Patent ID: 7730746

Claim:
An apparatus for forming and ejecting on demand a discrete liquid droplet that is characterized by a hollow shell, the center of which contains a select fill-gas, said apparatus containing a concentric arrangement of a liquid nozzle and a fill-gas nozzle with means to apply, control and synchronize pressure impulses to each nozzle independently, said apparatus comprising: an enclosed vessel having an interior for containing a liquid supply with pressure regulation, an impulse pressure generation chamber, and a liquid droplet discharge region containing an orifice; a liquid pressure impulse device that provides a physical impulse to the pressure generating chamber through the momentary compression of one of the impulse generating pressure chamber walls, said compressible wall of the pressure chamber including a flexible diaphragm member; a vessel having an interior for containing the fill-gas supply, gas pressure regulator, impulse pressure valve, and a gas discharge region through an orifice that is concentric with the liquid discharge orifice; and a fill-gas impulse pressure generator that provides a physical impulse of fill-gas in synchronism with the liquid ejection pressure impulse that cooperates to produce a gas filled hollow droplet from the orifice, said fill-gas impulse generator including a piezo-electric actuator valve that responds to electrical pulse generator signals to produce fill-gas pressure impulses in synchronism with fluid ejection pressure pulses.