Abstract: An apparatus for ejecting droplets of ink including: a passage for ink; an orifice disposed at one end of the passage; a pressure-applying device for applying a pressure wave to the ink within the passage; and a signal-supplying device for supplying an actuating signal to the pressure-applying device. The frequency of the signal is such that the displacement of the ink surface at the orifice due to the pressure wave is maximized.

Abstract: An ink jet printing head which includes a head body provided with an ink filling port (18), a plurality of rows of nozzles (32A.sub.1 through 32A.sub.5, 40B.sub.1 through 40B.sub.5) arrayed in a staggered formation, pressure chambers (21A.sub.1, 21A.sub.2, . . . , 21B.sub.1, 21B.sub.2, . . . ), one for each of the nozzles, and ink passages (28A.sub.1, . . . , 33A.sub.1, . . . , 38B.sub.1, . . . , 41B.sub.1, . . . ) connecting the ink filling port with the nozzles via corresponding pressure chambers. (19A.sub.1 through 19A.sub.5, 19B.sub.1 though 19B.sub.5). The pressure chambers are formed inside the head body and adjacent to the surface of at least one side of the head body. Piezoelectric elements are mounted on the outside of the head body at positions corresponding to the pressure chambers.