R&D Profile: Integrated Thermal Modulation and Deflection of Viscous Microjets with Applications to Continuous Inkjet Printing: E. Furlani, Eastman Kodak Research
Microfluidic devices are finding increasing use in a broad range of applications that involve the production and controlled delivery of micro-droplets. The most notable and commercially successful of these is inkjet printing wherein streams of picoliter-sized drops are ejected at high repetition rates onto a media to render an image.
Overview Courtesy of Dr. Edward P. Furlani, Senior Principal Scientist, Device Physics and Simulation, Eastman Kodak Research Laboratories
Dr. Furlani is a featured speaker at next month’s NSTI Nanotech 2008 conference
Researchers at Eastman Kodak have recently developed a novel CMOS/MEMS microfluidic device that enables the controlled production and redirection of streams of picoliter-sized droplets at frequency rates in the hundreds of kilohertz range . This device consists of a pressurized reservoir that feeds a micro-nozzle manifold with hundreds of active orifices, each of which produces a continuous jet of fluid. An integrated cylindrical blocking structure is suspended beneath each orifice as shown in Fig. 1. This structure splits the flow from the reservoir into two opposing flows that merge immediately beneath an orifice to form the jet. Each microjet is subjected to thermal modulation as it exits the orifice, which causes the formation of droplets downstream. Controlled thermal modulation is achieved using individually addressable resistive heater elements that are integrated into the nozzle plate around each orifice, and also into the suspended blocking structure. The heaters are configured to enable symmetric or asymmetric heating. Modulated symmetric heating produces a straight stream of droplets whereas asymmetric heating causes the stream to deflect as shown in Fig. 1 (a) and (b).
The ability to generate and redirect droplets at the microscale is useful for numerous applications including continuous inkjet printing in which only a fraction of the generated droplets are used to render an image; unused droplets are guttered and recirculated to the reservoir. The integrated CMOS-based thermal modulation and deflection capability of this novel device represents distinct advantages over conventional continuous inkjet printing systems that rely on piezoelectric driven droplet generation and electrostatic deflection that requires charged droplets. The advantages of this technology include a high level of integration, individually addressable orifices, which enable selective droplet generation and deflection at each orifice, low power consumption, and high reliability with low cost due to microfabrication processing. Further work is planned to characterize the performance of the device for various fluids and to increase the frequency response and resolution of the droplet generation.
 C.N. Delametter, J.M. Chwalek, and D.P. Trauernicht, “Deflection Enhancement for Continuous Ink Jet printers,” U.S.Patent 6,497,510, Issued Dec. 24, 2002.  E. P. Furlani, “Temporal instability of viscous liquid microjets with spatially varying surface tension,” J. Phys. A: Math. and Gen. 38, 263-276, 2005.  E. P. Furlani, B. G. Price, G. Hawkins, and A. G. Lopez, "Thermally Induced Marangoni Instability of Liquid Microjets with Application to Continuous Inkjet Printing", Proc. NSTI Nanotechnology Conference, 2006.  E. P. Furlani and K. C. Ng, "Numerical Analysis of Nonlinear Deformation and Breakup of Slender Microjets with Application to Continuous Inkjet Printing", Proc. NSTI Nanotechnology Conference, 2007.