It is found that the ejected droplet volume is varied from 9.4pl to 20.7pl at 3 levels for rectangular type and from 7.4pl to 27.4pl at 5 levels for circular type, while the velocity of the ejected droplet is increased from 0.8m/s to 1.7m/s for rectangular type and from 0.5m/s to 2.8m/s for circular type. On this basis, we have found that the present single-heater microinjectors using current path changing method show more droplet volume adjustment level and wider volume adjustment range than previous microinjectors. We have experimentally verified that the present current path changing method...