of resistive elements 16a 16b and 16c it should be noted that the number of resistive elements is merely representative it should also be noted that for the sake of clarity the resistive elements are shown greatly out of scale in fact the elements are small enough so that they will merely print the equivalent of dots in any event the elements 16 each have one end connected via a lead 18 to a heater current source 20 and another end grounded the heater current source 20 can be a current source which is connected via switching means to each of the leads 18 the switching means can selectively connect any one of the leads to the current source in this way selective dots can be printed furthermore the substrate 14 is bonded to piezoelectric element 22 the piezoelectric element 22 has a substrate 22a of piezoelectric material such as barium titanate fixed to opposed faces of the substrate 22a are electrodes 22b and 22c the electrodes are connected to a high frequency voltage source 24 the source 24 operating through the electrodes 22b and 22c causes the lengthwise vibration in the piezoelectric substrate 22a this vibration is carried over into the substrate.