Microlenses for acoustic printing

Claim 1

An acoustic printhead for ejecting individual droplets of ink on demand from a free surface of a supply of liquid ink, said ink having a predetermined acoustic velocity; said printhead comprising a solid substrate composed of a material having an acoustic velocity which is substantially higher than the acoustic velocity of said ink, said substrate being oriented with a first of its surfaces facing the free surface of said ink supply at a substantially constant distance therefrom, said first surface of said substrate being acoustically coupled to said ink and having at least one concave indentation formed therein to define an acoustic microlens having a predetermined aperture diameter and a predetermined focal length; and a piezoelectric transducer intimately coupled to an opposing surface of said substrate for generating an acoustic wave in said substrate for illuminating said microlens, such that said microlens launches a converging acoustic beam into said ink, with the focal length of said microlens being selected to cause said beam to come to focus approximately at said free surface; said acoustic wave having a wavelength in said substrate such that the aperture diameter of said microlens is less than an order of magnitude greater than said wavelength.