Piezoelectric micropumps

There are currently two basic design types for micropumps and dosing systems. They are the drop-on-demand design, which is also familiar from ink-jet printers, and the piezoelectric diaphragm pump, which is gaining ground.

Piezoelectric microdispensers (as found in the drop-ondemand system) consist of a capillary drawn out to a nozzle with defined diameter. The capillary is surrounded by a piezoceramic tube actuator which contracts when voltage is applied.

This creates a pressure wave in the column of liquid which propagates to the end of the capillary. The pressure energy is transformed into kinetic energy. Individual drops are generated and accelerated to a velocity of a few meters per second so that, when delivered in an arbitrary direction, they can travel over a path of a few centimeters. The volume of the drops emitted (picoliters) is a function of the properties of the medium to be transported, the dimensions of the capillary and the drive parameters of the PZT actuator.

Sketch of a membrane pump

A microdiaphragm pump comprises a valve unit and the pump diaphragm, which, together with the piezoelectric actuator, forms the pump drive. Operation is based on the deformation of a piezo element (disk, plate, etc.) connected to the diaphragm. Applying a voltage deforms the diaphragm (bending effect).

The bending of the diaphragm (metal or silicon) brings about a change in volume of the pump chamber and the medium is transported under the control of the inlet and outlet valves.

The fields of application for piezoelectric pumps are in medical engineering, biotechnology, chemical analysis and process engineering, where reliable dosing of minute amounts of liquids and gases is frequently required. In the automotive industry, fuel injection systems driven by multilayer stack actuators are also piezoelectric micropumps!