Abstract A reservoir supplies liquid through a conduit to a nozzle. The liquid is under small or zero static pressure. Surface tension at the nozzle prevents liquid flow when the system is not actuated. A section of the conduit terminating at the nozzle is designed to be capable of conducting pressure waves in the liquid from end to end of the section without the occurence of significant reflections within the section. An electroacoustic transducer is coupled to the liquid in the reflection-free section. When an electric pulse is applied to the transducer it applies a pressure pulse to the liquid sending a pressure wave to the nozzle where it causes ejection of a droplet. The pressure pulse also sends a pressure wave in the opposite direction. The system has energy absorbing means coupled to the liquid and adapted to absorb substantially all of the energy of the latter wave, thus preventing reflections which could return to the nozzle and interfere with ejection of a subsequent droplet. Two classes of energy absorbing means are described: (a) conduit walls of viscoelastic material which deform under the influence of the pressure wave and absorb energy therefrom, and (b) several forms of acoustic resistance elements within the conduit at the inlet end of the reflection-free section.
A pulsed droplet ejecting system comprising: a reservoir; liquid contained in said reservoir; a conduit communicating with said liquid in said reservoir and filled with said liquid, said conduit comprising a first section having an inlet end and an outlet end; a nozzle terminating said outlet end of said section and filled with said liquid; and an electroacoustic transducer coupled to said liquid in said section; said section, with said transducer coupled to the liquid therein, being dimensioned to conduct pressure waves in said liquid between said ends substantially free of internal reflections and being dimensioned relative to the properties of said liquid to have a given characteristic acoustic impedance; said transducer being adapted to apply a pressure pulse to said liquid whereby a first pressure wave travels in said liquid in said first section to said nozzle and causes ejection of a droplet therefrom, and whereby a second pressure wave travels in said liquid in said first section toward said inlet end of said section; said conduit comprising a second section which is attached to the inlet end of said first section and is comprised of viscoelastic material and is dimensioned relative to the properties of said liquid and to the properties of said viscoelastic material to have characteristic acoustic impedance substantially matching said characteristic acoustic impedance of said first section so that the said second pressure wave travels in said liquid from said first section into said second section without deleterious reflection at said inlet end of said first section and which is dimensioned relative to properties of said viscoelastic material so that said second wave is substantially fully absorbed by said viscoelastic material.
Claim 2
Dependent Claim
276 words
A pulsed droplet ejecting system comprising: a reservoir; liquid contained in said reservoir; a conduit communicating with said liquid in said reservoir and filled with said liquid, said conduit comprising a first section having an inlet end and an outlet end; a nozzle terminating said outlet end of said section and filled with said liquid; and an electroacoustic transducer coupled to said liquid in said section; said section, with said transducer coupled to the liquid therein, being dimensioned to conduct pressure waves in said liquid between said ends substantially free of internal reflections and being dimensioned relative to the properties of said liquid to have a given characteristic acoustic impedance; said transducer being adapted to apply a pressure pulse to said liquid whereby a first pressure wave travels in said liquid in said first section to said nozzle and causes ejection of a droplet therefrom, and whereby a second pressure wave travels in said liquid in said first section toward said inlet end of said section; said conduit comprising a second section which is attached to the inlet end of said first section and is comprised of viscoelastic material and is dimensioned relative to the properties of said liquid and to the properties of said viscoelastic material to have characteristic acoustic impedance substantially matching said characteristic acoustic impedance of said first section so that the said second pressure wave travels in said liquid from said first section into said second section without deleterious reflection at said inlet end of said first section and which is dimensioned relative to properties of said viscoelastic material so that said second wave is substantially fully absorbed by said viscoelastic material.
Claim 3
Dependent Claim
18 words
A pulsed droplet ejecting system as described in claim 1 in which said transducer is a piezoelectric transducer.
Claim 4
Dependent Claim
34 words
A pulsed droplet ejecting system as described in claim 2 in which said first conduit section is cylindrical and in which said piezoelectric transducer surrounds said section and is in stress transmitting engagement therewith.
Claim 5
Dependent Claim
66 words
A pulsed droplet ejecting system as described in claim 3 in which said second section is a viscoelastic tube having inside diameter smaller than the inside diameter of the inlet end of said first section, except that said second section is enlarged where it is attached to said inlet end with the inner surface of said enlarged portion engaging the outer surface of said inlet end.