There are different piezo printhead modes of operation: Bend, Shear and Chevron. Shear mode and Chevron are patented by Xaar.
In bend mode printheads, a piece of piezoelectric material is glued to the roof of the ink chamber. When an electric field is applied in the same direction in which the material is poled, the piece of material either lengthens or shrinks. If one side of the material is glued to the top of an ink chamber the lengthening causes the roof to bend. This creates a pressure change that displaces a volume of ink causing a drop to be ejected from the nozzle.
Shear mode printheads use a single piece of poled PZT for the actuator design. The electric current is applied perpendicular to the direction in which the material is poled. The deformation creates a shear effect (trapezoid shape) – see the animation below. The animation shows the walls of the channel shearing (moving) from side to side.
All Xaar’s latest bulk technology printheads have an actuator that is made of 2 pieces of oppositely poled piezo material joined (fused) together. When the electric field is applied, the 2 sections of the channel walls deflect at the join to create a 'chevron' shape. This occurs at a very high frequency within the printhead. The animation is slowed down to demonstrate chevron actuation in three adjacent channel walls.
The chevron design used by Xaar is very energy efficient which reduces the required drive voltage and therefore reduces power consumption. It also offers:
When the channel walls are flexed (actuated) in Chevron mode at a high frequency, an acoustic wave is created. This pressure wave forces the ink droplets out of the nozzles. The animation shows acoustic waves moving up and down the channel. This method of drop ejection is very efficient.
The walls vibrate at approximately 150 kHz.
Xaar's patented shared-wall design is a technique for increasing native resolution or channel density. Each channel has 2 walls made of piezoelectric material. These walls are therefore shared between adjacent channels and can be used to fire both of the adjacent channels independently. This structure is an efficient use of the piezo material leading to cost-effective, high nozzle density printheads.