MEMS bubble generator for large stable vapor bubbles
View Patent ↗A MEMS vapour bubble generator that uses a heater in thermal contact with a liquid to generate a bubble. The heater is energized by an electrical pulse that is shaped to have a relatively low power, sub-nucleating portion and a high power portion that nucleates the bubble. The thermal energy transferred to the liquid by the sub-nucleating portion speeds up the nucleation of the bubble across the surface of the heater during the nucleating portion. This produces larger, more stable bubble having a regular shape.
1. A MEMS vapour bubble generator comprising:
a chamber for holding liquid;
a heater positioned in the chamber for thermal contact with the liquid; and,
drive circuitry for providing the heater with an electrical pulse such that the heater generates a vapour bubble in the liquid,
the pulse having a pre-heat section for heating the liquid but not nucleating the vapour bubble and a trigger section subsequent to the pre-heat section for superheating some of the liquid to nucleate the vapour bubble; wherein,
the pre-heat section has a longer duration that the trigger section.
2. A MEMS vapour bubble generator according to claim 1 wherein the pre-heat section is at least two micro-seconds long.
3. A MEMS vapour bubble generator according to claim 1 wherein the trigger section is less than one micro-section long.
4. A MEMS vapour bubble generator according to claim 1 wherein the drive circuitry shapes the pulse using pulse width modulation.
5. A MEMS vapour bubble generator according to claim 4 wherein the pre-heat section is a series of sub-nucleating pulses.
6. A MEMS vapour bubble generator according to claim 1 wherein the drive circuitry shapes the pulse using voltage modulation.
7. A MEMS vapour bubble generator according to claim 1 wherein the time averaged power in the pre-heat section is constant and the time averaged power in the trigger section is constant.
8. A MEMS vapour bubble generator according to claim 1 used in an inkjet printhead to eject printing fluid from a nozzle in fluid communication with the chamber.
9. A MEMS vapour bubble generator according to claim 8 wherein the heater is suspended in the chamber for immersion in a printing fluid.
10. A MEMS vapour bubble generator according to claim 8 wherein the pulse is generated for recovering a nozzle clogged with dried or overly viscous printing fluid.