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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!

Active vibration damping

The damping of undesired vibrations in mechanical structures by means of piezoelectric components can be carried out either actively or passively. These methods are characterized as follows:

Active vibration damping

  • External power source and control electronics required
  • Application of countermovements in the control loop

Passive vibration damping

  • Energy conversion in the material itself
  • The electrical energy generated by the structural vibrations (mechanical energy) in the piezo elements is converted into heat for example, by means of resistors

In active vibration damping a structure exhibiting undesirable, weakly damped natural resonances is equipped with special actuators and sensors connected in a servoloop. The controller is set up so that in the vicinity of the intrinsic frequencies, the actuator behaves like a high-viscosity damper.
If one integrates piezoelectric elements (also termed adaptive materials), e. g. actuators, in the form of piezoceramic plates or disks, into a structure, it can then be equipped with sensor and actuator functions. With suitable control algorithms, it can then adapt itself to the desired conditions.

The principle consists in exciting vibrations in the piezo actuator by means of an electronic amplifier. Because the piezo is closely coupled with the mass of the assembly to be damped, if the force from the vibration introduced is opposite in phase from the unwanted vibrations, they can be neutralized or minimized.
Piezoelectric actuators, including multilayered elements (e. g. PICMA multilayer actuators), can be used anywhere where precisely dosed periodic counterforces are needed in structures. The applications are currently mainly in the fields of aerospace (e. g. for saving fuel; vibration damping of lattice structures for antennas, etc.), vehicle manufacture (e. g. noise minimization), and also increasingly in mechanical engineering (rotating drives), etc.
PICATM series actuator, embedded in a CFK structure