a piezoelectric pump or equivalent transducer is mounted on or within an ink jet printhead and is used to modulate the frequency or amplitude , or both , of oscillations of a liquid meniscus at a liquid ejection orifice of a nozzle plate . the liquid meniscus at the orifice has a natural resonant frequency and amplitude with respect to its equilibrium position , and the above modulation is performed in a controlled timed relation with respect to the phase of the natural oscillations of the meniscus at the liquid ejection orifice .