A micro droplet injector system

Droplet injectors are widely used in various applications, including inkjet printing, fuel injection, drug delivery, dosage, direct writing, etc. Among those applications, a high-frequency-response, high-spatial-resolution, and large-nozzle-array droplet injector ejecting high quality droplets (ejection without satellite droplets) is desired. Thermal bubble principle is chosen as the operation mean of the microinjector for its capability of high performance and potential in ejecting micrometer size droplet. To fabricate a large array of microinjectors in the micrometer size, micromachining technology was chosen to accomplish the design goals that can not be achieved by traditional machining ways.; Except the studies of the operation principles and design issues of the microinjector, this dissertation is mainly focused on two achievements: (1) the new concept--virtual chamber neck--which can reduce cross talk among chambers without decreasing frequency response, and (2) the new droplet tail cutting mechanism, which completely solves the satellite droplet problem. Satellite droplet formation has been one of the most well known and troublesome issues in thermal bubble jet design and posed an image-blurring problem in inkjet printing for decades. The microinjector completely eliminating satellite droplets and minimizes cross talk effect without reducing its frequency response, thanks to the new designs and the micro-fabrication technology. The microinjector has been demonstrated to eject ink droplets with the size of 12 {dollar}mu{dollar}m in diameter (0.9 pl in volume) at the frequency more than 30 kHz in high stability without satellite droplets. The microinjector is also fabricated in an array of 300 nozzles with the resolution capability of 900 dpi. To implement the microinjector array, a controlling system is designed and fabricated for the spatial and temporal control. Three techniques, including droplet trajectory visualization, droplet ejection velocity measurement, and droplet visualization, have been developed to characterize the droplet ejection sequence. Testing results show that the performance of the microinjector is superior to that of contemporary inkjet printheads. Except the application of inkjet printing, mixing control by distributed micro fuel injectors is also proposed. Preliminary results prove the concept of which the coherent jet flow structure can be controlled by the perturbation of liquid droplets.