(57) A fluid jet print head includes an orifice plate (22) defining a plurality of orifices
(24) from which fluid emerges, and a stimulator means (26) mounted in contact with
the orifice plate for vibrating the orifice plate to produce a series of bending waves.
The bending waves travel along the orifice plate and break up the fluid into drops
of substantially uniform size and spacing. The stimulator means includes a stimulator
member (28) of a length equal to an integer half wavelength of acoustic waves of a
frequency f passing therethrough. The stimulator member contacts the orifice plate
at one end of the member. A pair of piezoelectric crystals (32, 34) are mounted on
opposite sides of the stimulator member and , when driven by an A.C. drive signal,
cause acoustic waves of a frequency f to pass along the member. The member is supported
at a nodal plane. The member may enter the print head manifold and contact the orifice
plate internally, with a seal arrangement (46) being provided at a nodal plane along
the member.
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