Physics of piezoelectric shear mode inkjet actuators

Abstract: This thesis describes work on piezoelectric shear modeactuators used in dropon- demand ink printing applications.These actuators comprise an array of ink channels micromachinedinto bulk Pb(ZrxTi1-x)O3(PZT) ceramics.During this study, a new pulsed spectroscopic technique wasdeveloped to investigate functional properties of a singlechannel wall of the actuator. The pulse technique is based onrecording the transient current in response to a short voltagepulse applied to the channel wall. An electric field appliedperpendicular to the polarization will cause a shear motion ofthe wall. If a voltage pulse with a fast rise time is highenough in amplitude to actuate the wall, it will act like atuning fork and oscillate at it’s resonant frequencies.Because of the piezoelectric effect, the mechanicaloscillations of the wall can be seen as oscillations in thetransient current.Beside the pulsed technique, dielectric spectroscopy,ferroelectric hysteresis loop tracing and stroboscopy were usedas characterization techniques. The results obtained arediscussed in respect to temperature dependence, frequencydispersion, ferroelectric fatigue and acoustic resonancemodes.Another field of interest was the temperature inside theactuator. An electric circuit, based on the voltage dividerprinciple, was built to monitor the ink temperature as afunction of the printing pattern.‘Dummy walls’,located at the beginning and the end of the channel wall array,were used as temperature sensing elements. Since the dielectricpermittivity of the PZT channel walls depends on temperature,the capacitance of the‘dummy walls’changes withtemperature. The information obtained by this measurementtechnique was used to investigate alternative materials for thepassive components of the actuator.A further part was the development of a new actuator designcalled a‘Chevron actuator’. Chevron actuatorsinclude an additional PZT layer with polarization in theopposite direction to the base plate polarization. Thus, thewhole channel wall is used as the active part instead of usingjust the upper half as in the standard actuator. The mainadvantage of this technique is a reduced power consumption ofthe actuator and therefore less heat dissipation.Different approaches were used to construct Chevronactuators. Experiments determined the efficiency of theactuators and these results were used to make improvements. TheChevron actuators were characterized by the above mentionedtechniques and compared with standard Xaar actuators.