Shear Mode Piezoelectric

A cornerstone of Dimatix's patented technology, shear mode actuation of the piezoelectric material allows us to create many jet actuators using a single flat piece of piezoelectric material.

The piezoelectric material, as part of its fabrication, is poled. To accomplish this, a strong electric field is applied to the piezoelectric material and then removed. This results in a poling field with the same orientation as the initial electric field.

To actuate the piezoelectric material in extension mode, an electric field (weaker than the field used to pole the piezoelectric material) is applied. If the electric field is applied parallel to the poling field, then the piezoelectric material reacts in extension mode. In extension mode, the piezoelectric material lengthens in one dimension and shortens in the other.

If the electric field is applied perpendicular to the poling field, the piezoelectric material reacts in shear mode. In shear mode, the piezoelectric material shears like a deck of cards in one dimension, with no change in the other dimension.

Firing a Jet

By placing electrodes on the surface of the piezoelectric material, a section of the material can be made to move without affecting the surrounding material. By applying a voltage to the center electrode, an electric field is created between the center electrode and the ground electrodes. This creates the shear response in the piezoelectric material between the electrodes.

By coupling the piezoelectric material to a pumping chamber that communicates with a nozzle, an ink drop is formed. The actual motion of the piezoelectric material is approximately one millionth of an inch.

The Lung

Another key element of Dimatix's patented technology is the "lung". The name derives from the human lung, where active gas exchange takes place in the human body.

Lung technology is unique to Dimatix, and addresses one of the difficulties of inkjet - air and air bubbles. The lung removes air from the ink, which reduces the relative concentration of air in the ink. This allows the ink to quickly dissolve air bubbles in ink passages as well as eliminate sites where air bubbles may be generated. This leads to fast, reliable startups, and enables robust high frequency jetting.

The figure depicts a simplified lung. Ink travels in one port, travels past supported membranes, and then exits the lung. The membranes are permeable to air, but not to ink. As the ink travels through the lung, a moderate vacuum on the opposite side of the membrane from the ink causes air from the ink to pass through the membrane. In this way, ink leaving the lung has a reduced concentration of air compared to ink entering the lung. This reduced concentration of air makes the ink very effective at dissolving air bubbles anywhere in the jetting system.

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